JP3827532B2 - Key sheet and manufacturing method thereof - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to the field of electrical equipment and the field of electronic equipment. More specifically, the present invention relates to a key sheet of a pushbutton switch used particularly in the electronic equipment field and the portable electronic terminal field.
[0002]
[Prior art]
Many devices require multiple switches, so-called pushbutton switches. Recently, the use of pushbutton switches has increased due to the widespread use of mobile phones. The push button switch used for this is mainly composed of a key sheet and a metal tact switch. In recent mobile phones, those having a mechanism using a metal tact switch with a short stroke are often used. This switch mechanism mainly includes a key sheet composed of a plurality of push buttons having a display portion, a metal tact switch, a case for storing these, and the like.
[0003]
Many of the switch mechanisms having such a configuration are, for example, as shown in FIG. That is, the key sheet is made of a transparent resin film 1 having a printed display on the back surface, a thermoplastic resin 2 that is filled by injection molding into a recess formed in the transparent resin film 1 and heat-sealed, and a silicon rubber sheet. It consists of the object 3. What is composed of the transparent resin film 1 and the thermoplastic resin 2 is said to be a key top 4. The key top 4 and the sheet-like material 3 are integrated with an adhesive to form a key sheet 5. Yes.
[0004]
A switch board 7 attached to a case or the like is provided below the key sheet 5. A metal tact switch 6 is provided on the switch board 7 and corresponds to the key sheet 5. Since recent mobile phones have a wide display screen and a compact size, a type in which a cover body is folded in two is widespread.
[0005]
This two-fold cellular phone has a disadvantage that it becomes thicker when folded, and it is desired to make it as thin as possible. Conventionally, the thickness of the case is reduced by increasing the strength of the case, or by thinning the case using a high-strength magnesium alloy or aluminum alloy, or by thinning the thermoplastic resin and sheet of the key sheet. Etc. are done. However, thinning is limited in strength due to the characteristics of the material used, and it is difficult to make it thinner by taking advantage of the conventional shape due to various constraints.
[0006]
[Problems to be solved by the invention]
As described above, there is a limit to making a conventional mobile phone thinner, and a solution for a new idea has been demanded. The present invention has been made based on such a technical background and has been researched and developed in view of conventional problems, and achieves the following objects.
An object of the present invention is to provide a key sheet in which the structure of the key sheet is thinned, and as a result, the cellular phone is thinned, and a manufacturing method thereof.
Another object of the present invention is to provide a key sheet that simplifies the structure of the key sheet and achieves cost reduction, and a method for manufacturing the key sheet.
[0007]
[Means for Solving the Problems]
The key sheet of the present invention is a key sheet used in a control panel having a plurality of push buttons, and a transparent resin film having a thickness of 40 μ to 150 μ printed on the surface, and after forming the transparent resin film In a key sheet shaped article made of PC which is a thermoplastic resin injected into a concave portion on the printing surface side, a urethane-based UV paint having a breaking elongation after curing of 15% or more and 80% or less is applied to the key sheet shaped article. A UV coating layer is provided by UV coating to a uniform thickness on the entire surface including the convex portion on the thermoplastic resin side having the convex portion. The UV coating referred to in the present invention refers to a type of coating that is cured by ultraviolet irradiation. The UV coating refers to a series of coating / irradiation processes in which ultraviolet rays are irradiated and cured after coating.
[0008]
The key sheet manufacturing method of the present invention is a key sheet manufacturing method used in a control panel having a plurality of push buttons, and includes a step of printing on a transparent resin film having a thickness of 40 μm to 150 μm, A step of injecting a PC, which is a thermoplastic resin, into a concave portion on the printing surface side of the transparent resin film formed and forming a convex portion at the center portion, and a urethane system having a breaking elongation after curing of 15% or more and 80% or less And a UV coating step for uniformly coating the entire surface including the convex portions on the thermoplastic resin side having the convex portions .
[0009]
Next, the key sheet of the present invention will be described with reference to the example of the key sheet shown in FIG. The surface of the key sheet shaped object 11, that is, the pressing part 12 as a push button is composed of the film 13 as described above. This film 13 is a pre-printed transparent one. After the film 13 is formed into a push button shape, a thermoplastic resin 15 is injected into the concave portion 14 on the printed surface side to constitute a key top.
