Pressure-sensitive adhesive composition and surface protection film

Abstract

To provide an adhesive composition capable of forming an adhesive layer which has a high adhesive force (initial adhesive force), is excellent in followability to an adherend, hardly increases an adhesive force with time or under a high temperature and can be peeled off without an adhesive residue and to provide a surface protective film having the adhesive layer composed of the adhesive composition.SOLUTION: There is provided an adhesive composition comprising a styrene-based elastomer and a tackifier resin, wherein the styrene-based elastomer contains a styrene block copolymer having a structure represented by the general formula A-B or a hydrogenated product thereof (1) and a styrene block copolymer having a structure represented by the general formula (A-B)nC or a hydrogenated product thereof (2); the styrene block copolymer or the hydrogenated product thereof (1) has a weight average molecular weight (Mw1) of 50000 to 150000; the weight average molecular weight (Mw2) of the styrene block copolymer or the hydrogenated product thereof (2) is 2.5 times or more the weight average molecular weight (Mw1) of the styrene block copolymer or the hydrogenated product thereof (1); and the content of the styrene block copolymer or the hydrogenated product thereof (1) based on 100 wt.% of the styrene-based elastomer is 5 wt.% or more and 50 wt.% or less. A: an aromatic alkenyl polymer block, B: a conjugated diene polymer block, C: a component derived from a coupling agent, and n: an integer of 2 or more.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a pressure-sensitive adhesive composition capable of forming a pressure-sensitive adhesive layer that has high adhesive strength (initial adhesive strength), excellent conformability to an adherend, and is resistant to increasing adhesive strength over time or at high temperatures, and that can be peeled off without leaving any adhesive residue. The present invention also relates to a surface protection film having a pressure-sensitive adhesive layer made of the pressure-sensitive adhesive composition. [Background technology]

[0002] Conventionally, surface protection films (sometimes also referred to as protective tapes, etc.) having a base layer and a pressure-sensitive adhesive layer laminated on one side thereof have been widely used to protect the surfaces of components such as optical devices, metal plates, painted metal plates, resin plates, and glass plates (e.g., Patent Documents 1 to 3). In particular, surface protection films are used to protect the surfaces of optical components for liquid crystal displays. Some optical components, such as prism sheets and diffusion films, have an uneven surface on one or both sides, and in order to prevent damage to this uneven surface, the surfaces of the optical components are protected with a surface protection film before use.

[0003] Surface protection films are required to have high adhesive strength depending on the application. For example, when attached to an adherend having an uneven surface, a large contact area cannot be obtained, and peeling is likely to occur at the interface between the adherend and the surface protection film. In such applications, the surface protection film is required to have particularly high adhesive strength.

[0004] The use of styrene-based elastomers as pressure-sensitive adhesive layers for surface protection films has been investigated, but pressure-sensitive adhesive layers using styrene-based elastomers have the problem of insufficient adhesive strength when attached to adherends having uneven surfaces. In general, increasing the amount of tackifier resin in the adhesive layer is effective for improving adhesive strength. However, it is known that such adhesive layers, particularly when the adherend has an uneven surface, tend to have a problem of increased adhesive strength due to an increase in the contact area between the adherend and the adhesive layer over time or at high temperatures, which can lead to difficulty in peeling or the generation of adhesive residue. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 1-129085 [Patent Document 2] Japanese Patent Application Publication No. 6-1958 [Patent Document 3] Japanese Patent Application Publication No. 8-12952 Summary of the Invention [Problem to be solved by the invention]

[0006] An object of the present invention is to provide a pressure-sensitive adhesive composition capable of forming a pressure-sensitive adhesive layer that has high adhesive strength (initial adhesive strength), excellent conformability to an adherend, and that is resistant to increasing adhesive strength over time or at high temperatures, and that can be peeled off without leaving any adhesive residue. Another object of the present invention is to provide a surface protection film having a pressure-sensitive adhesive layer made of the pressure-sensitive adhesive composition. [Means for solving the problem]

[0007] The present invention relates to a pressure-sensitive adhesive composition containing a styrene-based elastomer and a tackifying resin, wherein the styrene-based elastomer is a styrene block copolymer (1) having a structure represented by the general formula AB or a hydrogenated product thereof, and a styrene block copolymer (2) having a structure represented by the general formula (AB) nand a styrene block copolymer or hydrogenated product thereof (2) having a structure represented by C, wherein the weight average molecular weight (Mw1) of the styrene block copolymer or hydrogenated product thereof (1) is 50,000 to 150,000, the weight average molecular weight (Mw2) of the styrene block copolymer or hydrogenated product thereof (2) is 2.5 times or more the weight average molecular weight (Mw1) of the styrene block copolymer or hydrogenated product thereof (1), and the content of the styrene block copolymer or hydrogenated product thereof (1) in 100% by weight of the styrene elastomer is 5% by weight or more and 50% by weight or less. A: Aromatic alkenyl polymer block B: Conjugated diene polymer block C: Components derived from coupling agents n: an integer of 2 or greater The present invention will be described in detail below.

[0008] In a surface protection film containing a pressure-sensitive adhesive layer made of a pressure-sensitive adhesive composition containing a styrene-based elastomer and a tackifier resin, increasing the storage modulus of the pressure-sensitive adhesive layer at high temperatures (around 80 to 120°C) is one way to prevent the adhesive strength from increasing over time or at high temperatures. Increasing the storage modulus of the pressure-sensitive adhesive layer at high temperatures can be achieved by increasing the molecular weight of the styrene-based elastomer, particularly the molecular weight of the hard segment of the styrene-based elastomer. However, increasing the molecular weight of the styrene-based elastomer increases the viscosity, making film formation difficult. Furthermore, increasing the storage modulus of the pressure-sensitive adhesive layer at room temperature (around 0 to 50°C) reduces adhesion when attached to an adherend, resulting in reduced adhesive strength (initial adhesive strength) and conformability to the adherend. In response to this, the present inventors have discovered a specific styrene elastomer, i.e., a styrene block copolymer having a structure represented by the general formula AB or a hydrogenated product thereof (1), and a copolymer of the general formula (AB) nThe inventors investigated the use of a styrene-based elastomer containing a styrene block copolymer having a structure represented by C or a hydrogenated product thereof (2). The inventors have found that by using such a styrene-based elastomer and adjusting its weight-average molecular weight and content within a specific range, it is possible to perform good film formation, and to improve the adhesion when attaching the pressure-sensitive adhesive layer to an adherend, thereby increasing the adhesive strength (initial adhesive strength), while suppressing the increase in adhesive strength over time or at high temperatures, thereby reducing adhesive residue. They have also found that it is possible to improve the conformability of the pressure-sensitive adhesive layer to the adherend. This has led to the completion of the present invention.

