PRESSURE-SENSITIVE ADHESIVE SHEET

[Technical Field]

[0001]

The present invention relates to a pressure-sensitive adhesive sheet, in particular to a pressure-sensitive adhesive sheet that is unsusceptible to flapping even at a high temperature and is suitable as thermal spray masking tape.

The present application claims priority to U. S. Provisional Application No. 62/199,493 filed on July 31, 2015; and the entire contents thereof are incorporated herein by reference.

[Background Art]

[0002]

In general, pressure-sensitive adhesive (PSA) has characteristics to be in a soft solid (viscoelastic) state in a room temperature range and adhere to adherends with some pressure. Because of such characteristics, PSA has been used in various fields, for instance, as a PSA sheet having a support provided with PSA at least on one face. Some PSA sheets are used when processing surfaces of objects, mainly for masking areas not to be processed. An example of such a PSA sheet for masking purposes is masking tape used in thermal spraying (thermal spray masking tape).

[0003]

Thermal spraying (e.g. flame spraying, plasma spraying, wire arc spraying, high velocity oxygen fuel (HVOF) spraying, etc.) is widely known as a process using a heat source (flame, etc.) and a coating material (possibly a coating precursor). In a typical thermal spray process, the coating material melted or heated is sprayed onto a target object to form a thin layer. Thermal spraying has advantages of being able to generate intense heat to melt a substance with a high melting point such as ceramic. In addition, thermal spraying can provide coatings over larger areas compared to other coating methods. In typical, when coating steel or copper surfaces, etc., coating materials such as metals, alloys and ceramic are used. The thermal spray process is ideal for applications such as aircraft engine hardware, engine parts, and metal rolling.

[0004]

Thermal spray masking tape is used in such a thermal spray process to prevent , , the coating material from depositmg on areas where coating is not desired m tne target object. Technical literatures related to thermal spray masking tapes include the documents listed below.

[Citation List]

[Patent Literature]

[0005]

[Patent Document l] WO 2010/017380

[Patent Document 2] WO 94/09079

[Patent Document 3] Japanese Patent Application Publication No. 2015-7229

[Summary of Invention]

[Technical Problem]

[0006]

One of the possible problems in thermal spraying with thermal spray masking tape is uneven coating and contamination caused by flapping of the tape. Here, the flapping of thermal spray masking tape refers to swinging and fluttering of partially peeled tape caused by the force of sprayed gas and particles. The uneven coating may occur because, for instance, the flapping tape prevents the thermally sprayed particles from reaching the surface to be treated. The contamination may occur due to the flapping tape touching (e.g. being beaten against) the surface of the target object, and so on.

Among thermal spraying methods, HVOF spraying involves thermally spraying the target object with high-temperature high-speed particles, ^' and therefore, it is especially susceptible to the occurrence of flapping of thermal spray masking tape.

[0007]

An objective of the present invention is thus to provide a PSA sheet which can be favorably used also as thermal spray masking tape.

[Solution to Problem]

[0008]

The PSA sheet provided by this description has first and second surfaces. The PSA sheet comprises a support having first and second faces and a PSA layer (first PSA layer) constituting the first surface of the PSA sheet on the first face side of the support.

[0009]

In an embodiment of the PSA sheet disclosed herein, the first surface of the PSA sheet may have, relative to stainless steel (SUS) at 200 °C, an adhesive strength (Slsus2oo) „ , _n „ , , „ .

of 1.5 N/m or greater. Suc a PSA sheet is less susceptible to flapping even when used as thermal spray masking tape under conditions where high-temperature high-speed particles are thermally sprayed, for instance, as in HVOF spraying. Hereinafter, the adhesive strength to SUS may be referred to as the "to-SUS adhesive strength." The properties of a PSA sheet resisting flapping may be referred to as "anti-flapping properties."

[0010]

In another embodiment of the PSA sheet disclosed herein, the first surface of the PSA sheet may have, relative to the second surface of the PSA sheet at 200 °C, an adhesive strength (S1BS2OO) greater than 2.5 N/in. Such a PSA sheet is less susceptible to flapping even when used as thermal spray masking tape, for instance, in an embodiment of at least partially overlapping application. Hereinafter, the adhesive strength of the first surface of the PSA sheet to the second surface thereof may be referred to as the "to- backside adhesive strength."

[0011]

In an embodiment of the art disclosed herein, the first surface of the PSA sheet may have an adhesive strength to SUS at 23 °C (Slsus2&) of 3.0 N/in or greater. Such a PSA sheet may provide greater handling during application to adherends at room temperature.

[0012]

In the PSA sheet according to an embodiment, the first PSA layer may comprise a sihcone-based PSA. With the first PSA layer comprising a sihcone-based PSA, the PSA sheet is likely to be obtained with the preferable properties disclosed herein. The sihcone- based PSA can be, for instance, a peroxide-curable sihcone-based PSA.

[0013]

In the PSA sheet according to an embodiment, the first PSA layer may comprise a sihcone-based PSA, with the sihcone-based PSA having a phenyl group content a of 1 % or higher based on its solid-state ²⁹ Si-NMR. With the first PSA layer comprising such a sihcone-based PSA, the PSA sheet is likely to be obtained suitably with excellent anti- flapping properties.

[0014]

In the PSA sheet according to an embodiment, the support may comprise a porous sheet. The porous sheet may comprise at least one species of fiber selected from a group consisting of glass fiber, carbon fiber, metal fiber, ceramic fiber and silicate fiber.

The support comprising such a porous sheet can suitably combine heat resistance and flexibility, ^' and therefore, it can be preferably used as the support of the PSA sheet disclosed herein.

[0015]

In an embodiment of the art disclosed herein, the PSA sheet may further comprise another PSA layer (second PSA layer) constituting the second surface of the PSA sheet on the second face side of the support. In such an embodiment, the PSA sheet may be improved in terms of ease of layering (for instance, overlapping) and shock absorption.

[0016]

In an embodiment of the art disclosed herein, the second surface of the PSA sheet may have an adhesive strength to SUS at 23 °C (S2sus2 ) of 3.0 N/in or greater. Such a PSA sheet shows great properties for overlapping application.

[0017]

In an embodiment of the art disclosed herein, the second surface of the PSA sheet has an adhesive strength to SUS at 200 °C (S2sus2oo) of 1.5 N/in or greater. Such a PSA sheet is less susceptible to flapping even when used, for instance, in an embodiment of at least partially overlapping application.

[0018]

The PSA sheet according to an embodiment, the second PSA layer may comprise a silicone-based PSA. With the second PSA layer comprising a silicone-based PSA, the PSA sheet can be obtained with the preferable properties disclosed herein. The silicone- based PSA may be, for instance, a peroxide-curable silicone-based PSA.

[0019]

In the PSA sheet according to an embodiment, the second PSA layer comprises a silicone-based PSA, with the silicone-based PSA having a phenyl group content a of 1 % or higher based on its solid-state ²⁹ Si-NMR. With the second PSA layer comprising such a silicone-based PSA, the PSA sheet is Hkely to be obtained suitably with excellent anti- flapping properties.

[0020]

A PSA sheet disclosed herein can be constituted as thermal spray masking tape (for instance, masking tape used in HVOF spraying) and favorably used in such applications. LBriet Description of Drawings!

[0021]

Fig. 1 shows a cross-sectional diagram schematically illustrating the configuration of the PSA sheet according to an embodiment.

[Description of Embodiments]

[0022]

Preferred embodiments of the present invention are described below. Matters necessary to practice this invention other than those specifically referred to in this description can be understood by a person skilled in the art based on the disclosure about implementing the invention in this description and common technical knowledge at the time of application. The present invention can be practiced based on the contents disclosed in this description and common technical knowledge in the subject field. In the drawings referenced below, a common reference numeral may be assigned to members or sites producing the same effects, and duplicated descriptions are sometimes omitted or simplified. The embodiments described in the drawings are schematized for clear illustration of the present invention, and do not necessarily represent the accurate sizes or reduction scales of products actually provided.

[0023]

As described above, the term "PSA" in this description refers to a material present in a soft solid (viscoelastic) state in a room temperature range and has a property to easily adhere to adherend with some pressure applied. As defined in "Adhesion- Fundamental and Practice by C. A. Dahlquist (McLaren & Sons (1966), P. 143), the PSA referred to herein can be a material having a property that satisfies complex tensile modulus E* (1Hz) < 10 ⁷ dyne/cm ² (typically, a material exhibiting the described characteristics at 25 °C).

[0024]

In this description, the term "adhesive face" refers to a surface that exhibits a peel strength of 0.1 N/20mm or greater when measured as follows: Based on JIS Z0237 (2004), the surface is press-bonded to a SUS304 stainless steel plate adherend with a 2 kg roller moved back and forth once in a measurement environment at 23 °C, and peeled after 30 minutes at a tensile speed of 300 mm/min in the 180° direction.

