WO2009093480A1

WO2009093480A1 - Film for keypad, keypad, and key sheet

Info

Publication number: WO2009093480A1
Application number: PCT/JP2009/050062
Authority: WO
Inventors: Hidekazu Saito; Yoshihiro Yamana; Hiroki Kimura
Original assignee: Kuraray Co., Ltd.
Priority date: 2008-01-23
Filing date: 2009-01-07
Publication date: 2009-07-30
Also published as: JPWO2009093480A1; TW200937472A

Abstract

A film for keypads is provided which is excellent in nontackiness, handleability, heat resistance, and dimensional-accuracy stability. Even when subjected especially to a heat treatment, the film causes no problems such as failures, e.g., warpage and shrinkage, and blocking with another film. This film enables a final product to be reduced in weight and size, and gives a keypad or key sheet which can be produced through simplified steps. Also provided are a keypad and a key sheet both employing the film. The film for keypads is made only of a thermoplastic polyurethane obtained by reacting a high-molecular polyol, an organic polyisocyanate, and a chain extender or is made of a thermoplastic polyurethane composition comprising the thermoplastic polyurethane as the main ingredient. This film has a tensile stress at 100% elongation as measured at 23°C (M100) of 18 MPa or higher.

Description

Keypad film, keypad and key sheet

The present invention relates to a film for a keypad used for an operation unit such as a communication terminal such as a cellular phone, various instruments, a keyboard for personal computer input, and a remote controller.

In recent years, a key manufactured by bonding a key top (button key) to a keypad obtained from a keypad film made of a resin film such as thermoplastic polyurethane, polyethylene terephthalate, polyester elastomer, etc. Sheets are widely used in operation units such as communication terminals such as mobile phones, various instruments, keyboards for PC input, and remote controllers, and several techniques related to such key sheets are known (for example, Patent Documents). (See 1 and 2 etc.). Among the materials of the keypad film constituting the keypad, thermoplastic polyurethane is particularly suitable because it has high durability in addition to moderate soft feeling and excellent cushioning properties. Several techniques related to keypad films made of thermoplastic polyurethane are also known.

For example, a thermoplastic polyurethane synthesized by using, as a synthesis component, at least an isocyanate and a polyol selected from hexamethylene diisocyanate or hydrogenated diphenylmethane diisocyanate as a keypad surface material to be laminated on silicone rubber or the like to form a keypad There has been proposed a method of forming a surface material made of polyurethane which is excellent in soft touch, does not cause yellowing, has high water resistance and heat resistance, and has little deterioration in physical properties by being composed of a resin (see Patent Document 3).

Resin pellets obtained by reacting an organic diisocyanate mainly composed of hexamethylene diisocyanate, a polymer polyol mainly composed of polycarbonate diol, and a chain extender mainly composed of an aliphatic diol having 2 to 10 carbon atoms. A polyurethane resin keypad obtained by thermoforming a thermoplastic polyurethane resin sheet obtained by melt-molding is excellent in secondary moldability, oleic acid resistance, discoloration resistance, transparency, and printability. It is known (see Patent Document 4; the film made of thermoplastic polyurethane specifically described in Patent Document 4 has a high tensile stress (M ₁₀₀ ) at 100% elongation at 23 ° C. ( The polyurethane of Synthesis Example 3) is also about 8 MPa).

By the way, when manufacturing a keypad or even a key sheet using a film for a keypad, an adhesive or printing ink is applied to solidify or fix it, or it is laminated with a layer made of another resin. Therefore, heat treatment is often performed. However, conventional thermoplastic polyurethane keypad films have a relatively low tensile stress, so that adhesives and printing inks are solidified or fixed as described above, and laminated with other resin layers. When the heat treatment was performed, problems such as film warping and shrinkage due to insufficient heat resistance and problems such as film sticking were likely to occur. When such warping or shrinkage of the film, or even sticking between the films occurs, the key sheet obtained is manually inserted into a predetermined position of the final product such as a mobile phone and then inserted after being flattened. There is a problem that the productivity of the final product decreases due to the requirement for special equipment, or the yield decreases due to the occurrence of many defective products that cannot be used as key sheets or keypads. . Therefore, as described above, the thermoplastic polyurethane has a high durability in addition to a moderate soft feeling and excellent cushioning properties, but in order to use it as a keypad film made of it, At present, the range of use is limited, and a solution to the above problem has been demanded. In particular, in recent years, mobile phones have become increasingly thinner for emphasizing design, and as a result, there is a tendency for thinner key sheets and keypads, and there is a strong demand for solutions to the above problems. It was done.

In addition, the keypad film made of a resin film such as a conventional thermoplastic polyurethane has a relatively small tensile stress as described above, and therefore has the purpose of maintaining the shape of the obtained key sheet. Therefore, a technique for laminating frame sheets has been proposed. For example, a base sheet (keypad) made of a resin film made of relatively soft thermoplastic polyurethane (tensile stress (M ₁₀₀ ) at 100% elongation at 23 ° C. of about 7 MPa), and a key top disposed on the base sheet In a key sheet provided with a specific printing adhesive layer, a technique of laminating a frame sheet has been proposed for the purpose of fixing and reinforcing the key top (button key) (see Patent Document 5).

However, when the frame sheets are laminated, there is a problem that the manufacturing process becomes complicated in addition to difficulty in achieving weight reduction and reduction in the final product such as a mobile phone.