[0009] The pressure-sensitive adhesive composition of the present invention contains a styrene-based elastomer and a tackifying resin. The styrene elastomer is a mixture of a styrene block copolymer (1) having a structure represented by the general formula AB or a hydrogenated product thereof and a styrene block copolymer (2) having a structure represented by the general formula (AB) n and (2) a styrene block copolymer having a structure represented by C or a hydrogenated product thereof. By containing the styrene-based elastomer, the pressure-sensitive adhesive layer formed from the pressure-sensitive adhesive composition of the present invention has a relatively low storage modulus at room temperature and a relatively high storage modulus at high temperatures. Therefore, when the pressure-sensitive adhesive composition of the present invention contains the styrene-based elastomer and the weight-average molecular weight and content thereof are within the ranges described below, the pressure-sensitive adhesive layer has improved film-forming properties and increased adhesion when attached to an adherend, resulting in a high adhesive strength (initial adhesive strength). However, the adhesive strength is less likely to increase over time or even at high temperatures, allowing the pressure-sensitive adhesive layer to be peeled off without leaving any adhesive residue. In addition, the pressure-sensitive adhesive layer also has improved conformability to the adherend. A: Aromatic alkenyl polymer block B: Conjugated diene polymer block C: Components derived from coupling agents n: an integer of 2 or greater

[0010] The styrene block copolymer having a structure represented by the general formula (AB) or its hydrogenated product (1) is a linear styrene block copolymer having an aromatic alkenyl polymer block represented by the general formula (A) and a conjugated diene polymer block represented by the general formula (AB) or its hydrogenated product. n The styrene block copolymer or hydrogenated product thereof (2) having a structure represented by C is a branched (radial) styrene block copolymer or hydrogenated product thereof having a structure in which a plurality of linear styrene block copolymers or hydrogenated products thereof protrude radially from a coupling agent at the center.

[0011] The aromatic alkenyl polymer block represented by A has repeating units derived from an aromatic alkenyl compound. Examples of the aromatic alkenyl compound include styrene, tert-butylstyrene, α-methylstyrene, p-methylstyrene, p-ethylstyrene, divinylbenzene, 1,1-diphenylethylene, vinylnaphthalene, vinylanthracene, N,N-diethyl-p-aminoethylstyrene, vinylpyridine, etc. Among these, styrene is preferred because it is easily available industrially.

[0012] The content of the repeating units derived from the aromatic alkenyl compound in the aromatic alkenyl polymer block represented by A is not particularly limited, but the lower limit is preferably 50% by weight, the upper limit is preferably 100% by weight, and the lower limit is more preferably 70% by weight. When the aromatic alkenyl polymer block represented by A contains a repeating unit derived from a compound other than the repeating unit derived from the aromatic alkenyl compound, the block having such a repeating unit derived from another compound is not particularly limited, and examples thereof include a conjugated diene polymer, an ethylene polymer, and a propylene polymer.

[0013] The conjugated diene polymer block represented by B has repeating units derived from a conjugated diene compound. Examples of the conjugated diene compound include 1,3-butadiene, isoprene, 2,3-dimethyl-1,3-butadiene, 1,3-pentadiene, 2-methyl-1,3-octadiene, 1,3-hexadiene, 1,3-cyclohexadiene, 4,5-diethyl-1,3-octadiene, 3-butyl-1,3-octadiene, myrcene, and chloroprene. These conjugated diene compounds may be used alone or in combination of two or more. Among these, 1,3-butadiene and isoprene are preferred because of their high polymerization reactivity and ease of industrial availability.

[0014] The content of the repeating units derived from the conjugated diene compound in the conjugated diene polymer block represented by B is not particularly limited, but the lower limit is preferably 50% by weight, the upper limit is preferably 100% by weight, and the lower limit is more preferably 70% by weight. When the conjugated diene polymer block represented by B contains a repeating unit derived from a compound other than the repeating unit derived from the conjugated diene compound, the block having such a repeating unit derived from another compound is not particularly limited, and examples thereof include an aromatic alkenyl polymer, an ethylene polymer, and a propylene polymer.

[0015] The coupling agent, which is the raw material for the component derived from the coupling agent represented by C above, is a polyfunctional compound that radially bonds the linear styrene block copolymer, i.e., the styrene block copolymer or its hydrogenated product (1). Examples of the coupling agent include silane compounds such as halogenated silanes and alkoxysilanes, tin compounds such as tin halides, epoxy compounds such as polycarboxylic acid esters and epoxidized soybean oil, acrylic esters such as pentaerythritol tetraacrylate, and divinyl compounds such as epoxy silanes and divinylbenzene. More specific examples include trichlorosilane, tribromosilane, tetrachlorosilane, tetrabromosilane, methyltrimethoxysilane, ethyltrimethoxysilane, vinyltrimethoxysilane, vinyltriethoxysilane, tetramethoxysilane, tetraethoxysilane, tetrachlorotin, and diethyl adipate.

[0016] There are no particular limitations on n as long as it is an integer of 2 or more, but it is preferably 3 or more. When n is 3, it is also called a three-branched type, and when n is 4, it is also called a four-branched type.

