Protective film and method for producing same

Abstract

To provide a protective film with an antifouling layer which is used by being stuck to a display screen and is easily peeled from the display screen by using an adhesive tape.SOLUTION: A protective film 1 for a display screen includes at least a base material film 2, an antifouling layer 3 formed on the front surface side of the base material film, and an adhesive layer 5 formed on the back surface side of the base material film, and has a design 4 formed by removing the antifouling layer in a part of the outer peripheral part of the protective film. The design can be formed by irradiating a part of the antifouling layer on the outer peripheral portion of the protective film with a UV laser to remove the antifouling layer.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a protective film that can be easily peeled off with adhesive tape after being attached to an adherend (display screen), and a method for producing the same. [Background technology]

[0002] In recent years, devices with display screens, such as smartphones (multi-function mobile phones), tablets, game consoles, and car navigation systems, have become increasingly popular, and as a result, transparent films (sheets) called protective films or protective sheets are often attached to the display screens.

[0003] Such protective films often become damaged, such as cracked, by impacts such as when the device is dropped. In such cases, the end user must remove the damaged protective film and replace it with a new one.

[0004] Therefore, the protective film is required to not peel off from the display screen during use, but also to be easily peeled off from the display screen when replacing it with a new protective film. Regarding screen protection films, which protect display screens during manufacturing, processing, transportation, and other processes and are removed by manufacturers before the screens reach the users, progress has been made in the development of films that satisfy the conflicting properties of adhesion during use and ease of removal after use (see, for example, Patent Document 1). However, in the case of protective films that users themselves apply to and peel off from the screen, screen protection is given top priority, and so they are often difficult to peel off.

[0005] One method for users to peel off the protective film from the display screen is to insert a pin or hard card between the protective film and the display screen to peel it off, but this method risks damaging the display screen.To avoid this, a method is used in which one end of adhesive tape (such as cellophane tape) is attached to the protective film, and the other end is grabbed and slowly pulled up to lift the protective film and peel it off.

[0006] However, a stain-resistant layer is often formed on the surface of a screen protection film to prevent sebum stains, etc. In many cases, the stain-resistant layer has water / oil repellency, and therefore the adhesive strength with the adhesive layer of the adhesive tape is weak. As a result, there is a problem that it is not easy to peel the protection film having the stain-resistant layer from the display screen using adhesive tape. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] WO2019 / 167479 Summary of the Invention [Problem to be solved by the invention]

[0008] The present invention addresses the problem of providing a protective film to be attached to the display screen of a smartphone, game console, tablet, car navigation system, or the like, which has an antifouling layer but can be easily peeled off with adhesive tape. [Means for solving the problem]

[0009] As a result of extensive research into solving the above-mentioned problems, the inventors discovered that by using a UV laser marker to mark a design (e.g., a logo, character, or company name) on a part of a protective film, the antifouling layer in the laser-irradiated part is removed, and the adhesive strength between the design part and the adhesive tape is increased, making it easier to peel off the protective film, and thus completed the present invention.

[0010] That is, the present invention provides a method for manufacturing a protective film for a display screen, comprising the steps of: Preparing a protective film having at least a substrate film and an antifouling layer formed on one side thereof; By irradiating a part of the anti-fouling layer on the outer periphery of the protective film with a UV laser, the anti-fouling layer is removed and a design is formed. It is characterized by:

[0011] It is preferable that the protective film has a rectangular shape, and the design is formed at one or more of the four corners of the protective film.

