JP7495938B2 - Adhesive Sheet - Google Patents

Description

The present invention relates to an adhesive sheet.

Polyvinyl chloride-based bundling tape is used to bundle electric wires and wiring in buildings and the like. After bundling the electric wires and wiring, the tape is repeatedly wrapped around the wires and wiring in a spiral shape to bundle them and provide them with electrical insulation, heat resistance, flame retardancy, abrasion resistance, and other properties. However, since this method of repeatedly wrapping tape requires a lot of work, in recent years, in order to reduce the amount of work required, there has been an increase in the use of a method in which a sheet is wrapped around the bundled electric wires and wiring and then fixed with a strong adhesive tape such as double-sided tape, and protective sheets with double-sided tape have been proposed for this purpose (Patent Documents 1 and 2).

In many cases, double-sided adhesive tapes are provided with a release paper to prevent the adhesive layer from adhering to the substrate before use. The release paper must be peeled off when the tape is used, but this process takes time, and the release paper becomes waste after peeling. Therefore, as adhesive sheets that do not use release paper, sheets with adhesive layers that fuse with heat (Patent Document 3) and sheets in which adhesive layers are bonded together using a pressure-sensitive adhesive (Patent Documents 4 and 5) have been proposed.

JP 2011-104840 A JP 2001-348547 A Japanese Patent Application Laid-Open No. 11-7856 JP 2013-168322 A JP 2016-056270 A

However, the method described in Patent Document 3 has the problem that the work time is long because the work of bonding with a heat sealer is required, and it cannot be used when the heat resistance of the object to be protected is low. In addition, the methods described in Patent Documents 4 and 5 use naturally obtained rubber as the adhesive. This natural rubber is known as a structure in which 1,4-cis-isoprene is polymerized, and when stored in a high-temperature environment, the isoprene skeleton is cut at the double bond, causing a decrease in molecular weight. Therefore, there is a concern that the adhesive will deteriorate in a high-temperature environment or a high-humidity environment, causing stickiness and peeling of the bond due to a decrease in adhesive strength. Therefore, there is a demand for an adhesive sheet that is less likely to become sticky and has a less decrease in adhesive strength even when stored in a high-temperature environment.

As a result of extensive research into these issues, the inventors have discovered that by using an adhesive sheet comprising a substrate containing a polyvinyl chloride resin and an adhesive layer containing a specific natural rubber, it is possible to obtain an adhesive sheet that is less sticky but has strong adhesion between the adhesive layers, and is less susceptible to deterioration in the usage environment.

That is, the pressure-sensitive adhesive sheet according to the present invention has the following features.
[1] An adhesive sheet having a substrate containing a vinyl chloride resin and a plasticizer, and an adhesive layer containing natural rubber, wherein, in pulse solid-state ^1H -NMR measurement of the adhesive layer, when the integral value of the ^1H intensity over the entire relaxation time is taken as 100%, the ^1H intensity ratio for a relaxation time of 0.10 milliseconds or less is 5 to 30%.
[2] The adhesive sheet according to [1], wherein the toluene insoluble matter rate of the adhesive layer is 75 mass% or more relative to the total mass of the adhesive layer.
[3] The adhesive sheet according to [1] or [2], wherein the sulfur element content in the adhesive layer is 1.0 mass% or less.
[4] The adhesive sheet according to any one of [1] to [3], wherein the adhesive layer contains an antioxidant, and the content of the antioxidant in the adhesive layer is 0.3 to 5.0 mass% relative to the total mass of the adhesive layer.
[5] The pressure-sensitive adhesive sheet according to [4], wherein the antioxidant is a hindered phenol-based antioxidant represented by the following formula (I):

(In formula (I), R ¹ and R ² each independently represent a substituted or unsubstituted hydrocarbon group having 1 to 4 carbon atoms, A represents a hydrogen atom, a carbon atom, or a substituted or unsubstituted hydrocarbon group having 1 to 18 carbon atoms, and n represents a number from 1 to 4.)

According to the present invention, it is possible to provide an adhesive sheet that is less sticky but has high adhesion between the adhesive layers, and is less susceptible to deterioration in the usage environment.

1 is a cross-sectional view showing one embodiment of a pressure-sensitive adhesive sheet of the present invention.

The following describes in detail the embodiments of the present invention, but the present invention is not limited to the following embodiments and can be implemented with appropriate modifications within the scope that does not impair the effects of the present invention.

[Adhesive sheet]
The adhesive sheet of the present invention is an adhesive sheet having a base material containing a vinyl chloride resin and a plasticizer, and an adhesive layer containing natural rubber, characterized in that, in pulse solid-state ^1H -NMR measurement of the adhesive layer, when the integrated value of the ^1H intensity over the entire relaxation time is taken as 100%, ^{the 1H} intensity ratio for a relaxation time of 0.10 milliseconds or less is 5 to 30%.
The pressure-sensitive adhesive sheet of the present invention preferably has the substrate and the pressure-sensitive adhesive layer provided on one surface of the substrate.
1 is a cross-sectional view showing one embodiment of the adhesive sheet of the present invention. The adhesive sheet 10 has a substrate 1 and an adhesive layer 2 provided on one surface of the substrate 1. In the adhesive sheet 10, when the integral value of the ¹ H intensity over the entire relaxation time in pulse solid-state ¹ H-NMR measurement of the adhesive layer 2 is taken as 100%, ^{the 1} H intensity ratio for a relaxation time of 0.10 milliseconds or less is 5 to 30%.

