WO2019159380A1

WO2019159380A1 - Method for applying pressure-sensitive adhesive sheet, surface protection method and method for preparing pressure-sensitive adhesive sheet

Info

Publication number: WO2019159380A1
Application number: PCT/JP2018/014525
Authority: WO
Inventors: Kousuke Yonezaki; Hakaru Horiguchi
Original assignee: Nitto Denko Corp
Current assignee: Nitto Denko Corp
Priority date: 2018-02-13
Filing date: 2018-04-05
Publication date: 2019-08-22
Anticipated expiration: 2020-08-13

Abstract

[Problem] Provided is a method for applying a pressure-sensitive adhesive (PSA) sheet suited for a large target area. [Solving Means] Provided is a method for applying a PSA sheet to a target area of an adherend. The method comprises: from a workpiece group comprising at least two species of initial PSA sheets differing in width, selecting, based on the width of the target area, one, two or more initial PSA sheets that are individually not wide enough to cover the target area; preparing a one-piece PSA sheet having a width large enough to cover the target area by processing the selected initial PSA sheets; and applying the PSA sheet to the target area.

Description

METHOD FOR APPLYING PRESSURE-SENSITIVE ADHESIVE SHEET, SURFACE PROTECTION METHOD AND METHOD FOR PREPARING PRESSURE-SENSITIVE ADHESIVE SHEET

The present invention relates to method for applying a pressure-sensitive adhesive sheet, surface protection method and method for preparing a pressure-sensitive adhesive sheet.
The present application claims priority to U. S. Provisional Patent Application No. 62/629,826 filed on February 13, 2018, the entire contents of which are incorporated herein by reference.

In general, pressure-sensitive adhesive (or PSA; the same applies hereinafter) has characteristics of being in a soft solid (viscoelastic) state in a room temperature range and easily adhering to adherend under some pressure. Because of these characteristics, for instance, as a PSA sheet having a substrate, PSA is widely used for purposes such as bonding, fixing and protecting various parts. A surface protection sheet using PSA typically has a PSA layer on one face of a substrate sheet formed of a material such as resin and is constituted so as to achieve a protection purpose when applied via the PSA layer to an adherend (an object to be protected). Conventional art documents disclosing PSA sheets usable as surface protection sheets include JP2017-186517A (Patent Document 1), JP5719194B2 (Patent Document 2), JP2012-131976A (Patent Document 3) and JP3571460B2 (Patent Document 4).

As the adherend (e.g. glass plates used for building materials such as window glass), for efficient production, transportation and so on, objects having large surface areas may be used, among which some have surface widths as large as about 2.6 m or greater, or even about 3 m or greater. In such an adherend having a large surface area (a large-surface adherend), the area to be covered with a PSA sheet applied thereto, that is, the target area for the PSA sheet application (or simply the “target area” hereinafter), may be a large surface area as well. On the other hand, when covering a large target area by PSA sheet application, in typical, several PSA sheets are applied successively to the adherend. However, according to such an application method, the application process needs to be repeated as many times as the number of PSA sheets used; and furthermore, their placement needs to be adjusted between the PSA sheets as well as between the respective PSA sheets and the target area, making the application work complicated. Thus, even for a large target area, it is desirable to apply one continuous PSA sheet having a size large enough to entirely cover the target area.

With respect to the length direction, the PSA sheet is not usually limited in size when it is supplied from a roll or the like; however, with respect to the width direction, it is limited by the PSA sheet manufacturing equipment, etc. Thus, production of a PSA sheet sufficient both in length and in width requires large-scale equipment that allows production of a wide PSA sheet. In addition, adherend objects (e.g. glass plates used for building materials) are not necessarily produced in the same size in a large quantity and their sizes can be different each time. Such a case requires an on-demand supply of a certain quantity of PSA sheets that meet the size requirement and may not be suited for handling by large-scale manufacturing equipment.

The present invention has been made in view of these circumstances with an objective to provide a method for applying a PSA sheet and a surface protection method suited for a large target area. Another related objective is to provide a method for efficiently preparing a desirably wide PSA sheet from initial PSA sheet(s) (workpiece(s)) that are individually not sufficiently wide.

The present description provides a method for applying a PSA sheet to a target area of an adherend. The application method includes determining the width of the target area (determining how wide the target area is). The application method includes: from a workpiece group including at least two species of initial PSA sheets differing in width, selecting, based on the width of the target area, one, two or more initial PSA sheets that are individually not wide enough to cover the target area. Here, the initial PSA sheets individually comprise a substrate layer and a PSA layer provided to at least one face of the substrate layer. The application method also includes preparing a one-piece PSA sheet having a width large enough to cover the target area by processing the selected initial PSA sheets. The application method further includes applying the PSA sheet to the target area. Hereinafter, the PSA sheet thus prepared by processing the initial PSA sheet(s) is also referred to as a final PSA sheet. As used herein, a final PSA sheet refers to a PSA sheet after the processing, and does not necessarily mean a PSA sheet as a finished product. Accordingly, the final PSA sheet may be further processed or treated, as needed, before it is applied to an adherend.

In the application method, from one, two or more initial PSA sheets that are individually not wide enough to cover the target area, a one-piece PSA sheet having a width large enough to cover the target area is prepared and the resulting PSA sheet is applied. Thus, as compared to the conventional method where several PSA sheets are successively applied, this method enables efficient application. In addition, because there is not such a case where a gap is formed between the several PSA sheets, it does not require a component (a third component) to fill a gap if any. The application method can be applied to a case where, with existing equipment, it is difficult to directly produce a PSA sheet wide enough to cover the target area because of, for instance, the width limitation of a given PSA composition coater (applicator) used for forming a PSA layer and width limitations of given dryer and UV illuminator used when forming a PSA layer from the PSA composition just applied. Thus, the application method disclosed herein can be particularly preferably employed when the target area has a relatively large width (e.g. a width of 1 m or greater, 2.6 m or greater, or even 3.0 m or greater).

The initial PSA sheets and the final PSA sheet prepared from the initial PSA sheets disclosed herein are typically identified by having a long side and a short side with respect to its plane (sheet face). By definition, the long side is longer than the short side and the short side is shorter than the long side. For instance, the short side may be approximately perpendicular to the long side. The length directions of the initial and final PSA sheets are in the directions along their long sides and the width directions are in their directions perpendicular to their length directions. Thus, as used herein, the “width” is defined as the length in the direction perpendicular to the length direction. Typical examples of the PSA sheet disclosed herein include a PSA sheet that is described as having a long length, a band shape, and a rectangular shape. The same applies to the initial PSA sheets.

As used herein, when the target area is rectangular, the “target area’s width” or the “width of the target area” refers to the short side length of the rectangle. When the target area is not rectangular, the target area’s width is the short side length of a rectangle circumscribing the target area. The concept of rectangle here includes a square. With a square, the long side length is equal to the short side length; and therefore, when the target area is a square, the target area’s width is the side length of the square. The target area can be, for instance, the entire surface area of one face of an adherend or part of the surface area of the one face. When the PSA sheet is applied entirely to one face of a flat adherend such as a glass plate and a steel plate, the adherend width is the target area’s width. The concept of determining the width of a target area includes: measuring the target area’s width, using an adherend whose target area’s width has been known; and obtaining data related to the target area’s width from a user of the PSA sheet. Thus, when the art disclosed herein is implemented, it is not always necessary to actually measure the target area’s width for each adherend; it is satisfactory that the width is known.

In this description, “a PSA sheet that is not individually wide enough to cover a target area” (or simply “an insufficiently-wide PSA sheet” hereinafter) indicates that the width of the initial PSA sheet is smaller than the target area’s width. In contrast, “a PSA sheet having a width large enough to cover a target area” (or simply “a wide-enough PSA sheet” hereinafter) indicates that the width of the initial PSA sheet is equal to or greater than the target area’s width.

In some embodiments of the art disclosed herein (including the PSA sheet application method, the surface protection method and the PSA sheet preparation method; the same applies hereinafter), the preparing the PSA sheet may include joining two of the initial PSA sheets to obtain a larger width (e.g. joining the sheets at their long sides). By the width-extending joining, a one-piece final PSA sheet can be obtained having a larger width than either of the initial PSA sheets prior to the joining process. Thus, a one-piece wide-enough PSA sheet can be prepared by: from the workpiece group, based on the target area’s width, suitably selecting at least two initial PSA sheets that are not individually wide enough, followed by joining them into one piece having a larger width. The widths of the at least two initial PSA sheets to be joined to obtain a larger width may be equal or different. The width-extending joining can be carried out by fusing or engaging the initial PSA sheets with each other; by bonding, adhesion, sewing using a connecting material or a subsidiary material; or by like method.

In a preferable embodiment of the art disclosed herein, the PSA sheet has first and second faces forming its outer surface. Here, the second face is the opposite face of the first face. At least either the first face or the second face is an adhesive face. The width-extending joining of the two initial PSA sheets is preferably carried out so as to form a final PSA sheet whose joined section is free of an uneven segment either in the first face or in the second face. Such a PSA sheet is free of an uneven segment such as a projection on either face; and therefore, for instance, the adhesive face of the final PSA sheet is likely to tightly adhere to an adherend without wrinkling, lifting, etc., caused by a possible uneven segment. In addition, when the PSA sheet is in a roll form, a defect caused by a possible uneven segment will not occur.

In some embodiments of the art disclosed herein, the width-extending joining can be preferably carried out by abutting lengthwise edge faces (i.e. long-side edge faces or edge faces of the sheets’ width directions) and fusing the abutted edge faces. By such width-extending abutting fusion, a one-piece wide-enough PSA sheet can be favorably prepared. For instance, the PSA sheet joined by fusion (typically by direct fusion) may have sufficient joint strength and may be of high quality with its adhesive face, back face, etc., as smooth as those of the initial PSA sheets before joined, etc. Such a PSA sheet may have good adhesive properties; for instance, when used as a protective sheet, it may provide good protection.

In a preferable embodiment of the art disclosed herein, the fusion is thermal fusion by laser irradiation (the at least two initial PSA sheets are thermally fused by laser irradiation). The thermal fusion by laser irradiation enables continuous joining of high quality, allowing efficient preparation of a PSA sheet with sufficient joint strength. In a typical embodiment, two or more initial PSA sheets are fused solely by thermal fusion by laser irradiation without using a joining member that may form an uneven segment. Thermal fusion by laser irradiation is also advantageous in that it preferably enables continuous gapless joining and it is less likely to cause formation of a channel that allows passage of water and the like in the thickness direction.

In a preferable embodiment, the resin species forming the substrate layers of the at least two initial PSA sheets are of equal type. In such an embodiment, the resulting one-piece PSA sheet is likely to have uniform properties over its entire width. When the resin species forming the substrate layers of two initial PSA sheets are of equal type, the two initial PSA sheets are likely to fuse with each other and good joint strength is likely to be obtained. For the same reason, in the at least two initial PSA sheets, the PSA species forming their PSA layers are of equal type. The art disclosed herein can be preferably implemented in an embodiment where between the at least two initial PSA sheets to be subjected to width-extending joining, the resin species forming their substrate layers are of equal type and the PSA species forming their PSA layers are of equal type.

In this description, that “the PSA species are of equal type” does not require them to have an equal composition, but rather indicates that they belong to the same category when they are classified by their types of base polymer such as being acrylic or rubber-based, etc. They do not need to have an equal monomer composition or PSA composition. For instance, when the base polymers in the PSA layers of two initial PSA sheets are both acrylic polymers, the PSA species forming these PSA layers are of equal type. Separately from this, that “PSAs are the same” means literally that they are the same PSA, basically having an equal composition. It is more preferable that the PSA layers of two initial PSA sheets to be subjected to width-extending joining comprises the same base polymer.

