Adhesive compositions, adhesives, adhesive sheets and surface protective films

Abstract

This invention provides an adhesive composition and an adhesive sheet. The adhesive composition can form an adhesive that achieves light peelability at low speeds and suppresses the increase in peel force at high speeds. The adhesive sheet can achieve light peelability at low speeds and suppress the increase in peel force at high speeds. This invention also provides an adhesive composition comprising an acrylic polymer and an epoxy crosslinking agent. The acrylic polymer is a monomeric polymer comprising a (meth)acrylate with a straight-chain alkyl group having 5 to 18 carbon atoms at the ester terminus. Furthermore, in another embodiment, an adhesive sheet is provided having an adhesive layer with a gel content of 70% or more. The adhesive layer is formed from an adhesive composition comprising an acrylic polymer and a crosslinking agent, wherein the acrylic polymer is a monomeric polymer comprising a (meth)acrylate with a straight-chain alkyl group having 5 to 18 carbon atoms at the ester terminus.

Description

Technical Field

[0001] This invention relates to an adhesive composition, an adhesive, an adhesive sheet, and a surface protective film. This application claims priority to Japanese Patent Application No. 2021-174056, filed on October 25, 2021, the entire contents of which are incorporated herein by reference. Prior Technology

[0002] Generally, adhesives (also known as pressure-sensitive adhesives, hereinafter the same) are in a soft solid (viscoelastic) state in the temperature range near room temperature, possessing the property of easily adhering to the substrate by pressure. Utilizing this property, adhesives are widely used in the form of adhesive sheets for purposes such as joining parts or surface protection. The aforementioned adhesives are, for example, formed from adhesive compositions comprising acrylic polymers and crosslinking agents. Patent documents 1-3 are cited as examples of prior art disclosing this technology. Previous technical documents Patent documents

[0003] Patent Document 1: Japanese Patent No. 4682299 Patent Document 2: International Publication No. 2021 / 125278 Patent Document 3: International Publication No. 2021 / 125247 Summary of the Invention

[0004] [The problem the invention aims to solve]

[0005] Adhesive sheets with an adhesive layer on one of the substrates are also suitable as surface protective films to prevent damage (scratches, stains, corrosion, etc.) to the surface of various items during processing or handling. In the usage scenario where the surface protective film, etc., achieves its protective purpose from the object being protected (adhesive body) and is then peeled off (re-peeled off), the adhesive is required to have light peelability so that it can be easily peeled off without leaving paste residue on the adhesive body.

[0006] Furthermore, assuming the actual peeling speed in the re-peeling operation is low or high, if the peeling force varies significantly depending on the peeling speed, it will affect the peeling workability and prevent efficient peeling. Therefore, the adhesive used in the re-peeling process must also ensure that the peeling force does not change significantly with different peeling speeds. Specifically, for the aforementioned adhesive, in addition to exhibiting light peeling properties at low speeds, the peeling force must also be kept low at high speeds (preventing the increase in peeling force at high speeds).

[0007] The present invention was made in view of the above circumstances, and its object is to provide an adhesive composition that can form an adhesive capable of achieving light peel strength at low-speed peeling and suppressing the increase in peel force at high-speed peeling. Furthermore, the present invention also aims to provide an adhesive sheet capable of achieving light peel strength at low-speed peeling and suppressing the increase in peel force at high-speed peeling. Other related objects include providing an adhesive formed from the above-described adhesive composition, an adhesive sheet having the adhesive, and a surface protective film comprising the adhesive sheet. [Technical means to solve the problem]

[0008] According to the specification, an adhesive composition comprising an acrylic polymer and an epoxy crosslinking agent is provided. The acrylic polymer is a monomeric polymer comprising a (meth)acrylate with a straight-chain alkyl group having 5 to 18 carbon atoms at the ester terminus. By using a (meth)acrylate with a relatively long straight-chain alkyl group having 5 to 18 carbon atoms, curability is increased based on the crosslinking or orientation of the alkyl group, resulting in lower adhesion during low-speed peeling and easier suppression of adhesion increase during high-speed peeling. By using an acrylic polymer comprising the above-mentioned monomer as a monomeric unit and an epoxy crosslinking agent, there is a tendency to achieve light peelability during low-speed peeling and suppression of peel force increase during high-speed peeling.

[0009] In some preferred embodiments, the aforementioned monomeric components further include (meth)acrylic acid. By using (meth)acrylic acid as a monomeric component constituting acrylic polymers, it is easy to form an adhesive that, when properly crosslinked with a crosslinking agent (e.g., an epoxy crosslinking agent), increases curability, exhibits light peel strength at low peel speeds, suppresses the increase in peel force at high peel speeds, and inhibits the increase in adhesion force over time.

[0010] In some preferred embodiments, the aforementioned alkyl (meth)acrylates having a straight-chain alkyl group with 5 to 18 carbon atoms at the ester terminus include n-heptyl acrylate (HpA). HpA is suitable for use in the aforementioned alkyl (meth)acrylates having a straight-chain alkyl group with 5 to 18 carbon atoms at the ester terminus.

[0011] Furthermore, according to the specification, an adhesive formed from any of the adhesive compositions disclosed herein is provided. This adhesive exhibits light peeling properties at low peeling speeds and suppresses the increase in peeling force at high peeling speeds. Therefore, after the adhesive is applied to the substrate to achieve its purpose, peeling (re-peeling) is easy regardless of the peeling speed.

[0012] In some preferred embodiments, the gel content of the aforementioned adhesive is 70% or higher. Adhesives with a gel content of 70% or higher are less prone to deformation or damage such as dents caused by external forces during manufacturing, and are less likely to cause changes in appearance. Such adhesives are easily formed into adhesive sheets with smooth surfaces. For example, when forming transparent adhesive sheets and inspecting the adhered objects through the adhesive sheet, high-precision inspection can be performed, which is preferable. Furthermore, adhesives with a higher gel content exhibit lighter peel strength at low peel speeds, suppress the increase in peel force at high peel speeds, and suppress the increase in adhesion force over time, which is also preferable.

[0013] Furthermore, according to the specification, an adhesive sheet is provided having an adhesive layer comprising any of the adhesives disclosed herein. When used as an adhesive sheet, the adhesive sheet disclosed herein exhibits light peelability at low peel speeds and suppresses the increase in peel force at high peel speeds, thus making it easy to peel regardless of the peel speed. Therefore, it is suitable as a surface protective film. After being applied to the protected object, the surface protective film is typically peeled off from the protected object (re-peeling) once its protective purpose has been achieved. By applying the adhesives disclosed herein to surface protection applications, the peelability during re-peeling is improved due to the lower dependence of peel force on peel speed.

[0014] Furthermore, according to the specification, an adhesive sheet is provided having an adhesive layer with a gel content of 70% or more. The adhesive layer is formed from an adhesive composition comprising an acrylic polymer and a crosslinking agent, wherein the acrylic polymer is a monomeric polymer comprising a (meth)acrylate alkyl ester with a linear alkyl group having 5 to 18 carbon atoms at the ester terminus. An adhesive layer with a gel content of 70% or more is less prone to deformation or damage such as dents caused by external forces during manufacturing, and is less likely to cause changes in appearance. Adhesive sheets having this type of adhesive layer tend to have a smooth surface, which is advantageous, for example, when configured as transparent adhesive sheets for inspecting the adhered object through the adhesive sheet, allowing for high-precision inspection. Furthermore, the adhesive sheet exhibits light peel strength at low peel speeds, suppresses the increase in peel force at high peel speeds, and suppresses the tendency for adhesion strength to increase over time.

[0015] In some preferred embodiments, the aforementioned crosslinking agent comprises an epoxy-based crosslinking agent. Furthermore, the aforementioned monomer component further comprises (meth)acrylic acid. By using these acrylic polymers and crosslinking agents, adhesive sheets that exhibit light peelability at low peel speeds, suppress the increase in peel force at high peel speeds, and suppress the increase in adhesion force over time can be readily obtained. Such adhesive sheets are suitable as surface protective films. After being applied to the protected object, the surface protective film is typically peeled off from the protected object (re-peeling) once its protective purpose has been achieved. By applying the adhesive sheets disclosed herein to surface protection applications, the peelability during re-peeling can be improved due to the lower dependence of peel force on peel speed.

[0016] In some preferred samples, after aging at 50°C for 3 days, the initial high-speed adhesion force of the surface protective film, measured at a tensile speed of 30 m / min, was less than 3.0 N / 25 mm. Surface protective films that meet this characteristic have low peel force even when peeled off at high speed from the object being protected by the adhered substrate, thus avoiding damage to the adhered substrate and making peeling easy. Simple Explanation of the Diagram

[0017] Figure 1 is a cross-sectional view showing the structure of an adhesive sheet according to one embodiment. Implementation

[0018] The preferred embodiments of the present invention will now be described. For matters other than those specifically mentioned in this specification, those skilled in the art can understand the necessary steps for implementing the invention based on the teachings on implementation described herein and prior technical knowledge at the time of application. The present invention can be implemented based on the content disclosed in this specification and prior technical knowledge in the field. Furthermore, in the following figures, components and parts that perform the same function are labeled with the same symbols for explanation, and repeated descriptions are omitted or simplified. Also, the embodiments described in the figures are modeled for the purpose of clearly illustrating the present invention, and may not accurately represent the dimensions or scaled-down proportions of the actual product provided.

[0019] As stated above in this specification, "adhesive" refers to a material that is a soft solid (viscoelastic) in the temperature range near room temperature and has the property of easily adhering to a substrate by pressure. The adhesive referred to here, as defined in "CA Dahlquist, 'Adhesion: Fundamental and Practice', McLaren & Sons (1966), p. 143", generally refers to a material that satisfies the property of having a complex tensile modulus of elasticity E*(1 Hz) < 10⁷ dyne / cm² (typically, a material with the above property at 25°C).

[0020] In this specification, "carbon derived from biomass" means carbon derived from biomass materials, i.e., carbon derived from renewable organic resources (renewable carbon). Typically, the aforementioned biomass materials refer to materials derived from biological resources (typically, photosynthetic plants) that can be sustainably reproduced in the presence of sunlight, water, and carbon dioxide. Therefore, materials derived from fossil resources that have been depleted through extraction (fossil resources are materials) are excluded from the concept of biomass materials here. The biomass carbon ratio of the adhesive composition and the adhesive, i.e., the proportion of biomass-derived carbon in the total carbon contained in the adhesive composition and the adhesive, can be estimated based on the carbon isotope content of mass number 14 as measured according to ASTM D6866.

[0021] In this specification, "(meth)acrylic monomer" refers to a monomer having at least one (meth)acrylic group in a molecule. Here, "(meth)acrylic" includes both acrylonitrile and methacrylic. Therefore, the concept of (meth)acrylic monomer here can include both monomers having an acrylonitrile (acrylic monomers) and monomers having a methacrylic group (methacrylic monomers). In this specification, "(meth)acrylic acid" broadly refers to acrylic acid and methacrylic acid.

[0022] <Adhesive Composition> (Acrylic polymer) The adhesive composition disclosed herein contains an acrylic polymer. Here, "acrylic polymer" refers to a polymer derived from a monomeric component containing more than 50% by weight of a (meth)acrylic monomer. The content of the (meth)acrylic monomer in the monomeric component is preferably 70% by weight or more, and may be 80% by weight or more. In some samples, the content of the (meth)acrylic monomer in the monomeric component may be 90% by weight or more, or 95% by weight or more, or even 100% by weight. On the other hand, considering the balance of adhesive properties, in some samples, the ratio of the (meth)acrylic monomer in the total monomeric component may, for example, be less than 99% by weight, less than 95% by weight, or even less than 93% by weight.

