Pressure-sensitive adhesive composition and surface protection sheet comprising the same

Abstract

The present invention relates to pressure sensitive adhesive compositions and surface protection sheets comprising the same. Disclosed is an acrylic pressure sensitive adhesive (PSA) composition having high low-fouling property and stain resistance, comprising an acrylic polymer produced by radical polymerization, wherein the acrylic polymer has a weight average molecular weight (M w ) of less than 830 kDa; the acrylic polymer has a relative half-peak width (PWHH) of 1.75 or less, or the acrylic polymer has an entanglement molecular weight (M e ) of less than 50 kg / mol. Also disclosed is a method for preparing the PSA composition, surface protection sheets comprising the same and related uses.

Description

TECHNICAL FIELD

[0001] The present invention relates to a pressure sensitive adhesive (PSA) composition containing an acrylic polymer produced by free radical polymerization (FRP), which can be used for a protective tape having excellent low-fouling and anti-fouling properties, and to a method for preparing a pressure sensitive adhesive (PSA) composition.

[0002] Further aspects of the present invention include a surface protection sheet comprising the pressure sensitive adhesive (PSA) composition, and its use for protecting surfaces having high low-fouling and anti-fouling requirements, such as physical vapor deposition coated layers (e.g. low-E coated glass), high-gloss coatings, medical applications or silicon wafers for chip cutting, etc., e.g. during tape application and / or after tape removal. BACKGROUND

[0003] Pressure sensitive adhesive (PSA) tapes, when no macroscopic residues are visible to the naked eye after tape removal, are often classified as low-residue type tapes. Examples of such PSA tapes are disclosed, for example, in JP 4525811 B2, JP 2014-224208 A, EP 1375621 A1, EP 3029121 A2, US 2016 / 0177151 A1, US 2019 / 0016935 A1, US 2019 / 0338164 A1, CN 110183981 A, etc.

[0004] However, PSA compositions or tapes that are also capable of reducing the amount of microscopic residues are different in nature. For example, the preparation of so-called ‘low-fouling’ or ‘anti-fouling’ PSA materials often requires particularly controlled polymerization techniques such as reversible addition-fragmentation chain-transfer (RAFT) (see, for example, WO 2011 / 152511 A1 or EP 3 006 533 A1 ), anionic polymerization (as in EP 3 006 533 A1 ) and Telluride-mediated polymerization (TERP), as disclosed in WO 2018 / 016407 A1, etc. However, such methods are not only complex, but also require special equipment and / or special catalysts, which leads to high production costs.

[0005] Another strategy to obtain low residue adhesives is based on excluding or reducing the content of low molecular weight species by focusing on the preparation of constituent polymers with high molecular weight (see, for example, EP 2457967 A1, US 6,602,599 B1, EP 2457968 A1, EP 1108770 A2 and US 2016 / 0185083 A1 ). However, this approach results in PSA compositions with high viscosity, which leads to difficulties in engineering and coating and / or requires large amounts of solvents, thus making the product and its manufacturing process expensive and non-sustainable.

[0006] Other approaches require special treatments to avoid residue after tape removal. For example, EP 2033996 A1 and US 2017 / 0278739 A1 suggest applying UV radiation before peeling the tape. Other publications describe treating the substrate surface after tape removal by heating (WO 2020 / 006387 A1, US 2016 / 0194516 A1 ) or washing (US 6,682,773 B2). However, such techniques require special equipment and complex operations from the end user and strictly limit the applicability of the produced tapes, especially because the treatment can not be tolerated by the protected substrate.

[0007] WO 2017 / 216108 A1 proposes to adjust the low adhesion strength to reduce fouling of the substrate, however it is not applicable to surface protection applications that can require high adhesion strength.

[0008] In these cases, it is the object of the present invention to provide a PSA composition and a surface protection sheet that can be produced in an environmentally friendly manner inexpensively without any special chemicals, equipment or methods, while leaving no or only a small amount of residue on the adherend, such as a substrate, upon removal. SUMMARY

[0009] The present invention solves these problems with the subject matter of the claims as limited herein. Further advantages of the present invention will be explained in further detail in the next section.

[0010] A first aspect of the present invention relates to an acrylic pressure sensitive adhesive composition comprising an acrylic polymer produced by free radical polymerization, wherein the acrylic polymer has a weight average molecular weight (Mw) of less than 830 kDa; and wherein the acrylic polymer has a relative peak width at half height (PWHH) of 1.75 or less or wherein the acrylic polymer has an entanglement molecular weight (M w ) of 1.75 or less or wherein the acrylic polymer has an entanglement molecular weight (M e) is less than 50 kg / mol, the relative half-peak width (PWHH) of the acrylic polymer is the ratio of the absolute half-peak width (PWHH) of the acrylic polymer to the absolute half-peak width (PWHH) of a reference acrylic polymer, the absolute half-peak width (PWHH) of the acrylic polymer being determined from the differential DSC signal of the acrylic polymer at the glass transition temperature (T g ) and the absolute half-peak width (PWHH) of the acrylic polymer being determined in the same manner as the absolute half-peak width (PWHH) of the acrylic polymer, and M e is calculated from the plateau modulus determined by rheological methods.

[0011] A second aspect of the present application relates to a method for producing the above-defined acrylic pressure-sensitive adhesive composition, which comprises radical polymerization of a monomer composition comprising acrylic acid and / or (meth)acrylic acid alkyl ester having an alkyl group with a carbon number of 3 or less.