Similarly, in this description, that “the resin species forming substrate layers are of equal type” does not require them to have an equal composition, but rather indicates that they belong to the same category when they are classified by their types of base polymer such as polyolefinic resin, poly(vinyl chloride)-based resin, polyurethane-based resin, etc. They do not need to have an equal monomer composition or resin composition. For instance, when the base polymers in substrate layers of two initial PSA sheets are both polyolefinic polymers, the resin species forming the substrate layers are of equal type. Separately from this, that “resins are the same” means literally that they are the same resin, basically having an equal composition. The substrate layers of the two initial PSA sheets to be subjected to width-extending joining more preferably includes an equal base polymer and particularly preferably have an essentially equal composition.

In some other embodiments of the art disclosed herein, preparing the final PSA sheet may include subjecting at least one of the initial PSA sheets to a width-broadening process. A one-piece wide-enough PSA sheet can be prepared by selecting an insufficiently-wide initial PSA sheet relative to the target area’s width from the workpiece group and subjecting the initial PSA sheet to a suitable width-broadening process.

In a preferable embodiment of the art disclosed herein, in the width-broadening process, the initial PSA sheet is broadened to a width that is greater than 1.0 times up to less than 1.45 times its original width prior to the process. By expanding the insufficiently-wide initial PSA sheet in the width direction by more than 1.0 times (e.g. 1.05 times or more), a wide-enough PSA sheet can be efficiently prepared. When the width-broadening ratio value is less than 1.45, degradation of quality associated with the width-broadening process can be reduced.

The width-broadening process may include a step of stretching the initial PSA sheet in the width direction while heating the initial PSA sheet. By stretching the initial PSA sheet while heating, degradation of quality caused by the width-broadening process can be reduced and a PSA sheet of more uniform quality can be prepared.

The width-broadening process may further include, after the stretching step, a step of maintaining the initial PSA sheet at a temperature within ±10 °C from or higher by more than 10 °C than the temperature in the stretching step. By carrying out this step, a PSA sheet having higher size stability can be prepared.

The width-broadening process may further include a step of cooling down the stretched initial PSA sheet. Natural or forced cooling after thermal stretching or maintaining at a certain temperature can preferably bring about a desirable PSA sheet.

In a preferable embodiment of the art disclosed herein, the substrate layer is a resin layer including a thermoplastic resin as the primary component. With the use of the thermoplastic resin as the primary component of the substrate layer, the joining of initial PSA sheets as well as the width-broadening process including the stretching step can be favorably carried out.

In a preferable embodiment, the substrate layer is formed from at least one species of resin selected from the group consisting of polyolefinic resin, poly(vinyl chloride)-based resin and polyurethane-based resin. The method disclosed herein can be favorably practiced, using an initial PSA sheet having a substrate layer that has such a composition.

In some embodiments of the art disclosed herein, the initial PSA sheet preferably satisfies at least one of the following: the substrate layer has a thickness of 25 μm to 150 μm; and the PSA layer has a thickness of 1 μm to 20 μm. The art disclosed herein can be favorably practiced, using an initial PSA sheet that satisfies one or each of the above.

In some embodiments of the art disclosed herein, the PSA layer can be an acrylic PSA layer including an acrylic polymer as the base polymer or a rubber-based PSA layer including a rubber-based polymer as the base polymer. The method disclosed herein can be favorably implemented, using an initial PSA sheet having a PSA layer that has such a composition.

The art disclosed herein can be implemented in an embodiment wherein the method further includes winding the PSA sheet in its length direction to form a PSA sheet roll, after a one-piece wide-enough PSA sheet is prepared and before the PSA sheet is applied to the target area. In this embodiment, the PSA sheet is unwound from the PSA sheet roll form and then applied to the target area. From the standpoint of the convenience during storage, transportation, processing and size stability (especially, width stability) of the PSA sheet, etc., it may be advantageous to apply the PSA sheet prepared from insufficiently-wide initial PSA sheets to the target area after once forming a roll of the PSA sheet.

The PSA sheet in the art disclosed herein can be an adhesively single-faced PSA sheet wherein the PSA layer is formed only on one face of the substrate layer. Such a single-faced PSA sheet can be preferably used as, for instance, a surface protective sheet.

The present description provides a surface protection method for protecting an adherend surface by applying the PSA sheet to a target area of the adherend. The surface protection method includes determining the width of the target area. The surface protection method includes: from a workpiece group consisting of at least two species of initial PSA sheets differing in width, based on the width of the target area, selecting one, two or more initial PSA sheets that are individually not wide enough to cover the target area. Here, the initial PSA sheets individually comprise a substrate layer and a PSA layer provided to at least one face of the substrate layer. The method includes preparing a one-piece final PSA sheet having a width large enough to cover the target area, by processing the selected initial PSA sheets. The surface protection method further includes applying the PSA sheet to the target area.

In the surface protection method, from insufficiently-wide initial PSA sheets, a one-piece wide-enough PSA sheet is prepared; and the resulting PSA sheet is applied to a target area to protect the adherend surface. According to this method, the entire width of the target area is covered with the one continuous PSA sheet, good protection can be provided. In addition, because the one-piece PSA sheet is applied to the target area, application of the PSA sheet is highly efficient. The surface protection method can also be applied to a case where existing equipment is not capable of directly producing a wide-enough PSA sheet. Thus, the surface protection method disclosed herein can be particularly preferably applied to a case where the target area has a relatively large width (e.g. a width of 1 m or greater, 2.6 m or greater, or even 3.0 m or greater). The PSA sheet used in the surface protection method can be considered as a surface protective sheet. The surface protective sheet can be an adhesively single-faced PSA sheet wherein the PSA layer is formed only on one face of the substrate layer.

This description provides a method for preparing a PSA sheet. The PSA sheet preparation method includes setting a width WS that the pressure-sensitive adhesive to be prepared should have. The preparation method further includes conducting an assessment on whether or not a workpiece group including at least two species of initial PSA sheets differing in width includes an initial PSA sheet having a width that is 0.7 times up to less than 1.0 times the width WS. Here, the initial PSA sheets individually comprise a substrate layer and a PSA layer formed on at least one face of the substrate layer. The preparation method further includes, based on the assessment, selecting one, two or more initial PSA sheets that individually have a width smaller than the width WS. The preparation method further includes preparing a one-piece PSA sheet having the width WS by processing the selected PSA sheet(s) .

According to this method, using insufficiently-wide initial PSA sheet(s), a PSA sheet having a desired width WS can be efficiently prepared. This method can be practiced, making effective use of initial PSA sheets that are already available (e.g. the PSA sheets in stock), without newly molding a substrate (e.g. resin film) used as the substrate layer or forming a PSA layer by applying and drying a PSA composition, etc. Thus, even for an order in a small quantity or a sudden request, a PSA sheet having a required width WS can be quickly prepared and provided. This method can also be applied to a case where certain existing equipment is not capable of directly producing a PSA sheet having the width WS. Thus, the PSA sheet preparation method disclosed herein can be particularly preferably employed for a case where the desired width WS is relatively large (e.g. 1 m or greater, 2.6 m or greater, or even 3.0 m or greater). The PSA sheet can be an adhesively single-faced PSA sheet wherein the PSA layer is formed only on one face of the substrate layer. The PSA sheet in such an embodiment can be preferably used as, for instance, a surface protective sheet.

In a preferable embodiment of the PSA sheet preparation method disclosed herein, based on the assessment, when the workpiece group includes an initial PSA sheet having a width that is 0.7 times up to less than 1.0 times the width WS, the final PSA sheet is prepared: by selecting one initial PSA sheet among initial PSA sheets individually having a width that is 0.7 times up to less than 1.0 times the width WS and subjecting the selected initial PSA sheet to a width-broadening process, or by selecting at least two initial PSA sheets individually having a width smaller than the width WS and joining these initial PSA sheets to obtain a larger width. On the other hand, when the workpiece group does not include an initial PSA sheet having a width that is 0.7 times up to less than 1.0 times the width WS, the final PSA sheet is prepared by selecting at least two initial PSA sheets individually having a width that is less than 0.7 times the width WS and joining these initial PSA sheets to obtain a larger width. According to this embodiment, to allow favorable preparation of the final PSA sheet, a suitable processing method is employed based on the width WS of the desired PSA sheet, for processing initial PSA sheet(s) in accordance with the width(s) of available initial PSA sheet(s).

Fig. 1 shows a diagram illustrating the PSA sheet application method according to an embodiment. Fig. 2 shows a diagram illustrating an example of the constitution of an initial PSA sheet obtained in a roll form. Fig. 3 shows a diagram illustrating the PSA sheet application method according to another embodiment. Fig. 4 shows a diagram illustrating an example of the method for preparing a one-piece PSA sheet by joining two initial PSA sheets at their lengthwise edges; Fig. 4(a) and Fig. 4(b) illustrate how two initial PSA sheets are abutted, Fig. 4(c) illustrates thermal fusion by laser irradiation, and Fig. 4(d) shows the one-piece PSA sheet prepared by fusion using a laser beam.

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 size or reduction scale.

As used herein, the term "PSA" refers to, as described earlier, a material that exists as a soft solid (a viscoelastic material) in a room temperature range and has a property to adhere easily to an adherend with some pressure applied. As defined in C. A. Dahlquist, "Adhesion : Fundamental and Practice" (McLaren & Sons (1966), P. 143), the PSA referred to herein is a material that has a property satisfying complex tensile modulus E* (1Hz) < 10⁷ dyne/cm² (typically, a material that exhibits the described characteristics at 25 °C).

With an example of a case where the adherend is a rectangular glass plate and the PSA sheet is applied to one entire face of the glass plate, some embodiments of the art disclosed herein are described below. In these embodiments, the one entire face of the glass plate is the target area. However, the art disclosed by this description is not limited to these embodiments.

<First embodiment>
The PSA sheet application method according to the present embodiment is an example where at least two insufficiently-wide initial PSA sheets selected from the workpiece group are joined together to obtain a larger width so as to prepare a one-piece wide-enough PSA sheet and the resulting PSA sheet is applied to the target area. When the purpose of applying the PSA sheet to the target area includes protection of the adherend surface, the application method can be considered as a surface protection method as well.

As shown in Fig. 1, this embodiment uses a workpiece group consisting of n species of initial PSA sheet 10s having different widths w1, w2 …wn. With respect to other features besides their widths, these initial PSA sheet 10s have constitutions that make them possible candidates for the PSA sheet applied to adherend 300. As shown in Fig. 2, each initial PSA sheet 10 has a substrate layer 11 and a PSA layer 12 provided to its first face (one face) 11A. As shown in Figs. 1 and 2, initial PSA sheet 10 may be wound in its length direction in a roll form. For instance, as shown in Fig. 2, in such a roll, initial PSA sheet 10 may have a release face on the second face 11B of substrate layer 11 so that, when wound, the second face is in contact with and protect the surface of PSA layer 12. Alternatively, initial PSA sheet 10 may be wound along with a release liner which is not shown in the drawings. As the release liner, commonly-used release paper and the like can be used without particular limitations. For instance, it is possible to use a release liner obtainable by subjecting a liner substrate such as plastic film and paper to a surface treatment using a known release agent such as silicone-based and long-chain alkyl-based types.

