JP7780247B2 - Polyester-based pressure-sensitive adhesive composition, pressure-sensitive adhesive, pressure-sensitive adhesive sheet, and optical member with pressure-sensitive adhesive layer - Google Patents

Description

The present invention relates to a polyester-based pressure-sensitive adhesive composition, a pressure-sensitive adhesive, a pressure-sensitive adhesive sheet, and an optical component with a pressure-sensitive adhesive layer. More specifically, the present invention relates to a polyester-based pressure-sensitive adhesive composition, a pressure-sensitive adhesive, a pressure-sensitive adhesive sheet, and an optical component with a pressure-sensitive adhesive layer that exhibits excellent adhesive strength and substrate adhesion, minimal yellowing, and excellent ultraviolet absorption.

Image display devices such as plasma displays (PDPs), liquid crystal displays (LCDs), organic light-emitting diode displays (OLEDs), electrophoretic displays (EPDs), and interferometric modulation displays (IMODs) are made up of a variety of components, and adhesives or adhesive sheets are used to bond and integrate these components. For example, touch panel displays use components for image display devices such as surface protection panels, touch panels, and image display panels, and adhesives or adhesive sheets are used to laminate these components.

For example, Patent Document 1 proposes a transparent adhesive sheet for bonding a surface protective layer or touch panel in an image display device to the display surface of an image display unit, or a transparent adhesive sheet for bonding a surface protective layer to a touch panel, which comprises (A) a (meth)acrylic acid alkyl ester having 4 to 18 carbon atoms in the alkyl group, (B) a polar monomer having a homopolymer glass transition temperature (Tg) of 50°C or higher, and (C) a (meth)acrylic acid ester represented by a specific formula or a copolymer of monomers containing a hydrophilic monomer having a homopolymer glass transition temperature (Tg) of 10°C or lower, and which has a tan δ of 0.13 or higher at 140°C and 1.0 Hz and a storage modulus of 8.9 × 10 ⁴ Pa or lower at 25°C and 1.0 Hz.

JP 2010-163591 A

However, the technology disclosed in Patent Document 1 and the adhesives that have been studied to date are acrylic adhesives containing acrylic resins, and because these acrylic adhesives contain soft acrylic resins, improvements in impact resistance are required. However, designing the acrylic resin to be hard in order to impart impact resistance results in reduced adhesive strength and poor adhesion to substrates.

In addition, in recent years, with the trend toward lighter and thinner displays, new technologies have been proposed, including the in-cell method, in which touch panel electrodes are integrated into LCD pixels, and the on-cell method, in which electrodes are directly attached to the glass substrate or protective panel of an LCD module to provide touch panel functionality. Other new configurations, also known as "touch-on-lens methods," incorporate touch panel functionality, previously achieved through lamination, directly into the LCD module. However, in the in-cell, on-cell, and touch-on-lens configurations described above, a single adhesive is used to attach the surface protective panel to the LCD module. This means that a single adhesive sheet or adhesive must provide the functionality required for both the surface protective panel and the LCD module, creating a demand for greater functionality than ever before. In particular, display module manufacturers are expected to incorporate optical functions, such as polarizing film and retardation film, directly into the LCD module and other components, in addition to touch panels, thereby minimizing the number of components. As functional layers, such as these functional films, become simplified and module configurations change, adhesive sheets must also have UV protection to protect these functional layers.

Under these circumstances, the present invention aims to provide a polyester-based pressure-sensitive adhesive composition that uses a polyester-based resin as a pressure-sensitive adhesive instead of an acrylic-based resin, and that has excellent adhesive strength and substrate adhesion, as well as minimal yellowing and excellent UV absorption. Furthermore, the present invention also aims to provide a pressure-sensitive adhesive, a pressure-sensitive adhesive sheet, and an optical component with a pressure-sensitive adhesive layer.

However, in light of these circumstances, the present inventors conducted extensive research and discovered that by adding a specific UV absorber to a polyester resin-containing pressure-sensitive adhesive composition, it is possible to obtain a polyester-based pressure-sensitive adhesive composition that exhibits excellent adhesive strength and substrate adhesion, as well as minimal yellowing and excellent UV absorption capabilities, and thus completed the present invention.

That is, a first aspect of the present invention is a polyester-based pressure-sensitive adhesive composition containing a polyester-based resin [I] containing structural units derived from a polycarboxylic acid (A) and structural units derived from a polyol (B), and an ultraviolet absorber [II], wherein the ultraviolet absorber [II] is at least one selected from the group consisting of a triazine-based compound, a triazole-based compound, and a cyanoacrylate-based compound.

The second aspect of the present invention is a pressure-sensitive adhesive obtained by crosslinking the polyester-based pressure-sensitive adhesive composition. The third aspect is a pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer containing the pressure-sensitive adhesive. The fourth aspect is an optical component with a pressure-sensitive adhesive layer, having a pressure-sensitive adhesive layer and an optical component, wherein the pressure-sensitive adhesive layer contains the pressure-sensitive adhesive.

In the present invention, it is not the case that any UV absorber can be incorporated into the polyester resin, but rather it has been discovered that a limited number of specific UV absorbers work well in combination with polyester resins. While it is common to incorporate a benzophenone-based UV absorber due to its excellent ability to absorb UV light in the long wavelength range, by incorporating a UV absorber that is at least one selected from triazine-based compounds, triazole-based compounds, and cyanoacrylate-based compounds rather than a benzophenone-based compound, the resin unexpectedly achieves excellent UV absorption in the long wavelength range without impairing adhesive strength, and also exhibits excellent resistance to yellowing, thereby achieving the objectives of the present invention.

The polyester-based pressure-sensitive adhesive composition of the present invention contains a polyester-based resin [I] containing structural units derived from a polycarboxylic acid (A) and structural units derived from a polyol (B), and an ultraviolet absorber [II], where the ultraviolet absorber [II] is at least one selected from triazine-based compounds, triazole-based compounds, and cyanoacrylate-based compounds. Therefore, the composition exhibits excellent adhesive strength and substrate adhesion, minimal yellowing, and excellent ultraviolet absorption capabilities, making it particularly useful as a pressure-sensitive adhesive for optical components.

The configuration of the present invention will be described in detail below, but these are merely examples of preferred embodiments.
In the present invention, the term "carboxylic acids" includes not only carboxylic acids but also carboxylic acid derivatives such as carboxylic acid salts, carboxylic acid anhydrides, carboxylic acid halides, and carboxylic acid esters.

The polyester-based pressure-sensitive adhesive composition of the present invention (hereinafter sometimes referred to as "pressure-sensitive adhesive composition") is characterized by containing a polyester-based resin [I] and a specific ultraviolet absorber [II]. The pressure-sensitive adhesive composition of the present invention contains the polyester-based resin [I] and the specific ultraviolet absorber [II] as essential components, and preferably contains at least one of a hydrolysis inhibitor [III] and a crosslinking agent [IV], and more preferably contains both the hydrolysis inhibitor [III] and the crosslinking agent [IV].
Each component constituting the pressure-sensitive adhesive composition of the present invention will be explained below in order.

<Polyester-based resin [I]>
The polyester resin [I] is usually obtained by copolymerizing copolymerization components containing a polycarboxylic acid (A) and a polyol (B) as constituent raw materials, and the polyester resin [I] has, as its resin composition, structural units derived from the polycarboxylic acid (A) and structural units derived from the polyol (B).

[Polycarboxylic acids (A)]
Examples of the polycarboxylic acids (A) used as constituent raw materials for the polyester resin [I] include dicarboxylic acids and tricarboxylic or higher polycarboxylic acids, and dicarboxylic acids are preferably used since they can stably produce the polyester resin [I].

Examples of the dicarboxylic acids include aliphatic dicarboxylic acids such as malonic acids, dimethylmalonic acids, succinic acids, glutaric acids, adipic acids, trimethyladipic acids, pimelic acids, 2,2-dimethylglutaric acids, azelaic acids, sebacic acids, fumaric acids, maleic acids, itaconic acids, thiodipropionic acids, diglycolic acids, and 1,9-nonanedicarboxylic acids;
aromatic dicarboxylic acids such as phthalic acids, terephthalic acids, isophthalic acids, benzylmalonic acids, diphenic acids, 4,4'-oxydibenzoic acids, and naphthalenedicarboxylic acids such as 1,8-naphthalenedicarboxylic acids, 2,3-naphthalenedicarboxylic acids, and 2,7-naphthalenedicarboxylic acids;
alicyclic dicarboxylic acids such as 1,3-cyclopentanedicarboxylic acids, 1,2-cyclohexanedicarboxylic acids, 1,3-cyclopentanedicarboxylic acids, 1,4-cyclohexanedicarboxylic acids, 2,5-norbornanedicarboxylic acids, and adamantanedicarboxylic acids;
etc.
Examples of the trivalent or higher polyvalent carboxylic acids include trimellitic acids, pyromellitic acids, adamantanetricarboxylic acids, and trimesic acids.
These polycarboxylic acids (A) can be used alone or in combination of two or more kinds.

Among the polycarboxylic acids (A), aromatic polycarboxylic acids, particularly asymmetric aromatic dicarboxylic acids (A-1), are preferably used to reduce the crystallinity of the polyester resin [I]. Examples of asymmetric aromatic dicarboxylic acids (A-1) include phthalic acids, isophthalic acids, 1,8-naphthalenedicarboxylic acids, 2,3-naphthalenedicarboxylic acids, and 2,7-naphthalenedicarboxylic acids. Of these, isophthalic acids are particularly preferred in terms of reactivity.

