JP4366346B2 - Surface protection film for touch panel - Google Patents

Description

The present invention relates to a protective film that is used by sticking to the surface of the touch panel for the purpose of protecting the surface of the touch panel, and when the touch pen is used for input, the handwriting of the touch pen is whitened by writing pressure and remains as a white handwriting mark. It is something that is not.

Display devices using a touch panel are used in a wide range of fields such as automobile navigation and various control devices, not limited to OA devices such as PDAs, personal computers, copiers, and mobile phones. Display screens are widely adopted. And since the said display screen for touchscreens needs to be excellent in light transmittance and impact resistance, it is comprised by laminating | stacking plastic films, such as a polyester film and a polycarbonate film. However, since these plastic films are easily scratched and easily smudged with fingerprints, etc., in order to prevent this, it is necessary to use a film subjected to hard processing or antifouling processing as the surface film of the display screen. As is known, in this case, scratches and dirt are difficult to be attached, but once the scratches are made, the touch panel needs to be replaced.

As means for solving such a problem, it is known that a display screen protective film is detachably attached to the surface of the display screen. For example, the following Patent Document 1 includes a laminate in which a rubber film is laminated on one side of a base film, the light transmittance of the laminate is 80% or more, and the rubber film surface is formed on a smooth surface. There has been disclosed a device which can be detachably attached to a display screen by a self-adhesive force of a smooth surface. This protective film for the display screen can prevent the display screen from being broken, dirty, scratched, etc., and can be easily attached to and detached from the display screen, so-called repairability is excellent, and a rubber film is combined to provide cushioning properties. It has excellent input followability when used as a surface protective film for touch panels, but when strong writing pressure is applied with an input jig such as a touch pen, permanent distortion remains on the protective film, There was a problem that gaps were formed between the lines, resulting in white streak-like handwriting traces, resulting in reduced visibility.
JP 2003-263115 A

As a touch panel capable of preventing the above-mentioned handwriting marks and maintaining good visibility, an antifouling layer is provided on the outermost surface of the touch panel body to which a display screen protective film should be attached, and the above protective film is applied to this antifouling layer. It is known that it is detachably attached via a silicone rubber adhesive layer on the back surface (see Patent Document 2 below). However, in this case, the antifouling layer is provided on the outermost layer of the touch panel body to improve the peelability of the protective film to prevent white streak-like handwriting traces, and therefore requires an antifouling layer. It cannot be applied to a touch panel having no antifouling layer, and lacks versatility.
JP 2004-94798 A

The present invention is a protective film that can be detachably attached to the surface of a display screen for a touch panel, and does not require an antifouling layer on the surface of the display screen, and is input with an input jig such as a touch pen. At the time, a surface protective film for a touch panel in which no white handwriting mark is formed at the input portion is provided.

The surface protective film for a touch panel according to the present invention comprises a self-adhesive layer laminated on one side of a base film, and the surface protection for a touch panel that can be detachably attached to the surface of the touch panel via the self-adhesive layer. In the film, the protective film is attached to the surface of the touch panel through the self-adhesive layer, and the writing pressure resistance, which is a measure of the difficulty of whitening due to the writing pressure when input using a touch pen, is 9 N or more. It is set. However, the above-mentioned writing pressure resistance is obtained by applying the above protective film to a hard-processed polyester film having a three-dimensional average roughness (SRa) of 0.0008 to 0.0015 μm and a thickness of 125 μm through the self-adhesive layer. This polyester film is fixed on a glass plate with the polyester film facing down, and a touch pen with a polyacetal tip formed in a spherical shape with a diameter of 0.8 mm on the protective film is 3.0 cm at a speed of 1 m / min. After the distance is reciprocated 25 times, it is defined by the maximum load (N) at which no whitening is observed by visually observing the presence or absence of white handwriting marks generated by the pressure applied to the touch pen.

The handwriting marks are due to the self-adhesive layer of the protective film being deformed by an external force, and when this deformation is excessive, permanent distortion occurs, and a gap is generated between the self-adhesive layer and the touch panel surface. Therefore, in order to prevent handwriting marks, the pressure resistance of the protective film is set to a certain level by combining the adhesive strength, elasticity, surface hardness, surface roughness, crosslinking density, thickness, material, etc. of the self-adhesive layer. In this invention, this pressure resistance is set to 9N or more as described above.