JP 2004-327307 A JP 2004-111258 A JP 2005-25960 A International Publication No. 2004/106401 Pamphlet JP 2007-66818 A

The present invention solves the above-mentioned problems, and is excellent in non-tackiness, handleability, heat resistance, and stability of dimensional accuracy, and in particular, heat treatment performed when an adhesive or printing ink is solidified or fixed. It is an object of the present invention to provide a keypad film that does not cause problems such as warp and shrinkage and problems such as sticking between films. A keypad and key sheet that can retain the shape without using a reinforcing material such as a frame sheet, can reduce the weight and size of final products such as mobile phones, and can simplify the manufacturing process. It is an object to provide a film for a keypad to be given. It is another object of the present invention to provide a keypad including at least a layer made of the keypad film, and a key sheet having at least the keypad and the keytop.

As a result of various studies by the present inventors to solve the above-mentioned problems, when forming a keypad film from thermoplastic polyurethane, the tensile stress at 100% elongation at 23 ° C. of the film (M ₁₀₀ ) [ Hereinafter, “tensile stress at 100% elongation at 23 ° C. (M ₁₀₀ )” may be simply referred to as “tensile stress (M ₁₀₀ )”. ] In a specific range, the warpage of the film during heat treatment or after the treatment is improved, and not only the processing process passability in the subsequent process is improved, but also the production yield is improved. . In addition, if the present inventors use the above-described keypad film, a reinforcing material is not necessary when manufacturing a keypad or a key sheet, leading to a reduction in weight and reduction of a final product such as a mobile phone, and a manufacturing process. It has also been found that simplification can be achieved. Based on these findings, further studies have been made and the present invention has been completed.

That is, the present invention
[1] A thermoplastic polyurethane obtained by reacting a polymer polyol, an organic polyisocyanate and a chain extender alone or a thermoplastic polyurethane composition mainly composed of the thermoplastic polyurethane, at 100% elongation at 23 ° C. A keypad film having a tensile stress (M ₁₀₀ ) of 18 MPa or more,
[2] The keypad film of [1], wherein the content of nitrogen atoms derived from isocyanate groups in the thermoplastic polyurethane is 4.5% by mass or more.
[3] The keypad film of [1] or [2], wherein the organic polyisocyanate is mainly composed of 4,4′-diphenylmethane diisocyanate,
[4] The keypad film according to any one of [1] to [3], wherein the chain extender is mainly composed of 1,4-butanediol,
[5] The keypad film of any one of [1] to [4], wherein the polymer polyol has a number average molecular weight of 500 to 8,000,
[6] The keypad film according to any one of [1] to [5], wherein the thickness is 20 to 300 μm,
[7] A keypad including at least a layer made of the keypad film according to any one of [1] to [6] above,
[8] A key sheet having at least the keypad and keytop of [7] above,
About.

According to the present invention, it is excellent in non-tackiness, handleability, heat resistance, and dimensional accuracy stability, and also warps, shrinks, etc. even by heat treatment applied particularly when an adhesive or printing ink is solidified or fixed. Thus, a keypad film can be obtained which does not cause problems such as the above-mentioned defect phenomenon and sticking between films. According to the keypad film of the present invention, the shape can be maintained without using a reinforcing material such as a frame sheet, so that the final product such as a mobile phone can be reduced in weight and reduced, and the manufacturing process can be simplified. Keypad and key sheet that can be used.

The present invention is described in detail below.
The keypad film of the present invention comprises a thermoplastic polyurethane alone obtained by reacting a polymer polyol, an organic polyisocyanate and a chain extender, or a thermoplastic polyurethane composition mainly composed of the thermoplastic polyurethane.

As the polymer polyol used in the present invention, any polymer polyol conventionally used in the production of polyurethane can be used. Examples of such polymer polyols include polyester polyols, polyether polyols, polycarbonate polyols, polyester polycarbonate polyols, polyolefin polyols, conjugated diene polymer polyols that may be hydrogenated, castor oil polyols, vinyl polymer polyols, and the like. These polymer polyols may be used alone or in combination of two or more. Among these, as the polymer polyol, one or more of polyester polyol, polyether polyol and polycarbonate polyol are preferably used, polyester polyol and / or polyether polyol are more preferably used, polyester diol and / or Alternatively, polyether diol is more preferably used.

As the polyester polyol, for example, according to a conventional method, a polyol component and a polycarboxylic acid component such as a polycarboxylic acid, an ester-forming derivative thereof such as an ester or an anhydride thereof are directly esterified or transesterified. Examples thereof include polyester polyols obtained and polyester polyols obtained by ring-opening polymerization of lactone using a polyol as an initiator.

