阅读说明：本技术 表面保护膜 (Surface protective film ) 是由 鎌田穣 谷新太 堀江利彦 加藤壮 于 2018-05-29 设计创作，主要内容包括：本发明的课题在于提供一种利用触控笔的运笔感受及对触控笔的耐擦伤性优异的表面保护膜。且提供如下的表面保护膜作为解决手段,所述表面保护膜在最表面具有包含聚氨基甲酸酯的保护层,所述聚氨基甲酸酯的国际橡胶硬度(IRHD)为87.0以上且98.0以下,tanδ峰值为0.6以上。(The invention provides a surface protective film which is excellent in pen feeling by a stylus and scratch resistance to the stylus. And a surface protection film having a protective layer comprising a polyurethane having an International Rubber Hardness (IRHD) of 87.0 or more and 98.0 or less and a tan delta peak of 0.6 or more on the outermost surface.)

1. A surface protective film characterized by comprising a base film,

having a protective layer comprising polyurethane on the outermost surface,

the polyurethane has an International Rubber Hardness (IRHD) of 87.0 or more and 98.0 or less and a tan delta peak of 0.6 or more.

2. The surface protective film according to claim 1, wherein the polyurethane has a tan δ peak temperature of-20 ℃ or higher and 60 ℃ or lower.

3. The surface protective film according to claim 1 or 2, wherein at least three layers of the protective layer comprising polyurethane, the transparent base film, and the adhesive layer are laminated in this order.

4. The surface protective film according to any one of claims 1 to 3, wherein the polyurethane is polycarbonate-based or polyester-based.

5. The surface protective film according to any one of claims 1 to 4, wherein the protective layer has a thickness of 50 μm or more and 300 μm or less.

6. A surface protective film laminate characterized in that a release film is laminated on the protective layer-side surface of the surface protective film according to any one of claims 1 to 5, and a release film is laminated on the other surface.

7. A method for producing a surface protection film, the surface protection film being characterized by having a protective layer comprising a polyurethane on an outermost surface, the polyurethane having an International Rubber Hardness (IRHD) of 87.0 or more and 98.0 or less and a tan delta peak of 0.6 or more, the method comprising:

the material composition is made to flow into the gap between a first gap maintaining member and a second gap maintaining member fed out from a pair of spaced rollers,

the material composition is heat-hardened while being held between the first gap maintaining member and the second gap maintaining member to form the protective layer.

8. The method of manufacturing a surface protective film according to claim 7, wherein one of the first gap maintaining member and the second gap maintaining member is a transparent base film of a surface protective film.

9. The method for producing a surface protective film according to claim 7 or 8, wherein the polyurethane has a tan δ peak temperature of-20 ℃ or higher and 60 ℃ or lower.

10. The method of manufacturing a surface protective film according to any one of claims 7 to 9, wherein the polyurethane is polycarbonate-based or polyester-based.

11. The method of manufacturing a surface protective film according to any one of claims 7 to 10, wherein one of the first gap maintaining member and the second gap maintaining member is a film on which a mold release treatment is not performed, and the other is a film on which a mold release treatment is performed.

12. The method of manufacturing a surface protective film according to any one of claims 7 to 11, wherein the other of the first gap maintaining member and the second gap maintaining member is a film having irregularities, and the material composition is held by a side of the film having irregularities.

Technical Field

The present invention relates to a surface protective film for protecting a transparent substrate on a display surface.

Background

In electronic devices including a display, such as a smart phone, a tablet Personal Computer (PC), and a portable music player, a surface protective film may be bonded to protect a transparent substrate on a display surface. The surface protective film is required to have light transmittance, non-coloring property, weather resistance, plasticizer resistance, stain resistance and the like. In recent years, these electronic devices are generally operated by a capacitive touch panel, and the feeling of pen movement, operability, scratch resistance, self-repairability in which a film pushed in by the tip of a stylus returns to its original state with time, and the like are newly required.

As such a surface protective film, for example, as patent document 1, the present applicant and others have proposed a surface protective film in which three layers of a protective layer comprising a thermosetting polyurethane as a cured product of a polyether polyol, an aliphatic isocyanate, an alcohol-based curing agent and a non-amine-based catalyst, a transparent base film and an adhesive layer are sequentially stacked, and as patent document 2, a surface protective film in which three layers of a protective layer comprising a polycarbonate-based polyurethane, a transparent base film and an adhesive layer are sequentially stacked.

Disclosure of Invention

Problems to be solved by the invention

The invention provides a surface protective film which is excellent in pen feeling by a stylus and scratch resistance to the stylus.

Means for solving the problems

The configuration of the present invention for solving the above problem is as follows.

1. A surface protective film characterized by having a protective layer comprising polyurethane on the outermost surface,

the polyurethane has an International Rubber Hardness (IRHD) of 87.0 or more and 98.0 or less and a tan delta peak of 0.6 or more.

2. The surface protective film according to claim 1, wherein the polyurethane has a tan δ peak temperature of-20 ℃ or higher and 60 ℃ or lower.

