Base polymer for adhesive agent, adhesive agent containing base polymer for adhesive agent, and adhesive tape and adhesive film using adhesive agent

Abstract

Provided is a polymer suitable as a base polymer for an adhesive agent. This base polymer for an adhesive agent has a branched structure including a lactic acid unit, a caprolactone unit, and a polyhydric alcohol unit containing three or more hydroxyl groups, wherein the proportion of the lactic acid unit is 20-50 mol%, the glass transition temperature is -15 °C or less, and at least one of Fα and Fε as represented by the following formulas is 0.35 or more.　Fα = Iα* / (Iα + Iα*) and Fε = Iε* / (Iε + Iε*), where Iα, Iα*, Iε, and Iε* are values obtained from the 1H NMR spectrum of the base polymer for an adhesive agent.

Description

Base polymer for adhesive, adhesive containing base polymer for adhesive, and adhesive tape and adhesive film using the adhesive

[0001] The present invention relates to a base polymer for adhesives, an adhesive containing the base polymer for adhesives, and an adhesive tape and an adhesive film using the adhesive, and more particularly to a base polymer for polyester-based adhesives, an adhesive containing the base polymer for adhesives, and an adhesive tape and an adhesive film using the adhesive.

[0002] It has been proposed to use a copolymer of a biodegradable polymer such as polylactic acid as an adhesive. For example, Japanese Patent Application Laid-Open No. 2011-88959 discloses an adhesive sheet using a polyester prepared using lactic acid and a dibasic acid. Non-Patent Document 1 proposes using a copolymer of polylactic acid and polycaprolactone as an adhesive.

[0003] JP 2011-88959 A

[0004] Shinya Takahashi, “Proposal for adhesives using renewable resources containing plant-derived ingredients,” Convertec, Processing Technology Research Group, February 2009, pp. 103-108 Mengyuan Zhang et. al., “Synthesis of Poly(l-lactide-co-ε-caprolactone) Copolymer: Structure, Toughness, and Elasticity”, Polymers 2021, 13, 1270, https: / / doi.org / 10.3390 / polym13081270

[0005] An object of the present invention is to provide a polymer suitable as a base polymer for a pressure-sensitive adhesive, a pressure-sensitive adhesive, a pressure-sensitive adhesive tape, and a pressure-sensitive adhesive film.

[0006] A base polymer for a pressure-sensitive adhesive according to one embodiment of the present invention is a polymer having a branched structure containing lactic acid units, caprolactone units, and trivalent or higher polyhydric alcohol units, the proportion of the lactic acid units being 20 to 50 mol %, the glass transition temperature being -15°C or lower, and at least one of Fα and Fε, represented by the following formula, being 0.35 or higher. Fα=Iα ＊ / (Iα + Iα ＊ ) Fε = Iε ＊ / (Iε + Iε ＊ ) where Iα, Iα ＊ , Iε and Iε ＊ is the base polymer for the pressure-sensitive adhesive １ is a value obtained from a H-NMR spectrum, and Iα is the integrated intensity of a signal derived from a proton of a methylene group, among methylene groups contained in a caprolactone unit, that is bonded to the carbonyl carbon of an ester bond and that is bonded to the caprolactone unit via the ester bond, and ＊ is the integrated intensity of a signal derived from a proton of a methylene group, among methylene groups contained in a caprolactone unit, which is bonded to the carbonyl carbon of an ester bond and is bonded to a lactic acid unit via the ester bond; Iε is the integrated intensity of a signal derived from a proton of a methylene group, among methylene groups contained in a caprolactone unit, which is bonded to the oxygen of an ester bond and is bonded to a caprolactone unit via the ester bond; Iε ＊ is the integrated intensity of the signal derived from the proton of the methylene group, which is one of the methylene groups contained in the caprolactone unit and is bonded to the oxygen of the ester bond and is bonded to the lactic acid unit via the ester bond.

[0007] An adhesive according to one embodiment of the present invention includes the above-mentioned base polymer for adhesives. An adhesive tape according to one embodiment of the present invention is an adhesive tape using the above-mentioned adhesive. An adhesive film according to one embodiment of the present invention is an adhesive film using the above-mentioned adhesive.

[0008] According to the present invention, a polymer suitable as a base polymer for a pressure-sensitive adhesive, a pressure-sensitive adhesive, a pressure-sensitive adhesive tape, and a pressure-sensitive adhesive film can be obtained.

[0009] Figure 1 shows the structure of the base polymer for adhesives. １FIG. 2A is a diagram showing a part of the chemical structure of a base polymer for an adhesive. FIG. 2B is a diagram showing another part of the chemical structure of a base polymer for an adhesive. FIG. 2C is a diagram showing yet another part of the chemical structure of a base polymer for an adhesive. FIG. 3 is a flow diagram of an example of a method for producing a base polymer for an adhesive. FIG. 4A is a diagram for explaining an outline of the production method of FIG. 3. FIG. 4B is a diagram for explaining an outline of the production method of FIG. 3. FIG. 4C is a diagram for explaining an outline of the production method of FIG. 3.

[0010] The present inventors have investigated methods for improving the performance of base polymers for polyester-based pressure-sensitive adhesives, and have obtained the following findings.

[0011] A polymer with a low glass transition temperature is preferred as a base polymer for adhesives. For example, the glass transition temperature of polylactic acid is about 60°C, and it is not suitable as a base polymer for adhesives when used alone. To adjust the glass transition temperature, it is effective to use a copolymer of two or more polyester resins.

[0012] A polymer with low crystallinity is preferred as a base polymer for adhesives, because high crystallinity accelerates solidification and reduces adhesiveness. In order to reduce crystallinity, it is preferable to use a random copolymer in which two or more polyester resins are irregularly bonded.

[0013] Specifically, a polymer having a branched structure containing lactic acid units, caprolactone units, and polyhydric alcohol units, in which the proportion of lactic acid units is 20 to 50 mol %, the glass transition temperature Tg is −15° C. or lower, and at least one of Fα and Fε represented by the following formula is 0.35 or higher, is suitable as a base polymer for adhesives. ＊ / (Iα + Iα ＊ ) Fε = Iε ＊ / (Iε + Iε ＊ ) where Iα, Iα ＊ , Iε and Iε ＊ is the polymer of interest １ This is a value obtained from the H-NMR spectrum.

