US20150320293A1

US20150320293A1 - Sticky cleaner for removing organic dirt

Info

Publication number: US20150320293A1
Application number: US14/762,703
Authority: US
Inventors: Teiji Sakashita; Satoshi Taguchi; Yumi KAWAI; Aya Nagatomo
Original assignee: Nitto Denko Corp; Nitoms Inc
Current assignee: Nitto Denko Corp; Nitoms Inc
Priority date: 2013-01-25
Filing date: 2014-01-16
Publication date: 2015-11-12
Also published as: KR20150109351A; KR102038735B1; CN104955371A; JP2014144023A; TWI604898B; WO2014115632A1; TW201436890A; JP6100539B2

Abstract

Provided is a sticky cleaner that can easily remove organic dirt adsorbed on a surface of an article with greater dirt-removing workability. The sticky cleaner provided by the present invention is used for removing organic dirt adsorbed on a flat surface of an article. The sticky cleaner comprises a dirt-collecting member that collects the organic dirt as it makes contact with the flat surface. In the dirt-collecting member, the part to make contact with the surface is formed with a PSA. The surface-contacting part of the dirt-collecting member exhibits an adhesive strength of less than 1 N/25 mm as a measured value based on the 180° peel test specified in JIS Z0237.

Description

TECHNICAL FIELD

The present invention relates to a sticky cleaner used for removing organic dirt. In particular, it relates to a sticky cleaner used for removing sebum and other organic dirt from a flat surface (e.g. a touch panel display/input screen) in a portable device such as a tablet terminal, smartphone and the Eke. The present application claims priority based on Japanese Patent Application No. 2013-012473 filed on Jan. 25, 2013 and the entire contents thereof are incorporated herein by reference.

BACKGROUND ART

A display typically formed of a liquid crystal panel or an organic EL panel is placed on a flat surface in a portable device, for instance, a portable personal computer (PC) such as notebook PCs, etc.; tablet terminal such as electronic books, etc.; mobile phone such as smartphones, etc.; mobile gaming device; various types of PDA (personal digital assistant); and the Eke. These portable devices are carried and used on a daily basis, and thus easily attract dust and organic dirt such as finger marks, cosmetics and sebum. In particular, recently wide-spread touch-screen portable devices are operated with a direct finger touch by a user to the display/input portion in which the display functions also as an input device, and thus are more likely to attract organic dirt such as finger marks, sebum, etc. Not just these portable devices, but also show window glass, glass tables, showcases and the like have flat surfaces. The organic dirt adsorbed on their surfaces degrades their exteriors, making them unsightly.
As means to remove organic dirt adsorbed on the display, a wipe (waste cloth) made of paper, woven fabric or non-woven fabric is used. For instance, when the dirt includes an oily component such as sebum and the like, wiping off dirt with a wipe is not necessarily easy to carry out, possibly spreading the dirt depending on how it is done or requiring multiple times of wiping, and so on. Dirt gradually accumulates with continuous use, requiring regular cleaning or a replacement with a new piece, which can be troublesome. Alternatively, there is a means where organic dirt is removed by wiping the surface with a suitable material (e.g. sponge or gauze) containing a suitable detergent (e.g. see Patent Document 1). However, not only is careful handling of the detergent necessary, but residual detergent can even affect the surface. This method thus requires elimination of the detergent and thus is not advantageous in terms of workability.

CITATION LIST

Patent Literature

[Patent Document 1] Japanese Patent Application Publication No. 2009-503161
[Patent Document 2] Japanese Patent Application Publication No. 2004-237023

SUMMARY OF INVENTION

Technical Problem

The present invention has been made to solve the conventional problem. An objective thereof is to provide a sticky cleaner that can easily remove organic dirt adsorbed on a surface of an article with greater dirt-removing workability.

Solution to Problem

To achieve the objective, the present invention provides a sticky cleaner used for removing organic dirt adsorbed on a flat surface of an article. The sticky cleaner comprises a dirt-collecting member that collects the organic dirt as it makes contact with the flat surface. In the dirt-collecting member, the part to make contact with the surface is formed with a pressure-sensitive adhesive (PSA). The surface-contacting part of the dirt-collecting member exhibits an adhesive strength of less than 1 N/25 mm as a measured value based on the 180° peel test specified by JIS Z0237.
According to a sticky cleaner (dirt remover) having such a constitution, by allowing the PSA constituting the dirt-collecting member to make contact with a flat surface of an article, organic dirt (e.g. finger marks and sebum residue of a person or cosmetics) adsorbed on the surface can be collected and easily removed therefrom. The surface-contacting part of the dirt-collecting member exhibits an adhesive strength of less than 1 N/25 mm as a measured value based on the 180° peel test specified by JIS Z0237. This means that the dirt-collecting member is easily releasable. Accordingly, when the cleaner is operated on a flat surface of an article (e.g. moved on the surface or taken away from the surface), it requires little force, thereby providing excellent dirt-removing workability. Furthermore, even when the article's surface (e.g. tablet terminal's display) is covered with removable protection film, because of the easy-release nature, it can clean the surface without removing the protection film (in other words, while keeping the article surface covered with the protection film). In addition, despite such easy-release nature, it can sufficiently remove organic dirt. As described above, the organic dirt includes sebum from the skin, and as evident from this, it may include inorganic substances such as sodium and potassium as well as their salts, etc.
In a preferable embodiment of the sticky cleaner disclosed herein, the surface-contacting part of the dirt-collecting member exhibits an adhesive strength of 0.01 N/25 mm to 0.5 N/25 mm as a measured value based on the 180° peel test specified in JIS Z0237. Such an easy-release cleaner can sufficiently remove organic dirt while providing greater dirt-removing workability.
In a preferable embodiment, the sticky cleaner disclosed herein comprises a cylindrical rolling member and the dirt-collecting member is arranged along the lateral surface of the rolling member. According to a cleaner having such a constitution, when the rolling member is allowed to rotate in the circumferential direction of the cylinder, the dirt-collecting member on the lateral surface can efficiently remove organic dirt on the flat surface. Since the dirt-collecting member can be released easily, the peel resistance during the rotation is low, leading to excellent dirt-removing workability.
In a preferable embodiment, the sticky cleaner disclosed herein further comprises a grip member that supports the rolling member in a freely rotatable manner. With this constitution, a user can hold the grip member and rotate the rolling member to efficiently remove organic dirt from the flat surface.
In a preferable embodiment of the sticky cleaner disclosed herein, the dirt-collecting member is constituted as an adhesively single-faced PSA sheet comprising a sheet of support substrate and a PSA layer placed above the support substrate, and the single-faced PSA sheet is wound with the PSA layer on the outside to form a PSA sheet roll. With a sticky cleaner having such a constitution, the lateral surface of the PSA sheet roll can be used to remove dirt from a flat surface. In accordance with the usage and the amount of dirt caught on the PSA layer, the lateral surface used for dirt removal can be eliminated from (typically peeled off) the roll to expose an unused section of the PSA layer on the lateral surface. In other words, the PSA layer can be easily refreshed to expose an unused section to the outer surface. Accordingly, a desirable level of dirt-removing ability can be constantly maintained.
Preferably, the PSA sheet roll disclosed herein is constituted to deter rail drawing phenomenon. Rail drawing herein refers to a phenomenon such that when the sheet roll is rolled (rotated) reversely to the winding direction (typically in a direction in which the wound single-faced PSA sheet is peeled) on the surface to be cleaned (a flat surface of an article), a band of the PSA sheet stays adsorbed on the surface to be cleaned, beginning from the outer circumferential end of the roll. Reduced occurrence of rail drawing allows for stress-free, smooth rotation of the roll on the flat surface, leading to great usability. In addition, it can also prevent wasteful use of the PSA sheet due to the occurrence of rail drawing (i.e. waste of the sheet due to unintentional adhesion of the PSA sheet to the surface).
In a preferable embodiment of the sticky cleaner disclosed herein, the PSA layer comprises an acrylic polymer at a ratio of 50% by mass or higher. The use of the acrylic polymer as the PSA can preferably bring about both removal of organic dirt and easy release. The acrylic polymer is preferably a crosslinked acrylic polymer. This further increases the ease of release. Alternatively, it is preferable that the acrylic polymer is a thermoplastic acrylic polymer. This facilitates formation of PSA layers.
Preferably, the PSA layer further comprises a plasticizer. The inclusion of the plasticizer can lighten the release and lead to greater dirt-removing workability. Even when the dirt-collecting ability is reduced as a result of use, it preferably exhibits an effect of regaining its dirt-collecting ability in relatively short time (e.g. several minutes or several hours) (dirt-collecting ability recovery effect).
In a preferable embodiment, the sticky cleaner disclosed herein is used for removing human sebum dirt as the organic dirt. The sticky cleaner having the prescribed constitution disclosed herein effectively removes human sebum dirt despite the easy-release nature. This has been made possible for the first time through the studies by the present inventors. The sticky cleaner is particularly suitable for removing human sebum dirt.
In a preferable embodiment of the sticky cleaner disclosed herein, the article is a portable device having a glass or synthetic resin display on the flat surface. The portable device is carried and used on a daily basis and is likely to attract organic dirt such as sebum. In particular, a portable device having a touch panel display (display/input member) is operated with a direct finger touch to the display/input portion, and thus is more likely to attract organic dirt such as finger marks, cosmetics, sebum dirt, etc. The sticky cleaner disclosed herein can easily remove such organic dirt; and therefore, it is particularly preferably used for removing dirt from a portable device having a display as described above (e.g. a touch panel display). Sticky cleaners have been conventionally used (e.g. see Patent Document 2). However, conventional roller cleaners are used for cleaning floors and carpets, but not intended for cleaning flat surfaces (e.g. touch panel display/input portions) of portable devices (e.g. tablet terminals and smartphones) as described above.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 shows a front view schematically illustrating the sticky cleaner according to an embodiment.