The content of such aromatic polycarboxylic acids, particularly asymmetric aromatic dicarboxylic acids (A-1), is preferably 1 to 90 mol%, particularly preferably 5 to 80 mol%, even more preferably 10 to 70 mol%, especially preferably 15 to 60 mol%, and even more preferably 20 to 50 mol%, based on the total polycarboxylic acids (A). If the content is too low, the adhesive strength at high temperatures tends to decrease, the resin tends to crystallize, and sufficient adhesive performance tends to be lost. If the content is too high, the initial adhesive strength (tack) tends to decrease.

In addition, in the present invention, from the viewpoint of improving initial adhesive strength (tack), it is preferable that the polycarboxylic acid (A) contains an aliphatic dicarboxylic acid (A-2) having 4 or more carbon atoms (including the carbon atoms in the carboxy group), and it is particularly preferable to contain an aliphatic dicarboxylic acid having 6 to 12 carbon atoms (including the carbon atoms in the carboxy group), such as adipic acid, azelaic acid, or sebacic acid.

The content of such aliphatic dicarboxylic acids (A-2) having 4 or more carbon atoms is preferably 5 to 100 mol % relative to the total polycarboxylic acids (A). It is particularly preferably 20 to 95 mol %, particularly preferably 30 to 90 mol %, even more preferably 40 to 85 mol %, and especially preferably 50 to 80 mol %. If the content is too low, the glass transition temperature of the polyester resin [I] will be too high, and sufficient adhesive strength will tend to be insufficient. However, if the content is too high, adhesive strength at high temperatures will tend to decrease, or the resin will crystallize, making it difficult to achieve sufficient adhesive performance.

In the present invention, from the viewpoint of adhesive properties, it is also preferable to use asymmetric aromatic dicarboxylic acids (A-1) and aliphatic dicarboxylic acids (A-2) having 4 or more carbon atoms in combination as the polycarboxylic acids (A). In this case, the molar ratio of the asymmetric aromatic dicarboxylic acids (A-1) to the aliphatic dicarboxylic acids (A-2) having 4 or more carbon atoms is preferably (A-1)/(A-2) = 1/99 to 90/10, particularly preferably 10/90 to 70/30, and even more preferably 20/80 to 60/40.

In addition, in the present invention, trivalent or higher polycarboxylic acids (A-3) can also be used to increase the number of branching points in the polyester resin [I]. Among these, trimellitic acids are preferred because they are relatively less likely to gel during production.

The content of such trivalent or higher polycarboxylic acids (A-3) is preferably 10 mol % or less, and particularly preferably 0.1 to 5 mol %, based on the total amount of polycarboxylic acids (A), in order to enhance the cohesive strength of the resulting adhesive. If the content is too high, gelation may easily occur during the production of the polyester resin [I].

[Polyol (B)]
The polyol (B) used as a constituent material of the polyester resin [I] includes dihydric alcohols and trihydric or higher polyols.

Examples of the dihydric alcohol include aliphatic diols such as ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, dipropylene glycol, 1,3-propanediol, 2,4-dimethyl-2-ethylhexane-1,3-diol, 2-methyl-1,3-propanediol, 2,2-dimethyl-1,3-propanediol (neopentyl glycol), 2-ethyl-2-butyl-1,3-propanediol, 2-ethyl-2-isobutyl-1,3-propanediol, 1,3-butanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 3-methyl-1,5-pentanediol, and 2,2,4-trimethyl-1,6-hexanediol;
Alicyclic diols such as 1,2-cyclohexanedimethanol, 1,3-cyclohexanedimethanol, 1,4-cyclohexanedimethanol, spiroglycol, tricyclodecane dimethanol, adamantanediol, and 2,2,4,4-tetramethyl-1,3-cyclobutanediol;
Examples of the aromatic diol include 4,4'-thiodiphenol, 4,4'-methylenediphenol, 4,4'-dihydroxybiphenyl, o-, m-, and p-dihydroxybenzene, 2,5-naphthalenediol, p-xylenediol, and ethylene oxide adducts and propylene oxide adducts thereof.
Further examples include fatty acid esters derived from castor oil, dimer diols derived from oleic acid, erucic acid, and the like, and glycerol monostearate.
Examples of the trihydric or higher polyols include pentaerythritol, dipentaerythritol, tripentaerythritol, glycerin, trimethylolpropane, trimethylolethane, 1,2,4-butanetriol, 1,2,5-pentanetriol, 1,2,6-hexanetriol, 1,3,6-hexanetriol, and adamantanetriol.
The above polyols (B) can be used alone or in combination of two or more kinds.

In the present invention, in order to lower the glass transition temperature (Tg) of the polyester resin [I] and improve its initial adhesive strength, it is preferable for the polyol (B) to contain a linear aliphatic diol (B-1), more preferably a linear aliphatic diol having 2 to 18 carbon atoms, and particularly preferably ethylene glycol, 1,3-propanediol, or 1,4-butanediol.

The content of the linear aliphatic diol (B-1) relative to the total polyol (B) is preferably 1 to 100 mol%, more preferably 2 to 80 mol%, particularly preferably 3 to 70 mol%, even more preferably 4 to 60 mol%, and especially preferably 5 to 50 mol%. If the content is too low, it tends to be difficult to achieve stable resin formation.

Furthermore, among the polyols (B), it is preferable to contain a diol (B-2) having a hydrocarbon group on the side chain, as this can disrupt crystallinity. Examples of such diols (B-2) having a hydrocarbon group on the side chain include aliphatic diols with a branched structure, such as dipropylene glycol, 2,4-dimethyl-2-ethylhexane-1,3-diol, 2-methyl-1,3-propanediol, 2,2-dimethyl-1,3-propanediol (neopentyl glycol), 2-methyl-2-ethyl-1,3-propanediol, 2-ethyl-2-butyl-1,3-propanediol, 2-ethyl-2-isobutyl-1,3-propanediol, 1,3-butanediol, 3-methyl-1,5-pentanediol, 2,2,4-trimethyl-1,6-hexanediol, and dimer diol.

The content of the diol (B-2) having a hydrocarbon group in the side chain is preferably 5 to 100 mol % of the total polyol (B), particularly 20 to 90 mol %, and even more preferably 40 to 80 mol %. If the content is too low, the resin tends to crystallize, making it difficult to achieve sufficient adhesive performance. Furthermore, if the content is too high, the reaction time in the production of polyester resin [I] tends to be longer.

Among the polyols (B), it is preferable to contain a diol (B-3) having an alicyclic structure, since this can disrupt crystallinity and increase the elastic modulus. Examples of the diol (B-3) having an alicyclic structure include alicyclic diols such as 1,2-cyclohexanedimethanol, 1,3-cyclohexanedimethanol, 1,4-cyclohexanedimethanol, spiroglycol, tricyclodecanedimethanol, adamantanediol, and 2,2,4,4-tetramethyl-1,3-cyclobutanediol.
Among these, 1,4-cyclohexanedimethanol is preferred from the viewpoint of reactivity.

The content of the diol (B-3) having an alicyclic structure is preferably 20 to 100 mol % of the total polyol (B), particularly 40 to 98 mol %, and even more preferably 60 to 95 mol %. If the content is too low, the resin tends to crystallize, making it difficult to achieve sufficient adhesive performance, and the elastic modulus tends to decrease, resulting in reduced impact resistance. Furthermore, if the content is too high, the reaction time in the production of polyester resin [I] tends to be longer.

Furthermore, in the present invention, it is preferable to use a trivalent or higher polyol (B-4) as the polyol (B) in order to form reaction sites with the crosslinking agent [IV] described below in the polyester resin [I] and increase cohesive strength. Among these, it is preferable to use trimethylolpropane, trimethylolethane, glycerin, pentaerythritol, 1,2,4-butanetriol, 1,2,5-pentanetriol, or 1,2,6-hexanetriol. Of these, it is particularly preferable to use trimethylolpropane because it is relatively less likely to form gels.

The content of such trihydric or higher polyol (B-4) is preferably 20 mol% or less, more preferably 0.1 to 10 mol%, and particularly preferably 0.5 to 5 mol%, based on the total content of polyol (B). If the content of such trihydric or higher polyol is too high, it tends to make it difficult to produce polyester resin [I].

The polyester resin [I] used in the present invention is produced by appropriately selecting the above-mentioned polycarboxylic acid (A) and polyol (B) and subjecting them to a polycondensation reaction in the presence of a catalyst using a known method.

The blending ratio of the polycarboxylic acids (A) to the polyol (B) is preferably 1 to 2 equivalents of polyol (B) per equivalent of polycarboxylic acids (A), and particularly preferably 1.1 to 1.7 equivalents. If the blending ratio of polyol (B) is too low, the acid value tends to be high, making it difficult to achieve a high molecular weight, while if it is too high, the yield tends to decrease.

During the polycondensation reaction, an esterification reaction is carried out first, followed by the polycondensation reaction.

