ADHESIVE STRUCTURE

TECHNICAL FIELD

The present disclosure relates to a composition for forming a sealing material, a sealing material, a thermally cured product of a sealing material, and a method for manufacturing an adhesive structure.

BACKGROUND ART

Vehicles such as automobiles and the like have discontinuous joints capable of overlapping members such as metal panels. An example of a general non-planar overlap joint includes a roof ditch. The roof ditch is formed in a front-back direction of a vehicle by folding and overlapping a roof panel and a side edge of a side panel of the vehicle with each other. As a material for making the members adhere to each other while sealing the joints as described above, a polyvinyl chloride sol is used particularly in the automobile industry (see, for example, Patent Documents 1 and 2).

SUMMARY OF INVENTION

However, the polyvinyl chloride sol is a sol-like paste containing polyvinyl chloride and a plasticizer, and when the polyvinyl chloride sol is heated, the polyvinyl chloride sol is solidified in the heated shape, so in the case of attempting to seal sites having a complicated shape with only the polyvinyl chloride sold, there may be a problem in that the polyvinyl chloride sol can be solidified without entering a gap between the sites, the gap remains unsealed, and the like. Therefore, the inventors of the present disclosure investigate a sealing material for sealing sites which are hardly sealed with the polyvinyl chloride sol.

The sealing material is preferably a thermosetting sealing material capable of expressing an adhesion by heating like the polyvinyl chloride sol from the viewpoint that production efficiency is not reduced when used in combination with the polyvinyl chloride sol. However, when the known thermosetting sealing material (for example, a sealing material made of an epoxy-based adhesive) is used, and heated together with the polyvinyl chloride sol, sufficient adhesive strength may not be obtained at a contact portion between a thermally cured product of the sealing material and a cured body (cured body containing polyvinyl chloride) derived from the polyvinyl chloride sol.

Therefore, an object of the present disclosure is to provide a sealing material capable of forming a cured body which exhibits good adhesive strength to a cured body derived from a polyvinyl chloride sol even when the sealing material is heated and cured together with the polyvinyl chloride sol in a state where the sealing material is in contact with the polyvinyl chloride sol.

SOLUTION TO PROBLEM

An aspect of the present disclosure relates to a composition for forming a sealing material including: a (meth)acrylic compound; an epoxy compound; a photopolymerization initiator; and a thermal curing agent, in which the (meth)acrylic compound contains a tetrahydrofuryl (mete)acrylate, and a content of the tetrahydrofuryl (mete)acrylate is 70% by mass or more with respect to a total mass of (meth)acrylic compound.

A content of the epoxy compound in the composition for forming a sealing material may be from 70 to 200 parts by mass with respect to 100 parts by mass of the (meth)acrylic compound.

The epoxy compound may contain a flexible epoxy compound.

Another aspect of the present disclosure relates to a sealing material including a photocured product of the composition for forming a sealing material.

Still another aspect of the present disclosure relates to a sealing material including: a (meth)acrylic polymer; an epoxy compound; and a thermal curing agent, in which the (meth)acrylic polymer contains at least 70% by mass or greater of constituent unit represented by Formula (1) below with respect to a total mass of the (meth)acrylic polymer.

In Formula (1), R represents a hydrogen atom or a methyl group.

A content of the epoxy compound in the sealing material may be from 70 to 200 parts by mass with respect to 100 parts by mass of the (meth)acrylic polymer.

The epoxy compound may contain a flexible epoxy compound.

The sealing material may be formed in a sheet shape.

Still another aspect of the present disclosure relates to a thermally cured product of the sealing material.

Still another aspect of the present disclosure is a method for manufacturing an adhesive structure having a structure in which a first cured body as a thermally cured product of the sealing material and a second cured body containing polyvinyl chloride adhere onto an adherend, the method including: arranging the sealing material and a polyvinyl chloride sol containing the polyvinyl chloride and a plasticizer on the adherend in a state where the sealing material is in contact with the polyvinyl chloride sol; and obtaining the adhesive structure by heating the sealing material and the polyvinyl chloride sol. ADVANTAGEOUS EFFECTS OF INVENTION

According to the present disclosure, there is provided a sealing material capable of forming a cured body which exhibits good adhesive strength to a cured body derived from a polyvinyl chloride sol even when the sealing material is heated and cured together with the polyvinyl chloride sol in a state where the sealing material is in contact with the polyvinyl chloride sol.

BRIEF DESCRIPTION OF DRAWINGS FIG. l is a schematic cross-sectional view showing an embodiment of a method for manufacturing an adhesive structure.

FIG. 2 is a schematic cross-sectional view showing a test piece used for an adhesive strength evaluation of an example. DESCRIPTION OF EMBODIMENTS

Hereinafter, preferred embodiments of the present disclosure will be described. However, the present disclosure is not limited to the following embodiments. In the present specification,“(meth)acrylic” means“acrylic” and“methacrylic” corresponding thereto. The same goes for expressions such as“(meth)acryloyl”,“(meth)acrylate” and the like.