[0014] Fα and Fε, which will be described in detail later, are indicators of the number of bonds between lactic acid units and caprolactone units (bonds between different units) in the target polymer. Higher Fα and Fε indicate a higher number of bonds between lactic acid units and caprolactone units.

[0015] Copolymers of polylactic acid and polycaprolactone are generally produced by ring-opening polymerization of L-lactide and ε-caprolactone. However, in this method, lactide, which is more reactive than caprolactone, polymerizes first, followed by caprolactone, resulting in a block polymer. Therefore, it is difficult to achieve Fα and Fε of 0.35 or more using this method.

[0016] The present inventors have discovered a method for producing a polyester copolymer that is completely different from the above-mentioned methods. Specifically, they have found that by heating and stirring two or more types of polyester resins (polyester resins as polymers, not monomers), decomposition and generation of ester bonds occur simultaneously, resulting in a polyester copolymer. They have also found that this method can increase Fα and Fε. The present invention has been completed based on these findings. Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

[0017] [Base polymer for pressure-sensitive adhesives] The base polymer for pressure-sensitive adhesives according to one embodiment of the present invention is a polymer having a branched structure containing lactic acid units, caprolactone units, and trihydric or higher polyhydric alcohol units, in which the proportion of lactic acid units is 20 to 50 mol %, the glass transition temperature Tg is −15° C. or lower, and at least one of Fα and Fε represented by the following formula is 0.35 or higher. Fα=Iα ＊ / (Iα + Iα ＊ ) Fε = Iε ＊ / (Iε + Iε ＊ ) where Iα, Iα ＊ , Iε and Iε ＊ is a base polymer for adhesives １ These are values ​​obtained from the H-NMR spectrum. Details of Fα and Fε will be described later.

[0018] [Structure] The base polymer for a pressure-sensitive adhesive according to this embodiment is a polymer having a branched structure containing lactic acid units, caprolactone units, and trihydric or higher polyhydric alcohol units (hereinafter simply referred to as "polyhydric alcohol units").

[0019] The polyhydric alcohol unit is a structural unit derived from a trivalent or higher alcohol. By using a polyhydric alcohol unit derived from a trivalent or higher alcohol, the PSA base polymer can have a branched structure, thereby improving cohesive strength.

[0020] The trihydric or higher alcohol is, for example, one or more selected from the group consisting of trimethylolpropane, glycerin, erythritol, pentaerythritol, glucose, acrylic polyol, polyester polyol, polyether polyol, epoxy polyol, polyolefin polyol, fluorine-containing polyol, and polyvinyl alcohol, and among these, trimethylolpropane and pentaerythritol are preferred.

[0021] The PSA base polymer according to this embodiment has a lactic acid unit ratio of 20 to 50 mol% in the polymer. If the lactic acid unit ratio is too high or too low, the desired properties of the PSA base polymer cannot be obtained. The lower limit of the lactic acid unit ratio is preferably 30 mol%, more preferably 40 mol%. The upper limit of the lactic acid unit ratio is preferably 48 mol%, more preferably 46 mol%.

[0022] The proportion of caprolactone units in the polymer is not particularly limited, but is, for example, 40 to 80 mol %. The lower limit of the proportion of caprolactone units is preferably 50 mol %, more preferably 53 mol %. The upper limit of the proportion of caprolactone units is preferably 70 mol %, more preferably 60 mol %.

[0023] The proportion of polyhydric alcohol units in the polymer is preferably 0.55 mol% or less. If the proportion of polyhydric alcohol units is too high, the polymer may gel (foam) and become unusable as a base polymer for pressure-sensitive adhesives. The upper limit of the proportion of polyhydric alcohol units is more preferably 0.50 mol%, and even more preferably 0.45 mol%. On the other hand, if the proportion of polyhydric alcohol units is too low, a sufficient branched structure may not be obtained, and an appropriate storage modulus may not be obtained. The lower limit of the proportion of polyhydric alcohol units is preferably 0.20 mol%, and even more preferably 0.30 mol%.

[0024] The PSA base polymer according to the present embodiment may further contain structural units other than lactic acid units, caprolactone units, and polyhydric alcohol units. The PSA base polymer according to the present embodiment may contain, for example, hydroxycarboxylic acid units other than lactic acid units and caprolactone units. The PSA base polymer according to the present embodiment may also contain structural units derived from dihydric alcohols (e.g., ethylene glycol, diethylene glycol, triethylene glycol, 1,3-butanediol, propylene glycol, polypropylene glycol, pentanediol, polyethylene glycol, tetraethylene glycol, etc.). The proportion of structural units other than lactic acid units, caprolactone units, and polyhydric alcohol units in the polymer is preferably 10 mol % or less, more preferably 5 mol % or less, and even more preferably 1 mol % or less. The proportion of each unit in the polymer may be, for example, １ It can be measured by H-NMR.

[0025] [Glass transition temperature, etc.] The base polymer for pressure-sensitive adhesives according to this embodiment has a glass transition temperature of -15°C or lower. If the glass transition temperature is too high, it will not be suitable as a base polymer for pressure-sensitive adhesives. The glass transition temperature can be adjusted by the molecular weight of the polymer, the ratio of lactic acid units to caprolactone units in the polymer, etc. The glass transition temperature is more preferably -20°C or lower, even more preferably -25°C or lower, and even more preferably -30°C or lower. The lower limit of the glass transition temperature is not particularly limited, but is, for example, -60°C.

[0026] The PSA base polymer according to this embodiment preferably has a number average molecular weight Mn of 10,000 to 30,000. The lower limit of the number average molecular weight Mn is more preferably 12,000, and even more preferably 13,000. The upper limit of the number average molecular weight Mn is more preferably 25,000, and even more preferably 20,000. In other words, the number average molecular weight Mn is more preferably 12,000 to 25,000, and most preferably 13,000 to 20,000.