In such esterification reactions, a catalyst is typically used. Specific examples include titanium-based catalysts such as tetraisopropyl titanate and tetrabutyl titanate, antimony-based catalysts such as antimony trioxide, germanium-based catalysts such as germanium dioxide, and catalysts such as zinc acetate, manganese acetate, and dibutyltin oxide. One or more of these may be used. Of these, antimony trioxide, tetrabutyl titanate, germanium dioxide, and zinc acetate are preferred due to their balance of high catalytic activity and color, with germanium dioxide being particularly preferred.

The amount of the catalyst blended is preferably 1 to 10,000 ppm by weight of all copolymerization components, particularly preferably 10 to 5,000 ppm, and even more preferably 20 to 3,000 ppm. If the blending amount is too small, the polymerization reaction tends to proceed insufficiently, while if the blending amount is too large, there is no benefit such as shortening the reaction time, and side reactions tend to occur more easily.

The reaction temperature during the esterification reaction is preferably 200 to 300°C, particularly preferably 210 to 280°C, and even more preferably 220 to 260°C. If the reaction temperature is too low, the reaction tends not to proceed sufficiently, while if it is too high, side reactions such as decomposition tend to occur easily. Furthermore, the pressure during the reaction is usually atmospheric pressure.

After the esterification reaction, a polycondensation reaction is carried out.
As reaction conditions for the polycondensation reaction, it is preferable to further compound the same amount of the same catalyst as used in the above esterification reaction, set the reaction temperature preferably to 220 to 280° C., particularly preferably 230 to 270° C., and gradually reduce the pressure of the reaction system to finally carry out the reaction at 5 hPa or less. If the reaction temperature is too low, the reaction tends not to proceed sufficiently, and if it is too high, side reactions such as decomposition tend to occur easily.

Thus, the polyester resin [I] used in the present invention is obtained.

The polyester resin [I] typically contains structural units derived from polycarboxylic acids (A) and polyols (B). However, when structural units derived from aromatic polycarboxylic acids, particularly asymmetric aromatic dicarboxylic acids (A-1), are included as structural units derived from polycarboxylic acids (A), the structural units derived from asymmetric aromatic dicarboxylic acids (A-1) preferably account for 1 to 90 mol %, particularly preferably 5 to 80 mol %, more preferably 10 to 70 mol %, even more preferably 15 to 60 mol %, and especially preferably 20 to 50 mol % of the structural units derived from polycarboxylic acids (A). If this content ratio is too low, the adhesive strength at high temperatures may decrease or the resin may crystallize, resulting in insufficient adhesive performance. If this content ratio is too high, the initial adhesive strength (tack) may decrease.

When structural units derived from aliphatic dicarboxylic acids (A-2) having 4 or more carbon atoms are included as structural units derived from polycarboxylic acids (A), the structural units derived from aliphatic dicarboxylic acids (A-2) having 4 or more carbon atoms preferably account for 5 to 100 mol %, more preferably 20 to 95 mol %, even more preferably 30 to 90 mol %, particularly preferably 40 to 85 mol %, and especially preferably 50 to 80 mol % of the structural units derived from polycarboxylic acids (A). If this content ratio is too low, the glass transition temperature of the polyester resin [I] will tend to be too high, making it difficult to achieve sufficient adhesive strength. However, if this content ratio is too high, adhesive strength at high temperatures will tend to decrease, or the resin will crystallize, making it difficult to achieve sufficient adhesive performance.

When the structural units derived from the trivalent or higher polycarboxylic acids (A-3) are included as structural units derived from the polycarboxylic acids (A), the structural units derived from the trivalent or higher polycarboxylic acids (A-3) preferably account for 10 mol % or less, and more preferably 0.1 to 5 mol %, of the structural units derived from the polycarboxylic acids (A). If this content ratio is too high, gelation tends to occur during the production of the polyester resin [I].

Furthermore, when the structural units derived from the linear aliphatic diol (B-1) are contained as structural units derived from the polyol (B), the structural units derived from the linear aliphatic diol (B-1) preferably account for 1 to 100 mol % of the structural units derived from the polyol (B), more preferably 2 to 80 mol %, even more preferably 3 to 70 mol %, particularly preferably 4 to 60 mol %, and especially preferably 5 to 50 mol %. If this content ratio is too low, the reactivity of the polyester resin [I] during production tends to decrease. However, if this content ratio is too high, the polyester resin [I] tends to crystallize, reducing the initial adhesive strength of the adhesive.

On the other hand, when the structural units derived from the diol (B-2) having a hydrocarbon group on the side chain are included as structural units derived from the polyol (B), the structural units derived from the diol (B-2) having a hydrocarbon group on the side chain preferably account for 5 to 100 mol %, particularly 20 to 90 mol %, and even more preferably 40 to 80 mol %, of the structural units derived from the polyol (B). If this content ratio is too low, the polyester-based resin [I] tends to crystallize, reducing the initial adhesive strength of the adhesive. If this content ratio is too high, the reactivity of the polyester-based resin [I] during production tends to decrease.

Furthermore, when structural units derived from the diol (B-3) having an alicyclic structure are included as structural units derived from the polyol (B), the structural units derived from the diol (B-3) having an alicyclic structure preferably account for 20 to 100 mol %, particularly 40 to 98 mol %, and even more preferably 60 to 95 mol %, of the structural units derived from the polyol (B). If this content ratio is too low, the resin tends to crystallize, making it difficult to achieve sufficient adhesive performance, and the elastic modulus tends to decrease, resulting in reduced impact resistance. However, if this content ratio is too high, the reaction time tends to be longer in the production of the polyester resin [I].

Furthermore, when structural units derived from the trivalent or higher polyol (B-4) are included as structural units derived from polyol (B), the structural units derived from the trivalent or higher polyol (B-4) preferably account for 10 mol % or less, and more preferably 0.1 to 5 mol %, of the structural units derived from polyol (B). If this content ratio is too high, the polyester resin [I] tends to gel during production, making production difficult.

Here, the proportions of structural units (compositional proportions) derived from each component of the polyester resin [I] can be determined, for example, by NMR.

The glass transition temperature (Tg) of the polyester resin [I] is -70 to 20°C, preferably -60 to 10°C, more preferably -50 to 0°C, particularly preferably -40 to -5°C, and especially preferably -30 to -10°C, from the viewpoint of adhesive properties. If the glass transition temperature (Tg) is too high, flexibility will be lost, initial adhesive strength will decrease, adhesive strength will not be exerted with pressure equivalent to finger pressure, and workability will tend to decrease. If the glass transition temperature (Tg) is too low, cohesive strength will decrease, and the adhesive sheet will be prone to deformation, tending to impair appearance.

Here, the glass transition temperature (Tg) of the polyester resin [I] is a value measured using a differential scanning calorimeter DSC Q20 manufactured by TA Instruments.
The measurement temperature range was −90 to 100° C., and the temperature rise rate was 10° C./min.

The weight-average molecular weight of the polyester resin [I] is 5,000 to 300,000 from the viewpoint of the cohesive strength of the adhesive. It is preferably 8,000 to 200,000, particularly preferably 10,000 to 150,000, and even more preferably 20,000 to 100,000. If the weight-average molecular weight is too small, the adhesive will not have sufficient cohesive strength, and heat resistance and mechanical strength tend to be reduced. Furthermore, if the weight-average molecular weight is too large, the polyester resin [I] is more likely to gel during production, making it difficult to obtain the resin, and its adhesion to the substrate tends to be reduced.

The weight-average molecular weight in this invention is the weight-average molecular weight converted to standard polystyrene molecular weight, and is measured using a high-performance liquid chromatograph (Waters, "ACQUITY APC System") equipped with four columns in series: one ACQUITY APC XT 450, one ACQUITY APC XT 200, and two ACQUITY APC XT 45.

The acid value of the polyester resin [I] is preferably 10 mgKOH/g or less, particularly 3 mgKOH/g or less, and even more preferably 1 mgKOH/g or less. If the acid value is too high, hydrolysis tends to proceed more easily, and when a metal layer or other layer is laminated to one side of the pressure-sensitive adhesive layer, corrosion tends to occur. For example, when a metal oxide thin film layer is formed, corrosion tends to occur, reducing the conductivity of the metal oxide thin film.

Here, the acid value of the polyester resin [I] is determined by neutralization titration in accordance with JIS K 0070.

<Ultraviolet absorber [II]>
The pressure-sensitive adhesive composition of the present invention contains the polyester resin [I] and the specific ultraviolet absorber [II]. By containing the polyester resin [I] and the specific ultraviolet absorber [II], the pressure-sensitive adhesive composition of the present invention exhibits the effects of being excellent in adhesive strength and substrate adhesion, less yellowing, and excellent ultraviolet absorption ability.
In the case of an acrylic resin that is commonly used as a pressure-sensitive adhesive composition, even if the acrylic pressure-sensitive adhesive composition contains the above-mentioned specific UV absorber [II], not all of the above-mentioned effects are achieved. The present invention has discovered that the above-mentioned effects, particularly excellent effects in yellowing resistance and UV absorption ability, can be achieved by selectively combining a polyester resin with the above-mentioned specific UV absorber.

The specific ultraviolet absorber [II] may be at least one selected from triazine compounds, triazole compounds, and cyanoacrylate compounds.