FIG. 2 shows a side view schematically illustrating the sticky cleaner according to an embodiment.

FIG. 3 shows a cross-sectional view schematically illustrating the dirt-collecting member constituting the sticky cleaner according to an embodiment.

FIG. 4 shows a perspective view schematically illustrating an example of usage of the sticky cleaner according to an embodiment.

FIG. 5 shows a diagram schematically illustrating the mechanism of dirt-removing ability recovery effect of the sticky cleaner according to an embodiment.

DESCRIPTION OF EMBODIMENTS

Preferred embodiments of the present invention are described below. Matters necessary to practice this invention other than those specifically referred to in this description may be understood as design matters to a person of ordinary skill in the art based on the conventional art in the pertinent field. The present invention can be practiced based on the contents disclosed in this description and technical common knowledge in the subject field.
The sticky cleaner disclosed herein is different from conventional sticky cleaners used for cleaning floors and carpets. It is used for removing organic dirt adsorbed on a flat surface of an article such as a portable device. The article on which the sticky cleaner disclosed herein is used is not particularly limited as long as it has a flat surface. Examples include show window glass, glass tables, showcases and the like. As organic dirt adsorbed on their flat surfaces (typically transparent glass surfaces) is unsightly, if found any, its quick removal is desirable. Thus, on their surface, the sticky cleaner disclosed herein can be preferably used.
Preferable examples of the article on which the sticky cleaner disclosed herein is used include various portable devices. The term portable device herein refers to a mobile device having a flat surface at least partially on the outside and is not limited to a particular device. Examples include portable devices such as notebook PCs; tablet terminals such as electronic books, etc.; smartphones and other mobile phones; mobile gaming devices; PDAs (mobile terminals) such as electronic organizers, etc.; and the like. Since these are carried and used on a daily basis, they are likely to attract dust and especially organic dirt such as finger marks, cosmetics and sebum. Some of these portable devices have displays such as liquid crystal displays, organic EL displays and the like on flat surfaces (typically glass or synthetic resin surfaces). Organic dirt on the displays makes information displayed thereon hard to see, thereby hindering the use. Moreover, depending on the amount of organic dirt adsorbed thereon, it might give a filthy impression. On portable devices having such displays, the sticky cleaner disclosed herein can be preferably used.
In particular, portable devices having touch panel display/input portions are likely to attract the organic dirt since users directly touch the displays with fingers. Thus, the sticky cleaner disclosed herein can be preferably used on them. Among them, tablet terminals such as electronic books and the like have relatively large displays; and therefore, they are considered as particularly preferable articles on which the sticky cleaner is used.
The sticky cleaner according to an embodiment is described below with reference to drawings. As shown in FIGS. 1 and 2, a sticky cleaner (or simply cleaner, hereinafter) 10 comprises a cylindrical holding member (core) 20 and a PSA sheet roll 30 held on the outer periphery of holding member 20. These holding member 20 and PSA sheet roll 30 are assembled to form a cylindrical rolling member. The holding member material is not particularly limited. A holding member made of a polyolefin or other synthetic resin as well as paper can be preferably used.
Cleaner 10 further comprises a grip member 40 in a form of a pole that supports holding member 20 in a freely rotatable manner. In particular, holding member 20 has a center hole (not shown in the drawings) formed where the central axis of the cylinder is located. A terminal section (one end) of grip member 40 is inserted through the center hole, whereby holding member 20 is installed on grip member 40 in a freely rotatable manner. To the other end of grip member 40, a handle 42 is attached. The materials of grip member and handle are not particularly limited. For instance, metal or synthetic resin pieces can be used.
PSA sheet roll 30 in cleaner 10 is formed by winding a PSA sheet 31 that serves as the dirt-collecting member. In particular, PSA sheet (dirt-collecting member) 31 is constituted as a single-faced PSA sheet 31 comprising, as shown in FIG. 3, a support substrate 36 in a form of a long sheet (band) and a PSA layer 32 placed on one face 36A of the support substrate 36. Single-faced PSA sheet 31 is wound with the PSA layer 32 on the outside and formed as a PSA sheet roll 30.
With respect to cleaner 10 having a constitution as described above, some applications are now described. As shown in FIG. 4, cleaner 10 is used for removing organic dirt adsorbed on a display 2 of a portable device 1. Display 2 in portable device 1 has a flat surface. An operator places cleaner 10 on the display 2 of portable device 1, grip a handle 42, and applies a prescribed amount of external force to cleaner 10. The force is then transmitted from grip member 40 to holding member 20, and the PSA layer 32 (a section of the dirt-collecting member that makes contact with the flat surface) placed on the outer periphery of holding member 20 rotationally moves on display 2. In FIG. 4, PSA sheet roll 30 moves on display 2 in the direction shown by the arrow. During this, the PSA layer 32 collects dust, fine particles, and especially organic dirt such as human finger marks, sebum and the like present on the display 2. By this means, cleaning (dirt removal) of display 2 is easily and certainly accomplished in the rotation direction of PSA sheet roll 30 (more specifically, the PSA sheet (dirt-collecting member) 31). The portable device in this embodiment is a tablet terminal whose display is entirely formed with flat tempered glass such as aluminosilicate glass and the like although it is not limited to this as indicated earlier.
The size of the cylindrical PSA sheet roll is not particularly limited. When it is used on portable devices such as tablet terminals, etc., its diameter (which refers to the diameter (outer diameter) before used; the same applies hereinafter) is preferably 4 mm or larger (e.g. 10 mm or larger, typically 20 mm or larger). From the standpoint of the maneuverability and portability, the diameter is preferably 50 mm or smaller (e.g. 35 mm or smaller, typically 30 mm or smaller).
In the PSA sheet roll, the PSA sheet preferably has cut lines (not shown in the drawings) at an interval of approximately the length of the circumference. The cut lines provide cutting means for efficiently refresh the PSA layer surface (outer surface of the dirt-collecting member) with a reduced cleaning (dirt-removing) ability after the cleaner is used several times. The cut lines can be, for instance, lines of long holes or wavy slits; intermittent slits such as perforation; and the like. The cut lines are preferably arranged to run across the PSA sheet in the width direction (direction perpendicular to the length direction). Refreshing the lateral surface of the dirt-collecting member is not limited to the cutting means. For instance, intermittent slits such as perforation can be spirally formed in a direction intersecting the winding direction of the PSA sheet roll (typically, in a direction intersecting the width direction at an angle between 30° and 60°). Alternatively, instead of intermittent slits such as perforation, the PSA sheet constituting the PSA sheet roll may comprise slits (continuous cut lines) at a prescribed interval. In this embodiment, the PSA sheet constituting the PSA sheet roll is fully cut in advance at the prescribed intervals in the winding direction of the roll. Thus, the outer surface of the PSA sheet roll can be peeled over the length of the prescribed interval to easily refresh the outer surface.
The cleaner 10 can be produced by suitably employing heretofore known techniques. For instance, PSA sheet roll 30 of cleaner 10 can be fabricated in the same manner as conventional roller cleaners. In other words, a PSA composition is applied to the surface 36A of a long sheet of support substrate 36 by various heretofore known coating means and subsequently allowed to dry to form a PSA layer 32. The PSA sheet 31 is wound around holding member 20 with the PSA layer 32 on the outside to form PSA sheet roll 30 in a form of a roll. A terminal section of grip member 40 is further attached to holding member 20 in a freely rotatable manner to construct cleaner 10. The structure of attachment of grip member 40 to holding member 20 can be similar to those in conventional roller cleaners and does not characterize the present invention. Accordingly, detailed description is omitted.
The sticky cleaner is not limited to the embodiment above. The sticky cleaner may be formed, for instance, solely with a dirt-collecting member. Examples of such a sticky cleaner include a cleaner formed solely with a dirt-collecting member in a form of a sphere, column, cylinder, hexahedron (e.g. cuboid), sheet, etc.