In this description, the term "non- adhesive face" refers to a surface that is not included in the adhesive face, typically a surface that exhibits a peel strength less than 0.1 N/20mm. A typical example included in the concept of non-adhesive face referred to herein is a surface that does not adhere (a surface that shows essentially no adhesion) to a SUS304 stainless steel plate when press-bonded to the stainless steel plate with a 2 kg roller moved back and forth once in a measurement environment at 23 °C.

[0025]

The PSA sheet (possibly in a form of a long piece such as tape) is in a form of a sheet having first and second surfaces. The PSA sheet comprises at least the first PSA layer forming the first surface and a support. As the support, a sheet-shaped support (a support sheet) having first and second faces can be used. Here, between the two faces of the support, the first face thereof refers to the face closer to the first surface of the PSA sheet. The face opposite from the first face of the support is referred to as the second face of the support. In an embodiment of the PSA sheet disclosed herein, the first PSA layer may be directly placed on the first face of the support. Part of the first PSA layer (typically, opposite part from the first surface of the PSA sheet) may be integrated into the support. The PSA sheet disclosed herein can be in an embodiment where the first PSA layer is placed via another layer on the first face of the support, ^" in an embodiment where the first PSA layer internally includes the support; or in an intermediate or combined embodiment of these.

[0026]

The PSA sheet disclosed herein preferably satisfies at least a property (A) or (B) described below.

[Property (A)]

The first surface of the PSA sheet shows a ixrSUS adhesive strength at 200 °C (Slsus2oo) of 1.5 N/in or greater.

[Property (B)]

The first surface of the PSA sheet has a to-backside adhesive strength at 200 °C (S1BS2OO) greater than 2.5 N/in.

The PSA sheet disclosed herein can be preferably implemented in any of the following: an embodiment satisfying only the property (A), an embodiment satisfying only the property (B), and an embodiment satisfying both the properties (A) and (B). The PSA sheet according to a preferable embodiment satisfies both the properties (A) and (B).

[0027]

Here, the to-SUS adhesive strength at 200 °C (to-SUS200°C adhesive strength) of the first surface of the PSA sheet can be obtained as follows: The first surtace ot the

PSA sheet is press-bonded to an SUS plate in an environment at 23 °C, 50 % RH and left standing in the same environment for 30 minutes; subsequently it is stored in an environment at 200 °C for 30 minutes and then subjected to measurement of 180° peel strength at a tensile speed of 300 mm/min. More specifically, the to-SUS200°C adhesive strength of the first surface can be measured according to the to-SUS200°C adhesive strength measurement method described later in Examples.

[0028]

In an embodiment, the to-SUS200°C adhesive strength of the first surface can be greater than 1.5 N/in, about 2.0 N/in or greater, about 2.5 N/in or greater (e.g. above 2.5 N/in), about 3.0 N/in or greater, or even about 3.5 N/in or greater. With increasing to- SUS200°C adhesive strength of the first surface, flapping tends to be better prevented during thermal spray processes. The first surface is not particularly limited in maximum to-SUS200°C adhesive strength. In an embodiment, the to-SUS200°C adhesive strength of the first surface can be, for instance, about 15 N/in or less, or even about 10 N/in or less, for example, about 5 N/in or less.

[0029]

The adhesive strength to the backside at 200 °C (to-backside200°C adhesive strength) of the first surface of the PSA sheet can be obtained as follows- ^' To the PSA sheet's second surface as the adherend surface with the PSA sheet has been fixed to an SUS plate, the first surface of the PSA sheet is press-bonded in an environment at 23 °C, 50 % RH and then left standing for 30 minutes in the same environment; subsequently, it is stored in an environment at 200 °C for 30 minutes and then subjected to measurement of 180° peel strength at a tensile speed of 300 mm/min. More specifically, the to- backside200°C adhesive strength of the first surface can be measured according to the to- backside200°C adhesive strength measurement method described later in Examples.

[0030]

In an embodiment, the to-backside200°C adhesive strength of the first surface can be about 2.7 N/in or greater, about 3.0 N/in or greater, about 3.5 N/in or greater, about 4.0 N/in or greater, about 4.5 N/in or greater, or even about 5.0 N/in or greater. With increasing to-backside200°C adhesive strength of the first surface, flapping tends to be better prevented during thermal spray processes when the sheet is used in a layered embodiment The first surface is not particularly limited in maximum to-backside200°C adhesive strength. In an embodiment, the to-backside200°C adhesive strength ot the first surface can be, for instance, about 20 N/in or less, about 15 N/in or less, or even about 10 N/in or less.

[0031]

<Support>

The support of the PSA sheet disclosed herein is not particularly limited as long as the PSA sheet can be obtained, satisfying at least the property (A) or (B). As the material constituting the support, various kinds of materials capable of enduring temperatures above 200 °C (more preferably temperatures above 300 °C) can be used. Non-limiting examples of materials capable of showing such heat resistance include non- metallic inorganic materials such as glass, ceramic and carbon materials; resin materials such as polyimide resin, aramide resin, polyetheretherketone (PEEK) resin,

polyetherketoneetherketoneketone (PEKEKK) resin, polyphenylene sulfide (PPS) resin, fluorine resin (e.g. polytetrafluoroetbylene (PTFE), tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PEA)), and silicone rubber; metalhc materials such as aluminum, stainless steel and copper, ^" and mixtures and composites of these materials. A support having a single-layer structure or a support having a layered structure with two or more layers formed of these materials can be used. Each layer can be a compact layer (e.g. essentially bubble-free resin film, a ceramic layer, metal, etc.) formed of one, two or more of the materials above or can be also a porous layer (e.g. a porous sheet).

[0032]

In the PSA sheet according to an embodiment, from the standpoint of the PSA sheet's handling properties and conformabihty to the adherend surface structure, etc., a support having suitable flexibility can be used. Such a support may comprise a porous sheet. The porous sheet can be a fabric sheet, such as of woven fabrics and non-woven fabrics. Non-limiting examples of the fiber constituting such a fabric sheet include glass fiber, carbon fiber, metal fiber (e.g. stainless steel fiber, steel fiber, titanium fiber, aluminum fiber, copper fiber, etc.), ceramic fiber (e.g. alumina fiber, silica fiber, alumina- silica fiber, zirconia fiber, potassium titanate fiber, rock wool, etc.), silicate fiber, and aramide fiber. Among these fibers, the porous sheet may consist of one species or may comprise two or more species in combination. The support may be formed of one, two or more porous sheets, or it may include a porous sheet and other layer(s). The PSA sheet according to an embodiment may comprise, as the support (porous support), a fabric sheet that comprises one, two or more species of fiber described above.

[0033]

In the PSA sheet according to an embodiment, a support comprising glass cloth (typically a support consisting of glass cloth) can be preferably used. Such a support may be favorable from the standpoint of the flexibility, heat resistance and strength at high temperatures. Examples of commercial glass cloth include glass cloth available from Bedford Weaving Mills, Inc., e.g. Style 1131, glass cloth available from JPS Composite Materials, glass cloth available from Nittobu, and glass cloth available from BGF

Industries, Inc.

[0034]

The size of the support is not particularly limited and can be suitably selected in accordance with the purpose and usage of the PSA sheet, etc. In an embodiment, the support may have a thickness of about 25 μηι or larger, about 50 μπι or larger, about 70 μπι or larger, or even about 80 μιη or larger. The thickness of the support can be, for instance, about 1000 μπι or smaller, about 500 μπι or smaller, about 300 μιη or smaller, or even about 200 μπι or smaller. In a typical embodiment, the thickness of the support can be about 115 μιη or larger, but about 130 μιη or smaller (e.g. about 125 μηι).

[0035]

<First PSAlayer>

The first PSA layer of the PSA sheet disclosed herein is not particularly limited in composition, thickness, etc., as far as it is formed to bring about the PSA sheet to satisfy at least the property (A) or (B). For example, the PSA constituting the first PSA layer can be one, two or more species selected among silicone-based PSA, fluorine-based PSA, polyamide-based PSA, acrylic PSA, rubber-based PSA, polyester-based PSA, polyurethane-based PSA, and polyether-based PSA. Among these, silicone-based PSA can be particularly preferably used.

[0036]

The silicone-based PSA in the art disclosed herein is not particularly limited. Any known silicone-based PSA or silicone-based PSA that can be prepared by known techniques can be used. Examples of the silicone-based PSA include peroxide-curable silicone-based PSA which crosshnks with an organic peroxide and addition-type (addition- curable) silicone-based PSA which crosshnks upon addition reaction. The silicone-based PSA can be of a single phase type or of a two phase type. For the silicone-based PSA, .

solely one species or a combination of two or more species can be used.