[0010]
A push rod portion 16 (convex portion) that contacts the metal tact switch 25 is formed at the center of the thermoplastic resin 15. Further, in the present invention, UV coating is performed over the entire surface including the push rod portion 16 on the thermoplastic resin 15 side of the key top composed of the film 13 and the thermoplastic resin 15. This UV coating layer 17 uses a UV curable resin that is relatively stretched (elastic and soft).
[0011]
Since this UV coating layer 17 also covers the push rod portion 16, it is possible to reduce and protect the impact on the mating metal tact switch that comes into contact. This will be described in more detail in comparison with a key sheet without UV coating. FIG. 3 shows a configuration in which UV coating is not performed, in which a thermoplastic resin 22 is injected into a molded film 21, and a push rod portion 23 is provided at the center.
[0012]
Although the key sheet 24 is partly used conventionally, it has a configuration that can be said to be only a “mere key top” when viewed from the inventors. The push rod portion 23 of the thermoplastic resin 22 not subjected to UV coating is configured to push the metal tact switch 25 provided on the switch substrate 26. In this configuration, since the configuration itself is very simple and the manufacturing cost is low, the cost can be reduced.
[0013]
However, since the push bar portion 23 is made of resin, specifically, made of PC (polycarbonate), if the contact with the metal tact switch 25 is repeated, the metal tact switch 25 is cracked or broken. May occur. This is because, in particular, the push bar portion 23 is in a state where the thermoplastic resin has been injected, so that it may not hit the metal tact switch 25 evenly due to a delicate design shape.
[0014]
It is easily affected by how the user pushes, and this configuration has many concerns and is a problem. For this reason, in order to dispel this concern, in products for Japan, the metal tact switch 25 is pressed against the metal tact switch 25 via silicone rubber or thermoplastic elastomer, or thin at the bottom of the push rod portion 23. Currently, silicone rubber sheets are laid to prevent impacts.
[0015]
The present invention is a result of research and development that solves such conventional problems and takes advantage of the conventional advantages. As described above, the UV coating including the push rod portion, specifically, the cured resin is used. It was decided to apply with a UV paint having a breaking elongation of 15% to 80%. As a result, since the push rod portion is coated with a flexible resin, there is no possibility of damaging the metal tact switch, and the conventional problems are solved.
[0016]
Next, the method for manufacturing the key sheet of the present invention will be specifically described. The film used is made of polyester such as polyethylene terephthalate resin (hereinafter referred to as PET), polyethylene naphthalate resin (hereinafter referred to as PEN), polycarbonate resin (hereinafter referred to as PC), or polybutylene terephthalate resin (hereinafter referred to as PBT) to PC. Can be used that is made of a compound mixed with a small amount.
[0017]
More specifically, since a film having an average thickness of 50 μm to 125 μm made of the above-described material is mass-produced for manufacturing a key sheet, it can be easily obtained as a commercial product. Screen printing is advantageous and advantageous for printing on the film. The ink to be used varies depending on the film material, and for a PC film, an ink using a PC polymer as a base polymer is preferable.
[0018]
In addition, it is preferable to use a two-component curable ink combined with a curing agent for a polyester film that has a generally weak adhesive force with the ink. This printing is performed on a film in advance. The selection of this ink is important. After the film is drawn, the thermoplastic resin is injected into the recess on the printing surface side of the film, so that the printed layer is securely fixed to the film and the ink is dissolved in the molten resin. This is because it is required that the ink is not removed and that the ink is not washed away.
[0019]
As described above, the film is drawn after printing. There are various drawing methods such as vacuum forming, pressure forming, press forming, and hot press forming. However, it is not limited to this, and other molding methods such as injection molding and roll molding may be used. Drawing is performed so that the printed surface is concave.
[0020]
In each molding method, empirical operations are required for the preheating temperature of the film, the shape and dimensions of the mold, the mold temperature, the molding pressure, the molding speed, and the like. Subsequently, the recessed portion of the film after drawing is placed on the upper side and inserted into an open injection mold, and then the mold is closed and a thermoplastic resin is injected through a gate installed on the recessed side.