3. The surface protective film according to 1 or 2, wherein at least three layers of the protective layer comprising polyurethane, the transparent base film, and the adhesive layer are sequentially laminated.

4. The surface protective film according to any one of claims 1 to 3, wherein the polyurethane is polycarbonate-based or polyester-based.

5. The surface protective film according to any one of claims 1 to 4, wherein the protective layer has a thickness of 50 μm or more and 300 μm or less.

6. A surface protective film laminate characterized in that a release film is laminated on the protective layer-side surface of the surface protective film according to any one of claims 1 to 5, and a release film is laminated on the other surface.

7. A method for producing a surface protection film, the surface protection film being characterized by having a protective layer comprising a polyurethane on an outermost surface, the polyurethane having an International Rubber Hardness (IRHD) of 87.0 or more and 98.0 or less and a tan delta peak of 0.6 or more, the method comprising:

the material composition is made to flow into the gap between a first gap maintaining member and a second gap maintaining member fed out from a pair of spaced rollers,

the material composition is heat-hardened while being held between the first gap maintaining member and the second gap maintaining member to form the protective layer.

8. The method of manufacturing a surface protective film according to claim 7, wherein one of the first gap maintaining member and the second gap maintaining member is a transparent base material film of a surface protective film.

9. The method for producing a surface protective film according to claim 7 or 8, wherein the polyurethane has a tan δ peak temperature of-20 ℃ or higher and 60 ℃ or lower.

10. The method for manufacturing a surface protective film according to any one of claims 7 to 9, wherein the polyurethane is polycarbonate-based or polyester-based.

11. The method of manufacturing a surface protective film according to any one of claims 7 to 10, wherein one of the first gap maintaining member and the second gap maintaining member is a film on which a mold release treatment is not performed, and the other is a film on which a mold release treatment is performed.

12. The method of manufacturing a surface protective film according to any one of claims 7 to 11, wherein the other of the first gap maintaining member and the second gap maintaining member is a film having irregularities, and the material composition is held by the one side of the film having the irregularities.

ADVANTAGEOUS EFFECTS OF INVENTION

The protective layer of the surface protective film according to the present invention, which contains polyurethane, has an International Rubber Hardness (IRHD) of 87.0 or more and 98.0 or less, and thus has good pen feeling with a stylus pen and a writing feeling as if writing with a pencil pen on paper. Further, the protective layer containing polyurethane has a tan δ peak of 0.6 or more, and thus the surface is less likely to be damaged even when the surface is abraded by a stylus pen operation, and the scratch resistance is excellent. The surface protective film of the present invention is excellent in light transmittance, non-tinting property, and weather resistance by using a protective layer containing polyurethane.

The protective layer of the surface protective film of the present invention has a thickness of 50 μm or more and 300 μm or less, but satisfies optical characteristics usable as a surface protective film, and further has excellent self-repairability. Further, the antiglare property can be provided by forming irregularities on the surface of the protective layer.

The protective layer containing the polycarbonate-based polyurethane is excellent in plasticizer resistance, and the protective layer containing the polyester-based polyurethane is excellent in plasticizer resistance and oil resistance. Therefore, even when these protective layers containing polyurethane come into contact with various rubber products or oil agents, discoloration, swelling, and the like are unlikely to occur.

The surface protective film laminate obtained by laminating the release film and the release film on the surface protective film of the present invention can prevent damage and fouling of the surface protective film and has excellent handleability.

According to the manufacturing method of the present invention, the surface protective film can be continuously manufactured. Further, a protective layer having a thickness of 50 μm or more and 300 μm or less, which is difficult to produce by a wet coating method, can be produced without degrading optical characteristics. In addition, unevenness can be easily formed on the surface of the protective layer by a transfer method.

Drawings

Fig. 1 is a view showing a surface protective film according to an embodiment of the present invention.

Fig. 2 is a view showing a transparent substrate on which a surface protective film according to one embodiment of the present invention is bonded to a display surface.

Fig. 3 is a view showing a surface protective film laminate.

Fig. 4 is a view showing a method for producing a protective layer of a surface protective film.

Description of the symbols

1: protective layer

2: transparent substrate film

3: adhesive layer

4: mold release film

5: release film

10: surface protective film

20: transparent substrate

30: surface protective film laminate

40: sheet-like article

40 a: material composition

41: casting machine

41 a: head part

42 a: first gap maintaining member

42 b: second gap maintaining member

43 a: conveying roller

43 b: conveying roller

44: conveying roller

45: auxiliary roller

46: heating device

47: conveying belt

Detailed Description

Fig. 1 and 2 show a surface protective film according to an embodiment of the present invention, and a transparent substrate on a display surface to which the surface protective film according to the embodiment is bonded. In fig. 1 and 2, the thickness of each layer does not mean an actual thickness.

The surface protection film 10 according to one embodiment is formed by sequentially laminating three layers, namely, a protection layer 1 including polyurethane, a transparent base film 2, and an adhesive layer 3. The surface protective film 10 according to an embodiment is bonded to the transparent substrate 20 via the adhesive layer 3.