[0037]

Examples of commercial silicone-based PSA include, for the peroxide -curable silicone-based PSA, product names KR-100, KR-101-10 and KR-130 available from Shin- Etsu Chemical Co., Ltd.; and, for the addition-type silicone-based PSA, product names KR-3700, KR-3701, X- 0-3237-1, X-40-3240 and X-40-3291-1 available from ShnrEtsu Chemical Co., Ltd. Other examples of commercial silicone-based PSA include product names DOW282, DOW280A and DOW7657 available from Dow Chemical Company; and MOMENTTVE PSA 518 and ΜΟΜΕΝΤΓνΈ CR 593 available from General Electric Company. These examples of commercial silicone-based PSA are not to limit the silicone- based PSA used in the PSA sheet disclosed herein.

[0038]

Silicone-based PSA can be generally formed from a silicone-based PSA composition comprising at least a silicone polymer. Such a silicone-based PSA composition typically further comprises silicone resin and may further comprise as necessary additives such as crosslinking agent, catalyst (curing agent), filler, plasticizer, anti-aging agent, anti-static agent, and colorant (pigment, dye, etc.).

[0039]

As the silicone polymer, a linear silicone polymer (gum) represented by general formula [R2SiO] _n can be typically used. Here, R in the formula can be the same or different organic groups, typically hydrocarbon groups (e.g. hydrocarbon groups having about 1 to 10 carbons). Non-limiting examples of hydrocarbon groups usable as R include alkyl groups (typically alkyl groups with about 1 to 3 carbons, e.g. methyl group), alkenyl groups, aryl groups (e.g. phenyl groups, naphthyl group), arylalkyl groups, and cycloalkyl groups (e.g. cyclohexyl group). The silicone polymer may comprise, as the organic group bonded to the silicon atom, one, two or more species among the organic groups (typically hydrocarbon groups) exemplified above.

[0040]

In a preferable embodiment of the silicone polymer, the repeat unit (R2S1O) in the general formula is primarily a dimethylsiloxane unit ((CH^SiO or dimethylated unit D). The ratio (by number of units) of dimethylsiloxane units in the repeat units in the silicone polymer is typically higher than 50 %, ^' it can be about 60 % or higher, about 70 % or higher, or even about 80 % or higher. L0041J

The silicone polymer may comprise, as the repeat unit (R2S1O) in the general formula, a repeat unit having a structure where at least one phenyl group is bonded to the silicon atom. Examples of the phenyl group -containing repeat unit (phenyl group- containing siloxane unit) include a monophenylsiloxane unit having a structure where one phenyl group is bonded to the silicone atom as well as a diphenylsiloxane unit (or diphenylated unit D) having a structure where two phenyl groups are bonded to the sihcon atom. In the monophenylsiloxane unit, the other organic group bonded to the sihcon atom can be an aforementioned alkyl group, alkenyl group, aryl group (excluding a phenyl group), arylalkyl group, cycloalkyl group, etc. Examples of the

monophenylsiloxane unit include an alkylphenylsiloxane unit having a structure where one phenyl group and one alkyl group (typically an alkyl group with about one to three carbons, e.g. a methyl group) are bonded to the silicon atom.

[0042]

In the sihcon polymer according to an embodiment, with the total number of R groups that are included in the repeat unit (R2S1O) forming the silicone polymer being 100 % by mole, the ratio of phenyl groups in these R groups can be about 1 % by mole or higher, about 2 % by mole or higher, about 3 % by mole or higher, about 4 % by mole or higher, about 5 % by mole or higher, about 6 % by mole or higher, or even about 7 % by mole or higher. With increasing ratio of phenyl groups, the adhesive strength at 200 °C (either one or both of to-SUS200°C adhesive strength and to-backside200°C adhesive strength; the same applies hereinafter unless otherwise noted) tends to increase. The maximum ratio of phenyl groups is not particularly limited. From the standpoint of making it easier to obtain a suitable level of adhesive strength at 23 °C (either one or both of to-SUS23°C adhesive strength and to-backside23°C adhesive strength; the same applies hereinafter unless otherwise noted), the ratio of phenyl groups can be, for instance, about 15 % by mole or lower.

[0043]

The weight average molecular weight of the silicone polymer can be, but is not particularly hmited to, usually about 15 x 10 or higher, about 28 x 10 ⁴ to about 100 x 10 ⁴ , or even about 50 x 10 ⁴ to about 90 x lO ⁴ .

[0044]

As the silicone resin, silicone-based resin that can be used in silicone-based PSA can be used without particular limitations. Examples include silicone resin formed of an organopolysiloxane which is formed of a (co)polymer having at least one species of unit selected among a unit M represented by general formula R3S1O1/2, a unit D represented by general formula R2S1O2/2 (i.e. R2S1O), a unit T represented by general formula RSi03/2, and a unit Q represented by general formula S1O4/2. Here, the R groups of the units M, D and T represent the same or different organic groups. R is typically a hydrocarbon group with about 1 to 10 carbons. Non-limiting examples of the hydrocarbon group that can be used as R may include alkyl groups (typically alkyl groups with about 1 to 3 carbons, e.g. methyl group), alkenyl groups, aryl groups (e.g. phenyl group, naphthyl group), arylalkyl groups, and cycloalkyl groups (e.g. cyclohexyl group). The silicone resin may comprise, as the organic group bonded to the silicon atom, one, two or more species among the groups exemplified above.

[0045]

In the silicone resin according to an embodiment, with the total number of R groups that are included in the units M, D and T forming the silicone resin being 100 % by mole, the ratio of phenyl groups in these R groups can be about 1 % by mole or higher, about 2 % by mole or higher, about 3 % by mole or higher, about 4 % by mole or higher, about 5 % by mole or higher, about 6 % by mole or higher, or even about 7 % by mole or higher. With increasing ratio of phenyl groups, the adhesive strength at 200 °C tends to increase. The maximum ratio of phenyl groups is not particularly limited. From the standpoint of making it easier to obtain a suitable level of adhesive strength at 23 °C, the ratio of phenyl groups can be, for instance, about 15 % by mole or lower.

[0046]

In the silicone resin that comprises at least a unit M and further comprises at least one species among units D, T and Q, the amount (by number of Si atoms) of the unit M in the silicone resin can be, but is not particularly limited to, for instance, about 30 % by mole or greater, or even about 50 % by mole or greater, with the total amount of the units M, D, T and Q being 100 % by mole. The amount of the unit M can be about 150 % by mole or less, or even about 130 % by mole or less. The silicone resin may have, as necessary, various functional groups such as a vinyl group as an organic group bonded to the Si atom. These functional groups may be capable of giving rise to crosslinking reactions. Examples of the silicone resin include MQ resin formed of units M and Q. The weight average molecular weight of the silicone resin is typically about 1000 or higher; it can be even about 1500 or higher. The weight average molecular weight of the silicone resin can be, for instance, about 20000 or lower, or even 10000 or lower.

[0047]

In the silicone-based PSA composition comprising silicone polymer and silicone resin, the ratio between the sihcone polymer and the si cone resin is not particularly hmited. In an embodiment, the amount of si cone resin added to 100 parts by weight of sihcone polymer can be, for instance, about 40 parts by weight or greater, about 100 parts by weight or greater, or even about 120 parts by weight or greater. The amount of sihcone resin added can be, for instance, about 220 parts by weight or less, or even about 180 parts by weight or less. In the silicone-based PSA composition, the sihcone polymer and the sihcone resin can be present as a simple mixture, a partial condensate formed by a reaction between the two, etc.

[0048]

From the standpoint of the handling properties and ease of apphcation, etc., the silicone-based PSA composition can be prepared as necessary in an embodiment comprising a solvent (typically an organic solvent). As the solvent, for instance, aromatic organic solvents such as toluene and xylene can be used, but it is not limited to these. The solvent may consist of one species of organic solvent or may be a solvent mixture comprising two or more species of organic solvents.

[0049]

The sihcone-based PSA composition (e.g. a sihcone-based PSA composition comprising sihcone polymer and sihcone resin) usuaUy comprises a crosshnking agent so as to form crosslinked sihcone-based PSA. As the crosshnking agent, although not particularly hmited to these, a peroxide-based crosshnking agent, SiH group -containing siloxane-based crosshriking agent (sihcone-based crosshnking agent), and the like can be used. For the crosshnking agent, solely one species or a combination of two or more species can be used.

