Photomelt adhesive particles and position-selective bonding method using the adhesive particles

Abstract

To provide light-melt adhesive particles that solve a problem of handling ability or the like in performing position-selective adhesion by using a conventional hotmelt adhesive, and a position-selective adhesion method that allows position-selective adhesion of fine location with excellent handling ability by using the light-melt adhesive particles.SOLUTION: Provided are light-melt adhesive particles having particles of a hotmelt adhesive and a layer of a material having a photothermal conversion function covering the particles, and a position-selective adhesion method having: an adhesive particles arranging process of arranging the light-melt adhesive particles on an adherend 1; an adhesive particles melting process of irradiating the light-melt adhesive particles with light to heat / melt particles of the hotmelt adhesive; a bonding process of bringing the light-melt adhesive particles into contact with an adherend 2 to bond them; and an adhesion process of gradually heating to solidify heated / molten adhesive particles to adhere the adherend 1 and the adherend 2 together.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to particles of a hot-melt adhesive coated with a material that generates heat upon light irradiation, and an adhesion method for realizing position-selective adhesion by heating and melting the hot-melt adhesive by irradiating the particles with light.

Background Art

[0002] A hot-melt (HM) adhesive is mainly composed of a thermoplastic polymer (resin or elastomer) having adhesiveness, etc. After melting by heating and then gradually heating and solidifying, it adheres between substrates (adherends) where the adhesive is disposed. Hot-melt adhesives have characteristics such as high adhesive strength, being excellent in safety and environmentally adaptable because they do not contain flammable organic solvents, etc. Therefore, they are widely used industrially for applications such as corrugated board adhesion, fixing of electronic components, rationalization of sewing work, and for plastic molded products, etc., and hot-melt adhesives made of various thermoplastic polymers have been proposed (Patent Documents 1, 2).

[0003] In addition, in the case of a hot-melt adhesive made of a thermoplastic resin having a low softening temperature and a large adhesive strength, there was a problem that the adhesive particles tended to aggregate. Therefore, in order to solve this problem, composite particles for a hot-melt adhesive having a shell-core structure in which a core portion made of a hot-melt adhesive is included in a shell of a resin or an inorganic substance having a high glass transition temperature have also been proposed (Patent Document 3).

[0004] When using, for example, a hot-melt adhesive mainly composed of an ethylene-vinyl acetate copolymer, it is heated and melted at a temperature of about 80 to 150°C. However, there were cases where the viscosity of the adhesive in the molten state was high and the handling property during adhesion became a problem. When using hot melt adhesive to selectively bond minute areas, a heating device such as a glue gun is used to position the heated and molten adhesive at the intended bonding location. However, handling issues include the fact that it takes time for the heating element of the device to heat up sufficiently after turning on the power, there is a risk of burns from contact with the heated element, and hot melt adhesive may be accidentally applied to areas where bonding is not desired, resulting in bonding in unwanted areas. Furthermore, when the adhesive is heated, the substrate (the object to be bonded) in contact with the adhesive is also heated, which can lead to deformation or damage to the substrate.

[0005] On the other hand, once the adhesive has hardened, it is not possible to modify the bonded area (the bonded position), so bonding must be completed before it hardens due to cooling. However, heated and melted adhesives usually harden quickly due to cooling, and especially when bonding fine parts, the amount of adhesive that is heated and melted is small, so the time from heating and melting to cooling and hardening is even shorter. Therefore, it is necessary to complete the bonding work in a short time, and for this reason, bonding using hot melt adhesives has the problem of poor handling, and in particular, it is difficult to selectively bond fine parts. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 55-110113 [Patent Document 2] Japanese Patent Publication No. 2001-187874 [Patent Document 3] Japanese Patent Publication No. 2007-269962 [Overview of the project] [Problems that the invention aims to solve]