[0012] A third aspect of the present application relates to a surface protection sheet, which comprises: a substrate layer; and a pressure-sensitive adhesive layer comprising the above-defined acrylic pressure-sensitive adhesive composition.

[0013] A fourth aspect of the present application relates to the use of the aforementioned surface protection sheet for protecting a PVD-based coating, a high-gloss coating, a silicon wafer, a glass surface, an optical member, and a medical device.

[0014] Preferred embodiments of the acrylic pressure-sensitive adhesive composition according to the present application and other aspects of the present application are described in the following description and claims. BRIEF DESCRIPTION OF DRAWINGS

[0015] Figure 1 DSC measurement (derivatized heat flow) for determining the PWHH of the acrylic polymers of Example 5 and Comparative Example 1 is shown. DETAILED DESCRIPTION

[0016] For a more complete understanding of the present application, reference is now made to the following description taken in conjunction with the accompanying drawings in which:

[0017] Pressure sensitive adhesive composition

[0018] In a first embodiment, the present application relates to an acrylic pressure-sensitive adhesive composition comprising an acrylic polymer produced by radical polymerization, wherein the acrylic polymer has a weight average molecular weight (M wThe relative half-width (PWHH) of the acrylic polymer is less than 830 kDa; and the relative half-width (PWHH) of the acrylic polymer is less than 1.75 or the entanglement molecular weight (M) of the acrylic polymer is less than 830 kDa. e The relative half-width (PWHH) of the acrylic polymer is less than 50 kg / mol. The PWHH of the acrylic polymer is the ratio of the absolute half-width (PWHH) of the acrylic polymer to the absolute half-width (PWHH) of a reference acrylic polymer. The absolute half-width (PWHH) of the acrylic polymer is determined at its glass transition temperature (T). g The differential DSC signal of the acrylic polymer was determined below the reference acrylic polymer, which was obtained by reacting ethyl acrylate and acrylic acid at a weight ratio of 100:5 at 10 mmol / L AIBN. The absolute half-width (PWHH) of the reference acrylic polymer was determined in the same manner as that of the acrylic polymer. e Calculated from the platform modulus determined by rheological methods.

[0019] In contrast to prior art compositions employing high molecular weight polymers, the acrylic pressure-sensitive adhesive compositions according to the present invention exhibit excellent low fouling and antifouling properties while providing favorable viscosity characteristics, which facilitates handling and coating processes without excessive use of organic solvents. From this perspective, the preferred weight-average molecular weight M of the acrylic polymer is... w Within the range of 120–800 kDa, more preferably 130–750 kDa, and particularly preferably 150–550 kDa. w There are no particular limitations on the determination method, and it may include, for example, light scattering or sedimentation equilibrium techniques. The weight-average molecular weight can be appropriately controlled by adjusting the concentrations of monomers and / or initiators during free radical polymerization and by solvent selection. For example, M can be increased by decreasing the initiator concentration or increasing the monomer concentration. w ,vice versa.

[0020] Molecular motion in relatively high molecular weight crosslinked polymer systems has been described in the repptation model (see, for example, De Gennes, J. Chem. Phys. 1971, 55, 572). Based on the assumption that residues after band removal are the result of material migration from the PSA matrix to the substrate, it can be followed that reduced molecular mobility, in turn, reduces migration and thus reduces residue formation. As mentioned above, a conventional method for reducing molecular mobility is to use high molecular weight polymers... w Polymers. The inventors have discovered that both free volume and chain mobility can be controlled by adjusting the entanglement molecular weight M. eto effectively reduce, the entanglement molecular weight is defined as the molecular weight between adjacent temporary entanglement points and is controlled by the molecular structure of the polymer. In particular, it has been found that by controlling the entanglement molecular weight (M e ) in the range of less than 50 kg / mol, preferably less than 25 kg / mol (e.g. 5 to 20 kg / mol), particularly preferably less than 20 kg / mol (e.g. 10 to 18 kg / mol), even if polymers with a relatively low weight average molecular weight (M w ) are used, the number of entanglements is sufficiently high to also reduce the molecular mobility in the PSA matrix and thus also the residue build-up at the tape-substrate interface. The entanglement molecular weight (M e ) can be calculated from the plateau modulus determined by rheological methods (e.g. as disclosed in C. Liu et al., Polymer 2006, 27, 4461-4479 or J. D. Ferry, Viscoelastic Properties of Polymers, 3rdEdition, John Wiley, New York 1980, etc.).

[0021] As an alternative to the usually cumbersome M e quantitative determination, it has been found that differential scanning calorimetry (DSC) can be used as a routine alternative to correlate the molecular mobility with the residue formation. In particular, it has been found that when the relative peak half width (PWHH) of the acrylic polymer is 1.75 or less, preferably 1.6 or less, more preferably 1.5 or less and particularly preferably less than 1.4, e.g. 0.9 to 1.3, residue build-up can be effectively reduced or prevented. Here, the relative peak half width (PWHH) of the acrylic polymer means the ratio of the absolute peak half width (PWHH) of the acrylic polymer determined from the differential DSC signal of the acrylic polymer at its glass transition temperature (T g ) to the absolute peak half width (PWHH) of a reference acrylic polymer, which is obtained by reacting ethyl acrylate and acrylic acid in a weight ratio of 100:5 at 10 mmol / l AIBN, wherein the absolute peak half width (PWHH) of the reference acrylic polymer is determined in the same way as the absolute peak half width (PWHH) of the acrylic polymer.