[0050]

As the peroxide-based crosshnking agent, for instance, diacyl peroxide, alkyl peroxy ester, peroxy dicarbonate, monoperoxy carbonate, peroxy ketal, dialkyl peroxide, hydroperoxide, ketone peroxide, and the like can be used. More specific examples include benzoyl peroxide (BPO), t-butyl peroxy benzoate, dicumyl peroxide, t-butyl cumyl peroxide, drt-butylperoxide, 2,5-dimethyl-2,5-di-t-butylperoxy hexane, 2,4-dichloro- benzoyl peroxide, di-t-butylperoxy-diisopropyl benzene, 1, l-bis(t-butylperoxy ⁾ -3,3,5- trimethylcyclohexane, and 2,5-dimethyl-2,5-di-t-butylperoxy hexene-3.

[0051]

As the siloxane-based crosshnking agent, it is suitable to use, for instance, a polyorganohydrogensiloxane having two or more sihcon atom-bonded hydrogen atoms per molecule. In such a polyorganohydrogensiloxane, the sihcon atoms to which the hydrogen atoms are bonded may have various other organic groups bonded thereto besides the hydrogen atoms. The organic groups include alkyl groups such as methyl group and ethyl group; aryl groups such as phenyl group, ^' and halogenated alkyl groups. From the standpoint of the ease of synthesis and ease of handling, the organic group is preferably a methyl group. The skeletal structure of the polyorganohydrogensiloxane can be linear, branched or cyclic, but is preferably linear.

[0052]

The amount of crosshnking agent used can be selected so that the first PSA layer is formed, capable of exhibiting the preferable properties disclosed herein. Although not particularly limited to this, for example, in an embodiment using a peroxide-based crosshnking agent such as benzoyl peroxide, the amount of crosshnking agent used to 100 parts by weight of solid content of the sihcone-based PSA composition can be, for instance, about 0.1 part by weight or greater, about 0.5 part by weight or greater, or even about 1 part by weight or greater. The amount of crosshnking agent used to 100 parts by weight of solid content of the sihcone-based PSA composition can be, for instance, about 10 parts by weight or less, about 5 parts by weight or less, or even about 2 parts by weight or less. The sihcone-based PSA can be crosslinked by a typical method.

[0053]

Although not particularly limited to this, in an embodiment where the first PSA layer comprises a sihcone-based PSA, as the sihcone-based PSA, it is preferable to use a sihcone-based PSA having a phenyl group (Ph) bonded to the sihcon atom (or a "Ph- containing sihcone-based PSA" hereinafter).

[0054]

The Ph-containing sihcone-based PSA preferably has a phenyl group content a of about 1 % or higher when determined by the next method. The phenyl group content a can be determined by solid-state ²⁹ Si-NMR analysis using as a sample the sihcone-based PSA (possibly sihcone-based PSA formed from a sihcone-based PSA composition comprising silicone polymer and silicone resin) and according to next formula :

Phenyl group content a (%) = (MF/ E) X 100

wherein, with the total number of units (by number of Si atoms) of units M, D, T and Q detected by the analysis being 100 % by mole, MR and Mp are obtained by miiltiplying the numbers of organic groups in the respective species of units by their corresponding molar fractions and combining the products to find the total value (MR) and multiplying the numbers of phenyl groups in the respective species of units by their corresponding molar fractions and combining the products to find the total value (Mp), respectively.

[0055]

The phenyl group content a can be about 2 % or higher, about 3 % or higher, about 4 % or higher, about 5 % or higher, about 6 % or higher, or even about 7 % or higher. With increasing phenyl group content a, the adhesive strength at 200 °C tends to increase. The maximum phenyl group content a is not particularly hmited. From the standpoint of obtaining suitable adhesive strength at 23 °C, the phenyl group content a can be, for instance, about 15 % or lower, or even about 10 % or lower.

[0056]

The Ph-containing silicone-based PSA preferably has a phenyl group content β of about 3 % or higher when determined by the next method. The phenyl group content 6 can be determined in the same manner as above by solid-state ²⁹ Si-NMR analysis using as a sample the silicone-based PSA and according to next formula:

Phenyl group content 6 (%) = (MDP/MDR) X 100

wherein, with the total number of units (by number of Si atoms) of units Μ, D, T and Q detected by the analysis being 100 % by mole, MDP and MDR are obtained with respect to the unit D by multiplying the numbers of organic groups in the respective species of unit D by their corresponding molar fractions and combining the products to find the total value (MDR) and multiplying the numbers of phenyl groups in the respective species of unit D by their corresponding molar fractions and combining the products to find the total value (MDP), respectively.

[0057]

The phenyl group content 6 can be about 5 % or higher, about 7 % or higher, about 10 % or higher, about 12 % or higher, or even about 14 % or higher. With increasing phenyl group content 6, the adhesive strength at 200 °C tends to increase. The maximum phenyl group content β is not particularly Hmited. From the standpoint of obtaining suitable adhesive strength at 23 °C, the phenyl group content 6 can be, for instance, about

30 % or lower, or even about 20 % or lower.

[0058]

The solid-state ²⁹ Si-NMR analysis of a silicone-based PSA can be carried out, for instance, by the method described later in Examples or by an equivalent method.

Hereinafter, a silicone-based PSA from which no Ph-bonded silicon atoms are detected in the solid-state ²⁹ Si-NMR analysis may be referred to as a "Ph-free silicone-based PSA." [0059]

In the silicone-based PSA (e.g. a Ph-containing silicone-based PSA), with the total number of units (by number of Si atoms) of units M, D, T and Q detected by the solid-state ²⁹ SrNMR analysis being 100 % by mole, the ratio of the unit D can be about 10 % by mole or higher, about 20 % by mole or higher, or even about 30 % by mole or higher. The ratio of the unit D can be about 80 % by mole or lower, about 70 % by mole or lower, or even about 50 % by mole or lower.

[0060]

The first PSA layer in the PSA sheet disclosed herein may comprise as necessary known additives that can be used in PSA, such as crosslinking agent, crosslinking aid, tackifier, plasticizer, stabilizer, leveling agent, antioxidant, colorant such as pigment and dye, filler, etc. These additives can be used solely as one species or in a combination of two or more species.

[0061]

The thickness of the first PSA layer can be selected to obtain desirable properties (e.g. adhesive strength) and is not particularly limited. In an embodiment, the first PSA layer can have a thickness of, for instance, about 10 μπι or greater, about 20 μηι or greater, about 25 μηι or greater, or even about 50 μιη or greater. With increasing thickness of the first PSA layer, the adhesive strength tends to increase. The maximum thickness of the first PSA layer is not particularly limited. From the standpoint of the cohesion and economical aspects, it can be, for instance, about 500 μηι or less, about 250 μιη or less, or even about 100 μπι or less. In an embodiment where the first PSA layer is partially integrated into the support (typically a porous support such as glass cloth), the thickness of the first PSA layer refers to the thickness from the first face of the support to the first surface of the PSA sheet unless otherwise specified.

[0062] The PSA sheet disclosed herein may satisfy the next property (C).

[Property (C)]

The first surface of the PSA sheet exhibits a to-SUS adhesive strength at 23 °C (S ISUS23) of 2.0 N/in or greater.

In application to an adherend (an object to be processed) that is typically carried out at room temperature (typically about 0 °C to 40 °C, e.g. about 10 °C to 30 °C), such a PSA sheet may be advantageous in view of the ease of application, conformabihty to the adherend surface structures, anti-lifting properties after applied (e.g. after the application up to a thermal spray process), and so on. This may also improve the anti-flapping properties. The adhesive strength to SUS at 23 °C (to-SUS23°C adhesive strength) of the first surface of the PSA sheet can be measured by the to-SUS23°C adhesive strength measurement method described later in Examples.

[0063]

In an embodiment, the to"SUS23°C adhesive strength of the first surface can be about 3.0 N/in or greater, about 5.0 N/in or greater, or even about 7.0 N/in or greater. The maximum to-SUS23°C adhesive strength of the first surface is not particularly limited. In an embodiment, the to-SUS23°C adhesive strength of the first surface can be, for instance, about 30 N/in or less, about 25 N/in or less, about 20 N/in or less, about 15 N/in or less, or even about 10 N/in or less.

[0064]

The PSA sheet disclosed herein may satisfy the next property (D).

[Property (D)]

The first surface of the PSA sheet has a ratio of to-SUS200°C adhesive strength (Slsus2oo) to to-SUS23°C adhesive strength (SISUS23) of 10 % or higher (e.g. 15 % or higher, 20 % or higher, 25 % or higher, or 30 % or higher).

Such a PSA sheet with a small decrease in adhesive strength at a high temperature (i.e. a PSA sheet with a large Slsus2oo/Slsus23 value) may exhibit excellent anti-flapping properties. The PSA sheet disclosed herein can be preferably made, for instance, in an embodiment that satisfies the properties (A), (C) and (D). The maximum value of S lsus2oo/S lsus23 is not particularly limited; it can be typically 90 % or lower, usually 70 % or lower, for instance, 50 % or lower.