[0007] The present invention aims to solve the problems of conventional hot-melt adhesives, particularly the handling difficulties when selectively bonding fine areas, and to provide photo-melt adhesive particles (adhesive particles that generate heat and melt upon light irradiation) that enable easy and reliable hot-melt bonding, and a position-selective bonding method that enables position-selective bonding of fine areas with excellent handling properties using said photo-melt adhesive particles. [Means for solving the problem]

[0008] The inventors, after diligent research to solve the above problems, have discovered that by using adhesive particles comprising a core made of hot-melt adhesive within an outer shell (shell) made of a material that generates heat upon irradiation with light (a material having photothermal conversion ability), placing these adhesive particles at the bonding location on a substrate (object to be bonded), and irradiating them with light to generate heat in the photothermal conversion ability material, thereby heating and melting the hot-melt adhesive, the handling problems during position-selective bonding of fine areas are solved, enabling easy and reliable bonding, and thus the present invention has been completed. Furthermore, it has been found that it is preferable to use polypyrrole or poly(N-alkylpyrrole) as the photothermal conversion ability material and to irradiate with light including near-infrared light. In other words, the problems of the present invention described above are solved by the following configuration.

[0009] The first aspect of the present invention is a photomelt adhesive particle characterized by having hot melt adhesive particles as a core and a layer of a material having photothermal conversion ability covering the particles as a shell. This photomelt adhesive particle is a particle with a so-called shell-core structure, having a shell consisting of a layer of a material having photothermal conversion ability and a core of hot melt adhesive particles contained within the shell.

[0010] The second aspect of the present invention is the first aspect of the photomelt adhesive particles, characterized in that the material having photothermal conversion ability is polypyrrole or poly(N-alkylpyrrole). Here, as the alkyl in poly(N-alkylpyrrole), a lower alkyl having 1 to 4 carbon atoms is exemplified.

[0011] The third aspect of the present invention is a photomelt adhesive particle of the first to third aspects of the present invention, characterized in that the hot melt adhesive contains as a base polymer a polymer selected from the group consisting of ethylene-vinyl acetate copolymer, polyolefin, thermoplastic elastomer, polyester, polyamide, and polyurethane.

[0012] The fourth aspect of this invention is, Adhesive particle arrangement step: Arrange photomelt adhesive particles on a substrate 1, the particles of which are hot melt adhesive particles, and the shell is a layer of a material having photothermal conversion ability that covers the particles. After the adhesive particle placement step, the photomelt adhesive particles are irradiated with light to generate heat in the material having photothermal conversion ability, thereby heating and melting the hot melt adhesive particles in an adhesive particle melting step. A bonding step of bringing the light-melt adhesive particles and the object to be bonded 2 into contact and bonding them, After the adhesive particle melting process and the bonding process, the heated and melted adhesive particles are cooled and solidified to bond the objects to be bonded 1 and 2. This is a position-selective bonding method characterized by having [a specific feature].

[0013] The fifth aspect of the present invention is the fourth aspect of the regioselective bonding method, characterized in that the material having photothermal conversion ability is polypyrrole or poly(N-alkylpyrrole).

[0014] The sixth aspect of the present invention is the fifth position-selective bonding method of the present invention, characterized in that the light irradiation is irradiation of light including near-infrared light.

[0015] The seventh aspect of the present invention is the sixth position-selective bonding method of the present invention, characterized in that the light irradiation is near-infrared light with a wavelength of 700 nm or more and 1200 nm or less, irradiated at a power of 50 mW or more.

[0016] The eighth aspect of the present invention is a position-selective bonding method of the present invention described in the fifth to seven aspects, characterized in that the particle size (maximum diameter) of the light-melt adhesive particles is 0.5 mm or more and 5 mm or less.

[0017] The ninth aspect of the present invention is the position-selective adhesion method of the eighth aspect of the present invention, characterized in that the thickness of the layer of the material having the photothermal conversion ability is 50 nm or more and 100 μm or less.

Effects of the Invention

[0018] The position-selective adhesion methods of the fourth to ninth aspects of the present invention can be implemented by using the photo-melt adhesive particles of the first to third aspects of the present invention. And, by the position-selective adhesion method of the present invention, the problem of handling property when selectively adhering fine portions of an adherend with a hot-melt adhesive is solved, and the fine portions can be surely and easily adhered at accurate positions. More specifically, for example, excellent effects as shown below can be obtained.