Glass plate 300 as the adherend has a known width WT. The width WT of the glass plate 300 is the width of the target area. In comparison of the widths of initial PSA sheet 10s in the workpiece group 90 and the width WT of glass plate 300, at least two initial PSA sheet 10s individually having a width smaller than the width WT are selected. By fusing the selected two initial PSA sheet 10s to obtain a larger width, a one-piece final PSA sheet 110 is prepared, having a width WS equal to or greater than width WT. In the present embodiment, the width-extending fusion can be carried out by abutting lengthwise edge faces of the two initial PSA sheets and thermally fusing the abutted edge faces by laser irradiation. Final PSA sheet 110 can be prepared, using, for instance, a processing apparatus 210 having a constitution outlined in Fig. 1. In this apparatus 210 (which can be considered as a processing apparatus for initial PSA sheets or as a preparing apparatus for the final PSA sheet), two initial PSA sheet 10s set on unwinding unit 211 are unwound and introduced into laser-irradiating unit 212 with their lengthwise edge faces abutted with each other, and the abutted lengthwise edge faces are irradiated by a laser beam and thermally fused together to form a one-piece final PSA sheet 110. The resulting PSA sheet 110 is wound in its length direction at winding unit 213 to form a PSA sheet roll 160. From the PSA sheet roll 160, PSA sheet 110 is unwound, cut to a suitable length and applied to adherend 300, whereby the single PSA sheet 110 can cover the entire width of adherend 300.

The width WS of PSA sheet 110 is suitably at least 1.0 times the target area’s width WT (the width of glass plate 300, here) and it can be, for instance, 1.0 times up to 1.2 times the width WT. Two initial PSA sheet 10s can be selected so as to form a one-piece final PSA sheet 110 having the width WS. Fig. 1 shows an example where two initial PSA sheets differing in width are selected from a workpiece group. However, two initial PSA sheets having an equal width can be selected as well. Three or more PSA sheets can be selected from the workpiece group as well.

<Second embodiment>
The PSA sheet application method according to this embodiment is an example where by subjecting one insufficiently-wide initial PSA sheet selected from the workpiece group to a width-broadening process, a one-piece wide-enough PSA sheet is prepared and the resulting PSA sheet is applied to the target area. When the purpose of applying the PSA sheet to the target area includes protection of the target area, the application method can be considered as a surface protection method as well.

As shown in Fig. 3, in comparison of the widths of initial PSA sheet 10s in a workpiece group 90 comparable to that in the first embodiment and the width WT of glass plate 300 as the adherend, one initial PSA sheet 10 having a width smaller than width WT is selected. For instance, initial PSA sheet 10 having a width that is 0.7 times up to less than 1.0 times the width WT of the glass plate can be preferably selected. The selected initial PSA sheet 10 is stretched in the width direction to prepare a one-piece PSA sheet 120 having a width WS equal to or greater than the width WT. PSA sheet 120 can be prepared, using, for instance, a processing apparatus 220 having a structure outlined in Fig. 3. In this apparatus 220, one initial PSA sheet 10 is set on unwinding unit 221, unwound, introduced into width-broadening unit 222, and stretched in the width direction. It is preferable that initial PSA sheet 10 is stretched while it is heated, using, for instance, a heater which is included in width-broadening unit 222, but not shown in the drawings. The resulting PSA sheet 120 is wound in its length direction at winding unit 223 to form a PSA sheet roll 170. From this PSA sheet roll 170, PSA sheet 120 is unwound, cut to a suitable length and applied to adherend 300, whereby the single PSA sheet 120 can cover the entire width of adherend 300.

<Fusion of edge faces>
The first embodiment described above is an example of an embodiment that includes fusing at least two initial PSA sheets selected from the workpiece group at their lengthwise edge faces to prepare a one-piece PSA sheet. By joining the initial PSA sheets by fusion of their lengthwise edge faces, the PSA sheet surface can be free of an uneven segment. As for the means of fusion, preferably thermal fusion (typically, thermal fusion by laser irradiation) can be employed to achieve joining of high quality. The final PSA sheet obtained by this method has a larger width than the respective initial PSA sheets used and has good adhesive properties. In addition, for instance, when used as a protective sheet, it can provide good protection. In particular, the fusion (preferably thermal fusion by laser irradiation, etc.) can preferably achieve gapless continuous joining and is less likely to form a channel (gap) that allows passage of water and the like in the thickness direction. This may be an important property in an application that requires surface-protecting properties. Because such a gap is absent, it does not require the sort of a third component for gap filling (possibly a known or conventional powder or liquid coating such as those used in conventional art where several PSA sheets are applied to the target area). This is advantageous in view of the level of surface protection and the efficiency of the protection work.
With reference to Fig. 4, a preferable embodiment of the method for fusing edge faces of initial PSA sheets is described more in detail below. However, the PSA sheet preparation method is not to be limited in the art disclosed herein.

As shown in Fig. 4(a), first and second

initial PSA sheets

50 and 60 are obtained for use in preparing PSA sheet 1. The first and second

initial PSA sheets

50 and 60 are formed as initial PSA sheets having release liners in which the surfaces of the respective PSA layers 52 and 62 are protected with

release liners

53 and 63. As

release liners

53 and 63, polyethylene terephthalate (PET) film whose PSA layer-side surface has been treated with a release agent is used. Other features about the first and second

initial PSA sheets

50 and 60 are as described earlier. Thus, further details are omitted here.

As shown in Fig. 4(b), the first and second

initial PSA sheets

50 and 60 obtained are abutted so that their lengthwise edge faces 50C and 60C face each other. In particular, lengthwise edge face 50C of the first initial PSA sheet 50 and lengthwise edge face 60C of the second initial PSA sheet 60 are placed face to face at a distance of about 100 μm or less (e.g. about 50 μm or less). Lengthwise edge faces 50C and 60C may be partially in contact with each other or may be in contact without a break.

Subsequently, as shown in Fig. 4(c), the border between the first and second

initial PSA sheets

50 and 60 which is the segment formed by abutting lengthwise edge faces 50C and 60C (i.e. the segment to be joined) is covered on top and bottom with

cover films

70 and 80. As the

cover films

70 and 80, a thermosetting resin film, a thermoplastic resin film having a higher melting point than the corresponding PSA sheet, a glass plate and the like are used. In this embodiment, as

cover films

70 and 80, a PET film having a thickness of about 20 μm to 500 μm (preferably about 25 μm to 150 μm) is used. For high-quality fusion, the widths of

cover films

70 and 80 are preferably about 5 mm or greater (e.g. 10 mm or greater). With the use of

cover films

70 and 80 having smooth surfaces, the first and second

initial PSA sheets

50 and 60 can be joined to a flush surface free of an uneven segment.

With the abutted segment enclosed in between

cover films

70 and 80, the first and second

initial PSA sheets

50 and 60 are loaded on a stage (not shown in the drawings). In the example shown in Fig. 4(c), both the first and second

initial PSA sheets

50 and 60 are loaded so that substrate layers 51 and 61 are on top with PSA layers 52/62 and release liners 53/63 are placed in this order toward the bottom. The abutted segment of the first and second

initial PSA sheets

50 and 60 is fastened (fixed in place) with a fastening member (not shown in the drawings) which is pressed over cover film 70 placed atop. As the fastening member, a transparent glass plate and the like are used. The fastening pressure exerted by the fastening member is not particularly limited. It can be selected from a range of, for instance, about 0.5 kgf/cm² to 100 kgf/cm² (preferably 1 kgf/cm² to 20 kgf/cm²). Assist gas can be supplied to the segment to be fused (e.g. the segment subject to laser irradiation) to make the cover films to tightly adhere to the initial PSA sheets.

The abutted segment of lengthwise edge faces 50C and 60C is fused to join the first and second

initial PSA sheets

50 and 60. In particular, the abutted segment of lengthwise edge faces 50C and 60C is irradiated by a laser beam R to thermally fuse the first and second

initial PSA sheets

50 and 60. According to thermal fusion by laser irradiation, high-quality fusion can be achieved. More specifically, by laser irradiation, at lengthwise edge faces 50C and 60C, the substrate layers 51 and 61 of the first and second

initial PSA sheets

50 and 60 are thermally fused together and their PSA layers 52 and 62 are also thermally fused together. PSA layers 52 and 62 may be viscoelastic bodies that deform (liquefy and spread) later to undergo autohesion even without thermal fusion. From the standpoint of the smoothness of the adhesive face, it is preferable that PSA layers 52 and 62 are to be thermally fused.

Cover films

70 and 80 are removed when appropriate after the thermal fusion is completed.

The method of laser irradiation is not particularly limited. It can be carried out by employing a known or conventional method or making a suitable modification thereto if necessary, by scanning the segment to be fused by a laser beam or by sending two initial PSA sheets through a laser beam. As the laser beam, a semiconductor laser is used in this embodiment, but it is not limited to this. Other than this, various types of laser beam can be used, such as an Nd-YAG laser, a fiber laser, a carbon dioxide laser, etc. As the oscillating method, a pulse laser can be employed, such as a CW laser (continuous wave laser) and a femtosecond laser. From the standpoint of the permeability relative to the resin material, the depth reached by the laser beam, the ease of fusion, etc., the laser beam preferably has a wavelength in the near-infrared range (specifically, in a range of 800 nm to 2000 nm). To increase the heat efficiency by the laser beam, the cover films and the edge faces to be fused may be provided (coated, etc.) with a laser absorber.

As described above, as shown in Fig. 4(d), PSA sheet 1 wherein two initial PSA sheets are joined by fusion is produced. PSA sheet 1 has a first section 2 formed of the first initial PSA sheet and a second section 4 formed of the second initial PSA sheet; and one lengthwise edge face of the first initial PSA sheet is directly fused to one lengthwise edge face of the second initial PSA sheet so that the first section 2 and the second section 4 are continuous. The PSA sheet 1 in this embodiment can be considered as a fused PSA sheet (or fused pressure-sensitive sheet) as well. Preferably, the fused segment 6 (the border between the first section 2 and the second section 4) of the two initial PSA sheets runs linearly in one direction in top view of PSA sheet 1; in stereo view, it is a portion formed by the linear segment extending in the thickness direction. More specifically, fused segment 6 continuously extends in the plane of PSA sheet 1, joined seamlessly.
As shown in Fig. 4(d), the resulting first face (adhesive face) 1A and second face (back face) 1B of the PSA sheet 1 are preferably smooth, including the fused segment 6. In particular, the first section 2 formed of the first initial PSA sheet 50 and the second section 4 formed of the second initial PSA sheet 60 are preferably free of an uneven segment. For instance, either on the first face 1A or on the second face 1B, it is preferably free of an uneven segment such as a projection (e.g. a segment projecting to a height of about 10 μm or greater, preferably about 5 μm or greater, typically 1 μm or greater). The adhesive face in fused segment 6 is free of a recess that may form a gap after applied to an adherend; or if any, the recess has a depth of about 1 μm or less (e.g. 0.5 μm or less). This can prevent defects (e.g. with respect to the tightness of adhesion to adherend, etc.) attributed to a possible uneven segment and further prevent permeation of water into the sealed face caused by a possible recess, etc. The first section 2 and the second section 4 are preferably joined at the fused segment 6, having sufficient strength. In the resulting PSA sheet 1, the adhesive face remains protected with

release liners

53 and 63. PSA sheet 1 thus obtained is used after arbitrarily cut to a suitable size or stored in a roll form, etc.

In this embodiment, the initial PSA sheets are joined by thermal fusion by laser irradiation. However, in the art disclosed herein, various techniques capable of joining initial PSA sheets can be employed. When initial PSA sheets are joined by fusion, a typical means of fusion is thermal fusion performed with respect to thermoplastic resins in PSA sheet materials. Thermally melted PSA sheet materials mix together and solidify again to be fused and joined. Examples of such thermal fusion techniques include hot pressing in addition to laser irradiation. Hot pressing can be carried out by pushing a heat plate heated to a certain temperature against a segment to be fused, optionally over a cover film, etc. When the edge faces of the initial PSA sheets are fused together, a meltable fastening material or various subsidiary materials may be used or may not be used.