In this embodiment, the dirt-collecting member is formed with, but not limited to, the support substrate and PSA layer. For instance, the dirt-collecting member may be formed solely with a PSA (substrate-free PSA). Alternatively, when the dirt-collecting member has a support substrate, the shape of the support substrate is not particularly limited. For instance, the dirt-collecting member may have a PSA layer on the outer surface of a spherical support substrate.
In this embodiment, the grip member supports the holding member in a freely rotatable manner, but it is not limited to this. For instance, the grip member may be directly or indirectly joined (connected or detachably joined) to the dirt-collecting member. In an example of such a sticky cleaner, a columnar or cuboid PSA body is fastened to one end of a pole-shaped grip member. Alternatively, the grip member may have a flat portion and the dirt-collecting member may be fastened to one face of the flat portion.
The dirt-collecting member (e.g. PSA sheet) disclosed herein is characterized by that the part (e.g. sticky surface) that makes contact with a flat surface of an article exhibits an adhesive strength of less than 1 N/25 mm as a measured value based on the 180° peel test specified in JIS Z0237. This means that the dirt-collecting member is easily releasable. A cleaner having such an easily releasable dirt-collecting member requires little force for the dirt-removing operation on the surface, providing excellent dirt-removing workability. More specifically, the cleaner can be moved more smoothly on a flat surface of an article and has advantages such that the cleaner can be easily separated from the surface after the dirt-removing operation. Even when the surface of the article (e.g. display of a tablet terminal) is covered with removable protection film (e.g. protection film made of a silicone-based or polyester-based synthetic resin, etc.), because of the easy-release nature, it can clean the surface without removing the protection film (i.e. while keeping the article surface covered with the protection film). In this case, the object to be cleaned is the surface of the protection film and such a surface is also included in the article's flat surface. From the standpoint of the dirt-removing workability, the adhesive strength is preferably 0.8 N/25 mm or less (e.g. 0.6 N/25 mm or less, typically 0.5 N/25 mm or less) or more preferably 0.57 N/25 mm or less (e.g. 0.55 N/25 mm or less, typically 0.4 N/25 mm or less). From the standpoint of the dirt-collecting ability, the adhesive strength is preferably 0.001 N/25 mm or greater (e.g. 0.01 N/25 mm or greater, typically 0.02 N/25 mm or greater) or more preferably 0.03 N/25 mm or greater (e.g. 0.05 N/25 mm or greater, typically 0.08 N/25 mm or greater).
In particular, the adhesive strength is measured according to the following procedures: The dirt-collecting member (typically a PSA sheet) is cut to a rectangular sheet to prepare a test piece. The test piece preferably has a length of about 100 mm to 200 mm and a width of about 15 mm to 30 mm. When the width is not 25 mm, the value in N/25 mm can be determined (by conversion) based on the ratio of actual width to 25 mm. The thickness is not particularly limited. The resulting test piece is adhered over its sticky face (e.g. PSA layer-side surface) to a stainless steel (SUS304) plate with a 2 kg roller moved back and forth once. When the test piece is sticky on each face such as in a double-faced PSA sheet, etc., it is preferable to back the surface opposite the measured surface with a polyethylene terephthalate (PET) film of about 25 μm in thickness. This is stored in an environment at 23° C. and 50% RH for 30 minutes. Based on JIS Z0237, using a tensile tester, in an environment at 23° C. and 50% RH, the 180° peel strength (N/25 mm) to SUS is measured. The tensile tester is not particularly limited and a heretofore known tensile tester can be used. For instance, measurements can be made with trade name “TENSILON” available from Shimadzu Corporation.
The dirt-collecting member (e.g. PSA sheet) disclosed herein may be characterized by that, instead of or in addition to the 180° peel strength to SUS, the part (e.g. sticky surface) that comes in contact with the article's flat surface exhibits a 180° peel strength of less than 1 N/25 mm to a glass plate. A cleaner having such an easily releasable dirt-collecting member provides excellent dirt-removing workability. From the standpoint of the dirt-removing workability, the adhesive strength is preferably 0.9 N/25 mm or less (e.g. 0.85 N/25 mm or less, typically 0.5 N/25 mm or less) or more preferably 0.57 N/25 mm or less (e.g. 0.55 N/25 mm or less, typically 0.4 N/25 mm or less). From the standpoint of the dirt-collecting ability, the adhesive strength is preferably 0.001 N/25 mm or greater (e.g. 0.01 N/25 mm or greater, typically 0.02 N/25 mm or greater) or more preferably 0.03 N/25 mm or greater (e.g. 0.05 N/25 mm or greater, typically 0.06 N/25 mm or greater). The 180° peel strength to the glass plate (180° peel strength to glass) can be measured similarly to the measurement of the 180° peel strength to SUS except that the glass plate (e.g. a commercial float glass plate) is used as the adherend.
The dirt-collecting member (e.g. PSA sheet) disclosed herein may be characterized by that, instead of or in addition to the 180° peel strength to SUS, the part (e.g. sticky surface) that comes in contact with the article's flat surface exhibits a 180° peel strength of less than 1 N/25 mm to polyethylene terephthalate (PET) film. A cleaner having such an easily releasable dirt-collecting member provides excellent dirt-removing workability. From the standpoint of the dirt-removing workability, the adhesive strength is preferably 0.9 N/25 mm or less (e.g. 0.8 N/25 mm or less, typically 0.6 N/25 mm or less) or more preferably 0.5 N/25 mm or less (e.g. 0.4 N/25 mm or less). From the standpoint of the dirt-collecting ability, the adhesive strength is preferably 0.001 N/25 mm or greater (e.g. 0.01 N/25 mm or greater, typically 0.02 N/25 mm or greater). The 180° peel strength to PET film (180° peel strength to PET) can be measured similarly to the measurement of the 180° peel strength to SUS except that PET film is used as the adherend.
When the sticky cleaner disclosed herein has a PSA sheet roll, the PSA sheet roll preferably has balanced adhesive strength (e.g. the measured value based on the 180° peel test) and unwinding force so that the occurrence of rail drawing is reduced on the article's flat surface (e.g. a surface formed of glass such as aluminosilicate glass or synthetic resin). The unwinding force herein refers to the force required to pull out the PSA sheet from the PSA sheet roll (i.e. resistive force against unwinding, which can be perceived as the adhesive strength to the back face of the PSA sheet (typically the back face of the support substrate). For instance, when the unwinding force is excessively low as compared with the adhesive strength, when the PSA sheet roll is rotated on a flat surface, the unwinding force may succumb to the adhesive strength between the PSA sheet (typically the PSA layer) and the surface to cause rail drawing. On the other hand, an excessively high unwinding force tends to result in unsmooth unwinding of the PSA sheet.
The unwinding force can be assessed as follows. In particular, the PSA sheet roll is set in a prescribed tensile tester. In an environment at a temperature of 23° C. and 50% RH, the outer circumferential end of the wound PSA sheet is mounted to the chuck of the tester and pulled at a rate of 300 mm/min to unwind the PSA sheet roll in the tangential direction. The unwinding force during this can be converted to and determined as the value per width (e.g. 150 mm) of PSA layer of the PSA sheet (N/150 mm). For instance, a preferable PSA sheet roll has an unwinding force of about 0.5 N/150 mm to 2.5 N/150 mm.
The PSA (e.g. PSA layer) constituting the dirt-collecting member (e.g. PSA sheet) is not particularly limited as long as it satisfies the peel strength to SUS. For instance, the PSA may be formed from an aqueous PSA composition such as a water-soluble PSA composition, water-dispersed PSA composition and the like or from a PSA composition such as a solvent-based PSA composition and the like. A solvent-free PSA formed from an active energy ray-curable PSA composition or a hot melt PSA composition can be preferably used as well. To remove human sebum dirt, a solvent-based PSA and solvent-free PSA are preferable. From the standpoint of the handling, a hot melt PSA is preferable.
The PSA can be an acrylic PSA, rubber-based PSA (e.g. natural rubber-based PSA), urethane-based PSA, silicone-based PSA, etc. From the standpoint of the adhesive properties and cost, a rubber-based PSA or an acrylic PSA can be preferably used.
In particular, from the standpoint of controlling the adhesive strength (ease of release), the PSA is preferably an acrylic PSA comprising an acrylic polymer as a base polymer (primary component among polymers, a primary adhesive component). The acrylic polymer can be synthesized from starting monomer(s) comprising, as the primary monomer, an alkyl (meth)acrylate having an alkyl group. The primary monomer herein refers to a monomer that accounts for 50% by mass or more of all the monomers. In the present description, the term “(meth)acrylate” comprehensively means acrylate and methacrylate. Similarly, the terms “(meth)acryloyl” and “(meth)acryl” comprehensively mean acryloyl and methacryloyl, and acryl and methacryl, respectively.