[0019] Conventionally, when selectively adhering a fine range with a hot-melt adhesive, the melted adhesive was placed at the adhesion position using a heating device such as a glue gun. However, due to reasons such as the high viscosity of the heated and melted adhesive, it was often difficult to put the hot-melt adhesive into fine gaps even when using a glue gun or the like. However, in the position-selective adhesion method of the present invention, the particles containing the hot-melt adhesive are placed at the adhesion position without being heated and melted, so that the placement of the adhesive in fine gaps and spaces where the adhesive could not be placed by the conventional method is realized, and accurate position-selective adhesion to the adhesion position is facilitated. Also, even when adhesive particles are placed at positions other than the adhesion position, if light is irradiated only on the adhesion position, only the irradiated portion adheres and the other positions do not adhere. Therefore, accurate position-selective adhesion is also facilitated from this point. That is, according to the present invention, position-selective adhesion with a hot-melt adhesive becomes easy.

[0020] In the conventional method, a heating device such as a glue gun or a power source for heating and melting the hot melt adhesive is required. The heating part of the heating device takes time to be heated to the temperature for melting the adhesive, and it is necessary to wait for the bonding operation. There is a risk of getting burned by contacting the heating part of the device. In some cases, the heating part may be brought into contact with the adherend (substrate) for heating, and in this case, deformation or damage of the adherend is likely to occur. On the other hand, in the position-selective bonding method of the present invention, the heating and melting of the hot melt adhesive are performed by light irradiation from the outside, and heating by a heating device is not required. That is, according to the present invention, bonding with a hot melt adhesive that does not require a heating device becomes possible, and bonding at a desired timing and non-contact bonding, for example, bonding by remote operation by light irradiation from a distance, become possible, so that the handling property of bonding can be improved. Also, the problems caused by the use of the heating device as described above can be solved. And since sunlight can be used as the light source, it can be said that it is an environmentally adaptable bonding technology.

[0021] When the material having the photothermal conversion ability that constitutes the shell of the optical melt adhesive particles of the present invention is polypyrrole, near-infrared light having a wavelength of about 800 nm or more and 1200 nm or less is preferably used as the irradiated light. However, as long as the light contains near-infrared light of the above wavelength at a predetermined intensity or more, the type of the light source is not particularly limited. Therefore, an infrared lamp that is widely used can be used. Also, since sunlight contains near-infrared light, bonding is also possible by sunlight irradiation. That is, in the present invention, sunlight can also be used as the light source.

Brief Description of the Drawings

[0022] [Figure 1] It is a diagram schematically showing an example of the optical melt adhesive particles of the present invention. [Figure 2] It is a plan view showing the PET film used in the examples. [Figure 3] It is a stereomicroscope image showing the optical melt adhesive particles spread by wetting in the examples.

Modes for Carrying Out the Invention

[0023] The following describes embodiments for carrying out the present invention with reference to the drawings, but the scope of the present invention is not limited to the following embodiments.

[0024] (The process leading to the completion of this invention) Polypyrrole and polyaniline are known materials that possess photothermal conversion capabilities. For example, J. Mater. Chem. 2007, 17(40), 4309, Chem. Commun. 2012, 48(71), 8934, and Polym. Chem. 2017, 8(17), 2609 disclose that polypyrrole generates heat (possesses photothermal conversion capabilities) when irradiated with light (near-infrared light, sunlight). There is also a reported study in which polystyrene particles coated with polypyrrole were irradiated with light, simultaneously causing heat generation and carbonization of the polypyrrole and thermal decomposition and vaporization of the polystyrene, thereby synthesizing carbon capsules (Langmuir 2021, 37, 15, 4599). Furthermore, an example has been disclosed in which polyaniline, a conjugated polymer, is sandwiched between polymer substrates that melt upon heating, and microwaves are irradiated to generate heat in the polyaniline, melting the polymer substrates, and then solidifying upon cooling to achieve adhesion (Polym. Eng. Sci., 1997, 37, 738-743).