Sealing Material

A sealing material according to an embodiment includes a composition containing a (meth)acrylic polymer, an epoxy compound, and a thermal curing agent, in which the (meth)acrylic polymer contains at least 70% by mass or greater of constituent unit represented by Formula (1) below with respect to a total mass of the (meth)acrylic polymer. A composition of the sealing material serves as a thermosetting adhesive, and is cured by a reaction of the epoxy compound and the thermal curing agent by heating to express an adhesion.

In Formula (1), R represents a hydrogen atom or a methyl group.

The sealing material is typically molded into a shape which can obtain shape followability to an adherend. The shape of the sealing material is not particularly limited, and may be appropriately changed according to a shape of the adherend, flexibility of the sealing material, and the like. The shape of the sealing material may be, for example, a sheet shape (for example, a tape shape). When the sealing material has the sheet shape, a protective film (a release liner or the like) may be provided on one side or both sides of a main surface of the sheet-like sealing material. Since the sealing material typically has stickiness at room temperature, the protective film is provided, so for example, a plurality of sheets wound in a roll shape or cut into a desired size or shape can be stored in a stacked state. A thickness of the sheet-like sealing material may be, for example, 0.05 mm or greater, 0.1 mm or greater, or 0.15 mm or greater, and may be 3 mm or less, 2.5 mm or less, or 2 mm or less.

The sealing material typically has property (heat melting property) which can melt and flow before being completely cured by heating. The sealing material preferably has suitable fluidity at, for example, 100°C. A viscosity (viscosity of the adhesive constituting the sealing material) of the sealing material at 100°C is preferably 50 Pa-s or greater and 400 Pa-s or greater. The viscosity (viscosity of the adhesive constituting the sealing material) of the sealing material at 100°C is preferably 1500 Pa-s or less and 1000 Pa-s or less. The viscosity is a value measured when temperature rises at a rate of 10 °C/minute to a target measurement temperature in air under normal pressure using a dynamic viscoelasticity measuring device. The viscosity can be adjusted by selecting the type and amount of each component contained in the sealing material.

The sealing material can be obtained by photocuring the composition for forming a sealing material described later. That is, the sealing material may contain a photocured product of the composition for forming a sealing material. The sealing material preferably includes only the photocured product of the composition for forming a sealing material. In the case of producing a sheet-like sealing material, for example, the composition for forming a sealing material is applied on a base material (for example, a protective film) to form a layer made of the composition for forming a sealing material, and then the layer is irradiated with light (active rays) to cure the composition for forming a sealing material. As a result, the sheet-like sealing material is obtained. The light is, for example, ultraviolet light (UV). An irradiation amount of light may be, for example, 0.1 J/cm2 or greater and 100 J/cm2 or less with respect to a total energy amount.

The sealing material can be used, for example, to make a first member and a second member adhere to each other and to seal a gap formed by the two members. Specifically, the sealing material is suitably used for sealing a U-shaped groove called a roof ditch formed by a roof panel of a vehicle and a side panel of the vehicle.

The sealing material can be used together with a polyvinyl chloride sol. According to the sealing material, it is possible to form a sealing material capable of forming a cured body (thermally cured product of a sealing material) which exhibits good adhesive strength to a cured body derived from a polyvinyl chloride sol even when the sealing material is heated and cured together with the polyvinyl chloride sol in a state where the sealing material is in contact with the polyvinyl chloride sol. A cause of obtaining such an effect is not clear, but the inventors of the present disclosure estimate the cause as follows.

When the known thermosetting sealing material (for example, a sealing material made of an epoxy-based adhesive) is heated and cured with the polyvinyl chloride sol in a state where the thermosetting sealing material is in contact with the polyvinyl chloride sol, as the cause that the sufficient adhesive strength cannot be obtained, it is considered that adhesiveness of the sealing material itself is insufficient, adhesiveness of a thermally cured product of the sealing material to polyvinyl chloride is reduced due to the intrusion of a plasticizer derived from the polyvinyl chloride sol into the sealing material during the heating and flow of the sealing material, and the like. On the other hand, according to the sealing material, it is possible to suppress the intrusion of the plasticizer during the heating and melting of the sealing material by appropriate polarity (for example, an SP value different from an SP value of the plasticizer) of the (meth)acrylic polymer containing a predetermined amount or more of a constituent unit represented by the Formula (1) and/or steric hindrance, and the like, so it is considered that a cured product having a high adhesion to the polyvinyl chloride is obtained after the sealing material is cured. In addition, since the specific (meth)acrylic polymer (in particular, the constituent unit represented by the Formula (1)) is easily compatible with an epoxy compound (in particular, an aromatic epoxy compound), the adhesiveness of the sealing material itself is increased, which is considered to be one of the causes of obtaining the above effects.

(Meth)acrylic Polymer

The (meth)acrylic polymer is a polymer (for example, a radical polymer) of a polymerizable monomer containing a compound containing a (meth)acryloyl group (hereinafter, also simply referred to as“(meth)acrylic compound”), and at least includes the constituent unit represented by the Formula (1) as the constituent unit derived from the (meth)acrylic compound. The constituent unit represented by the Formula (1) can be paraphrased to a constituent unit derived from tetrahydrofurfuryl(meth)acrylate.

R in the constituent unit represented by the Formula (1) is preferably a hydrogen atom. The (meth)acrylic polymer preferably contains more a constituent unit H in which R is a hydrogen atom than a constituent unit M in which R is a methyl group, and as a constituent unit represented by the Formula (1), it is more preferable to include only the constituent unit H in which R is a hydrogen atom.