[0022] The acrylic polymer included in the pressure-sensitive adhesive composition according to the present application is not particularly limited as long as it meets the above requirements. However, it is preferred to use at least two comonomers or more used for preparing the acrylic polymer.

[0023] In a preferred embodiment, the acrylic polymer comprises (meth)acrylic acid and / or (meth)acrylic acid alkyl esters having an alkyl group with a carbon number of 3 or less as monomer components. The (meth)acrylic acid alkyl esters having an alkyl group with a carbon number of 3 or less are further preferably selected from the group consisting of methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate and isopropyl (meth)acrylate. It should be noted that the expression "(meth)acrylate" as used herein generally encompasses both methacrylate and acrylate, as well as mixtures of both.

[0024] Although the entanglement molecular weight (M e ) and the PWHH not only depend on the choice of (co)monomers, but also on the presence or absence, type and concentration of other components such as chain transfer agents, crosslinking agents and initiators, etc., the desired ranges can be more easily achieved with the following (co)monomer choices.

[0025] Preferably, the total amount of acrylic acid and (meth)acrylic acid alkyl esters having an alkyl group with a carbon number of 3 or less is at least 15 parts by weight, preferably at least 15 parts by weight, further preferably at least 25 parts by weight, for example 25 parts by weight to 100 parts by weight, relative to 100 parts by weight of the total amount of monomer components.

[0026] If one or more (meth)acrylic acid alkyl esters having an alkyl group with a carbon number of 4 are present as monomer components (i.e. n-butyl (meth)acrylate, sec-butyl (meth)acrylate or isobutyl (meth)acrylate), their total content is preferably less than 97 parts by weight, more preferably less than 95 parts by weight, relative to 100 parts by weight of the total amount of monomer components.

[0027] In addition, when the acrylic polymer comprises one or more (meth)acrylic acid alkyl esters having an alkyl group with a carbon number of more than 4 as monomer components, their content is preferably less than 80 parts by weight, more preferably less than 60 parts by weight, further preferably less than 40 parts by weight, and particularly preferably less than 30 parts by weight, relative to 100 parts by weight of the total amount of monomer components. Examples of such monomers include, but are not limited to, hexyl (meth)acrylate, heptyl (meth)acrylate, octyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, decyl (meth)acrylate, isodecyl (meth)acrylate, lauryl (meth)acrylate, myristyl (meth)acrylate, cetyl (meth)acrylate, stearyl (meth)acrylate, behenyl (meth)acrylate, or mixtures of any two or more thereof.

[0028] Generally, it can be preferred that (meth)acrylic acid alkyl esters having an alkyl group with a carbon number of more than 4 are present in an amount of less than 95 parts by weight, preferably in an amount of less than 85 parts by weight, relative to 100 parts by weight of the total amount of monomer components.

[0029] It should be noted that other (co)monomers can be incorporated as long as the required M w and M e or PWWH ranges are met. For example, the acrylic polymer can further comprise one or more functional monomers. Although not particularly limited, examples of functional monomers that can be mentioned include one or more acrylates comprising a hydroxyl group, an epoxy group, an alkoxy group, an acyl group, an acyloxy group, a silyl group, a siloxy group, a silane group, a carboxylic acid group, a 1,3-dicarbonyl group, an isocyanate group, a sulfonic acid group, an anhydride group, an alkoxycarbonyl group, an aryloxycarbonyl group, an imino ether group, an imide ether group, an amide ether group, a lactone group, a lactam group, an amide group, an acetal group, a ketal group, a ketone group, an oxazolidinone group, a carbamate group, a carbonate group, a halide group, a dialkylamino group, an oxaziridine group, an aziridine group, an oxazolidine group, an ortho ester group, a urea group, an oxetane group, or a cyano group.

[0030] The method for the radical polymerization for preparing the acrylic polymer is not particularly limited and will be described below in connection with the second embodiment.

[0031] The acrylic pressure-sensitive adhesive composition according to the present application can further comprise a crosslinking agent. In terms of lower residue formation, among the crosslinking agents known in the art, a non-self-condensation type crosslinking agent is preferred over a self-condensation type crosslinking agent (e.g., isocyanate-based). As a particularly preferred non-self-condensation type crosslinking agent, a metal chelate, an epoxy-based crosslinking agent, or an aziridine-based crosslinking agent can be mentioned. Suitable metal chelates are generally polyfunctional metal chelates comprising a polyvalent metal and an organic compound covalently or coordinately bonded (e.g., through an oxygen atom) to the metal. Examples of polyvalent metal atoms include Al, Cr, Zr, Co, Cu, Fe, Ni, V, Zn, In, Ca, Mg, Mn, Y, Ce, Sr, Ba, Mo, La, Sn, and Ti. The organic compound has an atom, e.g., an oxygen atom, that forms a covalent or coordinate bond. Examples of the organic compound include alkyl esters, alcohols, carboxylic acids, ethers, and ketones. Examples of aziridine-type crosslinking agents include, but are not limited to, 1,4-bis(ethylideneiminocarbonylamino)benzene, 4,4'-bis(ethylideneiminocarbonylamino)-diphenylmethane, 1,8-bis(ethylideneiminocarbonylamino)octane, and 1,1'-(1,3-phenylenedicarbonyl)-bis-(2-methylaziridine).