As described above, the surface protective film of the present invention is attached to the surface of the transparent substrate, thereby preventing damage, cracks, dirt, and the like of the transparent substrate.

Protective layer "

The protective layer comprises polyurethane. The polyurethane is obtained by reacting a material composition containing at least a polyol, an isocyanate and an alcohol hardener. As will be apparent from the production method described in detail below, the polyurethane used in the present invention is thermosetting.

a. Polyhydric alcohols

As the polyhydric alcohol, there may be mentioned: polyoxyalkylene glycols such as polyethylene glycol, polypropylene glycol and polyoxytetramethylene glycol, and alkylene oxide adducts such as ethylene oxide and propylene oxide of bisphenol a and glycerin; polyester polyols obtained by polymerization of dibasic acids such as adipic acid, phthalic anhydride, isophthalic acid, maleic acid, and fumaric acid with glycols such as ethylene glycol, propylene glycol, 1, 4-butanediol, 1, 6-hexanediol, and trimethylolpropane; polycaprolactone-based polyols such as polycaprolactone diol, polycaprolactone triol, and polycaprolactone tetraol; polycarbonate-based polyols such as polycarbonate diol, polycarbonate triol and polycarbonate tetraol; and derivatives, modified forms, and mixtures thereof, in which a side chain or a branch structure is introduced.

Among these, polycarbonate-based polyurethanes obtained from polycarbonate-based polyols are excellent in plasticizer resistance and can prevent plasticizers from migrating and swelling due to contact with rubber products and the like. Polyester polyurethane obtained from polyester polyol is excellent in plasticizer resistance and oil resistance, and can prevent various oils such as plasticizers, hand creams and sun screens from swelling by migration.

a1. Polycarbonate polyol

The polycarbonate-based polyol may be, for example, a reaction product of a dialkyl carbonate and a diol. Further, as the polycarbonate-based polyol, for example, polycarbonate diol, polycarbonate triol, polycarbonate tetraol, derivatives and modified products thereof into which a side chain or a branch structure is introduced, and mixtures thereof can be used.

Examples of the dialkyl carbonate include: dialkyl carbonates such as dimethyl carbonate and diethyl carbonate, diaryl carbonates such as diphenyl carbonate, and alkylene carbonates such as ethylene carbonate. These may be used alone or in combination of two or more.

Examples of the diols include: 1, 4-butanediol, diethylene glycol, 1, 5-pentanediol, 1, 6-hexanediol, 1, 7-heptanediol, 1, 8-octanediol, 2-methyl-1, 8-octanediol, 1, 9-nonanediol, 1, 10-dodecanediol, 2-ethyl-1, 6-hexanediol, 3-methyl-1, 5-pentanediol, 2, 4-dimethyl-1, 5-pentanediol, neopentyl glycol, 1, 3-cyclohexanediol, 1, 4-cyclohexanedimethanol, 2' -bis (4-hydroxycyclohexyl) -propane, and the like. These may be used alone or in combination of two or more. The diol is preferably an aliphatic diol or alicyclic diol having 4 to 9 carbon atoms, and is preferably, for example, 1, 4-butanediol, diethylene glycol, 1, 5-pentanediol, 1, 6-hexanediol, 3-methyl-1, 5-pentanediol, 2, 4-dimethyl-1, 5-pentanediol, 1, 4-cyclohexanedimethanol, 1, 7-heptanediol, 1, 8-octanediol, 2-methyl-1, 8-octanediol, and 1, 9-nonanediol, alone or in combination of two or more. Further, it is more preferable that the branched structure is not present.

a2. Polyester polyol

Examples of the polyester polyol include polyester polyols obtained by polymerization of a dibasic acid such as succinic acid, adipic acid, phthalic anhydride, isophthalic acid, maleic acid, or fumaric acid with a diol such as ethylene glycol, propylene glycol, 1, 4-butanediol, 1, 6-hexanediol, or trimethylolpropane.

Among these, succinic acid-based polyurethane using succinic acid as a dibasic acid is particularly excellent in oil resistance, and is therefore preferable.

The number average molecular weight of the polyol is preferably 200 or more and 10,000 or less, more preferably 500 or more and 5,000 or less, and further preferably 800 or more and 3,000 or less. If the number average molecular weight is less than 200, the reaction may be too rapid and the handling may be poor, and the molded product may lose its flexibility and become brittle. On the other hand, if the number average molecular weight is more than 10,000, the viscosity becomes too high and the handling property is deteriorated, and the molded product may be crystallized and clouded. In the present invention, the number average molecular weight means a molecular weight calculated from a hydroxyl value of a polyol measured based on Japanese Industrial Standards (JIS) K1557. Note that, even if the numerical range is outside the above range, the numerical range is not excluded as long as the numerical range does not depart from the gist of the present invention.

b. Isocyanates

As the isocyanate, an isocyanate having two or more isocyanate groups in a molecule can be used without particular limitation. For example, tolylene diisocyanate, tolidine diisocyanate, diphenylmethane diisocyanate, polymethylene polyphenyl polyisocyanate, carbodiimidized diphenylmethane polyisocyanate, crude diphenylmethane diisocyanate, xylylene diisocyanate, 1, 5-naphthalene diisocyanate, tetramethylxylene diisocyanate, isophorone diisocyanate, hydrogenated diphenylmethane diisocyanate, hydrogenated xylylene diisocyanate, hexamethylene diisocyanate, dimer acid diisocyanate, norbornene diisocyanate, and the like can be used. Two or more of these may be used in combination.