[0023] One of the characteristics of the monomer components constituting the above-mentioned acrylic polymers is that they contain alkyl (meth)acrylates (hereinafter also referred to as "(meth)acrylate C5-18 linear alkyl esters") with straight-chain alkyl groups having 5 to 18 carbon atoms at the ester terminus. Although not particularly limited, it is believed that by using alkyl (meth)acrylates with relatively long straight-chain alkyl groups having 5 to 18 carbon atoms, the curability is increased based on the crosslinking or orientation of the alkyl groups, the adhesion force during low-speed peeling is suppressed to be low, and the increase in adhesion force during high-speed peeling is suppressed.

[0024] The above-mentioned (meth)acrylic acid C5-18 linear alkyl ester can also be represented by the following formula (1). CH₂=C(R₁)COOR₂(1) Here, R1 in formula (1) above is a hydrogen atom or a methyl group. Also, R2 is a straight-chain alkyl group with 5 to 18 carbon atoms. From the viewpoint of adhesive properties, the number of carbon atoms in the straight-chain alkyl group of the (meth)acrylate C5-18 straight-chain alkyl ester is preferably 14 or less, more preferably 12 or less, further preferably 11 or less, and especially preferably 10 or less (e.g., 9 or 8 or less). Furthermore, from the viewpoint of effectively exhibiting the effect or property of making the alkyl group a long chain, the number of carbon atoms is preferably 6 or more, more preferably 7 or more.

[0025] Specific examples of C5-18 linear alkyl esters of (meth)acrylate include: n-pentyl methacrylate, n-hexyl methacrylate, n-heptyl methacrylate, n-octyl methacrylate, n-nonyl methacrylate, n-decyl methacrylate, n-undecyl methacrylate, n-dodecyl methacrylate, n-tridecyl methacrylate, n-tetradecyl methacrylate, n-pentadecanyl methacrylate, n-hexadecyl methacrylate, n-heptadecyl methacrylate, and n-octadecyl methacrylate. C5-18 linear alkyl esters of (meth)acrylate can be used alone or in combination of two or more.

[0026] The proportion of (meth)acrylate C5-18 linear alkyl esters in the total monomer component is set according to its intended use or required characteristics. For example, it can be 1% by weight or more, appropriately 10% by weight or more, preferably 30% by weight or more, more preferably 50% by weight or more (e.g., exceeding 50% by weight), or 70% by weight or more, or 80% by weight or more, or 85% by weight or more, or 90% by weight or more, or 92% by weight or more, or 95% by weight or more. By increasing the amount of (meth)acrylate C5-18 linear alkyl esters used, the characteristics based on (meth)acrylate C5-18 linear alkyl esters can be effectively exhibited. On the other hand, from the viewpoint of copolymerizing acrylic monomers or other monomers containing functional groups as crosslinking points, the proportion of (meth)acrylate C5-18 linear alkyl esters in the total monomer component can, for example, be less than 99% by weight, less than 98% by weight, or less than 97% by weight. In other cases, from the viewpoint of obtaining the effects of other monomers, the upper limit of the proportion of (meth)acrylic acid C5-18 linear alkyl ester in the total monomer component can be 95% by weight or less, or 75% by weight or less, or 60% by weight or less, or 50% by weight or less (e.g., less than 50% by weight), or 30% by weight or less.

[0027] The proportion of (meth)acrylate C5-18 linear alkyl esters included as monomer components of the aforementioned acrylic polymers in the total amount of (meth)acrylate alkyl esters with chain-like alkyl groups at the ester end (hereinafter referred to as "(meth)acrylate chain-like alkyl esters") can be, for example, 1% by weight or more, appropriately 10% by weight or more, preferably 30% by weight or more, more preferably 50% by weight or more (e.g., more than 50% by weight), or 70% by weight or more, or 80% by weight or more, or 90% by weight or more, or 95% by weight or more, or 99% by weight or more. Furthermore, the aforementioned chain-like alkyl groups include both linear and branched alkyl groups, but do not include cyclic alkyl groups referred to as alicyclic alkyl groups. By increasing the amount of (meth)acrylate C5-18 linear alkyl esters used, the characteristics based on (meth)acrylate C5-18 linear alkyl esters can be effectively exhibited. The technology disclosed herein is preferably implemented in an acrylic polymer comprising only (meth)acrylate C5-18 linear alkyl esters as monomers of (meth)acrylate linear alkyl esters. Therefore, the maximum percentage of (meth)acrylate C5-18 linear alkyl esters in the total (meth)acrylate linear alkyl ester composition is 100% by weight. In other embodiments, from the viewpoint of obtaining the effect of using (meth)acrylate linear alkyl esters other than (meth)acrylate C5-18 linear alkyl esters, the percentage of (meth)acrylate C5-18 linear alkyl esters in the total (meth)acrylate linear alkyl ester composition can be 95% by weight or less, 75% by weight or less, 60% by weight or less, 50% by weight or less (e.g., less than 50% by weight), or 30% by weight or less.

[0028] In some formulations, C5-18 linear alkyl esters of (meth)acrylate may be used in combination with one or more C5-11 linear alkyl esters of (meth)acrylate and one or more C12-18 linear alkyl esters of (meth)acrylate. In such formulations, the ratio of the two can be set based on adhesive properties, or on the function and properties of the alkyl groups of each monomer. For example, the ratio of C5-11 linear alkyl esters of (meth)acrylate to C5-18 linear alkyl esters of (meth)acrylate may be, for example, 1% by weight or more, 10% by weight or more, 30% by weight or more, 50% by weight or more, 70% by weight or more, 90% by weight or more, or 99% by weight or more. Furthermore, the proportion of (meth)acrylic acid C5-11 linear alkyl esters in (meth)acrylic acid C5-18 linear alkyl esters can be 99% by weight or less, 90% by weight or less, or 80% by weight or less.

[0029] The above-mentioned (meth)acrylate C5-11 straight-chain alkyl esters are suitable for use in alkyl (meth)acrylates having a straight-chain alkyl group at the ester terminus with 10 or fewer carbon atoms (preferably 9 or fewer, for example 8 or fewer, preferably 7). The straight-chain alkyl group preferably has 6 or more carbon atoms.

[0030] In some preferred embodiments, the C5-18 linear alkyl ester of (meth)acrylate is n-heptyl (meth)acrylate. The effects of the technique disclosed herein are particularly well achieved by using n-heptyl (meth)acrylate. From the viewpoint of adhesive properties, n-heptyl acrylate is particularly preferred.

[0031] The proportion of n-heptyl (meth)acrylate in the total monomer component is set according to its intended use or required characteristics. For example, it can be 1% by weight or more, appropriately 10% by weight or more, preferably 30% by weight or more, even more preferably 50% by weight or more (e.g., exceeding 50% by weight), or 70% by weight or more, or 80% by weight or more, or 85% by weight or more, or 90% by weight or more, or 92% by weight or more, or 95% by weight or more. By increasing the amount of n-heptyl (meth)acrylate used, its performance can be effectively demonstrated. On the other hand, from the viewpoint of copolymerizing acrylic monomers or other monomers containing functional groups as crosslinking points, the proportion of n-heptyl (meth)acrylate in the total monomer component can be, for example, less than 99% by weight, less than 98% by weight, or less than 97% by weight. In other samples, from the viewpoint of obtaining the effects of various monomers other than (meth)acrylate, the proportion of (meth)acrylate in the total monomer components may be 95% by weight or less, or 75% by weight or less, or 60% by weight or less, or 50% by weight or less (e.g., less than 50% by weight), or 30% by weight or less.

[0032] The proportion of n-heptyl methacrylate in the total amount of (meth)acrylate alkyl esters included as monomer components of the aforementioned acrylic polymer can be, for example, 1% by weight or more, appropriately 10% by weight or more, preferably 30% by weight or more, more preferably 50% by weight or more (e.g., more than 50% by weight), or 70% by weight or more, or 80% by weight or more, or 90% by weight or more, or 95% by weight or more, or 99% by weight or more. Increasing the amount of n-heptyl methacrylate used can effectively demonstrate its performance. The technology disclosed herein can be preferably implemented using acrylic polymers composed solely of n-heptyl methacrylate as monomer components of the aforementioned (meth)acrylate alkyl esters. Therefore, the upper limit of the proportion of n-heptyl methacrylate in the total amount of the aforementioned (meth)acrylate alkyl esters is 100% by weight. In other samples, from the viewpoint of obtaining other effects of (meth)acrylate alkyl esters, the proportion of (meth)acrylate n-heptyl ester in the total (meth)acrylate alkyl ester may be 95% by weight or less, or 75% by weight or less, or 60% by weight or less, or 50% by weight or less (e.g., less than 50% by weight), or 30% by weight or less.

[0033] In some formulations, the monomeric components constituting the acrylic polymer may include (meth)acrylate alkyl esters ((meth)acrylate C19 or more alkyl esters) with a chain alkyl group having 19 or more carbon atoms at the ester terminus, or they may not contain them. One type of (meth)acrylate C19 or more alkyl ester may be used alone or in combination of two or more. The percentage of (meth)acrylate C19 or more alkyl esters in the total (meth)acrylate alkyl esters contained in the aforementioned monomeric components may, for example, be 90% by weight or less, 70% by weight or less, 50% by weight or less (e.g., less than 50% by weight), 30% by weight or less, 10% by weight or less, or 1% by weight or less. The technology disclosed herein is preferably implemented in a formulation where the monomeric components substantially do not contain (meth)acrylate C19 or more alkyl esters.

[0034] In some formulations, the aforementioned monomeric component may include alkyl (meth)acrylates (hereinafter also referred to as "biomass-derived alkyl (meth)acrylates") with a biomass-derived alkyl group at the ester terminus as the aforementioned alkyl (meth)acrylates. In recent years, environmental issues such as global warming have received increasing attention, with a desire to reduce the use of fossil fuels such as petroleum. Under these circumstances, there is also a need to reduce the use of fossil fuels in the field of adhesives. By using alkyl (meth)acrylates, acrylic adhesive compositions that take into account reducing dependence on fossil fuels can be suitably achieved.

[0035] There are no particular limitations on bio-based alkyl methacrylates, which can be, for example, bio-derived alkanols and esters of (meth)acrylate derived from bio- or non-bio-based sources. Examples of bio-derived alkanols include bioethanol, alkanols derived from plant-based raw materials such as palm oil or palm kernel oil, coconut oil, and castor oil. When the bio-derived alkanol has 3 or more carbon atoms, it can be linear or branched. In some cases, bio-derived alkanols and esters of (meth)acrylate derived from non-bio-based sources are used as bio-based alkyl methacrylates for synthesizing acrylic polymers. In these bio-based alkyl methacrylates, the more carbon atoms the alkanol has, the higher the percentage of bio-derived carbon atoms in the total carbon number of the bio-based alkyl methacrylate, i.e., the higher the bio-carbon ratio of the bio-based alkyl methacrylate. Therefore, in the aforementioned bio-based alkyl chain esters of (meth)acrylic acid, it is ideal for the alkyl chain derived from biomass to have a higher carbon number in terms of reducing dependence on fossil resources. On the other hand, if the alkyl chain constituting the (meth)acrylic acid alkyl chain ester has too many carbon numbers, it tends to be difficult to obtain adhesive properties such as adhesion, and it may also be disadvantageous in terms of production efficiency, such as synthesis or processing and cost. In the case of using bio-derived alkanols and non-bio-derived (meth)acrylic acid esters as the bio-based alkyl chain esters of (meth)acrylic acid, it is ideal to use materials that have a good balance between adhesive properties and reduced dependence on fossil resources (more specifically, the biomass carbon ratio of the aforementioned (meth)acrylic acid alkyl chain esters).