[0012] In the above method, the UV laser irradiation interval is preferably 40 to 220 μm, and the antifouling layer removal area is preferably 5 to 150 mm 2 It is preferable that:

[0013] The present invention also provides a protective film for a display screen, comprising: The film has at least a base film, an antifouling layer formed on the front side of the base film, and an adhesive layer formed on the back side of the base film; The protective film has a design formed by removing the antifouling layer on a part of the outer periphery. It is characterized by:

[0014] The design is preferably formed by UV laser irradiation. Note that the shapes of designs formed by UV laser irradiation are diverse, and the structure and characteristics of the area where the antifouling layer has been removed vary depending on the conditions of UV laser irradiation, etc. Therefore, even if it is possible to infer that the design formed by removing the antifouling layer is a design formed by UV laser irradiation by observing the design, it is impossible or impractical to directly identify the design by its structure or characteristics. [Effects of the Invention]

[0015] The protective film of the present invention has an antifouling layer, making it resistant to sebum stains and the like, while the antifouling layer has been removed from the design area, providing high adhesion between the design area and adhesive tape, making it easy to peel the protective film from the display screen by applying adhesive tape to the design area. [Brief explanation of the drawings]

[0016] [Figure 1]Fig. 1a is a diagram showing a schematic view of an example of a protective film according to the present invention, and Fig. 1b is a diagram showing a schematic view of the AA cross section of Fig. 1a. DETAILED DESCRIPTION OF THE INVENTION

[0017] The protective film used in the production method of the present invention has at least a substrate film and an antifouling layer formed on one surface (front surface) of the substrate film.

[0018] The substrate film used in the protective film of the present invention is preferably made of a colorless and transparent material having strength suitable for protecting the adherend (liquid crystal screen of a game console, smartphone, etc.). The substrate film can be a colorless and transparent glass film or synthetic resin film (plastic film) that has traditionally been used to protect display screens. Examples of plastic films include PET (polyethylene terephthalate) film and TAC (triacetyl cellulose) film.

[0019] The antifouling layer is formed over the entire surface or almost the entire surface of one side (front surface) of the substrate film. The composition of the antifouling layer is not particularly limited as long as it exhibits an antifouling effect. Such antifouling layers are well known in the art. Examples of antifouling layers include layers containing a silicone-based antifouling agent or a fluorine-based antifouling agent (e.g., a layer mainly composed of a silicone-based resin or a fluorine-based resin). Examples of silicone-based antifouling agents include organopolysiloxanes mainly composed of dimethylpolysiloxane, in which some of the methyl groups may be substituted with alkyl groups such as phenyl groups and ethyl groups, cyclohexyl groups, hydroxyl groups, etc. Examples of fluorine-based antifouling agents include fluorine alone, resins containing perfluoroalkyl groups or perfluoroalkylene ether groups, and organosilane compounds having perfluoropolyether groups. Fluorine-based resins may also be crosslinked with an isocyanate-based crosslinking agent.

[0020] In the present invention, a UV laser marker is used to remove a portion of the antifouling layer to form a design. Laser markers are used to mark the surfaces of metals, synthetic resins, silicon wafers, paper, etc., by irradiating them with laser light. Other methods for forming designs on the surface of an antifouling layer include silk printing and screen printing. However, when these methods are used, although the adhesive strength between the printed layer on the antifouling layer and the adhesive tape is high, the adhesive strength between the antifouling layer and the printed layer is low, so the adhesive tape may peel off the printed layer alone. Furthermore, unevenness may be created, resulting in poor appearance, and the ink may peel off during use, damaging the appearance.

[0021] In contrast, laser markers do not require ink and can mark directly on materials, allowing for the creation of highly durable designs. In addition to UV laser markers, other known laser markers include fiber laser markers, CO2 laser markers, and YAG laser markers. Generally, CO2 laser markers are considered suitable for transparent materials, while UV laser markers are generally not suitable for processing transparent materials. However, in this invention, the design applied to the substrate film (transparent film) does not need to be conspicuous; rather, it is desirable that it does not interfere with viewing the display screen (i.e., the design portion retains transparency so that the display screen can be seen through the design portion). In other words, it is important that the antifouling layer in the design portion has been removed, and high visibility of the design is not essential; a faint appearance is sufficient. Unlike fiber lasers and CO2 lasers, UV laser marking does not involve heat, and therefore can remove the antifouling layer without causing thermal deformation or thermal damage to the transparent material (such as clouding of the transparent material). This allows for the application of designs that are not obtrusive when viewing the display screen. On the other hand, laser markers that use heat to mark (such as CO2 laser markers) can cause the protective film to burn (turn black), melt, or become wavy, which can ruin the appearance, and can also cause the design to be too visible (low transparency and strong coloring), which can interfere with viewing the display screen.