[0032] In a preferred embodiment, the acrylic pressure-sensitive adhesive composition preferably comprises a chain transfer agent, further preferably in an amount of 0.001 to 5 parts by weight, preferably between 0.005 and 2 parts by weight, relative to 100 parts by weight of the total amount of the monomer component.

[0033] The chain transfer agent is not particularly limited and is typically selected from one or more thiol compounds, including monofunctional thiols and polyfunctional thiols. Monofunctional thiols include, but are not limited to, propanethiol, butanethiol, hexanethiol, octanethiol, n-dodecyl mercaptan (DDM), thioglycolic acid, mercaptopropionic acid, alkyl thioglycolate, mercaptoethanol, mercaptoundecanoic acid, thiolactic acid, and thiobutyric acid, with n-dodecyl mercaptan being preferred. Examples of polyfunctional thiols include trifunctional compounds such as trimethylolpropane tris(3-mercaptopropionate), tetrafunctional compounds such as pentaerythritol tetra(3-mercaptopropionate), pentaerythritol tetrathioglycolate, pentaerythritol tetrathiolactate, pentaerythritol tetrathiobutyrate; hexafunctional compounds such as dipentaerythritol hexa(3-mercaptopropionate), dipentaerythritol hexathioglycolate; and octafunctional thiols such as tripentaerythritol octa(3-mercaptopropionate) or tripentaerythritol octathioglycolate.

[0034] It should be appreciated that other optional additives can be included in the pressure sensitive adhesive composition, for example, including viscosity modifiers (thickeners, etc.), leveling agents, mold release modifiers, plasticizers, softeners, fillers, colorants (pigments, dyes, etc.), antistatic agents, preservatives, anti-aging agents, ultraviolet light absorbers, antioxidants, light stabilizers, and combinations thereof, etc.

[0035] Method of preparation

[0036] In a second embodiment, the present application relates to a method for producing the acrylic pressure sensitive adhesive composition according to the above-described first embodiment, which comprises radical polymerization of a monomer composition comprising acrylic acid and / or an alkyl (meth)acrylate having an alkyl group with a carbon number of 3 or less.

[0037] The constituent components of the acrylic polymer are described in the context of the above-described first embodiment.

[0038] The acrylic polymer can generally be synthesized by radical polymerization (FRP) (e.g., in the presence of a radical initiator, including solution polymerization, emulsion polymerization, bulk polymerization, and suspension polymerization, etc.) under standard conditions known to those skilled in the art. Its production does not require special chemicals, equipment, or methods, which makes the manufacture of the PSA composition simple and cost-effective.

[0039] In the solution polymerization which can be a preferable polymerization method, the starting monomer can be dissolved in a solvent at once, continuously or in batches. The solvent used can be appropriately selected from known or commonly used organic solvents. Examples thereof include, but are not limited to, one or more selected from the group consisting of aromatic compounds (e.g., toluene or xylene, etc.); aliphatic or alicyclic hydrocarbons (e.g., ethyl acetate, hexane, cyclohexane or methylcyclohexane, etc.); halogenated alkanes (e.g., 1,2-dichloroethane); lower alcohols (e.g., monohydric alcohol having a carbon number of 1 to 4), such as isopropyl alcohol, 1-butanol, sec-butyl alcohol, tert-butyl alcohol, etc.; ethers (e.g., butyl methyl ether); ketones (e.g., methyl ethyl ketone, acetylacetone); and the like.

[0040] The initiator generally used in the polymerization process can be appropriately selected from known or commonly used radical polymerization initiators. For example, it can be preferable to use an azo-based polymerization initiator. Examples of the azo-based polymerization initiator include 2,2'-azobis(isobutyronitrile) (AIBN), 2,2'-azobis(2-methylpropionamidine) disulfate, 2,2'-azobis(2-amidinopropane) dihydrochloride, 2,2'-azobis[2-(5-methyl-2-imidazolin-2-yl)propane] dihydrochloride, 2,2'-azobis(N,N'-dimethyleneisobutylamidine), 2,2'-azobis[N-(2-carboxyethyl)-2-methylpropionamidine] hydrate, 2,2'-azobis(4-methoxy-2,4-dimethylvaleronitrile), 2,2'-azobis(2,4-dimethylvaleronitrile), 2,2'-azobis(2-methylbutyronitrile), 1,1'-azobis(cyclohexane-1-carbonitrile), 2,2'-azobis(2,4,4-trimethylpentane), dimethyl-2,2'-azobis(2-methylpropionate), and the like. Other examples of the polymerization initiator include persulfates such as potassium persulfate, ammonium persulfate, and the like; peroxide-based initiators such as benzoyl peroxide, tert-butyl hydroperoxide, di-tert-butyl peroxide, tert-butyl peroxybenzoate, dicumyl peroxide, 1,1-bis(tert-butylperoxy)-3,3,5-trimethylcyclohexane, 1,1-bis(tert-butylperoxy)cyclododecane, hydrogen peroxide, and the like; substituted ethane-based initiators such as phenyl-substituted ethane, and the like; aromatic carbonyl compounds; and the like. Other examples of the polymerization initiator include redox-based initiators by combining a peroxide and a reducing agent (e.g., a peroxide and ascorbic acid, a peroxide and an iron (II) salt, and a persulfate and sodium bisulfite, etc.). Two or more initiators can be used in combination.

[0041] The amount of the polymerization initiator can be appropriately selected by a skilled person depending on the type of the initiator and the monomer composition, and is generally about 0.001 to 1 parts by weight, preferably 0.01 to 1 parts by weight, each relative to 100 parts by weight of the total amount of the monomer component.