In the present invention, the polyurethane forming the protective layer preferably uses an aliphatic isocyanate having no aromatic ring as the isocyanate component. The polyurethane obtained from the aliphatic isocyanate is less likely to be yellowed, and the polyurethane is prevented from being discolored by light or heat from a light source, sunlight, or the like, thereby preventing the transparency from being lowered.

c. Alcohol-based hardener

The polyurethane forming the protective layer of the present invention uses an alcohol-based curing agent as a curing agent. The alcohol-based hardener has less adverse effect on the human body and the environment than the amine-based hardener.

The alcohol-based curing agent is not particularly limited as long as it is an alcohol-based curing agent having two or more hydroxyl groups in the molecule. Examples thereof include: glycols such as ethylene glycol, 1, 3-propylene glycol, 2-methyl-1, 3-propylene glycol, 1, 3-butylene glycol, 1, 4-butylene glycol, 1, 5-pentanediol, neopentyl glycol (2, 2-dimethyl-1, 3-propylene glycol), 1, 6-hexanediol, polyethylene glycol, polypropylene glycol, polybutylene glycol, cyclohexanedimethanol, hydrogenated bisphenol a, triols such as glycerin, trimethylolpropane, butanetriol, pentatriol, hexanetriol, cyclopentanetriol, and cyclohexanetriol, and triols such as pentaerythritol, dipentaerythritol, and tetramethylolpropane. Among these, 1, 4-butanediol is preferable from the viewpoint of handling properties and mechanical properties, and a diol having a cyclic structure such as cyclohexanedimethanol or hydrogenated bisphenol a is preferable from the viewpoint of preventing clouding. From the viewpoint of handling properties and mechanical properties, trimethylolpropane is preferred as the trihydric alcohol.

In the case where a diol is used alone as the alcohol-based curing agent, the molded article may be crystallized and clouded, and in the case where a triol is used as the main component, the strength may be reduced. Specifically, it is preferably used in the range of 50 to 100 parts by weight of a diol and 50 to 0 parts by weight of a triol, and more preferably in the range of 60 to 80 parts by weight of a diol and 40 to 20 parts by weight of a triol. When cloudiness occurs when 1, 4-butanediol is used as the diol, a part or all of 1, 4-butanediol may be replaced with a diol having a cyclic structure.

d. Catalyst and process for preparing same

The polyurethane forming the protective layer of the present invention is preferably heat-cured in the presence of a non-amine catalyst. By using a non-amine catalyst, a polyurethane excellent in non-coloring property, transparency and weather resistance can be obtained. On the other hand, in the polyurethane thermally cured by the amine catalyst, the emitted light may become yellow and the appearance may be colored with the passage of time.

Examples of the non-amine catalyst include: organic tin compounds such as di-n-butyltin dilaurate, dimethyltin dilaurate, dibutyltin oxide, and octyltin, organic titanium compounds, organic zirconium compounds, tin carboxylates, and bismuth carboxylates. Among these, organotin compounds are preferable because the reaction rate can be easily controlled.

The non-amine catalyst is preferably added in an amount of 0.0005 wt% or more and 3.0 wt% or less based on the total amount of the a. If the content is less than 0.0005 wt%, the reaction rate may not be sufficiently increased, and a molded article may not be efficiently obtained. If the amount is more than 3.0 wt%, the following problems may occur: the reaction rate becomes too high, and a molded article having a uniform thickness cannot be obtained, and the heat resistance and weather resistance of the molded article are lowered, the light transmittance is lowered, and the molded article is colored. Note that, even if the numerical range is outside the above range, the numerical range is not excluded as long as the numerical range does not depart from the gist of the present invention.

e. Silicon-based additive

In the surface protective film of the present invention, the polyurethane forming the protective layer preferably contains a silicon-based additive. The polyurethane containing the silicon-based additive improves the sliding property and enables comfortable touch panel operation with a stylus or a finger. The lower limit of the amount of the silicon-based additive to the total amount of the above-mentioned a to c is preferably 0.05 wt% or more, more preferably 0.1 wt% or more, and still more preferably 0.3 wt% or more. The upper limit of the amount of the silicon-based additive added to the total amount of the above-mentioned a to c is preferably 10.0 wt% or less, more preferably 9.0 wt% or less, and further preferably 7.0 wt% or less. If the amount of the silicon-based additive added is less than 0.05 wt%, improvement of the sliding property may be insufficient, and if it exceeds 10.0 wt%, the sliding property may be too good to the contrary, and the pen tip of the stylus may be too slippery. Note that, even if the numerical range is outside the above range, the numerical range is not excluded as long as the numerical range does not depart from the gist of the present invention.

