JP7489538B2 - Adhesive tape - Google Patents

Description

The present invention relates to an adhesive tape.

Polyvinyl chloride adhesive tape is known as an adhesive tape for bundling and protecting electrical wires in automobiles. Polyvinyl chloride adhesive tape is an adhesive tape having a base layer made of polyvinyl chloride and also has electrical insulation properties.
In recent years, in the automotive industry, from the viewpoint of improving fuel efficiency by reducing the weight of the vehicle, there is a demand for miniaturization and weight reduction of parts arranged in the vehicle. Thinning of the substrate layer is effective for reducing the weight of the adhesive tape, and for example, a method of increasing the stretch ratio of the substrate layer to reduce the film thickness is available. However, simply increasing the stretch ratio to thin the substrate layer causes problems such as breakage of the substrate layer during film formation or pinholes in the substrate layer. In addition, thinning of the substrate layer makes it easier for cracks and fissures (hereinafter sometimes referred to as "cracks") to occur in the adhesive tape after bundling. Such cracks are more likely to occur when the bundling is stored in a low-temperature environment.

To address this issue, for example, Patent Document 1 describes an adhesive tape that includes a base layer containing polyvinyl chloride and an elastomer component, and has a tensile breaking elongation of 80% or more at -20° C. Patent Document 1 also describes that an adhesive tape that is less likely to crack at low temperatures can be obtained even if the base layer is made thinner.

JP 2017-119806 A

The adhesive tape of Patent Document 1 does not have a sufficiently thin base layer, and it is difficult to meet the demand for further weight reduction of the adhesive tape. In recent years, there has been a demand for lightweight adhesive tapes that are less susceptible to cracking even when stored in harsh low-temperature environments.
Therefore, an object of the present invention is to provide an adhesive tape which can suppress the occurrence of pinholes even when the base layer is made thin, and which is less likely to crack even when bundling is performed in a low-temperature environment of -30°C or below.

In order to solve the above problems, the present inventors conducted intensive research and discovered that by forming a base layer using a resin composition in which a certain amount of a plasticizer and an acrylic resin are blended with a polyvinyl chloride resin, and the resin composition has a melt rupture tension at 180°C within a certain range, it is possible to obtain an adhesive tape in which pinholes do not occur even when the base layer is made thin, and which is less likely to crack even in low-temperature environments of -30°C or lower, and thus completed the present invention.
That is, the present invention has the following aspects.
[1] An adhesive tape comprising a base layer and an adhesive layer provided on at least one surface of the base layer, the base layer being made of a resin composition containing a polyvinyl chloride resin and, relative to 100 parts by mass of the polyvinyl chloride resin, 40 to 70 parts by mass of a plasticizer and 1 to 10 parts by mass of an acrylic resin, and having a melt rupture tension of 0.02 to 0.10 N at 180°C.
[2] The pressure-sensitive adhesive tape according to [1], wherein the polyvinyl chloride resin has an average degree of polymerization of 700 to 1,800.
[3] The pressure-sensitive adhesive tape according to [1] or [2], wherein the melting point of the plasticizer is −60° C. or lower.
[4] The pressure-sensitive adhesive tape according to any one of [1] to [3], wherein the acrylic resin has a mass average molecular weight of 5×10 ⁵ to 50×10 ^{5 .}
[5] The pressure-sensitive adhesive tape according to any one of [1] to [4], wherein the thickness of the base layer is 0.03 to 0.10 mm.
[6] The pressure-sensitive adhesive tape according to any one of [1] to [5], which is used for bundling electric wires.
[7] Members bound together with the adhesive tape according to any one of [1] to [6].

According to the present invention, it is possible to provide an adhesive tape that can suppress the occurrence of pinholes even when the base layer is made thin, and is less likely to crack even when bundling is performed in a low-temperature environment of -30°C or below.

The present invention will be described in detail below, but the present invention is not limited to the following embodiments.
[Adhesive tape]
The pressure-sensitive adhesive tape according to the present invention is an adhesive tape comprising a base layer and an adhesive layer provided on at least one surface of the base layer, characterized in that the base layer is composed of a resin composition containing a polyvinyl chloride resin and, relative to 100 parts by mass of the polyvinyl chloride resin, 40 to 70 parts by mass of a plasticizer and 1 to 10 parts by mass of an acrylic resin, and having a melt rupture tension of 0.02 to 0.10 N at 180° C. The pressure-sensitive adhesive tape according to the present invention can suppress the occurrence of pinholes even if the base layer is made thin, and further is less likely to crack even when bundling is performed in a low-temperature environment of −30° C. or lower.

<Base layer>
The base layer is composed of a resin composition containing a polyvinyl chloride resin, 40 to 70 parts by mass of a plasticizer, and 1 to 10 parts by mass of an acrylic resin relative to 100 parts by mass of the polyvinyl chloride resin, and having a melt rupture tension of 0.02 to 0.10 N at 180°C.