[0027] The PSA base polymer according to this embodiment preferably has a weight average molecular weight Mw of 40,000 to 100,000. The lower limit of the weight average molecular weight Mw is more preferably 45,000, and even more preferably 50,000. The upper limit of the weight average molecular weight Mw is more preferably 90,000, and even more preferably 80,000. In other words, the weight average molecular weight Mw is more preferably 45,000 to 90,000, and most preferably 50,000 to 80,000.

[0028] The PSA base polymer according to this embodiment preferably has a number average molecular weight Mn of 10,000 to 30,000 and a weight average molecular weight Mw of 40,000 to 100,000. The lower limit of the number average molecular weight Mn is more preferably 12,000, and even more preferably 13,000. The upper limit of the number average molecular weight Mn is more preferably 25,000, and even more preferably 20,000. The lower limit of the weight average molecular weight Mw is more preferably 45,000, and even more preferably 50,000. The upper limit of the weight average molecular weight Mw is more preferably 90,000, and even more preferably 80,000. That is, it is more preferable that the number average molecular weight Mn is 12,000 to 25,000 and the weight average molecular weight Mw is 45,000 to 90,000, and it is most preferable that the number average molecular weight Mn is 13,000 to 20,000 and the weight average molecular weight Mw is 50,000 to 80,000.

[0029] The PSA base polymer according to this embodiment preferably has a number average molecular weight Mn of 10,000 to 30,000, and a dispersity (Mw / Mn) of 1.0 to 10.0. Alternatively, the PSA base polymer according to this embodiment preferably has a weight average molecular weight Mw of 40,000 to 100,000, and a dispersity (Mw / Mn) of 1.0 to 10.0. More preferably, the number average molecular weight Mn is 10,000 to 30,000, the weight average molecular weight Mw is 40,000 to 100,000, and a dispersity (Mw / Mn) of 1.0 to 10.0.

[0030] The base polymer for pressure-sensitive adhesives according to this embodiment preferably has a number average molecular weight Mn of 10,000 to 30,000, a weight average molecular weight Mw of 40,000 to 100,000, and a proportion of polyhydric alcohol units of 0.55 mol % or less.

[0031] The polydispersity (Mw / Mn) of the PSA base polymer according to this embodiment is, for example, 1.0 to 10.0. The lower limit of the polydispersity is preferably 1.5, and more preferably 2.0. The upper limit of the polydispersity is preferably 8.0, and more preferably 6.0.

[0032] The base polymer for a pressure-sensitive adhesive according to this embodiment preferably has a storage modulus at 20°C of 0.10 x 10 ５ ~1.5 x 10 ５ The lower limit of the storage modulus is more preferably 0.20 × 10 ５ Pa, and more preferably 0.50 × 10 ５ The upper limit of the storage modulus is more preferably 1.40 × 10 ５ Pa, and more preferably 1.30 × 10 ５ It is Pa.

[0033] [Fα and Fε] In the base polymer for pressure-sensitive adhesives according to this embodiment, at least one of Fα and Fε, which are represented by the following formula, is 0.35 or more. ＊ / (Iα + Iα ＊ ) Fε = Iε ＊ / (Iε + Iε ＊ ) where Iα, Iα ＊ , Iε and Iε ＊ is a base polymer for adhesives １ is a value obtained from a H-NMR spectrum, and Iα is the integrated intensity of a signal derived from a proton of a methylene group, among methylene groups contained in a caprolactone unit, that is bonded to the carbonyl carbon of an ester bond and that is bonded to the caprolactone unit via the ester bond, and ＊ is the integrated intensity of a signal derived from a proton of a methylene group, among methylene groups contained in a caprolactone unit, which is bonded to the carbonyl carbon of an ester bond and is bonded to a lactic acid unit via the ester bond; Iε is the integrated intensity of a signal derived from a proton of a methylene group, among methylene groups contained in a caprolactone unit, which is bonded to the oxygen of an ester bond and is bonded to a caprolactone unit via the ester bond; Iε ＊ is the integrated intensity of the signal derived from the proton of the methylene group, which is one of the methylene groups contained in the caprolactone unit and is bonded to the oxygen of the ester bond and is bonded to the lactic acid unit via the ester bond.

[0034] Figure 1 shows the structure of the base polymer for adhesives. １ This is an example of a H-NMR spectrum. １ The H-NMR spectrum was measured using a Bruker AVANCE NEO 700 MHz nuclear magnetic resonance (NMR) spectrometer, with the adhesive base polymer dissolved in deuterated chloroform at 10 mg / ml. TMS (tetramethylsilane) was used as the chemical shift standard.

[0035] In FIG. 1, α, α ＊ , β, γ, δ, ε and ε ＊ are signals derived from the protons of the methylene groups contained in the caprolactone units. ＊ is a signal derived from the proton of the methyl group contained in the lactic acid unit, and B and B ＊ is a signal derived from the proton of the methine group contained in the lactic acid unit.

[0036] Figures 2A to 2C show a portion of the chemical structure of the PSA base polymer. As described above, the PSA base polymer according to this embodiment contains lactic acid units LA (Figures 2B and 2C), caprolactone units CL (Figures 2A to 2C), and polyhydric alcohol units (not shown). As shown in Figure 2A, five methylene groups are present in the caprolactone unit CL. These methylene groups are referred to as α-, β-, γ-, δ-, and ε-position methylene groups, in order from those directly bonded to the carbonyl carbon of the ester bond.

[0037] The methylene group at the α-position is a methylene group bonded to the carbonyl carbon of the ester bond. The methylene group at the ε-position is a methylene group bonded to the oxygen of the ester bond. The α to ε signals in Figure 1 are signals due to the protons of the methylene groups at the α to ε positions, respectively.

[0038] The signal derived from the proton of the methylene group at the α-position appears at a different chemical shift when the methylene group is bonded to the caprolactone unit CL via an ester bond (see FIG. 2A) and when it is bonded to the lactic acid unit LA (see FIG. 2B). Here, the methylene group bonded to the carbonyl carbon of the ester bond and bonded to the lactic acid unit LA via the ester bond is referred to as the α ＊ The methylene group bonded to the caprolactone unit CL via the ester bond is referred to as the methylene group at the α-position (see FIG. 2A), as described above. ＊ The signal of α ＊ Specifically, the signal of α appears at about 2.30 to 2.35 ppm, while the signal of α ＊ The signal appears at about 2.35 to 2.50 ppm.