[0036] In the technology disclosed herein, any of the above-mentioned (meth)acrylate C5-18 linear alkyl esters, (meth)acrylate C1-4 linear alkyl esters, (meth)acrylate C5-18 branched alkyl esters, and (meth)acrylate C19 and above linear alkyl esters can be bio-based linear alkyl esters of (meth)acrylate. In the use of bio-based linear alkyl esters of (meth)acrylate as a (meth)acrylate C5-18 linear alkyl ester sample, the above-mentioned (meth)acrylate C5-11 linear alkyl ester can be a bio-based linear alkyl ester of (meth)acrylate, and the above-mentioned (meth)acrylate C12-18 linear alkyl ester can also be a bio-based linear alkyl ester of (meth)acrylate. In the use of two or more compounds as a (meth)acrylate linear alkyl ester sample for synthesizing acrylic polymers, at least a portion of it (e.g., one or two, or all of them) can be a (meth)acrylate bio-based linear alkyl ester.

[0037] In some preferred embodiments, one or more types of (meth)acrylate alkyl esters with a C5-18 straight-chain alkyl group derived from biomass (hereinafter also referred to as "biomass C5-18 straight-chain alkyl esters of (meth)acrylate") are used as C5-18 straight-chain alkyl esters of (meth)acrylate. By using biomass C5-18 straight-chain alkyl esters of (meth)acrylate, dependence on fossil fuel materials is reduced, and the effects of the technology disclosed herein (such as reducing adhesion during low-speed peeling and suppressing the increase in peeling force during high-speed peeling) are better achieved. The aforementioned biomass C5-18 straight-chain alkyl esters of (meth)acrylate are esters of biomass-derived alkanols and (meth)acrylates derived from biomass or non-biomass; for example, biomass-derived alkanols and (meth)acrylates derived from non-biomass can be used. In this compound, only the straight-chain alkyl group is derived from biomass.

[0038] From the viewpoint of adhesive properties, the number of carbon atoms in the straight-chain alkyl group of the (meth)acrylic acid biopolymer C5-18 straight-chain alkyl ester is preferably 14 or less, more preferably 12 or less, and even more preferably 11 or less, and particularly preferably 10 or less (e.g., 9 or 8 or less). Furthermore, the aforementioned number of carbon atoms is preferably 5 or more, more preferably 6 or more, and even more preferably 7 or more. For example, in the case of (meth)acrylic acid biopolymer C5-18 straight-chain alkyl ester using a biopolymer-derived alkanol and a non-biopolymer-derived (meth)acrylic acid ester, by increasing the number of carbon atoms in the straight-chain alkyl group, the biopolymer carbon ratio of the synthesized acrylic polymer can be increased.

[0039] The proportion of (meth)acrylic acid bio-C5-18 linear alkyl ester in the total (meth)acrylic acid C5-18 linear alkyl ester used as a monomer component in the above-mentioned acrylic polymers can be, for example, 1% by weight or more, appropriately 10% by weight or more, preferably 30% by weight or more, more preferably 50% by weight or more (e.g., more than 50% by weight), or 70% by weight or more, or 80% by weight or more, or 90% by weight or more, or 95% by weight or more, or 99% by weight or more. By increasing the usage ratio of (meth)acrylic acid bio-C5-18 linear alkyl ester, the bio-carbon ratio of the acrylic polymer can be increased, and its performance can be effectively demonstrated. The technology disclosed herein can be preferably implemented in the form of acrylic polymers composed only of (meth)acrylic acid bio-C5-18 linear alkyl ester as a monomer component of (meth)acrylic acid C5-18 linear alkyl ester. Therefore, the maximum percentage of bio-based C5-18 linear alkyl esters of (meth)acrylic acid in the total amount of C5-18 linear alkyl esters of (meth)acrylic acid is 100% by weight. In other samples, the percentage of bio-based C5-18 linear alkyl esters of (meth)acrylic acid in the total amount of C5-18 linear alkyl esters of (meth)acrylic acid may be 95% by weight or less, 70% by weight or less, 50% by weight or less (e.g., less than 50% by weight), 30% by weight or less, 10% by weight or less, or 1% by weight or less.

[0040] In some formulations, as biomass C5-18 linear alkyl esters of (meth)acrylate, one or more C5-11 linear alkyl esters of (meth)acrylate (hereinafter also referred to as "biomass C5-11 linear alkyl esters of (meth)acrylate") and one or more C12-18 linear alkyl esters of (meth)acrylate can be used together. In such formulations, the C12-18 linear alkyl ester of (meth)acrylate can be a biomass-derived linear alkyl ester (biomass C12-18 linear alkyl ester of (meth)acrylate) or a non-biomass-derived linear alkyl ester. From the viewpoint of improving the biomass carbon ratio of acrylic polymers, it is preferable that both the C5-11 linear alkyl ester of (meth)acrylate and the C12-18 linear alkyl ester of (meth)acrylate are biomass-derived materials. For example, the proportion of C5-11 linear alkyl esters of (meth)acrylic acid in C5-18 linear alkyl esters of (meth)acrylic acid can be, for example, 1% or more by weight, 10% or more by weight, 30% or more by weight, 50% or more by weight, 70% or more by weight, 90% or more by weight, or 99% or more by weight. Furthermore, the proportion of C5-11 linear alkyl esters of (meth)acrylic acid in C5-18 linear alkyl esters of (meth)acrylic acid can be 99% or less by weight, 90% or less by weight, 70% or less by weight, 50% or less by weight, 30% or less by weight, 10% or less by weight, or 1% or less by weight.

[0041] In some preferred embodiments, the C5-18 linear alkyl ester of (meth)acrylate uses n-heptyl (meth)acrylate having a n-heptyl group derived from biomass (hereinafter also referred to as "biomass heptyl (meth)acrylate"). By using biomass heptyl (meth)acrylate, dependence on fossil-based materials is reduced, and the effects of the technique disclosed herein are particularly well achieved. From the viewpoint of adhesive properties, biomass heptyl acrylate is particularly preferred.

[0042] The proportion of bio-heptyl (meth)acrylate in the total C5-18 linear alkyl ester of (meth)acrylate used as a monomer component in the above-mentioned acrylic polymers can be, for example, 1% by weight or more, appropriately 10% by weight or more, preferably 30% by weight or more, more preferably 50% by weight or more (e.g., more than 50% by weight), or 70% by weight or more, or 80% by weight or more, or 85% by weight or more, or 90% by weight or more, or 92% by weight or more, or 95% by weight or more. By increasing the proportion of bio-heptyl (meth)acrylate used, the bio-carbon ratio of the acrylic polymer can be increased, and its performance can be effectively demonstrated. The technology disclosed herein can be preferably implemented in the form of acrylic polymers composed solely of bio-heptyl (meth)acrylate as a monomer component of C5-18 linear alkyl ester of (meth)acrylate. Therefore, the maximum percentage of heptyl methacrylate in the total C5-18 linear alkyl methacrylate composition is 100% by weight. In other samples, the percentage of heptyl methacrylate in the total C5-18 linear alkyl methacrylate composition may be 95% by weight or less, 75% by weight or less, 60% by weight or less, 50% by weight or less (e.g., less than 50% by weight), 30% by weight or less, 10% by weight or less, or 1% by weight or less.

[0043] In addition to the aforementioned (meth)acrylate alkyl esters, the monomer components forming acrylic polymers may also include other monomers (copolymeric monomers) that can copolymerize with the aforementioned (meth)acrylate alkyl esters. One copolymeric monomer may be used alone, or two or more may be used in combination. These copolymeric monomers can be used to introduce crosslinking points into acrylic polymers or to improve the cohesive strength of acrylic polymers. The copolymeric monomers may be derived from biomass or non-biomass.

[0044] In some preferred formulations, carboxyl-containing monomers are used as comonomers. By combining carboxyl-containing monomers, which are used as comonomers to introduce crosslinking points into acrylic polymers, with crosslinking agents (such as epoxy crosslinking agents), cohesive strength is improved, it is easy to adjust to good adhesion that can be re-peeled, and the adhesion strength can be suppressed from increasing over time, for example, it is easy to form adhesives suitable for surface protection applications that can be re-peeled.

[0045] Examples of the aforementioned carboxyl-containing monomers include: acrylic acid, methacrylic acid, butenoic acid, and other vinyl unsaturated monocarboxylic acids; itconic acid, maleic acid, fumaric acid, and other vinyl unsaturated dicarboxylic acids and their anhydrides (maleic anhydride, itconic anhydride, etc.). Among these, acrylic acid and methacrylic acid are preferred, and acrylic acid is even more preferred. One of the aforementioned carboxyl-containing monomers may be used alone or in combination of two or more.

[0046] The content of the carboxyl-containing monomer (preferably (meth)acrylic acid) in the monomer component forming the acrylic polymer can be, for example, 0.01% by weight or more of the total monomer component, or 0.1% by weight or more, appropriately more than 0.5% by weight, and in some preferred samples, it can be 1% by weight or more (e.g., more than 1% by weight), or 2% by weight or more, or even 3% by weight or more. Furthermore, the content of the carboxyl-containing monomer (preferably (meth)acrylic acid) in the total monomer component is, for example, less than 15% by weight, appropriately set to 10% by weight or less, and in some preferred samples, it can be 8% by weight or less, or 6% by weight or less, or even 5% by weight or less. By using an appropriate amount of the carboxyl-containing monomer (preferably (meth)acrylic acid) within the above range, the agglomeration force is improved, and it is easy to adjust to a good adhesive force that can be peeled back, for example, easily forming an adhesive suitable for peeling back for surface protection applications.

[0047] The monomer components forming acrylic polymers may also include other comonomers. Other comonomers are defined as monomers that are different from the above-mentioned (meth)acrylate alkyl esters and carboxyl-containing monomers. Other comonomers may be used alone or in combination of two or more.