[0017] When the styrene block copolymer or hydrogenated product thereof (1) or the styrene block copolymer or hydrogenated product thereof (2) is a hydrogenated product, the hydrogenated product may be a partially hydrogenated product or a completely hydrogenated product. Among them, a hydrogenated product in which preferably 80% or more, more preferably 90% or more, and even more preferably 95% or more of the double bonds (unsaturated bonds) in the repeating units derived from the conjugated diene compound are converted to saturated bonds by hydrogenation is preferred. The hydrogenation ratio (hydrogenation rate) was measured using carbon tetrachloride as a solvent at 270 MHz. 1 The hydrogenation rate is calculated from the H-NMR spectrum.

[0018] The weight-average molecular weight (Mw1) of the styrene block copolymer or hydrogenated product thereof (1) has a lower limit of 50,000 and an upper limit of 150,000. If the weight-average molecular weight (Mw1) is 50,000 or more, the weight-average molecular weight (Mw2) of the styrene block copolymer or hydrogenated product thereof (2) also increases, resulting in a higher storage modulus of the pressure-sensitive adhesive layer at high temperatures. This prevents the adhesive strength from increasing over time or even at high temperatures, enabling peeling without adhesive residue. If the weight-average molecular weight (Mw1) is 150,000 or less, the weight-average molecular weight (Mw2) of the styrene block copolymer or hydrogenated product thereof (2) does not increase too much, preventing the storage modulus of the pressure-sensitive adhesive layer at room temperature from increasing too much. This improves adhesion when applied to an adherend, increases adhesive strength (initial adhesive strength), and improves conformability to the adherend. The preferred lower limit of the weight-average molecular weight (Mw1) is 60,000, and the preferred upper limit is 140,000, with a more preferred lower limit of 70,000 and a more preferred upper limit of 120,000.

[0019] The weight-average molecular weight (Mw2) of the styrene block copolymer or its hydrogenated product (2) is at least 2.5 times the weight-average molecular weight (Mw1) of the styrene block copolymer or its hydrogenated product (1). When the weight-average molecular weight (Mw2) is at least 2.5 times the weight-average molecular weight (Mw1), the pressure-sensitive adhesive layer has a high storage modulus at high temperatures, and the adhesive strength is less likely to increase over time or at high temperatures, allowing for peeling without adhesive residue. In this specification, when the weight-average molecular weight (Mw2) is at least 2.5 times the weight-average molecular weight (Mw1), the styrene-based elastomer is said to be radial. When the weight-average molecular weight (Mw2) is less than 2.5 times the weight-average molecular weight (Mw1), the styrene-based elastomer is said to be linear. The weight-average molecular weight (Mw2) is preferably at least 2.7 times, more preferably at least 3.0 times the weight-average molecular weight (Mw1). The weight average molecular weight (Mw) can be measured by the following method. The sample solution is filtered through a filter (material: polytetrafluoroethylene, pore diameter: 0.2 μm). The resulting filtrate is fed to a gel permeation chromatograph (e.g., Waters, 2690 Separations Model) and subjected to GPC measurement at a sample flow rate of 1 mL / min and a column temperature of 40°C. The polystyrene-equivalent molecular weight of the sample is measured to determine the weight-average molecular weight (Mw). For example, a GPC KF-806L (Showa Denko) is used as the column, and a differential refractometer is used as the detector.

[0020] The content (diblock ratio) of the styrene block copolymer or its hydrogenated product (1) relative to 100% by weight of the styrene elastomer has a lower limit of 5% by weight and an upper limit of 50% by weight. When the content of the styrene block copolymer or its hydrogenated product (1) is 5% by weight or more, the storage modulus of the pressure-sensitive adhesive layer at room temperature is not excessively increased, thereby improving adhesion when applied to an adherend, increasing adhesive strength (initial adhesive strength), and improving conformability to the adherend. When the content of the styrene block copolymer or its hydrogenated product (1) is 50% by weight or less, the storage modulus of the pressure-sensitive adhesive layer at high temperatures is high, preventing adhesive strength from increasing over time or even at high temperatures, allowing for peeling without leaving any adhesive residue. The preferred lower limit of the content of the styrene block copolymer or its hydrogenated product (1) is 10% by weight, and the preferred upper limit is 47% by weight, with a more preferred lower limit being 15% by weight and a more preferred upper limit being 45% by weight. In addition to the styrene block copolymer or hydrogenated product thereof (1) and the styrene block copolymer or hydrogenated product thereof (2), 100% by weight of the styrene elastomer may further contain other components. The diblock ratio can be calculated from the peak area ratio of each copolymer measured by gel permeation chromatography (GPC).

[0021] The weight ratio of the aromatic alkenyl polymer block represented by A to the conjugated diene polymer block represented by B in the entire styrene-based elastomer is not particularly limited. The content of the conjugated diene polymer block represented by B relative to the total of the aromatic alkenyl polymer block represented by A and the conjugated diene polymer block represented by B in the entire styrene-based elastomer is preferably 35% by weight at the lower limit and 90% by weight at the upper limit. When the content of the conjugated diene polymer block represented by B is within the above range, the pressure-sensitive adhesive layer exhibits improved film-forming properties, further improves adhesion when attached to an adherend, thereby increasing adhesive strength (initial adhesive strength), while preventing the adhesive strength from increasing over time or even at high temperatures, allowing peeling without adhesive residue, and further improving conformability to the adherend. The content of the conjugated diene polymer block represented by B is more preferably 45% by weight at the lower limit and 87% by weight at the upper limit.

[0022] Examples of the styrene-based elastomer include styrene-ethylenebutylene-styrene block copolymer (SEBS) type, styrene-ethylenepropylene-styrene block copolymer (SEPS) type, and styrene-isobutylene-styrene block copolymer (SIBS) type. For example, the styrene elastomer being of the SEBS type means that the styrene block copolymer or its hydrogenated product (1) and the styrene block copolymer or its hydrogenated product (2) have repeating units derived from styrene, repeating units derived from ethylene, and repeating units derived from butylene. That is, the aromatic alkenyl polymer block represented by A is a block having repeating units derived from styrene, and the conjugated diene polymer block (its hydrogenated product) represented by B is a block having repeating units derived from ethylene and repeating units derived from butylene.