The silicone additive may be contained in the polyurethane by adding the silicone additive to the material composition before thermosetting of the polyurethane and thermally hardening the material composition. The silicon-based additive is preferably a non-reactive silicon-based additive that does not form a covalent bond with the crosslinked network formed by the polyol, the isocyanate, and the alcohol-based hardener. The non-reactive silicon-based additive gradually bleeds out to the surface of the protective layer, and thus can impart sliding properties over a long period of time. The silicon-based additive is not particularly limited as long as it is a silicon-based additive that does not undergo phase separation from the material composition before thermal curing. For example, polyether-modified polydimethylsiloxane, polyaryl-modified polydimethylsiloxane, and long-chain alkyl-modified polydimethylsiloxane may be used. Specifically, KF352A, KF615A, X22-4515, KF410, KF412 and the like, which are commercially available from shin-Etsu chemical industries, Ltd.

The polyurethane forming the protective layer may contain various additives such as a colorant, a light stabilizer, a heat stabilizer, an antioxidant, a fungicide, a flame retardant, and a lubricant, as necessary, within a range not to impair the required characteristics.

The protective layer is a molded article comprising polyurethane obtained by curing a material composition comprising at least a polyol, an isocyanate and an alcohol-based curing agent in the presence of a catalyst, and the molding method may be any of a one-shot (one-shot) method, a prepolymer method and a quasi-prepolymer (quasi-prepolymer) method.

In the one-shot process, a polyurethane molded article can be produced by charging and curing a polyol, an isocyanate, an alcohol-based curing agent, an optional additive, and a catalyst at one time.

In the prepolymer method, a molded article of polyurethane can be produced by: a prepolymer having an isocyanate group at the end is prepared in advance by reacting a polyol with an excess amount of isocyanate in terms of stoichiometry (stoichimetry), and the prepolymer is cured by mixing a predetermined amount of an alcohol-based curing agent, an optional additive, and a catalyst.

In the quasi-prepolymer method, a molded product of polycarbonate-based polyurethane can be produced as follows: a part of the polyol is mixed with the alcohol-based curing agent in advance, the prepolymer is prepared using the remaining polyol and isocyanate, and a mixture of the polyol and the alcohol-based curing agent, an optional additive, and a catalyst, which have been mixed in advance, is mixed therewith to cure the prepolymer.

In the present invention, the ratio (-OH/-NCO: hereinafter referred to as α ratio) of the number of moles of hydroxyl groups (-OH) contained in the alcohol-based curing agent to the number of moles of isocyanate groups (-NCO) of the isocyanate or prepolymer in the material composition before thermal curing of the polyurethane is more preferably 0.8 to 1.5. If the α ratio is less than 0.8, the mechanical properties become unstable, and if it exceeds 1.5, the surface tackiness increases, and the good feeling of pen movement is impaired. Further, the α ratio is more preferably 1.05 or more and 1.3 or less because the polyurethane constituting the protective layer is appropriately deformed and the scratch resistance is improved.

Further, the polyurethane preferably does not contain an acrylic skeleton (acrylic skeleton or methacrylic skeleton). That is, the polyurethane forming the protective layer of the present invention preferably does not contain acrylic modified polyurethane. Polyurethane having an acrylic skeleton sometimes deteriorates flexibility of polyurethane, lowers mechanical strength such as abrasion resistance and tear strength, and also sometimes causes coloration of emitted light due to a residue of a catalyst used for introducing an acrylic skeleton or a methacrylic skeleton.

In the present invention, the polyurethane forming the protective layer is characterized in that: the International Rubber Hardness (IRHD) is 87.0-98.0, and the tan delta peak value is 0.6 or more.

If the international rubber hardness is less than 87.0, the pen point is pressed too far into the protective layer when the stylus is operated, and the movement of the pen becomes heavy. On the other hand, if the international rubber hardness is greater than 98.0, the pen point does not press into the protective layer, and therefore the feeling of resistance is small when the stylus pen is operated, and the movement of the pen becomes too gentle.

When the peak value of tan δ is less than 0.6, the scratch resistance of the polyurethane is insufficient, and the polyurethane is easily damaged when operated with a stylus pen or the like. When the peak value of tan δ is 0.6 or more, the scratch resistance is excellent, and it is difficult to leave scratches or flaws. The peak value of tan δ is preferably 1.39 or less. When the tan δ peak is larger than 1.39, plasticity may be high and the deformation may be difficult to repair.

The present inventors presume the reason why the scratch resistance is excellent if the tan δ peak is 0.6 or more, as follows.