<Substrate>
The adhesive sheet is required to bundle long objects such as electric wires and wiring, and to protect the long objects from various environments. Therefore, the base material of the adhesive sheet needs to be a resin that has electrical insulation, heat resistance, and flame retardancy, and can simultaneously achieve strength and flexibility. A vinyl chloride resin is suitable as a resin that can satisfy these requirements. The base material of the adhesive sheet of this embodiment contains a vinyl chloride resin and a plasticizer.
Examples of vinyl chloride resins include polyvinyl chloride, vinyl chloride-vinyl acetate copolymers, vinyl chloride-ethylene copolymers, vinyl chloride-propylene copolymers, etc. These may be used alone or in combination of two or more. Among these, polyvinyl chloride is preferred because it is excellent in flexibility, extensibility, and moldability, and is versatile and inexpensive to use.

The degree of polymerization of polyvinyl chloride is not particularly limited as long as it has the effect of the present invention, but from the viewpoint of obtaining good processability, an average degree of polymerization of 500 to 4000 is preferable, 800 to 3000 is more preferable, and 1000 to 2000 is particularly preferable.

The substrate contains a plasticizer to impart flexibility, extensibility and processability to the adhesive sheet.
As the plasticizer, a phthalic acid plasticizer, an isophthalic acid plasticizer, a terephthalic acid plasticizer, an adipic acid plasticizer and their polyester-based plasticizers, a phosphoric acid plasticizer, a trimellitic acid plasticizer, an epoxy-based plasticizer, etc., can be used. Among these, it is preferable to use a phthalic acid plasticizer, which is inexpensive and has a high plasticizing effect.
Examples of phthalic acid plasticizers include diisonyl phthalate (DINP), diheptyl phthalate (DHP), di-2-ethylhexyl phthalate (DOP), di-n-octyl phthalate (n-DOP), diisodecyl phthalate (DIDP), di-2-ethylhexyl isophthalate (DOIP), di-2-ethylhexyl terephthalate (DOTP), benzyl butyl phthalate (BBP), and tri-2-ethylhexyl trimellitate (TOTM). , di-2-ethylhexyl adipate (DOA), tricresyl phosphate (TCP), benzyl octyl adipate (BOA), adipic acid-propylene glycol based polyester, adipic acid-butylene glycol based polyester, phthalic acid-propylene glycol based polyester, diphenyl cresyl phosphate (DPCP), diisodecyl adipate, epoxidized soybean oil, epoxidized linseed oil, chlorinated paraffin, etc. These may be used alone or in combination of two or more. Of the above phthalic acid based plasticizers, DINP is more preferred because it has a particularly high plasticizing effect and has little impact on human health.

The content of the plasticizer in the substrate is preferably 20 to 100 parts by mass, more preferably 30 to 80 parts by mass, and even more preferably 40 to 60 parts by mass, per 100 parts by mass of the vinyl chloride resin. If the content of the plasticizer is 20 parts by mass or more, the extensibility of the adhesive sheet is likely to be improved, making it easier to bend a long protected object after covering it. If the content of the plasticizer is 100 parts by mass or less, the abrasion resistance of the adhesive sheet is unlikely to decrease, making it easier to prevent damage to the protected object due to abrasion.

If necessary, inorganic fillers, modifiers, or other additives can be blended into the base material to the extent that the effects of the present invention are not impaired. Examples of other additives include colorants, stabilizers, antioxidants, UV absorbers, and lubricants.

Examples of the inorganic filler include aluminum hydroxide, magnesium hydroxide, zirconium hydroxide, calcium hydroxide, potassium hydroxide, barium hydroxide, ammonium polyphosphate, polyamide phosphoric acid, zirconium oxide, magnesium oxide, zinc oxide, titanium oxide, molybdenum oxide, guanidine phosphate, hydrotalcite, snaketite, zinc borate, anhydrous zinc borate, zinc metaborate, barium metaborate, antimony oxide, antimony trioxide, antimony pentoxide, red phosphorus, talc, alumina, silica, boehmite, bentonite, sodium silicate, calcium silicate, calcium sulfate, calcium carbonate, magnesium carbonate, and carbon black. These may be used alone or in combination of two or more. Among the above inorganic fillers, talc, alumina, silica, calcium silicate, calcium sulfate, calcium carbonate, and magnesium carbonate are preferred, and more preferred is calcium carbonate, which is economical.
The inorganic filler may be one obtained by pulverizing a natural product, or one obtained by neutralizing and precipitating an aqueous solution or the like. It may also be one into which a functional group has been introduced using a surface treatment agent or the like. Examples of the surface treatment agent that can be used include fatty acids, rosin acid, lignin acid, and quaternary ammonium salts.

Examples of the modifier include vinyl chloride-vinyl acetate copolymer, vinyl chloride-ethylene copolymer, vinyl chloride-propylene copolymer, chlorinated polyethylene, chlorinated polyvinyl chloride, ethylene-vinyl acetate copolymer, acrylonitrile-butadiene-styrene copolymer, methyl methacrylate-butadiene-styrene copolymer, acrylonitrile-butadiene copolymer, methyl methacrylate-butyl acrylate copolymer, thermoplastic polyurethane, polyester-based thermoplastic elastomer, etc. These may be used alone or in combination of two or more.

The content of inorganic fillers, modifiers, and other additives is not particularly limited, and can be blended within a range that does not impair the effects of the present invention. For example, more than 0 parts by mass and 50 parts by mass or less can be blended with respect to 100 parts by mass of the vinyl chloride resin used in the base material.