Therefore, the surface protective film for a touch panel according to the present invention can be detachably attached to the surface of the touch panel to protect the surface of the touch panel, as in the case of the conventional protective film for a display screen. Since the pressure resistance is 9N or more, the surface protection film partially floats from the touch panel surface and is whitened by the input mark by the touch pen even when the touch pen is used for input from above the surface protection film. Therefore, the visibility is not deteriorated due to whitening, and the visibility is maintained well. However, if the above-mentioned writing pressure resistance is low and less than 9N, the above-mentioned handwriting mark is likely to be whitened and the visibility is liable to be lowered. When a particularly high writing pressure is applied as in a game machine, the above-mentioned writing pressure resistance is preferably 13N or more, particularly preferably 17N or more. In addition to the above-mentioned handwriting marks of touch pen input, some external force is applied when using the touch panel, and the portion where the external force is applied may be whitened to reduce visibility. It can be prevented by applying pressure.

The base film used in the present invention is a film made of polyester, polyamide, polyolefin, polycarbonate, acrylic resin, fluororesin, or the like. Of these, polyesters, polycarbonates, acrylic resins and polyolefins are preferable in terms of transparency, dimensional stability and economy, and as the polyolefin, norbornene resins are particularly preferable. These base films can be subjected to hard processing, antistatic processing, antifouling processing and antiglare processing, and by using these processed films, the characteristics as a surface protective film become more desirable. . Further, easy adhesion treatment, corona treatment, and plasma treatment can be performed, and by using a film subjected to these processes, adhesion to the self-adhesive layer can be strengthened. In addition, although the thickness of the said base film is not specifically limited, 5-500 micrometers, especially 10-200 micrometers are preferable at the point of handleability.

The self-adhesive layer used in the present invention may be any polymer having flexibility and transparency, and examples thereof include solid or liquid rubber, thermoplastic elastomer, and plastomer. Examples of rubber include silicone rubber, fluorine Examples thereof include rubber, acrylic rubber, ethylene propylene rubber, acrylonitrile butadiene rubber, butadiene rubber, styrene butadiene rubber, isoprene rubber, and urethane rubber. Examples of the thermoplastic elastomer or plastomer include polystyrene, polyurethane, polyester, and polyolefin. Moreover, the gel-like thing of various compositions may be sufficient. Moreover, what mixed 2 or more types of these may be used. The self-adhesive layer can be formed of silicone-based, acrylic-based and urethane-based pressure-sensitive adhesives, which can be used in combination, and may be a composite with the flexible polymer.

The above self-adhesive layer materials include reinforcing fillers, pigments, dyes, anti-aging agents, antioxidants, mold release agents, flame retardants, thixotropic agents, antistatic agents, and UV absorbers as necessary. , A crosslinking agent, a crosslinking aid, an adhesive, and the like can be blended.

The above self-adhesive layer is preferably formed by using silicone rubber or a silicone-based pressure-sensitive adhesive alone or in combination from the viewpoint of transparency, self-adhesiveness, low odor and molding processability. The same applies to any one of urethane rubber, polyurethane-based elastomer and polyurethane-based pressure-sensitive adhesive used alone or in combination of two or more. Also preferred are polystyrene elastomers and polyester elastomers. Among these, silicone rubber or a silicone-based pressure-sensitive adhesive and a combination of both are particularly preferable because they have little change in adhesive strength due to light or heat and are excellent in durability.

As a means of improving the above-mentioned pressure resistance, it is necessary to control the self-adhesive force with accuracy, but according to experiments, the pressure resistance is influenced by a very subtle difference in the adhesive force, so control of the self-adhesive force Therefore, it is necessary to evaluate the adhesive strength with high accuracy in order to set the pressure resistance. According to the knowledge of the present inventor, it is advantageous to evaluate the self-adhesive force by rolling the sphere on the surface of the self-adhesive layer of the surface protective film for touch panel and evaluating the rolling speed. Specifically, the surface protective film is fixed to a slope having an inclination angle of 1 degree so that the self-adhesive layer is on top, and a steel ball having a diameter of 6.75 mm and a mass of 1.25 g is formed on the surface of the self-adhesive layer. It is advantageous to calculate the speed from the time required for the steel ball to roll a distance of 8 cm along the above-mentioned slope, and to evaluate the rolling speed based on the following points. Correlation is good and evaluation is easy. That is, the self-adhesive strength is evaluated in consideration of factors such as the surface hardness, surface roughness and thickness of the self-adhesive layer as well as the crosslinking density and other characteristics of the constituent material itself of the self-adhesive layer.