In the embodiment above, the first and second initial PSA sheets used have an equivalent layer structure (a single-faced PSA sheet having a substrate layer) and are of equal type. However, the materials of the first initial PSA sheet and the second initial PSA sheet are not particularly limited as long as they can be fused together. From the standpoint of the ease of fusion, the joint strength, etc., the PSA species of the first initial PSA sheet and the second initial PSA sheet are preferably of equal type. It is more preferable that the same PSA is used. Similarly, the resin species forming the substrate layers of the first initial PSA sheet and the second initial PSA sheet are preferably of equal type. It is particularly preferable that the substrate layers of the first initial PSA sheet and the second initial PSA sheet have an essentially equal composition.

In this embodiment, the first initial PSA sheet and second initial PSA sheet may have an equal width, or they may have different widths as well. For instance, two species of initial PSA sheets differing in width can be used to produce three species of initial PSA sheets differing in width.

This embodiment uses release liners, but they are not necessary. In such a case, by directly covering the adhesive face of the initial PSA sheets with a transparent glass plate or cover film, the initial PSA sheets can be fixed in place without a problem. For a similar reason, cover film is not necessary and a fusion operation such as laser irradiation can be performed without cover film or with cover film placed only on top of the PSA sheet.

<Width-broadening process>
The second embodiment described above is an example of an embodiment that includes subjecting an initial PSA sheet selected from the workpiece group to a width-broadening process to prepare a one-piece PSA sheet. A preferable embodiment of the method for broadening the width of the initial PSA sheet is described more in detail below. However, the PSA sheet preparation method is not to be limited in the art disclosed herein.

The width-broadening process for the initial PSA sheet can be carried out by an arbitrary method where a final PSA sheet can be obtained having a larger width than the unprocessed initial PSA sheet. Such a width-broadening process can be considered as a process that allows the initial PSA sheet to undergo plastic deformation so as to have at least a larger width than its original width prior to the process. Non-limiting examples of the method that can be used for the width-broadening process for the initial PSA sheet include stretching, rolling, etc. From the standpoint of reducing degradation of quality caused by the width-broadening process, a preferable method may include a step of stretching the initial PSA sheet.

In the stretching step, the initial PSA sheet is preferably stretched in the width direction by a factor of greater than 1.0 up to less than 1.45. The stretch factor can be, for instance, 1.05 or greater, 1.1 or greater, or even 1.2 or greater. By increasing the stretch factor, the width of the PSA sheet can be efficiently increased. The stretch factor is preferably 1.4 or less (e.g. 1.35 or less). By limiting the stretch factor to or below a certain value, degradation of quality can be prevented and a PSA sheet available for practical use can be preferably produced.

The means of stretching is not particularly limited. For instance, with the two lengthwise edges of the initial PSA sheet fastened with a fixture (or chucks, clips), the initial PSA sheet is stretched by pulling it at a constant rate in the width direction. The stretching speed (the tensile speed in the width direction of the initial PSA sheet) can be suitably set in accordance with the material and thickness of the PSA sheet, etc. For instance, from the standpoint of the productivity, the stretching speed is suitably about 1 mm/s or higher (e.g. about 3 mm/s or higher). From the standpoint of reducing degradation of quality, it is suitably about 40 mm/s or lower (e.g. about 30 mm/s or lower, preferably 15 mm/s or lower, more preferably 10 mm/s or lower).

A preferable fixture has several chucks placed equidistantly in the length direction of the initial PSA sheet. As for the stretching work, the fixture may be moved (pulled) in the width direction only by its parts (e.g. chucks) placed on one long side of the initial PSA sheet or by its parts (e.g. chucks) placed on the two long sides of the initial PSA sheet. To deal with thermal expansion in the length direction of the workpiece, such several chucks may be placed on rails so that they can freely move in the length direction.

The stretching step can be carried out as the initial PSA sheet is heated. Thus, such a stretching step is also called a thermally-stretching step. For instance, the thermally-stretching step can be a step of placing the initial PSA sheet at room temperature (e.g. 20 °C, 50 % RH) in an oven heated to a certain temperature followed by stretching the initial PSA sheet in a heated state. The heating temperature (typically the temperature inside the oven) can be suitably selected in accordance with the resin species forming the initial PSA sheet, etc. For instance, it can be in a range of about 60 °C to 120 °C (preferably about 70 °C to 110 °C, typically about 80 °C to 100 °C).

The time for carrying out the stretching step in a heated state (the thermally stretching time) is suitably about 10 seconds or more, preferably about 15 seconds or more (e.g. about 20 seconds or more), or possibly about 30 seconds or more. The thermally stretching time is usually suitably about 3 minutes or less, for instance, about 1 minute or less. From the standpoint of smooth stretching, it is preferable to subject the initial PSA sheet, before the stretching step, to a pre-heating step at a temperature similar (about ±10 °C) to the heating temperature in the stretching step. The time for carrying out the pre-heating step is suitably about 10 seconds or more, preferably about 15 seconds or more, and suitably about 1 minute or less, for instance, preferably about 30 seconds or less.

After the stretching step, it is preferable to maintain the initial PSA sheet. In particular, it is preferable that the fixture is placed to maintain the width of the initial PSA sheet after stretched for a prescribed amount of time after completion of the stretching process. Practicing a maintenance step after the stretching step may enhance the size stability and uniformity of the resulting PSA sheet. The maintenance step can be carried out at a temperature similar to that set in the stretching step (within ±10 °C range from the temperature in the stretching step). Alternatively, it can be carried out at a temperature higher by more than 10 °C (e.g. by about 20 °C up to 40 °C) than the temperature in the stretching step. By this, greater effects can be obtained from practicing the maintenance step. The time for carrying out the maintenance step (the maintenance time) is suitably about 10 seconds or more, preferably about 15 seconds or more (e.g. about 20 seconds or more), or even about 30 seconds or more. From the standpoint of the productivity, etc., the maintenance time is usually suitably about 3 minutes or less, for instance, about 1 minute or less.

The initial PSA sheet stretched as described above is allowed to cool down by natural cooling at room temperature (e.g. 20 °C) or forced cooling using a cooling device (cool-down step). When natural cooling is employed, a PSA sheet of higher quality can be obtained. When forced cooling is employed, a PSA sheet can be produced efficiently. At an appropriate point of time before, during or after the cool-down step, from the stretched PSA sheet, one edge (typically each edge) of the width direction may be or may not be cut off for width adjustment, etc.

<Selection of PSA sheet preparation method>
In some embodiments of the PSA sheet application method disclosed herein, the selection of initial PSA sheet(s) from a workpiece group and the selection of a method for preparing a final PSA sheet from the initial PSA sheet(s) can be made based on an assessment conducted on whether or not, relative to the width WT of the target area, the workpiece group includes an initial PSA sheet whose ratio to the width WT is in a certain range. More specifically, for instance, these selections can be made as described next. In particular, an assessment is made on whether or not the workpiece group includes an initial PSA sheet having a width that is 0.7 times up to less than 1.0 times the width WT of the target area. From the results of the assessment, when the workpiece group includes an initial PSA sheet having a width that is 0.7 times up to less than 1.0 times the width WT, the final PSA sheet is prepared by selecting one initial PSA sheet from the initial PSA sheets individually having a width that is 0.7 times up to less than 1.0 times the width WT and subjecting the selected initial PSA sheet to a width-broadening process; or by selecting at least two initial PSA sheets individually having a width smaller than the width WT and joining these initial PSA sheets to obtain a larger width. On the other hand, when the workpiece group does not include an initial PSA sheet having a width that is 0.7 times up to less than 1.0 times the width WT, the final PSA sheet is prepared by selecting at least two initial PSA sheets individually having a width that is less than 0.7 times the width WT and joining these initial PSA sheets to obtain a larger width. According to such an embodiment, by effectively using initial PSA sheets that have been already produced and are not wide enough relative to the width WT of the target area, a wide-enough PSA sheet can be favorably prepared and applied to the target area. As for the method for preparing a PSA sheet from initial PSA sheets selected from the workpiece group, when the workpiece group includes an initial PSA sheet having a width that is 0.7 times the width WT or greater, a width-broadening process can be further selected; and when the workpiece group does not include an initial PSA sheet having a width that is 0.7 times the width WT or greater, a width-broadening process is not to be selected. By this, in either case, a PSA sheet of good quality can be prepared.

The PSA sheet preparation method disclosed herein can be practiced based on an assessment conducted on whether or not, relative to the width WS of a desired PSA sheet, the workpiece group includes an initial PSA sheet whose ratio to the width WS is in a certain range. More specifically, for instance, the method can be practiced as described next. In particular, an assessment is made on whether or not the workpiece group includes an initial PSA sheet having a width that is 0.7 times up to less than 1.0 times the width WS of the desired PSA sheet. When the workpiece group includes an initial PSA sheet having a width that is 0.7 times up to less than 1.0 times the width WS, the final PSA sheet is prepared by selecting one initial PSA sheet from the initial PSA sheets individually having a width that is 0.7 times up to less than 1.0 times the width WS and subjecting the selected initial PSA sheet to a width-broadening process; or by selecting at least two initial PSA sheets individually having a width smaller than the width WS and joining these initial PSA sheets to obtain a larger width. On the other hand, from the results of the assessment, when the workpiece group does not include an initial PSA sheet having a width that is 0.7 times up to less than 1.0 times the width WS, the final PSA sheet is prepared by selecting at least two initial PSA sheets individually having a width smaller than 0.7 times the width WS and joining the selected initial PSA sheets to obtain a larger width. According to such an embodiment, a wide-enough PSA sheet can be favorably prepared by effectively using initial PSA sheets that have been already produced and are not wide enough relative to the width WS of the desired PSA sheet. As for the method for preparing a PSA sheet from initial PSA sheets selected from the workpiece group, when the workpiece group includes an initial PSA sheet having a width that is 0.7 times the width WS or greater, a width-broadening process can be further selected; and when the workpiece group does not include an initial PSA sheet having a width that is 0.7 times the width WS or greater, a width-broadening process is not to be selected. By this, in either case, a PSA sheet of good quality can be prepared.

In the examples given above, for selecting a method for preparing a one-piece final PSA sheet from initial PSA sheet(s), the assessment is made with a dividing line at 0.7 times the width WT or width WS, but the dividing line is not limited to this. The art disclosed herein can also be favorably implemented in an embodiment where the dividing line is at, for instance, 0.8 times the width WT or width WS, 0.9 times, and so on. When the workpiece group includes an initial PSA sheet having a width that is at or above the dividing line up to less than 1.0 times the width WT or width WS, whether or not the final PSA sheet is prepared by a width-broadening process or by width-extending joining can be decided in accordance with the constitutions (e.g. materials of substrate layers) of initial PSA sheets, the productivity of the final PSA sheet, the manufacturing equipment for the final PSA sheet, etc. The art disclosed herein can be implemented in an embodiment where, for instance, when the workpiece group includes an initial PSA sheet having a width that is at or above a certain dividing line up to less than 1.0 times the width WT or width WS, the final PSA sheet is prepared by a width-broadening process; and when the workpiece group does not include an initial PSA sheet having such a width, the final PSA sheet is prepared by width-extending joining.

<PSA layer>
In the art disclosed herein, there are no particular limitations to the type of PSA forming the PSA layer of each initial PSA sheet in the workpiece group. The PSA layer may be formed from a PSA composition including, as the base polymer (the primary component among the polymers, i.e. a component accounting for 50 % by weight or more), one, two or more species selected among various polymers (adhesive polymers), such as acrylic, polyester-based, urethane-based, polyether-based, rubber-based, silicone-based, polyamide-based, and fluorinated polymers. The art disclosed herein can be preferably made, for instance, as a PSA sheet having an acrylic PSA layer or a rubber-based PSA layer.