[0025] The inventors have discovered that by coating the surface of a granular hot-melt adhesive with polypyrrole or poly(N-alkylpyrrole), a material having photothermal conversion capabilities, to create shell-core adhesive particles, and that irradiating these adhesive particles with light can melt the hot-melt adhesive due to the heat generated by the polypyrrole, and that irradiating light after placing these adhesive particles at the bonding location can melt the hot-melt adhesive due to the heat generated by the polypyrrole, thereby enabling hot-melt bonding. Furthermore, the inventors conceived that since the adhesive particles before melting can be easily and accurately placed at the bonding location (with excellent handling properties), even in minute areas, the aforementioned problems can be solved, and position-selective bonding becomes possible. Specifically, they discovered that when the shell-core hot-melt adhesive particles are placed on a substrate and then irradiated with light, heat is generated only where the particles are present, causing the hot-melt adhesive forming the particle core to melt and leak out, thereby achieving localized bonding of the substrate, thus completing the present invention.

[0026] (Composition and shape of hot melt adhesive particles of the present invention) As described above, the photomelt adhesive particles of the present invention are particles with a so-called shell-core structure, having a shell consisting of a layer of material having photothermal conversion ability and a core of hot-melt adhesive particles contained within this shell. Figure 1 is a schematic diagram showing an example of the photomelt adhesive particles of the present invention, which has a cubic shape. In Figure 1, (a) is a schematic perspective view showing the appearance of an example of the photomelt adhesive particles of the present invention (white dashed lines represent the edges of the cube), (b) is a schematic exploded perspective view showing the state in which the shell consisting of a layer of material having photothermal conversion ability has been peeled off from the core of the adhesive particle shown in Figure (a), and (c) is a schematic cross-sectional view showing the cross-section aa in Figure (a).

[0027] In the figure, 1 is a shell consisting of layers of a material having photothermal conversion ability, and 2 is the core of the hot-melt adhesive particles. The shape of the photomelt adhesive particles of the present invention is not particularly limited, and in addition to the cube shown in Figure 1, other shapes such as rectangular parallelepipeds, polyhedra with 6 or more faces such as columnar shapes, spheres, and even film-like, string-like, and stick-like shapes are also conceivable, and basically the shape is not limited as long as it fits into the reaction vessel. However, from the viewpoint of preventing the particles from rolling and facilitating placement at fine bonding positions, cubes or rectangular parallelepipeds are preferred.

[0028] (Regarding the shell of the photomelt adhesive particles of the present invention) The material constituting the shell is not particularly limited as long as it has a photothermal conversion function, that is, the function of converting irradiated light into heat, and can form a shell that covers the surface of the core. However, considering the ease of shell formation and the strength of the formed shell, organic polymer compounds or inorganic materials such as carbon materials that have a photothermal conversion function are preferred. Organic polymer compounds are preferred in terms of ease of coating onto the surface of hot melt adhesive particles. Specifically, poly(N-alkylpyrroles) such as polypyrrole, poly(N-methylpyrrole), and poly(N-ethylpyrrole), polyalkylanilines such as polyaniline and polytoluidine, poly(3,4-ethylenedioxythiophene), and polyalkylthiophene are used. Among these, polypyrrole or poly(N-alkylpyrrole) is particularly preferred in that it has excellent photothermal conversion function when irradiated with near-infrared light. Furthermore, polypyrrole and poly(N-alkylpyrrole) synthesized by polymerization usually contain dopants, but polypyrrole and poly(N-alkylpyrrole) containing impurities such as dopants can also be used, and polypyrrole and poly(N-alkylpyrrole) that are free of impurities, which can be obtained by removing impurities such as dopants, can also be used.