As the polyol component used in the production of the polyester polyol, those generally used in the production of polyester can be used. For example, ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, 1,3-propanediol, 2-methyl-1,3-propanediol, 2,2-diethyl-1,3-propanediol, 1,3-butanediol, 1,4-butanediol, 2-methyl-1,4-butanediol, neo Pentyl glycol, 1,5-pentanediol, 3-methyl-1,5-pentanediol, 1,6-hexanediol, 1,7-heptanediol, 1,8-octanediol, 2-methyl-1,8- Octanediol, 2,7-dimethyl-1,8-octanedioe Aliphatic diols having 2 to 15 carbon atoms such as 1,9-nonanediol, 2-methyl-1,9-nonanediol, 2,8-dimethyl-1,9-nonanediol, 1,10-decanediol; 1 such as cycloaliphatic diols such as 1,4-cyclohexanediol, cyclohexanedimethanol, cyclooctanedimethanol, dimethylcyclooctanedimethanol; aromatic dihydric alcohols such as 1,4-bis (β-hydroxyethoxy) benzene Diols having two hydroxyl groups per molecule; polyols having three or more hydroxyl groups per molecule such as trimethylolpropane, trimethylolethane, glycerin, 1,2,6-hexanetriol, pentaerythritol, diglycerin, etc. it can. In producing the polyester polyol, these polyols may be used alone or in combination of two or more. Among these, 1,4-butanediol is non-adhesive, has excellent melt moldability, has excellent mechanical properties such as tensile stress and tear strength, and has excellent heat resistance. It is preferable to use an aliphatic diol having 4 to 10 carbon atoms such as 3-methyl-1,5-pentanediol, 1,6-hexanediol, 1,8-octanediol, It is more preferable to use a linear aliphatic diol having 4 to 10 carbon atoms such as 1,6-hexanediol or 1,8-octanediol.

As the polycarboxylic acid component used in the production of the polyester polyol, those generally used in the production of polyester can be used. For example, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid , Sebacic acid, dodecanedioic acid, methylsuccinic acid, 2-methylglutaric acid, 3-methylglutaric acid, trimethyladipic acid, 2-methyloctanedioic acid, 3,8-dimethyldecanedioic acid, 3,7-dimethyldecanediate C4-C12 aliphatic dicarboxylic acid such as acid; cycloaliphatic dicarboxylic acid, dimer acid, hydrogenated dimer acid and other alicyclic dicarboxylic acid; terephthalic acid, isophthalic acid, orthophthalic acid, naphthalenedicarboxylic acid and other aromatic dicarboxylic acids Acid; Tri- or higher functional polycals such as trimellitic acid and pyromellitic acid Phosphate; and or their ester-forming derivatives. These polycarboxylic acid components may be used alone or in combination of two or more. Among them, aliphatic polyurethanes having 6 to 12 carbon atoms are thermoplastic polyurethanes that are non-adhesive, have excellent melt moldability, have excellent mechanical properties such as tensile stress and tear strength, and have excellent heat resistance. Dicarboxylic acids are preferred, adipic acid, azelaic acid and sebacic acid are more preferred, and adipic acid is even more preferred.

Examples of lactones used for producing polyester polyols include ε-caprolactone and β-methyl-δ-valerolactone.

Examples of the polyether polyol include polyethylene glycol, polypropylene glycol, polytetramethylene glycol, and poly (methyltetramethylene glycol) obtained by ring-opening polymerization of a cyclic ether in the presence of a polyol. , One or more of these can be used. Among them, non-adhesive, excellent melt moldability, excellent mechanical properties represented by tensile stress and tear strength, and thermoplastic polyurethane having excellent heat resistance. (Methyltetramethylene glycol) is preferably used.

Examples of the polycarbonate polyol include those obtained by a reaction between a polyol component and a carbonate compound such as dialkyl carbonate, alkylene carbonate, or diaryl carbonate. As the polyol component used for the production of the polycarbonate polyol, the polyol components exemplified above as the components that can be used for the production of the polyester polyol can be used. Examples of the dialkyl carbonate include dimethyl carbonate and diethyl carbonate. Examples of the alkylene carbonate include ethylene carbonate. Examples of the diaryl carbonate include diphenyl carbonate.

As the above-mentioned polyester polycarbonate polyol, for example, those obtained by simultaneously reacting a polyol component, a polycarboxylic acid component and a carbonate compound, or previously synthesized polyester polyol and polycarbonate polyol, respectively, and then combining them with a carbonate compound. Examples thereof include those obtained by reacting or reacting with a polyol component and a polycarboxylic acid component.

Specific examples of the polymer polyol include, for example, poly (1,4-tetramethylene adipate) diol, poly (3-methyl-1,5-pentamethylene adipate) diol, poly (ε-caprolactone) diol, poly Examples include tetramethylene glycol.

The number average molecular weight of the polymer polyol is preferably in the range of 500 to 8,000, more preferably in the range of 600 to 5,000, and further in the range of 800 to 3,000. preferable. By using a polymer polyol having a number average molecular weight in this range, a thermoplastic polyurethane that is non-adhesive, excellent in melt moldability, excellent in mechanical properties represented by tensile stress and tear strength, and excellent in heat resistance Is obtained. In addition, the number average molecular weight of the polymer polyol in this specification is a number average molecular weight calculated based on the hydroxyl value measured according to JIS K 1557.