The “acrylic PSA layer” here refers to a PSA layer including an acrylic polymer as the base polymer. Similarly, the “rubber-based PSA layer” refers to a PSA layer including a rubber-based polymer as the base polymer. The “acrylic polymer” refers to a polymer whose primary monomer (the primary component among the monomers, i.e. a component that accounts for 50 % by weight or more of the total amount of the monomers forming the acrylic polymer) is a monomer having at least one (meth)acryloyl group per molecule. Such a monomer may be referred to as an “acrylic monomer” hereinafter. As used herein, the “(meth)acryloyl group” comprehensively refers to acryloyl group and methacryloyl group. Similarly, the “(meth)acrylate” comprehensively refers to acrylate and methacrylate. Acrylic and rubber-based PSA layers are described below as favorable examples, but the PSA layer used in the art disclosed herein is not limited to these.

(Acrylic polymer)
A preferable example of the acrylic polymer is a polymer of a starting monomer mixture that includes an alkyl (meth)acrylate (or a monomer A hereinafter) and may further include another monomer (or a monomer B hereinafter) that is copolymerizable with the alkyl (meth)acrylate. The acrylic polymer typically has a monomer unit composition corresponding to the monomer composition of the starting monomer mixture.

A preferable monomer A is an alkyl (meth)acrylate represented by the next general formula (1):
CH₂=C(R¹)COOR² (1)
Here, R¹ in the formula (1) is a hydrogen atom or a methyl group. R² is an alkyl group having 1 to 20 carbon atoms. Hereinafter, such a range of the number of carbon atoms may be indicated as “C_1-20.” From the standpoint of the polymerization reactivity, polymerization stability, etc., an alkyl (meth)acrylate wherein R² is a C_1-16 alkyl group is preferable, and an alkyl (meth)acrylate wherein R² is a C_1-12 (typically C_1-10, e.g. C_1-8) alkyl group is more preferable.

Examples of an alkyl (meth)acrylate with R² being a C_1-20 alkyl group include methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, s-butyl (meth)acrylate, t-butyl (meth)acrylate, pentyl (meth)acrylate, isopentyl (meth)acrylate, hexyl (meth)acrylate, heptyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, n-octyl (meth)acrylate, isooctyl (meth)acrylate, n-nonyl (meth)acrylate, isononyl (meth)acrylate, n-decyl (meth)acrylate, isodecyl (meth)acrylate, undecyl (meth)acrylate, lauryl (meth)acrylate, tridecyl (meth)acrylate, tetradecyl (meth)acrylate, pentadecyl (meth)acrylate, hexadecyl (meth)acrylate, heptadecyl (meth)acrylate, octadecyl (meth)acrylate, nonadecyl (meth)acrylate, eicosyl (meth)acrylate, etc. These alkyl (meth)acrylates can be used solely as one species or in a combination of two or more species.

Examples of compounds that can be used as the monomer B may include functional group-containing monomers such as carboxy group-containing monomers (e.g. acrylic acid (AA)), acid anhydride group-containing monomers, hydroxy group-containing monomers (e.g. 2-hydroxyethyl (meth)acrylate), amide group-containing monomers, imide group-containing monomers, amino group-containing monomers, epoxy group-containing monomers, cyano group-containing monomers, keto group-containing monomers, monomers having nitrogen-containing rings, and alkoxysilyl group-containing monomers. These functional group-containing monomers may be useful for introducing crosslinking points into the acrylic polymer or for increasing the cohesiveness of the acrylic polymer. Functional group-containing monomers can be used solely as one species or in a combination of two or more species.

Other examples of compounds that can be used as the monomer B include vinyl ester-based monomers such as vinyl acetate; aromatic vinyl compounds; non-aromatic ring-containing (meth)acrylates; aromatic ring-containing (meth)acrylates; olefinic monomers; chlorine-containing monomers; isocyanate group-containing monomers; alkoxy group-containing monomers; and vinyl ether-based monomers. These can be used singly as one species or in a combination of two or more species. As the monomer B, one, two or more species can be used among polyfunctional monomers such as 1,6-hexanediol di(meth)acrylate. When using such a polyfunctional monomer, its amount used is not particularly limited. It is usually suitably about 2 % by weight or less (more preferably about 1 % by weight or less) of the total monomer content.

The monomer A content in the total monomer content can be, but is not particularly limited to, for instance, about 50 % by weight or greater; it is suitably about 60 % by weight or greater, preferably about 70 % by weight or greater, more preferably about 80 % by weight or greater, or yet more preferably about 85 % by weight or greater. With the inclusion of the monomer A in a prescribed amount, a PSA sheet having good adhesiveness can be favorably obtained. The art disclosed herein can be preferably implemented, for instance, in an embodiment where the monomer A content in the total monomer content is about 90 % by weight or greater. In an embodiment, the monomer A content can be about 95 % by weight or greater, or even about 97 % by weight or greater. In an embodiment using a monomer A and a monomer B together, from the standpoint of suitably obtaining the effects of the monomer B, the monomer A content in the total monomer content can be, for instance, 99.9 % by weight or less; it is usually preferably 99.5 % by weight or less, more preferably 99 % by weight or less, or about 97 % by weight or less (e.g. 95 % by weight or less).

When an aforementioned functional group-containing monomer is copolymerized in the acrylic polymer, the ratio of the functional group-containing monomer to all the monomers forming the acrylic polymer is usually preferably about 0.1 % by weight or higher (typically about 0.5 % by weight or higher, e.g. about 1 % by weight or higher), and preferably about 40 % by weight or lower (typically about 30 % by weight or lower, e.g. about 20 % by weight or lower).

(Rubber-based polymer)
In another preferable embodiment, the PSA layer can be a rubber-based PSA layer. Examples of the base polymer include natural rubber; styrene-butadiene rubber (SBR); polyisoprene; butene-based polymer synthesized with a butene (1-butene or cis- or trans-2-butene) and/or 2-methylpropene (isobutylene) as the primary monomer(s); A-B-A block copolymer rubber and a hydrogenation product thereof, e.g. styrene-butadiene-styrene block copolymer rubber (SBS), styrene-isoprene-styrene block copolymer (SIS), styrene-isobutylene-styrene block copolymer rubber (SIBS), styrene-vinyl-isoprene-styrene block copolymers (SVIS), hydrogenated SBS (styrene-ethylene/butylene-styrene block copolymer (SEBS)), and hydrogenated SIS ( styrene-ethylene-propylene-styrene block copolymers (SEPS)). These rubber-based polymers can be used singly as one species or in a combination of two or more species.

(Tg of base polymer)
The Tg value of the PSA layer’s base polymer (an acrylic polymer in an acrylic PSA layer) is not particularly limited. The Tg of the base polymer can be, for instance, about -70 °C or higher. In the PSA sheet according to a preferable embodiment, the base polymer of the PSA layer has a Tg of about -65 °C or higher. According to a base polymer having such a Tg, a PSA layer having good adhesive properties can be favorably formed. In an embodiment where the base polymer has a Tg of about -50 °C or higher (more preferably about -35 °C or higher), greater effects can be obtained. The Tg of the base polymer is usually suitably 0 °C or lower, preferably about -5 °C or lower, more preferably about -15 °C or lower, or yet more preferably about -20 °C or lower (e.g. about -25 °C or lower). In the PSA sheet according to another preferable embodiment, from the standpoint of the adhesion, etc., the base polymer of the PSA layer has a Tg of about -35 °C or lower, more preferably about -40 °C or lower, or yet more preferably about -45 °C or lower (e.g. about -55 °C or lower). The base polymer’s Tg can be adjusted by suitably changing the monomer composition (i.e. the monomer species used in the synthesis of the polymer and their ratio).

In the present description, the Tg of a polymer refers to the value determined by the Fox equation based on the Tg values of homopolymers of the respective monomers forming the polymer and the weight fractions (copolymerization ratio by weight) of the monomers. As shown below, the Fox equation is a relational expression between the Tg of a copolymer and glass transition temperatures Tgi of homopolymers of the respective monomers constituting the copolymer.
1/Tg = Σ(Wi/Tgi)
In the Fox equation, Tg represents the glass transition temperature (unit: K) of the copolymer, Wi the weight fraction (copolymerization ratio by weight) of a monomer i in the copolymer, and Tgi the glass transition temperature (unit: K) of homopolymer of the monomer i.

For the glass transition temperatures of homopolymers used for determining the Tg, the values found in known documents are used. For instance, with respect to the monomers listed below, for the glass transition temperatures of their homopolymers, the following values are used:
2-ethylhexyl acrylate: -70 °C
n-butyl acrylate: -55 °C
ethyl acrylate: -20 °C
methyl acrylate: 8 °C
n-butyl methacrylate: 20 °C
methyl methacrylate: 105 °C
2-hydroxyethyl acrylate: -15 °C
4-hydroxybutyl acrylate: -40 °C
vinyl acetate: 32 °C
styrene: 100 °C
acrylic acid: 106 °C
methacrylic acid: 228 °C
acrylonitrile: 104 °C

With respect to the Tg values of homopolymers other than the examples listed above, the values given in Polymer Handbook (3rd edition, John Wiley & Sons, Inc., Year 1989) are used. With respect to a monomer for which two or more values are listed in the Polymer Handbook, the highest value is used. When no values are given in the Polymer Handbook, values obtained by the measurement method described in Japanese Patent Application Publication No. 2007-51271 are used.

(Synthesis of base polymer)
The method for obtaining the base polymer (e.g. an acrylic polymer) is not particularly limited. Known polymerization methods can be suitably employed, such as solution polymerization, emulsion polymerization, bulk polymerization, and suspension polymerization. Alternatively, it is also possible to employ photopolymerization involving irradiation of light such as UV (typically carried out in the presence of a photopolymerization initiator) and active energy ray irradiation polymerization such as radiation polymerization involving irradiation of radioactive rays such as β rays and γ rays. As the monomer supply method in solution polymerization and emulsion polymerization, a suitable method can be employed among the all-at-once method where all the starting monomer mixture is supplied in one portion, gradual supply method, portion-wise supply method, etc. The polymerization temperature can be suitably selected in accordance with the monomer species, the solvent species, and the polymerization initiator species used, etc. The polymerization temperature is usually suitably about 20 °C or higher, preferably about 40 °C or higher, more preferably about 50 °C or higher; it can also be about 60 °C or higher, about 65 °C or higher, or even about 70 °C or higher. The polymerization temperature is usually suitably about 170 °C or lower (typically about 140 °C or lower), or preferably about 95 °C or lower (e.g. about 85 °C or lower).

The solvent (polymerization solvent) used in solution polymerization can be suitably selected among heretofore known organic solvents. For instance, it is preferable to use aromatic compounds (typically aromatic hydrocarbons) such as toluene, acetic acid esters such as ethyl acetate, aliphatic or alicyclic hydrocarbons such as hexane and cyclohexane, and the like.

The initiator used in the polymerization can be suitably selected among known or commonly-used polymerization initiators in accordance with the monomer species and the type of polymerization method. For instance, azo-based polymerization initiators such as 2,2’-azobisisobutyronitrile can be preferably used. Other examples of the polymerization initiator include persulfates such as potassium persulfate; peroxide-based initiators such as benzoyl peroxide; substituted ethane-based initiators; and aromatic carbonyl compounds. Yet other examples of the polymerization initiator include redox initiators by the combination of a peroxide and a reducing agent. These polymerization initiators can be used singly as one species or in a combination of two or more species. The polymerization initiator can be used in a usual amount. For instance, it can be selected from a range of about 0.005 part to 1 part by weight (typically about 0.01 part to 1 part by weight) to 100 parts by weight of the total monomer content.