[0023] When the styrene-based elastomer has a repeating unit derived from styrene, the content of the repeating unit derived from styrene in the entire styrene-based elastomer (styrene content) is not particularly limited, but a preferred lower limit is 5 wt% and a preferred upper limit is 20 wt%. If the styrene content is within the above range, the pressure-sensitive adhesive layer has improved film-forming properties, and the adhesion when attached to an adherend is further improved, resulting in higher adhesive strength (initial adhesive strength). Meanwhile, the adhesive strength is less likely to increase over time or even at high temperatures, allowing for peeling without leaving any adhesive residue, and further improving conformability to the adherend. A more preferred lower limit of the styrene content is 7 wt% and a more preferred upper limit is 15 wt%.

[0024] When the styrene elastomer has butylene-derived repeating units, the content of butylene-derived repeating units in the entire styrene elastomer (butylene content) is not particularly limited, but a preferred lower limit is 60% by weight and a preferred upper limit is 90% by weight. If the butylene content is within the above range, the pressure-sensitive adhesive layer exhibits improved film-forming properties, and the adhesive strength (initial adhesive strength) is increased due to improved adhesion when attached to an adherend. The adhesive strength is less likely to increase over time or at high temperatures, allowing for peeling without leaving any adhesive residue, and the adhesive layer also exhibits improved conformability to the adherend. A more preferred lower limit of the butylene content is 65% by weight and a more preferred upper limit is 85% by weight.

[0025] The MFR of the styrene-based elastomer is not particularly limited, but it is preferable that the MFR be 1 g / 10 min or more and 18 g / 10 min or less under a 21.2 N load at 230°C. If the MFR is 1 g / 10 min or more under a 21.2 N load at 230°C, the occurrence of fish eyes in the pressure-sensitive adhesive layer during film formation can be suppressed. If the MFR is 18 g / 10 min or less under a 21.2 N load at 230°C, the occurrence of streaks (dew marks) in the pressure-sensitive adhesive layer during film formation can be suppressed. It is more preferable that the MFR be 2 g / 10 min or more and 15 g / 10 min or less under a 21.2 N load at 230°C. MFR stands for melt flow rate, and is a measure of the fluidity of a resin in a solution state. MFR is the rate at which a molten resin is extruded through a die of specified length and diameter under specified conditions of temperature, load, and piston position inside the plastometer cylinder, and this rate is determined as the mass extruded in a specified time. MFR is expressed in grams per 10 minutes (g / 10 min). The method for measuring MFR is specified in JIS K7210, and can be measured, for example, using a melt indexer (G-02, manufactured by Toyo Seiki Seisakusho Co., Ltd.).

[0026] The hardness of the styrene-based elastomer is not particularly limited, but it is preferable that the hardness (Type A) is 30 or more and 40 or less. If the hardness is 30 or more, it is possible to prevent streaks (dye buildup) from forming in the pressure-sensitive adhesive layer during film formation. If the hardness is 40 or less, it is possible to prevent fisheyes from forming in the pressure-sensitive adhesive layer during film formation. It is more preferable that the hardness is 32 or more and 36 or less. Note that hardness (Type A) is a type of indentation hardness, and is determined from the indentation depth when a test load is applied using an indenter. Hardness (Type A) can be measured using a rubber durometer in accordance with JIS K 6253.

[0027] The density of the styrene elastomer is not particularly limited, but the preferred lower limit is 0.85 g / cm 3 , the preferred upper limit is 0.91 g / cm 3 When the density of the styrene-based elastomer is within the above range, the pressure-sensitive adhesive layer has improved film-forming properties, and the adhesive strength (initial adhesive strength) is increased due to further improved adhesion when the layer is attached to an adherend, while the adhesive strength is less likely to increase over time or even at high temperatures, allowing the layer to be peeled off without leaving any adhesive residue, and further improving the ability to conform to the adherend. A more preferred lower limit of the density is 0.86 g / cm. 3 , and a more preferred upper limit is 0.90 g / cm 3 is. The density can be measured in accordance with JIS K7112.

[0028] The method for producing the styrene-based elastomer is not particularly limited, and examples thereof include the following methods. First, step (a) is carried out to synthesize the aromatic alkenyl polymer block represented by A. Next, step (b) is carried out to synthesize a styrene block copolymer (1) having a structure represented by general formula AB by polymerizing a conjugated diene compound with the aromatic alkenyl polymer block represented by A. Next, the obtained styrene block copolymer (1) having a structure represented by general formula AB is subjected to a coupling reaction using a coupling agent to synthesize a styrene block copolymer (1) having a structure represented by general formula (AB). n Step (c) is carried out to obtain a styrene block copolymer (2) having a structure represented by C. The coupling rate at this time is not particularly limited, but from the viewpoint of adjusting the diblock ratio (the content of the styrene block copolymer or its hydrogenated product (1) relative to 100% by weight of the styrene elastomer) within the above-mentioned range, the lower limit is preferably 50% and the upper limit is preferably 97%. The lower limit of the coupling rate is more preferably 55%, more preferably 95%, and even more preferably 60%. If necessary, step (d) is carried out to hydrogenate the styrene block copolymer (1) and the styrene block copolymer (2).

[0029] The tackifier resin is not particularly limited, but preferably has a softening point of 80°C or higher, more preferably 90°C or higher and 140°C or lower. Examples of the tackifier resin include petroleum-based resins such as aliphatic copolymers, aromatic copolymers, aliphatic-aromatic copolymers, and alicyclic copolymers; coumarone-indene resins, terpene resins, terpene-phenol resins, rosin-based resins such as polymerized rosin; (alkyl)phenol resins; xylene resins; and hydrogenated versions of these. Tackifier resins commercially available as mixtures with polyolefin resins may also be used. These tackifier resins may be used alone or in combination of two or more. Among these, hydrogenated versions of the tackifier resin are preferred, as they prevent the adhesive strength of the pressure-sensitive adhesive layer from increasing over time or at high temperatures, allowing for peeling without leaving any adhesive residue.