[0022] If the material is transparent, the UV laser marker can select the area to be processed by changing the focal length. Therefore, even if a transparent top sheet (a sheet to protect the surface of the protective film) is attached to the anti-fouling layer, it is possible to remove only the anti-fouling layer without damaging the top sheet or base film.

[0023] The design formed by removing the antifouling layer is preferably located on the outer periphery of the protective film. The outer periphery of the protective film typically extends within 25 mm from the edge of the protective film, depending on the size of the protective film, but may also extend within 20 mm, 15 mm, or 10 mm. Because the most common shape of display screens is rectangular (including those with rounded corners), protective films are generally rectangular in size to match the display screen. For such rectangular protective films, the design can be formed on one or more of the four corners of the rectangle. For example, after application of the protective film, one or more designs may be formed at the position that will become the bottom right corner of the display screen, or one or more designs may be formed at each of the bottom left and right corners. Since the design is preferably inconspicuous when viewing the display screen, it is not necessary to form multiple designs. A preferred example is a protective film with one design formed at each of the four corners. From the viewpoint of ease of peeling, it is optimal to form the design without any margins around the edges of the protective film, but if design is a priority, it is preferable to form the design with a margin of about 0.5 mm to 2 mm (especially 0.7 mm to 1.5 mm) from the edge. Generally, the larger the area from which the antifouling layer is removed, the easier it is to peel the protective film.

[0024] Protective films come in a variety of adhesive strengths, and adhesive strength also varies depending on the substrate. For example, when measuring 180° peel adhesive strength on a glass substrate in accordance with JIS Z 0237:2009 (peel speed: 300 mm / min, measurement environment: 23°C, 50% RH), many smartphone surface protection films exhibit adhesive strengths of 20 to 80 mN / 25 mm. On the other hand, surface protection films for game consoles often use films with higher adhesive strengths (e.g., 100 to 180 mN / 25 mm).

[0025] For example, if the protective film is approximately 9cm x 16cm in size and has an adhesive strength of 150mN / 25mm, the UV laser irradiation interval (laser dot interval or hatching line interval) should be 60μm, and the antifouling layer removal area should be 1.5mm. 2 By doing so, it is believed that the adhesive strength between the adhesive tape and the design part will be higher than the adhesive strength between the protective film and the display screen. Therefore, from the viewpoint of ease of peeling, regardless of the adhesive strength of the protective film and the type of adherend, the antifouling layer removal area should be 5 mm 2 or more than 10mm 2 If the above conditions are met, it is believed that ease of peeling will be significantly improved compared to an untreated film. Note that, in this specification, the area where the antifouling layer has been removed does not include the area of ​​the laser-untreated part when the design is formed from a combination of the antifouling layer-removed part (laser-treated part) and the laser-untreated part, but if there are gaps between dots or hatched lines in the laser-treated part, the area of ​​those gaps is included in the area where the antifouling layer has been removed (for example, in the case of a design that shows a company name in alphabets and a logo mark in two lines, the area of ​​the logo mark and the alphabet mark is the area where the antifouling layer has been removed).