As a method for forming the substrate, for example, a method of melt-kneading a composition containing a vinyl chloride resin, a plasticizer, and, if necessary, an inorganic filler, a heat stabilizer, a light absorber, a pigment, and other additives, and then molding the composition to a predetermined thickness can be mentioned. The melt-kneading method is not particularly limited as long as it has the effect of the present invention, but for example, various mixers and kneaders equipped with a heating device such as a twin-screw extruder, a continuous or batch kneader, a roll, or a Banbury mixer can be used. The composition is mixed so as to be uniformly dispersed by the kneading method, and the resulting mixture is molded into a substrate by a conventional molding method such as a calendar method, a T-die method, or an inflation method. A calendar molding machine is preferable in terms of productivity, color change, uniformity of shape, etc. The roll arrangement method in the calendar molding can be, for example, a known method such as an L-type, an inverted L-type, or a Z-type, and the roll temperature is usually set to 150 to 200 ° C, preferably 155 to 190 ° C.

The thickness of the substrate varies depending on the intended use and application, but is preferably 100 to 2000 μm, more preferably 200 to 1000 μm, and even more preferably 300 to 500 μm.

<Adhesive layer>
The adhesive layer of the present invention contains natural rubber. The adhesive layer of the present invention is preferably composed of an adhesive containing natural rubber. The adhesive layer containing natural rubber has the property that the adhesive strength between the adhesive layers is high and the adhesive strength to the adherend other than the adhesive layer is low. Therefore, it can be suitably used for the adhesive sheet of the present invention in which only the adhesive layers are adhered to each other.

In the ^pressure -sensitive adhesive layer of the present invention, when the integral value of the ^1H intensity over the entire relaxation time is taken as 100%, ^{the 1H} intensity ratio for a relaxation time of 0.10 milliseconds or less is 5 to 30%. The intensity ratio is preferably 10 to 30%, more preferably 12 to 28%. The integral value for a relaxation time of 0.10 milliseconds or less in the pulse solid-state ^1H -NMR measurement is a value derived from the crosslink density of the natural rubber contained in the pressure-sensitive adhesive layer.
In the adhesive sheet of the present invention, if the ^1H intensity ratio for a relaxation time of 0.10 milliseconds or less is less than 5%, the adhesive layer will deteriorate in a high temperature or high humidity environment, and the adhesive sheet will become sticky. If the ^1H intensity ratio for a relaxation time of 0.10 milliseconds or less exceeds 30%, sufficient adhesive strength cannot be obtained when the adhesive layers are bonded together. The intensity ratio for a relaxation time of 0.10 milliseconds or less in pulse solid-state ^1H -NMR refers to a value measured under the following conditions.

About 5 g of the adhesive layer is collected from the adhesive sheet and dispensed into an NMR tube as a measurement sample, and NMR measurement is performed on the measurement sample by the following method.
Apparatus: NMR manufactured by Bruker Optics, model name "minispec mq20"
Pulse sequence: Solid Echo method Observation nucleus: ^1H
Measurement time: 10 seconds Number of points: 1000
Measurement temperature: 27°C Number of accumulations: 32 In this measurement, when the integral value of the ¹ H intensity over the entire relaxation time is taken as 100%, the integral value of ^{the 1} H intensity in the range of relaxation times of 0.10 milliseconds or less is taken as the ¹ H intensity ratio for relaxation times of 0.10 milliseconds or less.

The toluene insoluble content in the adhesive layer is preferably 75% by mass or more relative to the total mass of the adhesive layer. The toluene insoluble content is preferably 75 to 100% by mass, more preferably 85 to 100% by mass, and even more preferably 90 to 100% by mass. If the toluene insoluble content in the adhesive layer is within the above range, an increase in probe tack and a decrease in adhesive strength between adhesive layers in high temperature and high humidity environments can be suppressed. The toluene insoluble content in the adhesive layer can be measured, for example, by the following method.

The adhesive layer is taken out of the adhesive sheet by w1 [g], 100 mL of toluene is added with a whole pipette, and a rotor is inserted and then sealed. A stoppered Erlenmeyer flask is set in a thermostatic water bath (50°C ± 2°C) and stirred with a stirrer at a rotation speed of 600 revolutions/min for 2 hours. After stirring, the stoppered Erlenmeyer flask is cooled to 23°C or less with ice water. The sample is entirely filtered through a 270 mesh wire mesh whose weight has been measured in advance (the weight of the wire mesh before filtration is w2 [g]). The wire mesh after filtration is heated in an explosion-proof oven at 150°C for 1 hour, and then the weight of the wire mesh is measured (the weight of the wire mesh after filtration is w3 [g]). The toluene insoluble content in the adhesive layer is measured according to the following formula (1).
Toluene insoluble content (mass%)=((w3-w2)/w1)×100 (1)

The sulfur element content in the adhesive layer is preferably 1.0% by mass or less, more preferably 0.5% by mass or less, even more preferably 0.3% by mass or less, and particularly preferably 0.1% by mass or less. A low sulfur element content in the adhesive layer makes it difficult for devulcanization due to the presence of a crosslinked structure of sulfur atoms to occur, and improves storage stability under high temperature and high humidity environments.
The content of sulfur element in the adhesive layer can be calculated from the ratio of the spectral intensities of sulfur element by elemental analysis using an energy dispersive wide-angle X-ray device.