[0039] Similarly, the signal derived from the proton of the methylene group at the ε position appears at a different chemical shift when the methylene group is bonded to the caprolactone unit CL via an ester bond (see FIG. 2A) and when it is bonded to the lactic acid unit LA via an ester bond (see FIG. 2C). Here, the methylene group bonded to the oxygen of the ester bond and bonded to the lactic acid unit LA via the ester bond is referred to as ε. ＊ The methylene group bonded to the caprolactone unit CL via the ester bond is referred to as the methylene group at the ε-position (see FIG. 2C). As mentioned above, the methylene group bonded to the caprolactone unit CL via the ester bond is referred to as the methylene group at the ε-position (see FIG. 2A). ＊ The signal of ε ＊ Specifically, the ε signal appears at about 4.00 to 4.10 ppm, while the ε signal appears at about 4.00 to 4.10 ppm. ＊ The signal appears at about 4.10 to 4.20 ppm.

[0040] The signal derived from the proton of the methyl group of the lactic acid unit LA is also expressed as A or A depending on whether the partner of the ester bond is the lactic acid unit LA or the caprolactone unit CL. ＊ It is observed as: ＊is a signal that is originally located at A, but is shifted downfield from A by bonding with the caprolactone unit CL. Similarly, the signal originating from the methine group proton of the lactic acid unit LA is also shifted downfield from B or B. ＊ is observed as

[0041] Iα, Iα ＊ , Iε and Iε ＊ are α and α ＊ , ε and ε ＊ is the integrated intensity of the signal. １ The integrated intensity of the H-NMR signal is proportional to the number of protons. ＊ , Iε and Iε ＊ are the α-position and α ＊ position, ε position and ε ＊ This is an amount proportional to the number of protons in the methylene group at the position.

[0042] Therefore, Iα is a quantity proportional to the number of bonds between caprolactone units CL and CL (hereinafter referred to as "CL-CL bonds"), and Iα ＊ is an amount proportional to the number of bonds between caprolactone units CL and lactic acid units LA (hereinafter referred to as "CL-LA bonds"). ＊ / (Iα + Iα ＊ ) is the ratio of the number of CL-LA bonds to the sum of the number of CL-CL bonds and the number of CL-LA bonds.

[0043] Similarly, Iε is a quantity proportional to the number of CL-CL bonds, and Iε ＊ is a quantity proportional to the number of CL-LA bonds. Fε = Iε ＊ / (Iε + Iε ＊ ) is the ratio of the number of CL-LA bonds to the sum of the number of CL-CL bonds and the number of CL-LA bonds.

[0044] Larger Fα and Fε indicate a higher proportion of CL-LA bonds in the polymer. In other words, larger Fα and Fε indicate more frequent switching between caprolactone units CL and lactic acid units LA, and smaller blocks of consecutive caprolactone units CL and lactic acid units LA.

[0045] In the base polymer for pressure-sensitive adhesives according to this embodiment, at least one of Fα and Fε is 0.35 or more (35% or more). If at least one of Fα and Fε is 0.35 or more, excellent adhesiveness can be obtained. The lower limits of Fα and Fε are more preferably 0.38 or more, and even more preferably 0.40 or more. At least one of Fα and Fε may be 0.35, 0.38, or 0.40 or more, but more preferably both Fα and Fε are 0.35, 0.38, or 0.40 or more. The upper limits of Fα and Fε are not particularly limited, but are, for example, 0.80, and preferably 0.60.

[0046] [Method for producing adhesive base polymer] Next, an example of a method for producing an adhesive base polymer according to the present embodiment will be described. The production method described below is merely an example, and the adhesive base polymer according to the present embodiment is not limited to those produced by this method.

[0047] 3 is a flow diagram of an example of a method for producing a base polymer for a pressure-sensitive adhesive, which includes a decomposition step (step S1), a drying step (step S2), and a polymerizing step (step S3).

[0048] First, an overview of the manufacturing method shown in FIG. 3 will be described with reference to FIGS. 4A to 4C. In this manufacturing method, raw material 10 containing polylactic acid 11 and polycaprolactone 12 is heated and stirred in a reactor (step S2, see FIG. 3A). This simultaneously decomposes and generates ester bonds, yielding decomposition product 20, a low-molecular-weight polyester copolymer (see FIG. 3B). After drying decomposition product 20 (step S2), a polyhydric alcohol and a catalyst are added, and the mixture is heated and stirred under reduced pressure to increase the molecular weight (step S3). This results in polymer 30 having a branched structure containing lactic acid units 31, caprolactone units 32, and polyhydric alcohol units 33 (see FIG. 3C).

[0049] The polyhydric alcohol and catalyst may be added in advance in the decomposition step (step S1). That is, in the production method of Fig. 3, a trihydric or higher polyhydric alcohol may be added to the raw material or the decomposition product in at least one of the decomposition step (step S1) and the polymerizing step (step S3), and a catalyst may be added to the raw material or the decomposition product in at least one of the decomposition step (step S1) and the polymerizing step (step S3).

[0050] [Decomposition Step] Each step will be described in detail below. First, a raw material containing a first polyester resin and a second polyester resin, which is a polyester resin different from the first polyester resin, is heated to or above the melting point of the polyester resin with the lowest melting point among the polyester resins contained in the raw materials and stirred to obtain a decomposition product (decomposition step (step S1)).

[0051] In this embodiment, the first polyester resin is polylactic acid, and the second polyester resin is polycaprolactone. The raw materials may contain materials other than the first polyester resin and the second polyester resin. For example, the raw materials may further contain a polyester resin different from both the first polyester resin and the second polyester resin. Hereinafter, "the mass of the polyester resin contained in the raw materials" refers to the sum of the masses of all the polyester resins contained in the raw materials.

[0052] Each of the first polyester resin and the second polyester resin preferably has a weight average molecular weight of 10,000 or more, and more preferably 20,000 or more.