From the viewpoint of reducing the weight of the adhesive tape, the thickness of the base layer is preferably 0.10 mm or less. Moreover, from the viewpoint of preventing the tape from breaking during the bundling operation, the thickness is preferably 0.03 mm or more. From these viewpoints, the thickness of the base layer is preferably 0.03 to 0.10 mm, more preferably 0.03 to 0.06 mm, and particularly preferably 0.03 to 0.05 mm. The thickness of the base layer can be confirmed by removing only the adhesive layer of the adhesive tape with a solvent and then measuring the thickness using a thickness gauge (e.g., manufactured by Mitutoyo Corporation).

(Resin composition)
The resin composition according to the present invention is characterized in that it contains a polyvinyl chloride resin, 40 to 70 parts by mass of a plasticizer and 1 to 10 parts by mass of an acrylic resin relative to 100 parts by mass of the polyvinyl chloride resin, and has a melt rupture tension of 0.02 to 0.10 N at 180°C. In this specification, the "melt rupture tension at 180°C" means the melt tension value at the time when the resin ruptures when the resin molten at 180°C is wound at a certain speed range. The melt rupture tension of the resin composition means a value measured under the following conditions.
(Method of measuring melt fracture tension)
The melt rupture tension of the pellets of the resin composition is measured using a Capillograph (for example, an apparatus named "Capillograph 1D" manufactured by Toyo Seiki Seisakusho Co., Ltd.) under the following conditions.
(Measurement condition)
Resin temperature: 180°C
Piston speed: 10 mm/min
Capillary length: 40 mm
Capillary diameter: 1.0 mm
Winding speed: 1.0 to 6.0 m/min

The melt rupture tension of the resin composition at 180° C. is 0.02 to 0.10 N, preferably 0.02 to 0.09 N, and more preferably 0.03 to 0.08 N. If the resin composition has a melt rupture tension of 0.02 to 0.10 N at 180° C., it is possible to obtain a base layer that does not develop pinholes even when made thin. In addition, it is possible to obtain an adhesive tape that is less likely to develop cracks even when bundling is performed in a low-temperature environment of −30° C. or lower.
The winding speed at which the resin breaks at 180° C. is preferably 2.0 m/min or more, and more preferably 2.0 to 5.0 m/min. The winding speed at which the resin breaks means the winding speed at which the molten resin breaks when the molten resin at 180° C. extruded from the capillary is wound while changing the winding speed in the range of 1.0 to 6.0 m/min.
In one embodiment, it is more preferable that the melt breaking tension is 0.02 to 0.10 N when the winding speed at the time of breaking of the resin is 2.0 m/min or more. A resin composition having such melt properties is easy to prepare a substrate layer having a small thickness. In particular, a substrate layer having a small thickness can be easily prepared by a method of increasing the stretch ratio of the substrate layer to reduce the film thickness. Furthermore, a substrate layer that is less likely to generate pinholes even when made thin can be easily obtained. In addition, it is easy to prevent the film formability from decreasing due to the resin becoming too soft.

(Polyvinyl chloride resin)
Examples of polyvinyl chloride resins include homopolymers of vinyl chloride (hereinafter referred to as "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 has excellent strength, abrasion resistance, waterproofness, and dust resistance.
The average degree of polymerization of the polyvinyl chloride resin is not particularly limited as long as the effects of the present invention are obtained. From the viewpoint of easily adjusting the melt rupture tension of the base layer, the average degree of polymerization is preferably 700 to 1800, more preferably 1000 to 1300. The average degree of polymerization is a value measured according to JIS K6720-2.

(Plasticizer)
As the plasticizer, for example, phthalic acid ester, isophthalic acid ester, terephthalic acid ester, adipic acid ester, trimellitic acid ester and polyesters thereof, phosphoric acid-based plasticizers, epoxy-based plasticizers, etc. can be used.
Specific examples include diisononyl phthalate (DINP), diheptyl phthalate (DHP), di-2-ethylhexyl phthalate (DEHP), di-n-octyl phthalate (n-DOP), diisodecyl phthalate (DIDP), di-2-ethylhexyl isophthalate (DOIP), di-2-ethylhexyl terephthalate (DOTP), benzyl butyl phthalate (BBP), tri-2-ethylhexyl trimellitate (TOTM), di-2-ethylhexyl adipate (DOA), diisononyl adipate (DINA), and adipic acid. Examples of the polyisodecyl ether include diisodecyl ether (DIDA), di-2-ethylhexyl azelate (DOZ), di-2-ethylhexyl sebacate (DOS), tricresyl phosphate (TCP), benzyl octyl adipate (BOA), adipic acid-propylene glycol polyester, adipic acid-butylene glycol polyester, phthalic acid-propylene glycol polyester, diphenyl cresyl phosphate (DPCP), diisodecyl adipate, epoxidized soybean oil, epoxidized linseed oil, and chlorinated paraffin. These may be used alone or in combination of two or more.
Among the above plasticizers, plasticizers having a melting point of -60°C or less are preferred from the viewpoint of easily improving the breaking elongation in a low-temperature environment of -30°C or less and easily suppressing cracks. Examples of such plasticizers include diisononyl adipate (DINA, melting point: -68°C), di-2-ethylhexyl adipate (DOA, melting point: -68°C), diisodecyl adipate (DIDA, melting point: -70°C), di-2-ethylhexyl azelate (DOZ, melting point: -60°C), and di-2-ethylhexyl sebacate (DOS, melting point: -62°C). These plasticizers having a melting point of -60°C or less may be used alone or in combination of two or more. Of these, DINA and DOA are more preferred.

