LOW-FRICTION FILM, METHOD OF PRODUCING SAME, MOLDED ARTICLE, AND METHOD OF IMPROVING FINGER SLIDABILITY

Abstract

Prepared is a film having at least one surface having a kurtosis (Rku) of greater than or equal to 2 and total height (Rt) of greater than or equal to 1m.

The dynamic friction coefficient of the surface may be less than or equal to 0.25, and the relative dynamic friction coefficient may be less than or equal to 0.3.

The film includes a low-friction layer formed of a cured product of a curable composition including a curable resin, and the surface of the low-friction layer may have an Rku and an Rt within the range mentioned above.

The curable resin may include at least one selected from the group consisting of a (meth)acrylic polymer having a polymerizable group, a urethane (meth)acrylate, and a silicone (meth)acrylate.

The curable composition may further include a cellulose ester.

The curable composition may be free of fine particles.

The film can reduce the dynamic friction coefficient even if the surface of the film is formed of a wide range or materials.

Claims

1. A film having at least one surface having a kurtosis (Rku) of greater than or equal to 2 and a total height (Rt) of greater than or equal to 1 m.

2. The film according to claim 1, wherein a dynamic friction coefficient of a surface is less than or equal to 0.25.

3. The film according to claim 1, wherein a relative dynamic friction coefficient of a surface is less than or equal to 0.3.

4. The film according to claim 1, wherein: the film includes a low-friction layer, the low-friction layer being formed of a cured product of a curable composition comprising a curable resin and being disposed on a outermost layer; a surface of the low-friction layer has a kurtosis (Rku) of greater than or equal to 2 and a total height (Rt) of greater than or equal to 1 m.

5. The film according to claim 4, wherein the curable resin includes at least one selected from the group consisting of a (meth)acrylic polymer having a polymerizable group, a urethane (meth)acrylate, and a silicone (meth)acrylate.

6. The film according to claim 4, wherein the curable composition further includes a cellulose ester.

7. The film according to claim 4, wherein the curable composition includes no fine particle.

8. The film according to claim 4, wherein the low-friction layer is laminated on a substrate layer formed of a transparent resin.

9. The film according to claim 1, wherein the film has an abundance ratio of silicon atom at a surface of less than 10% and an abundance ratio of fluorine atom at a surface of less than 20%.

10. A method of producing the film described in claim 1, wherein the method includes curing a curable composition including a curable resin.

11. A molded article comprising the film described in claim 1 on a surface of the molded article.

12. The molded article according to claim 11, wherein the molded article is a touch panel display.

13. A method of improving finger slidability of a film, wherein the improving the finger slidability includes adjusting at least one surface of the film to have kurtosis (Rku) greater than or equal to 2 and the total height (Rt) greater than or equal to 1 m.

Description

EXAMPLE(S)

[0119] Hereinafter, the present invention is described in greater detail based on examples, but the present invention is not limited to these examples.

[0120] The raw materials used in Examples and Comparative Examples are as follows, and the low-friction film obtained was evaluated by the following method.

Raw Material

[0121] Acrylic-based polymer A having a polymerizable group: KRM8713B, available from Daicel-Allnex Ltd.

[0122] Acrylic-based polymer B having a polymerizable group: Cyclomer P, available from Daicel-Allnex Ltd.

[0123] Acrylic-based polymer: 8KX-078, available from Taisei Fine Chemical Co., Ltd.

[0124] Urethane modified co-polyester resin: Vylon (trade name) UR-3200, available from Toyobo Co., Ltd.

[0125] Cellulose acetate propionate: CAP-482-20, available from Eastman Chemical Company, degree of acetylation=2.5%, degree of propionylation=46%, number average molecular weight calibrated with polystyrene is 75000

[0126] Urethane acrylate: UA-53H available from Shin-Nakamura Chemical Co., Ltd.

[0127] Silicone acrylate: EBECRYL 1360, available from Daicel-Allnex Ltd.