[0053] The proportion of the first polyester resin (polylactic acid) in the raw material is preferably 55% by mass or less. The lower limit of the proportion of the first polyester resin (polylactic acid) is not particularly limited, but is, for example, 40% by mass, and preferably 45% by mass.

[0054] The polyester resin raw material is preferably pretreated into a powder or pellet form. Alternatively, a pulverizer may be provided at the raw material inlet of the reactor so that the raw materials are pulverized simultaneously with the inlet. Two or more polyester resins may be added one by one, or may be mixed in advance and added all at once.

[0055] As described above, in the decomposition step (step S1), one or both of a polyhydric alcohol (a trihydric or higher alcohol) and a catalyst (polymerization catalyst) may be added.

[0056] The polyhydric alcohol is a trihydric or higher alcohol. The trihydric or higher alcohol is, for example, one or more selected from the group consisting of trimethylolpropane, glycerin, erythritol, pentaerythritol, glucose, acrylic polyol, polyester polyol, polyether polyol, epoxy polyol, polyolefin polyol, fluorine-containing polyol, and polyvinyl alcohol, and among these, trimethylolpropane and pentaerythritol are preferred. The polyhydric alcohol is more preferably a tetrahydric or higher alcohol.

[0057] The amount of polyhydric alcohol (trihydric or higher polyhydric alcohol; the same applies hereinafter in this paragraph) added is preferably 0.10 to 0.50 parts by mass (phr) per 100 parts by mass of polyester resin contained in the raw material. The lower limit of the amount of polyhydric alcohol added is preferably 0.20 parts by mass per 100 parts by mass of polyester resin contained in the raw material. The upper limit of the amount of polyhydric alcohol added is preferably 0.40 parts by mass per 100 parts by mass of polyester resin contained in the raw material.

[0058] It is also preferable to add a dihydric alcohol in addition to the polyhydric alcohol. Examples of dihydric alcohols include ethylene glycol, diethylene glycol, triethylene glycol, 1,3-butanediol, propylene glycol, polypropylene glycol, pentanediol, polyethylene glycol, and tetraethylene glycol. Adding a dihydric alcohol in addition to a polyhydric alcohol can suppress excessive crosslinking during the polymerization process, which occurs when only a polyhydric alcohol is added. As a result, molecular crystallization is suppressed, resulting in a polymer with a superior storage modulus. Among the dihydric alcohols, polyethylene glycol is particularly preferable. This has the effect of lowering the glass transition temperature of the polymer.

[0059] The dihydric alcohol can be added in an amount that does not impair the effects of the invention. The addition of the dihydric alcohol does not inhibit the polymerization reaction of the polyhydric alcohol with the first polyester resin and the second polyester resin, and can effectively suppress excessive crosslinking of the polymer.

[0060] The catalyst is, for example, one or more selected from the group consisting of Zn, Sn, Fe, Al, Ti, Zn oxide, Sn oxide, Fe oxide, Al oxide, Ti oxide, organometallic salts of Zn, organometallic salts of Sn, organometallic salts of Fe, organometallic salts of Al, and organometallic salts of Ti, and among these, Zn oxide and organometallic salts of Sn (for example, tin octylate) are particularly preferred.

[0061] The amount of catalyst added depends on the type of catalyst, but is preferably 0.01 to 10.0 parts by mass per 100 parts by mass of polyester resin contained in the raw material. The lower limit of the amount of catalyst added is preferably 0.1 parts by mass, more preferably 0.4 parts by mass, and even more preferably 0.8 parts by mass per 100 parts by mass of polyester resin contained in the raw material. The upper limit of the amount of catalyst added is preferably 5.0 parts by mass, more preferably 3.0 parts by mass per 100 parts by mass of polyester resin contained in the raw material.

[0062] The reactor may be any reactor capable of stirring the raw materials in a heated state. The reactor is preferably one capable of controlling the atmosphere inside the reactor. Specifically, the reactor is preferably structured so that the interior can be sealed except for the raw material inlet and outlet, gas inlet and outlet (vent), water inlet, etc. The reactor is preferably made of metal, glass, or ceramic, and is particularly preferably made of metal. The reactor may be a batch type reactor or a continuous type reactor.

[0063] In the decomposition step (step S1), the moisture content at decomposition, as expressed by the following formula, is preferably 0.015 or more (1.5% or more): Moisture content at decomposition = mass of moisture in reactor / (mass of polyester resin contained in raw material + mass of polyhydric alcohol + mass of catalyst) In the above formula, if no polyhydric alcohol is added, 0 is substituted for the "mass of polyhydric alcohol." Similarly, if no catalyst is added, 0 is substituted for the "mass of catalyst."

[0064] If the moisture content at decomposition is too low, the polyester resin may not be sufficiently decomposed, making it difficult to increase Fα and Fε. The lower limit of the moisture content at decomposition is more preferably 0.100 (10.0%), even more preferably 1.000 (100.0%), and even more preferably 3.000 (300.0%). On the other hand, if the moisture content at decomposition is too high, the amount of energy consumed for heating and drying increases. The upper limit of the moisture content at decomposition is preferably 10.000 (1000.0%), more preferably 5.00 (500.0%).

[0065] The heating temperature during the decomposition step (step S1) (hereinafter referred to as "decomposition temperature") is a temperature equal to or higher than the melting point of the polyester resin with the lowest melting point among the polyester resins contained in the raw material. The higher the decomposition temperature, the more easily the reaction proceeds. The lower limit of the decomposition temperature is preferably 150°C, more preferably 200°C, and even more preferably 230°C. The decomposition temperature may be equal to or higher than the melting point of the polyester resin with the highest melting point among the polyester resins contained in the raw material. On the other hand, if the decomposition temperature is too high, bonds other than ester bonds may be broken. The upper limit of the decomposition temperature is preferably 300°C, more preferably 280°C, and even more preferably 270°C.

[0066] The time for the decomposition step (step S1) (hereinafter referred to as "decomposition time") is not particularly limited, but is preferably 3 minutes or more. If the decomposition time is too short, the reaction may not proceed, and Fα and Fε may not be increased. The lower limit of the decomposition time is more preferably 30 minutes, even more preferably 60 minutes, and even more preferably 90 minutes. The upper limit of the decomposition time is preferably 8 hours, even more preferably 6 hours, and even more preferably 3 hours.