Examples of the triazine compounds include 2-(2-hydroxy-4-methoxyphenyl)-4,6-diphenyl-1,3,5-triazine, 2-(2-hydroxy-4-ethoxyphenyl)-4,6-diphenyl-1,3,5-triazine, 2-(2-hydroxy-4-propoxyphenyl)-4,6-diphenyl-1,3,5-triazine, 2-(2-hydroxy-4-butoxyphenyl)-4,6-diphenyl-1,3,5-triazine, 2-(2-hydroxy-4-hexyloxyphenyl)-4,6-diphenyl-1,3,5-triazine, and 2-(2-hydroxy-4-octyloxyphenyl)-4,6-diphenyl-1 ,3,5-triazine, 2-(2-hydroxy-4-dodecyloxyphenyl)-4,6-diphenyl-1,3,5-triazine, 2-(2-hydroxy-4-benzyloxyphenyl)-4,6-diphenyl-1,3,5-triazine, 2,4-bis(2-hydroxy-4-butoxyphenyl)-6-(2,4-dibutoxyphenyl)-1,3-5-triazine, 2,4,6-tris(2-hydroxy-4-hexyloxy-3-methylphenyl)-1,3,5-triazine, 2-(2-hydroxy-4-[1-octyloxycarbonylethoxy]phenyl)-4,6-bis(4-phenylphenyl)-1,3,5-triazine, 2 -[4-[(2-hydroxy-3-dodecyloxypropyl)oxy]-2-hydroxyphenyl]-4,6-bis(2,4-dimethylphenyl)-1,3,5-triazine, 2-[4-[(2-hydroxy-3-tridecyloxypropyl)oxy]-2-hydroxyphenyl]-4,6-bis(2,4-dimethylphenyl)-1,3,5-triazine, 2-[4-[(2-hydroxy-3-(2'-ethyl)hexyl)oxy]-2-hydroxyphenyl]-4,6-bis(2,4-dimethylphenyl)-1,3,5-triazine, 2,4-bis(2,4-dimethylphenyl)-6-[2-hydroxy-4-(3-octyloxy- Examples of hydroxyphenyl triazines include 2,4-bis(2,4-dimethylphenyl)-6-[2-hydroxy-4-(3-nonyloxy-2-hydroxypropyloxy)-5-α-cumylphenyl]-s-triazine, 2,4-bis(2,4-dimethylphenyl)-6-[2-hydroxy-4-(3-decyloxy-2-hydroxypropyloxy)-5-α-cumylphenyl]-s-triazine, and 2-(2-hydroxy-4-acryloyloxyethoxyphenyl)-4,6-bis(2,4-dimethylphenyl)-1,3,5-triazine. These may be used alone or in combination. Of these, 2,4-bis(2-hydroxy-4-butoxyphenyl)-6-(2,4-dibutoxyphenyl)-1,3-5-triazine is preferred.

Commercially available examples of the above triazine compounds include "Tinuvin 400," "Tinuvin 405," "Tinuvin 460," "Tinuvin 477," and "Tinuvin 479," manufactured by BASF.

Examples of the triazole compounds include C7-C9-alkyl-3-[3-(2H-benzotriazol-2-yl)-5-(1,1-dimethylethyl)-4-hydroxyphenyl]propionether, 2-(2-hydroxy-5-methylphenyl)benzotriazole, 2-(2-hydroxy-5-tert-octylphenyl)benzotriazole, 2-(2-hydroxy-3,5-dicumylphenyl)phenylbenzotriazole, 2-(2-hydroxy-3-tert-butyl-5-methylphenyl)-5-chlorobenzotriazole, 2,2'-methylenebis[4-(1,1,3,3-tetramethylbutyl)-6-(2H-benzotriazol-2-yl)phenol], and 2-(2-hydroxy-3,5-di-tert-butylphenyl)benzotriazole. Examples of the benzotriazole include triazole, 2-(2-hydroxy-3,5-di-tert-butylphenyl)-5-chlorobenzotriazole, 2-(2-hydroxy-3,5-di-tert-amylphenyl)benzotriazole, 2-(2-hydroxy-5-tert-octylphenyl)benzotriazole, 2-(2-hydroxy-5-tert-butylphenyl)benzotriazole, 2-(2-hydroxy-4-octoxyphenyl)benzotriazole, 2,2'-methylenebis(4-cumyl-6-benzotriazolephenyl), 2,2'-p-phenylenebis(1,3-benzoxazin-4-one), and 2-[2-hydroxy-3-(3,4,5,6-tetrahydrophthalimidomethyl)-5-methylphenyl]benzotriazole. These may be used alone or in combination of two or more. Of these, C7-C9-alkyl-3-[3-(2H-benzotriazol-2-yl)-5-(1,1-dimethylethyl)-4-hydroxyphenyl]propionether is preferred.

Commercially available examples of the above triazole compounds include "Tinuvin PS," "Tinuvin 99-2," "Tinuvin 326," "Tinuvin 384-2," "Tinuvin 900," "Tinuvin 928," "Tinuvin 970," and "Tinuvin 1130," all manufactured by BASF.

Examples of the cyanoacrylate compounds include 2-ethylhexyl-2-cyano-3,3-diphenylacrylate, ethyl-2-cyano-3,3-diphenylacrylate, and octyl-2-cyano-3,3-diphenylacrylate. These may be used alone or in combination of two or more.

Commercially available cyanoacrylate compounds include, for example, "Uvinul 3035," "Uvinul 3039," and "Uvinul 3030," manufactured by BASF.

Among the above ultraviolet absorbers [II], triazine-based compounds and triazole-based compounds are preferred because they have superior adhesive strength, less yellowing, and excellent ultraviolet absorption ability.

The number-average molecular weight of the ultraviolet absorber [II] is preferably 180 to 1,500, more preferably 250 to 1,000, and particularly preferably 300 to 800. If the number-average molecular weight of the ultraviolet absorber [II] is too small, yellowing resistance tends to decrease, while if the number-average molecular weight is too large, adhesive strength tends to decrease.

The above-mentioned ultraviolet absorber [II] preferably has a maximum absorption wavelength of 300 to 395 nm, more preferably 320 to 390 nm, particularly preferably 330 to 380 nm, and especially preferably 340 to 370 nm. If the maximum absorption wavelength of the ultraviolet absorber [II] is too short, the ultraviolet absorption performance in the long wavelength region tends to decrease, while if the maximum absorption wavelength is too long, yellowing resistance tends to decrease.

The content of the ultraviolet absorber [II] is preferably 0.01 to 20 parts by weight, particularly preferably 0.1 to 10 parts by weight, and even more preferably 0.2 to 5 parts by weight, per 100 parts by weight of the polyester resin (I). If the content of ultraviolet absorber [II] is too high, adhesive strength tends to decrease, while if it is too low, ultraviolet absorption performance tends to decrease.

<Hydrolysis inhibitor [III]>
The pressure-sensitive adhesive composition of the present invention preferably further contains a hydrolysis inhibitor [III]. The hydrolysis inhibitor [III] is contained in order to ensure long-term durability.

The hydrolysis inhibitor [III] may be a conventionally known compound, such as a compound that reacts with and bonds to the carboxylic acid terminal groups of the polyester resin [I]. Specific examples include compounds containing functional groups such as carbodiimide groups, epoxy groups, and oxazoline groups. The hydrolysis inhibitor [III] may be used alone or in combination with two or more types. Among these, carbodiimide group-containing compounds are preferred because of their high effectiveness in eliminating the catalytic activity of protons derived from carboxylic acid terminal groups.

The carbodiimide group-containing compound may typically be a known carbodiimide compound having one or more carbodiimide groups (-N=C=N-) in the molecule. However, to improve durability under high temperature and humidity conditions, a compound having two or more carbodiimide groups in the molecule, i.e., a polyvalent carbodiimide compound, is preferred. Compounds having three or more, preferably five or more, and especially seven or more carbodiimide groups in the molecule are particularly preferred. The number of carbodiimide groups contained in the polyvalent carbodiimide compound in the molecule is typically 50 or less; too many carbodiimide groups tends to be undesirable because the molecular structure becomes too large.

As the carbodiimide group-containing compound, it is also preferable to use a high-molecular-weight polycarbodiimide produced by subjecting a diisocyanate to a decarboxylation condensation reaction in the presence of a carbodiimidization catalyst.

Such high molecular weight polycarbodiimides may be synthesized or commercially available products may be used. When synthesizing high molecular weight polycarbodiimides, for example, those obtained by subjecting the following diisocyanates to a decarboxylation condensation reaction may be used.

Examples of such diisocyanates include 4,4'-diphenylmethane diisocyanate, 3,3'-dimethoxy-4,4'-diphenylmethane diisocyanate, 3,3'-dimethyl-4,4'-diphenylmethane diisocyanate, 4,4'-diphenylether diisocyanate, 3,3'-dimethyl-4,4'-diphenylether diisocyanate, 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, 1-methoxyphenyl-2,4-diisocyanate, isophorone diisocyanate, 4,4'-dicyclohexylmethane diisocyanate, and tetramethylxylylene diisocyanate. These can be used alone or in combination of two or more.

Furthermore, from the standpoint of storage stability, it is preferable for the high-molecular-weight polycarbodiimide to have its terminal isocyanate groups blocked with a blocking agent. Examples of blocking agents include compounds having active hydrogen that reacts with isocyanate groups, or compounds having an isocyanate group. Examples include monoalcohols, monocarboxylic acids, monoamines, and monoisocyanates each having one substituent selected from a carboxy group, an amino group, and an isocyanate group.