As the organic polyisocyanate used in the present invention, any organic polyisocyanate conventionally used in the production of polyurethane can be used. Examples of such organic polyisocyanates include, for example, 4,4′-diphenylmethane diisocyanate, tolylene diisocyanate, phenylene diisocyanate, xylylene diisocyanate, 1,5-naphthylene diisocyanate, 3,3′-dichloro-4,4′- Examples thereof include aromatic diisocyanates such as diphenylmethane diisocyanate; aliphatic or alicyclic diisocyanates such as hexamethylene diisocyanate, isophorone diisocyanate, 4,4′-dicyclohexylmethane diisocyanate, and hydrogenated xylylene diisocyanate. These organic polyisocyanates may be used alone or in combination of two or more. Among these, 4,4'-diphenylmethane diisocyanate is a non-adhesive, excellent melt moldability, excellent mechanical properties represented by tensile stress and tear strength, and thermoplastic polyurethane with excellent heat resistance. It is preferable that it mainly comprises (preferably 50 mol% or more, more preferably 80 mol% or more, further preferably 95 mol% or more, particularly preferably 100 mol%).

As the chain extender used in the present invention, any chain extender conventionally used in the production of polyurethane can be used. Examples of such chain extenders include ethylene glycol, propylene glycol, 1,4-butanediol, 1,6-hexanediol, 1,4-bis (β-hydroxyethoxy) benzene, 1,4-cyclohexanediol, bis Diols such as (β-hydroxyethyl) terephthalate and xylylene glycol; hydrazine, ethylenediamine, propylenediamine, xylylenediamine, isophoronediamine, piperazine or derivatives thereof, phenylenediamine, tolylenediamine, xylenediamine, adipic acid dihydrazide, isophthalate Examples include diamines such as acid dihydrazide; amino alcohols such as aminoethyl alcohol and aminopropyl alcohol. These chain extenders may be used alone or in combination of two or more. Among these, the chain extender is a non-adhesive, excellent melt moldability, excellent mechanical properties represented by tensile stress and tear strength, and excellent in heat resistance. It is preferably mainly composed of an aliphatic diol of several 2 to 10 (preferably containing 50 mol% or more, more preferably 80 mol% or more, further preferably 95 mol% or more, particularly preferably 100 mol%), More preferably, it is mainly composed of butanediol (preferably 50 mol% or more, more preferably 80 mol% or more, further preferably 95 mol% or more, particularly preferably 100 mol%).

In the production of a thermoplastic polyurethane by reacting the above-mentioned polymer polyol, organic polyisocyanate and chain extender, the mixing ratio of each component depends on the hardness, mechanical performance, etc. to be imparted to the desired thermoplastic polyurethane. Although it is appropriately determined in consideration, it is preferable to use each component in such a ratio that the molar ratio of active hydrogen atom: isocyanate group present in the reaction system is within the range of 1: 0.9 to 1.1. It is more preferable to use each component at a ratio of 1: 0.95 to 1.05. By using each component in the above proportion, a thermoplastic polyurethane that is non-adhesive, excellent in melt moldability, excellent in mechanical properties represented by tensile stress and tear strength, and excellent in heat resistance is obtained. Can do.

The method for producing the thermoplastic polyurethane is not particularly limited, and may be performed using any of the known urethanization reaction techniques using a polymer polyol, an organic polyisocyanate, and a chain extender. Any of the shot methods can be employed. Among these, it is preferable to perform melt polymerization substantially in the absence of a solvent, and it is more preferable to employ a continuous melt polymerization method using a multi-screw extruder. The polymerization temperature at the time of melt polymerization is preferably in the range of 180 to 280 ° C.

When the above-described polymer polyol, organic polyisocyanate and chain extender are reacted to obtain a thermoplastic polyurethane, a urethanization reaction catalyst may be used. The kind in particular of the said urethanation reaction catalyst is not restrict | limited, Any of the urethanation reaction catalysts conventionally used for manufacture of a thermoplastic polyurethane can be used. Examples of the urethanization reaction catalyst include at least one compound selected from organic tin compounds, organic zinc compounds, organic bismuth compounds, organic titanium compounds, organic zirconium compounds, and amine compounds. Can do. A urethanization reaction catalyst may be used individually by 1 type, or may use 2 or more types together.

In the above thermoplastic polyurethane, the content of nitrogen atoms derived from isocyanate groups is preferably 4.5% by mass or more. Thermoplastic polyurethane having a content of nitrogen atoms derived from isocyanate groups within the above range is non-adhesive, excellent in melt moldability, excellent in mechanical properties represented by tensile stress and tear strength, and also in heat resistance. It will be excellent. The content of nitrogen atoms derived from isocyanate groups in the thermoplastic polyurethane is more preferably 4.5 to 6.5% by mass, further preferably 4.6 to 6.0% by mass, and more preferably 4.7 to The amount is particularly preferably 5.7% by mass, and most preferably 4.8 to 5.5% by mass.

The logarithmic viscosity of the thermoplastic polyurethane is a value obtained by measuring a solution obtained by dissolving the thermoplastic polyurethane in N, N-dimethylformamide (DMF) to a concentration of 0.5 g / dl at 30 ° C. Is preferably from 0.7 to 1.5 dl / g, more preferably from 0.8 to 1.4 dl / g, and even more preferably from 0.9 to 1.3 dl / g. A film containing a thermoplastic polyurethane having a logarithmic viscosity in the above range is non-adhesive, excellent in melt moldability, excellent in mechanical properties represented by tensile stress and tear strength, and excellent in heat resistance It becomes. In addition, the logarithmic viscosity ((eta) _inh ) of the thermoplastic polyurethane in this specification means the value measured by the method described in a following example.