[0067] The shear rate of stirring in the decomposition step (step S1) is preferably 50 to 1,000,000 / sec. If the shear rate is too low, the reaction may not proceed, and Fα and Fε may not be increased. On the other hand, if the shear rate is too high, bonds other than ester bonds may be broken. The lower limit of the shear rate is more preferably 100 / sec, even more preferably 1,000 / sec, and even more preferably 10,000 / sec. The upper limit of the shear rate is more preferably 500,000 / sec, and even more preferably 300,000 / sec.

[0068] [Drying Step] The decomposition product obtained in the decomposition step (step S1) is dried (drying step (step S2)).

[0069] The drying step (step S2) may be performed in the reaction vessel used in the decomposition step (step S1), or may be performed after transferring to a different vessel, etc. When the drying step (step S1) is performed using the reaction vessel used in the decomposition step (step S1), for example, the vent port or the like of the reaction vessel may be operated in a high-temperature state after completion of the decomposition step (step S1) to discharge the moisture in the reaction vessel as steam, and the reaction vessel may be held as is for a predetermined time to dry the decomposition product.

[0070] In the drying step (step S2), it is preferable to dry the product so that the moisture content after drying, expressed by the following formula, is 0.0015 or less (0.15% or less): Moisture content after drying = Mass of moisture contained in decomposition product / (Mass of polyester resin contained in raw material + Mass of polyhydric alcohol + Mass of catalyst) In the above formula, if no polyhydric alcohol is added, 0 is substituted for the "mass of polyhydric alcohol." Similarly, if no catalyst is added, 0 is substituted for the "mass of catalyst."

[0071] If the moisture content after drying is too high, it may be impossible to increase the molecular weight in the polymerizing step. The upper limit of the moisture content after drying is more preferably 0.0013 (0.13%), and even more preferably 0.0012 (0.12%). The upper limit of the moisture content after drying is not particularly limited, but from the viewpoint of efficiency, it is preferably 0.0001 (0.01%), more preferably 0.0005 (0.05%), and even more preferably 0.0008 (0.08%).

[0072] The heating temperature in the drying step (step S2) is preferably 80 to 140° C. If the heating temperature is too low, a long drying time is required to reduce the moisture content. On the other hand, if the drying temperature is too high, the decomposition products will volatilize, resulting in a low yield.

[0073] The time for the drying step (step S2) is not particularly limited, but is preferably 30 to 160 minutes.

[0074] [Polymerization Step] After the drying step (step S2), the decomposition product is heated and stirred in a reduced pressure environment (polymerization step (step S3)).

[0075] The polymerizing step (step S3) may be carried out in the reaction vessel used in the decomposition step (step S1), or may be carried out after transferring the reaction mixture to a different vessel.

[0076] If a polyhydric alcohol and a catalyst are not added to the raw material in the decomposition step (step S1), a polyhydric alcohol and a catalyst are added to the decomposition product in the polymerization step (step S3). As described above, in the production method of FIG. 3, a trihydric or higher polyhydric alcohol may be added to the raw material or the decomposition product in at least one of the decomposition step (step S1) and the polymerization step (step S3), and a catalyst may be added to the raw material or the decomposition product in at least one of the decomposition step (step S1) and the polymerization step (step S3). The preferred amount of addition, etc., is the same as when adding in the decomposition step (step S1).

[0077] The heating temperature (hereinafter referred to as "polymerization temperature") in the polymerizing step (step S3) is preferably 160 to 250°C. If the polymerization temperature is too high, the decomposition products may volatilize, resulting in a low yield. Furthermore, at even higher temperatures, the polymer may undergo thermal decomposition. On the other hand, if the polymerization temperature is too low, the molecular weight of the polymer may not be sufficiently increased. The lower limit of the polymerization temperature is more preferably 210°C, and even more preferably 220°C. The upper limit of the polymerization temperature is more preferably 240°C.

[0078] The time for the polymerizing step (step S3) (hereinafter referred to as "polymerization time") is preferably 30 to 480 minutes. If the polymerization time is too short, the molecular weight of the polymer may not be sufficiently large. On the other hand, if the polymerization time is too long, the polymer may gel (foam). Furthermore, if the polymerization time is too long, the molecular weight may become too high. If the molecular weight becomes too high, the glass transition temperature and storage modulus may become excessively high. The lower limit of the polymerization time is more preferably 60 minutes, and even more preferably 90 minutes. The upper limit of the polymerization time is more preferably 360 minutes, and even more preferably 300 minutes.

[0079] The shear rate of stirring in the polymerizing step (step S3) is preferably 50 to 1,000,000 / sec. If the shear rate is too low, the transesterification reaction may not proceed, and Fα and Fε may not be increased. On the other hand, if the shear rate is too high, bonds other than ester bonds may be broken. The lower limit of the shear rate is more preferably 100 / sec, even more preferably 1,000 / sec, and even more preferably 10,000 / sec. The upper limit of the shear rate is more preferably 500,000 / sec, and even more preferably 300,000 / sec.

[0080] The degree of vacuum in the polymerizing step (step S3) is preferably 1500 Pa or less, more preferably 1200 Pa or less, and even more preferably 1000 Pa or less.

[0081] Through the above steps, a polymer (base polymer for PSA) having a branched structure containing lactic acid units, caprolactone units, and polyhydric alcohol units is produced.

[0082] [Effects of this embodiment, etc.] The adhesive base polymer according to one embodiment of the present invention has been described above. The adhesive base polymer according to this embodiment is a polymer having a branched structure containing lactic acid units, caprolactone units, and trivalent or higher polyhydric alcohol units, in which the proportion of lactic acid units is 20 to 50 mol %, the glass transition temperature is -15°C or lower, and at least one of Fα and Fε is 0.35 or higher. The adhesive base polymer according to this embodiment has properties suitable for adhesives.

[0083] The adhesive base polymer according to the present embodiment can be used, for example, as a material for an adhesive constituting the adhesive layer of an adhesive tape or an adhesive film. The adhesive can be prepared, for example, by adding a dilution solvent, a crosslinking agent (e.g., HDI), and other additives (e.g., tackifier) ​​to the adhesive base polymer according to the present embodiment as needed. The adhesive tape and adhesive film can be produced, for example, by applying the adhesive to a sheet-like or film-like substrate and drying it.