[0065]

The PSA sheet disclosed herein may satisfy the next property (E). [Property (E)J

The first surface of the PSA sheet exhibits an adhesive strength to backside at 23 °C (S1BS2S) of 10 N/in or greater.

In an embodiment of at least partially overlapping application, where room- temperature application to adherends is typical, such a PSA sheet can be advantageous in view of the ease of application, conformability to the adherend surface structures, anti- lifting properties after applied (e.g. after the application up to a thermal spray process), and so on. This may also improve the anti-flapping properties. The adhesive strength to backside at 23 °C (to-backside23°C adhesive strength) of the first surface of the PSA sheet can be measured by the to-backside23°C adhesive strength measurement method described later in Examples.

[0066]

In an embodiment, the tO"backside23°C adhesive strength of the first surface can be about 15 N/in or greater, or even about 20 N/in or greater. The to-backside23°C adhesive strength of the first surface can be, for instance, about 50 N/in or less, about 40 N/in or less, or even about 30 N/in or less.

[0067]

<Backside layer>

The PSA sheet disclosed herein can further comprise a backside layer that forms the second surface of the PSA sheet on the second face side of the support. The configuration with the backside layer may allow for improvement of the PSA sheet durability (e.g. resistance to physical impact on the second surface). In an embodiment of the PSA sheet disclosed herein, the backside layer may be directly placed on the second face of the support. Part of the backside layer (typically, opposite part from the second surface of the PSA sheet) may be integrated into the support. The PSA sheet disclosed herein can also be in an embodiment where the backside layer is placed via other layer(s) on the second face of the support. The backside layer may be in an embodiment internally including the support, or may also be in an intermediate or combined embodiment of these.

[0068]

The material forming the backside layer is not particularly limited. In an embodiment, as the backside layer-forming material, it is possible to use various non- metallic inorganic materials, resin materials, and metal materials as well as mixtures and composite materials of these that can endure temperatures above 200 ^U C (jnore preferably temperatures above 300 °C).

[0069]

In an embodiment, the backside layer may comprise an elastic resin layer. Such a backside layer may allow for effective improvement of the resistance of the PSA sheet to physical impact (e.g. resistance to thermal spray processes and blast treatment) on the second surface of the PSA sheet. The elastic resin layer can be formed with, for instance, a silicone rubber-containing material, but is not particularly limited to this. The elastic resin layer may comprise as necessary known additives that can be added to resin materials, such as crosslinldng agent, crosslinking aid, tackifier, plasticizer, stabilizer, leveling agent, antioxidant, colorant such as pigment and dye, filler, etc. These additives can be used solely as one species or in a combination of two or more species. As the filler, for instance, ceramic powder, ceramic fiber, glass powder, glass fiber, metal powder, metal fiber and the like can be used.

[0070]

In an embodiment of the PSA sheet disclosed herein, the backside layer may be the second PSA layer. The PSA constituting the first PSA layer can be one, two or more species selected among, for instance, silicone-based PSA, fluorine-based PSA, polyamide- based PSA, acrylic PSA, rubber-based PSA, polyester-based PSA, polyurethane-based PSA, and polyetherbased PSA. Among these, silicone-based PSA can be particularly preferably used.

[0071]

In an embodiment, the PSA forming the first PSA layer and the PSA forming the second PSA layer can be selected from the same kinds of PSA. Such an embodiment tends to bring about a PSA sheet that shows great properties for overlapping application (e.g. a PSA sheet that satisfies one or each of the properties (B) and (E)). For instance, the PSA sheet disclosed herein can be preferably made in an embodiment where the PSA forming the first PSA layer and the PSA forming the second PSA layer are both silicone- based PSA. In the embodiment where the PSA forming the first PSA layer and the PSA forming the second PSA layer are of the same type, these PSA layers may have the same or different compositions. As the PSA forming the second PSA layer of a PSA sheet, although not particularly limited to these, for instance, the following can be used: a PSA having a composition obtainable by adding filler to the PSA forming the first PSA layer of the PSA sheet; a PSA having a composition obtainable by increasing the amount of crosslinking agent in the PSA forming the first PSA layer; a PSA having a composition that is the same type as the PSA forming the first PSA layer, but comprises a polymer that differs in (co)polymerization ratio of monomers (i.e. monomeric composition); and the like.

[0072]

In the PSA sheet according to an embodiment, the second PSA layer may comprise a Ph-containing sihcone-based PSA. For the Ph-containing sihcone-based PSA, a suitable species can be selected from the same species as the Ph-containing sihcone- based PSA species exemplified as usable species for the first PSA layer. In an

embodiment where the second PSA layer comprises a Ph-containing sihcone-based PSA, the PSA in the first PSA layer is not particularly limited. For instance, it can be a Ph- containing sihcone-based PSA, Ph-free sihcone-based PSA, non-silicone-based PSA, etc. For instance, the PSA sheet disclosed herein can be implemented in an embodiment where the second PSA layer comprises a Ph-containing sihcone-based PSA and the first PSA layer comprises either a Ph-containing sihcone-based PSA or a Ph-free sihcone-based PSA, or both.

[0073]

In the PSA sheet in an embodiment where both the first and second PSA layers comprise Ph-containing sihcone-based PSA, the phenyl group content a' of the Ph- containing sihcone-based PSA in the second PSA layer is not particularly hmited. The phenyl group content α' of the second PSA layer can be, for instance, comparable to the phenyl group content a of the first PSA layer. The phenyl group content a' of the second PSA layer can be either higher or lower than the phenyl group content a of the Ph- containing sihcone-based PSA in the first PSA layer. The phenyl group content α' of the second PSA layer can be determined in the same manner as the aforementioned phenyl group content a.

The phenyl group content 6' of the Ph-containing sihcone-based PSA in the second PSA layer is not particularly hmited. For instance, the phenyl group content 6' of the second PSA layer can be comparable to the phenyl group content β of the first PSA layer. The phenyl group content 6' of the second PSA layer can be either higher or lower than the phenyl group content 6 of the Ph-containing silicone-based PSA in the first PSA layer. The phenyl group content & of the second PSA layer can be determined in the same manner as the phenyl group content B described earlier.

In the PSA sheet according to an embodiment, the phenyl group content α' can be about 1.1 times the phenyl group content a or higher (e.g. about 1.1 to 2.0 times). In the PSA sheet according to another embodiment, the phenyl group content & can be about 1.1 times the phenyl group content 6 or higher (e.g. about 1.1 to 2.0 times).

[0074]

Although not particularly limited to this, in the PSA sheet in an embodiment where the backside layer is the second PSA layer, the second surface of the PSA sheet may have an adhesive strength to SUS at 23 °C (S2sus23) of 3.0 N/in or greater. Such a PSA sheet tends to show great properties for layering at room temperature. It is also likely to satisfy the property (E). The to-SUS23°C adhesive strength of the second surface can be measured in the same manner as the to-SUS23°C adhesive strength of the first surface except that the second surface is being measured. The to-SUS23°C adhesive strength of the second surface can be about 15 N/in or greater (e.g. about 20 N/in or greater). The t»-SUS23°C adhesive strength of the second surface can be about 50 N/in or less (e.g. about 40 N/in or less, or about 30 N/in or less).

[0075]

Although not particularly limited to this, in the PSA sheet in an embodiment where the backside layer is the second PSA layer, the second surface of the PSA sheet may have an adhesive strength to SUS at 200 °C (S2sus2oo) of 1.5 N/in or greater. Such a PSA sheet tends to be less susceptible to flapping even when used in an embodiment possibly involving at least partially overlapping application. It is also likely to satisfy the property (B). The to-SUS200°C adhesive strength of the second surface can be measured in the same manner as the to-SUS200°C adhesive strength of the first surface except that the second surface is being measured. The to-SUS200°C adhesive strength of the second surface can be about 3.0 N/in or greater (e.g. about 5.0 N/in or greater, or about 7.0 N/in or greater). The to-SUS200°C adhesive strength of the second surface can be about 30 N/in or less (e.g. about 25 N/in or less, about 20 N/in or less, about 15 N/in or less, or about 10 N/in or less).