[0128] PMMA Beads A: SSX-115, available from Sekisui Chemical Co., Ltd., average particle size 15 m

[0129] PMMA Beads B: SSX-110, available from Sekisui Chemical Co., Ltd., average particle size 10 m

[0130] Acrylic-based ultraviolet (UV) curable compound containing nano-silica: Z7501, available from JSR Corporation

[0131] Photoinitiator A: Irgacure 184 available from BASF Japan Ltd.

[0132] Photoinitiator B: Irgacure 907 available from BASF Japan Ltd.

[0133] Polyethylene terephthalate (PET) film: DIAFOIL available from Mitsubishi Plastics, Inc.

Thickness of Low-Friction Layer

[0134] Using an optical film thickness gauge, ten arbitrary points were measured, and an average value was calculated.

Surface Topography

[0135] In accordance with JIS B0601, using an optical surface roughness meter (VertScan R5500G available from Hitachi High-Tech Science Corporation), the total height (Rt) and the kurtosis (Rku) of the concavo-convexes were measured under the conditions of a scanning range of a 2.5 mm square and a scanning count of 2.

[0136] Dynamic friction coefficient and relative dynamic friction coefficient

[0137] Dynamic friction force (dynamic friction coefficient) was measured under measurement conditions (a load of 20 g and a speed of 25 mm/seconds) using a static and dynamic friction measuring machine (Handy Tribomaster TL201Ts, available from Trinity-Lab. Inc.).

[0138] As the contact probe, an artificial skin (BIOSKIN, available from Beaulux Co., Ltd.) was attached to a sponge sheet (Sukima-Yo Tape N-1 manufactured by Cemedine Co., Ltd.) having a thickness of 5 mm.

[0139] The relative dynamic friction coefficient was determined by dividing the dynamic friction force of the film, which is the subject of the measurement, by the dynamic friction force measured using glass (soda lime glass) as a specimen.

Finger Slidability

[0140] The evaluation of finger slidability was performed as follows: The obtained low-friction film was attached to an acrylic plate on the substrate layer side using an optical clear adhesive (OCA) film having a thickness of 25 m, to prepare a testing piece. Evaluation was carried out by sliding an index finger on the surface of the film (low-friction layer) of the test piece in the manner of operating a smartphone.

[0141] The evaluation results were interviewed on 20 subjects according to the following five tiered criteria.

[0142] One point: the finger does not slide very well, and the finger catches during operation

[0143] Two points: the finger catches at the onset of sliding, and feels high friction after sliding starts

[0144] Three points: the finger catches at the onset of sliding, but feels low friction after sliding starts

[0145] Four points: the finger slightly catches at the onset of sliding, but feels no friction during operation

[0146] Five points: the finger does not catch at the onset of sliding, and feels no friction during operation.

Example 1

[0147] 216 parts by weight of the acrylic-based polymer A having a polymerizable group, 1 part by weight of the PMMA beads A, 1 part by weight of the photoinitiator A, and 1 part by weight of the photoinitiator B were dissolved in 117 parts by weight of methyl ethyl ketone.

[0148] The solution was cast on a PET film using a wire bar #14, and then was left in an oven at 100 C. for 1 minute to evaporate the solvent and a low-friction layer having a thickness of about 12 m was formed.

[0149] Then, the low-friction layer was irradiated with ultraviolet rays from a high-pressure mercury lamp for about 5 seconds (total irradiation dose of about 100 mJ/cm.sup.2) and subjected to UV curing treatment, and a low-friction film was obtained.

Example 2

[0150] 50 parts by weight of the acrylic-based polymer B having a polymerizable group, 4 parts by weight of the cellulose acetate propionate, 76 parts by weight of the urethane acrylate, 1 part by weight of the silicone acrylate, 1 part by weight of the photoinitiator A, and 1 part by weight of the photoinitiator B were dissolved in a mixed solvent of 176 parts by weight of methyl ethyl ketone and 28 parts by weight of 1-butanol.