[0084] Products manufactured according to the present invention can realize efficient use of resources and energy, utilization of renewable resources, and reduction of environmental burden. By providing this invention to society, it will be possible to contribute to the achievement of Goal 12 (Responsible Consumption and Production) of the 17 Sustainable Development Goals (SDGs) established by the United Nations.

[0085] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

[0086] The polyester resin was decomposed, dried, and polymerized under the conditions shown in Tables 1 and 2 to produce a polymer.

[0087]

[0088]

[0089] In Tables 1 and 2, "PLA" represents polylactic acid having a number-average molecular weight of 78,000 and a weight-average molecular weight of 120,000, and "PCL" represents polycaprolactone having a number-average molecular weight of 15,000 and a weight-average molecular weight of 25,000. The melting points of polylactic acid and polycaprolactone were approximately 170°C and 60°C, respectively.

[0090] In Tables 1 and 2, "A1" represents pentaerythritol, and "A2" represents trimethylolpropane. In Tables 1 and 2, "C1" represents stannous octoate, and "C2" represents ZnO.

[0091] The various physical properties of the produced polymer were measured.

[0092] The ratio (mol%) of lactic acid units, caprolactone units, and polyhydric alcohol units was measured by proton nuclear magnetic resonance ( １ The product was analyzed by H-NMR. １ H-NMR spectra were measured using a nuclear magnetic resonance (NMR) ECA 500 MHz manufactured by JEOL, a nuclear magnetic resonance AVANCE III HD 400 MHz manufactured by Bruker, and a nuclear magnetic resonance AVANCE NEO 700 MHz manufactured by Bruker, by dissolving the PSA base polymer in deuterated chloroform at 10 mg / ml. TMS (tetramethylsilane) was used as the chemical shift standard.

[0093] The number average molecular weight Mn and the weight average molecular weight Mw were measured by dissolving the produced polymer in tetrahydrofuran at 0.5 wt % and subjecting it to gel permeation chromatography (GPC) using polystyrene as a standard substance.

[0094] The glass transition temperature Tg and heat of fusion were measured by differential scanning calorimetry (DSC). Using DSC, the temperature was first raised from -80°C to 200°C at a heating rate of 10°C / min to erase the thermal history, and then the temperature was lowered to -80°C at a heating rate of 10°C / min, and again measured at a heating rate of 10°C / min. The heat of fusion was determined from the area of ​​the endothermic peak that appeared in DTA during the second heating. The glass transition temperature Tg was taken as the temperature indicating the inflection point of the transition region that appeared in DTA during the second heating.

[0095] １ The presence or absence of a copolymer was confirmed from the H-NMR spectrum, and Fα and Fε were determined.

[0096] The storage modulus at 20°C was measured as follows: Using an Anton Paar MCR301 viscoelasticity tester, a test sample having a thickness of 0.5 mm was measured using parallel plates having a diameter of 8 mm, and the storage modulus at 20°C was measured at a frequency of 1 Hz and a strain of 1%.

[0097] For some samples, adhesive tapes were prepared from the polymer (adhesive base polymer) and the peel strength (adhesive strength) was measured. Specifically, 100 parts by weight of the prepared polymer was first dissolved in 100 parts by weight of ethyl acetate, and then 1 part by weight of isocyanate was added to prepare an adhesive. This adhesive was applied to a polyethylene terephthalate (PET) film and heated at 100°C for 3 minutes to dry the solvent, and then held at 40°C for 72 hours to crosslink and harden the adhesive layer, producing an adhesive tape.

[0098] ​The prepared adhesive tape was cut into strips measuring 150 mm long and 25 mm wide to prepare measurement samples. The MD direction (direction of adhesive application) of the adhesive tape was the length direction of the measurement sample, and the direction perpendicular to this was the width direction of the measurement sample. A stainless steel plate (SUS304BA plate) was prepared as the adherend. Under an environment of 23°C temperature and 50% humidity, the release liner was peeled from the adhesive tape, and the exposed adhesive layer was placed on one side of the adherend. A 2 kg roller was rolled back and forth once to apply a load and adhere the tape, and the adherend was left for 20 minutes. The length of the adhered portion was 80 mm. Then, using a tensile tester, the adhesive tape was peeled from the adherend at a peel speed of 300 mm / min and a peel angle of 180° using the 180° peel method in accordance with JIS Z0237:2009, and the adhesive strength (unit: N / 25 mm) was measured.

[0099] The results are shown in Tables 3 and 4.

[0100]

[0101]

[0102] In Tables 3 and 4, LA represents a lactic acid unit, CL represents a caprolactone unit, A1 represents a polyhydric alcohol unit derived from pentaerythritol, and A2 represents a polyhydric alcohol unit derived from trimethylolpropane.

[0103] As shown in Table 3, the polymers of Examples 1 to 3 had a lactic acid unit ratio of 20 to 50 mol %, a glass transition temperature Tg of −15° C. or lower, and Fα and Fε of 35% or higher. These polymers had a storage modulus at 20° C. of 0.10×10 ５ ~1.5 x 10 ５ and had properties suitable for a base polymer for a pressure-sensitive adhesive.

[0104] The polymer of Comparative Example 1 had a high storage modulus. This is thought to be because the proportion of lactic acid units was too low or because Fα and Fε were small. The low proportion of lactic acid units is thought to be due to the low proportion of polylactic acid in the raw material. It is thought that the low proportion of lactic acid units reduced the PLA-PCL bonds, leaving crystallized portions, which increased the storage modulus.

[0105] The polymer of Comparative Example 2 had a high storage modulus. It also had a high glass transition temperature (Tg). This is thought to be due to the fact that the proportion of lactic acid units was too high. The high proportion of lactic acid units is thought to be due to the high proportion of polylactic acid in the raw material. By increasing the proportion of lactic acid units (i.e., decreasing the proportion of caprolactone units), even if the caprolactone units are finely dispersed, the lactic acid units tend to be linked together in long chains. Therefore, it is thought that crystallized portions remained, resulting in a high storage modulus.