As the alkyl (meth)acrylate, for instance, a compound represented by a formula can be preferably used:
CH₂═CR¹COOR²
Herein, R¹in the formula is a hydrogen atom or a methyl group. R²is 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 storage elastic modulus of the PSA, etc., an alkyl (meth)acrylate having a C_1-14(e.g., C_1-10) alkyl group is preferable. The alkyl group may be linear or branched.
Examples of the alkyl (meth)acrylate having a C_1-20alkyl 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, isoamyl (meth)acrylate, neopentyl (meth)acrylate, hexyl (meth)acrylate, heptyl (meth)acrylate, octyl (meth)acrylate, isooctyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, nonyl (meth)acrylate, isononyl (meth)acrylate, decyl (meth)acrylate, isodecyl (meth)acrylate, bornyl (meth)acrylate, isobornyl (meth)acrylate, undecyl (meth)acrylate, dodecyl (meth)acrylate, tridecyl (meth)acrylate, tetradecyl (meth)acrylate, pentadecyl (meth)acrylate, hexadecyl (meth)acrylate, heptadecyl (meth)acrylate, octadecyl (meth)acrylate, nonadecyl (meth)acrylate and eicosyl (meth)acrylate. These alkyl (meth)acrylates may be used singly as one species or in a combination of two or more species. In particular, an alkyl (meth)acrylate having a C_4-9alkyl group is preferable. Preferable examples include n-butyl acrylate (BA), 2-ethylhexyl acrylate (2EHA) and isononyl acrylate. Among these, BA and 2EHA are more preferable.
The ratio of primary monomer to all the monomers is preferably 60% by mass or higher, more preferably 80% by mass or higher, or yet more preferably 90% by mass or higher. The upper Emit of the primary monomer ratio is not particularly limited. It is preferably 99% by mass or less (e.g. 98% by mass or less, typically 95% by mass or less). The acrylic polymer can be a polymerization product of essentially just the primary monomer.
To improve various properties such as the ease of release, etc., the starting monomers used in polymerization of the acrylic polymer may comprise, in addition to the primary monomer, a secondary monomer that can be copolymerized with the primary monomer. The secondary monomer encompasses not only a monomer, but also an oligomer. As such a secondary monomer, a monomer having a functional group (or “functional group-containing monomer” hereinafter) can be cited. The functional group-containing monomer can be added to incorporate crosslinking points into the acrylic polymer to increase the cohesive strength thereof. Examples of such a functional group-containing monomer include carboxyl-group-containing monomers, acid-anhydride-group-containing monomers, hydroxyl-group-containing monomers, amide-group-containing monomers, amino-group-containing monomers, epoxy-group (glycidyl group)-containing monomers, alkoxy-group-containing monomers, and alkoxysilyl-group-containing monomers. These can be used as a single kind alone, or in combination of two or more kinds. Among these, functional group-containing monomers having a functional group of carboxyl group, hydroxyl group, epoxy group, etc. are more preferable, and carboxyl-group-containing monomers and hydroxyl-group-containing monomers are yet more preferable because they can preferably introduce crosslinking points into the acrylic polymer and achieve an even higher cohesive strength in the acrylic polymer.
Examples of a carboxyl-group-containing monomer include ethylenic unsaturated monocarboxylic acids such as acrylic acid, methacrylic acid, crotonic acid, carboxyethyl (meth)acrylate, carboxypentyl (meth)acrylate, etc.; ethylenic unsaturated dicarboxylic acids such as itaconic acid, maleic acid, fumaric acid, citraconic acid, etc.; and the like. Among these, acrylic acid and/or methacrylic acid are preferable, and acrylic acid is especially preferable.
Examples of an acid-anhydride-group-containing monomers include acid anhydrides of the ethylenic unsaturated dicarboxylic acids listed above such as maleic acid anhydride, itaconic acid anhydride, etc.; and the like.
Examples of a hydroxyl-group-containing monomer include hydroxyalkyl (meth)acrylates such as 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, etc.; unsaturated alcohols such as N-methylol(meth)acrylamide, vinyl alcohol, allyl alcohol, 2-hydroxyethyl vinyl ether, 4-hydroxybutyl vinyl ether, diethylene glycol monovinyl ether, etc.; and the like.
Examples of an amide-group-containing monomer include (meth)acrylamide, N,N-dimethyl(meth)acrylamide, N-butyl(meth)acrylamide, N-methylol(meth)acrylamide, N-methylolpropane(meth)acrylamide, N-methoxymethyl(meth)acrylamide, N-butoxymethyl(meth)acrylamide, and the like.
Examples of an amino-group-containing monomer include aminoethyl (meth)acrylate, N,N-dimethylaminoethyl (meth)acrylate, t-butylaminoethyl (meth)acrylate, and the like.
Examples of an epoxy-group (glycidyl group)-containing monomer include glycidyl (meth)acrylate, methylglycidyl (meth)acrylate, allyl glycidyl ether, and the like.
Examples of an alkoxy-group-containing monomer include methoxyethyl (meth)acrylate, ethoxyethyl (meth)acrylate, and the like.
Examples of an alkoxysilyl-group-containing monomer include 3-(meth)acryloxypropyltrimethoxysilane, 3-(meth)acryloxypropyltriethoxysilane, 3-(meth)acryloxypropylmethyldimethoxysilane, 3-(meth)acryloxypropylmethyldiethoxysilane, and the like.
When an aforementioned functional group-containing monomer is used as a monomer constituting the acrylic polymer, the functional group-containing monomer (preferably a carboxyl group-containing monomer) is preferably added at 1 to 10% by mass (e.g., 2 to 8% by mass, typically 3 to 7% by mass) of all the monomers.
To increase the cohesive strength of the acrylic polymer, etc., another monomer besides the functional-group-containing monomer can be included as a secondary monomer. Examples of such a monomer include vinyl-ester-based monomers such as vinyl acetate, vinyl propionate, etc.; aromatic vinyl compounds such as styrene, substituted styrenes (α-methylstyrene, etc.), vinyl toluene, etc.; and the like.
The method for polymerizing the monomer or a monomer mixture is not particularly limited, and a general polymerization method heretofore known can be employed. Examples of such a polymerization method include solution polymerization, emulsion polymerization, bulk polymerization, and suspension polymerization. Among these, solution polymerization is preferable. The embodiment of the polymerization is not particularly limited and can be carried out with suitable selection of a heretofore known monomer supply method, polymerization conditions (temperature, time, pressure, etc.), and other components (polymerization initiator, surfactant, etc.) used besides the monomer. For instance, as the monomer supply method, the monomer mixture can be supplied to a reaction vessel all at once (all-at-once supply), or gradually supplied dropwise (continuous supply), or the mixture can be divided in several portions and each portion can be supplied at a prescribed time interval (portionwise supply). The monomer or the monomer mixture can be supplied as a solution or a dispersion containing part or all thereof dissolved in a solvent or emulsified in water.
The polymerization initiator is not particularly limited. Examples include azo-based initiators such as 2,2′-azobisisobutylonitrile, etc.; peroxide-based initiators such as benzoyl peroxide, etc.; substituted ethane-based initiators such as phenyl-substituted ethane, etc.; redox-based initiators combining a peroxide and a reducing agent such as a combination of a peroxide and sodium ascorbate, etc.; and the like. The amount of polymerization initiator used can be suitably selected in accordance with the type of polymerization initiator, types of monomers (composition of the monomer mixture) and so on. It is usually suitably selected from a range of, for instance, about 0.005 to 1 part by mass, relative to 100 parts by mass of all the monomers. The polymerization temperature can be, for example, around 20° C. to 100° C. (typically 40° C. to 80° C.).
A crosslinking agent is preferably added to the PSA composition. Preferable examples of a crosslinking agent for an acrylic PSA include organometallic salts such as zinc stearate, barium stearate, etc.; epoxy-based crosslinking agents; isocyanate-based crosslinking agents; and the like. Oxazoline-based crosslinking agents, aziridine-based crosslinking agents, metal-chelate-based crosslinking agents, and melamine-based crosslinking agents can also be used. These crosslinking agents can be used singly as one species or as two or more species together. Among these, epoxy-based crosslinking agents and isocyanate-based crosslinking agents are preferable because they can be preferably crosslinked to carboxyl groups and are likely to produce good maneuverability (typically easy-release nature) and even good acid resistance as well. Combined use of an epoxy-based crosslinking agent and an isocyanate-based crosslinking agent is particularly preferable. The amount of crosslinking agent added is not particularly limited. In order to achieve the adhesive strength in the preferable numerical value range, it can be about 0.01 to 10 parts by mass (e.g. 0.05 to 5 parts by mass, typically 0.1 to 5 parts by mass) relative to 100 parts by mass of the base polymer (e.g. an acrylic polymer). When an epoxy-based crosslinking agent (C_E) and an isocyanate-based crosslinking agent (C_I) are used together, their mass ratio value (C_E/C_I) is preferably 0.01 to 1 (e.g. 0.05 to 0.5, typically 0.1 to 0.4).