[0151] The solution was cast on a PET film using a wire bar #18, and then was left in an oven at 80 C. for 1 minute to evaporate the solvent and a low-friction layer having a thickness of about 9 m was formed.

[0152] Then, the low-friction layer was irradiated with ultraviolet rays from a high-pressure mercury lamp for about 5 seconds (total irradiation dose of about 100 mJ/cm.sup.2) and subjected to UV curing treatment, and a low-friction film was obtained.

Comparative Example 1

[0153] 216 parts by weight of the acrylic-based polymer A having a polymerizable group, 1 part by weight of the PMMA beads B, 1 part by weight of the photoinitiator A, and 1 part by weight of the photoinitiator B were dissolved in 117 parts by weight of methyl ethyl ketone.

[0154] The solution was cast on a PET film using a wire bar #14, and then was left in an oven at 100 C. for 1 minute to evaporate the solvent and a low-friction layer having a thickness of about 8 m was formed.

[0155] Then, the low-friction layer was irradiated with ultraviolet rays from a high-pressure mercury lamp for about 5 seconds (total irradiation dose of about 100 mJ/cm.sup.2) and subjected to UV curing treatment, and a low-friction film was obtained.

Comparative Example 2

[0156] 34.2 parts by weight of the acrylic-based polymer, 20 parts by weight of the urethane modified co-polyester resin, 166.3 parts by weight of the acrylic-based UV curable compound containing nano-silica, 0.2 parts by weight of the silicone acrylate, 1 part by weight of the photoinitiator A, and 1 part by weight of the photoinitiator B were dissolved in 179 parts by weight of methyl ethyl ketone.

[0157] The solution was cast on a PET film using a wire bar #16, and then was left in an oven at 80 C. for 1 minute to evaporate the solvent and a low-friction layer having a thickness of about 5 m was formed.

[0158] Then, the low-friction layer was irradiated with ultraviolet rays from a high-pressure mercury lamp for about 5 seconds (total irradiation dose of about 100 mJ/cm.sup.2) and subjected to UV curing treatment, and a low-friction film was obtained.

Comparative Example 3

[0159] PM-A15FLGM (available from ELECOM), a protective sheet for smartphones available in the market, was used as a comparative example of a film on which a finger slides well because it was proclaimed as an ultimate finger sliding film or a super smooth film on the package.

Comparative Example 4

[0160] PM-A15FLST (available from ELECOM), a protective sheet for smartphones available in the market, was used as a comparative example of a film on which a finger slides well because it was proclaimed to facilitate smooth finger sliding or to be a super smooth film on the package.

[0161] Table 1 shows the results of evaluating the properties of the low-friction films obtained in Examples and Comparative Examples.

TABLE-US-00001 TABLE 1 Examples Comparative Examples Items 1 2 1 2 3 4 Total height Rt (m) 2.47 3.94 0.73 1.72 0.47 0.47 Kurtosis Rku 45.89 4.48 25.53 1.80 3.46 3.69 Dynamic friction 0.22 0.10 >1.00 0.40 0.29 0.27 coefficient Relative dynamic 0.28 0.13 >1.27 0.51 0.37 0.34 friction coefficient Finger slidability 4 5 1 2 3 3

[0162] As is clear from the results of Table 1, the low-friction films of the Examples had a low dynamic friction coefficient, a low relative dynamic friction coefficient, and a superior finger slidability.

[0163] Meanwhile, as in Comparative Examples 1, 3, and 4, the finger slidability does not increase when only the kurtosis is high.

[0164] Further, even when only the total height is large, as in Comparative Example 2, the finger slidability is inferior to that of the Examples.

INDUSTRIAL APPLICABILITY

[0165] The low-friction film according to an embodiment of the present invention can be used as a surface-protecting or covering film for covering the surface of various molded articles such as touch panel displays of personal computers (tablet PCs, etc.) and smartphones, housings of consumer electronic products, building materials, or the like. In particular, the film is useful as a film that improves the tactile feel by imparting low friction to a part that is operated by hand touch.