According to experiments, the above rolling speed is preferably 0.5 to 4.2 m / min, particularly preferably 1.0 to 4.1 m / min, and most preferably 2.0 to 4.0 m / min. When the rolling speed is less than 0.5 m / min, the self-adhesive strength is excessive, the handwriting trace remains, and the visibility of the screen is lowered. Especially when the rolling speed is 0.1 m / min or less, It becomes difficult to peel off the protective film attached to the touch panel, and in some cases, adhesive residue is generated. On the other hand, if it exceeds 4.2 m / min, the self-adhesive force is insufficient, and the protective film attached to the touch panel tends to fall off. That is, by controlling the self-adhesive strength of the self-adhesive layer with the above rolling speed, the above-mentioned writing pressure resistance can be set to 9 N or more.

The specific means for setting the above self-adhesive strength to 0.5 to 4.2 m / min is not particularly limited, and examples thereof include a method of optimizing the crosslink density and thickness of the self-adhesive layer surface. In addition to the usual crosslinking methods using peroxides and other crosslinking agents, this crosslinking method is a method of crosslinking by irradiating active rays such as ultraviolet rays, electron beams, and γ rays, and addition type crosslinking using a platinum catalyst. The method can be used. Especially, the bridge | crosslinking by an active ray is preferable at the point which can bridge | crosslink a surface layer preferentially. When the crosslink density is increased, the rolling speed increases, and when the crosslink density is decreased, the rolling speed decreases.

The thickness of the self-adhesive layer is preferably 5 to 100 μm, particularly preferably 5 to 60 μm, more preferably 6 to 40 μm, and most preferably 7 to 30 μm. If the thickness is less than 5 μm, the sticking property is insufficient and sticking to the touch panel becomes difficult. If the thickness exceeds 100 μm, the pressure resistance decreases, and handwriting marks remain when input with a touch pen, etc. Decreases. Increasing the above thickness to 500 μm or more also improves the writing pressure resistance. In this case, however, the input reaction becomes dull, and in some cases, it does not react at all.

As described above, the silicone rubber and the pressure-sensitive adhesive are most preferable as a material for the self-adhesive layer because they are stable to light and heat and are excellent in durability. However, this silicone rubber or pressure-sensitive adhesive is used. In this case, the amount of the low molecular siloxane in the self-adhesive layer is 1500 ppm or less, particularly preferably 1000 ppm or less, more preferably 800 ppm or less, and most preferably 500 ppm or less. However, the amount of the low-molecular siloxane is a cyclic siloxane composed of the dimethylsiloxane unit D, and the trimer, tetramer,. Is the sum of the contents of D3 to D10, and is described as “ΣD3 to 10”. When input, handwriting marks are likely to remain, and the visibility is significantly reduced. The reason for this is not clear, but it is assumed that the presence of a large amount of low molecular weight siloxane on the surface of the self-adhesive layer reduces the crosslinking density and surface hardness of the surface of the self-adhesive layer. In addition, although the specific means to make low molecular siloxane amount ((SIGMA) D3-10) 1500 ppm or less is arbitrary, the method of using silicone with low low molecular siloxane content, the material is heat-processed before laminating | stacking with a base film. Examples of the method include a method of heat treatment when laminated with a base film or after lamination.

In the surface protective film for a touch panel of the present invention, the light transmittance thereof is 80% or more, particularly preferably 85% in a state where the above-mentioned base film and self-adhesive layer are laminated, and in the case of less than 80%, Since visibility deteriorates, it is not preferable in use.

The delamination strength of the base film and the self-adhesive layer is preferably 4 N / 20 mm or more, and if it is less than 4 N / 20 mm, delamination is likely to occur due to external force during use. Moreover, the method of laminating the self-adhesive layer on the base film is not particularly limited, but a method of laminating the self-adhesive layer on the surface of the base film by coating or extrusion is preferable.

The self-adhesive layer preferably has a small change in adhesive force even when left in a high temperature environment, a high humidity environment or a low temperature environment. In addition, it is preferable that the rolling force is maintained in the range of 0.5 to 4.2 m / min without the adhesive force exceeding the appropriate range. When the self-adhesive layer has the durability as described above, handwriting marks are not generated in almost all environments where the use of the touch panel is assumed.