[0048] The following monomers can be cited as non-limiting examples of other copolymerizable monomers. Hydroxyl monomers: for example, hydroxyalkyl esters of methacrylates such as 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, 3-hydroxypropyl acrylate, 2-hydroxybutyl acrylate, and 4-hydroxybutyl acrylate; unsaturated alcohols such as vinyl alcohol and allyl alcohol. Monomers containing sulfonic acid or phosphoric acid groups: for example, styrene sulfonic acid, allyl sulfonic acid, sodium vinyl sulfonate, 2-(meth)acrylamide-2-methylpropanesulfonic acid, (meth)acrylamide propanesulfonic acid, (meth)acrylic acid sulfonyl propane, (meth)acryloxynaphthalene sulfonic acid, 2-hydroxyethylacrylamide phosphate, etc. Monomers containing epoxy groups: for example, glycidyl acrylate or 2-ethyl glycidyl ether of (meth)acrylate, etc. Monomers containing cyano groups: for example, acrylonitrile, methacrylonitrile, etc. Monomers containing isocyanate groups: for example, (meth)acrylate 2-isocyanate ethyl ester, etc. Monomers containing an amino group: for example, (meth)acrylamide; N,N-dimethyl(meth)acrylamide, N,N-diethyl(meth)acrylamide, N,N-dipropyl(meth)acrylamide, N,N-diisopropyl(meth)acrylamide, N,N-di(n-butyl)(meth)acrylamide, N,N-di(tert-butyl)(meth)acrylamide, etc.; N,N-dialkyl(meth)acrylamide; N-ethyl(meth)acrylamide, N-isopropyl(meth)acrylamide, N-butyl(meth)acrylamide, N-n-butyl(meth)acrylamide N-alkyl (meth)acrylamide; N-vinyl acetamide and other N-vinyl carboxylic amines; monomers having hydroxyl and acetyl groups, such as N-(2-hydroxyethyl)(meth)acrylamide and other N-hydroxyalkyl (meth)acrylamides; monomers having alkoxy and acetyl groups, such as N-methoxymethyl (meth)acrylamide, N-methoxyethyl (meth)acrylamide, N-butoxymethyl (meth)acrylamide and other N-alkoxyalkyl (meth)acrylamides; and N,N-dimethylaminopropyl (meth)acrylamide, N-(meth)acrylamide, etc. Monomers containing a ring containing a nitrogen atom: for example, N-vinyl-2-pyrrolidone, N-methylvinylpyrrolidone, N-vinylpyridine, N-vinylpiperidone, N-vinylpyrimidine, N-vinylpiperidine, N-vinylpyrrole, N-vinylimidazolium, N-vinylpyrazole, N-vinylpyrazole, N-(meth)propenylo-2-pyrrolidone, N-(meth)propenylopiperidine, N-( Methylpropenylpyrrolidone, N-vinylpyrrolidone, N-vinyl-3-pyrrolidone, N-vinyl-2-caprolactone, N-vinyl-1,3-vinyl-2-one, N-vinyl-3,5-pyrrolidone, N-vinylpyrazole, N-vinylisothiazole, N-vinylisothiazole, N-vinylpyrrolidone, etc. (e.g., N-vinyl-2-caprolactone and other lactamines). Monomers having a succinimide skeleton: for example, N-(meth)propenylioxymethylene succinimide, N-(meth)propenyli-6-oxyhexamethylene succinimide, N-(meth)propenyli-8-oxyhexamethylene succinimide, etc. Maleimides: for example, N-cyclohexylmaleimide, N-isopropylmaleimide, N-laurylmaleimide, N-phenylmaleimide, etc. Iconioids: such as N-methyl iconioid, N-ethyl iconioid, N-butyl iconioid, N-octyl iconioid, N-2-ethylhexyl iconioid, N-cyclohexyl iconioid, N-lauryl iconioid, etc. (Meth)acrylate aminoalkyl esters: for example, (meth)acrylate aminoethyl ester, (meth)acrylate N,N-dimethylaminoethyl ester, (meth)acrylate N,N-diethylaminoethyl ester, (meth)acrylate tributylaminoethyl ester. Monomers containing alkoxy groups: for example, 2-methoxyethyl acrylate, 3-methoxypropyl acrylate, 2-ethoxyethyl acrylate, propoxyethyl acrylate, butoxyethyl acrylate, ethoxypropyl acrylate, and other alkoxyalkyl esters of methacrylate; methoxyethylene glycol acrylate, methoxypolypropylene glycol acrylate, and other alkoxyalkyl glycol esters of methacrylate. Ethylene esters: such as vinyl acetate, vinyl propionate, etc. Vinyl ethers: For example, vinyl alkyl ethers such as methyl vinyl ether or ethyl vinyl ether. Aromatic vinyl compounds: for example, styrene, α-methylstyrene, vinyltoluene, etc. Olefins: such as ethylene, butadiene, isoprene, isobutene, etc. (Meth)acrylates having alicyclic hydrocarbon groups: for example, cyclopentyl (meth)acrylate, cyclohexyl (meth)acrylate, isopropyl (meth)acrylate, dicyclopentyl (meth)acrylate, etc. (Meth)acrylates having aromatic hydrocarbon groups: for example, phenyl (meth)acrylate, phenoxyethyl (meth)acrylate, benzyl (meth)acrylate, etc. And (meth)acrylates containing heterocyclic rings, such as tetrahydrofurfuryl (meth)acrylate; (meth)acrylates containing halogen atoms, such as (meth)acrylates containing vinyl chloride or fluorine atoms; (meth)acrylates containing silicon atoms, such as silicone methacrylate; and (meth)acrylates obtained from terpene compound derivative alcohols.

[0049] The monomer components constituting acrylic polymers may or may not include the aforementioned other comonomers. Furthermore, the amount of these other comonomers can be appropriately selected according to the purpose and application, and there is no particular limitation. The content of other comonomers in the monomer components is, for example, appropriately set to less than 50% by weight (e.g., less than 30% by weight), preferably less than 10% by weight, more preferably less than 5% by weight, and may be set to less than 3% by weight (e.g., less than 1% by weight). The technology disclosed herein can be preferably implemented with the monomer components substantially free of other comonomers.

[0050] The biomass carbon ratio of the monomer components constituting the aforementioned acrylic polymer (the biomass carbon ratio of the acrylic polymer) can be, for example, 1% or more, appropriately 10% or more, preferably 30% or more, more preferably 50% or more (e.g., exceeding 50%), or 60% or more, or 65% or more, or 70% or more, or 80% or more, or 90% to 100%. Through this design, an acrylic adhesive that takes into account the reduction of dependence on fossil-based materials can be obtained.

[0051] There are no particular limitations on the method for obtaining acrylic polymers, and various polymerization methods known as synthesis methods for acrylic polymers, such as solution polymerization, emulsion polymerization, bulk polymerization, suspension polymerization, and photopolymerization, can be appropriately employed. For example, solution polymerization is preferred. From the viewpoint of transparency or adhesive properties, solution polymerization may be advantageous. The monomer supply method during solution polymerization can appropriately employ a one-time addition method that supplies all monomer raw materials at once, a continuous supply (droplet addition) method, or a batch supply (droplet addition) method. The polymerization temperature during solution polymerization can be appropriately selected according to the type of monomer and solvent used, the type of polymerization initiator, etc., for example, it can be set to about 20°C to 170°C (typically, about 40°C to 140°C).

[0052] The solvent used for solution polymerization (polymerization solvent) can be appropriately selected from previously known organic solvents (toluene, ethyl acetate, etc.). The initiator used for polymerization can be appropriately selected from previously known polymerization initiators (e.g., azo-based polymerization initiators such as 2,2'-azobisisobutyronitrile (AIBN) or peroxide-based initiators, depending on the type of polymerization method). The amount of polymerization initiator used is the usual amount, for example, it can be selected from a range of approximately 0.005 to 1 part by weight relative to 100 parts by weight of monomer (typically approximately 0.01 to 1 part by weight).

[0053] While not specifically limited, the weight-average molecular weight (Mw) of acrylic polymers is generally preferably 10 × 10⁴ or higher. Acrylic polymers with this Mw readily exhibit adhesive properties exhibiting good cohesiveness. In some cases, from the viewpoint of peelability and cohesive strength, the Mw of the acrylic polymer is, for example, preferably 30 × 10⁴ or higher, preferably 50 × 10⁴ or higher, and can be 70 × 10⁴ or higher, or even exceeding 100 × 10⁴, 110 × 10⁴ or higher, 120 × 10⁴ or higher, or 130 × 10⁴ or higher. By setting the Mw of the acrylic polymer to a specific value or higher, the cohesive strength of the adhesive is enhanced, and it is easier to prevent paste residue from forming on the surface of the adherend. Furthermore, from the viewpoint of adhesion to the adherend, the Mw of acrylic polymers is generally suitable to be approximately 500 × 10⁴ or less, possibly 300 × 10⁴ or less, or even 100 × 10⁴ or less (e.g., less than 100 × 10⁴). By setting the Mw below a specific value, the adhesive exhibits moderate fluidity, making it easier to achieve good wetting (adhesion) to the adherend. With good wetting properties, for example in surface protection applications, the protective film will not peel off from the adherend during use, thus better fulfilling its protective function. For acrylic polymers obtained by solution polymerization, an Mw within the aforementioned preferred range is particularly significant.

[0054] The molecular weight (Mw) of acrylic polymers can be determined by gel permeation chromatography (GPC) and expressed as a value converted from standard polystyrene. Specifically, a commercial product named "HLC-8220GPC" (manufactured by Tosoh Corporation) can be used as the GPC measuring device, and the value can be determined under the conditions described below. The same applies to the examples described below. [GPC Measurement Conditions] Sample concentration: 0.1% by weight (tetrahydrofuran solution) Sample injection volume: 10 μL Dissolution solution: Tetrahydrofuran (THF) Flow rate: 1.0 mL / min Column temperature (measurement temperature): 40℃ Tube column: Sample columns: 1 "TSKguardcolumn SuperHZ-H" + 2 "TSKgel SuperHZM-H" (manufactured by Tosoh Corporation) Reference tubing: 1 piece of product named "TSKgel SuperH-RC" (manufactured by Tosoh Corporation) Detector: Differential refractometer (RI) Standard sample: polystyrene

[0055] (Cross-linking agent) The adhesive composition disclosed herein includes a crosslinking agent. The crosslinking agent can be used to improve the cohesive strength of the adhesive. The crosslinking agent can be selected from various crosslinking agents known in the field of adhesives. Examples of such crosslinking agents include: epoxy crosslinking agents, isocyanate crosslinking agents, aziridine crosslinking agents, melamine crosslinking agents, peroxide crosslinking agents, urea crosslinking agents, metal alkoxide crosslinking agents, metal chelate crosslinking agents, metal salt crosslinking agents, carbodiimide crosslinking agents, amine crosslinking agents, etc. One crosslinking agent can be used alone or in combination of two or more. The crosslinking agent can be derived from biomass or non-biomass. From the viewpoint of producing acrylic adhesives that take into account reducing dependence on fossil-based materials, it is preferable to use crosslinking agents derived from biomass. The technology disclosed herein can be preferably implemented in a manner where both the acrylic polymer and the crosslinking agent contained in the adhesive composition are derived from biomass.

[0056] There is no particular limitation on the amount of crosslinking agent used. The amount of crosslinking agent can be selected from, for example, 0.1 to 20 parts by weight relative to 100 parts by weight of the acrylic polymer. From the viewpoint of achieving a good balance between improved cohesiveness and adhesion to the adherend, the amount of crosslinking agent relative to 100 parts by weight of the acrylic polymer is generally preferably 15 parts by weight or less, specifically 10 parts by weight or less, 8 parts by weight or less, or 7 parts by weight or less. Alternatively, it can be appropriately set to 0.5 parts by weight or more, or 1 part by weight or more. By setting the amount of crosslinking agent within an appropriate range, the cohesiveness of the adhesive can be improved, paste residue on the adherend can be prevented, and adhesion to the adherend can be obtained.

[0057] In some applications, the crosslinking agent preferably includes at least an epoxy-based crosslinking agent. One epoxy-based crosslinking agent may be used alone or in combination of two or more. The epoxy-based crosslinking agent may be derived from biomass or non-biomass. From the viewpoint of producing acrylic adhesives that take into account reducing dependence on fossil-based materials, it is preferable to use a biomass-derived epoxy-based crosslinking agent. Furthermore, epoxy-based crosslinking agents may also be used in combination with other crosslinking agents, such as isocyanate-based crosslinking agents.