The surfactant (emulsifier) used in emulsion polymerization is not particularly limited. Commonly-known anionic surfactants, nonionic surfactants and the like can be used. A surfactant having a radically polymerizable functional group can also be used. For the surfactant, solely one species or a combination of two or more species can be used. The amount of surfactant is usually preferably about 0.1 part by weight or greater (e.g. about 0.5 part by weight or greater) to 100 parts by weight of the total monomer content; and it is preferably about 10 parts by weight or less (e.g. about 5 parts by weight or less) to 100 parts by weight of the total monomer content.

In the emulsion polymerization, as necessary, various heretofore known chain transfer agents (which can be considered also as a molecular weight-adjusting agent or polymerization degree-adjusting agent) can be used. For the chain transfer agent, solely one species or a combination of two or more species can be used. As the chain transfer agent, mercaptans can be preferably used, such as n-dodecyl mercaptan, t-dodecyl mercaptan, and thioglycolic acid. When using a chain transfer agent, its amount can be, for instance, about 0.01 part to 1 part by weight to 100 parts by weight of the total monomer content. The art disclosed herein can also be preferably practiced in an embodiment that uses no chain transfer agent.

The PSA layer can be formed from various forms of PSA compositions. Examples of the forms of PSA compositions include a solvent-based PSA composition containing the PSA (adhesive component(s)) in an organic solvent, a water-dispersed PSA composition containing at least part of the PSA dispersed in an aqueous solvent, an active energy ray-curable PSA composition formulated so as to cure with active energy rays such as UV rays and radioactive rays to form PSA, and a hot-melt PSA composition which is applied in the molten state by heating and forms PSA when it cools to near room temperature.

(PSA composition)
In the art disclosed herein, the PSA composition used to form the PSA layer preferably includes a crosslinking agent. With the use of crosslinking agent, the cohesive strength can be suitably adjusted. The type of crosslinking agent used is not particularly limited. Examples include oxazoline-based crosslinking agents, aziridine-based crosslinking agents, isocyanate-based crosslinking agents, epoxy-based crosslinking agents, melamine-based crosslinking agents, peroxide-based crosslinking agents, urea-based crosslinking agents, metal alkoxide-based crosslinking agents, metal chelate-based crosslinking agents, metal salt-based crosslinking agents, carbodiimide-based crosslinking agents, hydrazine-based crosslinking agents, amine-based crosslinking agents, and silane coupling agents. These can be used solely as one species or in a combination of two or more species. For instance, it is preferable to use one, two or more species selected from a group consisting of oxazoline-based crosslinking agents, aziridine-based crosslinking agents, isocyanate-based crosslinking agents and epoxy-based crosslinking agents.

The crosslinking agent content (the total amount of crosslinking agent) in the PSA composition disclosed herein is not particularly limited and can be suitably selected in view of the composition and the molecular weight of the base polymer so as to obtain favorable properties after crosslinked. While no particular limitations are imposed, the amount of the crosslinking agent used to 100 parts by weight of the base polymer (typically an acrylic polymer) is usually about 0.01 part by weight or greater, suitably about 0.1 part by weight or greater, or preferably about 1 part by weight or greater (e.g. about 2 parts by weight or greater). From the standpoint of the adhesion, etc., the amount of the crosslinking agent is usually suitably about 15 parts by weight or less (preferably about 10 parts by weight or less, e.g. about 5 parts by weight or less) to 100 parts by weight of the base polymer.

The PSA composition may include, as necessary, various optional additives generally known in the field of PSA compositions, such as tackifier such as rosin-based tackifier, peel-adjusting agent such as a phosphate, viscosity-adjusting agent (thickner, etc.), crosslinking accelerator, plasticizer, softener, filler, anti-static agent, anti-aging agent, UV-absorber, antioxidant and photo-stabilizing agent. With respect to these various optional additives, heretofore known species can be used by typical methods. Because these additives do not characterize the present invention in particular, details are omitted.

(Formation of PSA layer)
As for the method for providing the PSA layer to a support substrate which forms the substrate layer, it is possible to employ a direct method where the PSA composition as described above is directly provided (typically applied) to the support substrate and subjected to a curing treatment; a transfer method where the PSA composition is applied to a suitable release face (e.g. a releasable surface of a transfer sheet) and subjected to a curing treatment to form a PSA layer on the surface followed by applying and transferring the PSA layer to the support substrate; and so on. The curing treatment may include one, two or more processes selected among drying (heating), cooling, crosslinking, supplemental copolymerization reaction, aging, etc. The curing treatment referred to herein may encompass, for instance, a process (heating process, etc.) simply to allow a PSA composition containing a solvent to dry, a process simply to cool down (solidify) a heat-melted PSA composition. When the curing treatment includes two or more processes (e.g. drying and crosslinking), these processes may be performed at once or stepwise.

The PSA composition can be applied, for instance, using a commonly used coater such as a gravure roll coater, reverse roll coater, kiss roll coater, dip roll coater, bar coater, knife coater and spray coater. From the standpoint of accelerating the crosslinking reaction, increasing the productivity, etc., the PSA composition is preferably dried with heat. The drying temperature may vary depending on the object (a support substrate, etc.) to which the PSA composition is applied, but it can be, for instance, about 40 °C to 150 °C.

The thickness of the PSA layer is not particularly limited. From the standpoint of preventing adhesive transfer to the adherend, the thickness of the PSA layer is usually about 50 μm or less, suitably about 30 μm or less, preferably about 15 μm or less, or more preferably about 8 μm or less (e.g. less than 6 μm). In another embodiment, from the standpoint of the ease of removal, etc., the thickness of the PSA layer is suitably about 5 μm or less, about 4 μm or less, or possibly, for instance, 3 μm or less. From the standpoint of the adhesion, the thickness of the PSA layer is usually suitably about 0.5 μm or greater, preferably about 1 μm or greater, or more preferably greater than 2 μm. The thickness of the PSA layer is greater than 3 μm, for instance, greater than 4 μm.

<Substrate layer>
As the substrate layers of each initial PSA sheet, a resin film, a rubber sheet, a foam sheet, a composite of these, etc., can be used. Examples of the rubber sheet include natural rubber sheets, butyl rubber sheets, polybutadiene rubber sheets. Examples of the foam sheet include polyurethane foam sheets, and polychloroprene rubber foam sheets. In the art disclosed herein, the substrate layer is preferably a resin layer that includes a thermoplastic resin as the primary component (component accounting for the highest content among the resins in the substrate layer, preferably a resin component accounting for 50 % by weight or more). The use of thermoplastic resin as the primary component of the substrate layer preferably enables thermal fusion/joining of initial PSA sheets. The substrate layer including a thermoplastic resin as its primary component may also be advantageous from the standpoint of the width-extending properties of the initial PSA sheet.

The art disclosed herein can be preferably applied to a PSA sheet wherein the substrate layer is a resin film. The concept of “resin film” here refers to film typically obtained by molding a thin layer from a resin composition primarily including resin components as described below; it should be distinguished from so-called non-woven and woven fabrics. In other words, the concept of resin film excludes non-woven and woven fabrics. A resin film (non-foamed resin film) which is essentially not foamed can be preferably used. Here, the non-foamed resin film refers to resin film that has not been deliberately subjected to a foaming process. In particular, the resin film may have an expansion ratio lower than about 1.1 (e.g. lower than 1.05, typically lower than 1.01).

Examples of the resin components forming the resin film include polyolefinic resins (polyethylene, polypropylene, ethylene-propylene copolymer, ethylene-vinyl acetate copolymer, etc.), poly(vinyl chloride)-based resins (typically soft poly(vinyl chloride)-based resin); poly(vinyl acetate)-based resin, poly(vinyl alcohol)-based resin, polyurethane-based resins (ether-based polyurethane, ester-based polyurethane, carbonate-based polyurethane, etc.), urethane (meth)acrylate-based resin, thermoplastic elastomers (olefinic elastomer, styrene-based elastomer, acrylic elastomer, etc.), polyester-based resins (polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, polybutylene naphthalate, etc.), polycarbonate-based resin, polyamide-based resin, and polyimide-based resin (thermoplastic polyimide, polyether imide, polyamide-imide, etc.), cellulose-based resin (triacetylcellulose, etc.), poly(methyl methacrylate)-based resin, norbornene-based resin, polyoxymethylene-based resin, polyether ether ketone-based resin, polystyrene-based resin, and polymethylpentene. Among these resins, solely one species or a combination of two or more species can be used.

While no particular limitations are imposed, in the PSA sheet according to an embodiment, it is preferable to use a substrate layer that includes, as its primary component(s), one, two or more species of resin selected from the group consisting of polyolefinic resin, poly(vinyl chloride)-based resin, polyurethane-based resin, thermoplastic elastomer and polyester-based resin (typically a substrate layer including such resin in an amount exceeding 50 % by weight). In another embodiment, in view of the performance, ease of handling, costs, etc., a substrate layer including a polyolefinic resin layer, polyester-based resin layer or polyvinyl chloride-based resin layer can be preferably used. Among the resin materials, in view of the heat stability, the lightness of weight, etc., polyolefinic resins, polyurethane-based resins and olefinic elastomers are preferable; in view of the handling properties, etc., polyolefinic resins and olefinic elastomers are particularly preferable.

The PSA sheet disclosed herein can be preferably made in an embodiment having a substrate layer that includes a polyolefinic resin as the primary component, that is, an embodiment wherein the substrate layer is polyolefinic resin film. For instance, it is preferable to use polyolefinic resin film in which 50 % by weight or more of the entire substrate layer is polyethylene (PE) resin or polypropylene (PP) resin. In other words, in the polyolefinic resin film, the combined amount of PE resin and PP resin may account for 50 % by weight or more of the entire substrate layer.

The PP resin may include, as the primary component, various polymer species (propylene-based polymers) that include propylene as a monomer unit. The PP resin may be formed essentially of one, two or more species of propylene-based polymer. The concept of propylene-based polymer here includes homopolypropylene as well as a random copolymer of propylene and other monomer(s) (random polypropylene) and a block copolymer (block polypropylene). The concept of propylene-based polymer here includes, for instance, the following species:
Propylene homopolymer (homopolypropylene), for instance, isotactic polypropylene;
Random copolymer (random polypropylene) of propylene and other α-olefin(s) (typically, one, two or more species selected from ethylene and α-olefins having 4 to 10 carbon atoms), preferably random polypropylene synthesized with propylene as the primary monomer (i.e. the monomer accounting for 50 % by weight or more of the total monomer content);
Block copolymer (block polypropylene) of propylene and other α-olefin(s) (typically, one, two or more species selected from ethylene and α-olefins having 4 to 10 carbon atoms), preferably block polypropylene synthesized with propylene as the primary monomer (i.e. the monomer accounting for 50 % by weight or more of the total monomer content).

The PE resin can be various types of polymer (ethylene-based polymer) synthesized with ethylene as a monomer. The PE resin may be essentially formed of one, two or more species of ethylene-based polymer. The ethylene-based polymer can be an ethylene homopolymer or a copolymer (random copolymer, block copolymer, etc.) of ethylene as the primary monomer and other α-olefin(s) as secondary monomer(s). Favorable examples of the α-olefins include α-olefins having 3 to 10 carbon atoms such as propylene, 1-butene (which can be a branched 1-butene), 1-hexene, 4-methyl-1-pentene and 1-octene. For instance, it is preferable to use PE resin that includes, as the primary component, an ethylene-based polymer in which an α-olefin as the secondary monomer is copolymerized up to about 10 % by weight (typically up to about 5 % by weight).

The PE resin may include a copolymer of ethylene and a monomer (functional monomer) containing other functional group(s) in addition to a polymerizable functional group, copolymer of an ethylene-based polymer copolymerized with such a functional monomer, or the like. Examples of a copolymer of ethylene and a functional monomer include ethylene-vinyl acetate copolymers (EVA), ethylene-acrylic acid copolymers (EAA), ethylene-methacrylic acid copolymers (EMAA), ethylene-methyl acrylate copolymers (EMA), ethylene-ethyl acrylate copolymers (EEA), ethylene-methyl methacrylate copolymers (EMMA), and copolymers of ethylene and (meth)acrylic acid (i.e. acrylic acid and/or methacrylic acid) crosslinked by metal ions.