[0076]

The thickness of the backside layer can be suitably selected in accordance with the purpose and way of use of the PSA sheet, etc. In an embodiment, the backside layer (e.g. the second PSA layer) can have a thickness of, for instance, about 10 μιη or larger, about 20 μηι or larger, or even about 25 μη or larger. With increasing thickness of the backside layer, the durability (e.g. resistance to physical impact on the second surface) of the PSA sheet tends to increase. The maximum thickness of the backside layer is not particularly krnited. From the standpoint of the handling properties and economical aspects, it can be, for instance, about 500 μηι or smaller, about 250 μιη or smaller, or even about 100 μπι or smaller. In an embodiment where part of the backside layer is integrated into the support (typically a porous support such as glass cloth), the thickness of the backside layer refers to the thickness from the second face of the support to the second surface of the PSA sheet unless otherwise specified.

[0077]

The PSA sheet disclosed herein (possibly in a form of a long piece such as tape) may have, for instance, a cross-sectional structure shown in Fig. 1. PSA sheet 1 has first and second surfaces llA and 12A. PSA sheet 1 has a support sheet 15 (e.g. a porous support such as glass cloth), a first PSA layer 11 placed on the first face 15A of support 15 and a second PSA layer (backside layer) 12 placed on the second face 15B of support 15. Of the first PSA layer 11, the outer surface forms the first surface (first adhesive face) 11A of PSA sheet 1 and the inner side is integrated into support 15. Of the second PSA layer 12, the outer surface forms the second surface (second adhesive face) 12A of PSA sheet 1 and the inner side is integrated into support 15. PSA sheet 1 can be used in an embodiment of, for instance, thermal spray masking tape applied over the first surface 11A to an adhere nd (an area to be masked in the object subject to a thermal spray process). PSA sheet 1 may also be used in an embodiment where the first surface llA of a PSA sheet 1 is applied, overlapping the second surface 12A of another PSA sheet 1. It can also be used in an embodiment where an area of the second surface 12A of a PSA sheet 1 is applied over another area of the second surface 12Aof the PSA sheet 1.

[0078]

As shown in Fig. 1, PSA sheet 1 prior to use (before applied to an adherend) can be in an embodiment where it is layered with a release finer 21 whose first and second faces 21A and 2 IB are both release faces and wound in a roll. In the double-faced PSA sheet in such an embodiment, the second and first surfaces 12A and 11A are protected with the first and second faces 21A and 2 IB of release finer 21, respectively. Fig. 1 shows an example of wound PSA sheet 1 with the first surface HAon the inner circumference side. PSA sheet 1 prior to use can be, however, in a wound form with the first surface 11A on the outer circumference side. Alternatively, PSA sheet 1 prior to use can be in an embodiment where its first and second surfaces llA and 12A are protected individually with two separate release liners.

[0079]

The configuration of the PSA sheet disclosed herein is not limited to the example shown in Fig. 1. For instance, in place of the second PSA layer 12 in the example shown in Fig. 1, it may have a backside layer (e.g. a silicone rubber layer) forming a non- adhesive second surface 12A. The second surface 12A being non-adhesive indicates that the second surface is a non-adhesive face. It may not have the second PSA layer 12 in the example shown in Fig. 1 or a backside layer; instead, the second face 15B of support 15 may form the second surface 12A of PSA sheet 1. Besides these, the PSA sheet disclosed herein can be made in a configuration having a non-adhesive elastic resin layer between the second face 15B of support 15 and the second PSA layer 12 (e.g. a configuration with "first PSA layer/support/elastic resin layer/second PSA layer"), a configuration having a non-adhesive elastic resin layer between the first face 15A of support 15 and the first PSA layer 11 (e.g. a configuration with "first PSA layer/elastic resin layer/support/second PSA layer"), a configuration having two supports with an adhesive or non-adhesive elastic resin layer between these supports (e.g. a configuration with "first PSA layer/first support/elastic resin layer/second support/second PSA layer"), etc. Between a certain layer constituting the PSA sheet disclosed herein and an adjacent layer or between the certain layer and the support, another layer may be provided as necessary to increase the tightness of adhesion, etc.

[0080]

The thickness of the PSA sheet disclosed herein can be suitably selected in accordance with the purpose and way of use of the PSA sheet, etc., with no particular limitations. In an embodiment, the PSA sheet may have a thickness of, for instance, about 50 μηι or larger, about 100 μηι or larger, or even about 150 μιη or larger. With increasing thickness of the PSA sheet, the durability (e.g. resistance to physical impact on the second surface) tends to increase. In an embodiment, the thickness of the PSA sheet can be, for instance, about 2000 μιη or smaller, about 1000 μιη or smaller, about 500 μπι or smaller, or even about 300 μπι or smaller. With decreasing thickness of the PSA sheet, the PSA sheet's ease of handling and conformability to surface structures tend to increase. The thickness of the PSA sheet here refers to the thickness from the first surface to the second surface, not including the thickness of the release liner.

[0081]

<Fabrication of PSA sheet>

The PSA sheet disclosed herein can be produced by providing the first PSA layer at least on the first face side of a support. The method for providing the first PSA layer is not particularly limited. With respect to the first PSA layer, for instance, a PSA composition can be applied to a support and allowed to dry or cure as necessary to form the first PSA layer on the support (a direct method). Alternatively, a PSA composition can be applied to a suitable release face and allowed to dry and cure as necessary to form the first PSA layer on the release face and the first PSA layer can be applied over the first face of a support to provide the first PSA layer on the support (a transfer method). The method for applying the PSA composition is not particularly limited. Examples of known application methods include kiss coating, gravure coating, bar coating, knife coating, and wire coating. In the PSA sheet comprising a second PSA layer, the second PSA layer can be formed by various methods similar to those for the first PSA layer.

[0082]

The PSA sheet in an embodiment comprising the first and second PSA layers can be produced, for instance, using a porous release finer. A preferable release liner may be resistant to temperatures around or above 150 °C. A porous release liner formed with a flexible material resistant to these temperatures is preferable. The porous release finer may be formed also from an arbitrary material having an air permeability of 5 sec/lOOcc to 30000 sec/lOOcc. The air permeability of the porous release liner is more preferably about 5 sec/lOOcc to 3000 sec/lOOcc, or particularly preferably about 5 sec/lOOcc to 300 sec/lOOcc.

[0083]

Examples of a material usable for the porous release liner include plastic film such as polyethylene terephthalate and polytetrafluoroethylene and non-woven fabric such as crepe paper. Examples of usable commercial porous release liner include Fiber Mark products such as CREPE PAPER #94389, CREPE PAPER #60403 and CREPE PAPER #94096. Thick crepe paper is preferable since it shows greater release properties. The grammage of the porous release liner is not particularly limited, ^' it can be, for instance, about 30 g/m ² to 300 g/m ² , or preferably about 50 g/m ² to 150 g/m ² . In an embodiment, a porous release liner (e.g. crepe paper) having a grammage of about 70 g/m ² to 105 g/m ² can be used.

[0084]

The properties of the porous release liner can be suitably selected in accordance with the purpose. The thickness of the porous release hner can be usually about 50 μηι to about 500 μηι, preferably about 150 μηι or larger (typically about 150 μηι to about 500 μηι). In the present invention, with increasing thickness of the porous release Hner, the release of the PSA layer (i.e. the release of the PSA layer from the porous release hner in use) tends to be facilitated.

[0085]

The porous release Hner can be treated on the surface with a suitable surface treatment agent. The surface treatment agent can be selected arbitrarily. Examples of suitable surface treatment agents include a long-chain alkyl branched polymer and fluorosiHcone. Examples of commercial fluorosihcone surface treatment agents include Dow Corning products SYLOFF Q2-7785 and SYLOFF Q2-7786. Examples of commercial long-chain alkyl branched polymer surface treatment agents include

ESCOAT® P-20 (polyvinyl octadecyl carbamate). From the standpoint of improving (i.e. facihtating) the separation of the porous release Hner from the PSA layer, ESCOAT® P-20 is preferable. The number of carbons in the long-chain alkyl group is preferably 12 to 24, or more preferably 14 to 22. These surface treatment agents can be used solely as one species or in a combination of two or more species. The porous release Hner may be treated on one or each face with such a surface treatment agent.

[0086]

There are no particular limitations to the method for fabricating a porous release Hner treated with such a surface treatment agent. The thickness of the coating (surface treatment layer) formed from the surface treatment agent can be suitably selected in accordance with the purpose. It is usuaHy about 0.1 μιη to about 100 μπι. The coating amount of the surface treatment agent can be suitably selected in accordance with the purpose. It is usuaHy about 0.05 g/m ² to 1.0 g/m ² (e.g. about 0.07 g/m ² to 0.7 g/m ² ).

[0087]

Such a porous release Hner can be favorably used in a PSA sheet production method that includes directly applying the first and second PSA compositions used for forming the first and second PSA layers onto the first and second faces of a support (e.g. a porous support such as glass cloth), respectively. For instance, the first PSA composition is applied to the first face of the support and allowed to dry and cure to tbrm the hrst PSA layer. The porous release liner is then layered over the surface of the first PSA layer and the resultant is wound in a roll. The roll is subsequently unwound and the second PSA composition is applied to the second face of the support having the first PSA layer on its first face and allowed to dry and cure to form the second PSA layer. The resulting double- faced PSA tape is wound in a roll.