(Adhesive)
The adhesive layer of the present invention is preferably composed of an adhesive containing natural rubber.
As the natural rubber, for example, an uncrosslinked natural rubber emulsion having a solid content of 30 to 80% by mass, a crosslinked natural rubber emulsion having a solid content of 30 to 80% by mass, etc. can be used. As such natural rubber, commercially available products can be used, for example, crosslinked natural rubber emulsions manufactured by Resitex Co., Ltd. (product names "SS58" and "PC-518R"), crosslinked natural rubber emulsions manufactured by Musashino Chemical Co., Ltd. (product name "S#55"), and natural rubber emulsions manufactured by Resitex Co., Ltd. (product names "HA LATEX" and "DPL-30C") can be used. These can be used alone or in combination of two or more types.
In one embodiment of the present invention, the natural rubber contained in the adhesive preferably contains crosslinked natural rubber. The content of crosslinked natural rubber in the adhesive is preferably 50% by mass or more, and more preferably 50 to 100% by mass, based on the total mass of natural rubber in the adhesive. By containing crosslinked natural rubber, the adhesive strength between adhesive surfaces can be further increased.

The adhesive may also contain a crosslinking agent. Examples of crosslinking agents include sulfur-based compounds and organic peroxide-based compounds. Examples of sulfur-based compounds include sulfur, sulfur chloride, sulfur dichloride, polymeric polysulfides, morpholine disulfide (4,4'-dithiodimorpholine), alkylphenol disulfide, tetramethylthiuram disulfide, dipentamethylene thiuram tetrasulfide, and selenium dimethyldithiocarbamate. Examples of organic peroxide-based compounds include dialkyl peroxides (di-t-butyl peroxide, dicumyl peroxide, di-t-butylcumyl peroxide, etc.), diacyl peroxides (dibenzoyl peroxide, etc.), ketone peroxides (methyl ethyl ketone peroxide, etc.), alkyl peresters (t-hexyl peroxy laurate, etc.), and peroxycarbonates (t-butyl peroxy isopropyl carbonate, etc.). These may be used alone or in combination of two or more. Among these crosslinking agents, it is particularly preferable to use an organic peroxide compound, since devulcanization due to the presence of a crosslinked structure of sulfur atoms is unlikely to occur, and therefore the storage stability in a high temperature and high humidity environment is excellent.

When the adhesive contains a crosslinking agent, the content of the crosslinking agent is preferably 0.1 to 10% by mass, more preferably 0.3 to 5% by mass, and even more preferably 0.5 to 3% by mass, relative to the total mass of the adhesive. If the content of the crosslinking agent is 0.1% by mass or more, stickiness due to deterioration of the adhesive layer is unlikely to occur. If it is 10% by mass or less, sufficient adhesive strength is easily obtained when the adhesive layers are bonded together.

The adhesive may contain an antioxidant. Examples of antioxidants include phenolic compounds (4,4-thiobis(3-methyl-6-t-butylphenol), 2,5-di-t-butylhydroquinone, 2,6-di-t-butyl-p-cresol, etc.), phosphorus compounds (diphenylnonylphenyl phosphite, triphenyl phosphite, tris(nonylphenyl)phosphite, etc.), and sulfur compounds (bis(2-methyl-4-(3-n-alkylthiopropionyloxy)-5-t-butylphenyl)sulfide, 2,2-thiodiethylenebis(3-(3,5-t-butyl-4-hydroxyphenyl)propionate, dilaurylthiopropionate, etc.). Among these, phenolic antioxidants are preferred from the viewpoint of suppressing oxidation of the natural rubber contained in the adhesive in a high-temperature environment, and hindered phenolic antioxidants represented by the following formula (I) are more preferred.

In the above formula (I), R ¹ and R ² each independently represent a substituted or unsubstituted hydrocarbon group having 1 to 4 carbon atoms, A represents a hydrogen atom, a carbon atom, or a substituted or unsubstituted hydrocarbon group having 1 to 18 carbon atoms, and n represents a number from 1 to 4.
In the above formula (I), R ¹ and R ² are preferably an unsubstituted alkyl group having 1 to 4 carbon atoms, more preferably a methyl group or a t-butyl group. R ¹ and R ² may be the same or different.
In the above formula (I), A represents a hydrogen atom, a carbon atom, or a substituted or unsubstituted hydrocarbon group having 1 to 18 carbon atoms. Examples of the substituent include an ether group, a carboxyl group, a carbonyl group, an amino group, an amide group, an imide group, a thioether group, a thiocarboxyl group, a dithiocarboxyl group, a thiocarbonyl group, and a thioamide group.
Examples of the hindered phenol-based antioxidant represented by the above formula (I) include octadecyl-3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate, ethylene-bis(oxyethylene)-bis-(3-(5-t-butyl-4-hydroxy-m-tolyl)propionate, pentaerythritol-tetrakis-(3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate), and the like.
In addition, as the hindered phenol-based antioxidant having the structure represented by the above formula (I) in the molecule, a commercially available product may be used. Examples of such commercially available products include "Irganox (registered trademark) 1076", "Irganox 1010", and "Irganox 245" (all trade names) manufactured by BASF Corporation. These antioxidants may be used alone or in combination of two or more.
When the adhesive contains an antioxidant, the content is preferably 0.3 to 5 parts by mass, more preferably 0.5 to 4 parts by mass, based on 100 parts by mass of natural rubber in the adhesive. If the content of the antioxidant is within the above range, the storage property is improved. In addition, the proportion of the antioxidant in the adhesive layer can be easily controlled within a preferred range. In one aspect of the present invention, the content of the antioxidant in the adhesive layer is preferably 0.3 to 5.0% by mass, more preferably 0.5 to 4.0% by mass, based on the total mass of the adhesive layer.