[0026] As mentioned above, the minimum area of ​​the antifouling layer that needs to be removed to increase the adhesive strength with the adhesive tape is 1.5 mm. 2 However, if the area where the antifouling layer is removed is small, it is difficult to recognize the design, and it is difficult to know where to apply the adhesive tape when peeling it off. Therefore, the total area where the antifouling layer is removed for one design is 15 mm 2 or more than 25mm 2More preferably, it is 30 mm or more. 2 Above, 40mm 2 or more, or 50 mm 2 It may be more than that. On the other hand, since the antifouling effect cannot be achieved in the area where the antifouling layer is removed, it is preferable that the area where the antifouling layer is removed in one design is not too large. For example, 150 mm 2 Less than or equal to 125mm 2 The following is appropriate: 100mm 2 Below, 90mm 2 or less, or 80 mm 2 It may be the following:

[0027] The design formed by removing the stain-resistant layer is not particularly limited, but preferred examples include designs that have decorative or source-indicating features such as game characters, company logos, company names, etc. However, decorative features are not essential, and simple designs such as squares, triangles, circles, etc. are also acceptable as long as the adhesive tape placement can be identified.

[0028] The design may be constructed by combining parts where the antifouling layer has been removed and parts where it has not, but if the overall size of the design is too large, it will be an eyesore when viewing the display screen. Therefore, the overall size of one design is preferably within a 25mm square, and may be within a 20mm square, 15mm square, 12mm square, or 10mm square (for example, in the case of a design that displays a company name in alphabetical form and a logo mark in two lines, both the logo mark and the alphabet mark will fit within a square of the above size). On the other hand, as mentioned above, if the design is too small, it will be difficult to determine the position where the adhesive tape will be applied, so it is preferable that at least part of or all of the design is larger than a 3mm square, and more preferably larger than a 4mm square or 5mm square.

[0029] In design formation, the narrower the UV laser irradiation interval, the more visible the design can be. Furthermore, when the same design is formed by changing the irradiation interval, the narrower the irradiation interval (the higher the irradiation density), the stronger the adhesive strength between the design part and the adhesive tape. The irradiation interval is preferably 40 to 220 μm, but may also be 50 to 210 μm or 60 to 200 μm. For example, if the design is small (e.g., the design is within a 3 mm square, 4 mm square, or 5 mm square), a narrower irradiation interval will improve the visibility and peelability of the design, so the irradiation interval may be set to approximately 40 to 80 μm, 50 to 70 μm, or 55 to 65 μm. On the other hand, when the design is large, even if the irradiation interval is long, peelability is sufficiently high, and a wider irradiation interval can form a design with higher transparency. Therefore, the irradiation interval may be about 80 to 220 μm, about 90 to 210 μm, or about 100 to 200 μm.

[0030] As a UV laser irradiation device that can be used in the manufacturing method of the present invention, a commercially available UV laser marker can be used (for example, the MD-U series (e.g., MD-U1000C), a 3-axis UV laser marker manufactured by Keyence Corporation).

[0031] The design portion may be opaque, but more preferably, it has enough transparency to allow the display screen to be seen through the design portion when the protective film is attached to the display screen. In other words, although the visibility of the display screen is inferior compared to the non-design portion, it is preferable that the design portion is transparent (semi-transparent) enough to allow the color, outline, etc. of the image displayed on the screen to be discerned through the design portion.

[0032] The protective film used in the manufacturing method of the present invention may have at least a substrate film and an antifouling layer formed on the front side of the substrate film. The completed protective film has an adhesive layer and a release film on the back side of the substrate film, which may be present before or after the design is formed. The protective film of the present invention may also have other layers or components. For example, a blue light-cutting layer may be formed between the substrate film and the adhesive layer on the back side thereof, or the protective film may further have a top sheet (to be peeled off when used) on the antifouling layer side.

[0033] Furthermore, the process of forming a design on the antifouling layer of the base film by UV laser irradiation may be carried out before or after cutting the long base film (raw roll) having the antifouling layer to the desired size (the size corresponding to the display screen).

[0034] Although UV laser irradiation is usually performed from the anti-fouling layer side, it can also be performed with the anti-fouling layer exposed, or with the anti-fouling layer covered with a colorless and transparent top sheet. Because the focal length of the UV laser can be changed as long as the material is transparent, it is possible to mark only the anti-fouling layer and form a design even when a top sheet is attached to the anti-fouling layer.