The content of the plasticizer in the base layer is 40 to 70 parts by mass, preferably 45 to 65 parts by mass, and more preferably 50 to 60 parts by mass, per 100 parts by mass of polyvinyl chloride resin. If the amount of the plasticizer in the base layer is within the above range, the occurrence of pinholes can be suppressed even if the base layer is made thin.

(Acrylic resin)
Examples of acrylic resins include polymers mainly composed of acrylic acid, acrylic acid esters such as methyl acrylate, ethyl acrylate, n-butyl acrylate, isobutyl acrylate, 2-ethylhexyl acrylate, etc., and methacrylic acid esters such as methyl methacrylate, ethyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, 2-ethylhexyl methacrylate, etc. These acrylic resins may be used alone or in combination of two or more.

In the pressure-sensitive adhesive tape according to the present invention, from the viewpoint of easily adjusting the melt rupture tension at 180° C. of the resin composition constituting the base layer to the range of 0.02 to 0.10 N, the mass average molecular weight (Mw) of the acrylic resin is preferably 5×10 ⁵ to 50×10 ⁵ , more preferably 15×10 ⁵ to 40×10 ⁵ , and particularly preferably 25×10 ⁵ to 35×10 ^5. By combining an acrylic resin having such an Mw with a polyvinyl chloride resin, the melt rupture tension of the resin composition can be easily adjusted to a certain range. In addition, even if the base layer is made thin, the occurrence of pinholes is easily suppressed. The Mw of the acrylic resin means a value calculated in terms of polystyrene using GPC. In addition, the details of the measurement conditions are as follows.
(GPC measurement conditions)
Column: GPC K-806L 10 μm 8.0 × 300 mm × 2 Temperature: 40 ° C.
Mobile phase: THF
Flow rate: 1.0 mL/min Sample concentration: 0.1% by mass
Injection volume: 100 μL

As the acrylic resin, commercially available products may be used. Examples of commercially available products include those manufactured by Mitsubishi Chemical Corporation under the trade names "Metablen (registered trademark) P-551A (Mw 1.5 million)" and "Metablen P-530A (Mw: 3 million)"; and those manufactured by Kaneka Corporation under the trade names "Kane Ace (registered trademark) PA-20 (Mw: 1 million)" and "Kane Ace PA-30 (Mw: 3 million)".

The content of the acrylic resin in the resin composition is 1 to 10 parts by mass per 100 parts by mass of polyvinyl chloride resin. By blending 1 to 10 parts by mass of the acrylic resin, it becomes easier to adjust the melt rupture tension of the resin composition to a certain range. In addition, pinholes and tape breakage caused by thinning the base layer can be suppressed.

Pinholes are likely to occur when the base layer is thinned, particularly when the base layer is thinned by stretching it to increase the stretch ratio. It is presumed that this is because micro-separation occurs between molecules when the resin constituting the base layer is stretched, causing the resin to break. The inventors of the present application have found that by adding a certain amount of acrylic resin to the resin composition constituting the base layer, the number of entanglement points between the molecules increases, making the resin less likely to break even when the base layer is stretched. In addition, since the Tg (glass transition temperature) of the acrylic resin is lower than the Tg of the polyvinyl chloride resin, it is believed that the resin softens due to the resin properties of the acrylic resin, and the elongation of the resin itself is also improved. Furthermore, it has been found that if the resin composition contains a certain amount of acrylic resin, and the melt tension at the time when the molten resin (180°C) is wound at a certain speed range and the resin breaks is 0.02 to 0.10 N, the occurrence of pinholes can be more effectively suppressed even when the base layer is stretched to a small thickness. In this manner, the resin composition according to the present invention, which combines a polyvinyl chloride resin, a plasticizer, and an acrylic resin so as to satisfy specific melt properties, can effectively suppress the occurrence of pinholes even when the base material layer is made thinner by increasing the draw ratio of the base material layer.