[0021]
As the thermoplastic resin, PC and transparent ABS are common and preferable. More specifically, a general injection molding PC having a molecular weight of 18000 or more is preferable. An ultra-high fluid type PC, which has high fluidity and is unlikely to cause ink flow, has a low molecular weight and is brittle. When this is applied to the push rod portion 16 of the key sheet shown in FIG. 2, the push rod portion 16 is easily broken, which is not preferable in the present invention. A key sheet shaped article 11 is obtained by such molding.
[0022]
The key sheet shaped article 11 is coated on the thermoplastic resin 15 side using a UV paint having a breaking elongation of 15% or more and 80% or less after curing, and UV-cured by irradiating with ultraviolet rays. And As physical properties of the UV paint, those other than elongation are preferably those having a tensile strength of 10 MPa or more and a Young's modulus of 20 MPa or more. In consideration of good adhesion to PC, urethane-based UV paint is preferable. For the application, it is preferable to use a spindle type coating apparatus because it gives a uniform application thickness, and the application thickness is more preferably 10 μm or more, preferably 15 μm or more after curing.
[0023]
DETAILED DESCRIPTION OF THE INVENTION
In describing an embodiment of the present invention, an outline of a cellular phone will be described as an example of a usage target of the present invention. FIG. 4 is a perspective view of a portable telephone equipped with the key sheet of the present invention. The portable telephone 31 is constituted by a telephone body 32 made of synthetic resin, and has a two-fold configuration. In the telephone body 32, an electronic device such as an IC for realizing a telephone function is housed.
[0024]
The telephone body 32 is divided into two parts by a split surface 36 at the center in the thickness direction. A case cover 33 is disposed on the upper surface of the telephone body 32, and a rear surface body 35 is disposed and fixed on the rear surface. The case cover 33 fulfills both functions of the control panel and the telephone body 32, and a plurality of push buttons 34 are arranged to constitute a key group 37.
[0025]
The case cover 33 and the back main body 35 are integrally fixed by a known fixing means such as a screw or a notch. The case cover 33 is provided with a push button 34 indicated by a key sheet produced by a method described later. The lid portion 38 is provided with a liquid crystal display device 39 and the like. When the lid portion 38 is folded through the hinge 40, the key group 37 is covered by the lid portion 38 and protected together with the liquid crystal display device 39 and the like, so that it can be stored compactly in a pocket such as a jacket. . The problem is to make the thickness when the lid portion 38 and the main body 32 are combined as thin as possible.
[0026]
Next, details of the key sheet of the present invention will be described. After the printed film is formed, a thermoplastic resin is injected and integrally formed to form a key top shape. That is, a key top shape that becomes a key top prototype with a thermoplastic resin is first molded by injection molding, and after molding, UV coating is applied to the thermoplastic resin side of the key top as described above. Examples will be described in the following examples.
[0027]
[Example]
The PEN film 13 having a thickness of 50 μm was printed with the display portion 18 such as the numbers shown in FIG. FIG. 5 shows the back side of the printed film 13. In other words, numbers are printed with two-component curable black ink ("MP4 Black" manufactured by Seiko Advance) and air-dried, then solid-printed with semi-transparent silver metallic ink ("MP4 semi-transparent silver metallic") and air-dried The solid ink was printed with a transparent ink (“MP4 Medium” manufactured by the company) and baked at 110 ° C. for 3 hours.
[0028]
Drawing was carried out with a hot press molding machine with the print side down. The film was previously exposed to hot air at 80 ° C. for 15 seconds and then placed between molds maintained at 90 ° C., and press-molded with a drawing depth of 1 mm at a deep location. Subsequently, the drawn film was inserted into a mold maintained at 80 ° C., and PC (“Panlite L-1225L” manufactured by Teijin Chemicals Ltd.) was injected at an injection temperature of 310 ° C.
[0029]
As a result, a key sheet shaped article 11 which becomes a prototype of the key sheet as shown in FIG. 2 was obtained. The detailed shape of one push button portion is shown in FIG. The formed film 13 constituting the push button switch has an elliptical shape with a substantially diameter of 8 mm, and the protruding dimension of the push rod portion 16 is 0.3 mm. This is placed on the spindle-type coating line upside down, and UV paint ("Desolite P1010-1" manufactured by JSR) adjusted to non-filler specifications while rotating is spray-coated with UV paint obtained by diluting the paint viscosity with cyclohexanone. .