A ratio of the constituent unit represented by the Formula (1) is 70% by mass or greater and preferably 75% by mass or greater with respect to the total mass of the (meth)acrylic polymer, from the viewpoint of further improving the adhesiveness to the polyvinyl chloride. The (meth)acrylic polymer may contain only the constituent unit represented by the Formula (1) and a terminal group (for example, a functional group derived from a polymerization initiator, and a functional group derived from a chain transfer agent). The ratio of the constituent unit represented by the Formula (1) may be 100% by mass or less, 95% by mass or less, or 90% by mass or less. The (meth)acrylic polymer may further contain other constituent units other than the constituent unit represented by the Formula (1). The other constituent units are, for example, a constituent unit derived from a compound having a polymerizable carbon- carbon double bond, and more preferably a constituent unit derived from a (meth)acrylic compound. Examples of the (meth)acrylic compound include (meth)acrylates such as n- butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, 2-phenylethyl (meth)acrylate, and isobornyl (meth)acrylate, (meth)acrylamide such as dimethyl (meth)acrylamide, and the like. Among them, alkyl (meth)acrylate is preferable, and from the viewpoint of reducing an odor of the sealing material, alkyl (meth)acrylate (for example, 2-ethylhexyl (meth)acrylate) containing an alkyl group having 8 or more carbon atoms is more preferable.

The (meth)acrylic polymer may include, as other constituent units, a constituent unit containing a functional group (hereinafter, also referred to as a“crosslinkable functional group”) capable of forming a structure which is directly crosslinked with an epoxy compound or a structure which is indirectly crosslinked with the epoxy compound via a thermal curing agent. The (meth)acrylic polymer forms the structure which is crosslinked with the epoxy compound, so the strength of the cured body tends to be improved. The functional group capable of forming the structure which is directly crosslinked with the epoxy compound is, for example, a functional group which reacts with an epoxy group (oxirane ring) and contains at least one nucleophilic or electrophilic moiety (for example, active hydrogen atom), and examples thereof include a phenolic hydroxyl group and the like. The functional group capable of forming the structure which is indirectly crosslinked with the epoxy compound is a functional group capable of reacting with the thermal curing agent, and examples thereof include an epoxy group. Examples of the constituent unit containing a crosslinkable functional group include a constituent unit derived from compounds such as glycidyl (meth)acrylate, hydroxypropyl acrylate, and oxetane. From the viewpoint of preventing the fluidity from excessively decreasing, it is preferable that the crosslinking between the (meth)acrylic polymers by a bifunctional or higher (meth)acrylate compound and the like such as hexanediol diacrylate is as small as possible.

The ratio of the constituent unit containing the crosslinkable functional group is preferably 10% by mass or less and more preferably 7% by mass or less with respect to the total mass of the (meth)acrylic polymer, from the viewpoint of improving the fluidity during heating. The ratio of the constituent unit containing the crosslinkable functional group is preferably 0.001% by mass or greater and 3% by mass or greater with respect to the total mass of the (meth)acrylic polymer, from the viewpoint of improving the strength of the thermally cured product.

When the (meth)acrylic polymer is a polymer (copolymer) of a plurality of types of compounds, the arrangement of each constituent unit is not particularly limited. The (meth)acrylic polymer may be an alternating copolymer, a random copolymer, a block copolymer, a graft copolymer or the like.

A weight average molecular weight of the (meth)acrylic polymer may be 3000 or greater and 300000 or less. In addition, a weight average molecular weight is a polystyrene conversion value which uses a calibration curve by standard polystyrene by a gel permeation chromatography method (GPC).

A melting point of the (meth)acrylic polymer is preferably lower than a curing initiation temperature of the epoxy compound, from the viewpoint of the heat melting property of the sealing material. The melting point of the (meth)acrylic polymer may be, for example, 140°C or lower or 120°C or lower, and may be 80°C or higher or 90°C or higher.

The content of the (meth)acrylic polymer in the sealing material is preferably 20% by mass or greater, more preferably 30% by mass or greater, and still more preferably 35% by mass or greater with respect to the total mass of the sealing material, from the viewpoint of further improving the adhesiveness to the polyvinyl chloride. The content of the (meth)acrylic polymer in the sealing material is preferably 70% by mass or less, more preferably 60% by mass or less, and still more preferably 50% by mass or less with respect to the total mass of the sealing material, from the viewpoint of further improving the adhesiveness to the polyvinyl chloride.

The epoxy compound is a compound containing two or more epoxy groups in one molecule, and preferably a compound containing 2 to 4 epoxy groups. Among the compounds containing the two or more epoxy groups in one molecule, the compounds corresponding to the (meth)acrylic polymer and the (meth)acrylic compound do not correspond to the epoxy compound.

The epoxy compound includes a compound (for example, polymer compound) generally called an epoxy resin. From the viewpoint of the shape stability of the sealing material and the viewpoint of not increasing the crosslinking density after the heat curing, an epoxy equivalent of the epoxy compound may be 80 g/eq. or greater or 90 g/eq. or greater, and from the viewpoint of the compatibility with other components and the flexibility of the sealing material, the epoxy equivalent of the epoxy compound may be 1000 g/eq. or less or 600 g/eq. or less. The epoxy equivalent is a value determined in accordance with JIS K 7236.