When a solvent-based PSA is used, preferable examples of a solvent for use include aliphatic hydrocarbons such as hexane, heptane, mineral spirit, etc.; alicyclic hydrocarbons such as cyclohexane, etc.; aromatic hydrocarbons such as toluene, xylene, solvent naphtha, tetralin, dipentene, etc.; alcohols such as butyl alcohol, isobutyl alcohol, cyclohexyl alcohol, 2-methylcyclohexyl alcohol, tridecyl alcohol, etc.; esters such as methyl acetate, ethyl acetate, isopropyl acetate, butyl acetate, etc.; ketones such as acetone, methyl ethyl ketone, etc.
The molecular weight (Mw: weight average molecular weight) of the base polymer (e.g. an acrylic polymer) to be used (synthesized) is not particularly limited, but a polymer (e.g., an acrylic polymer) having a weight average molecular weight (Mw) of approximately 30×10⁴to 100×10⁴can be used preferably.
The acrylic polymer constituting the PSA in the art disclosed herein can be a thermoplastic polymer. A typical example thereof is an acrylic block copolymer. Can be preferably used an acrylic block copolymer comprising at least one acrylate block (which hereinafter may be referred to as an Ac block) and at least one methacrylate block (which hereinafter may be referred to as an MAc block). For instance, preferable is a block copolymer having a structure in which Ac blocks and MAc blocks are positioned alternately. The total number of Ac blocks and MAc blocks is preferably 3 or larger (e.g., 3 to 5).
In typical, the Ac block preferably comprises an alkyl acrylate as the primary monomer (i.e. the component that accounts for 50% by mass or more among the block-constituting monomeric units). Of the monomeric units, 75% by mass or more (e.g. 90% by mass or more) can be an alkyl acrylate. In a preferable embodiment, the monomeric units constituting the Ac block in the acrylic block copolymer (in an acrylic block copolymer comprising two or more Ac blocks, possibly at least one of the Ac blocks or all the Ac blocks) essentially consist of one, two or more species (typically one species) of alkyl acrylate. Alternatively, the Ac block may be a copolymer of an alkyl acrylate and another monomer (e.g. an alkyl methacrylate, etc.).
Examples of the Ac block-constituting alkyl acrylate include methyl acrylate, ethyl acrylate, n-propyl acrylate, isopropyl acrylate, n-butyl acrylate (BA), isobutyl acrylate, tert-butyl acrylate, n-pentyl acrylate, n-hexyl acrylate, n-heptyl acrylate, n-octyl acrylate, 2-ethylhexyl acrylate (2EHA), nonyl acrylate, isononyl acrylate, decyl acrylate, dodecyl acrylate, stearyl acrylate, etc. For example, a constitution where the Ac block-constituting monomers essentially consist of BA alone, 2EHA alone, or both BA and 2EHA can be preferably used.
It is typically preferable that the MAc block comprises an alkyl methacrylate as the primary monomer. Of all the monomers constituting the MAc, 75% by mass or more (e.g. 90% by mass or more) can be an alkyl methacrylate. In a preferable embodiment, the monomeric units constituting the MAc block (in an acrylic block copolymer comprising two or more MAc blocks, possibly at least one of the MAc blocks or all the MAc blocks) contained in the acrylic block copolymer essentially consist of only one, two or more species (typically one species) of alkyl methacrylate. Alternatively, the MAc block may be a copolymer of an alkyl methacrylate and another monomer (e.g., an alkyl acrylate).
The alkyl methacrylate constituting the MAc block may be an alkyl methacrylate whose alkyl group has 1 to 20 (preferably 1 to 14) carbon atoms. Specific examples thereof include methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, tert-butyl methacrylate, n-pentyl methacrylate, n-hexyl methacrylate, n-heptyl methacrylate, n-octyl methacrylate, 2-ethylhexyl methacrylate, nonyl methacrylate, isononyl methacrylate, decyl methacrylate, dodecyl methacrylate, stearyl methacrylate, etc.
In a preferable embodiment, of the monomers constituting the MAc block, 50% by mass or greater (or 75% by mass or greater, or essentially all) is an alkyl methacrylate having an alkyl group with 1 to 4 carbon atoms. Especially preferable alkyl methacrylates include methyl methacrylate (MMA) and ethyl methacrylate (EMA). For example, the monomers preferably employed may consist essentially of MMA alone, EMA alone, both MMA and EMA, or the like.
The acrylic block copolymer in the art disclosed herein may be a copolymer comprising A blocks and B blocks positioned alternately such as type AB, type ABA, type ABAB, type ABABA, etc., with the A block having been formed of a polymer having a rigid structure with excellent cohesive strength and elasticity, and the B block having been formed of a polymer having a flexible structure with excellent viscosity. A PSA comprising as its base polymer an acrylic block copolymer having such a structure may form a PSA layer combining cohesive strength and elasticity as well as viscosity at high levels. A PSA having such a composition can be preferably used as a hot melt PSA. An acrylic block copolymer (such as type ABA, type ABABA, etc.) having a structure with A blocks at both termini of the molecule can be preferably used. An acrylic block copolymer having such a structure is preferable because it is likely to have a good balance of cohesion and thermoplasticity.
When the acrylic block copolymer comprises two or more A blocks, the compositions, molecular weights (polymerization degrees), structures, etc., of these A blocks can be the same with or different from each other. When the acrylic block copolymer comprises two or more B blocks, the same is true with the B blocks.
As the A Nock, can be preferably used an MAc Nock as those described above. As the B block, can be preferably used an Ac block as those described above. In a preferable embodiment, the acrylic block copolymer is a triblock copolymer having a structure of MAc-Ac-MAc (type ABA). For instance, can be preferably used a triblock copolymer with two MAc blocks having essentially identical monomer compositions.
The ratio of mass of MAc block (when two or more MAc blocks are contained, their total mass) to mass of Ac block (when two or more Ac blocks are contained, their total mass) in the acrylic block copolymer is not particularly limited, but can be preferably in a range such that the mass ratio MAc block/Ac block is 4/96 to 90/10 (usually 7/93 to 80/20, preferably 10/90 to 70/30, e.g., 20/80 to 50/50). At a large MAc block ratio, there is a tendency for reduced adhesive strength, allowing for easy release. At a large Ac block ratio, there is a tendency for an increased organic dirt-collecting ability.
As the acrylic block copolymer, in usual, can be suitably used an acrylic block copolymer having a weight average molecular weight (Mw) of about 3×10⁴to 30×10⁴. The acrylic block copolymer has a Mw of preferably about 3.5×10⁴to 25×10⁴or more preferably about 4×10⁴to 20×10⁴(e.g., 5×10⁴to 15×10⁴). Too small a Mw of the acrylic block copolymer may decrease the adhesive properties (e.g., cohesion) or lower the ease of release. Too large a Mw tends to lead to insufficient thermoplasticity of the acrylic block copolymer. The Mw of the acrylic block copolymer described here refers to a value based on standard polystyrene that is determined by gel permeation chromatography (GPC) with respect to a sample prepared by dissolving the copolymer in a suitable solvent (e.g., tetrahydrofuran (THF)).
In the acrylic block copolymer in the art disclosed herein, a monomer (other monomer) other than an alkyl acrylate and an alkyl methacrylate may be copolymerized. Examples of the other monomer include vinyl compounds having functional groups such as alkoxyl group, epoxy group, hydroxyl group, amino group, amide group, cyano group, carboxyl group, acid anhydride group, etc.; vinyl esters such as vinyl acetate; aromatic vinyl compounds such as styrene; vinyl group-containing heterocyclic compounds such as N-vinylpyrrolidone and the like. Alternatively, it can be an alkyl acrylate having a structure with an acryloyl group coupled to a fluorinated alkyl group, a fluorinated alkyl acrylate and a fluorinated alkyl methacrylate. The other monomer may be used, for instance, to adjust the properties (adhesive properties, ease of molding, etc.) of the PSA layer and its content is suitably 20% by mass or less (e.g. 10% by mass or less, typically 5% by mass or less) of all the monomers constituting the acrylic block copolymer. In a preferable embodiment, the acrylic block copolymer is essentially free of the other monomers.