[0030] The content of the tackifier resin is not particularly limited, but a preferred lower limit is 3 parts by weight and a preferred upper limit is 50 parts by weight per 100 parts by weight of the styrene-based elastomer. If the content of the tackifier resin is 3 parts by weight or more, the adhesive strength of the PSA layer is sufficiently high. If the content of the tackifier resin is 50 parts by weight or less, the adhesive strength of the PSA layer is less likely to increase over time or at high temperatures, allowing for peeling with less adhesive residue. A more preferred lower limit of the content of the tackifier resin is 5 parts by weight and a more preferred upper limit is 40 parts by weight.

[0031] The pressure-sensitive adhesive composition of the present invention may further contain, as necessary, known additives such as an adhesion modifier, a plasticizer, an emulsifier, a softener, fine particles, a filler, a pigment, a dye, a silane coupling agent, an antioxidant, a surfactant, and a wax.

[0032] The MFR of the pressure-sensitive adhesive composition of the present invention is not particularly limited, but it is preferable that the MFR under a 21.2 N load at 190°C is 1 g / 10 min or more and 20 g / 10 min or less. If the MFR under a 21.2 N load at 190°C is 1 g / 10 min or more, the occurrence of fish eyes in the pressure-sensitive adhesive layer during film formation can be suppressed. If the MFR under a 21.2 N load at 190°C is 20 g / 10 min or less, the occurrence of streaks (dew marks) in the pressure-sensitive adhesive layer during film formation can be suppressed. It is more preferable that the MFR under a 21.2 N load at 190°C is 2 g / 10 min or more and 15 g / 10 min or less.

[0033] The hardness of the pressure-sensitive adhesive composition of the present invention is not particularly limited, but it is preferable that the hardness (Type A) is 15 or more and 30 or less. If the hardness is 15 or more, it is possible to prevent streaks (dye buildup) from forming in the pressure-sensitive adhesive layer during film formation. If the hardness is 30 or less, it is possible to obtain a pressure-sensitive adhesive layer with sufficient adhesive strength. It is more preferable that the hardness is 17 or more and 28 or less.

[0034] The pressure-sensitive adhesive composition of the present invention preferably has a phase-separated structure containing spherical island components with an average particle size of 10 nm or more and 100 nm or less. By having such a phase-separated structure, the pressure-sensitive adhesive layer has a relatively low storage modulus at room temperature and a relatively high storage modulus at high temperatures, thereby improving adhesion when attached to an adherend and increasing adhesive strength (initial adhesive strength). However, the adhesive strength is less likely to increase over time or at high temperatures, allowing peeling without leaving any adhesive residue. The average particle size of the spherical island components is more preferably 15 nm or more and 80 nm or less. The presence of a phase-separated structure in the PSA composition and the average particle size of the spherical island components in the phase-separated structure can be confirmed and measured by observing the phase-separated structure of the PSA layer using a transmission electron microscope (TEM) (e.g., JEM-2100, manufactured by JEOL Ltd.).

[0035] The present invention also includes a surface protection film having a substrate layer and a pressure-sensitive adhesive layer made of the pressure-sensitive adhesive composition of the present invention. The base layer is not particularly limited, but preferably contains a polyolefin resin. The polyolefin resin is not particularly limited, and conventionally known polyolefin resins can be used, such as polypropylene (PP) resin and polyethylene (PE) resin. Examples of the polypropylene resin include homopolypropylene, random polypropylene, block polypropylene, etc. Examples of the polyethylene resin include high-pressure low-density polyethylene, linear low-density polyethylene, high-density polyethylene, etc. Among these, polypropylene resin is preferred from the viewpoints of transparency, rigidity, and heat resistance, and homopolypropylene or a copolymer of propylene and at least one α-olefin is more preferred.

[0036] The substrate layer preferably contains two or more polyolefin resins having different melting points, which can prevent the substrate layer from becoming narrower than the set width during film formation, a phenomenon known as neck-in. The two or more polyolefin resins having different melting points are preferably two or more resins having different melting points selected from the group consisting of polypropylene resins and polyethylene resins.

[0037] The MFR of the resin constituting the substrate layer is not particularly limited, but it is preferable that the MFR be 3 g / 10 min or more and 15 g / 10 min or less under a 21.2 N load at 190°C. If the MFR is 3 g / 10 min or more under a 21.2 N load at 190°C, the occurrence of fisheyes in the substrate layer during film formation can be suppressed. If the MFR is 15 g / 10 min or less under a 21.2 N load at 190°C, the occurrence of streaks (stains) in the substrate layer during film formation can be suppressed. It is more preferable that the MFR be 5 g / 10 min or more and 13 g / 10 min or less under a 21.2 N load at 190°C.

[0038] Furthermore, the difference in MFR between the resin constituting the base layer and the pressure-sensitive adhesive composition constituting the pressure-sensitive adhesive layer under a load of 21.2 N at 190°C is preferably 10 g / 10 min or less. If the difference in MFR is 10 g / 10 min or less, the occurrence of roughness at the interface between the base layer and the pressure-sensitive adhesive layer can be suppressed. The difference in MFR is more preferably 5 g / 10 min or less. Note that the MFR of either the resin constituting the base layer or the pressure-sensitive adhesive composition constituting the pressure-sensitive adhesive layer may be greater.

[0039] The substrate layer may contain additives such as antistatic agents, release agents, antioxidants, weathering agents, and crystal nucleating agents, and resin modifiers such as polyolefins, polyesters, polyamides, and elastomers, within the range that does not impair the effects of the present invention.