The epoxy compound is an aliphatic epoxy compound having an aliphatic structure, an alicyclic epoxy compound having an alicyclic structure, an aromatic epoxy compound having an aromatic structure, or a heterocyclic epoxy compound having a heterocyclic structure. Among them, the aromatic epoxy compound is preferable.

Examples of the aromatic epoxy compound include a bisphenol type epoxy compound and a novolak type epoxy compound. Examples of the bisphenol type epoxy compound include a bisphenol A type epoxy compound, a dimer acid modified bisphenol A type epoxy compound, a bisphenol F type epoxy compound, and the like. Examples of the novolac type epoxy compound include a phenol novolac type epoxy compound, a cresol novolac type epoxy compound and the like.

As the epoxy compound, in addition to the above, for example, aliphatic epoxy compounds such as hexanediol glycidyl ether, glycidyl amine type epoxy compounds such as p-aminophenol triglycidyl, brominated epoxy compounds, and alicyclic epoxy compounds can be used. The epoxy compound is preferably a bisphenol type epoxy compound, a glycidyl amine type epoxy compound, or a novolac type epoxy compound, more preferably a bisphenol type epoxy compound, and still more preferably a bisphenol A type epoxy compound.

The epoxy compound may be a commercially available product. Examples of the commercially available product include YDF-170, YD-128, YD-011, YDPN-638, and YDCN-700-3 (available from Nippon Steel & Sumikin Chemical Co., Ltd.), MY0510 (available from Huntsman Corporation), jERlOOl (available from Mitsubishi Chemical Corporation), and the like. One type of the epoxy compound may be used alone, and may be used in combination of 2 or more types thereof. When two or more types of epoxy compounds are used in combination, from the viewpoint of shape stability and flexibility of the sealing material, an epoxy compound having an epoxy equivalent of 150 to 250 g/eq. and an epoxy compound having an epoxy equivalent of 400 to 600 g/eq. are preferably used in combination.

From the viewpoint of the adhesive property and the hardness of the thermally cured product, the content of the epoxy compound is preferably 70 parts by mass or more, and more preferably 80 parts by mass or greater, and still more preferably 90 parts by mass or greater with respect to 100 parts by mass of the (meth)acrylic polymer. From the viewpoint of the shape stability of the sealing material, the content of the epoxy compound is preferably 200 parts by mass or less, more preferably 150 parts by mass or less, and still more preferably 110 parts by mass or less with respect to 100 parts by mass of the (meth)acrylic polymer.

Typically, as the content of the epoxy compound increases, the extensibility of the thermally cured product tends to decrease, but in order to improve the extensibility of the thermally cured product, a flexible epoxy compound can be used as the epoxy compound. The flexible epoxy compound is a compound in which a flexible skeleton (for example, a long chain alkyl skeleton, a polyalkylene oxide skeleton or the like) is introduced into the epoxy compound, and as the compound, for example, a compound having a bisphenol skeleton and a flexible skeleton and the like has been known. By using the flexible epoxy compound, the extensibility after the thermosetting can be improved, and the occurrence of defects such as cracks and peeling can be further suppressed.

As the flexible epoxy compound, a bisphenol A alkylene oxide modified epoxy compound is preferably used. Examples of the bisphenol A alkylene oxide modified epoxy compound include a compound having a partial structure represented by Formula (2) below.

In the Formula (2), R1 and R2 each independently represent an alkylene group, and nl and n2 are integers of 0 or greater (however, nl + n2 is 1 or greater).

The alkylene group of R1 and R2 may be linear for or branched. The number of carbon atoms of the alkylene group is, for example, 1 to 5. The alkylene group is preferably an ethylene group or an isopropylene group.

Commercially available products of the flexible epoxy compound include ADEKA Resin EP-4000, ADEKA Resin EP-4005, ADEKA Resin EP-70001, ADEKA Resin EPU- 1 IF, ADEKA Resin EPU-15F (available from ADEKA Corporation), and the like.

In the present embodiment, it is particularly preferable to use a combination of the flexible epoxy compound and the bisphenol A type epoxy compound. By using the bisphenol A type epoxy compound in combination with a compound (flexible epoxy compound) which is more excellent in flexibility after the thermosetting than the bisphenol A type epoxy compound, it is possible to further increase the extensibility and adhesiveness after the thermosetting.

The content of the flexible epoxy compound is preferably 10% by mass or greater, more preferably 15% by mass or greater, and still more preferably 20% by mass or greater with respect to the total mass of the epoxy compound, from the viewpoint of further increasing the extensibility of the thermally cured product. The content of the flexible epoxy compound is preferably 60% by mass or less, more preferably 55% by mass or less, and still more preferably 50% by mass or less with respect to the total mass of the epoxy compound, from the viewpoint of giving a predetermined hardness to the thermally cured product.