The content of the acrylic resin in the resin composition is preferably 1 to 5 parts by mass, more preferably 1 to 3 parts by mass, per 100 parts by mass of polyvinyl chloride resin, from the viewpoint of easily adjusting the melt rupture tension of the resin composition at 180°C within a certain range and controlling the effects of the resin properties of the acrylic resin. By blending 1 to 10 parts by mass, preferably 1 to 5 parts by mass of a high molecular weight acrylic resin per 100 parts by mass of polyvinyl chloride resin, preferably polyvinyl chloride having an average degree of polymerization of 700 to 1800, the occurrence of pinholes due to thinning of the base layer can be more effectively suppressed.

(Other additives)
The resin composition may contain other additives as long as they do not impair the effects of the present invention.
Examples of other additives include inorganic fillers, modifiers, dispersants, colorants, light absorbers, lubricants, antiblocking agents, antistatic agents, stabilizers, and antioxidants.

In order to prevent the resin composition from adhering to a laminating roll or the like and contaminating the device during the production of the pressure-sensitive adhesive tape, an inorganic filler may be blended into the resin composition.
Examples of inorganic fillers 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, smectite, zinc borate, anhydrous zinc borate, zinc metaborate, barium metaborate, antimony oxide, antimony trioxide, antimony pentoxide, red phosphorus, talc, kaolin, clay, alumina, silica, boehmite, bentonite, sodium silicate, calcium silicate, calcium sulfate, calcium carbonate, magnesium carbonate, carbon black, etc. These may be used alone or in combination of two or more.

Examples of modifiers include chlorinated polyethylene, ethylene-vinyl acetate copolymer, acrylonitrile-butadiene-styrene copolymer, methyl methacrylate-butadiene-styrene copolymer, methyl methacrylate-butyl acrylate copolymer, etc. These may be used alone or in combination of two or more.

When additives other than the above-mentioned plasticizers, inorganic fillers, and modifiers are blended, the blending amount is not particularly limited as long as it does not impair the effects of the present invention. For example, more than 0 parts by mass and 10 parts by mass or less can be blended with respect to 100 parts by mass of polyvinyl chloride resin.

<Adhesive Layer>
The pressure-sensitive adhesive tape according to the present invention includes a pressure-sensitive adhesive layer provided on at least one surface of the aforementioned base layer. The pressure-sensitive adhesive layer is preferably provided directly on one surface of the base layer.

The adhesive constituting the adhesive layer is not particularly limited as long as it has the effect of the present invention, and any adhesive that is used in conventional adhesive tapes can be used as appropriate. Specifically, examples of the adhesive that can be used include acrylic adhesives, rubber adhesives, silicone adhesives, and urethane adhesives.

The acrylic pressure-sensitive adhesive may be, for example, one containing an acrylic polymer as a main component. The term "main component" means that the proportion of the acrylic polymer in the acrylic pressure-sensitive adhesive is 50% by mass or more.
Examples of the acrylic polymer include polymers of alkyl (meth)acrylates and carboxy-containing unsaturated monomers.
Examples of (meth)acrylic acid alkyl esters include methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, n-propyl acrylate, n-propyl methacrylate, isopropyl acrylate, isopropyl methacrylate, n-butyl acrylate, n-butyl methacrylate, isobutyl acrylate, isobutyl methacrylate, sec-butyl acrylate, sec-butyl methacrylate, tert-butyl acrylate, tert-butyl methacrylate, 2-ethylhexyl acrylate, 2-ethylhexyl methacrylate, n-octyl acrylate, n-octyl methacrylate, isooctyl acrylate, isooctyl methacrylate, n-nonyl acrylate, n-nonyl methacrylate, isononyl acrylate, isononyl methacrylate, etc. These may be used alone or in combination of two or more.

The carboxyl group-containing unsaturated monomer is not particularly limited as long as it is copolymerizable with the above-mentioned (meth)acrylic acid alkyl ester and has the effect of the present invention, and examples of the monomer that can be used include acrylic acid, methacrylic acid, itaconic acid, fumaric acid, maleic acid, etc. These may be used alone or in combination of two or more.

The acrylic polymer may be a copolymer containing monomers other than the alkyl (meth)acrylates and carboxy-containing unsaturated monomers exemplified above.
Examples of other monomers include hydroxyl group-containing monomers such as 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, and hydroxyhexyl (meth)acrylate; nitrogen-containing (meth)acrylates such as (meth)acrylamide, acryloylmorpholine, and (meth)acrylonitrile; vinyl acetate, styrene, vinylidene chloride, and vinyl propionate. These may be used alone or in combination of two or more.