[0029] If the shell is too thin, the amount of material with photothermal conversion properties decreases, resulting in less heat generation due to light irradiation, and preventing sufficient heating and melting of the hot-melt adhesive particles in the core. Here, "sufficiently heating and melting the hot-melt adhesive particles" means melting the particles so that they can be easily deformed and spread to an area where sufficient adhesion can be achieved. Therefore, the shell thickness should be selected to be greater than or equal to the thickness required to sufficiently heat and melt the hot-melt adhesive particles in the core. However, this thickness varies depending on the type of material with photothermal conversion properties, the size of the core, the type of hot-melt adhesive (softening point), etc., so the optimal thickness should be selected considering these factors. When the material having photothermal conversion function is polypyrrole or poly(N-alkylpyrrole), the core is a cube with a maximum diameter of 2 mm or less, and the hot-melt adhesive is mainly composed of a resin with a softening point of 50 to 100°C, such as ethylene-vinyl acetate resin, the shell thickness can usually be 50 nm to 100 μm, but preferably it is in the range of 100 nm to 800 nm.

[0030] (Regarding the core of the photomelt adhesive particles of the present invention) The core consists of hot-melt adhesive particles, and while their size is not particularly limited, they must be large enough (in volume) to ensure that the amount of hot-melt adhesive is greater than or equal to the amount required to obtain sufficient (desired) adhesive strength. On the other hand, if the core is large, the photo-melt adhesive particles will also be large, which may make it difficult to place the photo-melt adhesive particles into fine gaps. Furthermore, the heat generated by light irradiation of the shell's photothermal conversion material may not be sufficient to melt the entire core. Therefore, an appropriate size is selected by considering the amount required to obtain sufficient (desired) adhesive strength, the shape and size of the area where the adhesive particles are placed, and the amount of heat generated by light irradiation of the shell. When the material having photothermal conversion function is polypyrrole or poly(N-alkylpyrrole), and the hot-melt adhesive is mainly composed of a resin with a softening point of 50 to 100°C, such as ethylene-vinyl acetate resin, the core size is usually preferably about 0.5 mm to 5 mm in maximum diameter, and more preferably about 0.5 mm to 1.5 mm.

[0031] The material constituting the core is not particularly limited as long as it is an adhesive solid that melts due to the heat generated by light irradiation of the shell. Thermoplastic resins and elastomers commonly used as hot-melt adhesives can be used, and they should be selected from among them considering the type, size, shape, and required strength of the bonded object.

[0032] The hot-melt adhesive used to form the core can be any hot-melt adhesive that has been widely used in the past and is not particularly limited. However, specific examples include those using polymers selected from the group consisting of ethylene-vinyl acetate copolymer, polyolefin, thermoplastic elastomer, polyester, polyamide, and polyurethane as the base polymer. Hot melt adhesives typically use a base polymer, and, as needed, contain tackifiers, plasticizers (softeners), waxes, antioxidants, fillers, and various other additives to adjust the adhesive's properties. Examples of tackifiers include terpene resins, rosin, and various petroleum resins; examples of plasticizers (softeners) include mineral oil, liquid paraffin, and liquid polybutene; and examples of antioxidants include hindered phenol type, hindered amine type, phosphorus-based, and sulfur-based antioxidants. Furthermore, various additives can be listed, including inorganic fillers, ultraviolet absorbers, nucleating agents, antistatic agents, flame retardants, and antibacterial agents.

[0033] (Method for producing photomelt adhesive particles according to the present invention) The cores that make up the light-melt adhesive particles, i.e., the hot-melt adhesive particles, can be produced by melting the hot-melt adhesive and molding and solidifying it into granules. For example, they can be produced by melting the hot-melt adhesive with a glue gun, injecting it, and then cutting it into appropriate sizes. Alternatively, the molten hot-melt adhesive may be atomized by methods such as lowering the temperature after it has been reduced to a droplet state. The shell is obtained by forming a layer of the shell-forming material on the surface of the hot-melt adhesive particles (core) prepared as described above. For example, if the shell-forming material is polypyrrole, the shell can be formed by carrying out the reaction (oxidative polymerization) represented by the following formula (I) in a solution containing the hot-melt adhesive particles prepared as described above, thereby precipitating the reaction product (polymer) on the surface of the hot-melt adhesive particles.