The ASTM D hardness of the thermoplastic polyurethane is preferably 52 or more, more preferably 55 or more, and further preferably 58 or more. The thermoplastic polyurethane having ASTM D hardness in the above range is non-adhesive, excellent in melt moldability, excellent in mechanical properties represented by tensile stress and tear strength, and excellent in heat resistance. In addition, the ASTM D hardness of the thermoplastic polyurethane in this specification is a value measured according to ASTM D2240.

The keypad film of the present invention is composed of the above thermoplastic polyurethane alone or a thermoplastic polyurethane composition mainly composed of the thermoplastic polyurethane. The content of the thermoplastic polyurethane in the thermoplastic polyurethane composition is preferably 50% by mass or more, more preferably 80% by mass or more, and further preferably 95% by mass or more.

The thermoplastic polyurethane composition is within the range that does not impair the effects of the present invention, and if necessary, a mold release agent, a reinforcing agent, a colorant, a flame retardant, an ultraviolet absorber, an antioxidant, a weather resistance improver. , Light resistance improver, hydrolysis resistance improver, antifungal agent, antibacterial agent, stabilizer, urethanization catalyst deactivator, etc .; glass fiber, polyester fiber, etc .; talc, silica, etc. Inorganic components; various coupling agents; optional components such as resins other than the thermoplastic polyurethane described above can be contained. The content of these optional components in the thermoplastic polyurethane composition is preferably 50% by mass or less, more preferably 20% by mass or less, and still more preferably 5% by mass or less.

The tensile stress (M ₁₀₀ ) of the keypad film of the present invention is required to be 18 MPa or more. When the keypad film has a tensile stress (M ₁₀₀ ) in the above range, the heat treatment does not cause defects such as warping or shrinkage, or sticking between films, and no reinforcing material is used. Even so, a keypad or a key sheet that can retain the shape is provided. The tensile stress (M ₁₀₀ ) of the keypad film is preferably 18 to 30 MPa, more preferably 18 to 25 MPa. The tensile stress (M ₁₀₀ ) in the present specification is a value measured according to JIS K 7311-1995.

By using those having a predetermined tensile stress (M ₁₀₀₎ as the thermoplastic polyurethanes that constitute the keypad film, tensile stress of keypad film of the present invention (M ₁₀₀₎ easily in the above range be able to. That is, when the keypad film of the present invention consist above thermoplastic polyurethane alone, thermoplastic polyurethane having a tensile to be assigned to keypad film stress (M ₁₀₀₎ to the same tensile stress (M ₁₀₀₎ Can be used. As the thermoplastic polyurethane, as described above, it can be obtained by reacting a polymer polyol, an organic polyisocyanate, and a chain extender, and the tensile stress (M ₁₀₀ ) is within the above range. Although there is no limitation, in order to ensure that the tensile stress (M ₁₀₀ ) of the thermoplastic polyurethane, and thus the obtained keypad film, is within the above range, specific examples of the thermoplastic polyurethane used include (i) poly The content of nitrogen atoms derived from isocyanate groups obtained by reacting (1,4-tetramethylene adipate) diol, 4,4′-diphenylmethane diisocyanate and 1,4-butanediol is 4.8% by mass or more. A thermoplastic polyurethane, (ii) poly (3-methyl-1,5-pentamethylene A thermoplastic polyurethane obtained by reacting diol, 4,4′-diphenylmethane diisocyanate and 1,4-butanediol, wherein the content of nitrogen atoms derived from isocyanate groups is 4.7% by mass or more; iii) The content of nitrogen atoms derived from isocyanate groups obtained by reacting poly (ε-caprolactone) diol, 4,4′-diphenylmethane diisocyanate and 1,4-butanediol is 4.9% by mass or more. The content of nitrogen atoms derived from isocyanate groups obtained by reacting thermoplastic polyurethane and (iv) polytetramethylene glycol, 4,4′-diphenylmethane diisocyanate and 1,4-butanediol is 5.1% by mass. Is it a group consisting of thermoplastic polyurethane Such as at least one thermoplastic polyurethane chosen may be mentioned.
Further, when the keypad film of the present invention is composed of the above-mentioned thermoplastic polyurethane composition, the thermoplastic resin having a predetermined tensile stress (M ₁₀₀ ) in consideration of the types and blending amounts of the above optional components. By using polyurethane, the tensile stress (M ₁₀₀ ) of the keypad film can be easily within the above range.

The method for producing the keypad film of the present invention is not particularly limited, and any of the known film-forming production techniques using a thermoplastic polyurethane obtained by reacting a polymer polyol, an organic polyisocyanate and a chain extender. For example, any of extrusion molding, injection molding, inflation molding, calendar molding, press molding, and the like can be employed. Among these, it is preferable to employ extrusion molding or inflation molding, and it is more preferable to employ extrusion molding or inflation molding using a single screw extruder. In this case, the cylinder temperature of the single-screw extruder is preferably in the range of 180 to 230 ° C.

Key pad thickness film of the present invention is not particularly limited, the thermoplastic content or the thermoplastic polyurethane hardness nitrogen atom derived from the isocyanate groups of the polyurethane or obtained keypad film for tensile stress, (M ₁₀₀ However, it is preferably 20 to 300 μm, more preferably 30 to 200 μm from the viewpoints of film production ease, heat resistance, and post-processing passability. 40 to 150 μm is more preferable.