Thermal Curing Agent

As a thermal curing agent, various thermal curing agents known in the art to be usable as a thermal curing agent for an epoxy compound can be used. Examples of the thermal curing agent can include the compound which can react with the epoxy group (oxirane ring) of the epoxy compound and can form a crosslinked structure (crosslinked polymer network). Examples of the compounds include a compound which reacts with the epoxy group and contains at least one nucleophilic or electrophilic moiety (for example, active hydrogen atom). As the thermal curing agent, a latent curing agent which is inactive at around room temperature and activated by heat is preferably used. Examples of the latent curing agent include dicyandiamide and a derivative thereof, a hydrazide compound, a boron trifluoride-amine complex, a reaction product of an amine compound with an isocyanate compound or a urea compound (urea derivative), and the like. Among them, the dicyandiamide is preferably used. Commercially available products suitable as the thermal curing agent include EH-3636AS (available from ADEKA Corporation).

The thermal curing agent also includes a“curing accelerator” to increase a cure reaction rate of the epoxy compound. In the typical aspect, the curing accelerator is a multifunctional compound. The curing accelerator may be the latent curing accelerator which is inactive around room temperature and activated by heating. Examples of the curing accelerator include an imidazole compound, a reaction product of an amine compound with an epoxy compound (amine-epoxy adduct), a urea derivative, and the like. Commercially available products of the suitable latent curing accelerator include 2MZA- PW and 2PHZ-PW (available from Shikoku Kasei Kogyo Co., Ltd.).

One type of the thermal curing agent may be used alone, and two or more types of the thermal agents may be used in combination. The latent curing agent and the latent curing accelerator may be used in combination as the thermal curing agent for the epoxy compound.

The content of the thermal curing agent may be 0.1 parts by mass or greater, 1 part by mass or greater, or 3 parts by mass or greater, and 80 parts by mass or less, 60 parts by mass or less, or 50 parts by mass or less with respect to 100 parts by mass of the epoxy compound, from the viewpoint of realizing the good crosslinking reaction of the epoxy compound.

The sealing material may further contain other components other than the components described above, as long as the effects of the present disclosure are not impaired. Examples of the other components include a molding aid, a filler, an antioxidant, a colorant (pigment or the like), and the like.

Examples of the molding aid include polyvinyl butyral, a phenoxy resin and the like. By using the molding aid, it is possible to improve the strength of the sealing material and enhance the moldability. The content of the molding aid may be from 5 to 50 parts by mass with respect to 100 parts by mass of the (meth)acrylic compound.

As the filler, it is possible to use an organic filler or an inorganic filler according to the purpose such as increasing a weight of an adhesive constituting the sealing material, reducing a weight, imparting flame resistance, imparting thermal conductivity, modifying, controlling a flow, and coloring. Examples of the filler include calcium carbonate particles, mica particles, talc particles, hollow glass beads, aluminum hydroxide particles, magnesium hydroxide particles, silica particles (including fumed silica), and the like. The content of the filler may be from 0.1 to 20 parts by mass with respect to 100 parts by mass of the (meth)acrylic compound.

Examples of the antioxidant include Irganox 1010 (available from BASF Japan Ltd.) and the like. The content of the antioxidant may be from 0.1 to 1.0 part by mass with respect to 100 parts by mass of the (meth)acrylic compound.

As the colorant, the known organic pigments and inorganic pigments can be used. The content of the pigment may be 0.1 to 2.0 parts by mass with respect to 100 parts by mass of the (meth)acrylic compound.

The sealing material preferably does not contain a shock absorber. The shock absorber has, for example, a core-shell structure, and a shock absorber in which a part of an epoxy resin is impregnated and dispersed is used. When the sealing material contains the shock absorber, it may be difficult to obtain sufficient heat melting property. Examples of the shock absorber include Paraloid BTA 731 (The Dow Chemical Company) and the like.

The sealing material of the present embodiment described above has various advantages as compared with the polyvinyl chloride sol. For example, the polyvinyl chloride sol may not provide sufficient sealability to a site having a complicated shape, but the sealing material of the present embodiment has the shape stability and can be not only processed and/or molded (for example, shape (for example, a sheet shape) according to the application site by punching) into a shape according to the application site, but also maintains its own shape at room temperature, and can be melted when heated to follow the complicated shape, such that the sealing material of the present embodiment can improve the sealability of the site having the complicated shape. In addition, the polyvinyl chloride sol needs to be shaped by brushing or the like after application to an adherend, and since the polyvinyl chloride sol is cured as it is when heated, the sealability cannot be secured depending on a skill level of a worker. Also, in the polyvinyl chloride sol, even the control of the thickness or the uniform appearance is obtained depending on a skill level of a worker. Since the sealing material of the present embodiment has a predetermined shape, the sealing material can be performed at a preset thickness, and easily has a uniform appearance regardless of a skill level of a worker. As described above, the sealing material of the present embodiment can be suitably used as a substitute for the polyvinyl chloride sol. By using such a sealing material in combination with the polyvinyl chloride sol, the sealing property to a site (for example, a screw portion in a joint provided with a screw, and the like) having a complicated shape can be improved.

Next, the composition (composition for forming a sealing material) for forming the sealing material above will be described.