Commercially available carbodiimide group-containing compounds include, for example, the Carbodilite (registered trademark) series manufactured by Nisshinbo Chemical Inc. Among these, Carbodilite (registered trademark) "V-01," "V-02B," "V-03," "V-04K," "V-04PF," "V-05," "V-07," "V-09," and "V-09GB" are preferred due to their excellent compatibility with organic solvents.

The carbodiimide equivalent weight of the carbodiimide group-containing compound is preferably 50 to 10,000, particularly 100 to 1,000, and even more preferably 150 to 500. The carbodiimide equivalent weight refers to the chemical formula weight per carbodiimide group.

Furthermore, examples of epoxy group-containing compounds used as the hydrolysis inhibitor [III] include glycidyl ester compounds and glycidyl ether compounds. These can be used alone or in combination of two or more types.

Specific examples of glycidyl ester compounds include benzoic acid glycidyl ester, t-Bu-benzoic acid glycidyl ester, p-toluic acid glycidyl ester, cyclohexanecarboxylic acid glycidyl ester, pelargonic acid glycidyl ester, stearic acid glycidyl ester, lauric acid glycidyl ester, palmitic acid glycidyl ester, behenic acid glycidyl ester, versatic acid glycidyl ester, oleic acid glycidyl ester, linoleic acid glycidyl ester, linolenic acid glycidyl ester, behenolic acid glycidyl ester, stearolic acid glycidyl ester, terephthalic acid diglycidyl ester, and isophthalic acid Examples include diglycidyl ester, diglycidyl phthalate ester, diglycidyl naphthalenedicarboxylic acid ester, diglycidyl methyl terephthalate ester, diglycidyl hexahydrophthalate ester, diglycidyl tetrahydrophthalate ester, diglycidyl cyclohexanedicarboxylic acid ester, diglycidyl adipic acid ester, diglycidyl succinate ester, diglycidyl sebacic acid ester, diglycidyl dodecanedioate, diglycidyl octadecanedicarboxylic acid ester, triglycidyl trimellitate, and tetraglycidyl pyromellitic acid ester. These may be used alone or in combination of two or more.

Specific examples of glycidyl ether compounds include phenyl glycidyl ether, o-phenyl glycidyl ether, 1,4-bis(β,γ-epoxypropoxy)butane, 1,6-bis(β,γ-epoxypropoxy)hexane, 1,4-bis(β,γ-epoxypropoxy)benzene, 1-(β,γ-epoxypropoxy)-2-ethoxyethane, 1-(β,γ-epoxypropoxy)-2-benzyloxyethane, 2,2-bis-[p-(β,γ-epoxypropoxy)phenyl]propane, and bisglycidyl polyethers obtained by reacting bisphenols such as 2,2-bis-(4-hydroxyphenyl)propane and 2,2-bis-(4-hydroxyphenyl)methane with epichlorohydrin. These compounds can be used alone or in combination of two or more.

Preferred examples of the oxazoline group-containing compound include bisoxazoline compounds. Specific examples include 2,2'-bis(2-oxazoline), 2,2'-bis(4-methyl-2-oxazoline), 2,2'-bis(4,4-dimethyl-2-oxazoline), 2,2'-bis(4-ethyl-2-oxazoline), 2,2'-bis(4,4'-diethyl-2-oxazoline), 2,2'-bis(4-propyl-2-oxazoline), 2,2'-bis(4-butyl-2-oxazoline), and 2,2'-bis(4-hexyl-2-oxazoline). 2,2'-bis(4-phenyl-2-oxazoline), 2,2'-bis(4-cyclohexyl-2-oxazoline), 2,2'-bis(4-benzyl-2-oxazoline), 2,2'-p-phenylenebis(2-oxazoline), 2,2'-m-phenylenebis(2-oxazoline), 2,2'-o-phenylenebis(2-oxazoline), 2,2'-p-phenylenebis(4-methyl-2-oxazoline), 2,2'-p-phenylenebis(4,4-dimethyl-2-oxazoline), 2,2'-m-phenylenebis(4-methyl-2-oxazoline), 2,2'-m-phenylenebis(4,4-dimethyl-2-oxazoline), 2,2'-ethylenebis(2-oxazoline), 2,2'-tetramethylenebis(2-oxazoline), 2,2'-hexamethylenebis(2-oxazoline), 2,2'-octamethylenebis(2-oxazoline), 2,2'-decamethylenebis(2-oxazoline), 2,2'-ethylene Examples include 2,2'-tetramethylenebis(4,4-dimethyl-2-oxazoline), 2,2'-9,9'-diphenoxyethanebis(2-oxazoline), 2,2'-cyclohexylenebis(2-oxazoline), and 2,2'-diphenylenebis(2-oxazoline). Of these, 2,2'-bis(2-oxazoline) is most preferred from the standpoint of reactivity with the polyester resin (A). These can be used alone or in combination of two or more.

The hydrolysis inhibitor [III] preferably has low volatility, and therefore it is preferable to use one having a high number average molecular weight, usually 300 to 10,000, preferably 1,000 to 5,000.
Furthermore, from the viewpoint of hydrolysis resistance, it is preferable to use a hydrolysis inhibitor [III] having a high weight-average molecular weight. The weight-average molecular weight of the hydrolysis inhibitor [III] is preferably 500 or more, more preferably 2000 or more, and even more preferably 3000 or more. The upper limit of the weight-average molecular weight is usually 50,000.
If the molecular weight of the hydrolysis inhibitor [III] is too small, the hydrolysis resistance tends to decrease, whereas if the molecular weight is too large, the compatibility with the polyester resin [I] tends to decrease.

The content of the hydrolysis inhibitor [III] is preferably 0.01 to 10 parts by weight, particularly preferably 0.1 to 5 parts by weight, even more preferably 0.3 to 3 parts by weight, and especially preferably 0.5 to 2 parts by weight, per 100 parts by weight of the polyester resin [I]. If the content is too high, turbidity tends to occur due to poor compatibility with the polyester resin [I], while if the content is too low, sufficient durability tends to be difficult to achieve.

The content of the hydrolysis inhibitor [III] is preferably optimized depending on the acid value of the polyester resin [I], and the molar ratio [(b)/(a)] of the total number of moles (b) of functional groups of the hydrolysis inhibitor [III] in the polyester pressure-sensitive adhesive composition to the total number of moles (a) of acidic functional groups of the polyester resin in the polyester pressure-sensitive adhesive composition is preferably 0.5≦(b)/(a), particularly preferably 1≦(b)/(a)≦1000, and even more preferably 1.5≦(b)/(a)≦100.
If the molar ratio of (b) to (a) is too low, the moist heat resistance tends to decrease, whereas if the molar ratio of (b) to (a) is too high, the compatibility with the polyester resin [I] tends to decrease, and the adhesive strength, cohesive strength, and durability tend to decrease.

<Crosslinking agent [IV]>
Examples of the crosslinking agent [IV] include compounds having a functional group that reacts with at least one of the hydroxyl group and the carboxyl group contained in the polyester resin [I], such as polyisocyanate compounds and polyepoxy compounds. Among these, it is particularly preferable to use polyisocyanate compounds, as they can achieve a good balance between initial adhesive strength, mechanical strength, and heat resistance.

Examples of such polyisocyanate compounds include polyisocyanates such as tetramethylene diisocyanate, hexamethylene diisocyanate, isophorone diisocyanate, tolylene diisocyanate, diphenylmethane diisocyanate, hydrogenated diphenylmethane diisocyanate, xylylene diisocyanate, hydrogenated xylylene diisocyanate, tetramethylxylylene diisocyanate, 1,5-naphthalene diisocyanate, and triphenylmethane triisocyanate. Other examples include adducts of the above polyisocyanates with polyol compounds such as trimethylolpropane, and biuret and isocyanurate forms of these polyisocyanate compounds. The above polyisocyanate compounds may also be used in which the isocyanate moiety is blocked with phenol, lactam, or the like. These crosslinking agents [IV] may be used alone or in combination.

The content of the crosslinking agent [IV] can be appropriately selected depending on the molecular weight of the polyester resin [I] and the intended use. In general, the crosslinking agent [IV] is preferably contained in a proportion such that the reactive group contained in the crosslinking agent [IV] is 0.2 to 10 equivalents, particularly preferably 0.5 to 5 equivalents, and further preferably 0.5 to 3 equivalents, per equivalent of at least one of the hydroxyl group and the carboxy group contained in the polyester resin [I].
If the equivalent number of the reactive group contained in the crosslinking agent [IV] is too small, the cohesive strength tends to decrease, whereas if it is too large, the flexibility tends to decrease.

In addition, in the reaction between the polyester resin [I] and the crosslinking agent [IV], organic solvents that do not have functional groups that react with the components [I] and [IV] can be used, such as esters such as ethyl acetate and butyl acetate, ketones such as methyl ethyl ketone and methyl isobutyl ketone, and aromatics such as toluene and xylene. These can be used alone or in combination of two or more.

<Urethanization catalyst [V]>
The pressure-sensitive adhesive composition of the present invention preferably further contains a urethanization catalyst [V].
As the urethanization catalyst [V], for example, an organometallic compound, a tertiary amine compound, etc. These may be used alone or in combination of two or more kinds.