[0042] The polymerization process can generally be initiated by a method known in the art, for example, by heating the above-described composition containing the starting monomer(s) and the radical polymerization initiator to 20 to 100°C, typically 40 to 90°C. The polymerization temperature can be appropriately selected depending on the kind of monomer to be used, the type of solvent, the type of polymerization initiator, and the like.

[0043] The crosslinking agent (for example, the above-described non-self-condensation type crosslinking agent) can be added during the heating step or after the heating step.

[0044] The acrylic polymer composition thus produced can be diluted with an organic solvent to obtain a viscosity suitable for a coating process. Since the acrylic polymer present in the composition of the present application has a relatively low weight average molecular weight (Mw w ), an additional organic solvent is only required in a small amount or not at all to obtain the desired coating viscosity, which contributes to easier handling and, in particular, to the environmental friendliness of the PSA composition and the surface protection sheet of the present application.

[0045] Surface protection sheet and related uses

[0046] In a third embodiment, the present application relates to a surface protection sheet comprising: a substrate layer; and a pressure sensitive adhesive layer containing the acrylic pressure sensitive adhesive composition according to the above-described first embodiment.

[0047] For the substrate layer, a resin film is preferably used. Such a resin film can be formed of various types of resin materials. The resin material can be appropriately selected by a skilled person depending on the intended use of the surface protection sheet (for example, to impart transparency, mechanical strength, thermal stability, water repellency, and / or isotropy). In a preferred embodiment, the substrate layer comprises a polyolefin (for example, polyethylene, polypropylene, a polyolefin having a cyclic or norbornene structure, an ethylene-propylene copolymer, or the like), a polyester (including but not limited to, for example, polyethylene terephthalate (PET), polyethylene naphthalate (PEN), or polybutylene terephthalate, and the like), a polyacrylate (for example, polymethyl methacrylate), a polystyrene (for example, including derivatives such as acrylonitrile-styrene copolymer, and the like), a polyamide (for example, nylon 6, nylon 6,6, an aromatic polyamide, or the like), a polyvinyl chloride, a polyvinylidene chloride, a polycarbonate, or a combination thereof. Further, resin materials based on cellulose, polyimide, polysulfone, polyethersulfone, polyether ether ketone, polyphenylene sulfide, polyvinyl alcohol, poly(vinyl butyral), polyarylate, polyformal, or epoxy-based, and the like can be mentioned as examples. The resin material constituting the resin film can be a blend of two or more substances therein.

[0048] The thickness of the base material layer can be appropriately selected depending on the intended application of the surface protective sheet. Generally, the thickness of the base material layer is appropriately from about 1 μm to 2000 μm, for example, from about 5 μm to 1000 μm.

[0049] The thickness of the pressure-sensitive adhesive layer is also not particularly limited and can be appropriately selected by the skilled person. A typical thickness range is from 0.1 μm to 200 μm, for example, from about 0.5 μm to 100 μm.

[0050] The pressure-sensitive adhesive composition can be directly coated onto the base material layer to be in contact therewith. Alternatively, one or more intermediate layers can be interposed between the base material layer and the adhesive layer. Such intermediate layers are not particularly limited and can include one or more of a foam layer or a structural layer.

[0051] When coating the PSA composition, various methods conventionally known in the field of surface protective films can be appropriately employed, such as roll coating, gravure roll coating, reverse roll coating, roll brush coating, spray coating, air-knife coating, and die coating, etc.

[0052] The surface protective sheet disclosed herein can be provided in a form in which a release liner is adhered to the adhesive surface opposite to the base material layer side. For the release liner, a material based on paper, a woven material, a metal foil, or a polymer film (including but not limited to polyester resins such as polyethylene terephthalate (PET), acrylic resins such as polymethyl methacrylate (PMMA), polycarbonate, triacetyl cellulose (TAC), polysulfone, polyarylate, polyimide, polyvinyl chloride, polyvinyl acetate, polyethylene (PE), polypropylene (PP), ethylene-propylene copolymer, cyclic olefin-based polymer, and combinations thereof) can be used. The thickness of the release liner can be, for example, from about 5 μm to 200 μm, and is generally preferably from about 10 μm to 100 μm.

[0053] When applied on the surface of the adherend after removal, the surface protective sheet according to the present application advantageously leaves no or only a very small amount of residue on the surface of the adherend.

[0054] Specific detection methods, such as color measurement, surface free energy (SFE) by contact angle, or even chemical methods such as mass spectrometry (e.g. TOF-Sims) are required to observe the remaining residue. For example, when leaving an adhesive residue, the SFE of the glass substrate tends to decrease compared to the original surface. In this regard, it is preferred that the difference in SFE between the original blank glass surface and the same glass surface which has previously had a surface protective sheet adhered to it is less than 8 mN / m, more preferably less than 5 mN / m, even more preferably less than 2 mN / m. It is further preferred that the SFE of the glass surface after removal of the tape is higher compared to the untreated original glass surface. The SFE can be measured according to methods known in the art, one example of which will be further illustrated in the experimental section below.