The loss tangent (tan δ) is a ratio (E "/E ') of the memory elastic modulus (E') to the loss elastic modulus (E"). The storage elastic coefficient E' corresponds to the amount of elastic component in the polyurethane and the loss elastic coefficient E ″ corresponds to the amount of viscous component in the polyurethane. When tan δ is measured while changing the temperature, it increases before a certain temperature, and decreases when the temperature is exceeded. That is, when tan δ is measured while changing the temperature, the maximum value appears. The temperature at which the maximum value appears is tan δ peak temperature (glass transition temperature), and the maximum value is tan δ peak.

the tan δ peak is related to the amount of fine elements that can move without being constrained at the tan δ peak temperature. Therefore, the larger the tan δ peak is, the more likely fine deformation occurs.

In the rotational writing test, the polyurethane is stretched when the stylus passes through the polyurethane, and is restored after passing through the polyurethane, and therefore, fine expansion and contraction are repeated. When the peak value of tan δ is 0.6 or more, it is estimated that the balance between a trace amount of elastic component and a trace amount of viscous component in polyurethane is good, and polyurethane functions like a fine spring against a fine expansion and contraction at the time of rotational writing, and the polyurethane is less likely to be broken even when repeatedly subjected to tension, frictional heat, or the like by pressure from a pen.

Further, the hardness, the peak value of tan δ, and the peak temperature of tan δ can be adjusted by controlling the distance between the crosslinking points or the morphology (morphology) of the hard segment/soft segment. Specifically, the molecular weight or molecular skeleton of the urethane soft segment constituting the polyurethane, the number of functional groups and the amount of the hard segment, the divalent/trivalent mixing ratio of the alcohol-based curing agent, and the like can be adjusted.

The peak temperature of tan delta of the polyurethane forming the protective layer is preferably-20 ℃ or higher and 60 ℃ or lower. When the tan δ peak temperature is within the above range, the viscoelastic properties are good under the environment where the film is used as a surface protective film, and the self-repairability, scratch resistance, and the like are good.

In addition, in terms of scratch resistance, it is preferable that the polyurethane forming the protective layer has a storage modulus of elasticity of 1.0 × 10 at 25 ℃⁷Above and 5.0X 10⁹And a tan delta value at 25 ℃ of 0.3 or more.

The thickness of the protective layer is preferably 50 μm or more and 300 μm or less, and more preferably 100 μm or more and 200 μm or less. The protective layer has a thickness of 50 to 300 μm, and thus the stylus pen has excellent feeling of pen movement and sliding property, and excellent handling property and self-repairability. If the thickness of the protective layer is less than 50 μm, the feeling of pen movement and self-repairability are reduced. If the thickness of the protective layer is more than 300 μm, the feeling of pen movement, slidability, workability, and self-repairability are reduced, and it is difficult to form the protective layer with a uniform thickness. When the thickness of the protective layer is 50 μm or more and 300 μm or less, the performance required for the surface protective film can be exhibited in good balance, and the production is also easy.

Transparent substrate film "

The transparent substrate film holds a protective layer. The material constituting the transparent base film is not particularly limited as long as it is excellent in transparency, flexibility, and mechanical strength, and polyethylene terephthalate (PET), polyethylene naphthalate (PEN), Polycarbonate (PC), a cyclic olefin resin (COP), Polyimide (PI), and the like can be preferably used.

The thickness of the transparent base film is preferably 50 μm or more and 500 μm or less. In the surface protective film of the present invention, since the thermal expansion coefficient of the polyurethane forming the protective layer is generally higher than that of the material constituting the transparent base film, if the thickness of the transparent base film is less than 50 μm, the transparent base film cannot completely resist the shrinkage of the protective layer at low temperatures, and the surface protective film may be peeled off from the transparent substrate. If the thickness of the transparent base film is more than 500 μm, the volume of the surface protective film becomes large, and the cost increases. In addition, the operability when the touch panel display is attached to the surface is reduced. The following "method for producing a protective layer" will be described in detail, but the protective layer may be formed directly on the transparent base film. In the case of using the above-mentioned production method, the transparent base film is preferably thick in order to prevent deformation upon heating when the material composition is thermally cured to form the protective layer. Note that, even if the numerical range is outside the above range, the numerical range is not excluded as long as the numerical range does not depart from the gist of the present invention.

Adhesive layer "

The adhesive layer is used for bonding the surface protection film on the transparent substrate on the surface of the display. The type of the adhesive is not particularly limited, and adhesives including acrylic resins, epoxy resins, urethane resins, silicone resins, and the like can be used. Among these, an adhesive containing an acrylic resin can be applied even to a transparent substrate subjected to surface treatment such as stain-proofing treatment or low-reflection treatment. Further, an adhesive containing a silicone resin is excellent in Wetting (Wetting) properties, hardly generates bubbles when attached to a transparent substrate, has good removability, and hardly generates adhesive residue when peeled off. The thickness of the adhesive layer is usually in the range of 5 μm or more and 60 μm or less, but can be appropriately adjusted according to the required specifications.

Surface protective film "

The surface protection film 10 according to one embodiment is formed by sequentially laminating three layers, namely, a protection layer 1 including polyurethane, a transparent base film 2, and an adhesive layer 3. The surface protective film of the present invention may be formed by laminating at least the three layers in this order, and may include, for example, an intermediate layer for improving adhesion between the layers or a blue light cut-off layer for cutting off blue light.