The present invention relates to a surface protective film for a touch panel, in which a self-adhesive layer is laminated on one side of a base film, and can be detachably attached to the surface of the touch panel via the self-adhesive layer. Since it is set to 9N or more, it can be used by being detachably attached to the touch panel surface in the same way as in the past, and handwriting marks will remain even when drawing with an input jig such as a touch pen. Therefore, the visibility is not deteriorated due to handwriting marks. In particular, the invention according to claim 2 evaluates and sets the self-adhesive strength of the self-adhesive layer laminated on the base film by the rolling speed of the steel ball under specific conditions, so that the self-correlation that is highly correlated with the writing pressure resistance The adhesive force can be set with high accuracy, and the writing pressure resistance can be set well and easily. Further, the invention according to claim 3 correlates with the self-adhesive force and controls the rolling speed of the steel ball as a scale by the crosslink density of the self-adhesive layer surface and the thickness thereof. Easy to set adhesive strength or pressure resistance. In the invention according to claim 4, since the self-adhesive layer is formed of a silicone rubber or adhesive having a low amount of low-molecular-weight siloxane, it is excellent in writing pressure resistance, stable against heat and light, and durable. Excellent in properties.

Embodiment 1
As the silicone rubber compound, a transparent silicone rubber compound is prepared. After the silicone rubber compound is dissolved in toluene, an adhesion improver is blended and stirred to obtain a rubber solution. On the other hand, a polyethylene terephthalate film having a light transmittance of 80% or more is used for the base film, the surface thereof is hard-processed, and the back surface is subjected to an easy adhesion treatment. After the solution is dried, the solution is applied to a thickness of 5 to 100 μm and dried to form a self-adhesive layer. The surface of the self-adhesive layer is made of polyethylene terephthalate, and the average surface roughness Ra is 0.12 μm or less. Laminate the cover film after the mold treatment. Next, a laminate composed of a base film, a self-adhesive layer and a cover film is introduced into an electron beam irradiation apparatus, and the self-adhesive layer and the base film are simultaneously irradiated with an electron beam from the cover film side and simultaneously crosslinked. After cross-linking adhesion, the cover film is peeled off to obtain a surface protective film for a touch panel.

However, the adhesive force of the self-adhesive layer is controlled by the drying temperature after application of the rubber solution, the thickness of the self-adhesive layer, the irradiation dose at the time of electron beam irradiation, the acceleration voltage, the number of irradiations, and the like. That is, the protective film is fixed to a slope having an inclination angle of 1 degree so that the self-adhesive layer is on top, and a steel ball having a diameter of 6.75 mm and a mass of 1.25 g is rolled on the surface of the self-adhesive layer, The rolling speed of the steel ball is calculated from the time required for the steel ball to roll a distance of 8 cm along the slope, and the rolling speed is used as an index of the adhesive force, which is 0.5 to 4.2 m / The drying temperature after application of the rubber solution or the number of times of electron beam irradiation is controlled so as to make the minute, and the writing pressure resistance is set to 9 N or more. In addition, the drying temperature and the like are set so that the amount of low molecular siloxane (ΣD3 to 10) in the self-adhesive layer made of silicone rubber is 1500 ppm or less. Moreover, the kind and compounding quantity of the said adhesive improvement agent are selected so that the delamination strength of a base film and a self-adhesion layer may be set to 4 N / 20mm or more.

Embodiment 2
A hydrogenated styrene-based elastomer is used in place of the transparent silicone rubber compound of the first embodiment, and a polyester film is used as a base film in the same manner as in the first embodiment, and the hydrogenated elastomer layer is a self-adhesive layer. A protective film for a touch panel is obtained. However, the hydrogenated styrene elastomer preferably has a rubber hardness of 30 to 90 degrees.