The PE resin is not particularly limited in density. The concept of PE resin here includes all of the following: high density polyethylene (HDPE), medium density polyethylene (MDPE), low density polyethylene (LDPE) and linear low density polyethylene (LLPDE). In an embodiment, the density of the PE resin can be, for instance, about 0.90 g/cm³ to 0.94 g/cm³. Preferable PE resins include LDPE and LLDPE. The PE resin may include one, two or more species of LDPE and one, two or more species of LLDPE. There are no particular limitations to the respective blend ratios of LDPE and LLDPE, or to the LDPE to LLDPE blend ratio. They can be suitably selected to form a PE resin having desirable properties. As the substrate layer of the PSA sheet disclosed herein, it is preferable to use polyethylenic resin film such as LLDPE film whose LLDPE content is higher than 50 % by weight (preferably about 75 % by weight or higher, e.g. about 90 % by weight or higher) and LDPE film whose LDPE content is higher than 50 % by weight (preferably about 75 % by weight or higher, e.g. about 90 % by weight or higher). Laminate resin film including such polyethylenic resin film as a component can be used as well.

The resin film (e.g. polyolefinic resin film) used as the substrate layer of the PSA sheet disclosed herein may include, as necessary, suitable components allowable in the substrate layer. Examples of additives that can be suitably added include filler, colorant (pigment such as inorganic pigment, dye), antioxidant, photostabilizer (including radical scavenger and UV absorber), antistatic agent, plasticizer, slip agent, and anti-blocking agent. Each additive can be added, for instance, in an amount similar to a typical amount in the field of resin film used as substrate layers and the like of PSA sheets.

The substrate layer may have a mono-layer structure or a multi-layer structure formed of two, three or more layers. In a multi-layer structure, it is preferable that at least one layer (preferably each layer) is formed of aforementioned resin film. For instance, in a preferable substrate layer, 75 % or more (more preferably 90 % or more) of the thickness is attributed to mono-layer or multi-layer (typically mono-layer) polyolefinic resin film. The substrate layer may be entirely formed of mono-layer or multi-layer polyolefinic resin film. From the standpoint of the cost-effectiveness, it is preferable to use a substrate layer formed of mono-layer resin film (e.g. LLDPE film, LDPE film, etc.).

The method for producing the substrate layer can be suitably selected among heretofore known methods and is not particularly limited. For instance, when resin film is used as the substrate layer, it is possible to use resin film fabricated by suitably employing a heretofore known general film-forming method such as inflation molding, extrusion, T-die cast molding, and calendar roll molding.

In an embodiment where at least one face (the PSA layer-side face) of the substrate layer is a resin film surface, the resin film surface can be subjected to a heretofore known surface treatment such as corona discharge treatment, plasma treatment, ozone exposure, flame exposure, UV irradiation, acid treatment, alkali treatment, and primer coating. These surface treatments may enhance the tightness of adhesion between the substrate layer and the PSA layer, or the anchoring of the PSA layer onto the substrate layer. In an embodiment using polyolefinic resin film as the substrate layer, it is particularly meaningful to provide these surface treatments.

The thickness of the substrate layer is not particularly limited. The thickness of the substrate layer can be, for instance, about 800 μm or less (typically about 250 μm or less). In an embodiment, the thickness of the substrate layer (typically, non-foamed resin film) is preferably about 150 μm or less, more preferably about 100 μm or less, or yet more preferably less than 65 μm, for instance, less than 55 μm. When the substrate layer’s thickness is limited to or below a certain value, thermal fusion (preferably by laser irradiation, etc.) can be efficiently carried out. From the standpoint of adherend protection, handling properties, etc., the substrate layer’s thickness is typically about 10 μm or greater, or it can be preferably about 25 μm or greater, more preferably greater than 30 μm, or yet more preferably greater than 40 μm, for instance, greater than 45 μm. When the substrate layer’s thickness is at or above a certain value, the surface areas of edge faces to be thermally fused will increase and sufficient bonding strength is likely to be obtained. The substrate layer having at least a certain thickness can also be advantageous from the standpoint of the ease of processing when subjecting the substrate layer to a width-broadening process such as stretching, rolling, etc.

<Initial PSA sheets (workpieces)>
The art disclosed herein is implemented using one, two or more initial PSA sheets selected from the workpiece group including at least two species of initial PSA sheets. The initial PSA sheets in the workpiece group may differ in at least one feature among their widths, thicknesses, lengths, substrate layer’s constitutions (e.g. thicknesses, materials, structures, physical properties, and optional surface treatment thereof), PSA layer’s constitutions (e.g. thicknesses, compositions, adhesive properties, surface conditions thereof) and so on. Thus, the workpiece group may include several species of initial PSA sheets that differ in thickness while having an equal width. The workpiece group may include, for instance, 3 or more, 5 or more, or even 10 or more species of initial PSA sheets. The maximum number of species is not particularly limited. In some embodiments, in view of the practicality such as the ease of inventory control and storage space saving, the number of species can be, for instance, 500 or less, 100 or less, 50 or less, or even 20 or less. Members of the workpiece group may exclude a species of initial PSA sheet that does not make a possible candidate for a reason other than its width in view of the purpose and use mode of the PSA sheet applied to a target area. The reason other than its width can be, for instance, an aforementioned feature (e.g. the material of its substrate layer, adhesive properties, etc.) that may make it a different type of initial PSA sheet.

The workpiece group preferably includes at least two species of initial PSA sheets differing in width. The workpiece group may include, for instance, 3 or more, 5 or more, or even 7 or more species of initial PSA sheets differing in width. While no particular limitations are imposed, from a practical standpoint, the number of species can be, for instance, 100 or less, 50 or less, 20 or less, or even 15 or less. According to the art disclosed herein, even with a workpiece group consisting of a relatively small number of species of initial PSA sheets, by suitably selecting and processing initial PSA sheet(s), a one-piece final PSA sheet corresponding to the target area’s width can be prepared. From such a standpoint, in some embodiments, the number of species of initial PSA sheets differing in width can be, for instance, 10 or less, 6 or less, 4 or less, or even 3 or less.

The thicknesses of initial PSA sheets are not particularly limited. From the standpoint of the handling properties and lightweight properties, etc., they individually have a thickness of usually suitably about 1000 μm or less (typically about 300 μm or less, e.g. about 150 μm or less). In an embodiment, the initial PSA sheets may individually have a thickness of preferably about 120 μm or less, more preferably about 100 μm or less, or yet more preferably about 75 μm or less, for instance, less than 60 μm. The initial PSA sheets may individually have a thickness of typically greater than 20 μm, preferably greater than 30 μm, or more preferably greater than 40 μm, for instance, greater than 45 μm.

In some embodiments, initial PSA sheets forming the workpiece group may be in roll forms in which long initial PSA sheets are wound in their length directions to form rolls. Initial PSA sheets in such roll forms have good storage and handling properties and thus are preferable. With initial PSA sheets in roll forms, for instance, it is facile to carry out the following procedure in a continuous manner: preparing a wide-enough PSA sheet from one, two or more insufficiently-wide PSA sheets and winding the final PSA sheet in its length direction to form a PSA sheet roll.

In the art disclosed herein, when the final PSA sheet prepared from initial PSA sheets is formed as a PSA sheet roll prior to use (e.g. before applied to an adherend), the diameter of the PSA sheet roll is not particularly limited. From the standpoint of the ease of winding, it is advantageous that the diameter of the PSA sheet roll is not excessively large. From such a standpoint, the diameter of the PSA sheet roll is usually suitably about 1 m or smaller, or preferably about 50 cm or smaller. In view of the efficiency of use, storage, transportation, etc., the PSA sheet roll suitably has a diameter of about 5 cm or larger (e.g. about 15 cm or larger).

In the application method or the surface protection method disclosed herein, the final PSA sheet prepared from initial PSA sheets is not particularly limited as far as having a width wide enough to cover the width WT of a target area. In some preferable embodiments, the width of the PSA sheet may be, for instance, about 1 m or greater, about 2 m or greater, about 2.6 m or greater, greater than 2.6 m, or even 3 m or greater. The maximum width of the PSA sheet is not particularly limited. From the standpoint of the productivity, handling properties, etc., it is usually suitably about 5 m or less, for instance, about 4 m or less. The PSA sheet has a length (the distance in the length direction) equal to or greater than the width.

<Applications>
According to the PSA sheet application method disclosed herein, a target area can be covered entirely across its width with one continuous PSA sheet. Because of this feature, the application method can be preferably applied for purposes involving various types of adherend, such as their protection, reinforcement, decoration (installation of design features), adjustment of surface conditions and optical properties, etc. When the purpose of applying the PSA sheet includes protection of the adherend surface, the application method can also be considered as a surface protection method. For instance, by applying the PSA sheet to a target area of an adherend (which can be one entire face of the adherend) such as a metal plate, a coated steel plate, a synthetic resin plate and a glass plate, the application method is favorable as a surface protection method to prevent the adherend surface from receiving damage (scratches, contamination, etc.) while these are being processed or transported. As the PSA sheet used in such a surface protection method, a surface protective sheet formed of an adhesively single-faced PSA sheet having a PSA layer on one face of a substrate layer can be preferably used. The surface protective sheet provides surface protection to an adherend when applied to the adherend and will be removed after completion of the protection period. According to the art disclosed herein, even when the target area has a large surface area, one continuous PSA sheet having a size large enough to cover the entire target area can be applied to the target area. Thus, the art disclosed herein can be preferably practiced in an embodiment to cover one entire face of a relatively large adherend, for instance, an adherend having a width of about 2.6 m or greater.