[0040] The thickness of the substrate layer is not particularly limited, but a preferred lower limit is 25 μm and a preferred upper limit is 200 μm. If the thickness of the substrate layer is within the above range, the handleability of the surface protection film is improved. A more preferred lower limit of the thickness of the substrate layer is 50 μm and a more preferred upper limit is 188 μm.

[0041] The thickness of the pressure-sensitive adhesive layer is not particularly limited, but a preferred lower limit is 3 μm and a preferred upper limit is 30 μm. If the thickness of the pressure-sensitive adhesive layer is 3 μm or more, the adhesive strength is sufficiently high. If the thickness of the pressure-sensitive adhesive layer is 30 μm or less, it can be more easily peeled. A more preferred lower limit of the thickness of the pressure-sensitive adhesive layer is 5 μm and a more preferred upper limit is 20 μm.

[0042] The method for producing the surface protection film of the present invention is not particularly limited, and examples include a method in which a pressure-sensitive adhesive layer is laminated on a substrate layer previously obtained by T-die molding or inflation molding by a known lamination method such as extrusion lamination, extrusion coating, etc. Other examples include a method in which the substrate layer and the pressure-sensitive adhesive layer are formed into independent films, and then the obtained films are laminated by dry lamination, and a method in which the resin constituting the substrate layer and the pressure-sensitive adhesive composition of the present invention are co-extruded by the T-die method.

[0043] The surface protection film of the present invention has high adhesive strength (initial adhesive strength), excellent conformability to the adherend, and is resistant to increasing adhesive strength over time or at high temperatures, allowing it to be peeled off without leaving any adhesive residue. The surface protection film of the present invention may be used to protect the surface of an adherend having a smooth surface, but is particularly effective when used to protect the surface of an adherend having an uneven surface.

[0044] The surface protective film of the present invention is suitable for use in protecting the surfaces of components such as optical devices, metal plates, painted metal plates, resin plates, glass plates, etc. In particular, it is particularly suitable for protecting optical components having an uneven surface on one or both sides, such as prism sheets and diffusion films. [Effects of the Invention]

[0045] According to the present invention, it is possible to provide a pressure-sensitive adhesive composition capable of forming a pressure-sensitive adhesive layer that has high adhesive strength (initial adhesive strength), excellent conformability to an adherend, and is resistant to increasing adhesive strength over time or at high temperatures, and that can be peeled off without leaving any adhesive residue. Furthermore, according to the present invention, it is possible to provide a surface protection film having a pressure-sensitive adhesive layer made of the pressure-sensitive adhesive composition. DETAILED DESCRIPTION OF THE INVENTION

[0046] The following examples will explain the present invention in more detail, but the present invention is not limited to these examples.

[0047] <Styrene-based elastomer> In the examples and comparative examples, resins 1 to 17 shown in Table 1 were used as the styrene-based elastomer. The synthesis methods of resins 1 to 8 and 15 to 17 are as follows.

[0048] (Synthesis of Resin 1) (Synthesis Example 1) A reaction vessel purged with nitrogen was charged with 500 parts by weight of degassed and dehydrated cyclohexane, 10 parts by weight of styrene, and 5 parts by weight of tetrahydrofuran, and 0.13 parts by weight of n-butyllithium was added at a polymerization initiation temperature of 40°C, followed by temperature-raised polymerization to obtain an aromatic alkenyl polymer block (Block A). After the polymerization conversion rate of the aromatic alkenyl polymer block reached approximately 100%, the reaction mixture was cooled to 15°C, and then 90 parts by weight of 1,3-butadiene was added. The temperature was then increased and polymerization was continued to obtain a conjugated diene polymer block (Block B). This resulted in a styrene block copolymer (1) having a structure represented by the general formula AB. After the polymerization conversion rate reached nearly 100%, 0.06 parts by weight of tetrachlorosilane was added as a coupling agent to carry out the coupling reaction. After the coupling reaction was completed, the mixture was left for 10 minutes while hydrogen gas was supplied at a pressure of 0.4 MPa-Gauge. This yielded a styrene block copolymer (2) having a structure represented by the general formula (AB)4C.

[0049] Next, 0.03 parts by weight of diethylaluminum chloride and 0.06 parts by weight of bis(cyclopentadienyl)titanium furfuryloxychloride were added to the reaction vessel and stirred. The hydrogenation reaction was initiated at a hydrogen gas supply pressure of 0.7 MPa-Gauge and a reaction temperature of 80°C. Once hydrogen absorption was complete, the reaction solution was returned to room temperature and pressure and withdrawn from the reaction vessel. This yielded a styrene elastomer containing a hydrogenated styrene block copolymer (1) having a structure represented by the general formula AB and a hydrogenated styrene block copolymer (2) having a structure represented by the general formula (AB)4C. A portion of the polymer was taken out and subjected to GPC analysis to determine the weight average molecular weight (Mw).

[0050] (Synthesis of Resins 2 to 8 and Resins 15 to 17) (Synthesis Examples 2 to 11) A styrene-based elastomer was obtained in the same manner as in the synthesis of Resin 1 (Synthesis Example 1), except that the weight ratio of block A to block B, the coupling rate in the coupling reaction, the type of coupling agent, the hydrogenation rate in the hydrogenation reaction, etc. were changed as shown in Table 1. As the coupling agent, tetrachlorosilane was used for resins 2 to 5 and 15 to 17, and methyldichlorosilane was used for resins 6 to 8. As a result, radial styrene-based elastomers were obtained for resins 2 to 5 and 15 to 17, and linear styrene-based elastomers were obtained for resins 6 to 8.

[0051] The following commercially available products were used as resins 9 to 14. These resins were linear styrene-based elastomers. DR1321P (hydrogenated styrene butadiene rubber (HSBR), manufactured by JSR Corporation) DR1320P (hydrogenated styrene butadiene rubber (HSBR), manufactured by JSR Corporation) G1645 (styrene-ethylene butylene-styrene block copolymer (SEBS), manufactured by Kraton) G1643 (styrene-ethylene butylene-styrene block copolymer (SEBS), manufactured by Kraton) G1657 (styrene-ethylene butylene-styrene block copolymer (SEBS), manufactured by Kraton) Septon 2063 (styrene-ethylene propylene-styrene block copolymer (SEPS), manufactured by Kuraray Co., Ltd.)