[0055] The surface protective sheet of the present application provides satisfactory adhesive strength to a wide range of adherends, and thus can be used for a variety of applications. In view of the excellent low-fouling property and low-staining property, the surface protective sheet can be preferably used in applications where, for example, the surface of a member such as a silicon wafer, a metal plate (e.g. an aluminum plate or a steel plate), a coated plate, a resin plate, a laminated metal plate or a glass plate, an optical member such as a polarizing plate or a liquid crystal panel, or an electronic member, is protected by attaching the sheet to the surface of any such member during transportation, installation or handling of the member or for the purpose of permanent protection.

[0056] Thus, in a fourth embodiment, the present application relates to the use of the surface protective sheet according to the third embodiment for protecting PVD-based coatings, high-gloss coatings, silicon wafers, glass surfaces, optical members and medical devices, which applications require particularly high low-fouling and stain-proof properties.

[0057] It will be understood that the preferred features of the first to fourth embodiments can be freely combined in any combination, except for combinations of at least some features which are mutually exclusive.

[0058] Examples

[0059] Preparation of pressure-sensitive adhesive composition and surface protective sheet

[0060] Examples

[0061] For the preparation of example 1, the monomers ethyl acrylate (100 g) and acrylic acid (6 g) were dissolved in ethyl acetate. The mixture was degassed for 1 hour using a nitrogen flow of 0.5 liter per minute. Subsequently, the mixture was heated to 58°C and then azobisisobutyronitrile (AIBN; 10 mmol / l) was added as initiator. The reaction mixture started to exotherm and was kept at constant temperature for 5 hours. After that, the mixture was heated to 70°C to react all remaining monomers and initiator. After cooling, the polymer solution was used for adhesive formulation. To prepare PSA tapes, a non-self-condensing crosslinker was added and the mixture was diluted with solvent to obtain the desired coating viscosity. PE sheets were coated via roll-over-roll method to a dry adhesive thickness between 2 and 10 pm. The weight average molecular weight of the polymer was determined by GPC to be M w = 510 kg / mol, M e < 50 kDa, calculated from density and plateau modulus determined by rheological methods.

[0062] Example 2 was prepared in the same way as example 1, except that 70 g of ethyl acrylate, 5 g of acrylic acid and dodecyl mercaptan (0.3 g) were reacted in ethyl acetate at 6 mmol / L AIBN (M w = 385 kg / mol; M e < 50 kDa).

[0063] Example 3 was prepared in the same way as example 1, except that ethyl acrylate (100 g), acrylic acid (6 g) and dodecyl mercaptan (0.2 g) were reacted in ethyl acetate at 6 mmol / L benzoyl peroxide (M w = 150 kg / mol; M e < 50 kDa).

[0064] Example 4 was prepared in the same way as example 1, except that ethyl acrylate (80 g), butyl acrylate (26 g), acrylic acid (6 g) and dodecyl mercaptan (0.05 g) were reacted in ethyl acetate at 6 mmol / L AIBN (M w = 394 kg / mol; M e < 50 kDa).

[0065] Example 5 was prepared in the same way as example 1, except that ethyl acrylate (20 g), butyl acrylate (102 g), acrylic acid (6 g) and dodecyl mercaptan (0.05 g) were reacted in ethyl acetate at 6 mmol / L AIBN (M w = 487 kg / mol; M e < 50 kDa).

[0066] Example 6 (Mw= 630 kg / mol; MwGPC= 630 kg / mol) was prepared in the same way as Example 1 except that butyl acrylate (90 g) and acrylic acid (5 g) were reacted in ethyl acetate at 6 mmol / L benzoyl peroxide. w = 630 kg / mol; MwGPC= 630 kg / mol e <50 kDa).

[0067] Example 7 (Mw= 435 kg / mol; MwGPC= 435 kg / mol) was prepared in the same way as Example 1 except that butyl acrylate (129 g) and acrylic acid (6 g) were reacted in ethyl acetate at 6 mmol / L AIBN. w = 435 kg / mol; MwGPC= 435 kg / mol e >50 kDa).

[0068] Comparative examples

[0069] Comparative Example 1 (Mw= 613 kg / mol; MwGPC= 613 kg / mol) was prepared in the same way as Example 1 except that butyl methacrylate (75 g), isooctyl acrylate (70 g), 2-hydroxyethyl acrylate (3 g), and acrylic acid (2 g) were reacted in toluene and acetone at 1.8 mmol / L AIBN. The weight average molecular weight of the polymer was determined by GPC to be Mw= 613 kg / mol, MwGPC= 613 kg / mol. w = 613 kg / mol; MwGPC= 613 kg / mol e >50 kDa) calculated from the density and the plateau modulus determined by rheology.

[0070] Comparative Example 2 (Mw= 529 kg / mol; MwGPC= 529 kg / mol) was prepared in the same way as Example 1 except that 2-ethylhexyl acrylate (185 g) and acrylic acid (7 g) were reacted in ethyl acetate at 6 mmol / L AIBN. w = 529 kg / mol; MwGPC= 529 kg / mol e >50 kDa).

[0071] Comparative Example 3 (Mw= 830 kg / mol; MwGPC= 830 kg / mol) was prepared in the same way as Example 1 except that butyl acrylate (90 g) and acrylic acid (5 g) were reacted in ethyl acetate at 2 mmol / L benzoyl peroxide. w = 830 kg / mol; MwGPC= 830 kg / mol e <50 kDa).

[0072] Comparative Example 4 (Mw= 478 kg / mol; MwGPC= 478 kg / mol) was prepared in the same way as Example 1 except that ethyl acrylate (80 g), 2-ethylhexyl acrylate (37 g), acrylic acid (6 g), and dodecyl mercaptan (0.04 g) were reacted in ethyl acetate at 6 mmol / L AIBN. w = 478 kg / mol; MwGPC= 478 kg / mol e >50 kDa).