The keypad film of the present invention can be used as it is to make a keypad composed of a single layer made of the keypad film, but the keypad film of the present invention and other layers are laminated. A keypad may be formed from the stacked body. Examples of the material constituting the other layer include resins such as polyester, polyamide, polycarbonate, silicone, thermoplastic polyurethane, thermosetting polyurethane, and polyolefin; metal; paper; cotton cloth and the like. The keypad may have a layer composed of paint or ink, a layer composed of an adhesive, a primer, or the like as the other layer.
When forming a layer composed of the above-mentioned paint or ink, or a layer composed of an adhesive or a primer, it is preferable to perform heat treatment. Examples of the temperature of the heat treatment include 40 to 120 ° C. Examples of the heat treatment time include 10 seconds to 3 hours.

A single layer of the keypad film of the present invention or a laminate in which the keypad film of the present invention and other layers are laminated, if necessary, by cutting, punching, cutting, or the like to have desired dimensions and shapes. By processing into a keypad, a keypad can be manufactured. Further, a desired groove or hole may be formed on the keypad by grinding or laser. In addition, the keypad has an irregularity for arranging the key top; an irregularity for arranging the pusher for pressing the key switch installed on the lower surface of the key sheet; Various irregularities such as irregularities for enabling the pusher to have a function may be provided. These irregularities are subjected to compression molding (press molding), vacuum molding, etc. on a single layer of the keypad film of the present invention or a laminate in which the keypad film of the present invention and other layers are laminated. Can be formed.

By arranging a key top such as a button key at a predetermined position of the keypad, a key sheet having the keypad and the keytop can be obtained. The key sheet may have a pusher in addition to the key top. Arrangement of key tops and pressers on the keypad can be performed using an adhesive such as a chemically reactive adhesive (such as an adhesive containing cyanoacrylate) or a UV adhesive.

The keypad or key sheet obtained by using the keypad film of the present invention is preferably used as a member constituting an operation unit of a communication terminal such as a mobile phone, various instruments, a keyboard for personal computer input, a remote control, etc. Can do.

EXAMPLES The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples. In the examples and comparative examples, the melt viscosity, logarithmic viscosity, and ASTM D hardness of the thermoplastic polyurethane, and the tensile stress (M ₁₀₀ ) and heat resistance of the keypad film were measured or evaluated by the following methods.

The melt viscosity of the thermoplastic polyurethane, which was dried under reduced pressure (less than 10 torr) at 80 ° C. for 2 hours using a flow tester (manufactured by Shimadzu Corporation) with a melt viscosity of thermoplastic polyurethane, was 490.3 N (50 kgf). Nozzle size = diameter 1 mm × length 10 mm, measured at a temperature of 200 ° C.

Logarithmic viscosity of thermoplastic polyurethane 200 ml of N, N-dimethylformamide (DMF) per gram of keypad film obtained in the following examples or comparative examples was added and stirred at room temperature for 24 hours, followed by filtration to separate DMF. The solution was collected. When an insoluble material was generated, an operation of adding 200 ml of DMF to the insoluble material, stirring for 1 hour and separating by filtration was repeated 3 times. The collected filtrates were combined, and DMF was distilled off from the filtrate, followed by vacuum drying at room temperature for 24 hours. The mass of the obtained polyurethane component was measured, and almost all of the thermoplastic polyurethane contained in the keypad film was measured. It was confirmed that 100% was extracted. When the extraction rate was less than 100%, it was judged that the part that was not extracted was insoluble in DMF because the molecular weight of the thermoplastic polyurethane was sufficiently high, and was excluded from the log viscosity measurement target. .
The extracted thermoplastic polyurethane was dissolved again in DMF to a concentration of 0.5 g / dl, and the flow time at 30 ° C. of the DMF solution of the thermoplastic polyurethane was measured using an Ubbelohde viscometer. The logarithmic viscosity (η _inh ) of the thermoplastic polyurethane was determined by the equation.
Logarithmic viscosity of thermoplastic polyurethane (η _inh ) = [ln (t / t ₀ )] / c
[Wherein, t represents the flow time (second) of the DMF solution of thermoplastic polyurethane, t ₀ represents the flow time (second) of the solvent (DMF), and c represents the concentration (g / dl) of the DMF solution of thermoplastic polyurethane. . ]

A thermoplastic polyurethane produced in the following examples or comparative examples was injection-molded using a mold having a mirror finished ASTM D hardness surface of thermoplastic polyurethane (cylinder temperature 185 to 210 ° C., mold temperature 30 ° C. ), A disk-shaped molded product (diameter 120 mm, thickness 2 mm), and a product obtained by superimposing three obtained disk-shaped molded products in accordance with ASTM D2240. The ASTM D hardness of the plastic polyurethane) was measured.

Tensile stress of keypad film (M ₁₀₀ )
A dumbbell-shaped test piece (5 mm in width at the center) defined in JIS K 7311-1995 was produced from a keypad film obtained in the following examples or comparative examples. Using “Instron 5566” manufactured by Instron Japan Company Limited, the tensile stress when the dumbbell-shaped test piece was stretched 100% under the conditions of a temperature of 23 ° C. and a tensile speed of 300 mm / min was measured. The tensile stress (M ₁₀₀ ) of the keypad film was used.