Such an acrylic block copolymer can be readily synthesized by a known method (e.g. see JP2001-234146, JPH11-323072), or a commercial product is readily available. Examples of the commercial product include trade name “LA POLYMER” series (e.g., those with product numbers LA2140e, LA2250, etc.) available from Kraray Co., Ltd., trade name “NABSTAR” available from Kaneka Corporation, and the like. As the method for synthesizing the acrylic block copolymer, living polymerization can be preferably employed. According to living polymerization, while keeping the weatherability inherent in the acrylic polymer, because of the excellent structure control unique to the living polymerization, an acrylic block copolymer having excellent thermoplasticity can be synthesized. Since the molecular weight distribution can be controlled in a narrow range, insufficient cohesion caused by the presence of low molecular weight components can be reduced to obtain an easily releasable PSA (even a PSA sheet (dirt-collecting member)).
When the PSA (e.g. PSA layer) in the art disclosed herein comprises an acrylic block copolymer, solely one species or a combination of two or more species of acrylic block copolymer can be used. In addition to the acrylic block copolymer, to control the adhesive properties, etc., it may comprise, as an optional component, a component other than an acrylic block copolymer. Examples of the optional component include a polymer and an oligomer excluding acrylic block copolymers. The amount of the polymer or oligomer (or “optional polymer” hereinafter) is suitably 50 parts by mass or less relative to 100 parts by mass of the acrylic block copolymer, preferably 10 parts by mass or smaller, or more preferably 5 parts by mass or smaller. In a preferable embodiment, the PSA layer may be essentially free of polymers other than the acrylic block copolymer.
The PSA composition in the art disclosed herein preferably comprises a plasticizer. The inclusion of plasticizer increases the ease of release. It also lowers the viscosity of the composition and thus the application is further facilitated. In yet another aspect, the inclusion of plasticizer also increases the organic dirt-collecting ability on the PSA surface. The organic dirt collected on the PSA surface is absorbed into the PSA (e.g. PSA layer) and dispersed therein. Thus, even when the dirt-collecting ability is reduced by repeated use, the dirt-collecting ability recovers in relatively short time (e.g. several minutes or several hours) as a unique effect (dirt-collecting ability recovery effect).
The dirt-collecting ability recovery effect is described with reference to FIG. 5. As schematically illustrated in FIG. 5, when the PSA layer 32 in dirt-collecting member (PSA sheet) 31 is allowed to make contact with a flat surface 2 of an article 1 such as a portable device, etc., the PSA layer 32 collects organic dirt 50 adsorbed on the surface 2. The PSA layer 32 has a property to not only collect organic dirt 50, but also causes it to migrate into the layer. Thus, the organic dirt 50 caught on the surface of PSA layer 32 migrates with time into the PSA layer 32, leading to a lower presence of organic dirt 50 on the surface of PSA layer 32; and eventually, the surface of PSA layer 32 will be essentially free of the presence of organic dirt 50. In other words, the surface regains the same state as before the sticky cleaner is used. Accordingly, the term “recovery effect” refers to an effect such that when the PSA collects organic dirt and the dirt-collecting ability is temporarily reduced, the dirt-collecting ability recovers in a prescribed time period (e.g. several minutes, preferably several hours) and the PSA (e.g. PSA layer) regains the ability to collect dirt. It encompasses that the dirt-collecting ability requires short time for recovery.
Examples of plasticizer include phthalic acid esters such as dioctyl phthalate, diisononyl phthalate, diisodecyl phthalate, dibutyl phthalate, etc.; adipic acid esters such as dioctyl adipate, diisononyl adipate, etc.; trimellitic acid esters such as trioctyl trimellitate, etc.; sebacic acid esters; and the like. Softeners such as processed oil are also included in the plasticizer. These can be used singly as one species or in a combination of two or more species. Among them, adipic acid esters are preferable.
The amount of plasticizer added is not particularly limited. For instance, it is suitably 1 part by mass or greater to 100 parts by mass of the base polymer (e.g. an acrylic polymer). The amount added is preferably 5 parts by mass or greater, more preferably 10 parts by mass or greater, yet more preferably 15 parts by mass or greater, or particularly preferably 20 parts by mass or greater. The amount added is suitably 100 parts by mass or less, preferably 80 parts by mass or less, more preferably 70 parts by mass or less, yet more preferably 60 parts by mass or less, or particularly preferably 50 parts by mass or less. From the standpoint of balancing the dirt-collecting ability and dirt-collecting ability recovery effect, the amount of plasticizer added is preferably 40 parts by mass or less (e.g. 20 to 40 parts by mass, typically 25 to 35 parts by mass) to 100 parts by mass of the base polymer.
The PSA composition (or PSA, PSA layer) in the art disclosed herein can include, as other components, various additives known in the PSA field, such as tackifier, surfactant, chain transfer agent, anti-aging agent, antioxidant, UV ray absorber, photostabilizer, antistatic agent, colorant (pigment, dye, etc.) and so on. The types and amounts of these non-essential additives can be the same as usual types and amounts in this type of PSA.
When the PSA (e.g. PSA layer) is formed from the PSA composition disclosed herein, the formation method is not particularly limited. For instance, it is possible to apply a method where the PSA composition is directly provided (typically applied) to a substrate, using a heretofore known application means such as die coater, gravure roll coater and the like, and allowed to dry.
The thickness of the PSA layer can be suitably selected in accordance with the purpose and is not particularly limited. From the standpoints of making sufficient use of the dirt-collecting ability and increasing the recovery of the dirt-collecting ability, the thickness of the PSA layer is preferably about 10 μm or larger (e.g. 30 μm or larger, typically 50 μm or larger). When it is important to reduce the weight or size, etc., the thickness of the PSA layer is preferably 300 μm or smaller (e.g. 100 μm or smaller, typically 70 μm or smaller). The PSA layer may be formed entirely over one face of the support substrate. Alternatively, for instance, a non-sticky region (dry edge) free of the PSA layer may be included along each edge of the support substrate's width direction.
When the dirt-collecting member disclosed herein comprises a support substrate as in this embodiment, as the support substrate, materials formed with various types of synthetic resin, non-woven fabric or paper can be used. The material of the support substrate can be a fabric, rubber sheet, foam sheet, metal foil, a composite of these, etc.
Examples of synthetic resin include a polyolefin (polyethylene, polypropylene, ethylene-propylene copolymers, etc.), polyester (polyethylene terephthalate, etc.), vinyl chloride resin, vinyl acetate resin, polyimide resin, polyamide resin, fluorocarbon resin, and the Eke. In particular, a support substrate made of polyethylene terephthalate (PET) can be preferably used. Examples of paper include Washi, kraft paper, glassine paper, high-grade paper, synthetic paper, top-coated paper, and the Eke. Examples of a fabric include a woven fabric and a non-woven fabric of a single species or a blend, etc., of various fibrous substances. Examples of the fibrous substance include cotton, staple fiber, Manila hemp, pulp, rayon, acetate fiber, polyester fiber, polyvinyl alcohol fiber, polyamide fiber, polyolefin fiber, and the like. Examples of a rubber sheet include a natural rubber sheet, a butyl rubber sheet, and the Eke. Examples of a foam sheet include a polyurethane foam sheet, a polychloroprene rubber foam sheet, and the like. Examples of metal foil include aluminum foil, copper foil, and the like. The support substrate may contain as necessary various additives such as filler (inorganic filler, organic filler, etc.), anti-aging agent, antioxidant, UV ray absorber, photostabilizer, anti-static agent, lubricant, plasticizer, colorant (pigment, dye, etc.), and the like.
When the dirt-collecting member is a single-faced PSA sheet having a PSA layer formed on a single face of a support substrate, the back face (PSA layer-free face) of the support substrate is preferably subjected to a surface treatment such as coating of a silicone-based release agent and the like to adjust the unwinding force of the PSA sheet roll to a suitable range (typically a release treatment to prevent the unwinding force from becoming excessively high).
The thickness of the support substrate can be suitably selected in accordance with the purpose and is not particularly limited. In general, the thickness is preferably about 20 μm or larger (e.g. 30 μm or larger, typically 40 μm or larger), but suitably about 200 μm or smaller (e.g. 100 μm or smaller, typically 70 μm or smaller).
Several working examples related to the present invention are described below although the present invention is not to be limited to these specific examples. In the following explanation, the terms “parts” and “%” are based on the mass unless specifically stated otherwise.