[0034] [ka]

[0035] The reaction represented by formula (I) (oxidative polymerization) is, for example, https: / / pubs.rsc.org / en / content / articlelanding / 2009 / jm / b816839c https: / / pubs.rsc.org / en / content / articlelanding / 1997 / JM / a700237h https: / / pubs.acs.org / doi / 10.1021 / acsami.0c19758 This can be done in accordance with the conditions described therein.

[0036] (Configuration of the position-selective bonding method of the present invention) As described above, the position-selective bonding method of the present invention comprises an adhesive particle placement step, an adhesive particle melting step, a joining step, and a bonding step.

[0037] In the adhesive particle placement step, the photomelt adhesive particles of the present invention obtained as described above are placed at the bonding position of one of the objects to be bonded (object 1). At the placement stage, since the photomelt adhesive particles are not melted particles, they can be easily and accurately placed even in minute areas, such as minute gaps.

[0038] After the adhesive particle placement step, the photo-melt adhesive particles are irradiated with light to generate heat in the photothermal conversion material that forms the shell. This heat then melts the hot-melt adhesive that forms the core (adhesive particle melting step). Since heating by a heating device is not required for the heat generation, there are no problems associated with the use of a heating device, and because it is done by light irradiation, heat generation is possible from a distance, and heat generation in minute areas is also easy.

[0039] Light irradiation can be performed using a light irradiation device that has a light source emitting near-infrared light or the like and can irradiate the object with a predetermined intensity, but sunlight can also be used. For example, sunlight can be focused with a lens or the like and irradiated. The irradiation is performed with a light intensity (light energy) that is sufficient to melt the hot-melt adhesive of the core due to the heat generated by the shell. The light source, irradiation device, distance from the bonding position to the light source, irradiation time, etc., are selected so that the light energy of the irradiation is sufficient to sufficiently melt the hot-melt adhesive.

[0040] The bonding process involves bringing photomelt adhesive particles, which are placed on the object to be bonded 1, into contact with the other object to be bonded (object 2), which is intended to be bonded to object 1, thereby bonding objects 1 and 2 together. The bonding process may be performed after the adhesive particle melting process, that is, after the hot melt adhesive has melted. However, if object 1 or object 2 is made of a material that transmits near-infrared light, the bonding process may be performed before the adhesive particle melting process. In this case, after bringing the photomelt adhesive particles, which are placed on object 1, into contact with object 2, light containing near-infrared light or the like is irradiated onto the photomelt adhesive particles from outside object 1 or object 2 (through object 1 or object 2).

[0041] After the adhesive particle melting process and the bonding process, the bonding position of the adherends (adherend 1 and adherend 2) is usually pressurized so that the hot melt adhesive sandwiched between the adherends is spread apart. Due to the pressurization, the molten hot melt adhesive leaks out from the photomelt adhesive particles and is spread apart, increasing the bonding area and resulting in better bonding strength.

[0042] After the adhesive particle melting process and the joining process, and optionally after further pressurization, the heated and melted hot melt adhesive, and optionally the hot melt adhesive that has been spread by pressurization, solidifies by slowing down the heat, and the objects to be bonded 1 and 2 are bonded together. [Examples]

[0043] Experiment 1 (Preparation of photomelt adhesive particles) By cutting a commercially available hot-melt adhesive (glue stick) with a utility knife, we prepared approximately cubic particles 1 with sides of 1.15 ± 0.17 mm, made from a hot-melt adhesive consisting of 55% by mass of ethylene-vinyl acetate resin, 40% by mass of petroleum resin, and 5% by mass of paraffin, with a melting point of 76.7°C to 84.2°C. To 100g of water, 1.0g of particle 1, 0.1g of pyrrole, and 0.94g of FeCl3·6H2O (with a molar ratio of pyrrole to FeCl3·6H2O of 3:7) were added and stirred at room temperature at 600rpm with a magnetic stirrer for 24 hours to carry out the reaction shown in equation (I) above. As a result, a polypyrrole layer was formed on the surface of particle 1, and photomelt adhesive particles with a shell-core structure were produced. The photomelt adhesive particles were approximately cubic particles with sides of 1.18±0.20mm.