[0052] [Table 1]

[0053] <Tackifying resin> In the examples and comparative examples, tackifier resins 1 to 3 (TF1 to TF3) shown in Table 2 were used as tackifier resins.

[0054] [Table 2]

[0055] <Resin that constitutes the base layer> In the examples and comparative examples, resins A to J shown in Table 3 were used as resins constituting the base layer.

[0056] [Table 3]

[0057] Example 1 As raw materials for the base layer, a resin composition was obtained by blending 80 parts by weight of Resin A and 20 parts by weight of Resin I. As raw materials for the pressure-sensitive adhesive layer, a pressure-sensitive adhesive composition was obtained by blending 100 parts by weight of Resin 1 as a styrene-based elastomer and 30 parts by weight of TF1 as a tackifying resin. The resin composition obtained above was used as the raw material for the base layer, and the adhesive composition obtained above was used as the raw material for the adhesive layer, and they were co-extruded by the T-die method to obtain a surface protection film with a base layer of 35 μm and an adhesive layer of 5 μm. Using the same formulation as the adhesive layer of the surface protection film, the mixture was kneaded for 5 minutes in a Plastomiller at 200°C, and then pressed at 180°C and room temperature to prepare a 5 mm thick pressed sheet sample. The hardness (Type A) of the prepared sample was measured using a sheet durometer. The MFR was also measured at 190°C under a 21.2 N load using a melt indexer (G-02, manufactured by Toyo Seiki Seisakusho Co., Ltd.). The MFR of the base layer of the surface protection film was measured at 190°C under a load of 21.2 N using a melt indexer (G-02, manufactured by Toyo Seiki Seisaku-sho, Ltd.).

[0058] (Examples 2 to 15, Comparative Examples 1 to 13) Surface protection films were obtained in the same manner as in Example 1, except that the styrene elastomer, tackifier resin, and base resin constituting the substrate layer were changed as shown in Tables 4 and 5.

[0059] <Rating 1> The surface protection films obtained in Examples 1 to 15 and Comparative Examples 1 to 13 were evaluated as follows. The results are shown in Tables 4 and 5.

[0060] (1) Evaluation of film formation properties (1-1) Evaluation of streaks (eye discharge) on the adhesive layer Using the same formulations as in Examples 1 to 15 and Comparative Examples 1 to 13, after cleaning the mold lip, surface protection films were continuously produced at an extrusion rate of 300 kg / h, and the time until the first streak defect mode occurred on the adhesive layer side was evaluated using an appearance sensor. 〇: 20 hours or more ×: Less than 20 hours

[0061] (1-2) Evaluation of fisheyes in the adhesive layer Using a fisheye sensor, the number of fisheyes with a size of 100 μm or more in the flow direction (number / m 2 The number of fish eyes, which are characterized by their occurrence in the adhesive layer, was also evaluated. ◎: 2 or less 〇: More than 2 but less than 10 ×: 10 or more

[0062] (1-3) Evaluation of interface roughness (base layer-adhesive layer) Using a green light, the presence or absence of a pattern at the interface between the pressure-sensitive adhesive layer and the substrate layer was visually evaluated. ◎: When the surface protection film was placed between two polarizing plates and the polarizing plates were placed in a closed Nicol position, no pattern was observed at the interface between the adhesive layer and the base material layer. ◯: No pattern was observed at the interface between the adhesive layer and the base material layer with the naked eye, but when the surface protection film was placed between two polarizing plates and the polarizing plates were placed in a closed Nicol position, a pattern was observed at the interface between the adhesive layer and the base material layer. ×: A pattern was observed on the interface between the adhesive layer and the base material layer by direct visual inspection.

[0063] (4) Measurement of initial adhesive strength A test specimen was prepared by attaching a 25 mm wide surface protection film to the adherend (PMMA plate, manufactured by Kuraray Co., Ltd.) so that it covered the adherend. The film was attached by pressing with a 2 kg pressure rubber roller at a speed of 300 mm / min in an environment of 23°C and 50% RH. The resulting test piece was left for 30 minutes in an environment of 23°C and 50% relative humidity. After leaving it, the surface protection film was peeled from the adherend in a 180° direction at a pulling rate of 300 mm / min in accordance with JIS Z0237, and the initial adhesive strength was measured. The initial adhesive strength was also evaluated according to the following criteria. ◎:5.5N / 25mm or more ○: 5.0N / 25mm or more, less than 5.5N / 25mm ×: Less than 5.0N / 25mm

[0064] (5) Measurement of adhesion growth rate The test piece obtained in the same manner as in (4) above was left for 168 hours in a temperature environment of 50°C. After leaving it, the test piece was taken out to room temperature and left for a further 60 minutes, and then the surface protection film was peeled from the adherend in the 180° direction at a pulling rate of 300 mm / min in accordance with JIS Z0237, and the adhesive strength over time was measured. Using the obtained initial adhesive strength and adhesive strength over time, the rate of change from the initial adhesive strength to the adhesive strength over time (adhesion increase rate) was calculated using the following formula and evaluated according to the following criteria. Adhesion growth rate (%) = (adhesion strength over time / initial adhesion strength) x 100 ◎: 125% or less ○: Over 125% and under 150% ×: 150% or more

[0065] (6) Evaluation of adhesive residue In the above (5), after the surface protection film was peeled off from the adherend, the adherend was inspected and evaluated for the presence or absence of adhesive residue. Evaluation was made according to the following criteria. ○: No adhesive residue was observed ×: Adhesive residue was observed

[0066] (7) Evaluation of conformability to the substrate A surface protection film was attached to the prism layer of an adherend having a prism layer (the pitch of the irregularities in the prism layer was 24 μm, and the repulsive force when the surface on the prism layer side was displaced by 1 μm was 0.05 mN) to prepare a test specimen. The attachment was performed by pressing at a speed of 300 mm / min using a 2 kg pressure rubber roller in an environment of 23°C and a relative humidity of 50%RH. The obtained test piece was left for 30 minutes in an environment of 23°C and a relative humidity of 50% RH, after which it was judged whether or not the surface protection film had lifted. The presence or absence of lifting was determined by measuring the resilience using a microindentation hardness tester (Elionix ultra-microindentation hardness tester, model ENT-2100) in accordance with JIS Z2255, which measures the load-displacement curve. 〇: No float was observed ×: Floating was observed

[0067] [Table 4]

[0068] [Table 5]

[0069] (Examples 16 to 19) Surface protection films were obtained in the same manner as in Example 1, except that the base resin constituting the substrate layer was changed as shown in Table 6.