[0058] Epoxy crosslinking agents can be used without particular restriction as compounds having two or more epoxy groups in one molecule. Preferably, epoxy crosslinking agents have three to five epoxy groups in one molecule. One epoxy crosslinking agent can be used alone or in combination of two or more. Specific examples of epoxy crosslinking agents include: N,N,N',N'-tetraglycidyl-m-phenylenediamine, 1,3-bis(N,N-diglycidylaminomethyl)cyclohexane, 1,6-hexanediol diglycidyl ether, polyethylene glycol diglycidyl ether, polyglycerol polyglycidyl ether, etc. Commercially available epoxy crosslinking agents include: products named "TETRAD-C" and "TETRAD-X" manufactured by Mitsubishi Gas Chemical Co., Ltd.; products named "Epiclon CR-5L" manufactured by DIC Corporation; products named "Denacol EX-512" manufactured by Nagase Chemical Co., Ltd.; and products named "TEPIC-G" manufactured by Nissan Chemical Industries Co., Ltd.

[0059] The amount of epoxy crosslinking agent used relative to 100 parts by weight of acrylic polymer can be approximately 0.1 parts by weight or more, or 0.5 parts by weight or more, or 1.0 parts by weight or more, or even more than 1.5 parts by weight. From the viewpoint of achieving a higher performance effect, the amount of epoxy crosslinking agent used relative to 100 parts by weight of acrylic polymer can be, for example, more than 2.0 parts by weight, or 2.5 parts by weight or more, or 3.0 parts by weight or more, or 3.5 parts by weight or more. Furthermore, the amount of epoxy crosslinking agent used relative to 100 parts by weight of acrylic polymer is typically appropriately set to 20 parts by weight or less, but can be 10 parts by weight or less, or 8 parts by weight or less, or 6 parts by weight or less, or even 5 parts by weight or less (e.g., less than 5 parts by weight). By setting the amount of epoxy crosslinking agent used within an appropriate range, the cohesive force of the adhesive can be improved, making it easy to adjust to a good, peelable adhesion. Furthermore, suppressing the increase in adhesion over time prevents the formation of paste residue on the adherends and achieves tight adhesion to the adherends. Additionally, by limiting the amount of epoxy crosslinking agent used, a transparent adhesive can be easily formed.

[0060] In some samples, from the perspective of suppressing the increase of high-speed peeling over time, the amount of epoxy crosslinking agent used can exceed 4 parts by weight, or more than 4.5 parts by weight, or more than 5 parts by weight, or more than 5.5 parts by weight, relative to 100 parts by weight of acrylic polymer.

[0061] When using carboxyl-containing monomers (e.g., (meth)acrylic acid) and epoxy crosslinking agents, the ratio (WB / WA) of the amount of epoxy crosslinking agent used (WB) to the amount of carboxyl-containing monomers used (or their total amount when using two or more carboxyl-containing monomers) (by weight) is not particularly limited. However, from the viewpoint of improving the cohesive strength of the adhesive, it is preferably 0.7 or more, more preferably 0.8 or more, and even more preferably 0.9 or more (e.g., 1.0 or more), and particularly preferably 1.1 or more. Furthermore, the above ratio (WB / WA) is generally 3.0 or less, but may be 2.0 or less, 1.8 or less, 1.6 or less, 1.4 or less, or 1.3 or less.

[0062] Isocyanate-based crosslinking agents are suitable for use as polyisocyanate-based crosslinking agents having two or more isocyanate groups per molecule. The number of isocyanate groups per molecule of the polyisocyanate-based crosslinking agent is preferably 2 to 10, for example, 2 to 4, typically 2 or 3. Examples of such polyisocyanate-based crosslinking agents include: aromatic polyisocyanates such as toluene diisocyanate and xylene diisocyanate; alicyclic isocyanates such as isophorone diisocyanate; and aliphatic polyisocyanates such as hexamethylene diisocyanate. More specifically, examples include: lower aliphatic polyisocyanates such as butyl diisocyanate, pentamethyl diisocyanate, and hexamethylene diisocyanate; alicyclic polyisocyanates such as cyclopentyl diisocyanate, cyclohexyl diisocyanate, and isophorone diisocyanate; aromatic diisocyanates such as 2,4-toluene diisocyanate, 4,4'-diphenylmethane diisocyanate, phenyl diisocyanate, and polymethylene polyphenyl diisocyanate; trimethylolpropane / toluene diisocyanate trimer adduct (manufactured by Tosoh, trade name "Coronate L"), trimethylolpropane / hexamethylene diisocyanate trimer adduct (manufactured by Tosoh, trade name "Coronate HL"), and isocyanurate derivatives of hexamethylene diisocyanate (manufactured by Tosoh, trade name "Coronate L"). Isocyanate adducts such as pentamethylene diisocyanate (manufactured by Mitsui Chemicals, trade name "Stabio D-370 N"), polyisocyanates such as polyether polyisocyanates and polyester polyisocyanates, adducts of these polyisocyanates with polyols, and polyisocyanates formed by multifunctionalizing these polyisocyanates through isocyanurate bonds, biuret bonds, urethane bonds, etc. For example, in applications where transparency of the adhesive is required, aliphatic diisocyanates such as pentamethylene diisocyanate and hexamethylene diisocyanate, or isocyanurates of these aliphatic diisocyanates, are preferred.

[0063] The adhesive composition disclosed herein may also include a catalyst. By using a catalyst, the curing reaction of the adhesive composition (typically, the crosslinking reaction of the aforementioned crosslinking agent) can be carried out efficiently, easily achieving stable adhesion from an early stage after the adhesive sheet is manufactured. The catalyst is also called a crosslinking catalyst. Examples of catalysts include: tin (Sn) compounds (tin-based catalysts), zirconium (Zr) compounds (zirconium-based catalysts), titanium (Ti) compounds (titanium-based catalysts), iron (Fe) compounds (iron-based catalysts), aluminum (Al) compounds (aluminum-based catalysts), zinc (Zn) compounds (zinc-based catalysts), and bismuth (Bi) compounds (bismuth-based catalysts). Typically, these are organometallic compounds with a metal at the active center, also called organometallic catalysts. One catalyst can be used alone or in combination of two or more. The technology disclosed herein can be implemented even without a catalyst.

[0064] Various previously known additives may be incorporated into the above adhesive composition as needed. Examples of such additives include: surface lubricants, leveling agents, adhesive-improving resins, plasticizers, softeners, fillers, colorants (pigments, dyes, etc.), antistatic agents, antioxidants, preservatives, light stabilizers, ultraviolet absorbers, polymerization inhibitors, silane coupling agents, etc. The content of these additives, as optional components, can be appropriately set according to the intended use. For example, if the amount of any of the above additives used is less than 10 parts by weight relative to 100 parts by weight of the acrylic polymer, it is appropriately set to approximately 3 parts by weight or less (e.g., approximately 1 part by weight or less).

[0065] (Form of adhesive composition) The form of the adhesive composition disclosed herein is not particularly limited, but it is preferably an aqueous adhesive composition or a solvent-based adhesive composition. Here, an aqueous adhesive composition refers to an adhesive composition in which the adhesive (adhesive layer forming component) is contained in a solvent (aqueous solvent) with water as the main component. This concept encompasses either a water-dispersible adhesive composition containing the adhesive dispersed in water or a water-soluble adhesive composition containing the adhesive dissolved in water. Furthermore, a solvent-based adhesive composition refers to an adhesive composition in which the adhesive is contained in an organic solvent. The organic solvent contained in the solvent-based adhesive composition can be one or more of the organic solvents (such as toluene or ethyl acetate) used in the above-mentioned solution polymerization without particular limitation. From the viewpoint of adhesive properties, the technology disclosed herein can be preferably implemented in the form of an adhesive layer formed by a solvent-based adhesive composition. The effects of the technique disclosed herein can be better achieved in a state having a solvent-based adhesive layer formed from a solvent-based adhesive composition.

[0066] (Gel fraction) The gel fraction of the adhesive composition disclosed herein after drying is preferably 70% or higher. Adhesives with a gel fraction of 70% or higher are less prone to deformation or damage such as dents caused by external forces during manufacturing, and are less likely to cause changes in appearance. Such adhesives are easily formed into adhesive sheets with smooth surfaces, and are therefore preferable when forming transparent adhesive sheets for inspection of the adhered objects through the adhesive sheet, allowing for high-precision inspection. Furthermore, by setting a higher gel fraction, it is easier to form an adhesive that exhibits light peel strength at low peel speeds, suppresses the increase in peel force at high peel speeds, and suppresses the increase in adhesion force over time. From this perspective, the aforementioned gel fraction is preferably greater than 80%, and can exceed 85% (e.g., 90% or higher). The aforementioned gel fraction can be 100%, but from the viewpoint of adhesion to the adhered objects, it may not reach 99%, or even 95% (e.g., 94% or lower). The drying conditions for the adhesive composition used to determine the above-mentioned gel fraction were 130°C for 3 minutes. Specifically, the above-mentioned gel fraction was determined using the method described in the following examples. The gel fraction of the adhesive composition after drying can be the gel fraction of the adhesive (layer), therefore the gel fraction of the adhesive (layer) constituting the adhesive sheet can also be set from the above range.

[0067] (Biomass carbon ratio) In some formulations, the adhesive composition contains biomass-derived materials, and the biomass carbon ratio of its non-volatile components (also the biomass carbon ratio of the adhesive) can be a specific value or higher. For example, the biomass carbon ratio of the non-volatile components of the adhesive composition can be 1% or higher, 10% or higher, preferably 30% or higher, and more preferably 50% or higher. A higher biomass carbon ratio of the adhesive means that less fossil fuel materials, such as petroleum, are used. From this perspective, the higher the biomass carbon ratio of the adhesive, the better. For example, the biomass carbon ratio of the non-volatile components of the adhesive composition can be 55% or higher, 60% or higher, 65% or higher, 70% or higher, 75% or higher, 80% or higher, or even exceed 80%. The upper limit of the biomass carbon ratio is defined as 100%, but it can be below 99%. From the viewpoint of material availability, it can be below 95% or even below 90%. From the viewpoint of easily achieving good adhesive properties, in some formulations, the biomass carbon ratio of the non-volatile components of the adhesive composition can be, for example, below 90%, below 85%, or even below 80%.

[0068] <Adhesive Sheets> According to this specification, an adhesive sheet is provided, which has an adhesive layer formed by any of the adhesive compositions disclosed herein. The adhesive sheet may be a substrate-attached adhesive sheet having the adhesive layer in the form of the adhesive layer on one or both sides of a non-peelable substrate (supporting substrate), or a substrate-free adhesive sheet (i.e., an adhesive sheet without a non-peelable substrate) in which the adhesive layer is held in place by a release liner. The adhesive sheet disclosed herein exhibits light peelability at low peel speeds and suppresses the increase in peel force at high peel speeds, thus making it easy to peel regardless of the peel speed. Furthermore, it has a tendency to suppress the increase in adhesion force over time. Therefore, it is suitable as a surface protective film for peeling after use.