The adhesive may contain an appropriate amount of filler as necessary. By containing an appropriate amount of filler, the stickiness of the adhesive layer is easily reduced. In addition, the filler and natural rubber form a pseudo-crosslinked structure, which restricts the mobility of the molecules and further improves the thermal stability. Furthermore, while maintaining the adhesion between the adhesive surfaces to a certain extent, the probe tack is easily reduced. Examples of such fillers include inorganic fine particles. Specific examples of inorganic fine particles include carbon black, silica, talc, alumina, sodium silicate, calcium silicate, calcium sulfate, calcium carbonate, magnesium carbonate, magnesium oxide, zinc oxide, titanium oxide, boehmite, bentonite, hydrotalcite, and the like. Among these, carbon black, silica, alumina, and calcium carbonate, which have good dispersibility in the adhesive component and little impact on human health, are preferred, and calcium carbonate is particularly preferred from the viewpoint of economy. These inorganic fine particles may be used alone or in combination of two or more.
When the pressure-sensitive adhesive contains inorganic fine particles, the content thereof is preferably from 5 to 100 parts by mass, and more preferably from 10 to 50 parts by mass, based on 100 parts by mass of natural rubber.

The adhesive may contain rubber components other than natural rubber, such as synthetic rubber, if necessary. Examples of synthetic rubber include butadiene rubber, isoprene rubber (butyl rubber), styrene-butadiene rubber, acrylonitrile-butadiene rubber, methyl methacrylate-butadiene rubber, chloroprene rubber, acrylic rubber, and thermoplastic elastomers (ethylene-propylene rubber, ethylene-propylene-diene rubber, styrene-butadiene-styrene block copolymer, styrene-isoprene-styrene block copolymer, styrene-ethylene-styrene copolymer, styrene-ethylene-butadiene-styrene copolymer, and styrene-ethylene-propylene-styrene copolymer). Of these, styrene-butadiene rubber, acrylonitrile-butadiene rubber, and methyl methacrylate-butadiene rubber are preferred, as they do not inhibit the adhesive properties of the adhesive components and are less sticky. When the adhesive contains other synthetic rubbers, the content is preferably 40% by mass or less, and more preferably 1 to 25% by mass, based on the total mass of the adhesive.

The adhesive may contain a tackifier as necessary. When a tackifier is contained, it is preferable that the amount of the tackifier is less than 20% by mass relative to the total mass of the adhesive in order to prevent the adhesive layer from becoming sticky. Examples of the tackifier include rosin resin, hydrogenated rosin resin, rosin ester resin, rosin modified phenolic resin, phenolic resin, alkylphenolic resin, terpene resin, terpene phenolic resin, coumarone resin, indene resin, coumarone-indene resin, coumarone-indene-styrene resin, styrene resin, xylene resin, styrene-maleic acid resin, aliphatic petroleum resin, alicyclic petroleum resin, aromatic petroleum resin, aliphatic hydrocarbon-aromatic hydrocarbon copolymer petroleum resin, etc. These may be used alone or in combination of two or more.

The adhesive may contain surfactants, viscosity modifiers, antioxidants, and other additives, as long as they do not impair the adhesive performance. The content of these additives in the adhesive is not particularly limited as long as they have the effect of the present invention, and is preferably, for example, 20% by mass or less of the total mass of the adhesive.

It is preferable that the adhesive is also resistant to the plasticizer in the substrate. If the plasticizer resistance of the adhesive is low, the plasticizer that seeps out from the substrate may migrate to the adhesive, causing increased stickiness and reduced adhesive strength. It is preferable that the adhesive used in the adhesive layer of the present invention has a solubility in the plasticizer in the substrate of less than 20% by mass and a mass increase rate after swelling of less than 200% by mass, and more preferably a solubility of less than 10% by mass and a mass increase rate after swelling of less than 100% by mass.

From the viewpoints of exerting adhesive strength and maintaining the structure of the adhesive layer, the thickness of the adhesive layer is preferably 3 to 100 μm, and more preferably 10 to 50 μm. By making the thickness of the adhesive layer 3 μm or more, it becomes easier to exert adhesive strength sufficient for bundling long items. Furthermore, by making the thickness of the adhesive layer 100 μm or less, it becomes easier to maintain the structure of the adhesive layer, and cohesive failure of the adhesive becomes less likely to occur.

<Middle class>
In one embodiment of the present invention, it is preferable to provide an intermediate layer between the substrate and the adhesive layer for the purpose of further improving the adhesion between the substrate and the adhesive layer.
Examples of materials constituting the intermediate layer include methyl methacrylate grafted natural rubber.
Methyl methacrylate grafted natural rubber is a polymer obtained by graft copolymerization of natural rubber and methacrylic acid. Such a polymer has affinity with both the polyvinyl chloride resin constituting the substrate and the adhesive constituting the adhesive layer, and therefore by forming an intermediate layer using this polymer, the adhesion between the substrate containing the polyvinyl chloride resin and the adhesive layer is more likely to be improved. In addition, the material constituting the intermediate layer may be one obtained by copolymerizing the methyl methacrylate grafted natural rubber with other monomers. Examples of the other monomers include methacrylic acid esters such as methyl acrylate, ethyl acrylate, n-butyl acrylate, i-butyl acrylate, t-butyl acrylate, 2-ethylhexyl acrylate, methyl methacrylate, ethyl methacrylate, n-butyl methacrylate, i-butyl methacrylate, t-butyl methacrylate, and 2-ethylhexyl methacrylate, styrene, acrylonitrile, and methacrylic acid. These other monomers may be used alone or in combination of two or more.

Other synthetic rubbers may be added to the material constituting the intermediate layer as necessary. Examples of synthetic rubbers include butadiene rubber, isoprene rubber, styrene-butadiene rubber, acrylonitrile-butadiene rubber, methyl methacrylate-butadiene rubber, chloroprene rubber, acrylic rubber, thermoplastic elastomers (e.g., ethylene-propylene rubber, ethylene-propylene-diene rubber, styrene-butadiene-styrene block copolymer, styrene-isoprene-styrene block copolymer, styrene-ethylene-styrene copolymer, styrene-ethylene-butadiene-styrene copolymer, styrene-ethylene-propylene-styrene copolymer, etc.), acrylic rubber, and urethane rubber. These may be used alone or in combination of two or more.