Example 1

To a three-neck flask, were placed 2-ethylhexyl acrylate (2EHA) and acrylic acid (AA) at a mass ratio 2EHA:AA=95:5. Toluene was used as the solvent. Under a nitrogen flow, benzoyl peroxide was added as a polymerization initiator. The reaction mixture was heated to 60° C. and the reaction was carried out for 2 hours. The reaction mixture was further heated to 80° C. and the reaction was carried out for 1 hour to prepare a solution of an acrylic polymer A having a weight average molecular weight (Mw) of about 50×10⁴to 60×10⁴. Subsequently, to 100 parts of polymeric non-volatiles of the acrylic polymer solution, were mixed 30 parts of a plasticizer (diisononyl adipate “MONOCIZER W-242” available from DIC Corporation), 0.1 part of an epoxy-based crosslinking agent (“TETRAD-C” available from Mitsubishi Gas Chemical Inc.) and 2 parts of an isocyanate-based crosslinking agent (“CORONATE L” available from Nippon Polyurethane Industry Co., Ltd.) to prepare an acrylic PSA composition.
The resulting acrylic PSA composition was applied to a surface of a 38 μm thick PET support substrate sheet (width: approximately 8 cm) and allowed to dry to fabricate a single-faced PSA sheet having a PSA layer of about 80 μm in thickness (adhesive thickness) formed on the single face of the support substrate. The resulting single-faced PSA sheet was wound around the surface of a drum-shaped holding member (20 mm diameter) to form a PSA sheet roll. The holding member was installed on an end of a grip member in a freely rotatable (rolling) manner to construct a cleaner as schematically shown in FIGS. 1 and 2.

Example 2

The amount of epoxy-based crosslinking agent was increased to 0.5 part relative to 100 parts of polymeric non-volatiles of the acrylic polymer solution. Otherwise, in the same manner as Example 1, a cleaner according to Example 2 was constructed.

Example 3

The amount of plasticizer added was increased to 60 parts relative to 100 parts of polymeric non-volatiles of the acrylic polymer solution. Otherwise, in the same manner as Example 2, a cleaner according to Example 3 was constructed.