Example 1
A commercially available transparent silicone rubber compound (rubber hardness 20 degrees) was dissolved in toluene, and then attached to 100 parts of silicone rubber, and 3 parts of trimethylolpropane trimethacrylate was blended as an adhesion improver and stirred to obtain a rubber solution. . On the other hand, a hard film is applied to the surface of a polyethylene terephthalate film having a thickness of 125 μm and a light transmittance of 92%, and an easy adhesion treatment is applied to the back surface to form a base film. Is dried to a thickness of 10 μm, dried in an oven at a temperature of 95 ° C. to form a self-adhesive layer, and then the surface of the above self-adhesive layer made of silicone rubber film is made of polyethylene terephthalate with a thickness of 75 μm. Then, a cover film subjected to a release treatment with an average surface roughness Ra of 0.04 μm was laminated.

The laminate composed of the base film, the self-adhesive layer and the cover film is introduced into an electron beam irradiation apparatus, and the electron beam irradiation is performed from the cover film side at an irradiation dose of 15 Mrad and an acceleration voltage of 200 KV. At the same time, the self-adhesive layer was cross-linked and bonded to the base film, and then the above cover film was peeled off to obtain the surface protective film for touch panel of Example 1.

Example 2
In Example 1, the thickness of the self-adhesive layer made of silicone rubber after drying was changed to 35 μm, and the others were the same as Example 1 to obtain the surface protective film for touch panel of Example 2.

Example 3
A surface protective film for a touch panel of Example 3 was obtained in the same manner as in Example 2 except that the drying temperature was changed to 110 ° C. in Example 2.

Comparative Example 1
In Example 1 above, the thickness of the self-adhesive layer after drying was changed to 50 μm, and the drying temperature was changed to 80 ° C., respectively, and the surface protective film for touch panel of Comparative Example 1 was obtained in the same manner as Example 1. It was.

Comparative Example 2
In the above Comparative Example 1, the thickness of the self-adhesive layer after drying was changed to 300 μm, and the others were the same as Comparative Example 1 to obtain a surface protective film for a touch panel of Comparative Example 2.

Example 4
In Example 1 described above, electron beam irradiation (irradiation dose 15 Mrad, acceleration voltage 200 KV) was performed twice from the cover film side, and the surface protective film for touch panel of Example 4 was obtained in the same manner as Example 1 except for the above. It was.

Example 5
In Comparative Example 1, the drying condition was changed to 95 ° C., and electron beam irradiation was performed twice from the cover film side at an irradiation dose of 15 Mrad and an acceleration voltage of 200 KV as in Example 4, and the others were the same as in Comparative Example 1. Thus, a surface protective film for a touch panel of Example 5 was obtained.

Example 6
In Example 5 above, after the electron beam irradiation, the cover film was peeled off and then dried in an oven at a temperature of 110 ° C. to obtain a surface protective film for a touch panel of Example 6.

Example 7
In Example 2, the thickness of the self-adhesive layer made of the silica rubber was changed to 25 μm after drying, and electron beam irradiation from the cover film side was performed 3 times at an irradiation dose of 15 Mrad and an acceleration voltage of 200 KV. In the same manner as described above, a surface protective film for a touch panel of Example 7 was obtained.

Example 8
In Example 5, the electron beam irradiation was performed three times from the cover film side at an irradiation dose of 15 Mrad and an acceleration voltage of 200 KV, and the other processes were performed in the same manner as in Example 5 to obtain the surface protective film for touch panel of Example 8.

Example 9
A commercially available hydrogenated styrene elastomer (rubber hardness 80 degrees) was dissolved in toluene to obtain a rubber solution. On the other hand, a hard film was processed on the surface of a film made of polyethylene terephthalate having a thickness of 100 μm and a light transmittance of 92%, and an easy adhesion treatment was performed on the back surface to obtain a base film. The above rubber solution is applied to the surface of the base film for easy adhesion so that the thickness after drying is 50 μm, dried at 95 ° C. using an oven, and then the surface of the rubber film is made of polyethylene terephthalate. A cover film having a release treatment of 75 μm and an average surface roughness Ra of 0.04 μm was laminated.

A laminate composed of the base film, rubber film and cover film is introduced into an electron beam irradiation apparatus, and the electron beam irradiation is performed from the cover film side with an irradiation dose of 5 Mrad and an acceleration voltage of 200 KV to form a self-adhesive layer of the rubber film. The self-adhesive layer was cross-linked and adhered to the base film at the same time, and then the cover film was peeled off to obtain the surface protective film for a touch panel of Example 9.