[0069] FIG1 schematically illustrates the construction of an adhesive sheet according to one embodiment. The adhesive sheet 1 is configured as a single-sided adhesive sheet with a substrate, comprising a sheet-like support substrate (e.g., a resin film) 10 having a first surface 10A and a second surface 10B, and an adhesive layer 21 disposed on the first surface 10A side. The adhesive layer 21 is fixedly disposed on the first surface 10A side of the support substrate 10, meaning it is not intended to separate from the support substrate 10. This single-sided adhesive sheet 1 is suitable as a surface protective film for attaching its adhesive surface to the surface of an adhered object (a protected object, such as an optical component like a polarizing plate). As shown in FIG1, the adhesive sheet 1 before use can be a component of an adhesive sheet 100 with a release liner, in which the surface (adhesive surface) 21A of the adhesive layer 21 is protected by a release liner 31, at least on the side opposite to the adhesive layer 21, which is a release surface. Alternatively, it can be in the following form (roll form): the release liner 31 is omitted, and the support substrate 10 with the second side 10B as the release surface is used. By winding the adhesive sheet 1, the adhesive surface 21A is protected by contacting the second side (back side) 10B of the support substrate 10.

[0070] The aforementioned release liner (also known as release film) can be used for release liners with a release layer on the surface of a liner substrate such as a resin film or paper, or for release liners containing low-adhesion materials such as polyolefin resins (e.g., polyethylene, polypropylene) or fluorine resins. The release layer can be formed, for example, by surface treatment of the liner substrate with release agents such as silicone-based, long-chain alkyl-based, fluorine-based, or molybdenum sulfide. The liner substrate, similar to the substrate of the adhesive sheet described below, is suitable for use with materials formed from biomass or reusable materials (reusable films, etc.).

[0071] Furthermore, the concept of adhesive sheets here can include those referred to as adhesive tape, adhesive labels, adhesive films, etc. Adhesive sheets can be in roll form or in single sheet form. They can also be processed into various shapes and forms.

[0072] The formation of an adhesive (layer) from an adhesive composition can be carried out by previously known methods. For example, in the case of a double-sided adhesive sheet without a substrate, the adhesive sheet can be formed by applying an adhesive composition to a peelable surface (peel surface), and then hardening the adhesive composition to form an adhesive layer (a layer containing adhesive) on that surface. Alternatively, in the case of an adhesive sheet with a substrate, it is preferable to use the following method (direct method): forming an adhesive layer by directly applying (typically coating) an adhesive composition to the substrate and allowing it to harden. Another method (transfer method) can also be used: forming an adhesive layer on a peelable surface (peel surface) by applying an adhesive composition to it and allowing it to harden, and then transferring the adhesive layer to the substrate. The peel surface can be the surface of a release liner or the back of a peeled substrate, etc. Furthermore, the curing of the above-mentioned adhesive composition can be achieved by subjecting the adhesive composition to curing treatments such as drying, crosslinking, polymerization, and cooling. Two or more curing treatments can be performed simultaneously or in stages.

[0073] The adhesive composition can be coated using known or conventional coating machines such as gravure roller coaters, reverse roller coaters, contact roller coaters, dip roller coaters, die coaters, bar coaters, doctor blade coaters, and spray coaters. Alternatively, the adhesive composition can be coated using methods such as dip coating or curtain coating. From the perspective of promoting cross-linking reactions and improving manufacturing efficiency, the drying of the adhesive composition is preferably carried out under heat. The drying temperature can be set to around 40~150°C, and is usually preferably set to around 60~130°C. After the adhesive composition is dried, aging can be performed for purposes such as adjusting the component transfer within the adhesive layer, carrying out cross-linking reactions, and mitigating any possible strain within the substrate or adhesive layer.

[0074] While not particularly limited, the thickness of the adhesive layer is, for example, appropriately approximately 1 μm or more, preferably approximately 3 μm or more (e.g., approximately 5 μm or more). From the viewpoint of adhesion to the adhered object, the above-mentioned thickness is preferably approximately 10 μm or more, more preferably approximately 14 μm or more, and even more preferably approximately 17 μm or more. Furthermore, the above-mentioned thickness can be, for example, approximately 100 μm or less, appropriately approximately 50 μm or less (e.g., approximately 30 μm or less), and preferably approximately 25 μm or less. An adhesive layer having the above-mentioned thickness is suitable as an adhesive layer for use as a surface protective film.

[0075] (Substrate) The material used as the support substrate for the adhesive sheet disclosed herein is not particularly limited; for example, a resin film may be preferred. The resin film may be formed by molding various resin materials into a film shape. Preferably, the resin material is one that exhibits excellent properties in one or more of the following: transparency, mechanical strength, thermal stability, water resistance, and isotropy. For example, a resin film comprising a resin material mainly composed of polyesters such as polyethylene terephthalate (PET), polyethylene naphthalate (PEN), and polybutylene terephthalate, celluloses such as diacetyl cellulose and triacetyl cellulose, polycarbonate, and acrylic polymers such as polymethyl methacrylate (i.e., containing more than 50% by weight of the component) may be used as the substrate. Other examples of resin materials constituting the above-mentioned resin film include those with the following main components: styrene-based polymers such as polystyrene and acrylonitrile-styrene copolymers; polyolefins (e.g., polyethylene, polypropylene, cyclic or non-olefinic polyolefins, ethylene-propylene copolymers, etc.); polyvinyl chloride; nylon 6, nylon 6,6, aromatic polyamides, etc. Alternatively, a resin film containing resin materials with polyimides, polyurethanes, polyether ethers, polyether ether ketones, polyphenylene sulfides, fluorinated resins, polyvinyl alcohol, polyvinyl acetate, polyvinylidene chloride, polyvinyl butyral, polyarylates, polyoxymethylene, epoxy resins, etc., as main components can be used as a substrate. The resin material constituting the above-mentioned resin film can be a blend of two or more of these components.

[0076] Furthermore, in this specification, "resin membrane" refers to a non-porous structure, typically meaning a resin membrane that is substantially free of air bubbles (no voids). Therefore, the above-mentioned resin membrane is a concept distinct from foamed membranes or non-woven and woven fabrics.

[0077] Other examples of substrates include: foam sheets containing foams such as polyurethane foam, polyethylene foam, and polychloroprene foam; woven and non-woven fabrics made of various fibrous materials (such as natural fibers like hemp and cotton, synthetic fibers like polyester and vinylon, and semi-synthetic fibers like acetate); paper such as Japanese paper, high-grade paper, kraft paper, and crepe paper; metal foils such as aluminum foil and copper foil; and glass. Substrates incorporating these compositions are also possible. Examples of substrates with such composite structures include: substrates with a structure in which metal foil and the aforementioned plastic film are laminated; and plastic sheets reinforced with inorganic fibers such as glass cloth.

[0078] The substrate can be formed from biomass-derived materials or from non-biomass-derived materials. From the perspective of manufacturing adhesive sheets that take into account reducing dependence on fossil-derived materials, it is preferable to use biomass-derived substrate materials (typically resin films).

[0079] Furthermore, the substrate can be formed using reusable or recycled materials (also known as reusable materials). Resin films are suitable for use as reusable materials. Resin films (such as polyester films like PET films) are reusable; therefore, regardless of whether plant-derived materials are used, the used resin film can be reused, enabling sustainable production and reducing environmental impact. Such reusable or recycled resin films are also called reusable films. The aforementioned reusable materials (e.g., reusable films) can be formed from biomass-derived materials or from non-biomass-derived materials.

[0080] In some preferred embodiments, a resin film (polyester resin film) formed by molding a resin (polyester resin) with polyester as the main component (containing more than 50% by weight) into a film is used as the substrate. For example, the resin film (PET film) with PET as the main polyester component or the resin film (PEN film) with PEN as the main polyester component can be preferably used.

[0081] The substrate can be a single layer or a multilayer structure. Therefore, the resin film that can be used as a substrate can also be a single layer or a multilayer structure with two or more layers (e.g., a three-layer structure). A single-layer resin film is preferred as the substrate.

[0082] The aforementioned substrate (typically a resin film) can be formulated with various additives such as antioxidants, ultraviolet absorbers, antistatic components, plasticizers, and colorants (pigments, dyes, etc.) as needed.

[0083] Surface treatments such as chromic acid treatment, ozone exposure, flame exposure, high-voltage electric shock exposure, and ionization radiation treatment can be applied to the adhesive layer side surface of the substrate. Such surface treatments can, for example, improve the adhesion between the substrate and the adhesive layer. In some embodiments, a primer treatment can be applied to the adhesive layer side surface of the substrate. From the viewpoint of adhesion to silicone-based adhesives, a silicone primer treatment is preferred. In some embodiments, a hard coating treatment can be applied to the back side of the substrate. This improves the scratch resistance of the back side of the substrate, providing superior protective performance when using adhesive sheets as protective sheets. Furthermore, in other embodiments, from the viewpoint of suppressing static electricity generation, the substrate can undergo antistatic treatment. Additionally, the substrate can undergo various treatments such as anti-fouling, anti-fingerprint adhesion, anti-glare, and anti-reflective treatments.

[0084] The thickness of the substrate can be appropriately selected considering the purpose, intended use, and application of the adhesive sheet. In terms of strength and workability, a substrate thickness of approximately 10 μm or more is suitable, preferably approximately 20 μm or more, and more preferably approximately 30 μm or more (e.g., 35 μm or more). Furthermore, from a cost perspective, a substrate thickness of approximately 200 μm or less is suitable, preferably approximately 150 μm or less, more preferably approximately 100 μm or less, and even more preferably approximately 75 μm or less (e.g., 50 μm or less). Substrates with the above thicknesses are suitable, for example, as substrates for surface protective films.

[0085] (characteristic) <Initial adhesion force F0> In some preferred embodiments, the initial low-speed adhesion force (F0 Low) of the fully aged adhesive sheet (preferably a surface protective film) measured at a tensile speed of 300 mm / min is preferably 3.0 N / 25 mm or less. Here, the aging of the adhesive sheet can be performed, for example, by storing the adhesive sheet at 50°C for 3 days. The adhesive sheet (preferably a surface protective film) that meets this characteristic is easy to peel because it suppresses the increase in adhesion force over time and the peel force when peeled from the adhered object (e.g., the protected object) is suppressed to be low. From the viewpoint of peelability, the initial low-speed adhesion force (F0 Low) is more preferably 1.0 N / 25 mm or less (e.g., 0.2 N / 25 mm or less), more preferably 0.14 N / 25 mm or less (e.g., less than 0.14 N / 25 mm), and particularly preferably 0.12 N / 25 mm or less (e.g., 0.1 N / 25 mm or less). From the viewpoint of adhesion to the adherend or protection of the adherend, the aforementioned initial low-speed adhesion force (F0 Low) is appropriately 0.01 N / 25 mm or more, and may be 0.03 N / 25 mm or more, or may be 0.05 N / 25 mm or more. Specifically, the aforementioned initial low-speed adhesion force (F0 Low) is measured using the method described in the following examples.

[0086] In some preferred embodiments, the initial high-speed adhesion force (F0 High) of the fully aged adhesive sheet (preferably a surface protective film) measured at a tensile speed of 30 m / min is preferably 5.0 N / 25 mm or less. Here, the aging of the adhesive sheet can be performed, for example, by storing the adhesive sheet at 50°C for 3 days. Adhesive sheets that meet this characteristic tend to exhibit excellent peelability regardless of the peeling speed because the peeling force is suppressed when peeling from the adherend at a relatively fast speed. From the viewpoint of peelability, the initial high-speed adhesion force (F0 High) is more preferably 3.0 N / 25 mm or less (e.g., 2.0 N / 25 mm or less), more preferably 1.5 N / 25 mm or less, and particularly preferably 1.2 N / 25 mm or less (e.g., 1.0 N / 25 mm or less). From the viewpoint of adhesion to the adherend or protection of the adherend, the aforementioned initial high-speed adhesion (F0 High) is appropriately 0.1 N / 25 mm or more, and may be 0.3 N / 25 mm or more, or may be 0.5 N / 25 mm or more. Specifically, the aforementioned initial high-speed adhesion (F0 High) is measured using the method described in the following examples.