Example 4

Were mixed 100 parts (non-volatiles) of a commercial acrylic Nock copolymer (acrylic polymer B) and 30 parts of a plasticizer (diisononyl adipate “MONOCIZER W-242” available from DIC Corporation) to prepare a hot melt acrylic PSA. The resulting acrylic PSA was melted and applied to a surface of a 38 μm thick PET support substrate sheet (width: approximately 8 cm) to fabricate a single-faced PSA sheet having a PSA layer of about 50 μm in thickness (adhesive thickness) formed on the support substrate. Using the resulting single-faced PSA sheet, otherwise in the same manner as Example 1, a cleaner according to Example 4 was constructed.

Example 5

The amount of plasticizer added was increased to 100 parts relative to 100 parts (non-volatiles) of the acrylic Nock copolymer. Otherwise, in the same manner as Example 4, a cleaner according to Example 5 was constructed.

Example 6

A commercial roller floor cleaner (trade name “COLOCOLO” available from Nitoms, Inc.) was used as Example 6.

[Measurement of 180° Peel Strength to SUS]

The PSA sheet according to each example was cut to 200 mm by 25 mm to obtain a rectangular test piece. The test piece was adhered over the sticky surface (PSA layer-side surface) to a stainless steel (SUS304) plate with a 2 kg roller moved back and forth once. The resultant was stored in an environment at 23° C. and 50% RH for 30 minutes. Based on JIS Z0237, using a tensile tester, in an environment at 23° C. and 50% RH, the 180° peel strength (N/25 mm) to SUS was measured at a peel angle of 180° and at a tensile speed of 300 mm/min. Measurements were made with “TENSILON” available from Shimadzu Corporation. The results are shown in Table 1.

[Measurement of 180° Peel Strength to Glass]

With respect to the PSA sheets according to Examples 1 to 3, using a glass plate as the adherend, otherwise in the same manner as the 180° peel strength to SUS, the 180° peel strength (N/25 mm) to glass was measured. As the glass plate, a commercial float glass plate was used. The results are shown in Table 1.

[Measurement of 180° Peel Strength to PET]

With respect to the PSA sheets according to Examples 1 to 3, using a PET film (50 μm thick) as the adherend, otherwise in the same manner as the 180° peel strength to SUS, the 180° peel strength (N/25 mm) to PET was measured. The results are shown in Table 1.

[Assessment of Dirt Removal Rate]

A tablet terminal (iPad®, a product of Apple Inc.) was obtained and the display (flat surface made of aluminosilicate glass) was thoroughly cleaned with each cleaner and subjected to a measurement of gloss value G0 (60° measurement angle), using a handy gloss meter “Gloss Checker IG-331” available from Horiba, Ltd. Subsequently, sebum on the tester's face and other body skin was rubbed on fingers and the organic sebum dirt on the fingers was rubbed on and transferred to an area of the display of the tablet terminal. The organic dirt was transferred in an amount to yield a gloss value of about 60 (G1). The display's surface having the sebum dirt was cleaned with the cleaner according to each example. In particular, the PSA sheet roll of the cleaner according to each example was allowed to rotate once. The rolling speed was about 0.5 msec. The pressure applied by the operator for the rotation was about 700 g. The display was then subjected to a measurement of gloss value G2 (60° measurement angle) to determine the dirt removal rate (%) based on an equation: dirt removal rate (%)=(G2−G1)/(G0−G1)×100. Two measurements were taken and their average value was recorded. The results are shown in Table 1.

TABLE 1

Ex. 1	Ex. 2	Ex. 3	Ex. 4	Ex. 5	Ex. 6

Composition (parts)
Acrylic polymer A	100	100	100	—	—	—
Acrylic polymer B	—	—	—	100	100
Plasticizer	30	30	60	30	100
Epoxy-based crosslinking agent	0.1	0.5	0.5	—	—
Isocyanate-based crosslinking agent	2	2	2	—	—
180° Peel strength (N/25 mm)
To SUS	0.80	0.16	0.09	0.04	0.02	9.7
To Glass	0.82	0.11	0.06	—	—	—
To PET	0.36	0.08	0.02	—	—	—
Dirt removal rate (%)	100	99	99	100	93	89

As shown in Table 1, the cleaners according to Examples 1 to 5 were easily releasable, exhibiting adhesive strengths of less than 1 N/25 mm as measured values based on the 180° peel test specified in JIS Z0237. Despite the easy-release nature as described above, the cleaners according to these examples achieved greater organic dirt-removing abilities than the cleaner according to Example 6 having relatively strong adhesive strength. Similarly to usual dirt, at least a certain adhesive strength has been considered necessary also with respect to organic dirt such as human sebum dirt and the like. It has been validated, however, that even a PSA as poorly adhesive as the PSA sheets of the respective examples can even exhibit sufficient dirt-removing abilities. This has been revealed for the first time through the studies by the present inventors. For instance, even on a portable device surface covered with removable protection film, because of the easy-release nature, a sticky cleaner as easily releasable as those described above can be expected to clean the surface (in this case, the surface of the protection film) without removing the protection film. A person skilled in the art would recognize this because of the low peel strength to PET which is a synthetic resin.
Although specific embodiments of the present invention have been described in detail above, these are merely for illustrations and do not limit the scope of claims. The art according to the claims includes various modifications and changes made to the specific embodiments illustrated above.

REFERENCE SIGNS LIST

1 portable device (article)
2 surface (display)
10 sticky cleaner
20 holding member
30 PSA sheet roll
31 PSA sheet (dirt-collecting member)
32 PSA layer
36 substrate
40 grip member
42 handle
50 organic dirt

Claims

1. A sticky cleaner used for removing organic dirt adsorbed on a surface of an article, the sticky cleaner comprising

a dirt-collector that collects the organic dirt as the dirt-collector makes contact with the surface of the article,

the dirt-collector has a surface-contacting part to make contact with the surface of the article, the surface-contacting part being formed with a pressure-sensitive adhesive, and

the surface-contacting part of the dirt-collector exhibits an adhesive strength of less than 1 N/25 mm as a measured value based on the 180° peel test specified by JIS Z0237.

2. The sticky cleaner according to claim 1, wherein the surface-contacting part of the dirt-collector exhibits an adhesive strength of 0.01 N/25 mm to 0.5 N/25 mm as the measured value based on the 180° peel test specified in JIS Z0237.

3. The sticky cleaner according to claim 1, wherein the sticky cleaner comprises a cylindrical rolling member, and the dirt-collector is arranged along the lateral surface of the rolling member.

4. The sticky cleaner according to claim 3, further comprising a grip that rotatably supports the rolling member.

5. The sticky cleaner according to claim 1, wherein

the dirt-collector is an adhesively single-faced pressure-sensitive adhesive sheet comprising a sheet of support substrate and a pressure-sensitive adhesive layer placed above the support substrate, and

the single-faced pressure-sensitive adhesive sheet is wound with the pressure-sensitive adhesive layer on the outside to form a pressure-sensitive adhesive sheet roll.

6. The sticky cleaner according to claim 5, wherein the pressure-sensitive adhesive layer comprises an acrylic polymer at a ratio of 50% by mass or higher.

7. The sticky cleaner according to claim 6, wherein the acrylic polymer is a crosslinked acrylic polymer.

8. The sticky cleaner according to claim 6, wherein the acrylic polymer is a thermoplastic acrylic polymer.

9. The sticky cleaner according to claim 6, wherein the pressure-sensitive adhesive layer further comprises a plasticizer.

10. The sticky cleaner according to claim 1 used for removing human sebum dirt as the organic dirt.

11. The sticky cleaner according to claim 1, wherein the article is a portable device having a flat surface on which a glass or synthetic resin display is present.