[0073] Comparative Example 5 (M w = 409 kg / mol, M e > 50 kDa).

[0074] PWHH measurements

[0075] The relative peak half-height (PWHH) of the polymers of Examples 2-7 and Comparative Examples 1-5 was determined by DSC as the absolute peak half-height (PWHH) of each polymer determined from the differential DSC signal at the glass transition temperature (T g ) of the reference acrylic polymer of Example 1. The results are listed in Table 1 below.

[0076] The PWHH was calculated from the normalized derivative heat flow (DSC trace). As an example, the difference in relative PWHH of the polymers of Example 5 and Comparative Example 1 is shown in Figure 1 . It is noted that both polymers exhibit comparable glass transition temperatures (T g ) showing that the PWHH is not dependent on the T g but can be controlled, in particular, by monomer selection.

[0077] Residue detection method

[0078] Color measurement

[0079] The coated glass for color measurements was supplied by Guardian Industries and used as received. The glass samples were stored at 23 °C and 50% relative humidity (rH) prior to use.

[0080] The sample was laminated with tape on the coated side and the composite was aged at 60 °C for 2 days. The composite was allowed to sit at 23 °C, 50% rH for 1 hour before the tape was removed by hand. Color measurements were made on the coated side of the glass covered on the back side with black EPDM foam using a Konica Minolta CM-5 spectrophotometer in reflectance-SCI mode and an 8 mm illumination area. The presence of residue after tape removal tends to change the color of the coated side by increasing the optical path length. The average of six measurements was calculated for a* and b* and the absolute difference from the original coating (also measured after aging) was determined (in Table 1, "+" indicates small, "0" intermediate, "-" large differences).

[0081] SFE measurement

[0082] SFE measurements were performed using a paper towel and the following analytical grade solvents for cleaning of uncoated glass: acetone, 4-hydroxy-4-methylpentan-2-one and again acetone. The substrates were placed at 23 °C and 50 % rH for at least 60 minutes prior to tape application.

[0083] The tape sample was laminated on an analytical substrate and the composite was aged for 2 days at 60 °C. The composite was placed at 23 °C, 50 % rH for 1 hour and then the tape was removed by hand. Surface free energy (SFE) measurements were performed on a Krüss DSA25E using the double sessile drop method. The contact angles of methylene iodide and water were used to calculate the SFE by the OWRK (Owens, Wendt, Rabel und Kaelble) method (see D.H. Kaelble, Dispersion-Polar Surface Tension Properties of Organic Solids. In: J. Adhesion 2 (1970), P. 66-81.; D. Owens; R. Wendt, Estimation of the Surface Free Energy of Polymers. In: J. Appl. Polym. Sci. 13 (1969), P. 1741-1747.; W. Rabel, Einige Aspekte der Benetzungstheorie und ihre Anwendung auf die Untersuchung und der von Polymeren. In: Farbe und Lack 77, 10 (1971), p. 997-1005). The average of six measurements for each sample and the original surface (without tape application) was taken. The amount of residue correlates with the reduction of the SFE of the original glass surface. In Table 1, "+" means a particularly small or negative difference (i.e. increase) between the surface free energy of the blank glass surface and the glass surface after tape removal, "o" means an intermediate difference (i.e. acceptable small reduction) between the two, and "-" means a large difference (i.e. high reduction) between the two.

[0084] For the preparation of the samples, each PSA mixture was diluted with solvent to an applicable coating viscosity. For the viscosity evaluation in Table 1, "+" means a good PSA viscosity, while "-" means an unacceptably high viscosity, requiring a large amount of solvent to sufficiently dilute to achieve coating.

[0085] Table 1

[0086]

[0087] The experimental results summarized in Table 1 show that the inventive PSA compositions leave no or only very little residue on the adherend, while at the same time providing excellent viscosity properties to facilitate coating. Furthermore, the PSA compositions are produced in a simple and inexpensive manner without the need for excessive use of organic solvents. In this regard, Examples 1 to 5, wherein the normalized PWHH is less than 1.4, perform particularly well.

[0088] On the other hand, in the case of Comparative Examples 1, 2, 4 and 5, a large amount of residue was observed, which exhibited similar M w However, a higher PWWH or M e .

[0089] With regard to Comparative Example 3, also a small amount of residue was observed. However, the individual samples exhibited an undesirably high viscosity and required a large amount of organic solvent to achieve sufficient coatability.

[0090] Numerous other features, modifications and improvements will occur to those skilled in the art once the above disclosure has been appreciated.