[0087] <Adhesion Force F1 over Time> In some preferred embodiments, the fully aged adhesive sheet (preferably a surface protective film), after being bonded to the substrate and stored at 50°C for 7 days, preferably exhibits a low-speed adhesion force (F1 Low) of less than 3.0 N / 25 mm when measured at a tensile speed of 300 mm / min. Here, the aging of the adhesive sheet can be performed, for example, by storing the adhesive sheet at 50°C for 3 days. The adhesive sheet (preferably a surface protective film) that meets these characteristics is easy to peel off because it suppresses the increase in adhesion force over time and has a lower peel force when peeled from the substrate (e.g., the protected object). From the viewpoint of peelability, the aforementioned low-speed adhesion over time (F1 Low) is preferably 1.0 N / 25 mm or less (e.g., 0.2 N / 25 mm or less), more preferably 0.14 N / 25 mm or less (e.g., less than 0.14 N / 25 mm), and particularly preferably 0.12 N / 25 mm or less (e.g., 0.1 N / 25 mm or less). From the viewpoint of adhesion to the substrate or protection of the substrate, the aforementioned low-speed adhesion over time (F1 Low) is appropriately 0.01 N / 25 mm or more, may be 0.03 N / 25 mm or more, or may be 0.05 N / 25 mm or more. Specifically, the aforementioned low-speed adhesion over time (F1 Low) is measured using the method described in the following examples.

[0088] In some preferred embodiments, the time-dependent high-speed adhesion (F1 High) measured at a tensile speed of 30 m / min after the fully aged adhesive sheet (preferably a surface protective film) is bonded to the substrate and stored at 50°C for 7 days is preferably 5.0 N / 25 mm or less. Here, the aging of the adhesive sheet can be performed, for example, by storing the adhesive sheet at 50°C for 3 days. Adhesive sheets that meet this characteristic tend to exhibit excellent peelability regardless of the peeling speed because the peeling force is suppressed when peeled from the substrate at a relatively fast speed. From the viewpoint of peelability, the time-dependent high-speed adhesion F1 High is more preferably 3.0 N / 25 mm or less (e.g., 2.0 N / 25 mm or less), more preferably 1.5 N / 25 mm or less, and particularly preferably 1.2 N / 25 mm or less (e.g., 1.0 N / 25 mm or less). From the viewpoint of adhesion to the adherend or protection of the adherend, the aforementioned high-speed adhesion over time (F1 High) is appropriately 0.1 N / 25 mm or more, may be 0.3 N / 25 mm or more, or may be 0.5 N / 25 mm or more. Specifically, the aforementioned high-speed adhesion over time (F1 High) is measured using the method described in the following examples.

[0089] In some applications, the adhesive sheet preferably has a transparency of approximately 50% or more of total light transmittance. More preferably, it is a transparent adhesive sheet with a total light transmittance of 80% or more (e.g., 85% or more). For applications requiring transparency, the upper limit of the total light transmittance can be around 99% or less (e.g., 95% or less). Adhesive sheets with this transparency are preferred, for example, when inspecting the adhered object through the adhesive sheet, allowing for high-precision inspection. This adhesive sheet is suitable as a surface protective film. The total light transmittance value can be obtained according to JIS K 7361-1.

[0090] <Application> Adhesive sheets having an adhesive layer formed by the adhesive composition disclosed herein can be used for various applications. The adhesive disclosed herein exhibits light peelability regardless of peeling speed and excellent peeling performance upon re-peeling. Therefore, it is suitable, for example, as a surface protective film that, after being applied to a protected object, is typically peeled off (re-peeled) from the protected object once its protective purpose is achieved. The protected object of the aforementioned surface protective film is not particularly limited and can be used as a protective film for various articles, parts, etc. For example, the surface protective film is particularly suitable as a surface protective film for protecting the surface of optical components (e.g., optical components used as components of liquid crystal display panels such as polarizers and waveplates) during processing or transportation. More specifically, the surface protective film is suitable for protecting optical components used as components of liquid crystal display panels, plasma display panels (PDPs), organic electroluminescent (EL) displays, etc., during manufacturing and transportation. In particular, it can be used as a surface protective film for optical components such as polarizing plates (polarizing films, such as reflective polarizing films), waveplates, phase retardation plates, optical compensation films, brightness enhancement films, light diffusion sheets, and reflective sheets used in liquid crystal display panels.

[0091] Furthermore, the adhesive compositions disclosed herein may contain acrylic polymers with a high biomass ratio in some forms, thus helping to reduce dependence on fossil-based materials by using them in various applications instead of conventional acrylic adhesives (i.e., acrylic adhesives with a low biomass ratio). Typically, the adhesive sheets disclosed herein are suitable for use as adhesive sheets (e.g., surface protective films) to reduce dependence on fossil-based materials. [Example]

[0092] The following describes some embodiments related to the present invention, but it is not intended to limit the invention to those embodiments. Furthermore, unless otherwise specified, "parts" in the following description are based on weight.

[0093] <Experimental Example 1> Preparation of Acrylic Polymers (Preparation Example A1) 95 parts of n-heptyl acrylate (HpA) and 5 parts of acrylic acid (AA), along with ethyl acetate (polymerization solvent), were added to a flask equipped with a reflux flask, stirrer, nitrogen inlet, and thermometer, with a solid content concentration of 30%. Then, 0.2 parts of azobisisobutyronitrile (AIBN) were added as a polymerization initiator. Nitrogen gas was introduced while stirring slowly, and the liquid temperature in the flask was maintained at approximately 60°C for 6 hours for polymerization. Afterward, the mixture was cured at 70°C for 2 hours to obtain a solution of acrylic polymer (A1). The weight average molecular weight (Mw) of the obtained acrylic polymer (A1) was 770,000. Furthermore, HpA is a compound synthesized using bio-derived heptyl alcohol, possessing a bio-derived heptyl group at the ester terminus.

[0094] (Preparation Example A2) 95 parts of heptyl acrylate (HpA) and 5 parts of acrylic acid (AA), along with ethyl acetate (polymerization solvent), were added to a flask equipped with a reflux flask, stirrer, nitrogen inlet, and thermometer, with a solid content concentration of 40%. Then, 0.2 parts of AIBN as a polymerization initiator were added. Nitrogen gas was introduced while stirring slowly, and the liquid temperature in the flask was maintained at approximately 60°C for 6 hours for polymerization. Afterward, the mixture was aged at 70°C for 2 hours to obtain a solution of acrylic polymer (A2). The Mw of the obtained acrylic polymer (A2) was 1.37 million. Furthermore, HpA is a compound synthesized using bio-derived heptyl alcohol, possessing a bio-derived heptyl group at the ester terminus.

[0095] (Preparation Example A3) 95 parts of n-butyl acrylate (BA) and 5 parts of acrylic acid (AA), along with ethyl acetate (polymerization solvent), were added to a flask equipped with a reflux flask, stirrer, nitrogen inlet, and thermometer, with a solids concentration of 30%. Then, 0.2 parts of AIBN, used as a polymerization initiator, were added. Nitrogen gas was introduced while stirring slowly, and the liquid temperature in the flask was maintained at approximately 60°C for 6 hours for polymerization. Afterward, the mixture was cured at 70°C for 2 hours to obtain a solution of acrylic polymer (A3). The resulting acrylic polymer (A3) had a molecular weight of 820,000.

[0096] (Preparation Example A4) 95 parts of 2-ethylhexyl acrylate (2EHA), 5 parts of acrylic acid (AA), and ethyl acetate (polymerization solvent) were added to a flask equipped with a reflux flask, stirrer, nitrogen inlet, and thermometer, with a solid content concentration of 40%. Then, 0.2 parts of AIBN as a polymerization initiator were added. Nitrogen gas was introduced while stirring slowly, and the liquid temperature in the flask was maintained at approximately 60°C for 6 hours for polymerization. Afterward, the mixture was cured at 70°C for 2 hours to obtain a solution of acrylic polymer (A4). The Mw of the obtained acrylic polymer (A4) was 770,000.

[0097] <Example 1> (Preparation of adhesive composition) The acrylic polymer (A1) obtained in Preparation Example A1 was diluted with ethyl acetate until the solid content concentration reached 22%. An epoxy crosslinking agent (B1) (manufactured by Mitsubishi Gas Chemical Co., Ltd., trade name "Tetrad C") was added to the solution at a ratio of 6 parts (solid content) to 100 parts of the solid content of the solution and stirred to obtain the acrylic adhesive composition of this example.

[0098] (Production of adhesive sheet) The aforementioned freshly prepared acrylic adhesive composition was coated onto a polyethylene terephthalate (PET) film (38 μm thick), and dried at 130°C for 3 minutes to remove the solvent, thereby forming an adhesive layer (21 μm thick). Subsequently, a release film was used to cover the surface of the adhesive layer, and the film was aged at 50°C for 3 days to obtain the adhesive sheet of this example.

[0099] <Example 2> Except that the acrylic polymer used was changed to the acrylic polymer (A2) obtained in Preparation Example A2, the adhesive composition was prepared in the same manner as in Example 1, and the adhesive sheet of this example was obtained by using the adhesive composition in the same manner as in Example 1.

[0100] <Comparative Example 1> Except that the acrylic polymer used was changed to the acrylic polymer (A3) obtained in Preparation Example A3, the adhesive composition was prepared in the same manner as in Example 1, and the adhesive sheet of this example was obtained by using the adhesive composition in the same manner as in Example 1.

[0101] <Comparative Example 2> Except that the acrylic polymer used was changed to the acrylic polymer (A4) obtained in Preparation Example A4, the adhesive composition was prepared in the same manner as in Example 1, and the adhesive sheet of this example was obtained by using the adhesive composition in the same manner as in Example 1.

[0102] <Evaluation> (Adhesive gel fraction) A freshly prepared adhesive composition solution was coated onto a PET film (38 μm thick) that had undergone peeling treatment. The film was then dried at 130°C for 3 minutes to remove the solvent, thus forming an adhesive layer (21 μm thick). W1 (g) was extracted from the formed adhesive layer and encapsulated in a porous PTFE (Polytetrafluoroethylene) sheet to prepare a sample. The sample was placed in a glass bottle, immersed in ethyl acetate solution, and allowed to stand for 7 days. The sample was then removed and dried at 130°C for 2 hours. The dried sample was weighed, and the weight of the porous PTFE sheet was subtracted to determine the dried adhesive weight W2 (g). Substituting W1 and W2 into the following formula, the gel fraction [%] was calculated. Gel fraction [%] = (W2 / W1) × 100 Porous PTFE sheets may be made from products manufactured by Nitto Denko Corporation under the name "TEMISH" or equivalent products.