[0106] The polymer of Comparative Example 3 gelled (foamed) during the polymerization, which is believed to be due to the addition of too much polyhydric alcohol.

[0107] The polymers of Comparative Examples 4 and 5 had large storage moduli, even though the ratio of lactic acid units to caprolactone units, molecular weight, etc. were similar to those of Examples 1 to 3. This is thought to be because Fα and Fε were too small. The small Fα and Fε are thought to be due to the low water content at the time of decomposition or the short polymerization time.

[0108] The polymer of Comparative Example 6 had a small storage modulus, which is thought to be because the polymer of Comparative Example 6 did not contain a polyhydric alcohol unit.

[0109] The polymer of Comparative Example 7 had a high storage modulus and a high glass transition temperature Tg. This is thought to be because the polymerization time was too long and the molecular weight was too large.

[0110] The reference examples in Table 3 are based on Figure 2B in Non-Patent Document 2 (Mengyuan Zhang et. al., "Synthesis of Poly(l-lactide-co-ε-caprolactone) Copolymer: Structure, Toughness, and Elasticity", Polymers 2021, 13, 1270, https: / / doi.org / 10.3390 / polym13081270). １ Fα and Fε were determined from the data of “PLCL (1:1-18h)” in the H-NMR spectrum.

[0111] In Non-Patent Document 2, these copolymers are prepared by ring-opening polymerization of L-lactide and ε-caprolactone. "PLCL (1:1-18h)" represents data obtained by adding L-lactide and ε-caprolactone in a molar ratio of 1:1 and polymerizing for 18 hours. Non-Patent Document 2 also lists data for polymerization times of 24 and 30 hours, but the Fα and Fε values ​​for the 18-hour polymerization time were greatest (Fα for the 24-hour data was 25.2%, and Fα for the 36-hour data was 23.9%). Non-Patent Document 2 also includes data for copolymers produced using L-lactide and ε-caprolactone in molar ratios of 2:1 and 3:1, but the proportions of lactic acid units in these copolymers were even higher than those in the Reference Example.

[0112] In the Reference Example, Fα and Fε were less than 35%, even though the proportion of lactic acid units was higher than in Examples 1 to 3. This shows that it is difficult to increase Fα and Fε using the conventional method of producing a copolymer by ring-opening polymerization of L-lactide and ε-caprolactone.

[0113] Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments, and various modifications are possible within the scope of the invention.

Claims

1. A base polymer for pressure-sensitive adhesives, which is a polymer having a branched structure containing lactic acid units, caprolactone units, and trihydric or higher polyhydric alcohol units, the proportion of said lactic acid units being 20 to 50 mol%, the glass transition temperature being -15°C or lower, and at least one of Fα and Fε, represented by the following formula, being 0.35 or higher. Fα=Iα ＊ / (Iα+Iα ＊ ) Fε = Iε ＊ / (Iε + Iε ＊ ) where Iα, Iα ＊ , Iε and Iε ＊ The base polymer for pressure sensitive adhesives １ A value obtained from a H-NMR spectrum, Iα is an integral intensity of a signal derived from a proton of a methylene group that is bonded to a carbonyl carbon of an ester bond among methylene groups contained in a caprolactone unit and is bonded to a caprolactone unit via the ester bond, and Iα ＊ is the integral intensity of a signal derived from a proton of a methylene group, which is a methylene group bonded to the carbonyl carbon of an ester bond among methylene groups contained in a caprolactone unit and is bonded to a lactic acid unit via the ester bond, Iε is the integral intensity of a signal derived from a proton of a methylene group, which is a methylene group bonded to the oxygen of an ester bond among methylene groups contained in a caprolactone unit and is bonded to a caprolactone unit via the ester bond, Iε ＊ is the integrated intensity of a signal derived from a proton of a methylene group that is bonded to an oxygen atom of an ester bond among methylene groups contained in a caprolactone unit and is bonded to a lactic acid unit via the ester bond.

2. The base polymer for pressure-sensitive adhesives according to claim 1, wherein both Fα and Fε are 0.35 or more.

3. The base polymer for pressure-sensitive adhesives according to claim 1, having a number average molecular weight Mn of 10,000 to 30,000.

4. The base polymer for pressure-sensitive adhesives according to claim 1, having a weight average molecular weight Mw of 40,000 to 100,000.

5. The base polymer for pressure-sensitive adhesives according to claim 1, having a number average molecular weight Mn of 10,000 to 30,000 and a weight average molecular weight Mw of 40,000 to 100,000.

6. The base polymer for pressure-sensitive adhesives according to claim 1, having a dispersity Mw / Mn of 1.0 to 10.

0.

7. The base polymer for pressure-sensitive adhesives according to claim 6, having a number average molecular weight Mn of 10,000 to 30,000.

8. The base polymer for pressure-sensitive adhesives according to claim 6, having a weight average molecular weight Mw of 40,000 to 100,000.

9. The base polymer for pressure-sensitive adhesives according to claim 6, having a number average molecular weight Mn of 10,000 to 30,000 and a weight average molecular weight Mw of 40,000 to 100,000.

10. The base polymer for pressure-sensitive adhesives according to claim 1, wherein the proportion of said polyhydric alcohol units is 0.55 mol % or less.

11. The base polymer for pressure-sensitive adhesives according to claim 1, having a number average molecular weight Mn of 10,000 to 30,000, a weight average molecular weight Mw of 40,000 to 100,000, and a proportion of the polyhydric alcohol units of 0.55 mol % or less.

12. The base polymer for pressure-sensitive adhesives according to claim 1, wherein the trihydric or higher polyhydric alcohol unit is a structural unit derived from at least one of trimethylolpropane and pentaerythritol.

13. The storage modulus at 20°C is 0.10 x 10 ５ ~1.5 x 10 ５ The base polymer for pressure-sensitive adhesives according to claim 1 , 14. A pressure-sensitive adhesive comprising the pressure-sensitive adhesive base polymer according to any one of claims 1 to 13.

15. An adhesive tape using the adhesive according to claim 14.

16. An adhesive film using the adhesive according to claim 14.

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