The composition for forming a sealing material according to an embodiment contains a (meth)acrylic compound, an epoxy compound, a photopolymerization initiator, and a thermal curing agent. In the composition for forming a sealing material, the (meth)acrylic compound contains tetrahydrofurfuryl (meth)acrylate. The content of the tetrahydrofurfuryl (meth)acrylate is 70% by mass or greater with respect to the total mass of the (meth)acrylic compound. The composition for forming a sealing material is cured by polymerizing the (meth)acrylic compound by light irradiation to form the sealing material of the embodiment described above. The composition for forming a sealing material may further contain a photopolymerizable compound (a compound which can be polymerized with the (meth)acrylic compound) other than the (meth)acrylic compound.

(Meth)acrylic Polymer

A (meth)acrylic compound is a compound containing a (meth)acryloyl group, and contains at least tetrahydrofurfuryl (meth)acrylate. The (meth)acrylic polymer described above is obtained by polymerizing the (meth)acrylic compound and other photopolymerizable compounds optionally contained.

The content of tetrahydrofurfuryl (meth)acrylate is preferably adjusted so that the proportion of the constituent unit represented by the Formula (1) in the (meth)acrylic polymer obtained after photocuring is in the above range. The content of the tetrahydrofurfuryl (meth)acrylate is, for example, 70% by mass or greater and preferably 75% by mass or greater with respect to the total mass of the (meth)acrylic compound. The content of the tetrahydrofurfuryl (meth)acrylate is, for example, 100% by mass or less, 95% by mass or less, or 90% by mass or less with respect to the total mass of the (meth)acrylic compound.

The (meth)acrylic compound may further contain the above-described (meth)acrylic compound which can be a constituent unit of the (meth)acrylic polymer. For example, the (meth)acrylic compound may further contain an alkyl (meth)acrylate containing an alkyl group having 8 or more carbon atoms. In addition, the (meth)acrylic compound may further contain a (meth)acrylic compound containing a crosslinkable functional group. The content of the (meth)acrylic compound containing the crosslinkable functional group may be, for example, 10% by mass or less or 7% by mass or less and 0.001% by mass or more or 3 mass% or greater with respect to the total mass of the (meth)acrylic compound.

The content of the (meth)acrylic compound in the composition for forming a sealing material is preferably adjusted so that the content of the (meth)acrylic polymer in the sealing material obtained after photocuring is in the above-described range. The content of the (meth)acrylic compound may be, for example, 20% by mass or greater, 30% by mass or greater, or 35% by mass or greater, and 70% by mass or less, 60% by mass or less, or 50% by mass or less with respect to the total mass of the composition for forming a sealing material.

The photopolymerization initiator is, for example, a photoradical polymerization initiator. As the photopolymerization initiator, a cleavage type or a hydrogen withdrawing type is effective. Examples of the cleavage type photopolymerization initiator include benzoethyl ether, diethoxyacetophenone, 2,2-dimethoxy-l,2-diphenylethane-l-one (2,2- dimethoxy-2-phenylacetophenone), 2-hydroxy -2-methyl- 1 -phenylpropan- 1 -one, 1 - hydroxycyclohexyl phenyl ketone, 2-hydroxy-l-{4-[4-(2-hydroxy-2-methyl-propionyl)- benzyl] -phenyl } -2-methyl-propan- 1 -one, 2-methyl- 1 -[4-(methylthio)phenyl]-2- morpholinopropan- 1 -one, 2-benzyl-2-dimethylamino- 1 -[4-(morpholino)phenyl]- 1 - butanone, 2-dimethylamino-2-(4-methylbenzyl)- 1 -(4-morpholine-4-yl-phenyl)-butan- 1 - one, bis(2,4,6-trimethylbenzoyl)-phenyl phosphine oxide, 2,4,6-trimethylbenzoyl- diphenyl-phosphine oxide, and the like. Examples of the hydrogen withdrawing type photopolymerization initiator include benzophenone, 2,4-diethylthioxanthone and the like. The content of the photopolymerization initiator may be 0.05 parts by mass or more and 0.5 parts by mass or less with respect to 100 parts by mass of the (meth)acrylic compound, from the viewpoint that the composition for forming a sealing material can be sufficiently photocured. When the composition for forming a sealing material further includes a photopolymerizable compound (a compound which can be polymerized with a (meth)acrylic compound) other than the (meth)acrylic compound, the content of the photopolymerization initiator with respect to 100 parts by mass of the photopolymerizable compound may be in the above range.

As the epoxy compound and the thermal curing agent, the epoxy compound and the thermal curing agent contained in the sealing material described above are used.

The content of the epoxy compound is preferably adjusted so that the content of the epoxy compound in the sealing material obtained after photocuring is in the above- described range. The preferable range of the content of the epoxy compound in the composition for forming a sealing material with respect to 100 parts by mass of the (meth)acrylic compound is the same as the preferable range of the content of the epoxy compound in the sealing material with respect to 100 parts by mass of the (meth)acrylic polymer.

The content of the thermal curing agent is preferably adjusted so that the content of the thermal curing agent in the sealing material obtained after photocuring is in the above- described range. The range of the content of the thermal curing agent in the composition for forming a sealing material with respect to 100 parts by mass of the epoxy compound may be the same as the range exemplified as the content of the thermal curing agent in the sealing material with respect to 100 parts by mass of the epoxy compound. Other Components

The composition for forming a sealing material may contain other components which can be included in the above-described sealing material.