Examples of the organometallic compounds include zirconium compounds, iron compounds, tin compounds, titanium compounds, lead compounds, cobalt compounds, and zinc compounds.
Examples of zirconium compounds include zirconium naphthenate and zirconium acetylacetonate.
Examples of iron compounds include iron acetylacetonate and iron 2-ethylhexanoate.
Examples of tin compounds include dibutyltin dichloride, dibutyltin oxide, and dibutyltin dilaurate.
Examples of titanium compounds include dibutyltitanium dichloride, tetrabutyltitanate, and butoxytitanium trichloride.
Examples of lead compounds include lead oleate, lead 2-ethylhexanoate, lead benzoate, and lead naphthenate.
Examples of the cobalt-based compounds include cobalt 2-ethylhexanoate and cobalt benzoate.
Examples of zinc compounds include zinc naphthenate and zinc 2-ethylhexanoate.

Examples of the tertiary amine compounds include triethylamine, triethylenediamine, and 1,8-diazabicyclo-(5,4,0)-undecene-7.

Among these urethane-forming catalysts [V], organometallic compounds are preferred in terms of reaction rate and pot life of the PSA layer, with zirconium compounds being particularly preferred, and zirconium acetylacetonate being especially preferred.

[Catalytic inhibitor]
In the pressure-sensitive adhesive composition of the present invention, it is preferable to incorporate a catalytic inhibitor into the urethanation catalyst [V] in order to extend the pot life and improve the coatability.
Examples of catalyst action inhibitors include β-ketoesters such as methyl acetoacetate, ethyl acetoacetate, octyl acetoacetate, oleyl acetoacetate, lauryl acetoacetate, and stearyl acetoacetate, and β-diketones such as acetylacetone, 2,4-hexanedione, and benzoylacetone. These are keto-enol tautomeric compounds that protect the urethanization catalyst [V], thereby reducing the catalytic activity of the urethanization catalyst [V] in a solution state, suppressing excessive viscosity increase and gelation of the PSA composition after blending, and extending the pot life of the PSA composition.
Among these, acetylacetone is preferably used as the catalyst inhibitor from the viewpoint of the balance between pot life and curing speed. These catalyst inhibitors can be used alone or in combination of two or more.

The blending ratio (weight ratio) of catalytic inhibitor to urethanization catalyst [V] is preferably in the range of 0.001:1 to 15:1 (catalytic inhibitor:urethanization catalyst [V]), more preferably 0.005:1 to 13:1, and particularly preferably 0.01:1 to 10:1. If the amount of catalytic inhibitor is too low relative to the amount of urethanization catalyst [V], the pot life tends to be short and the coatability tends to be reduced, while if the amount is too high, the curing rate tends to be reduced.

<Silane coupling agent [VI]>
The pressure-sensitive adhesive composition of the present invention preferably further contains a silane coupling agent [VI].
Examples of the silane coupling agent [VI] include amino group-containing silane coupling agents, epoxy group-containing silane coupling agents, vinyl group-containing silane coupling agents, (meth)acryloyl group-containing silane coupling agents, mercapto group-containing silane coupling agents, isocyanate group-containing silane coupling agents, etc. These may be used alone or in combination of two or more kinds.

Examples of the amino group-containing silane coupling agent include 3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, 3-(2-aminoethyl)aminopropyltrimethoxysilane, and 3-phenylaminopropyltrimethoxysilane.

Examples of the epoxy group-containing silane coupling agent include 3-glycidoxypropyltrimethoxysilane, 3-glycidoxypropylmethyldimethoxysilane, 3-glycidoxypropylmethyldiethoxysilane, 3-glycidoxypropyltriethoxysilane, and 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane.

Examples of the vinyl group-containing silane coupling agent include vinyltriacetoxysilane, vinyltrimethoxysilane, and vinyltriethoxysilane.

Examples of the (meth)acryloyl group-containing silane coupling agent include 3-(meth)acryloxypropyltrimethoxysilane, 3-(meth)acryloxypropylmethyldimethoxysilane, 3-(meth)acryloxypropylmethyldiethoxysilane, and 3-(meth)acryloxypropyltriethoxysilane.

Examples of the mercapto group-containing silane coupling agent include 3-mercaptopropyltrimethoxysilane, 3-mercaptomethyldimethoxysilane, and 3-mercaptotriethoxysilane.

Examples of the isocyanate group-containing silane coupling agent include isocyanurate group-containing silane coupling agents such as tris-(trimethoxysilylpropyl)isocyanurate, and 3-isocyanatepropyltriethoxysilane.

Of these silane coupling agents, epoxy group-containing silane coupling agents are preferred, with 3-glycidoxypropyltrimethoxysilane being particularly preferred.

The content of the silane coupling agent [VI] is usually 0.01 to 10 parts by weight, preferably 0.02 to 5 parts by weight, particularly preferably 0.03 to 3 parts by weight, and further preferably 0.1 to 1 part by weight, based on 100 parts by weight of the polyester resin [I].
If the content of the silane coupling agent [VI] is too high, the adhesive strength tends to decrease, whereas if it is too low, the adhesion to the substrate tends to decrease.

In addition to the above-mentioned polyester resin [I], UV absorber [II], hydrolysis inhibitor [III], crosslinking agent [IV], etc., the adhesive composition of the present invention can also contain additives such as antioxidants such as hindered phenols, softeners, UV absorbers other than those mentioned above, stabilizers, antistatic agents, tackifiers, as well as inorganic or organic fillers, powders such as metal powders, pigments, and other particulate additives, provided the effects of the present invention are not impaired. These can be used alone or in combination of two or more types.

In addition to the above-mentioned additives, the pressure-sensitive adhesive composition of the present invention may also contain small amounts of impurities contained in the raw materials used to manufacture the components of the pressure-sensitive adhesive composition.

Such a pressure-sensitive adhesive composition can be obtained, for example, by preparing the above-mentioned polyester resin [I], ultraviolet absorber [II], and optional components as necessary, and blending and dispersing them during the production of polyester resin [I], or by blending them into a solution of polyester resin [I] dissolved in an organic solvent and dispersing them using a mixing roller.

The adhesive of the present invention is made from the above-mentioned adhesive composition, i.e., the adhesive composition is crosslinked (cured).

The pressure-sensitive adhesive sheet of the present invention has a pressure-sensitive adhesive layer containing the pressure-sensitive adhesive. The pressure-sensitive adhesive sheet may be a pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer on one or both sides of a supporting substrate, or may be a substrate-less double-sided pressure-sensitive adhesive sheet that does not have a substrate. The pressure-sensitive adhesive sheet of the present invention is particularly suitable as a pressure-sensitive adhesive sheet for optical members used for bonding optical members.
In the present invention, the term "sheet" also includes "film" and "tape."

<Adhesive sheet>
The pressure-sensitive adhesive sheet can be produced, for example, as follows.
Such a pressure-sensitive adhesive sheet can be produced according to a known general method for producing a pressure-sensitive adhesive sheet. For example, the pressure-sensitive adhesive composition is applied to one surface of a substrate, followed by drying to form a pressure-sensitive adhesive layer, and a release sheet is attached to the surface (the surface opposite to the surface that contacts the substrate), followed by curing as necessary, thereby obtaining the pressure-sensitive adhesive sheet of the present invention, which has a substrate and a pressure-sensitive adhesive layer, and in which the pressure-sensitive adhesive layer is provided on at least one surface of the substrate.

Alternatively, the pressure-sensitive adhesive sheet of the present invention can be obtained by coating the pressure-sensitive adhesive composition on a release sheet, drying it to form a pressure-sensitive adhesive layer, laminating a substrate to the surface (the side opposite to the surface that contacts the release sheet), and curing the layer as necessary.

In addition, a substrateless double-sided PSA sheet can be produced by forming a PSA layer on a release sheet and then laminating the release sheet and another release sheet to its surface (the side opposite the surface that comes into contact with the release sheet).

When using the resulting adhesive sheet or substrate-less double-sided adhesive sheet, the release sheet is peeled off from the adhesive layer and the adhesive layer is then attached to the adherend.

Examples of the substrate include polyester resins such as polyethylene naphthalate, polyethylene terephthalate, polybutylene terephthalate, and polyethylene terephthalate/isophthalate copolymer; polyolefin resins such as polyethylene, polypropylene, and polymethylpentene; polyethylene fluoride resins such as polyvinyl fluoride, polyvinylidene fluoride, and polyethylene fluoride; polyamides such as nylon 6 and nylon 6,6; vinyl polymers such as polyvinyl chloride, polyvinyl chloride/vinyl acetate copolymer, ethylene-vinyl acetate copolymer, ethylene-vinyl alcohol copolymer, polyvinyl alcohol, and vinylon; cellulose resins such as cellulose triacetate and cellophane; acrylic resins such as polymethyl methacrylate, polyethyl methacrylate, polyethyl acrylate, and polybutyl acrylate; polystyrene; polycarbonate; polyarylate; polyimide; and synthetic resin sheets made of cycloolefin polymers, etc.
Metal foils such as aluminum, copper, and iron;
Paper such as fine paper and glassine paper;
Examples include woven fabrics and nonwoven fabrics made of glass fibers, natural fibers, synthetic fibers, etc.
These substrates can be used as a single layer or as a multi-layer structure in which two or more types are laminated.

Of these, substrates made of polyethylene terephthalate and polyimide are particularly preferred, with polyethylene terephthalate being particularly preferred due to its excellent adhesion to adhesives. Furthermore, polyethylene terephthalate having a thin metal layer is preferred because it provides excellent adhesion between the substrate and adhesive, can maintain the substrate stably without corroding the thin metal layer, and can significantly enhance the effects of the adhesive used in the present invention.