The haze value of the surface protective film is preferably 0.1% or more and 40% or less. The total light transmittance of the surface protective film is preferably 90% or more. If the haze value is greater than 40% or the total light transmittance is less than 90%, the visibility of the display is reduced. In the case where a blue light cut-off layer that cuts off visible light in the blue region is provided, the total light transmittance is preferably 60% or more. When the haze value of the surface protective film is 0.1% or more and less than 3%, a clear appearance can be obtained. When the haze value of the surface protective film is 3% or more and 40% or less, the surface protective film can be provided with antiglare properties. In addition, the surface protective film having antiglare properties makes it difficult for scratches attached to the surface of the protective layer to be revealed. In order to set the haze value of the surface protective film to 3% or more and 40% or less, the surface protective film may have irregularities formed on the surface thereof. The shape of the surface roughness of the protective layer is not particularly limited as long as it has the above-mentioned haze value and total light transmittance, and it may be adjusted as appropriate in accordance with the refractive index, light absorption, or the like of the material used, and usually, the average length (RSm) of the roughness curve element is about 10 μm to 80 μm. The arithmetic average roughness Ra is about 0.01 to 0.3 μm, and the maximum height Rz is about 0.1 to 2.0 μm.

In order to protect the surface protective film of the present invention until it is attached to the transparent substrate on the surface of the display, a surface protective film laminate can be produced by attaching a release film to the surface of the surface protective film on the protective layer side and attaching a release film to the other surface. Fig. 3 shows a surface protective film laminate 30 in which a release film 4 and a release film 5 are bonded to a surface protective film 10 according to an embodiment. In fig. 3, the thickness of each layer does not mean an actual thickness.

The release film is a film for preventing dirt, dust adhesion, damage, and the like of the protective layer, and is preferably a film obtained by subjecting the surface of the protective layer to release treatment. When the release film subjected to the release treatment is peeled from the protective layer, the release agent migrates to the surface of the protective layer, and slidability can be imparted to the surface of the protective layer immediately after the release film is peeled, so that touch operation can be performed without discomfort immediately after use. The following "method for producing a protective layer" will be described in detail, but the protective layer may be formed directly on the release film. In this case, the thickness of the release film is preferably 50 μm or more and 300 μm or less, and more preferably, is thick, in order to prevent deformation during heating when the material composition is thermally cured to form a protective layer.

The release film is preferably bonded to the adhesive layer in order to prevent dirt, dust adhesion, reduction in adhesive force, and the like. The release film is not particularly limited, and a film obtained by subjecting the surface of the side to be bonded to the adhesive layer to a release treatment can be preferably used.

Method for producing protective layer "

The protective layer may be manufactured by: the uncured material composition is poured into a gap between a first gap maintaining member and a second gap maintaining member fed by a pair of spaced rollers, and the material composition is introduced into a heating apparatus while being held between the two gap maintaining members, and the material composition is thermally cured to produce polyurethane. The material composition contains at least a polyol, an isocyanate (or a urethane prepolymer composed of these), and an alcohol-based curing agent.

Fig. 4 is a schematic view showing a method for manufacturing the protective layer. Hereinafter, a method for producing the protective layer will be described with reference to fig. 4.

The material composition 40a is poured into a gap between a first gap maintaining member 42a and a second gap maintaining member 42b fed by a pair of conveying rollers 43a and 43b arranged at a distance from each other by using a casting machine 41. The first gap maintaining member 42a and the second gap maintaining member 42b are introduced into the heating device 46 in a state of holding the material composition 40a therebetween. The material composition 40a is heat-cured while being held between the first gap maintaining member 42a and the second gap maintaining member 42b, and becomes the sheet-like article 40 of polyurethane.

In fig. 4, 44 is a conveying roller for conveying the first gap maintaining member 42a and the second gap maintaining member 42b, 45 is an auxiliary roller, and 47 is a conveying belt for conveying the first gap maintaining member 42a and the second gap maintaining member 42b holding the material composition 40a therebetween in the heating device 46.

The first gap maintaining member 42a and the second gap maintaining member 42b are not particularly limited as long as they are materials that do not thermally deform when the material composition is thermally cured. For example, a long film containing a polymer material such as polyethylene terephthalate (PET), polyethylene naphthalate (PEN), Polycarbonate (PC), cycloolefin resin (COP), Polyimide (PI), or the like can be used. In the schematic view shown in fig. 4, a long film made of a polymer material is used as the gap maintaining member, but an endless belt made of a metal material such as aluminum or the like may be used.

The first gap maintaining member 42a and the second gap maintaining member 42b are stretched and conveyed with the same tension in a state where the material composition 40a is held therebetween, and therefore the gap can be maintained at a constant size. The material composition 40a is sandwiched between the first gap maintaining member 42a and the second gap maintaining member 42b, and is cured while maintaining a constant thickness, thereby forming the sheet-like object 40 having excellent thickness accuracy. By the above-mentioned manufacturing method, a sheet-like object 40 having a thickness of 50 μm or more, which is difficult to be realized by coating, and having practical optical characteristics as a protective layer of a surface protective film can be continuously formed.