Heat Resistance of Keypad Film Fifty test pieces (length 100 mm × width 100 mm) were produced from the keypad film obtained in the following examples or comparative examples. For each of these 50 test pieces, screen ink (“IPX screen ink” manufactured by Teikoku Ink Manufacturing Co., Ltd.) was applied in a square shape of 50 mm in length and 50 mm in width at the center, And left for 1 hour. The state of the test piece after the hot air drying treatment was observed and the heat resistance of the test piece was evaluated according to the following criteria, and this was regarded as the heat resistance of the keypad film.
[Evaluation criteria for heat resistance]
3: In the total number of test pieces (50 sheets), the screen ink application part was not warped or contracted at all, and the smoothness was maintained.
2: The number of test pieces in which the smoothness was maintained without warping or shrinkage in the screen ink application part was 46 to 49. (In 1 to 4 test pieces, warpage and shrinkage were observed in the screen ink application part.)
1: The number of test pieces in which the smoothness was maintained without warping or shrinkage in the screen ink application portion was 45 or less. (In five or more test pieces, warpage and shrinkage were observed in the screen ink application part.)

Abbreviations for each component used in the examples and comparative examples are shown below.
[Polymer polyol]
POH-1 : Polyester diol POH-2 produced by reacting 3-methyl-1,5-pentanediol with adipic acid and having a number of hydroxyl groups per molecule of 2.00 and a number average molecular weight of 1,500 : Polyester diol POH-3 produced by reacting 1,4-butanediol and adipic acid and having a number of hydroxyl groups per molecule of 2.00 and a number average molecular weight of 1,000: 1,4-butanediol Polyester diol POH-4 having a number of hydroxyl groups per molecule of 2.00 and a number average molecular weight of 2,000 produced by reacting adipic acid with adipic acid: 2.00 hydroxyl groups per molecule average molecular weight of polytetramethylene glycol POH-5 1,000: 1 hydroxyl group per molecule is 2.00, positive number average molecular weight of 1,000 (.Epsilon.-caprolactone) diol POH-6: a mixture of 3-methyl-1,5-pentanediol and 1,6-hexanediol ([the number of moles of 3-methyl-1,5-pentanediol: [1,6 -Mole number of hexanediol] = 9: 1) Polycarbonate diol having a number of hydroxyl groups per molecule of 2.00 and a number average molecular weight of 1,000 [organic polyisocyanate]
MDI : 4,4′-diphenylmethane diisocyanate HDI : hexamethylene diisocyanate [chain extender]
BD : 1,4-butanediol

[Example 1]
(1) Production of thermoplastic polyurethane (PU-1) A polymer polyol (POH-1), an organic polyisocyanate (MDI) and a chain extender (BD) are mixed at a molar ratio of POH-1: MDI: BD of 1. 0: 6.1: 5.1 (the content of the nitrogen atom derived from the isocyanate group is 4.9% by mass), and these two axes rotate in the coaxial direction so that the total supply amount thereof is 200 g / min. Continuously fed to the front of the heating zone of a screw type extruder (single diameter 30 mmφ, L / D = 36; heating zone divided into three zones: front, center and rear), polymerization temperature of 260 ° C. Polyurethane formation reaction was carried out by continuous melt polymerization under the conditions. The obtained melt was continuously extruded into water as a strand, and then cut with a pelletizer to obtain pellets. The obtained pellets were dehumidified and dried at 95 ° C. for 4 hours to obtain thermoplastic polyurethane (PU-1). The melt viscosity and ASTM D hardness of the obtained thermoplastic polyurethane (PU-1) were measured by the methods described above. The results are shown in Table 1.
(2) Manufacture of keypad film Single-screw type extruder (cylinder diameter: 25 mmφ, cylinder temperature: 180 to 200 ° C., equipped with T-die) thermoplastic polyurethane (PU-1) obtained in (1) above Then, the film was extruded from a T-die onto a 30 ° C. cooling roll, cooled, and wound up to produce a keypad film having a thickness of 100 μm. Using the obtained keypad film, the logarithmic viscosity of the thermoplastic polyurethane contained therein, the tensile stress (M ₁₀₀ ) of the keypad film, and the heat resistance were measured by the methods described above. The results are shown in Table 1.

[Examples 2 to 5]
(1) Production of thermoplastic polyurethane (PU-2 to PU-5) Polymer polyol (POH-2 to POH-5), organic polyisocyanate (MDI) and chain extender (BD) are shown in Table 1 below. Thermoplastic polyurethanes (PU-2 to PU-5) were produced in the same manner as in Example 1 except that they were used in proportions. With respect to each of the obtained thermoplastic polyurethanes (PU-2 to PU-5), the melt viscosity and ASTM D hardness were measured by the methods described above. The results are shown in Table 1.
(2) Production of keypad film Using the thermoplastic polyurethane (PU-2 to PU-5) obtained in (1) above, a keypad film having a thickness of 100 μm was prepared in the same manner as in Example 1. Manufactured. Using the obtained keypad film, the logarithmic viscosity of the thermoplastic polyurethane contained therein, the tensile stress (M ₁₀₀ ) of the keypad film, and the heat resistance were measured by the methods described above. The results are shown in Table 1.