[0030]
The UV coating layer 17 was formed by passing through a mercury lamp portion irradiated with ultraviolet rays for several seconds and allowing it to pass through for several seconds after passing through the 60 ° C. environment for 10 minutes and the 80 ° C. environment for 5 minutes. The cured product was taken from the line, and the UV coating film thickness of the UV coating layer 17 was measured and found to be 15 to 17 μm. In addition, when the physical properties of the 30 μm-thick UV ink obtained by separately coating and peeling on a silicone rubber sheet were measured using various test machines, the elongation at break was 30%, the tensile strength was 12 MPa, and the Young's modulus was 40 MPa. there were.
[0031]
A keystroke test was carried out by assembling the key sheet with the UV coating obtained above and the key sheet with no UV coating only into the case and the switch substrate. The keys were repeatedly pressed at a speed of 2.5 times / second at 400 g and disassembled and observed every 200,000 times. As a result, between the 400,000 times and 800,000 times, three accidents occurred on the key sheet side that was not UV-painted. The metal tact switch 25 has cracks 27, and the click feeling is lowered to be turned on with a weak press, and a part 28 of the push rod portion 23 on the key sheet side is crushed as shown in FIG. Thus, when the comparison was made under the same conditions, troubles occurred in the key sheet that had not been subjected to UV coating, and thus the effectiveness of UV coating was confirmed.
[0032]
【The invention's effect】
According to the present invention, since the printed film is drawn and then PC-injected and then UV-coated, the manufacturing method is improved while maintaining high functionality, and the production cost of the key sheet is reduced. I went down. In addition, since the push rod part of the key sheet shaped material is covered with a soft resin that has been three-dimensionally cured, when the pushbutton switch is pressed, the soft resin is slightly deformed and the stress concentration on the metal part is suppressed and destroyed. The risk of doing so is gone. Further, when the pushbutton switch is released, the soft resin that is three-dimensionally cured tends to return to its original shape, so that deformation is small. In addition, the manufacturing method of the present invention has been reduced in production steps and simplified as compared with the conventional method, so that it has achieved high productivity at low cost and has become an efficient manufacturing method.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view showing a conventional pushbutton switch configuration.
FIG. 2 is a cross-sectional view showing a key sheet configuration of the present invention.
FIG. 3 is a cross-sectional view showing another example of a conventional push button switch configuration.
FIG. 4 is a perspective view of a two-fold type mobile phone to which the present invention is applied.
FIG. 5 is a partial view showing the back side of a number printed film.
FIG. 6 is a sectional view showing a single pushbutton switch configuration including a key sheet of the present invention.
FIG. 7 is a cross-sectional view showing a single pushbutton switch configuration showing that it has been damaged by a conventional key sheet.
[Explanation of symbols]
11 ... Key sheet shape
13 ... Film
14 ... recess
15 ... Thermoplastic resin
16 ... Push rod 17 ... UV coating layer

Claims (2)

A key sheet used in a control panel having a plurality of push buttons,
A transparent resin film having a thickness of 40 μm to 150 μm printed on the surface;
In the key sheet shape product consisting of PC which is a thermoplastic resin injected into the concave portion on the printing surface side after molding this transparent resin film,
UV coating of urethane-based UV paint having a breaking elongation after curing of 15% or more and 80% or less to a uniform thickness over the entire surface including the convex part on the thermoplastic resin side having the convex part of the key sheet shape. A key sheet provided with a UV paint layer. A method of manufacturing a key sheet used in a control panel having a plurality of push buttons,
Printing on a transparent resin film having a thickness of 40 μm to 150 μm;
A step of injecting a PC, which is a thermoplastic resin, into a concave portion on the printing surface side of the squeezed transparent resin film and forming a convex portion in the center portion;
And sequentially applying a urethane-based UV coating having a breaking elongation after curing of 15% or more and 80% or less to a uniform thickness over the entire surface including the convex portion on the thermoplastic resin side having the convex portion. A method for manufacturing a key sheet.

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