[0088]

In producing a PSA sheet with the first and second PSA layers being of silicone- based PSA (i.e. a PSA sheet with two silicone -based PSA layers) by such a procedure, depending on the composition of the silicone-based PSA and curing conditions, etc., bubbles may have formed inside the first PSA layer while the second PSA composition is being dried. It is thought, for instance, that the bubbles form due to side products of a free radical reaction formed during curing of the silicone-based PSA. The use of the porous release finer can effectively reduce the formation of bubbles also in a production method where both the first and second PSA layers are formed by the direct method. For example, when a benzoyl peroxide-curable silicone-based PSA is used, benzoic acid side product is likely to cause formation of bubbles, ^' however, with the use of a porous release finer such as those described above, the formation of bubbles may be avoided. This may be because the benzoic acid can be eliminated to the outside via fine pores of the porous release finer.

[0089]

In producing the PSA sheet disclosed herein, the temperature at which the silicone-based PSA composition is allowed to dry and cure can be, but is not particularly limited to, for instance, about 100 °C to about 200 °C; it is usually preferably on or above about 150 °C (typically about 150 °C to about 200 °C).

[0090]

The PSA sheet disclosed herein shows excellent anti-flapping properties as described above. Thus, it is useful in a process of causing solid or liquid particles to hit the surface of a target object, a process of exposing the target object surface to a liquid stream, air stream, etc., and like process, for protecting or masking areas not to be processed in the target object. Examples of such processes include a thermal spray process, blasting process (e.g. sand blasting process), shot peening process, painting process, ceramic coating process and the like of surfaces of target objects. The PSA sheet disclosed herein is less susceptible to napping even at high temperatures; and thereiore, it can be preferably used as thermal spray masking tape. For instance, it is favorable as thermal spray masking tape for use in HVOF thermal spraying or plasma thermal spraying, and is particularly preferable as thermal spray masking tape for use in HOVF thermal spraying.

[0091]

The matters disclosed by this description include the following:

(1) A PSA sheet having first and second surfaces, comprising:

a support having first and second faces, and,

on the first face side of the support, a PSA layer (first PSA layer) forming the first surface of the PSA sheet, wherein

the first surface of the PSA sheet shows an adhesive strength of 1.5 N/in or greater to stainless steel at 200 °C.

(2) A PSA sheet having first and second surfaces, comprising:

a support having first and second faces, and,

on the first face side of the support, a PSA layer (first PSA layer) forming the first surface of the PSA sheet, wherein

the first surface of the PSA sheet shows an adhesive strength greater than 2.5 N/in to the second surface of the PSA sheet at 200 °C.

(3) The PSA sheet according to (l) or (2) above, wherein the first surface of the PSA sheet shows an adhesive strength of 3.0 N/in or greater to stainless steel at 23 °C.

(4) The PSA sheet according to any of (l) to (3) above, wherein the first PSA layer comprises a sihcone-based PSA.

(5) The PSA sheet according to any of (l) to (4) above, wherein the first PSA layer comprises a peroxide-curable sihcone-based PSA.

(6) The PSA sheet according to any of (l) to (5) above, wherein the first PSA layer comprises a sihcone-based PSA, with the sihcone-based PSA having a phenyl group content a of about 1 % or higher based on its solid-state ²⁹ SrNMR.

(7) The PSA sheet according to any of (l) to (6) above, wherein the first PSA layer comprises a sihcone-based PSA, with the sihcone-based PSA having a phenyl group content 6 of about 3 % or higher based on its solid-state ²⁹ Si"NMR.

(8) The PSA sheet according to any of (l) to (7), wherein the first PSA layer has a thickness of about 25 μηι or larger. L0092J

(9) The PSA sheet according to any of (l) to (8) above, wherein the support comprises a porous sheet.

(10) The PSA sheet according to (9) above, wherein the porous sheet comprises at least one species of fiber selected from a group consisting of glass fiber, carbon fiber, metal fiber, ceramic fiber and silicate fiber.

(11) The PSA sheet according to (9) or (lO) above, comprising glass cloth as the porous sheet.

(12) The PSA sheet according to any of (9) to (ll) above, wherein the porous sheet has a thickness of about 80 μπι or larger, but about 200 μηι or smaller.

[0093]

(13) The PSA sheet according to any of (l) to (12) above, further comprising, on the second face side of the support, another PSA layer (second PSA layer) forming the second surface of the PSA sheet.

(14) The PSA sheet according to (13) above, wherein the second surface of the PSA sheet shows an adhesive strength of 3.0 N/in or greater to stainless steel at 23 °C.

(15) The PSA sheet according to (13) or (14) above, wherein the second surface of the PSA sheet shows an adhesive strength of 1.5 N/in or greater to stainless steel at

200 °C.

(16) The PSA sheet according to any of (13) to (15) above, wherein the second PSA layer comprises a silicone-based PSA.

(17) The PSA sheet according to any of (13) to (16) above, wherein the second PSA layer comprises a peroxide-curable sihcone-based PSA.

(18) The PSA sheet according to any of (13) to (17) above, wherein the second PSA layer comprises a sihcone-based PSA, with the sihcone-based PSA having a phenyl group content a' of about 1 % or higher based on its solid-state ²⁹ Si-NMR.

(19) The PSA sheet according to any of (13) to (18) above, wherein the second PSA layer comprises a sihcone-based PSA, with the sihcone-based PSA having a phenyl group content 6' of about 3 % or higher based on its solid-state ²⁹ Si-NMR.

(20) The PSA sheet according to any of (13) to (19) above, wherein the second PSA layer has a thickness of about 25 μιη or larger.

(21) The PSA sheet according to any of (l) to (20) above, having a thickness of about 100 μηι or larger, but about 500 μιη or smaller from the first surface to the second surface.

(22) The PSA sheet according to any of (l) to (21) above, formed as thermal spray masking tape.

[Examples]

[0094]

Several examples related to the present invention are described below, but the present invention is not to be limited to these examples.

[0095]

In Examples 1 and 2 below, solid-state ²⁹ SrNMR analysis of the PSA was carried out under the following conditions.

[Solid-state ²⁹ Si-NMR conditions]

(1) Measurement system and measurement conditions

System used: Bruker Biospin AVANCE III 400WB

Nucleus analyzed: ²⁹ Si

Frequency observed: 79.5 MHz

Analytical method: DD MAS (Dipolar Decoupling / Magic Angle Spinning)

Probe diameter: 7mm

Spinning speed: 5kHz

Standard chemical shift: silicone rubber ( ²⁹ Si: -22.3 ppm)

Temperature of analysis: room temperature

(2) Analytical procedure

The surface of the PSA layer of interest was scratched with a needle to collect a sample. The collected sample was placed in a tube of 7 mm diameter. At a spinning speed of 5 kHz, at room temperature, the sample was analyzed by ²⁹ Si DD/MAS NMR. As the external standard, silicone rubber (-22.3 ppm) was used.

[0096]

<Fabrication of PSA sheets>

(Example l)

To 100 parts by weight of solid content of a silicone-based PSA (product name XR37-B6722 available from Momentive Performance Materials Worldwide Inc.) which comprised a silicone polymer primarily comprising dimethylsiloxane units as constituent units and also had diphenylsiloxane units, was added 1.6 parts by weight of benzoyl peroxide. The mixture was stirred and dispersed with a dispersion mixer to prepare a PSA composition PI. The PSA composition PI was apphed to the first face of glass cloth

(Style 1131 available from Bedford Weaving Mills, Inc.) of about 125 μιη in thickness as the support and allowed to dry and cure at 180 °C for 6 minutes. On the first face of the glass cloth, the PSA layer of 35 μπι in thickness (i.e. the first PSA layer covering the first face of the glass cloth to a thickness of 35 μηι) was thus formed.

[0097]

The silicone unit ratio of the first PSA layer (PSA layer formed from the PSA composition Pi) was determined based on the solid-state ²⁹ Si-NMR to be 27.28 % by mole (by number of Si atoms, the same applying hereinafter) trimethylated unit M

((CH ₃ )3SiOi/ ₂ ), 33.47 % by mole dimethylated unit D ((CHs^SiC^a), 5.88 % diphenylated unit D ((C ₆ H ₅ )2Si02/2), and 33.37 % by mole unit Q3 (Si(OH)0 ₂ / ₃ ) and unit Q4 (S1O4/2) combined. From this result, the phenyl group contents a and β of the first PSA layer were determined to be 7.3 % and 14.9 %, respectively.