The thickness of the intermediate layer is preferably 0.1 to 3 μm, more preferably 0.2 to 2 μm, and particularly preferably 0.3 to 1 μm, from the viewpoints of adhesion between the substrate and the adhesive layer and maintaining the structure of the intermediate layer.

<Method of manufacturing adhesive sheet>
The adhesive sheet of the present invention can be produced, for example, by a method in which a solution, emulsion, or dispersion of an adhesive, which is a mixture of natural rubber and, if necessary, a tackifier, a filler such as inorganic fine particles, a plasticizer, a surfactant, a viscosity modifier, an anti-aging agent, and other additives, is applied to one side of a substrate, dried in a drying oven, and then wound into a roll.
In one embodiment of the method for producing an adhesive sheet of the present invention, a solution, emulsion or dispersion of a material constituting an intermediate layer may be applied to one side of the substrate, and an intermediate layer may be formed in a drying process in which the intermediate layer is dried in a drying oven. Then, a solution, emulsion or dispersion of the adhesive described above may be applied onto the intermediate layer and dried, and then the adhesive sheet may be produced by winding it up into a roll.
For the purpose of alleviating stress during winding, improving adhesion between the intermediate layer and the adhesive layer, and improving affinity between the adhesive layer components, the method may further include a step of aging the adhesive sheet wound into a roll for a predetermined time and a step of performing heat treatment at a predetermined temperature. Examples of methods for applying the adhesive and the material constituting the intermediate layer include a positive rotation roll method, a reverse roll method, a gravure roll method, a spray method, a kiss roll method, a bar method, a knife method, a comma method, a lip die method, and the like.
In addition, from the viewpoints of safety and environmental load, it is preferable to use an emulsion or dispersion with water as the form of coating of the pressure-sensitive adhesive. In addition, it is preferable to carry out aging or heat treatment for a time and at a temperature at which the performance of the pressure-sensitive adhesive sheet is sufficiently stable, and in particular, in the case of the pressure-sensitive adhesive sheet of the present invention, it is preferable to carry out the aging or heat treatment at a temperature equal to or higher than the softening point or glass transition point of the intermediate layer or the pressure-sensitive adhesive layer.
Specifically, the heat treatment temperature of the adhesive sheet is preferably, for example, 100° C. or higher and 130° C. or lower. The aging time is preferably 1 hour or higher and 6 hours or lower. By carrying out the aging or heat treatment under these conditions, it becomes easier to transfer the necessary amount of plasticizer from the substrate to the adhesive, and it becomes easier to suppress deterioration of the substrate and the adhesive due to excessive heat.

The thickness of the adhesive sheet of the present invention is preferably 50 to 1000 μm, more preferably 100 to 600 μm. Having a thickness of the adhesive sheet below this upper limit makes it easier to wrap the sheet around the object to be protected, and having a thickness above the lower limit sufficiently prevents mechanical damage and wear to the object to be protected after wrapping.

<Applications>
The pressure-sensitive adhesive sheet of the present invention can protect the surface or inside of an object to be protected from mechanical damage or abrasion, and can also be used as a sheet for electrical insulation or blocking ultraviolet radiation from sunlight, etc. In particular, it can be suitably used as a sheet for bundling and protecting long objects such as electric wires and wiring by bonding the pressure-sensitive adhesive layers together after covering the objects.
That is, another embodiment of the pressure-sensitive adhesive sheet of the present invention is its use as a protective sheet.
Another embodiment of the pressure-sensitive adhesive sheet of the present invention is its use as a bundling sheet.
Another embodiment of the pressure-sensitive adhesive sheet of the present invention is its use as an ultraviolet ray blocking sheet.
Another embodiment of the pressure-sensitive adhesive sheet of the present invention is its use as an electrical insulating sheet.
When the adhesive sheet of the present invention is used for the above-mentioned purposes, the method of use may include, for example, a method including a step of wrapping the adhesive sheet around the object to be protected, and then bonding the adhesive layers of the adhesive sheet together to bind them. When wrapping the adhesive sheet, it is preferable to wrap the adhesive sheet so that the adhesive layer of the adhesive sheet and the object to be protected are in contact with each other. In addition, when bonding the adhesive layers together, it is preferable to bond them together by a method of pressing the adhesive layers together using hands or a suitable tool. When bonding the adhesive layers together, from the viewpoint of the adhesive surface being difficult to peel off and difficult to interfere with the outside, the width of the bonding part is preferably 5 to 50 mm, and the area of the bonding part is preferably 50 to ^10,000 mm2.

Another aspect of the present invention is an adhesive sheet having a substrate containing polyvinyl chloride and DINP, and an adhesive layer containing natural rubber provided on one surface of the substrate, in which, in pulse solid-state ¹ H-NMR measurement of the adhesive layer, when the integrated value of the ¹ H intensity over the entire relaxation time is taken as 100%, the ¹ H intensity ratio at a relaxation time of 0.10 milliseconds or less is 5 to 30%. The natural rubber preferably contains crosslinked natural rubber. The adhesive layer preferably further contains a hindered phenol-based antioxidant represented by the formula (I). The thickness of the adhesive layer is preferably 10 to 50 μm.

The present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited to these examples.