[0044] Experiment 2 (Measurement of heat generation due to light irradiation) Photomelt adhesive particles, prepared in the same manner as in Experiment 1, were immersed in toluene to peel off the polypyrrole layer of the shell from the hot-melt adhesive core, thereby producing hot-melt adhesive particles and polypyrrole films. The hot-melt adhesive particles and polypyrrole films thus obtained, as well as the photomelt adhesive particles prepared in Experiment 1, were each subjected to 1 mm square irradiation of near-infrared light from a near-infrared lamp for 7 seconds, followed by a 7-second pause in irradiation. This process was repeated five times (total irradiation energy of 200 mW for the five irradiations). Surface temperatures during and after irradiation were measured using a thermal camera. The peak temperatures (highest temperatures reached during irradiation) are shown in Table 1.

[0045] [Table 1]

[0046] The results in Table 1 show that the photomelt adhesive particles of the present invention generate heat to approximately 211°C, far exceeding the melting temperature of hot melt adhesive particles, when irradiated with near-infrared light. On the other hand, hot melt adhesive particles not coated with a polypyrrole film generate almost no heat even when irradiated with near-infrared light.

[0047] Experiment 3 (Experiment on adhesion of PET film using photomelt adhesive particles of the present invention) As the substrate, a PET film manufactured by Toray Industries, Inc. was cut with a utility knife to a thickness of 250 μm, a long side of 100 mm, a short side of 25 mm, and a mass of approximately 0.87 g. The photomelt adhesive particles obtained in Experiment 1 were placed approximately in the center of the overlapping portion of the PET film shown in Figure 2 (the portion 12.5 mm from the short side).

[0048] Photomelt adhesive particles placed on a PET film were irradiated with a near-infrared laser (NIR laser: wavelength 808 nm) for 7 seconds (distance between photomelt adhesive particles and NIR laser: approximately 3 cm, irradiation area 1 mm × 5 mm, output 200 mW). Within approximately 3 seconds after the end of NIR laser irradiation, another PET film (of the same type and shape as above) was placed on top of the photomelt adhesive particles, and a 100 g weight was placed on top for 30 seconds to apply compressive stress and attempt to bond the PET films together. As a control experiment, the same experiment was also performed with hot melt adhesive particles that were not coated with a polypyrrole film (the same particles as particle 1 prepared in Experiment 1).

[0049] (Measurement of adhesive strength) The PET film bonded as described above was subjected to a shear peel test using a testing machine (AGS-X, manufactured by Shimadzu Corporation) under conditions of a tensile speed of 2 mm / min and an ambient temperature of 23°C. Subsequently, the adhesive strength (N) obtained from the shear peel test was calculated by dividing it by the area (mm²) over which the photomelt adhesive particles were spread. 2 By dividing by (adhesion area) (Figure 3), the adhesive strength (N / mm²) of the light-melt adhesive particles can be calculated. 2 ) was sought.

[0050] (Discussion of experimental results) After conducting the aforementioned adhesion experiment, when the upper PET film was lifted, the lower PET film also lifted, clearly demonstrating that the PET films were bonded together by the photomelt adhesive particles. Furthermore, even when the bonded PET films were held by hand and shaken vigorously, they remained adhered to each other. However, in an adhesion experiment using hot-melt adhesive particles without a polypyrrole coating (control), the PET films did not bond to each other.