[0103] (Initial adhesion force F0 to the glass) Prepare multiple adhesive sheets, cut to a width of 25 mm and a length of 80 mm. Clean them by wiping them 10 times with a clean cloth soaked in ethanol. Press a 2 kg roller onto the clean sodium glass plate obtained by rolling and reciprocating once to prepare an adhesion evaluation sample. After placing the evaluation sample at room temperature for 30 minutes, use a high-speed peel tester to measure the adhesion [N / 25 mm] under the conditions of a peel angle of 180° and a tensile speed of 300 m / min and a peel angle of 180° and a tensile speed of 30 m / min. The glass plate used as the adherend is a sodium glass plate (trade number "S200423") or equivalent manufactured by Matsunami Glass Co., Ltd. The high-speed peel tester used is a product named "VPA-H200" or equivalent manufactured by Kyowa Interface Science Co., Ltd.

[0104] (The force F1 applied to the glass over time) Prepare multiple adhesive sheets, cut to a width of 25 mm and a length of 80 mm. Clean them by wiping them 10 times with a clean cloth soaked in ethanol. Press a 2 kg roller onto the clean sodium glass plate obtained by rolling and reciprocating once to prepare samples for adhesion evaluation. Place the above evaluation samples at 50°C for 7 days. After 7 days, remove the samples and let them stand at room temperature (23°C) for 1 hour. Then, use a high-speed peel tester to measure the adhesion [N / 25 mm] under the conditions of a peel angle of 180° and a tensile speed of 300 m / min and a peel angle of 180° and a tensile speed of 30 m / min. The glass plate used for the adherend is a sodium glass plate (trade number "S200423") or equivalent manufactured by Matsunami Glass Co., Ltd. The high-speed peel tester used is a product named "VPA-H200" or equivalent manufactured by Kyowa Interface Science Co., Ltd.

[0105] Table 1 summarizes each case and provides the evaluation results.

[0106] [Table 1] Table 1 Example 1 Example 2 Comparative Example 1 Comparative Example 2 acrylic polymers type A1 A2 A3 A4 monomer HpA / AA HpA / AA BA / AA 2EHA / AA Number of copies 100 100 100 100 Molecular weight (Mw) 77×10⁴ 137×10⁴ 82×10⁴ 77×10⁴ Crosslinking agent type B1 B1 B1 B1 Number of copies 6 6 6 6 Thickness of the adhesive layer [μm] twenty one twenty one twenty one twenty one Adhesive gel fraction [%] 97 99 99 97 Initial adhesion force to the glass F0 [N / 25 mm] low-speed peeling (300 mm / min) 0.07 0.07 0.18 0.14 High-speed peeling (30 m / min) 0.74 0.77 3.89 0.76 The contact force F1 [N / 25 mm] on the glass is measured over time. low-speed peeling (300 mm / min) 0.07 0.06 0.19 0.11 High-speed peeling (30 m / min) 0.67 0.64 3.41 0.49

[0107] As shown in Table 1, in Examples 1 and 2, which used adhesive compositions containing acrylic polymers comprising (meth)acrylate C5-18 linear alkyl esters as monomer components and crosslinking agents, compared with Comparative Example 1 using n-butyl acrylate and Comparative Example 2 using 2-ethylhexyl acrylate, the initial adhesion was lower at low-speed peeling, and a tendency to suppress the increase in adhesion was also observed at high-speed peeling. Furthermore, in Examples 1 and 2, which used adhesive compositions containing acrylic polymers comprising (meth)acrylate C5-18 linear alkyl esters as monomer components and crosslinking agents, the difference between the initial adhesion F0 and the adhesion over time F1 was small, suppressing the increase in adhesion over time.

[0108] <Experimental Example 2> Preparation of Acrylic Polymers (Preparation Example A5) 95 parts of heptyl acrylate (HpA) and 5 parts of acrylic acid (AA), along with ethyl acetate (polymerization solvent), were added to a flask equipped with a reflux flask, stirrer, nitrogen inlet, and thermometer, with a solid content concentration of 30%. Then, 0.3 parts of azobisisobutyronitrile (AIBN) were added as a polymerization initiator. Nitrogen gas was introduced while stirring slowly, and the liquid temperature in the flask was maintained at approximately 60°C for 2 hours for polymerization. Subsequently, the mixture was aged at 70°C for 6 hours to obtain a solution of acrylic polymer (A5). The weight average molecular weight (Mw) of the obtained acrylic polymer (A5) was 550,000. Furthermore, HpA is a compound synthesized using bio-derived heptyl alcohol, possessing a bio-derived heptyl group at the ester terminus.

[0109] <Example 3> (Preparation of adhesive composition) The acrylic polymer (A5) obtained in Preparation Example A5 was diluted with ethyl acetate until the solid content concentration reached 22%. An epoxy crosslinking agent (B1) (manufactured by Mitsubishi Gas Chemical Co., Ltd., trade name "Tetrad C") was added to the solution at a ratio of 6 parts (solid content) to 100 parts of the solid content of the solution and stirred to obtain the acrylic adhesive composition of this example.

[0110] (Production of adhesive sheet) The aforementioned freshly prepared acrylic adhesive composition was coated onto a polyethylene terephthalate (PET) film (38 μm thick), and dried at 130°C for 3 minutes to remove the solvent, thereby forming an adhesive layer (21 μm thick). Subsequently, a release film was used to cover the surface of the adhesive layer, and the film was aged at 50°C for 3 days to obtain the adhesive sheet of this example.

[0111] <Example 4> (Preparation of adhesive composition) The acrylic polymer (A5) obtained in Preparation Example A5 was diluted with ethyl acetate until the solid content concentration reached 22%. An epoxy crosslinking agent (B1) (manufactured by Mitsubishi Gas Chemical Co., Ltd., trade name "Tetrad C") was added to the solution at a ratio of 5 parts (solid content) to 100 parts of the solid content of the solution and stirred to obtain the acrylic adhesive composition of this example. (Production of adhesive sheet) Except that the acrylic adhesive composition of this example is used instead of the acrylic adhesive composition of Example 3, the adhesive sheet of this example is obtained by the same method as in Example 3.

[0112] <Example 5> (Preparation of adhesive composition) The acrylic polymer (A5) obtained in Preparation Example A5 was diluted with ethyl acetate until the solid content concentration reached 22%. An epoxy crosslinking agent (B1) (manufactured by Mitsubishi Gas Chemical Co., Ltd., trade name "Tetrad C") was added to the solution at a ratio of 4 parts (solid content) to 100 parts of the solid content of the solution and stirred to obtain the acrylic adhesive composition of this example. (Production of adhesive sheet) Except that the acrylic adhesive composition of this example is used instead of the acrylic adhesive composition of Example 3, the adhesive sheet of this example is obtained by the same method as in Example 3.

[0113] <Example 6> The acrylic polymer (A5) obtained in Preparation Example A5 was diluted with ethyl acetate until the solid content concentration reached 22%. An epoxy crosslinking agent (B1) (manufactured by Mitsubishi Gas Chemical Co., Ltd., trade name "Tetrad C") was added to the solution at a ratio of 6 parts (solid content) to 100 parts of the solid content of the solution and stirred to obtain the acrylic adhesive composition of this example.

[0114] (Production of adhesive sheet) The aforementioned freshly prepared acrylic adhesive composition was coated onto a polyethylene terephthalate (PET) film (38 μm thick), and dried at 130°C for 3 minutes to remove the solvent, thereby forming an adhesive layer (5 μm thick). Subsequently, a release film was used to cover the surface of the adhesive layer, and the film was aged at 50°C for 3 days to obtain the adhesive sheet of this example.

[0115] <Evaluation> Using the same method as in Example 1, the adhesive gel fraction, initial adhesion F0 to glass, and time-dependent adhesion F1 to glass in Examples 3-6 were determined. A summary of each example and the evaluation results are shown in Table 2.

[0116] [Table 2] Table 2 Example 3 Example 4 Example 5 Example 6 acrylic polymers type A5 A5 A5 A5 monomer HpA / AA HpA / AA HpA / AA HpA / AA Number of copies 100 100 100 100 Molecular weight (Mw) 55×10⁴ 55×10⁴ 55×10⁴ 55×10⁴ Crosslinking agent type B1 B1 B1 B1 Number of copies 6 5 4 6 Thickness of the adhesive layer [μm] twenty one twenty one twenty one 5 Adhesive gel fraction [%] 98 96 95 98 Initial adhesion force to the glass F0 [N / 25 mm] low-speed peeling (300 mm / min) 0.05 0.07 0.08 0.03 High-speed peeling (30 m / min) 0.41 0.42 0.69 0.16 The contact force F1 [N / 25 mm] on the glass is measured over time. low-speed peeling (300 mm / min) 0.05 0.07 0.08 0.03 High-speed peeling (30 m / min) 0.40 0.59 0.82 0.13

[0117] As shown in Tables 1 and 2, in Examples 3-6, which used adhesive compositions containing acrylic polymers comprising (meth)acrylate C5-18 linear alkyl esters as monomer components and crosslinking agents, compared with Comparative Example 1 using n-butyl acrylate and Comparative Example 2 using 2-ethylhexyl acrylate, the initial adhesion was lower at low-speed peeling, and even at high-speed peeling, a tendency to suppress the increase in adhesion was confirmed. Comparing the results of Examples 1-3, the tendency for the adhesion to change over time at high-speed peeling differed due to differences in the molecular weight (Mw) of the acrylic polymers. Furthermore, comparing the results of Examples 3-5, it was confirmed that by reducing the amount of crosslinking agent, the adhesion over time at high-speed peeling tended to increase. Furthermore, the results of Example 6 confirmed that even when the adhesive layer thickness was set to 5 μm, the effects of the present invention were still evident.

[0118] The specific examples of the present invention have been described in detail above, but these are merely illustrative and do not limit the scope of the patent application. The technology described in the patent application includes various changes and modifications made to the specific examples illustrated above.

[0119] 1: Adhesive sheet 10: Supporting substrate 10A: First page 10B: Second side (back side) 21: Adhesive layer 21A: Adhesive surface 31: Peeling the liner 100: Adhesive sheet with release liner

Claims

1. An adhesive composition comprising an acrylic polymer and an epoxy crosslinking agent, wherein the epoxy crosslinking agent has 3 to 5 epoxy groups in one molecule, and the acrylic polymer is a monomeric polymer comprising an alkyl (meth)acrylate having a straight-chain alkyl group having 5 to 11 carbon atoms at the ester terminus.

2. The adhesive composition of claim 1, wherein the monomeric component further comprises (meth)acrylic acid.

3. The adhesive composition of claim 1 or 2, wherein the above-mentioned alkyl (meth)acrylate having a straight-chain alkyl group having 5 to 11 carbon atoms at the ester terminus comprises n-heptyl acrylate.

4. An adhesive formed from an adhesive composition of any one of claims 1 to 3.

5. An adhesive sheet having an adhesive layer comprising an adhesive as claimed in claim 4.

6. An adhesive sheet having an adhesive layer with a gel content of more than 80%, wherein the adhesive layer is formed from an adhesive composition comprising an acrylic polymer and a crosslinking agent, wherein the acrylic polymer is a monomeric polymer comprising an alkyl (meth)acrylate having a straight-chain alkyl group having 5 to 11 carbon atoms at the ester terminus.

7. The adhesive sheet as claimed in claim 6, wherein the crosslinking agent comprises an epoxy crosslinking agent.

8. The adhesive sheet as claimed in claim 6 or 7, wherein the monomeric component further comprises (meth)acrylic acid.

9. A surface protective film comprising an adhesive sheet as claimed in any one of claims 5 to 8.

10. The surface protective film of claim 9, after aging at 50°C for 3 days, has an initial high-speed adhesion force of less than 3.0 N / 25 mm as measured at a tensile speed of 30 m / min.

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