The composition for forming a sealing material preferably contains a chain transfer agent from the viewpoint of controlling a molecular weight of the (meth)acrylic polymer. Examples of the chain transfer agent include carbon tetrabromide, a mercapto compound and the like. Examples of the mercapto compound include ethanethiol, butanethiol, dodecanethiol, mercaptoethanol (thioglycol), 3-mercaptopropanol, thioglycerin (mercaptoglycerin), thioglycolic acid (mercaptoacetic acid), 2-mercaptopropionic acid (thiolactic acid), 3-mercaptopropionic acid, a-mercaptoisobutyric acid, methyl mercaptopropionate, ethyl mercaptopropionate, and the like.

The content of the chain transfer agent may be 0.1 parts by mass or greater and 1.0 part by mass or less with respect to 100 parts by mass of the (meth)acrylic compound. When the composition for forming a sealing material further includes a photopolymerizable compound (a compound which can be polymerized with a (meth)acrylic compound) other than the (meth)acrylic compound, the content of the chain transfer agent with respect to 100 parts by mass of the photopolymerizable compound may be in the above range.

Next, an adhesive structure using the sealing material of the present embodiment and a method for manufacturing the same will be described with reference to the drawings.

Adhesive Structure and Method for Manufacturing Same

FIG. l is a schematic cross-sectional view showing an embodiment of a method for manufacturing an adhesive structure. An adhesive structure 10 illustrated in FIG. 1 has a structure in which a first cured body 11 as a thermally cured product of a sealing material and a second cured body 12 containing polyvinyl chloride adheres onto an adherend 3.

The method for manufacturing an adhesive structure 10 includes a step (a) of preparing an adherend 3 (see (a) of FIG. 1), a step (b) of arranging a sealing material 1 and a polyvinyl chloride sol 2 containing polyvinyl chloride and a plasticizer on the adherend 3 in a state where the sealing material 1 and the polyvinyl chloride are in contact with each other (see (b) of FIG. 1), and a step (c) of obtaining an adhesive structure 10 by heating the sealing material 1 and the polyvinyl chloride sol 2 (see (c) of FIG. 1). The adherend 3 illustrated in FIG. 1 includes a first member 4, a second member 5, and a screw 6 which penetrates and fixes the first member 4 and the second member 5. The adherend 3 is, for example, a U-shaped groove called a roof ditch formed by a roof panel (first member 4) of a vehicle and a side panel (second member 5) of the vehicle. In FIG. 1, the adherend 3 is configured by a plurality of members, but the adherend may be configured by one member.

Examples of the materials of the adherend 3 may include glass, metal (for example, iron, aluminum, titanium, and an alloy (for example, stainless steel) containing at least one thereof), plastic, wood, ceramics, and the like. When the adherend 3 is constituted by a plurality of members, the plurality of members may be formed of the same material, or may be formed of different materials.

In the step (b), as illustrated in (b) of FIG. 1, the sealing material 1 and the polyvinyl chloride sol 2 are preferably arranged on the adherend 3 so that a portion where the screw 6 of the adherend 3 is provided is sealed by the sealing material 1. The sealing material 1 and the polyvinyl chloride sol 2 may be arranged so that one of the sealing material 1 and the polyvinyl chloride sol 2 overlaps the other thereof, and may be arranged adjacent to each other without overlapping. As the polyvinyl chloride sol, the known polyvinyl chloride sol mainly made of the polyvinyl chloride (for example, polyvinyl chloride particles) and the plasticizer can be used.

In the step (c), the sealing material 1 and the polyvinyl chloride sol 2 are cured to form the first cured body 11 and the second cured body 12, respectively. As shown in (c) of FIG. 1, the sealing material 1 is melted by heating, and can fill a gap between the portion where the screw 6 of the adherend is provided and a stepped portion. As described above, according to the method according to the present embodiment, it is possible to improve the sealability of the site having the complicated shape.

A heating temperature and a heating time in the step (c) are preferably temperature and time at which the sealing material 1 can be melted and can flow before being cured, and the sealing material 1 and the polyvinyl chloride sol 2 can be sufficiently cured. The heating temperature may be, for example, 60°C or higher or 100°C or higher, and may be 200°C or lower or 180°C or lower. The heating may be performed in two or more steps where the heating temperature is changed. For example, in the first heating step, the heating temperature may be 60°C to 100°C, and in the subsequent second heating step, the heating temperature may be 80°C to 200°C. The heating time may be, for example, 5 minutes or longer or 10 minutes or longer, and 60 minutes or less or 30 minutes or less through one or more steps. The heating time of each step when heating is performed in two or more steps may be set appropriately.

EXAMPLES

Hereinafter, the present disclosure will be more specifically described with reference to Examples, but the present disclosure is not limited to the Examples. Examples 1 to 7 and Comparative Examples 1 to 4

Preparation of Composition for Forming Sealing Material

Components (i) to (vii) shown in the following Table 1 below were prepared. Subsequently, components (i), (ii), (iii), and (v) were mixed in blending amounts (unit: part by mass) shown in the following Tables 2 to 4, and were stirred at a temperature of 60°C or lower until a homogeneous mixture is obtained. After the resulting mixture (a) was cooled to room temperature, the mixture (a) after cooling was added with components (iv), (vi) and (vii) in the blending amounts (unit: part by mass) shown in the following Tables 2 to 4 and stirred at room temperature. As a result, the composition for forming a sealing material was obtained.