Matters disclosed by this description include the following:
(1) A method for applying a PSA sheet to a target area of an adherend, the method comprising
determining the width of the target area;
from a workpiece group comprising at least two species of initial PSA sheets differing in width, selecting, based on the width of the target area, one, two or more initial PSA sheets that are individually not wide enough to cover the target area, wherein the initial PSA sheets individually comprise a substrate layer and a PSA layer provided to at least one face of the substrate layer;
preparing a one-piece PSA sheet having a width large enough to cover the target area by processing the selected initial PSA sheets; and
applying the PSA sheet to the target area.
(2) A surface protection method for protecting an adherend surface by applying a PSA sheet to a target area of the adherend, the method comprising
determining the width of the target area;
from a workpiece group comprising at least two species of initial PSA sheets differing in width, selecting, based on the width of the target area, one, two or more initial PSA sheets that are individually not wide enough to cover the target area, wherein the initial PSA sheets individually comprise a substrate layer and a PSA layer provided to at least one face of the substrate layer;
preparing a one-piece PSA sheet having a width large enough to cover the target area by processing the selected initial PSA sheets; and
applying the PSA sheet to the target area.
(3) The method according to (1) or (2) above, wherein the preparing the PSA sheet includes joining the two initial PSA sheets to obtain a larger width.
(4) The method according to (3) above, wherein the two initial PSA sheets are joined by abutting lengthwise edge faces thereof and fusing the abutted edge faces.
(5) The method according to (4) above, wherein the abutted edge faces are thermally fused by laser irradiation.
(6) The method according to any of (3) to (5) above, wherein the two initial PSA sheets have an equal constitution including their widths or an equal constitution except for their widths.
(7) The method according to any of (1) to (6) above, wherein the preparing the PSA sheet includes subjecting at least one of the initial PSA sheets to a width-broadening process.
(8) The method according to (7) above, wherein, in the width-broadening process, the initial PSA sheet is broadened to a width that is greater than 1.0 times up to less than 1.45 times its original width prior to the process.
(9) The method according to (7) or (8) above, wherein the width-broadening process comprises a step of stretching the initial PSA sheet in the width direction while heating the same.
(10) The method according to any of (7) to (9) above, wherein the width-broadening process further comprises, after the stretching step, a step of maintaining the initial PSA sheet at a temperature within ±10 °C from or higher by more than 10 °C than the temperature in the stretching step.
(11) The method according to any of (7) to (10) above, wherein the width-broadening process further comprises, after the stretching step, a step of cooling down the stretched initial PSA sheet.
(12) The method according to any of (1) to (11) above, wherein the substrate layer is a resin layer comprising a thermoplastic resin as its primary component.
(13) The method according to any of (1) to (12) above, wherein the substrate layer is formed from at least one species of resin selected from the group consisting of polyolefinic resin, poly(vinyl chloride)-based resin and polyurethane-based resin.
(14) The method according to any of (1) to (13) above, wherein the substrate layer has a thickness of 25 μm to 150 μm
(15) The method according to any of (1) to (14) above, wherein the PSA layer is an acrylic PSA layer comprising an acrylic polymer as its base polymer or a rubber-based PSA layer comprising a rubber-based polymer as its base polymer.
(16) The method according to any of (1) to (15) above, wherein the PSA layer has a thickness of 1 μm to 20 μm.
(17) The method according to any of (1) to (16) above, the method further comprising winding the PSA sheet in its length direction to form a PSA sheet roll, after the PSA sheet is prepared and before the PSA sheet is applied to the target area.
(18) The method according to any of (1) to (17) above, wherein the PSA sheet is an adhesively single-faced PSA sheet wherein the PSA layer is formed only on one face of the substrate layer.
(19) The method according to any of (1) to (18) above, wherein the target area has a width of 1 m or greater, 2.6 m or greater, or 3.0 m or greater
(20) The method according to any of (1) to (19) above, wherein the PSA sheet is prepared to have a width WS that is 1.0 times or greater (e.g. 1.0 times up to 1.2 times) the width WT of the target area.
(21) The method according to any of (1) to (20) above, wherein
an assessment is conducted on whether or not the workpiece group includes an initial PSA sheet having a width that is 0.7 times up to less than 1.0 times the width WT;
based on the assessment,
when the workpiece group includes an initial PSA sheet having a width that is 0.7 times up to less than 1.0 times the width WT, the PSA sheet is prepared
by selecting one initial PSA sheet among the initial PSA sheets individually having a width that is 0.7 times up to less than 1.0 times the width WT and subjecting the selected initial PSA sheet to a width-broadening process, or
by selecting at least two initial PSA sheets individually having a width smaller than the width WT and joining the selected initial PSA sheets to obtain a larger; and
when the workpiece group does not include an initial PSA sheet having a width that is 0.7 times up to less than 1.0 times the width WT, the PSA sheet is prepared by selecting at least two initial PSA sheets individually having a width that is less than 0.7 times the width WT and joining the selected initial PSA sheets to obtain a larger width.
(22) A method for preparing a PSA sheet, the method comprising
setting a width WS that the PSA sheet to be prepared should have;
conducting an assessment on whether or not a workpiece group comprising at least two species of initial PSA sheets differing in width includes an initial PSA sheet having a width that is 0.7 times up to less than 1.0 times the width WS, wherein the initial PSA sheets individually comprise a substrate layer and a PSA layer formed on at least one face of the substrate layer;
based on the assessment, selecting one, two or more initial PSA sheets that individually have a width smaller than the width WS;
preparing a one-piece PSA sheet having the width WS by processing the selected PSA sheet(s).
(23) The method according to (22) above, wherein:
based on the assessment,
when the workpiece group includes an initial PSA sheet having a width that is 0.7 times up to less than 1.0 times the width WS, the PSA sheet is prepared
by selecting one initial PSA sheet from the initial PSA sheets individually having a width that is 0.7 times up to less than 1.0 times the width WS and subjecting the selected initial PSA sheet to a width-broadening process, or
by selecting at least two initial PSA sheets individually having a width smaller than the width WS and joining the selected initial PSA sheets to obtain a larger; and
when the workpiece group does not include an initial PSA sheet having a width that is 0.7 times up to less than 1.0 times the width WS, the PSA sheet is prepared by selecting at least two initial PSA sheets individually having a width smaller than 0.7 times the width WS and joining the selected initial PSA sheets to obtain a larger width (e.g. joining these initial PSA sheets at their long sides).
(24) The method according to (22) or (23) above, wherein the width WS is 1 m or greater, 2.6 m or greater, or 3.0 m or greater.
(25) The method according to any of (22) to (25) above, further comprising winding the PSA sheet in its length direction to form a PSA sheet roll.

1: PSA sheet
1A: first face
1B: second face
2: first section
4: second section
6: thermally fused part
10: initial PSA sheet
11: substrate layer
11A: first face
11B: second face
12: PSA layer
50: first initial PSA sheet
50C: edge face
51: substrate layer
52: PSA layer
53: release liner
60: second initial PSA sheet
60C: edge face
61: substrate layer
62: PSA layer
63: release liner
70, 80: cover film
90: workpiece group
110, 120: PSA sheets
160, 170: PSA sheet rolls
210, 220: processing apparatus
211, 221: unwinding unit
212: laser-irradiating unit
213, 223: winding unit
222: stretching unit
300: adherend
300A: target area
R: laser beam
WT: width of target area
WS: width of PSA sheet
w1, w2…wn: widths of corresponding initial PSA sheets

Claims

A method for applying a pressure-sensitive adhesive sheet to a target area of an adherend, the method comprising:
determining the width of the target area;
from a workpiece group comprising at least two species of initial pressure-sensitive adhesive sheets differing in width, selecting, based on the width of the target area, one, two or more initial pressure-sensitive adhesive sheets that are individually not wide enough to cover the target area, wherein the initial pressure-sensitive adhesive sheets individually comprise a substrate layer and a pressure-sensitive adhesive layer provided to at least one face of the substrate layer;
preparing a one-piece pressure-sensitive adhesive sheet having a width large enough to cover the target area by processing the selected initial pressure-sensitive adhesive sheets; and
applying the pressure-sensitive adhesive sheet to the target area.
The method according to Claim 1, wherein the preparing the pressure-sensitive adhesive sheet includes joining the two initial pressure-sensitive adhesive sheets to obtain a larger width.
The method according to Claim 2, wherein the two initial pressure-sensitive adhesive sheets are joined by abutting lengthwise edge faces thereof and fusing the abutted edge faces.
The method according to Claim 3, wherein the abutted edge faces are thermally fused by laser irradiation.
The method according to any one of Claims 2 to 4, wherein the two initial pressure-sensitive adhesive sheets have an equal constitution including their widths or an equal constitution except for their widths.
The method according to Claim 1, wherein the preparing the pressure-sensitive adhesive sheet includes subjecting at least one of the initial pressure-sensitive adhesive sheets to a width-broadening process.
The method according to Claim 6, wherein, in the width-broadening process, the initial pressure-sensitive adhesive sheet is broadened to a width that is greater than 1.0 times up to less than 1.45 times its original width prior to the process.
The method according to Claim 6 or 7, wherein the width-broadening process comprises a step of stretching the initial pressure-sensitive adhesive sheet in its width direction while heating the same.
The method according to any one of Claims 6 to 8, wherein the width-broadening process further comprises, after the stretching step, a step of maintaining the initial pressure-sensitive adhesive sheet at a temperature within ±10 °C from or higher by more than 10 °C than the temperature in the stretching step.
The method according to any one of Claims 6 to 9, wherein the width-broadening process further comprises, after the stretching step, a step of cooling down the stretched initial pressure-sensitive adhesive sheet.
The pressure-sensitive adhesive sheet according to any one of Claims 1 to 10, wherein the substrate layer is a resin layer comprising a thermoplastic resin as its primary component.
The method according to any one of Claims 1 to 11, wherein the substrate layer is formed from at least one species of resin selected from the group consisting of polyolefinic resin, polyvinyl chloride-based resin and polyurethane-based resin.
The method according to any one of Claims 1 to 12, wherein the substrate layer has a thickness of 25 μm to 150 μm.
The method according to any one of Claims 1 to 13, wherein the pressure-sensitive adhesive layer is an acrylic pressure-sensitive adhesive layer comprising an acrylic polymer as its base polymer or a rubber-based pressure-sensitive adhesive layer comprising a rubber-based polymer as its base polymer.
The method according to any one of Claims 1 to 14, wherein the pressure-sensitive adhesive layer has a thickness of 1 μm to 20 μm.
The method according to any one of Claims 1 to 15, further comprising winding the pressure-sensitive adhesive sheet in its length direction to form a pressure-sensitive adhesive sheet roll, after the pressure-sensitive adhesive sheet is prepared and before the pressure-sensitive adhesive sheet is applied to the target area.
The method according to any one of Claims 1 to 16, wherein the pressure-sensitive adhesive sheet is an adhesively single-faced pressure-sensitive adhesive sheet having the pressure-sensitive adhesive layer provided solely to one face of the substrate layer.
A surface protection method for protecting an adherend surface by applying a pressure-sensitive adhesive sheet to a target area of the adherend, the method comprising:
determining the width of the target area;
from a workpiece group comprising at least two species of initial pressure-sensitive adhesive sheets differing in width, selecting, based on the width of the target area, one, two or more initial pressure-sensitive adhesive sheets that are individually not wide enough to cover the target area, wherein the initial pressure-sensitive adhesive sheets individually comprise a substrate layer and a pressure-sensitive adhesive layer provided to at least one face of the substrate layer;
preparing a one-piece pressure-sensitive adhesive sheet having a width large enough to cover the target area by processing the selected initial pressure-sensitive adhesive sheets; and
applying the pressure-sensitive adhesive sheet to the target area.
A method for preparing a pressure-sensitive adhesive sheet, the method comprising:
setting a width WS that the pressure-sensitive adhesive to be prepared should have;
conducting an assessment on whether or not a workpiece group comprising at least two species of initial pressure-sensitive adhesive sheets differing in width includes an initial pressure-sensitive adhesive sheet having a width that is 0.7 times up to less than 1.0 times the width WS, wherein the initial pressure-sensitive adhesive sheets individually comprise a substrate layer and a pressure-sensitive adhesive layer formed on at least one face of the substrate layer;
based on the assessment, selecting one, two or more initial pressure-sensitive adhesive sheets that individually have a width smaller than the width WS;
preparing a one-piece pressure-sensitive adhesive sheet having the width WS by processing the selected initial pressure-sensitive adhesive sheets.
The method according to Claim 19, wherein:
based on the assessment,
when the workpiece group includes an initial pressure-sensitive adhesive sheet having a width that is 0.7 times up to less than 1.0 times the width WS, the pressure-sensitive adhesive sheet is prepared
by selecting one initial pressure-sensitive adhesive sheet from the initial pressure-sensitive adhesive sheets individually having a width that is 0.7 times up to less than 1.0 times the width WS and subjecting the selected initial pressure-sensitive adhesive sheet to a width-broadening process, or
by selecting at least two initial pressure-sensitive adhesive sheets individually having a width smaller than the width WS and joining the selected initial pressure-sensitive adhesive sheets to obtain a larger width; and
when the workpiece group does not include an initial pressure-sensitive adhesive sheet having a width that is 0.7 times up to less than 1.0 times the width WS, the pressure-sensitive adhesive sheet is prepared by selecting at least two initial pressure-sensitive adhesive sheets individually having a width smaller than 0.7 times the width WS and joining the selected initial pressure-sensitive adhesive sheets to obtain a larger width.