Claims

1. An acrylic pressure-sensitive adhesive composition comprising an acrylic polymer produced by radical polymerization, wherein the weight average molecular weight (M w ) of the acrylic polymer is less than 830 kDa; wherein the acrylic polymer comprises, as a monomer component, (meth)acrylic acid and / or (meth)acrylic acid alkyl ester having an alkyl group with a carbon number of 3 or less, and the total amount of the (meth)acrylic acid and the (meth)acrylic acid alkyl ester having an alkyl group with a carbon number of 3 or less is at least 15 parts by weight with respect to 100 parts by weight of the total amount of the monomer component; wherein the acrylic polymer comprises, as a monomer component, one or more (meth)acrylic acid alkyl ester having an alkyl group with a carbon number of 4 or more in an amount of less than 85 parts by weight with respect to 100 parts by weight of the total amount of the monomer component; and wherein the acrylic polymer has a relative half-height width (PWHH) of 1.75 or less or wherein the acrylic polymer has an entanglement molecular weight (M e ) of less than 50 kg / mol, The relative half-peak width (PWHH) of the acrylic polymer is the ratio of the absolute half-peak width (PWHH) of the acrylic polymer to the absolute half-peak width (PWHH) of a reference acrylic polymer, the absolute half-peak width (PWHH) of the acrylic polymer being determined from the differential DSC signal of the acrylic polymer at the glass transition temperature (T g ) and the absolute half-peak width (PWHH) of the reference acrylic polymer being determined in the same manner as the absolute half-peak width (PWHH) of the acrylic polymer, and wherein the reference acrylic polymer is obtained by reacting ethyl acrylate and acrylic acid in a weight ratio of 100:5 at 10 mmol / 1 AIBN, and wherein the acrylic polymer has a glass transition temperature (Tg) of from 50 to 100°C, and wherein the acrylic polymer has a glass transition temperature (Tg) of from 50 to 100°C, and wherein the acrylic polymer has a glass transition temperature (Tg) of from 50 to 100°C, and wherein the acrylic polymer has a glass transition temperature (Tg) of from 50 to 100°C, and wherein the acrylic polymer has a glass transition temperature (Tg) of from 50 to 100°C, and wherein the acrylic polymer has a glass transition temperature (Tg) of from 50 to 100°C, and wherein the acrylic polymer has a glass transition temperature (Tg) of from 50 to 100°C, and wherein the acrylic polymer has a glass transition temperature (Tg) of from 50 to 100°C, and wherein the acrylic polymer has a glass transition temperature (Tg) of from 50 to 100°C, and wherein the acrylic polymer has a glass transition temperature (Tg) of from 50 to 100°C, and wherein the acrylic polymer has a glass transition temperature (Tg) of from 50 to 100°C, and wherein the acrylic polymer has a glass transition temperature (Tg) of from 50 to 100°C, and wherein the acrylic polymer has a glass transition M e Calculated from plateau modulus determined by rheological methods.

2. The acrylic pressure-sensitive adhesive composition according to claim 1, wherein the relative half-height width (PWHH) of the acrylic polymer is 1.6 or less.

3. The acrylic pressure-sensitive adhesive composition according to claim 1, wherein the weight average molecular weight Mw of the acrylic polymer is 100,000 to 1,000,000. w in the range of 120 to 800 kDa.

4. The acrylic pressure sensitive adhesive composition of claim 1, wherein the entanglement molecular weight M e of the acrylic polymer is less than 25 kg / mol, M e calculated from the plateau modulus determined by rheological methods.

5. The acrylic pressure-sensitive adhesive composition according to claim 1, wherein the (meth)acrylic acid alkyl ester having an alkyl group with a carbon number of 3 or less is selected from the group consisting of (meth)acrylic acid methyl ester, (meth)acrylic acid ethyl ester, (meth)acrylic acid n-propyl ester, and acrylic acid isopropyl ester.

6. The acrylic pressure-sensitive adhesive composition according to claim 1, wherein the total amount of the (meth)acrylic acid and the (meth)acrylic acid alkyl ester having an alkyl group with a carbon number of 3 or less is at least 25 parts by weight with respect to 100 parts by weight of the total amount of the monomer component.

7. The acrylic pressure-sensitive adhesive composition according to claim 1, further comprising a chain transfer agent selected from one or more thiol compounds.

8. The acrylic pressure-sensitive adhesive composition according to claim 1, further comprising a crosslinking agent.

9. The acrylic pressure-sensitive adhesive composition according to claim 1, wherein the acrylic polymer comprises, as a functional monomer component, one or more acrylic ester comprising a hydroxyl group, an epoxy group, an alkoxy group, an acyl group, an acyloxy group, a silyl group, a siloxy group, a silane group, a carboxylic acid group, a 1,3-dicarbonyl group, an isocyanate group, a sulfonic acid group, an anhydride group, an alkoxycarbonyl group, an aryloxycarbonyl group, an imino ether group, an imide ether group, an amide ether group, a lactone group, a lactam group, an amide group, an acetal group, a ketal group, a ketone group, an oxazolidinone group, a carbamate group, a carbonate group, a halide group, a dialkylamino group, an oxaziridine group, an aziridine group, an oxazolidine group, an ortho ester group, a urea group, an oxetane group, or a cyano group.

10. A method for producing the acrylic pressure-sensitive adhesive composition according to any one of claims 1 to 9, comprising radical polymerization of a monomer composition comprising (meth)acrylic acid and / or (meth)acrylic acid alkyl ester having an alkyl group with a carbon number of 3 or less.

11. A surface protection sheet comprising: a substrate layer; and a pressure-sensitive adhesive layer comprising the acrylic pressure-sensitive adhesive composition according to any one of claims 1 to 9.

12. The surface protection sheet according to claim 11, wherein the substrate layer comprises a polyolefin, a polyester, a polyacrylate, a polystyrene, a polyamide, a polyvinyl chloride, a polyvinylidene chloride, a polycarbonate, or a combination thereof.

13. Use of the surface protection sheet according to claim 11 or 12 for protecting PVD-based coatings, high-gloss coatings, silicon wafers, glass surfaces, optical members, and medical devices.

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