Example 10
In Example 9 above, the hydrogenated styrene elastomer was changed to one having a rubber hardness of 40 degrees, the thickness after drying of the rubber layer was changed to 60 μm, and the irradiation dose of electron beam irradiation was changed to 10 Mrad. In the same manner as in Example 9, the surface protective film for a touch panel of Example 10 was obtained.

Comparative Example 3
In said Example 10, the electron beam irradiation was abbreviate | omitted and the surface protection film for touchscreens of the comparative example 3 was obtained like Example 10 in others.

Example 11
In Example 1 above, the thickness of the self-adhesive layer made of silicone rubber after drying was changed to 3 μm, and the others were similar to Example 1 to obtain a surface protective film for a touch panel of Example 11.

Regarding the surface protective films for touch panels of Examples 1 to 11 and Comparative Examples 1 to 3, the pressure resistance, the self-adhesive strength of the self-adhesive layer, the amount of low molecular siloxane (ΣD3 to 10), the easy peelability to the touch panel, and the sticking The properties and durability were evaluated as described below and listed in Table 1 below. However, in Table 1, the amount of low molecular siloxane (ΣD3 to 10) was abbreviated as ΣD.

Pen pressure resistance: A protective film for evaluation is attached to a hard-processed polyester film having a three-dimensional average roughness (SRa) of 0.0008 to 0.0015 μm and a thickness of 125 μm through the self-adhesive layer. The film is fixed on a glass plate with the film facing down, and a touch pen with a polyacetal tip formed in a spherical shape with a diameter of 0.8 mm is reciprocated at a speed of 1 m / min. Then, the presence or absence of white handwriting marks generated by the pressure applied to the touch pen is observed with the naked eye, and the maximum load (gf) at which no whitening is observed is defined as the pressure resistance. However, the initial load of the writing pressure is changed from the initial load of 1N at a pitch of 1N, and the maximum load at which the above whitening does not occur is defined as the pressure resistance.

Self-adhesive strength of the self-adhesive layer (rolling speed of the steel ball): The protective film for evaluation is fixed to the slope with an inclination angle of 1 degree so that the self-adhesive layer is on the surface, and the surface of the self-adhesive layer has a diameter of 6 Roll a steel ball with a diameter of .75 mm and a mass of 1.25 g, calculate the speed (m / min) by measuring the time required for the steel ball to roll a distance of 8.0 cm, and repeat this five times. The average value (m / min) was defined as self-adhesive strength.

Low molecular siloxane amount (ΣD3 to 10): 1 g of a sample was taken from the self-adhesive layer of the protective film, extracted with 10 ml of acetone containing 20 μg / ml of n-tetradecane at room temperature, and then capillary gas chromatograph (manufactured by Hitachi, Ltd.) , G-3500), and measured under the following conditions.
Column: J & W DURABOND. DB-5MS
Column temperature: Increased from 50 ° C. to 280 ° C. at a rate of 10 ° C. per minute.
Inlet temperature: 270 ° C
Carrier gas: Helium detector: Hydrogen flame ionization detector (detection temperature 300 ° C)
Injection volume: 2 μl

Easy peelability: A protective film is attached to a transparent analog touch panel of resistance film type and left to stand in a room temperature atmosphere for 250 hours. The thing which cannot be made was set as x.

Adhesiveness: When a protective film is applied to a resistive analog transparent analog touch panel, ○ indicates that it can be applied cleanly without any problem, △ indicates that it can be applied but has an appearance problem, and X indicates that it cannot be applied. .

Durability: A protective film is attached to a polyester film (“Cosmo Shine A4300” manufactured by Toyobo Co., Ltd., thickness 100 μm), in an atmosphere at a temperature of 70 ° C. (in a high temperature environment), an atmosphere at a temperature of 40 ° C. and a humidity of 90%. (In a high humidity environment) and in an atmosphere at a temperature of −20 ° C. (under a low temperature environment) for 250 hours, and then measure the rolling speed by the steel ball rolling method to calculate the rate of change of the rolling speed. When the change rate is 30% or less and the rolling speed is 0.5 to 4.2 m / min, the change rate is 30% or less, but the rolling speed is out of the above range. ◯, the rate of change exceeds 30%, and the rolling speed of 0.5 to 4.2 m / min is Δ, and the rate of change is over 30% and the rolling speed is out of the above range as x. did.