[0098]

To the surface of the first PSA layer, a release liner was adhered. As the release finer, was used a porous release finer obtained by treating each face of crepe paper (product name CREPE PAPER #94389 available from FiberMark) with a long-chain alkyl release agent (product name ESCORT® P-20, a polyvinyl octadecyl carbamate available from Anderson Chemical Company). Subsequently, to the second face of the glass cloth, the PSA composition PI was apphed and allowed to dry and cure at 180 °C for 6 minutes to form the second PSA layer of 35 μπι in thickness on the second face of the glass cloth. To the surface of the second PSA layer, was adhered the same release finer as the one adhered to the first PSA layer.

[0099]

In such a manner, a PSA sheet according to Example 1 was obtained, formed of the first and second PSA layers placed on the first and second faces of glass cloth, respectively. The first and second surfaces (adhesive faces) of the PSA sheet are formed with the first and second PSA layers, respectively, with each adhesive face protected with the release liner. The PSA sheet was about 195 μιη thick overall (the thicknesses of the release liners not included).

[0100]

(Example 2)

In this example, in place of the sihcone-based PSA used in Example 1, was used a silicone-based PSA (product name DOW282 available from Dow Chemical Company) which comprised a silicone polymer primarily comprising dimethylsiloxane units as constituent units and was free of diphenylsiloxane units. To 100 parts by weight of solid content of the silicone-based PSA, was added 1.6 parts by weight of benzoyl peroxide. The mixture was stirred and dispersed with a dispersion mixer to prepare a PSA composition Nl. In place of the PSA composition PI, the PSA composition Nl was used. Otherwise in the same manner as Example 1, a PSA sheet according to Example 2 was obtained. The silicone unit ratio of the first PSA layer of the PSA sheet according to this Example (PSA layer formed from the PSA composition Nl) was determined based on the solid-state ²⁹ Si- NMR to be 25.94 % by mole trimethylated unit M ((CHDsSiOi/z), 43.75 % by mole dimethylated unit D ((CHa^SiOaz), and 30.31 % by mole umt Q3 (Si(OH)0 ₂ / ₃ ) and unit Q4 (S1O42) combined. No diphenylated unit D ((CeHk^S^s) was detected.

[0101]

(Example 3)

The first and second PSA layers were both 80 μηι in thickness (in glass cloth- covering thickness). Otherwise in the same manner as Example 1, a PSA sheet according to this Example was obtained.

[0102]

(Example 4)

Were blended silicone-based PSAXR37-B6722 used in Example 1 and silicone- based PSADOW282 used in Example 2 at a XR37"B6722:DOW282 weight ratio of 3:1. To 100 parts by weight of solid content of this blend, was added 1.6 parts by weight of benzoyl peroxide. The mixture was stirred and dispersed with a dispersion mixer to prepare a PSA composition P2. In place of the PSA composition PI, was used the PSA composition P2. Otherwise in the same manner as Example 1, a PSA sheet according to this Example was obtained. The phenyl group content a of the first PSA layer was determined in the same manner as Example 1 and found to be 5.5 %.

[0103]

(Example 5)

The XR37-B6722:DOW282 blend ratio (weight ratio) was 1:1. Otherwise in the same manner as the preparation of the PSA composition P2, a PSA composition P3 was prepared. In place of the PSA composition Pi, was used the PSA composition P3.

Otherwise in the same manner as Example 1, a PSA sheet according to this Example was obtained. The phenyl group content a of the first PSA layer was determined in the same manner as Example 1 and found to be 3.7 %.

[0104]

(Example 6)

The first and second PSA layers were both 20 μχη in thickness (in glass cloth- covering thickness). Otherwise in the same manner as Example 1, a PSA sheet according to this Example was obtained.

[0105]

<Evaluation of Properties>

(Measurement of to ^_ SUS23°C adhesive strength)

The PSA sheet according to each Example was cut to a 1 inch wide strip to prepare a test piece. In an environment at 23 °C, 50 % RH, the release Uner covering the first surface of the test piece was removed and the exposed first surface (first adhesive face) was press-bonded to a stainless steel plate (SUS plate) as the adherend with a 2 kg roller moved back and forth once. Subsequently, using a tensile tester, based on JIS Z0237:2009, the 180° peel strength (N/in) was measured at 23 °C at a tensile speed of 300 mm min.

[0106]

(Measurement of to-SUS200°C adhesive strength)

The PSA sheet according to each Example was cut to a 1 inch wide strip to prepare a test piece. In an environment at 23 °C, 50 % RH, the release hner covering the first surface of the test piece was removed and the exposed first surface (first adhesive face) was press-bonded to an SUS plate as the adherend with a 2 kg roller moved back and forth once. This was left standing in the environment at 23 °C, 50 % RH for 30 minutes, then set in a tensile tester and stored in an environment at 200 °C for 30 minutes. Subsequently based on JIS Z0237-2009, at a tensile speed of 300 mm/min, the 180° peel strength (N/in) at 200 °C was measured.

[0107]

(Measurement of to-backside23°C adhesive strength)

The PSA sheet according to each Example was cut to a 1 inch wide strip and the release hner covering the first surface was removed. The first surface of the PSA sheet was fixed to the SUS plate by bonding with heat-resistant adhesive. Subsequently, from the PSA sheet bonded to the SUS plate, the release hner covering the second surface was removed to expose the second surface, thereby preparing an adherend tor measurement of to-backside adhesive strength. To the exposed second surface of the adherend, the first adhesive face of the PSA sheet of interest was press-bonded. Otherwise in the same manner as the to-SUS23°C adhesive strength, the ixrbackside23 ⁰ C adhesive strength was measured.

[0108]

(Measurement of to-backside200°C adhesive strength)

The PSA sheet of interest was press-bonded over the first adhesive face to the exposed second surface of the adherend for measurement of to-backside adhesive strength. Otherwise in the same manner as the to-SUS200°C adhesive strength, the ter backside200°C adhesive strength was measured.

[0109]

(Thermal spray test)

The PSA sheet according to each Example was cut to a 1 inch wide strip to prepare a test piece. In an environment at 23 °C, 50 % RH, the release hners covering the first and second surfaces of each test piece were removed. With the first surface on the inside, the test piece was wrapped three times around the circumference of a 50 mm diameter column of a steel material (an object subject to thermally spraying). The surface of the steel material used had been blasted with #24 alumina grit in advance. With respect to each test piece, for the first round, the first surface was applied to the surface of the steel material; for the second and third rounds, the first surface was applied over the second surface (backside face) of the previous round of the same test piece. The sample was stored in an environment at 23 °C, 50 % RH and then subjected to the following thermal spray test.

For the thermal spray test, was used an HVOF thermal spraying system JP- 5000 available from Praxair, Inc. While the steel material wrapped with the test piece was kept horizontally and rotated around the axis at a speed of 150 rpm, the steel material was thermally sprayed, vertically downward, over the outer circumferential surface. The tip of the thermal spray gun was at 380 mm above the outer circumferential surface of the steel material. As the thermal spray material, tungsten carbide particles of 15 μιη to 45 μ ι in average particle diameter were used. The thermal spraying conditions were adjusted so as to obtain a speed of thermally sprayed particles of about Mach 2 and a flame speed of about Mach 6. The thermal spray gun was moved at a speed of 25 mm/sec in the direction of the axis of the steel material and a 500 mm segment including the area wrapped with the test piece was thermally sprayed five times. The process was recorded in motion and the video was visually inspected to judge whether or not flapping occurred in the test piece wrapped around the steel material during the thermal spray process.

The steel material after the thermal spray test was allowed to cool to room temperature. The test piece was then removed from the steel material and the length of the test piece that remained after the thermal spraying was measured.

[0110]

Table 1 summarizes the results of the tests described above.

[0111]

[Table l]

Table 1

[0112]

As shown in Table 1, with respect to the PSA sheets of Examples 2 and 6, flapping was observed in the thermal spray test; however, with respect to the PSA sheets of Examples 1 and 3 to 5, no flapping was found. As compared to the PSA sheets of Examples 2 and 6, the PSA sheets of Examples 1 and 3 to 5 showed higher resistance to thermal spraying with longer lengths remaining after the thermal spray test.

[0113]

Although specific embodiments of the present invention have been described in detail above, these are merely for illustrations and do not limit the scope of claims. The art according to the claims includes various modifications and changes made to the specific embodiments illustrated above.

[Reference Signs List]

[0114] l: PSA sheet

1 : first PSA layer

1A: first surface (surface of first PSA layer)2: second PSA layer (backside layer)

2A '· second surface (surface of second PSA layer)5: support

5A: first face

5B: second face

1: release liner

1A: first face

IB: second face