Examples of rubber-based adhesives include those obtained by appropriately blending at least one rubber component selected from the group consisting of natural rubber, styrene-isoprene-styrene block copolymer (SIS), styrene-butadiene-styrene block copolymer (SBS), hydrogenated products of the styrene-based block copolymers (SIPS, SEBS), styrene-butadiene rubber (SBR), polyisoprene rubber (IR), polyisobutylene (PIB), and butyl rubber (IIR), with at least one tackifier selected from the group consisting of rosin-based resins, terpene-based resins, petroleum-based resins, etc. Also included are adhesives of graft polymers obtained by polymerizing (meth)acrylic esters with the aforementioned rubber components.

Examples of silicone-based adhesives include silicone rubber mixed with silicone resin or silicone oil.

Examples of urethane-based adhesives include those obtained by reacting polyols such as polyether polyols and polyester polyols with polyisocyanates such as tolylene diisocyanate (TDI), diphenylmethane diisocyanate (MDI), hexamethylene diisocyanate (HDI), and xylylene diisocyanate (XDI).

The adhesive forming the adhesive layer may contain any additives to the above-mentioned adhesive.
Examples of additives include softeners, tackifiers, surface lubricants, leveling agents, antioxidants, corrosion inhibitors, light stabilizers, ultraviolet absorbers, heat stabilizers, polymerization inhibitors, silane coupling agents, lubricants, inorganic or organic fillers, metal powders, pigments, etc. These may be used alone or in combination of two or more.

Examples of tackifiers include petroleum-based resins such as aliphatic copolymers, aromatic copolymers, aliphatic-aromatic copolymers, and alicyclic copolymers, coumarone-indene resins, terpene resins, terpene phenol resins, rosin-based resins such as polymerized rosin, (alkyl)phenol resins, xylene resins, and hydrogenated versions of these. These may be used alone or in combination of two or more.

It is preferable to use a rubber-based adhesive as the adhesive, as this tends to exhibit good adhesive properties even in low-temperature environments of -30°C or below. Furthermore, rubber-based adhesives made of natural rubber or SBR are more preferable.

The thickness of the pressure-sensitive adhesive layer is, for example, preferably from 5 to 50 μm, and more preferably from 10 to 20 μm, from the viewpoints of weight reduction of the pressure-sensitive adhesive tape and ease of bundling.
The pressure-sensitive adhesive layer may be composed of a plurality of layers. When the pressure-sensitive adhesive layer is composed of a plurality of layers, it is preferable that the total thickness of the pressure-sensitive adhesive layer is adjusted to be within the above range.

<Middle class>
In one embodiment of the present invention, an intermediate layer may be provided between the base layer and the pressure-sensitive adhesive layer. The intermediate layer is not particularly limited as long as it has the effects of the present invention, and for example, various films, cloths, etc. can be used.

From the viewpoint of reducing the weight of the adhesive tape, the total thickness of the adhesive tape of the present invention is preferably 0.03 to 0.10 mm, and more preferably 0.04 to 0.07 mm.

[Method of manufacturing adhesive tape]
The pressure-sensitive adhesive tape according to the present invention can be produced by a method including the steps of: melt-kneading the above-mentioned resin composition, and then forming the resulting film into a film of a predetermined thickness, width and length to obtain a base layer; and applying a pressure-sensitive adhesive to at least one surface of the base layer to form a pressure-sensitive adhesive layer.
Step (I) is a film-forming step of the substrate layer. In step (I), the melt-kneading method of the resin composition is not particularly limited as long as it has the effect of the present invention, and various mixers and kneaders equipped with heating devices such as twin-screw extruders, continuous and batch kneaders, rolls, and Banbury mixers can be used. The resin composition in which the raw materials are uniformly dispersed by the above method can be formed into a sheet-like film by a conventional method such as a calendar method, a T-die method, or an inflation method to form a substrate layer. From the viewpoint of thickness accuracy, it is more preferable to use the calendar method.

The temperature of the calendar roll when melt-kneading the resin composition is preferably 160 to 200°C, and more preferably 170 to 190°C, from the viewpoints of stretching at an appropriate melt breaking tension and forming a film at or below the thermal decomposition temperature of the vinyl chloride resin.