In the present invention, it is also preferable to use an optical laminate in which an ITO electrode film is formed as a thin film on a polyethylene terephthalate (PET) substrate, the PET side of the film has an adhesive layer, the PET substrate and a polycarbonate (PC) film are laminated via the adhesive layer, and an acrylic film is further laminated (layer structure: ITO electrode film/PET substrate/adhesive layer/PC film/acrylic film).

The release sheet can be, for example, any of the various synthetic resin sheets, paper, cloth, nonwoven fabrics, etc. exemplified above as the substrate, which have been subjected to a release treatment. Among these, it is preferable to use a silicone-based release sheet.

The thickness of the substrate is preferably, for example, 1 to 1000 μm, particularly preferably 2 to 500 μm, and even more preferably 3 to 300 μm.

The above-mentioned adhesive composition may be applied using, for example, a gravure roll coater, reverse roll coater, kiss roll coater, dip roll coater, bar coater, knife coater, spray coater, comma coater, etc.

As drying conditions after applying the pressure-sensitive adhesive composition, a drying temperature of 60 to 140°C is preferred, with 80 to 120°C being particularly preferred. The drying time is preferably 0.5 to 30 minutes, with 1 to 5 minutes being particularly preferred.

The conditions for the curing treatment are typically room temperature (23°C) to 70°C, and typically 1 to 30 days. Specifically, the treatment can be carried out under conditions such as 1 to 20 days at 23°C, preferably 3 to 14 days at 23°C, or 1 to 10 days at 40°C.

The thickness of the adhesive layer of the above-mentioned adhesive sheet and substrate-less double-sided adhesive sheet is preferably 2 to 500 μm, particularly preferably 5 to 300 μm, and even more preferably 10 to 200 μm. If the thickness of such an adhesive layer is too thin, the adhesive strength tends to decrease, while if it is too thick, it becomes difficult to apply uniformly and problems such as the inclusion of air bubbles in the coating tend to occur. When considering impact absorption properties, a thickness of 50 μm or more is preferable.

The thickness of the adhesive layer is determined using a Digimatic Indicator (Mitutoyo Corporation, ID-C112B) by subtracting the measured thickness of the components other than the adhesive layer from the measured thickness of the entire adhesive sheet.

The gel fraction of the pressure-sensitive adhesive layer is preferably 10% by weight or more from the standpoint of durability and adhesive strength, particularly preferably 15 to 80% by weight, and even more preferably 20 to 70% by weight. If the gel fraction is too low, the cohesive strength will decrease, which tends to reduce durability. However, if the gel fraction is too high, there is a concern that the adhesive strength will decrease due to the increased cohesive strength.

The gel fraction is an indicator of the degree of crosslinking and can be calculated, for example, using the following method. An adhesive sheet (without a separator) consisting of an adhesive layer formed on a polymer sheet substrate (e.g., PET film) is wrapped in a 200-mesh SUS wire mesh and immersed in toluene at 23°C for 24 hours. The gel fraction is calculated as the weight percentage of the undissolved adhesive component remaining in the wire mesh after immersion relative to the weight of the adhesive component before immersion. The weight of the substrate is subtracted, however.

Furthermore, such adhesive sheets may be provided with a release sheet on the outside of the adhesive layer, if necessary, to protect the adhesive layer. Furthermore, in adhesive sheets in which the adhesive layer is formed on one side of the substrate, it is also possible to apply a release treatment to the surface of the substrate opposite the adhesive layer, thereby utilizing this release-treated surface to protect the adhesive layer.

The pressure-sensitive adhesive of the present invention can be used to bond various components, but is preferably used as a pressure-sensitive adhesive for optical components, used to bond optical components. By laminating a pressure-sensitive adhesive layer made of such a pressure-sensitive adhesive composition onto an optical component, the above-mentioned optical component with the pressure-sensitive adhesive layer can be obtained.

Examples of such optical components include transparent electrode films such as ITO electrode films and inorganic or organic conductive films such as polythiophene, polarizing plates, retardation plates, elliptically polarizing plates, optical compensation films, brightness enhancement films, electromagnetic wave shielding films, near-infrared absorbing films, and AR (anti-reflection) films. Among these, an ITO electrode film is particularly preferred because it is particularly effective when the optical component is a transparent electrode film and provides high adhesive strength. ITO electrode films are often formed as a thin film on a substrate such as glass or PET, but in the present invention, as already mentioned, it is particularly preferred to use a film in which the ITO electrode film is formed as a thin film on a PET substrate.
The film is also suitable for use as a light extraction film provided on the light emitting surface of a surface emitter of an organic EL element, or as a light diffusion sheet for a liquid crystal display.

It is preferable that the optical component with the pressure-sensitive adhesive layer further has a release film on the surface of the pressure-sensitive adhesive layer opposite the optical component surface. When the component is put into practical use, the release film is peeled off and the pressure-sensitive adhesive layer is attached to an adherend. It is preferable to use a silicone-based release film as this release film.

The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the following examples as long as it does not depart from the gist of the invention. In the examples, "parts" and "%" are by weight unless otherwise specified.
The glass transition temperature of the polyester resin [I] in the following examples was measured according to the method described above.

Prior to the examples, the following ingredients were prepared:

[Production of Polyester Resin [I]]
The mol % of each component of the polybasic carboxylic acids (A) described in the following production examples indicates the molar ratio when the total amount of the polybasic carboxylic acids (A) is taken as 100 mol %.
Furthermore, the mol % of each component of the polyol (B) described in the following production examples indicates the molar ratio when the total amount of the polyol (B) is taken as 100 mol %.

[Polyester Resin [I-1]]
A reactor equipped with a heater, a thermometer, a stirrer, a rectification column, a nitrogen inlet tube, and a vacuum device was charged with 76.6 parts of isophthalic acid, 186.5 parts of sebacic acid, and 173.6 parts of azelaic acid as polycarboxylic acids (A), 14.3 parts of ethylene glycol and 349 parts of cyclohexanedimethanol as polyols (B), and 0.04 parts of germanium dioxide as a catalyst, and the internal temperature was gradually raised to 250°C, and an esterification reaction was carried out over 4 hours.
Thereafter, the internal temperature was raised to 270° C., the pressure was reduced to 1.33 hPa, and a polycondensation reaction was carried out over 3 hours to produce a polyester resin [I-1].
The resulting polyester resin [I-1] had a glass transition temperature of −25° C. and a weight-average molecular weight of 60000. The final component ratio was isophthalic acid/sebacic acid/azelaic acid=20 mol%/40 mol%/40 mol% as the polycarboxylic acid (A), and ethylene glycol/cyclohexanedimethanol=8 mol%/92 mol% as the polyol (B).

[Ultraviolet absorber [II]]
[II-1]: Triazine-based ultraviolet absorber (manufactured by BASF, "Tinuvin 460", number average molecular weight 630, maximum absorption wavelength 349 nm)
[II-2]: Triazole-based ultraviolet absorber (manufactured by BASF, "Tinuvin 384-2", number average molecular weight 451.6, maximum absorption wavelength 345 nm)
[II'-1]: Benzophenone-based ultraviolet absorber (manufactured by BASF, "Uvinul 3050", number average molecular weight 246, maximum absorption wavelength 346 nm)

[Hydrolysis inhibitor [III]]
[III-1]: Aromatic polycarbodiimide compound in which the isocyanate terminal is substituted with a substituent derived from polyethylene glycol monomethyl ether (manufactured by Nisshinbo Chemical Inc., "Carbodilite V-04PF")

[Crosslinking agent [IV]]
[IV-1]: Trimethylolpropane/tolylene diisocyanate adduct (manufactured by Tosoh Corporation, "Coronate L55E")

[Urethanization catalyst [V]]
[V-1]: Zirconium-based compound diluted with acetylacetone to a solids concentration of 1% (manufactured by Matsumoto Fine Chemical Co., Ltd., "Orgatics ZC-150")

[Silane coupling agents [VI]]
[VI-1]: 3-glycidoxypropyltrimethoxysilane (manufactured by Shin-Etsu Silicones Co., Ltd., "KBM-403")

Example 1
The polyester resin [I-1] obtained above was diluted with toluene to a solids concentration of 50%, and this polyester resin [I-1] solution (100 parts as solids) was blended with 3 parts of an ultraviolet absorber [II-1], 1.5 parts of a hydrolysis inhibitor [III-1], 2.25 parts (solids) of a crosslinking agent [IV-1], 0.02 parts (solids) of a urethanization catalyst [V-1], and 0.1 parts of a silane coupling agent [VI-1], followed by stirring and mixing to obtain a pressure-sensitive adhesive composition.

Example 2
A pressure-sensitive adhesive composition was obtained in the same manner as in Example 1, except that 3 parts of the ultraviolet absorber [II-1] was changed to 4 parts of [II-2].

(Comparative Example 1)
A pressure-sensitive adhesive composition was obtained in the same manner as in Example 1, except that 3 parts of the ultraviolet absorber [II-1] was changed to 1.5 parts of [II'-1].