[Comparative Examples 1 to 4]
(1) Production of thermoplastic polyurethane (PU-6 to PU-9) Polymer polyol (POH-1, POH-2 or POH-4), organic polyisocyanate (MDI) and chain extender (BD) Thermoplastic polyurethanes (PU-6 to PU-9) were produced in the same manner as in Example 1 except that the proportions shown in Table 2 were used. With respect to each of the obtained thermoplastic polyurethanes (PU-6 to PU-9), the melt viscosity and ASTM D hardness were measured by the methods described above. The results are shown in Table 2.
(2) Production of keypad film Using the thermoplastic polyurethane (PU-6 to PU-9) obtained in (1) above, a 100 μm thick keypad film was prepared in the same manner as in Example 1. Manufactured. Using the obtained keypad film, the logarithmic viscosity of the thermoplastic polyurethane contained therein, the tensile stress (M ₁₀₀ ) of the keypad film, and the heat resistance were measured by the methods described above. The results are shown in Table 2.

[Comparative Example 5]
(1) Production of thermoplastic polyurethane (PU-10) Polymer polyol (POH-6), organic polyisocyanate (HDI) and chain extender (BD) are mixed at a molar ratio of POH-6: HDI: BD of 1. 0: 4.2: 3.2 (the content of the nitrogen atom derived from the isocyanate group is 5.9% by mass), and these two axes rotate in the coaxial direction so that the total supply amount is 78 g / min. Continuously fed to the front of the heating zone of a screw type extruder (single diameter 30 mmφ, L / D = 36; heating zone divided into three zones: front, center and rear), polymerization temperature of 190 ° C. Polyurethane formation reaction was carried out by continuous melt polymerization under the conditions. The obtained melt was continuously extruded into water as a strand, and then cut with a pelletizer to obtain pellets. The obtained pellets were dehumidified and dried at 60 ° C. for 4 hours to obtain thermoplastic polyurethane (PU-10). The melt viscosity and ASTM D hardness of the obtained thermoplastic polyurethane (PU-10) were measured by the methods described above. The results are shown in Table 2. Using the thermoplastic polyurethane (PU-10), a disk-shaped molded product (diameter: 120 mm, thickness: 2 mm) in the same manner as described above in the section of the ASTM D hardness measurement method for thermoplastic polyurethane. A hardness test using a type A durometer in accordance with JIS K 7311-1995 was conducted using a product obtained by superimposing three obtained disk-shaped molded articles.
(2) Production of Keypad Film A keypad film having a thickness of 100 μm was produced in the same manner as in Example 1 using the thermoplastic polyurethane (PU-10) obtained in (1) above. Using the obtained keypad film, the logarithmic viscosity of the thermoplastic polyurethane contained therein, the tensile stress (M ₁₀₀ ) of the keypad film, and the heat resistance were measured by the methods described above. The results are shown in Table 2.

As is clear from Tables 1 and 2, the keypad films of Examples 1 to 5 whose tensile stress (M ₁₀₀ ) satisfies the provisions of the present invention were obtained by hot air drying at 90 ° C. for 1 hour after application of the screen ink. However, the screen ink application part is not warped or contracted, and the smoothness is maintained, and it can be seen that the screen ink application part has excellent heat resistance required for a keypad film. On the other hand, the keypad films of Comparative Examples 1 to 5 whose tensile stress (M ₁₀₀ ) does not satisfy the provisions of the present invention were subjected to a number of tests by hot air drying treatment at 90 ° C. for 1 hour after application of the screen ink. In the strip, warping and shrinkage are observed in the screen ink application part, and it can be seen that it does not have the excellent heat resistance required for the keypad film.

According to the present invention, it is excellent in non-tackiness, handleability, heat resistance, and dimensional accuracy stability, and also warps, shrinks, etc. even by heat treatment applied particularly when an adhesive or printing ink is solidified or fixed. There is provided a keypad film that does not cause problems such as the above-mentioned defective phenomenon and film sticking. According to the keypad film of the present invention, when a key sheet is placed at a predetermined position of a final product such as a mobile phone, the key sheet is flattened manually, or a special device is required. It can solve the problem that the productivity of the final product is reduced and the problem that the yield is reduced due to the occurrence of many defective products that cannot be used as key sheets or keypads. Thinning can also be achieved. In addition, according to the keypad film of the present invention, a keypad and a key sheet that can retain the shape without using a reinforcing material such as a frame sheet are provided, thereby reducing the weight and size of the final product. In addition, the manufacturing process can be simplified.

Claims

Tensile stress at 100% elongation at 23 ° C. consisting of a thermoplastic polyurethane alone or a thermoplastic polyurethane composition mainly composed of the thermoplastic polyurethane obtained by reacting a polymer polyol, an organic polyisocyanate and a chain extender A film for a keypad having (M 100 ) of 18 MPa or more.
The keypad film according to claim 1, wherein the content of nitrogen atoms derived from isocyanate groups in the thermoplastic polyurethane is 4.5% by mass or more.
The keypad film according to claim 1 or 2, wherein the organic polyisocyanate mainly comprises 4,4'-diphenylmethane diisocyanate.
The keypad film according to any one of claims 1 to 3, wherein the chain extender mainly comprises 1,4-butanediol.
5. The keypad film according to claim 1, wherein the polymer polyol has a number average molecular weight of 500 to 8,000.
6. The keypad film according to claim 1, wherein the film has a thickness of 20 to 300 μm.
A keypad comprising at least a layer made of the keypad film according to any one of claims 1 to 6.
A key sheet having at least the keypad and keytop according to claim 7.