Table 1
Writing pressure resistance (N) Adhesive strength (m / min) ΣD (ppm) Easy peelability Adhesiveness Durability Example 1 19 1.75 520 ○ ○ ◎
Example 2 10 0.88 1080 ○ ○ ◎
Example 3 14 1.12 780 ○ ○ ◎
Example 4 22 3.45 270 ○ ○ ◎
Example 5 9 1.74 1290 ○ ○ ◎
Example 6 15 2.21 930 ○ ○ ◎
Example 7 18 2.71 600 ○ ○ ◎
Example 8 13 2.32 970 ○ ○ ◎
Example 9 18 3.14-○ ○ △
Example 10 9 0.67 − ○ ○ Δ
Example 11 17 3.93 250 ○ △ ○
Comparative Example 1 4 0.40 1680 ○ ○ ○
Comparative Example 2 3 0.17 3120 ○ ○ ○
Comparative Example 3 6 0.33 − ○ ○ ×

As can be seen in Table 1 above, Examples 1 to 8 and Example 11 have a low molecular weight siloxane amount (ΣD3 to 10) in the silicone rubber as the self-adhesive layer of 1500 ppm or less, and the rolling speed of the steel ball. Since the expressed adhesive strength is controlled in the range of 0.5 to 4.2 m / min, the writing pressure resistance is set to 9N or more, and the handwriting marks of the touch pen are not whitened, and the visibility is high. It was maintained well and excellent in easy peelability, sticking property and durability. In contrast, Comparative Examples 1 and 2 use silicone rubber, but the amounts of low molecular siloxanes (ΣD3 to 10) are 1680 ppm and 3120 ppm, respectively, so that the adhesive strength is 0.4 m / min and 0.17 m, respectively. / Min, writing pressure resistance was less than 9N, handwriting marks were whitened, and visibility was reduced. In particular, in Comparative Example 2, since the thickness of the self-adhesive layer was as large as 300 μm, the adhesive strength was greatly increased. In Examples 9 and 10, hydrogenated styrene-based elastomers were used, but the self-adhesive strength was 0.5-4. 4 by selecting the rubber hardness and the thickness of the self-adhesive layer and adopting electron beam crosslinking. The pressure was controlled in the range of 2 m / min. Therefore, the same pressure resistance, easy peelability and sticking properties as those of Examples 1 to 8 and 11 were provided. In particular, Example 9 uses an elastomer having a higher rubber hardness than Example 10, so that the writing pressure resistance is also improved compared to Example 10. On the other hand, Comparative Example 3 used the same hydrogenated styrene elastomer as Example 10, but omitted electron beam cross-linking, resulting in increased adhesion and insufficient writing pressure resistance.

Claims (4)

In the surface protective film for a touch panel, which is formed by laminating a self-adhesive layer on one side of the base film and can be detachably attached to the surface of the touch panel by the self-adhesive force of the self-adhesive layer, the protective film, Is attached to a hard-processed polyester film having a three-dimensional average roughness (SRa) of 0.0008 to 0.0015 [mu] m and a thickness of 125 [mu] m through a self-adhesive layer, and is fixed on a glass plate with the polyester film facing down. A brush which was added to the touch pen after reciprocating a distance of 3.0 cm at a speed of 1 m / min on a touch pen having a polyacetal tip formed in a spherical shape with a diameter of 0.8 mm on the protective film. When the maximum load (N) where no whitening is observed is observed with the naked eye for the presence or absence of white handwriting marks generated by pressure, the pressure resistance is 9 N or more. Surface protective film for a touch panel, characterized in that it. The self-adhesive strength of the self-adhesive layer is such that the surface protective film for touch panel is fixed to a slope with an inclination angle of 1 degree so that the self-adhesive layer is on top, the diameter of the self-adhesive layer is 6.75 mm, and the mass is 1.25 g The surface protective film for touchscreens of Claim 1 currently controlled so that the rolling speed may be set to 0.5-4.2m / min when rolling the steel ball of this. The surface protective film for a touch panel according to claim 2, wherein the rolling speed, which is a measure of the self-adhesive force, is controlled by the crosslinking density of the self-adhesive layer surface and the thickness of the self-adhesive layer. The surface protective film for a touch panel according to any one of claims 1 to 3, wherein the self-adhesive layer comprises one or a mixture of a silicone rubber and a silicone adhesive, and the amount of low molecular siloxane (ΣD3 to 10) is 1500 ppm or less. .