[Example 1]
(Preparation of substrate)
100 parts by mass of polyvinyl chloride (manufactured by Taiyo Vinyl Co., Ltd., product name "TH-1000") as a vinyl chloride resin was blended with 40 parts by mass of Diisonyl Phthalate Co., Ltd. (manufactured by JPlus Corporation, product name "DINP") as a plasticizer, and further blended with 1 part by mass of fatty acid zinc (manufactured by Tokyo Fine Chemical Co., Ltd., product name "EMBILIZER (registered trademark) A1341") as a stabilizer and 0.2 parts by mass of stearic acid (manufactured by NOF Corporation, product name "Sakura Stearic Acid") as a lubricant. The mixture was kneaded for 10 minutes with a twin roll at a roll temperature of 170°C and then formed into a thickness of 400 μm to obtain a substrate.

(Preparation of adhesive sheet)
A crosslinked natural rubber emulsion (manufactured by Resitex Co., Ltd., product name "SS58") and a natural rubber emulsion (manufactured by Resitex Co., Ltd., product name "DPL-30C") were blended so that the solid contents were 95 parts by mass and 5 parts by mass, respectively, and 1 part by mass of an antioxidant (manufactured by BASF, product name "Irganox 1010") was further added to obtain an emulsion of an adhesive. The emulsion was applied to the surface of the substrate and heated and dried at 110°C for 1 minute in an oven to obtain an adhesive sheet having a substrate with a thickness of 400 μm and an adhesive layer with a thickness of 40 μm. The solid content blend of the emulsion used in Example 1 is shown in Table 1.

[Examples 2 to 16, Comparative Examples 1 to 5]
Except for changing the blending amounts of the crosslinked natural rubber emulsion, natural rubber emulsion, crosslinking agent, and antioxidant in Example 1, pressure-sensitive adhesive sheets were obtained in the same manner as in Example 1. The solids blending amounts of the emulsions used in Examples 2 to 16 and Comparative Examples 1 to 5 are shown in Tables 1 and 2. The blending amounts of the crosslinked natural rubber emulsion and natural rubber emulsion used in each Example and Comparative Example refer to the solids blending amounts. Details of the raw materials used shown in Tables 1 and 2 are as follows:
<Ingredients used>
(Natural rubber)
Crosslinked natural rubber 1: Crosslinked natural rubber emulsion (manufactured by Resitex Co., Ltd., product name "SS58").
Crosslinked natural rubber 2: Crosslinked natural rubber emulsion (manufactured by Musashino Chemical Co., Ltd., product name "S#55").
Crosslinked natural rubber 3: Crosslinked natural rubber emulsion (manufactured by Resitex Co., Ltd., product name "PC-518R").
Natural rubber 1: Natural rubber emulsion (manufactured by Resitex Co., Ltd., product name "HA LATEX").
Natural rubber 2: Natural rubber emulsion (manufactured by Resitex Co., Ltd., product name "DPL-30C").
Crosslinking agent: tetramethylthiuram disulfide (manufactured by Resitex Co., Ltd., trade name "TT Vulcanizing Agent").
Antioxidant 1: a hindered phenol-based antioxidant represented by the above formula (I) (an antioxidant in which n is 4, R ¹ and R ² are t-butyl groups, and A is a carbon atom in the above formula (I)) (manufactured by BASF Japan Ltd., product name "Irganox 1010").
Antioxidant 2: a hindered phenol-based antioxidant represented by the above formula (I) (an antioxidant in which n is 1, R ¹ and R ² are t-butyl groups, and A is an octadecyl group in the above formula (I)) (manufactured by BASF Japan Ltd., product name "Irganox 1076").
Antioxidant 3: Hindered phenol-based antioxidant (manufactured by BASF Japan Ltd., product name "Irganox 1520L").

[Evaluation of Adhesive Layer]
The adhesive layer in the adhesive sheet was sampled and then subjected to pulse solid-state ^1H -NMR measurement, elemental analysis, and toluene insoluble content measurement. The results are shown in Tables 1 and 2.

< ^1H intensity ratio with relaxation time of 0.10 milliseconds or less>
About 5 g of the adhesive layer was collected from the adhesive sheet obtained in each Example and Comparative Example and dispensed into an NMR tube. The measurement sample was subjected to pulsed solid-state ¹ H-NMR measurement and calculation was performed according to the measurement method described above.

<Toluene insoluble content>
The adhesive layer w1 [g] was taken from the adhesive sheet obtained in each Example and Comparative Example, 100 mL of toluene was added with a whole pipette, and a rotor was inserted and then sealed. Then, a stoppered Erlenmeyer flask was set in a thermostatic water bath (50°C ± 2°C) and stirred with a stirrer at a rotation speed of 600/min for 2 hours. After stirring, the stoppered Erlenmeyer flask was cooled to 23°C or less with ice water. The obtained sample was entirely filtered through a 270 mesh wire mesh whose weight had been measured in advance (the weight of the wire mesh before filtration was taken as w2 [g]). The wire mesh after filtration was heated in an explosion-proof oven at 150°C for 1 hour, and then the weight of the wire mesh was measured (the weight of the wire mesh after filtration was taken as w3 [g]). The toluene insoluble content in the adhesive layer was measured according to the following formula (1).
Toluene insoluble fraction (mass%)=((w3−w2)/w1)×100 (1)

<Elemental analysis>
A sample of the adhesive layer having a size of about 400 μm×50 mmφ was taken from the adhesive sheet obtained in each of the Examples and Comparative Examples, and the element contents of the sample were quantified under the following conditions.
Equipment: Shimadzu Corporation Energy Dispersive Wide-Angle X-ray Equipment, Model "EDX-720"
Analysis conditions: FP method Thickness setting: 400 μm
Detected element: Sulfur Spectrum: S-Kα

<Adhesive strength evaluation>
The adhesive sheets obtained in each of the Examples and Comparative Examples were evaluated for stickiness, adhesive strength between the adhesive layers, and changes in physical properties in a high temperature and high humidity environment according to the following conditions.
Three samples of the adhesive sheet of each example were prepared, and each sample was left for 30 days in the following environments: 23°C x 50% RH (normal state), 65°C x 5% RH (high temperature and dry), and 65°C x 95% RH (high temperature and high humidity). After that, the samples were left to stand for 24 hours in the 23°C x 50% RH environment, and the probe tack (stickiness) and adhesive strength between the adhesive layers of each sample were measured under the following conditions.