[0035] One example of a preferred manufacturing method is a method in which a protective film (raw material) having an anti-fouling layer formed on the front side of a base film, optionally with a top sheet covering the anti-fouling layer attached, an adhesive layer formed on the back side of the base film, and a release film covering the adhesive layer attached is cut into a square of a size corresponding to the display screen, and then one or two of the four corners are irradiated with a UV laser to remove the anti-fouling layer and form the design.

[0036] On the other hand, when an adhesive layer containing a blue light-blocking substance (such as a yellowish pigment that absorbs blue light) is provided on the back surface of the base film, or when a blue light-blocking layer is provided between the base film and the adhesive layer, it is preferable to perform UV laser irradiation before forming these layers, and then form these layers on the back surface of the base film. This is because UV lasers react to pigments, etc., and if the base film is colored by the blue light-blocking substance, etc., a highly visible design (a design with low transparency and strong color development) is formed compared to when a colorless, transparent material is irradiated with a UV laser.

[0037] The adhesive layer, blue light cut layer, release film, top sheet covering the antifouling layer, etc. can be those already used for protective films for liquid crystal screens, and are available on the market.For example, a protective film having an antifouling layer on the front side of a substrate film, an adhesive layer on the back side, and a release film on the adhesive layer side is commercially available, and can be used in the present invention.As such, the present invention is excellent in versatility because it can improve the releasability of a conventional protective film simply by UV laser processing.

[0038] Furthermore, according to the present invention, since only a portion of the antifouling layer is removed, the antifouling properties of areas other than the design area are not affected. Furthermore, since only the antifouling layer can be removed, the substrate film remains completely (or substantially) undamaged, and the screen protection effect of the substrate film is not adversely affected. Furthermore, the present invention facilitates peeling by improving the adhesive strength between the protective film and the adhesive tape, rather than weakening the adhesive strength between the protective film and the display screen, thereby achieving both strong adhesion to the display screen during use and easy peeling after use.

[0039] The present invention will be described in more detail below with reference to examples and FIG. 1, but the present invention is not limited to the examples and drawings. [Example]

[0040] Production of the protective film according to the present invention A protective film 1 was prepared (raw protective film) consisting of a substrate film 2 (a PET film 153 μm thick, 100 m long, and 1.1 m wide) having a 3 μm thick, colorless, transparent fluorine-based anti-fouling layer 3 on the front side and a 50 μm thick, colorless, transparent silicone-based adhesive layer 5 on the back side, in which the anti-fouling layer is covered with a colorless, transparent top sheet (53 μm thick) (not shown in Figure 1), and the adhesive layer on the back side is covered with a colorless, transparent release film 6 (40 μm thick). Thereafter, the original protective film was cut to prepare a rectangular protective film having a size of about 16 cm x about 9 cm. After cutting, the bottom right corner of the protective film surface (see Figure 1a) was irradiated with a UV laser using a UV laser marker (Keyence Corporation; MD-U1000C) to remove the antifouling layer and form design 4 (the area of ​​the antifouling layer removed was 50 to 100 mm). 2 The input parameters for the laser marker were: laser power 50%, scan speed: 3000 mm / sec, pulse frequency: 40 kHz, printing content / type: solid fill, pattern: diagonal lines, direction: left → right, right → left, angle: 0, irradiation interval (distance between diagonal lines): 100 μm. The focal length was also adjusted so that only the anti-fouling layer between the top sheet and the base film was removed.

[0041] Figure 1 shows a schematic diagram of the protective film 1 produced in Example 1. In Figure 1, the top sheet covering the antifouling layer 3 is omitted, and the protective film is depicted as having a base film 2, an antifouling layer 3, a design 4 formed by removing the antifouling layer, an adhesive layer 5, and a release film 6. Figure 1a shows a plan view, and Figure 1b shows a cross-sectional view taken along line AA. Design 4 was slightly whitish and less transparent than other areas, but still maintained transparency.