(Comparative Example 2)
To the acrylic resin [I'] solution (100 parts as solid content) obtained below, 4 parts of ultraviolet absorber [II-2], 0.4 parts (solid content) of crosslinking agent [IV-1], and 0.1 parts of silane coupling agent [VI-1] were blended, stirred, and mixed to obtain a pressure-sensitive adhesive composition.
[Production of acrylic resin [I']]
A four-necked round-bottom flask equipped with a reflux condenser, a stirrer, a nitrogen gas inlet, and a thermometer was charged with 38.8 parts of butyl acrylate, 60 parts of methyl acrylate, 1.0 part of hydroxyethyl methacrylate, 0.2 parts of 2-(dimethylamino)ethyl acrylate, 60 parts of ethyl acetate, and 8 parts of methyl ethyl ketone. After heating to reflux, 0.5 parts of azobisisobutyronitrile (AIBN) was added as a polymerization initiator, and the mixture was reacted at the ethyl acetate reflux temperature for 7 hours. The mixture was then diluted with 98 parts of ethyl acetate and 20 parts of methyl ethyl ketone to produce a solution of acrylic resin [I'].
The resulting acrylic resin [I'] had a glass transition temperature of -21°C and a weight average molecular weight of 530,000.

(Comparative Example 3)
A pressure-sensitive adhesive composition was obtained in the same manner as in Comparative Example 2, except that 4 parts of the ultraviolet absorber [II-2] was changed to 1.5 parts of [II'-1].

The resulting adhesive composition was evaluated as follows, and the results are shown in Table 1 below.

<Production of substrate-less double-sided adhesive sheet>
The pressure-sensitive adhesive compositions obtained in the Examples and Comparative Examples were applied using an applicator to a 38 μm-thick PET release film (Mitsui Chemicals Tocello, Inc., SP-PET-03-BU) (Fα), and dried at 100°C for 4 minutes to obtain pressure-sensitive adhesive sheets with a release film having a pressure-sensitive adhesive layer thickness of 50 μm.
Next, the surface of the adhesive layer of the obtained adhesive sheet with release film was covered with a 38 μm thick PET release film (manufactured by Mitsui Chemicals Tocello, Inc., SP-PET-01-BU) (Fβ) which had a different peel strength from the release film (Fα), and the film was subjected to curing treatment at 40° C. for 7 days to obtain a substrate-less double-sided adhesive sheet.

<Adhesive sheet evaluation>
[Adhesive strength]
The release film (Fβ) on one side of the substrateless double-sided pressure-sensitive adhesive sheet obtained above was peeled off, and the pressure-sensitive adhesive layer was transferred to a PET film (100 μm) to prepare a pressure-sensitive adhesive sheet for evaluation. The obtained pressure-sensitive adhesive sheet for evaluation was cut to a width of 10 mm, and the separator on the other side was peeled off, and the exposed pressure-sensitive adhesive layer was attached to an alkali-free glass plate (manufactured by Corning, Eagle XG), and then pressure-bonded by autoclave treatment (50 ° C, 0.5 MPa, 20 minutes) to prepare a test piece having a configuration of PET film / pressure-sensitive adhesive layer / alkali-free glass plate.
The 180-degree peel strength of the test specimens was measured at 23°C and 50% RH at a peel rate of 60 mm/min using a thermostatic tensile tester (Shimadzu Corporation, Autograph AG-X 50N), and the results were evaluated according to the following criteria. The results are also shown in Table 1.
(Evaluation criteria)
○・・・More than 5N/10mm △・・・More than 3N/10mm and 5N/10mm or less ×・・・3N/10mm or less

[Adhesion to substrate]
The release film (Fβ) on one side of the substrateless double-sided pressure-sensitive adhesive sheet obtained above was peeled off, and the pressure-sensitive adhesive layer was transferred to a PET film (100 μm) to prepare a pressure-sensitive adhesive sheet for evaluation. The obtained pressure-sensitive adhesive sheet for evaluation was cut to a width of 10 mm, and the separator on the other side was peeled off, and the exposed pressure-sensitive adhesive layer was attached to an alkali-free glass plate (manufactured by Corning, Eagle XG), and then pressure-bonded by autoclave treatment (50 ° C, 0.5 MPa, 20 minutes) to prepare a test piece having a configuration of PET film / pressure-sensitive adhesive layer / alkali-free glass plate.
The 180-degree peel strength of the test specimens was measured at 23°C and 50% RH using a thermostatic tensile tester (Shimadzu Corporation, Autograph AG-X 50N) at a peel rate of 60 mm/min. The peel mode was evaluated according to the following criteria. The results are also shown in Table 1.
(Evaluation criteria)
○: Peeling at the adherend interface ×: Peeling at the substrate interface or cohesive failure

[Yellowing resistance]
The release film (Fβ) on one side of the substrateless double-sided PSA sheet obtained above was peeled off, the PSA layer was transferred to an alkali-free glass plate (Corning Eagle XG), and the release film (Fα) on the other side was peeled off to prepare a test piece having a PSA layer/alkali-free glass configuration. The b ^* value of the obtained test piece was measured using a color difference meter (Nippon Denshoku Industries Co., Ltd., SE6000) and evaluated according to the following criteria. The results are also shown in Table 1.
(Evaluation criteria)
○: 2 or less ×: More than 2

[UV absorption ability]
The release film (Fβ) on one side of the substrateless double-sided PSA sheet obtained above was peeled off, the PSA layer was transferred to an alkali-free glass plate (Corning Eagle XG), and the release film (Fα) on the other side was peeled off to prepare a test piece having a PSA layer/alkali-free glass configuration. The UV transmittance (%) of the obtained test piece at 380 nm was measured using a UV-visible-near-infrared spectrophotometer (JASCO Corporation, V-7200) and evaluated according to the following criteria. The results are also shown in Table 1.
(Evaluation criteria)
○: 5% or less △: 5% or more but 10% or less ×: More than 10%

The results in Table 1 above show that the pressure-sensitive adhesive compositions of Examples 1 and 2 are excellent in adhesive strength and substrate adhesion, while also exhibiting little yellowing and excellent ultraviolet absorption ability.
In contrast, the pressure-sensitive adhesive composition of Comparative Example 1 had adhesive strength, substrate adhesion, and UV absorption ability, but yellowing was observed, and its performance as a pressure-sensitive adhesive for optical components was poor. Furthermore, Comparative Examples 2 and 3, which used acrylic resins, had poor substrate adhesion, but there was no particular difference in adhesive strength and UV absorption ability depending on the type of UV absorber. This also shows that the combination with a UV absorber is very important for pressure-sensitive adhesive compositions containing polyester resins.

The pressure-sensitive adhesive composition of the present invention has excellent adhesive strength and adhesion to substrates, while exhibiting little yellowing and excellent UV absorption. Therefore, pressure-sensitive adhesives and pressure-sensitive adhesive sheets using the composition are suitable for use in bonding optical components such as displays and the optical films and substrates that make up such displays.

Claims (12)

A polyester -based pressure-sensitive adhesive composition comprising a polyester-based resin [I] containing a structural unit derived from a polyvalent carboxylic acid (A) and a structural unit derived from a polyol (B) (excluding polyester-based resins having a glass transition temperature in the range of -80 to 0°C and having a hydroxyl group and/or a carboxyl group in the side chain) , and an ultraviolet absorber [II],
the polycarboxylic acids (A) contain asymmetric aromatic dicarboxylic acids (A-1) and aliphatic dicarboxylic acids (A-2) having 4 or more carbon atoms, and the content ratio (molar ratio) of the asymmetric aromatic dicarboxylic acids (A-1) to the aliphatic dicarboxylic acids (A-2) having 4 or more carbon atoms is (A-1)/(A-2)=1/99 to 60/40;
the ultraviolet absorber [II] is at least one selected from a triazine-based compound and a triazole-based compound,
The polyester-based pressure-sensitive adhesive composition is characterized in that it contains 0.01 to 10 parts by weight of a silane coupling agent [VI] per 100 parts by weight of a polyester-based resin [I]. The polyester-based pressure-sensitive adhesive composition according to claim 1, characterized in that the glass transition temperature (Tg) of the polyester-based resin [I] is -70 to 20°C. The polyester-based pressure-sensitive adhesive composition according to claim 1 or 2, characterized in that the number-average molecular weight of the ultraviolet absorber [II] is 180 to 1,500. The polyester-based pressure-sensitive adhesive composition according to any one of claims 1 to 3, characterized in that the ultraviolet absorber [II] has a maximum absorption wavelength of 300 to 395 nm. The polyester-based pressure-sensitive adhesive composition according to any one of claims 1 to 4, further comprising a hydrolysis inhibitor [III]. The polyester-based pressure-sensitive adhesive composition according to any one of claims 1 to 5, further comprising a crosslinking agent [IV]. A pressure-sensitive adhesive characterized by crosslinking the polyester-based pressure-sensitive adhesive composition according to any one of claims 1 to 6. An adhesive sheet having an adhesive layer containing the adhesive of claim 7. The adhesive sheet according to claim 8, characterized in that it comprises a substrate and an adhesive layer, the adhesive layer being provided on at least one surface of the substrate. The adhesive sheet of claim 8, characterized in that the adhesive sheet is a substrateless type that does not have a substrate. The pressure-sensitive adhesive sheet according to any one of claims 8 to 10, characterized in that it is used for bonding optical components. An optical member with a pressure-sensitive adhesive layer, comprising a pressure-sensitive adhesive layer and an optical member, wherein the pressure-sensitive adhesive layer contains the pressure-sensitive adhesive described in claim 7.