Table 1

Table 2

Table 3 Table 4

Production of Sealing Material Sheet

Two transparent PET films whose surfaces are coated were prepared, and the composition for forming a sealing material obtained was applied onto one of the PET films. Thereafter, the other PET film was disposed on a layer made of the composition for forming a sealing material. A gap (thickness of the layer made of the composition for forming a sealing material) between the two PET films was 0.5 mm. Subsequently, a sheet-like sealing material (sealing material sheet) was obtained by irradiating UV light from above the obtained laminate. In addition, an irradiation amount (total energy amount) of the UV light was 1 J/cm2.

Evaluation

The evaluation described below was performed using the sealing material of Example and Comparative Example. Adhesive Strength Evaluation (Measurement of Shear Adhesion)

FIG. 2 is a schematic cross-sectional view showing a test piece for measuring shear adhesion. The test piece of FIG. 2 was produced in the following procedure, and the adhesive strength was evaluated. In this evaluation, it was determined that the adhesive strength is good when the shear adhesion is greater than 1.50 MPa. The results are shown in Table 5. In the table, in the adhesive strength evaluation, one in which the cured product (cured product containing polyvinyl chloride) derived from the polyvinyl chloride sol is cohesively fractured is defined as fracture mode A, and one in which peeling occurs at an interface between the cured product derived from the polyvinyl chloride sol and the thermally cured product of the sealing material is defined as fracture mode B. When the fracture mode is A, the adhesive strength at the interface between the cured product derived from the polyvinyl chloride sol and the thermally cured product of the sealing material is estimated to be better than the measured value.

(1) Two substrates 21a and 21b whose surfaces were subjected to electrodeposition coating were prepared.

(2) By arranging the polyvinyl chloride sol (sol-like composition containing polyvinyl chloride and a plasticizer) on one substrate 21a in a layer of 30 mm long x 17 mm wide ^c 1.2 mm thick, a polyvinyl chloride sol layer 22 was formed.

(3) An aluminum wire 23 (diameter of 1.6 mm) was disposed as a spacer on both sides (positions adjacent to both ends in a width direction) of the polyvinyl chloride sol layer 22.

(4) The sealing material sheet produced was cut out in a rectangular shape having 25 mm long x 12 mm wide, and disposed on the other substrate 21b.

(5) The two substrates 21a and 21b overlap so that an area of a contact portion (overlapping portion) of the polyvinyl chloride sol layer 22 and the sealing material sheet 24 was 25 mm long x 12 mm wide, thereby obtaining a laminate.

(6) The laminate obtained in (5) was clipped to maintain a temporarily fixed state during baking in an oven.

(7) The clipped laminate was heated in the oven. The heating conditions were 140°C and 25 minutes.

(8) The laminate after heating was cooled to room temperature, and this was used as the test piece 20 for measuring shear adhesion. (9) The shear adhesion between the two substrates of the test piece 20 was measured using a Tensilon universal tester manufactured by Orientec Co., Ltd. The measurement was performed at room temperature, and a test speed was 50 mm/min.

The elongation of the thermally cured product of the sealing material was evaluated in the following procedure. In the present evaluation, it was determined that the extensibility was good when the rupture elongation was greater than 50%. The results are shown in Table 5.

(1) The sealing material sheet produced was cut out in a rectangular shape having 30 cm long ^c 12 cm wide, and disposed on the PET film whose surface is treated with silicone.

(2) The laminate obtained in (1) was heated in the oven. The heating conditions were 140°C and 30 minutes.

(3) The laminate after heating was cut out into a JIS No. 3 dumbbell shape.

(4) After the PET film was peeled off, both ends of the laminate cut out in (3) were covered with a tape having a width of 25 mm so that an exposed portion of 50 mm remains at a central part. This was used as a test piece for elongation evaluation.

(5) An upper part of the test piece was fixed by a gripping tool so that an inner edge of the tape covering the laminate is parallel to a lower end of the upper part of the tensile tester.

(6) The lower part of the test piece was fixed by the gripping tool on the lower part of the tensile tester.

(7) The gripping tool was operated at a displacement speed of 50 mm/min, and an operation distance until the test piece is ruptured was measured.

(8) The rupture elongation was calculated based on the following equation.

Rupture elongation (unit: %) = operation distance (unit: mm)/50 (unit: mm) x 100

Odor Evaluation

The odor of the sealing material was evaluated according to the following procedure. (1) The sealing material sheet produced was cut out in a rectangular shape having 100 mm long x 25 mm wide, and was put into a glass bottle (capacity of 900 ml).

(2) After an opening of the glass bottle is sealed with an aluminum foil, the glass bottle was left at room temperature for 24 hours.

(3) The aluminum foil was removed, and the odor in the glass bottle was evaluated based on the following criteria.

5 : Strong odor

4: Strong odor but no bad smell

3 : Moderate odor

2: Weak odor

1 : No odor

Table 5

Reference Signs List

1 Sealing material

2 Polyvinyl chloride sol

3 Adherend

10 Adhesive structure

11 First cured body

12 Second cured body