[0042] When the release film was peeled off from this protective film and applied to the liquid crystal screen of a game console, the design was faintly visible, making it possible to recognize the position where the adhesive tape had been applied, while the design part remained transparent, allowing the display screen to be seen through the design part. In addition, after peeling off the top sheet covering the stain-resistant layer, one end of adhesive tape (Nitto Denko Corporation: No. 31B) was applied diagonally to the bottom left corner of the protective film where no design was formed and the bottom right corner where a design was formed, and the other end was lifted to compare the ease of peeling off the protective film. The adhesive tape did not adhere well to the bottom left corner where no design was formed, and the protective film did not lift even when the adhesive tape was lifted, resulting in the adhesive tape being peeled off. In contrast, when adhesive tape was applied to the design part of the bottom right corner, the adhesive tape adhered firmly to the protective film, and the protective film lifted when the adhesive tape was lifted, making it easy to peel off the protective film. [Example]

[0043] Peel test A protective film with an adhesive strength of 150 mN / 25 mm (catalog value: adherend PET) and a structure similar to that of Example 1 was irradiated with a UV laser to remove part of the antifouling layer, and a 125 mm 2 A roughly square design was formed at the bottom right corner of the protective film (irradiation interval: 100 μm). Adhesive tape (Nitto Denko Corporation: No. 31B) was applied to the area where the anti-fouling layer had not been removed (untreated area) and the area with the design (area where the anti-fouling layer had been removed), and the adhesive strength (bonding strength) between the protective film and the adhesive tape was measured. The test method conformed to JIS Z 0237:2009 "Testing Method for Adhesive Tapes and Adhesive Sheets" (testing machine: load tensile testing machine, peel angle: 180°, peeling speed: 300 mm / min). The adhesive strength between the untreated area and the adhesive tape was 61 mN / 25 mm, but the adhesive strength between the designed area and the adhesive tape was 3010 mN / 25 mm, confirming that removing the anti-fouling layer significantly improved the adhesive strength between the protective film and the adhesive tape.

[0044] Next, by changing the UV laser irradiation interval to 60 μm to 120 μm and removing the antifouling layer, the same shape design (125 mm 2 The adhesive strength was measured in the same manner as above. It was confirmed that the adhesive strength tended to increase as the laser irradiation interval became narrower, but the adhesive strength ranged from 3410 to 2757 mN / 25 mm. Regardless of the irradiation interval used, it was confirmed that the adhesive strength was significantly improved compared to the adhesive strength between the untreated area and the adhesive tape (61 mN / 25 mm).

[0045] The results of Example 2 confirmed that when the antifouling layer is not removed, the adhesive strength between the protective film and the adhesive tape is lower than the adhesive strength between the protective film and the LCD screen, making it difficult to peel off the protective film using adhesive tape; on the other hand, when the antifouling layer is removed, the adhesive strength between the removed part and the adhesive tape increases significantly, exceeding the adhesive strength between the protective film and the LCD screen, making it possible to peel off the protective film using adhesive tape. [Explanation of symbols]

[0046] 1 protective film 2. Base film 3. Anti-fouling layer 4 Design 5 Adhesive layer 6 Release film

Claims

1. 1. A method for manufacturing a protective film for a display screen, comprising: Preparing a protective film having at least a substrate film and an antifouling layer formed on one side thereof; By irradiating a part of the anti-fouling layer on the outer periphery of the protective film with a UV laser, the anti-fouling layer is removed and a design is formed. A method for producing a protective film, comprising:

2. The manufacturing method according to claim 1 , wherein the protective film is rectangular, and the design is formed at one or more of the four corners of the protective film.

3. The UV laser irradiation interval is 40 to 220 μm, and the antifouling layer removal area is 5 to 150 mm ２ The method according to claim 1 or 2, wherein

4. A protective film for a display screen, The adhesive tape has at least a base film, an antifouling layer formed on the front side of the base film, and an adhesive layer formed on the back side of the base film, A protective film having a design formed by removing an antifouling layer on a part of the outer periphery of the protective film.

5. The protective film according to claim 4 , wherein the design is formed by UV laser irradiation.

Images