The film-forming step of the substrate layer may be a thinning step of the substrate layer. For example, when the substrate layer is formed by a calendaring method, the method of thinning the substrate layer includes "a method of narrowing the roll gap of the calendar roll to reduce the thickness of the substrate layer" (hereinafter referred to as "thin film method 1") and "a method of stretching the substrate layer to increase the stretch ratio to reduce the thickness of the substrate layer" (hereinafter referred to as "thin film method 2"). In the method for producing the pressure-sensitive adhesive tape according to the present invention, it is preferable that the step (I) includes the thin film method 2. It is more preferable to carry out the thin film method 2 after the thin film method 1.
As described above, the thin film method 2 is usually difficult to adopt because pinholes occur or the resin breaks. However, the adhesive tape according to the present invention uses a resin composition containing a specific amount of acrylic resin and having a melt break tension at 180°C within a certain range to form the substrate layer, so that the thin film method 2 can suppress the occurrence of pinholes. When the molten resin rolled by the calendar roll is recovered by increasing the speed of the roll in the next step (for example, a take-off roll, etc.), the speed ratio between the speed of the calendar roll and the take-off roll (speed of the take-off roll/speed of the calendar roll) is preferably 1.6 to 3.3, more preferably 2.0 to 3.3. With the above speed ratio, the thickness of the substrate layer is easily adjusted to 0.1 mm or less, preferably to a range of 0.03 to 0.05 mm.
The speed of the calender roll is preferably 30 to 50 m/min, more preferably 35 to 45 m/min, and the speed of the take-off roll is preferably 50 to 170 m/min, more preferably 70 to 150 m/min.
Furthermore, when the rolled resin (substrate layer) is stretched to increase the stretch ratio, the thickness of the resin after stretching relative to the thickness of the rolled resin (i.e., final thickness of substrate layer/thickness of substrate layer after rolling) is preferably 0.3 to 0.6, and more preferably 0.3 to 0.5.

[Application]
As described above, the adhesive tape according to the present invention can be suitably used as a tape for bundling and protecting electric wires in automobiles. The adhesive tape according to the present invention can reduce the weight of the tape by thinning the base layer. Therefore, it is possible to contribute to the demand for weight reduction in the automotive field and the demand for improved fuel efficiency. It should be noted that the use of the adhesive tape according to the present invention is not limited to bundling and protecting electric wires in automobiles.

More preferred aspects of the present invention are as follows.
<1> An adhesive tape comprising a base layer and an adhesive layer provided on at least one surface of the base layer, wherein the base layer is made of a resin composition that contains polyvinyl chloride having an average degree of polymerization of 700 to 1800, and, relative to 100 parts by mass of the polyvinyl chloride, 40 to 70 parts by mass of a plasticizer having a melting point of -60°C or lower and 1 to 5 parts by mass of an acrylic resin, and has a melt break tension of 0.02 to 0.10 N at 180°C and a take-up speed of the resin at break of 2.0 m/min or more.
<2> The pressure-sensitive adhesive tape according to <1>, wherein the thickness of the base layer is 0.03 to 0.06 mm.
<3> The pressure-sensitive adhesive tape according to <1> or <2>, wherein the acrylic resin has a Mw of 5×10 ⁵ to 50×10 ⁵ .
<4> A method for producing the pressure-sensitive adhesive tape according to any one of <1> to <3>, comprising a step of thinning the base material layer by increasing the stretch ratio of the base material layer.
<5> The method for producing an adhesive tape described in <4>, wherein the step of thinning the base layer includes sandwiching a molten resin between rolling rolls and rolling it, and then increasing the speed of a take-off roll to stretch the rolled resin.
<6> The method for producing an adhesive tape according to <5>, wherein the speed of the take-off roll is 1.6 to 3.3 times the speed of the rolling roll.

The present invention will be described in detail below with reference to examples, but the present invention is not limited to the following description.

[Example 1]
(Making adhesive tape)
A resin composition was obtained by blending 55 parts by mass of diisononyl adipate (DINA) and 3 parts by mass of an acrylic resin (manufactured by Mitsubishi Chemical Corporation, product name "Metabrene P-530A", Mw: 3 million) as a plasticizer with 100 parts by mass of polyvinyl chloride (manufactured by Taiyo Vinyl Co., Ltd., product name "TH-700", average polymerization degree 700). The resin composition was melt-kneaded in a Banbury mixer so that each component was uniformly dispersed, and then placed in a calendar molding machine and rolled by adjusting the roll temperature so that the resin temperature was 180 ° C. The rolled resin was stretched at a speed ratio of 2.0 between the calendar roll and the next roll (take-off roll) to obtain a substrate layer having a thickness of 0.05 mm.

The adhesive was a rubber-based adhesive containing 30 parts by mass (solids) of styrene-butadiene copolymer latex (manufactured by E-Tech Co., Ltd., product name "KT4615B"), 50 parts by mass (solids) of graft polymer latex obtained by graft polymerizing natural rubber with methyl methacrylate (manufactured by Resitex Co., Ltd., product name "MG-40S"), and 20 parts by mass (solids) of a petroleum resin-based emulsion tackifier (manufactured by Arakawa Chemical Industries Co., Ltd., product name "AP-1199-NT"), which was applied to one side of the base layer by a gravure method to form an adhesive layer. The thickness of the adhesive layer was 0.01 mm. Thereafter, the tape was wound into a tape log shape and cut to a width of 19 mm to obtain an adhesive tape.
The melt breaking tension of the resin composition, the film formability of the base layer (pinhole evaluation), the tensile breaking elongation of the base layer in a low-temperature environment, and the crack evaluation of the pressure-sensitive adhesive tape in a low-temperature environment were evaluated under the following conditions. The results are shown in Table 1.