The head 41a of the casting machine 41 is preferably located closer to either of the conveying rollers than the central portions of the conveying rollers 43a and 43b (the central portion of the gap formed by the first gap maintaining member 42a and the second gap maintaining member 42 b), and is preferably located at a distance equal to or less than the radius of the conveying rollers. That is, the head 41a of the casting machine 41 is preferably located directly below the center of the pair of conveying rollers 43a and 43b and between the center axis of one of the conveying rollers. The shortest distance between the tip of the head 41a and the surface of the conveying roller is preferably 5cm or less. By disposing the head 41a in this manner, the thickness accuracy of the sheet-like object 40 is further improved, and at the same time, air bubbles are less likely to be mixed into the uncured material composition 40a flowing into the gap between the first gap maintaining member 42a and the second gap maintaining member 42b, and the mixed air bubbles are more likely to escape.

The conveyance rollers 43a and 43b may have only a conveyance function, but are preferably hot rollers. If the conveying roller is a heating roller, the curing reaction can be performed immediately after the material composition 40a is held in the gap between the first gap maintaining member 42a and the second gap maintaining member 42b, and the thickness can be maintained more uniformly until the material composition 40a is introduced into the heating device 46, whereby the sheet 40 having a higher thickness accuracy can be formed. The temperature of the conveying surface when heating the conveying roller is preferably set to 10 ℃ or higher and 60 ℃ or lower. If the temperature is less than 10 ℃, the viscosity of the material composition 40a becomes high and bubbles are hard to escape, and the curing reaction becomes slow and the thickness accuracy of the sheet-like object 40 is lowered. If the temperature exceeds 60 ℃, the material composition 40a may be hardened on the conveying roller or air bubbles may enter the sheet-like object 40.

The heating device 46 is a heating furnace having a heater, and may be a heating device capable of raising the temperature in the furnace to the curing temperature of the material composition 40 a. The heating condition (curing condition) in the heating apparatus 46 is not particularly limited, and may be set as appropriate according to the composition of the material composition 40a, and for example, may be set under the conditions of 40 ℃ to 160 ℃,1 minute to 180 minutes.

The long-sized laminate composed of the first gap maintaining member 42a, the sheet-like polyurethane material 40, and the second gap maintaining member 42b is carried out from the heating device 46. The sheet 40 of the long laminate serves as a protective layer of the surface protective film of the present invention.

Method for producing surface protective film laminate "

In the above-described manufacturing method, one of the first gap maintaining member 42a and the second gap maintaining member 42b may be the transparent base material film 2 in the surface protection film 10 according to an embodiment. Further, the other of the first gap maintaining member 42a and the second gap maintaining member 42b may be the release film 4. Hereinafter, a case where the first gap maintaining member 42a is the transparent base film 2 and the second gap maintaining member 42b is the release film 4 will be described as an example.

By the above-described manufacturing method, the long-sized laminate including the first gap maintaining member 42a serving as the transparent base material film, the sheet 40 of polyurethane serving as the protective layer, and the second gap maintaining member 42b serving as the release film is carried out. In this case, it is preferable that a film which is not subjected to release treatment is used as the first gap maintaining member 42a which is a transparent base film, and a film which is subjected to release treatment is used as the second gap maintaining member 42b which is a release film.

The long-sized surface protective film laminate 30 can be obtained by forming an adhesive layer on the surface of the long-sized laminate discharged from the heating device on the side of the first gap maintaining member 42a by coating or the like, and bonding a release film on the adhesive layer. In addition, a laminate in which a transparent base material film/an adhesive layer/a release film are sequentially laminated may be used as the first gap maintaining member 42 a. Further, by using a film having irregularities as the second gap-maintaining member 42b and using the surface-retaining material composition 40a having irregularities, irregularities can be transferred to the outermost surface of the sheet-like object 40, and antiglare properties can be imparted to the obtained protective layer.

With the present manufacturing method, the surface protective film laminate 30 can be continuously manufactured by so-called roll-to-roll. The surface protective film laminate 30 thus produced has the release film 4 and the release film 5 on both surfaces, respectively, and is excellent in handleability, for example, by preventing damage and contamination of the surface protective film.

The surface protective film laminate may be wound into a roll and shipped, or may be cut into a sheet and shipped. Further, the adhesive layer may be formed by coating or the like in a display factory or the like in the form of an elongated laminate composed of the first gap maintaining member 42a, the polyurethane sheet 40, and the second gap maintaining member 42b or in the form of a sheet laminate obtained by cutting the elongated laminate, and then bonded to a transparent substrate of a display.

The above-mentioned production method is an example, and for example, the above-mentioned production method may be a method in which the protective layer produced by the above-mentioned "production method for a protective layer" and a sheet-like or roll-like transparent base film are laminated to each other.