[0051] After the bonding experiment described above, the photomelt adhesive particles in the bonded area were observed under a stereomicroscope. It was confirmed that the molten photomelt adhesive particles were crushed, causing the hot-melt adhesive component to leak and spread across the PET film (Figure 3). From Figure 3, the area over which the photomelt adhesive particles spread was 9.77 ± 1.16 mm².2 This was determined. Furthermore, the adhesive strength was determined by the shear peel test (described in the measurement of adhesive strength), and the adhesive strength (N) was measured to be 12.00 ± 1.25 N. By dividing this adhesive strength (N) by the area over which the light-melt adhesive particles were spread, the adhesive strength (N / mm²) of the light-melt adhesive particles was calculated. 2 The result was 1.24±0.18N / mm². 2 This demonstrated that excellent adhesive strength was achieved. [Industrial applicability]

[0052] As described above, the photo-melt adhesive particles of the present invention are shell-core adhesive particles formed by coating hot-melt adhesive particles with a material having photothermal conversion ability. The position-selective bonding method of the present invention is characterized by placing these photo-melt adhesive particles at the bonding position of the object to be bonded and using the heat generated by light irradiation to melt the hot-melt adhesive particles and perform bonding. Therefore, unlike conventional hot-melt bonding, no heating means are required, and since the placement of the adhesive particles is performed before melting, it is easy to accurately place the particles in minute areas, enabling accurate placement of adhesive in minute gaps and spaces, and facilitating position-selective bonding with hot-melt adhesive. Furthermore, since heat can be generated only where the particles are present by light irradiation, and there is no heating of the object to be bonded by a heating means, thermal deformation and damage to the object to be bonded can be suppressed. Therefore, it is conceivable that this method can be applied to the electronic equipment and automobile fields where localized bonding of parts with complex shapes is required, and it is thought to contribute to the development of these fields. [Explanation of Symbols]

[0053] 1. Shell (a layer of material with photothermal conversion capabilities) 2 cores (hot melt adhesive particles)

Claims

1. Photo-melt adhesive particles comprising hot-melt adhesive particles as a core and a layer of a material having photothermal conversion ability covering the particles as a shell, characterized in that the maximum diameter of the core is 0.5 mm or more and 5 mm or less.

2. The photomelt adhesive particles according to claim 1, characterized in that the material having photothermal conversion ability is polypyrrole or poly(N-alkylpyrrole).

3. The photomelt adhesive particles according to claim 1 or 2, characterized in that the hot melt adhesive contains a polymer selected from the group consisting of ethylene-vinyl acetate copolymer, polyolefin, thermoplastic elastomer, polyester, polyamide, and polyurethane as a base polymer.

4. Adhesive particle arrangement step: Arrange photomelt adhesive particles on a substrate 1, with hot melt adhesive particles as the core, a layer of photothermal conversion material covering the particles as the shell, and the maximum diameter of the core being 0.5 mm or more and 5 mm or less. After the adhesive particle placement step, the photo-melt adhesive particles are irradiated with light to generate heat in the material having photothermal conversion ability, thereby heating and melting the photo-melt adhesive particles of the hot-melt adhesive in an adhesive particle melting step. A bonding step of bringing the light-melt adhesive particles and the object to be bonded 2 into contact and bonding them, After the adhesive particle melting process and the bonding process, the heated and melted photomelt adhesive particles are cooled and solidified to bond the objects to be bonded 1 and 2. A position-selective bonding method characterized by having [a specific feature].

5. The position-selective bonding method according to claim 4, characterized in that the material having photothermal conversion ability is polypyrrole or poly(N-alkylpyrrole).

6. The position-selective bonding method according to claim 5, characterized in that the light irradiation is irradiation of light including near-infrared light.

7. The position-selective bonding method according to claim 6, characterized in that the light irradiation is near-infrared light with a wavelength of 700 nm or more and 1200 nm or less, irradiated at a power of 50 mW or more.

8. The photomelt adhesive particles according to claim 1 or 2, characterized in that the thickness of the layer of the material having photothermal conversion ability is 50 nm or more and 100 μm or less.

9. The position-selective bonding method according to claim 7, characterized in that the thickness of the layer of the material having photothermal conversion ability is 50 nm or more and 100 μm or less.

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