[0070] <Rating 2> The surface protection films obtained in Example 1 and Examples 16 to 19 were evaluated as follows. The results are shown in Table 6.

[0071] (1) Evaluation of film formation properties (1-1) Evaluation of streaks (stains) on the base layer Using the same formulation as in Example 1 and Examples 16 to 19, after cleaning the mold lip, surface protection films were continuously produced at an extrusion rate of 300 kg / h, and the time until the first streak defect mode occurred on the substrate layer side was evaluated using an appearance sensor. 〇: 20 hours or more ×: Less than 20 hours

[0072] (1-2) Evaluation of fisheyes in the base layer Using a fisheye sensor, the number of fisheyes with a size of 100 μm or more in the flow direction (number / m 2 The number of fish eyes, which are characterized by their occurrence in the base material layer, was evaluated. ◎: 2 or less 〇: More than 2 but less than 10 ×: 10 or more

[0073] (1-3) Evaluation of interface roughness (base layer-adhesive layer) Using a green light, the presence or absence of a pattern at the interface between the pressure-sensitive adhesive layer and the substrate layer was visually evaluated. ◎: When the surface protection film was placed between two polarizing plates and the polarizing plates were placed in a closed Nicol position, no pattern was observed at the interface between the adhesive layer and the base material layer. ◯: No pattern was observed at the interface between the adhesive layer and the base material layer with the naked eye, but when the surface protection film was placed between two polarizing plates and the polarizing plates were placed in a closed Nicol position, a pattern was observed at the interface between the adhesive layer and the base material layer. ×: A pattern was observed on the interface between the adhesive layer and the base material layer by direct visual inspection.

[0074] (2) Evaluation of width fluctuation (neck-in) The variation rate of the product width of the surface protection film after cooling with a chill roll was evaluated relative to the outlet width of the mold. ○: Small: Product width / mold exit width is 70% or more, 100% or less ×: Large: Product width / mold outlet width is less than 70%

[0075] [Table 6] [Industrial Applicability]

[0076] According to the present invention, it is possible to provide a pressure-sensitive adhesive composition capable of forming a pressure-sensitive adhesive layer that has high adhesive strength (initial adhesive strength), excellent conformability to an adherend, and is resistant to increasing adhesive strength over time or at high temperatures, and that can be peeled off without leaving any adhesive residue. Furthermore, according to the present invention, it is possible to provide a surface protection film having a pressure-sensitive adhesive layer made of the pressure-sensitive adhesive composition.

Claims

1. A pressure-sensitive adhesive composition containing a styrene-based elastomer and a tackifying resin, The styrene elastomer is a mixture of a hydrogenated styrene block copolymer (1) having a structure represented by the general formula A-B and a copolymer of the general formula (A-B) ｎ and a hydrogenated styrene block copolymer (2) having a structure represented by C, and a styrene-ethylene butylene-styrene block copolymer (SEBS) type containing the hydrogenated styrene block copolymer (2) having a structure represented by C, The weight average molecular weight (Mw1) of the hydrogenated styrene block copolymer (1) is 50,000 to 150,000, the weight average molecular weight (Mw2) of the hydrogenated styrene block copolymer (2) is 2.5 times or more the weight average molecular weight (Mw1) of the hydrogenated styrene block copolymer (1); The content of the hydrogenated styrene block copolymer (1) in 100% by weight of the styrene elastomer is 5% by weight or more and 50% by weight or less. A pressure-sensitive adhesive composition characterized by: A: Block having a repeating unit derived from styrene B: a block having a repeating unit derived from ethylene and a repeating unit derived from butylene C: Component derived from coupling agent n: an integer of 2 or more

2. 2. The pressure-sensitive adhesive composition according to claim 1, wherein the pressure-sensitive adhesive composition has an MFR of 1 g / 10 min or more and 20 g / 10 min or less at 190° C. under a load of 21.2 N.

3. 3. The pressure-sensitive adhesive composition according to claim 1, wherein the styrene elastomer has an MFR of 1 g / 10 min or more and 18 g / 10 min or less at 230° C. under a load of 21.2 N.

4. 4. The pressure-sensitive adhesive composition according to claim 1, 2 or 3, which has a phase-separated structure containing spherical island components having an average particle size of 10 nm or more and 100 nm or less.

5. 5. The pressure-sensitive adhesive composition according to claim 1, wherein the pressure-sensitive adhesive composition has a hardness (type A) of 15 or more and 30 or less.

6. A surface protection film comprising a substrate layer and a pressure-sensitive adhesive layer comprising the pressure-sensitive adhesive composition according to claim 1 .

7. The surface protection film according to claim 6, wherein the difference in MFR between the resin constituting the base layer and the pressure-sensitive adhesive composition constituting the pressure-sensitive adhesive layer at a load of 21.2 N and 190°C is 10 g / 10 min or less.

8. 8. The surface protection film according to claim 6, wherein the substrate layer contains two or more polyolefin resins having different melting points.

9. 9. The surface protection film according to claim 8, wherein the two or more polyolefin resins having different melting points are two or more resins having different melting points selected from the group consisting of polypropylene resin and polyethylene resin.

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