<Measurement of melt rupture tension of resin composition>
The resin composition was melt-kneaded using a 40 mm diameter pellet extruder (manufactured by Tanabe Plastics Co., Ltd., product name "PASC21-A-S") to obtain resin pellets. Next, the obtained resin pellets were measured using a Capilograph (manufactured by Toyo Seiki Seisakusho Co., Ltd., device name "Capilograph 1D") under the following conditions to measure the winding speed when the resin first broke and the melt breakage tension at that time.
Resin temperature: 180°C
Piston speed: 10 mm/min Capillary length: 40 mm
Capillary diameter: 1.0 mm
Winding speed: 1.0 to 6.0 m/min

<Evaluation of Base Layer>
The resin composition was formed into a film having a thickness of 0.05 mm to prepare a substrate layer. Specifically, the resin composition was put into a calendar molding machine and rolled by adjusting the roll temperature so that the resin temperature was 180° C. Then, the speed ratio between the calendar roll and the next roll (take-off roll) was set to 2.0 to obtain a substrate layer having a thickness of 0.05 mm.

(Evaluation of film-forming properties of substrate layer (pinhole evaluation))
The obtained base layer was cut into 100 mm squares to prepare samples. Five samples of the base layer were inspected for hole defects by a transmission method using a plain surface inspection device (manufactured by Nireco Corporation, product name "Mujiken+"), and evaluated according to the following evaluation criteria.
(Evaluation criteria)
Good: No pinholes were present in any of the five samples.
Unacceptable: There was one or more samples with ^one or more pinholes measuring 0.04 mm2 or more.
Film formation impossible: The substrate layer broke during film formation.

(Tensile elongation at break of base layer)
The obtained base layer was cut to a size of 10 mm in width and 100 mm in length, and after storing for 1 hour in a thermostatic bath (manufactured by Shimadzu Corporation, product name "TCR2W-200P+125-X") at -30°C in accordance with the test method for "tensile properties of plastics" described in JIS K 7161, the tensile elongation at break at -30°C was measured under the following conditions using a tensile tester (manufactured by Shimadzu Corporation, product name "Autograph AGC-X").
(Measurement condition)
Distance between chucks: 50 mm
Tensile speed: 300 mm/min

<Crack evaluation of adhesive tape>
The obtained adhesive tape was processed to a width of 19 mm and a length of 300 mm. Next, the adhesive tape was wrapped 10 times in a half-wrap around a 10 mm diameter bundle of 20 1.0 mm diameter wires to prepare a test specimen. The test specimen was stored at -30°C for 1 hour, and then the center of the bundle of wires was folded by hand in an atmosphere of -30°C. Thereafter, the adhesive tape was visually checked for the presence or absence of cracks or breaks that would interfere with its use. The bundling workability was evaluated by rating the adhesive tape as "good" when there were no cracks or cracks in the adhesive tape and "poor" when there were large cracks or cracks in the adhesive tape.

[Examples 2 to 8, Comparative Examples 1 to 6]
A substrate layer having the thickness shown in Tables 1 and 2 was prepared in the same manner as in Example 1, except that the resin composition was formulated as shown in Tables 1 and 2. Thereafter, a pressure-sensitive adhesive layer was formed with a thickness of 0.01 mm on one side of the substrate layer using the same pressure-sensitive adhesive as in Example 1, to obtain a pressure-sensitive adhesive tape. The melt rupture tension of the resin composition, the film-forming property of the substrate layer (pinhole evaluation), the tensile rupture elongation of the substrate layer in a low-temperature environment, and the crack evaluation of the pressure-sensitive adhesive tape in a low-temperature environment were evaluated in the same manner as in Example 1. The results are shown in Tables 1 and 2.

[Example 9]
A resin composition was prepared according to the formulation shown in Table 1, and the resin composition was melt-kneaded in a Banbury mixer so that each component was uniformly dispersed. Thereafter, the resin composition was put into a calendar molding machine and rolled by adjusting the roll temperature so that the resin temperature was 180 ° C. The speed ratio between the calendar roll and the next roll (take-off roll) was 3.3 to obtain a base layer having a thickness of 0.03 mm. On one side of this base layer, a 0.01 mm thick adhesive layer was formed using the same adhesive as in Example 1 to obtain an adhesive tape. The melt rupture tension of the resin composition, the film-forming property of the base layer (pinhole evaluation), the tensile rupture elongation of the base layer in a low temperature environment, and the crack evaluation of the adhesive tape in a low temperature environment were evaluated in the same manner as in Example 1. In Example 9, a base layer sample having a thickness of 0.03 mm was prepared and the above evaluation was performed. The results are shown in Table 1.