(Probe Tack Test)
According to ASTM D 2979, a probe tack tester (NS PROBE TACK TESTER manufactured by Nichiban Co., Ltd.) was used to measure the load when a cylindrical probe having a diameter of 5 mm was brought into contact with the sample at a speed of 1 cm/sec in an environment of 23° C., and then the probe was brought into contact for 0.02 seconds and peeled off at a speed of 1 cm/sec. The obtained probe tack value was evaluated according to the following evaluation criteria. Also, an A rating was considered to be acceptable.
<Evaluation criteria>
A: In all samples in the normal state, in the high temperature environment, and in the high temperature and high humidity environment, the probe tack value was 4 N/ ^cm2 or less.
B: In any of the samples in the normal state, in the high temperature environment, and in the high temperature and high humidity environment, the probe tack value exceeded 4 N/ ^cm2 .

<Adhesive strength between adhesive layers>
Two test pieces with a width of 10 mm and a length of 120 mm were prepared from each sample of the adhesive sheet, and the adhesive layers of the test pieces were bonded together in an area of 10 mm x 100 mm in an environment of 23 ° C., and the test pieces were rolled back and forth at a speed of 5 mm / sec with a pressure roller with a load of 2 kg, and then left for 20 minutes. Next, the load was measured when the test pieces were peeled off at a speed of 300 mm / min in an environment of 23 ° C. The peeling direction of the test pieces was set so that the angle between the two test pieces after peeling was 180 °. The adhesive strength between the adhesive layers was evaluated according to the following evaluation criteria. In addition, A rating was considered to be a pass.
<Evaluation criteria>
A: In all samples in the normal state, in the high temperature environment, and in the high temperature and high humidity environment, the adhesive strength between the adhesive layers was 4 N/10 mm or more.
B: In any of the samples in the normal state, in the high temperature environment, and in the high temperature and high humidity environment, the adhesive strength between the adhesive layers was less than 4 N/10 mm.

As shown in Tables 1 and 2, the adhesive sheets of Examples 1 to 16, which satisfy the configuration of the present invention, are less sticky, but have high adhesive strength between the adhesive layers, and are less susceptible to deterioration in high temperature or high humidity environments. On the other hand, the adhesive sheets of Comparative Examples 1 to 5, which do not satisfy the configuration of the present invention, were inferior in either the stickiness evaluation or the adhesive strength between the adhesive layers.

1: Substrate 2: Adhesive layer 10: Adhesive sheet

Claims (7)

An adhesive sheet having a substrate containing a vinyl chloride resin and a plasticizer, and an adhesive layer containing only natural rubber as a resin component ,
The natural rubber includes crosslinked natural rubber crosslinked with an organic peroxide compound,
An adhesive sheet, wherein, in pulse solid-state ¹ H-NMR measurement of the adhesive layer, the ¹ H intensity ratio for a relaxation time of 0.10 milliseconds or less is 5 to 30% when the integral value of the ¹ H intensity over the entire relaxation time is taken as 100%. An adhesive sheet having a substrate containing a vinyl chloride resin and a plasticizer, and an adhesive layer containing only natural rubber as a resin component ,
the proportion of the crosslinked natural rubber to the total mass of the natural rubber is 50 to 95% by mass,
An adhesive sheet, wherein, in pulse solid-state ¹ H-NMR measurement of the adhesive layer, the ¹ H intensity ratio for a relaxation time of 0.10 milliseconds or less is 5 to 30% when the integral value of the ¹ H intensity over the entire relaxation time is taken as 100%. An adhesive sheet having a substrate containing a vinyl chloride resin and a plasticizer, and an adhesive layer containing only natural rubber as a resin component,
the natural rubber comprises only crosslinked natural rubber,
An adhesive sheet, wherein, in pulse solid-state ¹ H-NMR measurement of the adhesive layer, the ¹ H intensity ratio for a relaxation time of 0.10 milliseconds or less is 5 to 30% when the integral value of the ¹ H intensity over the entire relaxation time is taken as 100%. The adhesive sheet according to any one of claims 1 to 3, wherein the toluene insoluble content of the adhesive layer is 75% by mass or more relative to the total mass of the adhesive layer. The adhesive sheet according to any one of claims 1 to 4, wherein the sulfur element content in the adhesive layer is 1.0 mass% or less. The adhesive sheet according to any one of claims 1 to 5, wherein the adhesive layer contains an antioxidant, and the content of the antioxidant in the adhesive layer is 0.3 to 5.0 mass% relative to the total mass of the adhesive layer. The pressure-sensitive adhesive sheet according to claim 6 , wherein the antioxidant is a hindered phenol-based antioxidant represented by the following formula (I):

(In formula (I), R ¹ and R ² each independently represent a substituted or unsubstituted hydrocarbon group having 1 to 4 carbon atoms, A represents a hydrogen atom, a carbon atom, or a substituted or unsubstituted hydrocarbon group having 1 to 18 carbon atoms, and n represents a number from 1 to 4.)

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