Details of the raw materials listed in Tables 1 and 2 are as follows.
(Polyvinyl chloride resin)
Polyvinyl chloride resin 1: Polyvinyl chloride (average polymerization degree 500) (manufactured by Taiyo Vinyl Co., Ltd., product name "TH-500").
Polyvinyl chloride resin 2: Polyvinyl chloride (average polymerization degree 700) (manufactured by Taiyo Vinyl Co., Ltd., product name "TH-700").
Polyvinyl chloride resin 3: Polyvinyl chloride (average polymerization degree 1000) (manufactured by Taiyo Vinyl Co., Ltd., product name "TH-1000 (for soft use)").
Polyvinyl chloride resin 4: Polyvinyl chloride (average polymerization degree 1300) (manufactured by Taiyo Vinyl Co., Ltd., product name "TH-1300").
Polyvinyl chloride resin 5: Polyvinyl chloride (average polymerization degree 1700) (manufactured by Taiyo Vinyl Co., Ltd., product name "TH-1700").
Polyvinyl chloride resin 6: Polyvinyl chloride (average polymerization degree 2000) (manufactured by Taiyo Vinyl Co., Ltd., product name "TH-2000").
(Plasticizer)
DINA: diisononyl adipate (manufactured by J Plus Co., Ltd., trade name "DINA", melting point: -68°C).
DINP: diisononyl phthalate (manufactured by J Plus Corporation, trade name "DINP", melting point: -45°C).
(Acrylic resin)
Acrylic resin: trade name "Metablen P-530A" (Mw: 30 x 10 ⁵ ), manufactured by Mitsubishi Chemical Corporation.

As shown in Tables 1 and 2, the adhesive tape according to the present invention was able to effectively suppress the occurrence of pinholes even when the thickness of the base layer was reduced to as thin as 0.05 mm. It was also found that even when the base layer was made thin, cracks were unlikely to occur in the adhesive tape in a low-temperature environment of -30°C.
On the other hand, in Comparative Example 1, in which the melt rupture tension at 180 ° C. was less than 0.02, and Comparative Example 2, in which the melt rupture tension was more than 0.10 N, pinholes occurred in the base layer. In Comparative Example 3, in which the plasticizer was less than 40 parts by mass, the resin broke and it was not possible to form a base layer. Since the resin composition of Comparative Example 3 had a melt rupture tension of more than 0.10 N at 180 ° C., it is considered that the tension of the molten resin was too high and the elongation required for film formation could not be obtained. On the other hand, in Comparative Example 4, in which the plasticizer was more than 70 parts by mass, the tension of the molten resin was too low and pinholes occurred in the base layer. In Comparative Example 5, which did not contain an acrylic resin, the resin broke during the process of stretching the base layer. In Comparative Example 6, in which the acrylic resin was more than 10 parts by mass, the melt rupture tension was too low and pinholes occurred. In addition, in the crack evaluation of the pressure-sensitive adhesive tapes of Comparative Examples 1, 2, 4, and 6 in which pinholes had occurred in the base layer, the evaluation results varied due to the influence of the pinholes in a low-temperature environment of -30°C, and appropriate evaluation was not possible.
From the above results, it was confirmed that the adhesive tape according to the present invention can suppress the occurrence of pinholes even when the base layer is made thin, and is less susceptible to cracking even in a low-temperature environment of -30°C.

Claims (6)

An adhesive tape comprising a base layer and an adhesive layer provided on at least one surface of the base layer,
The adhesive tape is configured such that the base layer contains a polyvinyl chloride resin, and, relative to 100 parts by mass of the polyvinyl chloride resin, 40 to 70 parts by mass of a plasticizer having a melting point of -60°C or lower , and 1 to 10 parts by mass of an acrylic resin, and the resin composition has a melt rupture tension of 0.02 to 0.10 N at 180°C. The adhesive tape according to claim 1, wherein the polyvinyl chloride resin has an average degree of polymerization of 700 to 1800. The pressure-sensitive adhesive tape according to claim 1 or 2 , wherein the acrylic resin has a mass average molecular weight of 5×10 ⁵ to 50×10 ⁵ . The pressure-sensitive adhesive tape according to any one of claims 1 to 3 , wherein the base layer has a thickness of 0.03 to 0.10 mm. The pressure-sensitive adhesive tape according to claim 1 , which is used for bundling electric wires. A member bound with the adhesive tape according to any one of claims 1 to 5 .