JP2003272466A - Spring member made of stainless steel foil and switch - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a spring member made of stainless steel foil having a low contact electric resistance value even if a silver and gold plated layer is not applied to its surface and having high durability and to provide a switch provided with this spring member. <P>SOLUTION: This spring member made of stainless steel foil is constituted in such a way that stainless steel foil is rolled to a thickness of 30 to 70 μm by cold rolling and has a dull surface on its surface and surface roughness Rz of the dull surface is 0.3 to 1.0 μm. Furthermore, when surface roughness Rz in the direction of rolling of the spring member is A and surface roughness Rz in the direction orthogonal to the direction of rolling is B, A/B is 0.8 to 1.1 in this spring member made of stainless steel foil and the switch is provided with the spring member. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a spring material made of stainless steel foil, which is one of the components of various switches, and a switch provided with this spring material.

[0002]

2. Description of the Related Art In recent years, various electronic devices have been provided with push button switches for turning on and off electricity, or switches (operation keys) for inputting data. A typical electronic device is a mobile phone. As one of the components constituting these switches, a spring material made of austenitic stainless steel such as SUS301 and SUS304 is used. For example, in an operation switch (dome switch) of a mobile phone, a spring material made of stainless steel foil having a thickness of about 40 to 70 μm is formed into a gentle dome shape by press working in order to make the feel of the operation comfortable. Wood is used.

FIG. 7 shows an example of the structure of a dome switch which has been conventionally used. In FIG. 7, the circuit board 1 is provided with a first fixed contact 2 and a second fixed contact 3. Above the fixed contacts 2 and 3, a spring member 4 formed of a thin plate in a gentle arc shape is installed, and the second fixed contact 3 and the spring member 4 are fixed in a contact state. A synthetic resin sheet member 5 or the like is installed above the arcuate spring member 4 via a spacer 6 in order to prevent dust or the like from entering the inside of the switch. A push button (operation key) 7 is installed on the upper portion of the sheet-shaped member 5. In such a dome switch, when the push button 7 is pushed, the arcuate portion 4a of the arcuate spring member 4 is pushed down, and the arcuate spring member 4 and the first fixed contact 2 come into contact with each other. Then, a current flows between the first fixed contact 2 and the second fixed contact 3. Then, when the push of the push button 7 is released, the arc portion 4a returns to the original position, and the conduction between the fixed contacts 2 and 3 is cut off. Conventionally, as the material of the arc-shaped spring member 4, austenitic stainless steels SUS301 and SUS304 have been used.

In the spring material made of stainless steel foil used for these various switches, the durability which can endure the operation of hundreds of thousands to millions of times, and the reliable contact even with a light pressing force, so-called soft touch. It is required that the contact electric resistance value of the spring member portion that contacts the contact portion so that the current between them can be turned on and off as low as possible and stable, and that the manufacturing cost is low.

For improving durability, conventionally, austenitic stainless steel sheets are cold-rolled by a multi-stage rolling mill through a plurality of rolling passes in which the reduction ratio and the like are appropriately set to work-harden the spring material. The strength (hardness and tensile strength) is being improved. Many proposals for this measure have already been proposed.

For example, JP-A-9-192712 discloses a method for manufacturing a high hardness austenitic stainless steel sheet which is rolled from an austenitic stainless steel sheet to a target thickness to give a predetermined target hardness. The correlation between the rolling temperature, the rolling reduction, and the hardness of the austenitic stainless steel to be rolled is calculated in advance, and the number of rolling passes and the target passes are set so that the target thickness and hardness are achieved in the final rolling pass based on the correlation. It is disclosed that the rolling temperature, the rolling reduction and the hardness after each pass are determined for rolling.
Further, in the publication, a SUS301 steel plate having a plate thickness of 0.6 mm is rolled by a plurality of rolling passes so as to have a plate thickness of 0.3 mm and the target hardness is set to Hv400, 460, 520. By appropriately setting these rolling temperature and reduction rate from the correlation between the reduction rate and hardness,
It is described that a steel plate satisfying the target hardness was obtained.

In various switches, in order to reliably turn on / off the energization of the contact portions with a light pressing force, the contact between the contact portions has not conventionally been a surface contact or a line contact, but a contact surface of the contact surface. It is said that it is desirable to provide fine concavo-convex to the point contact (Japanese Patent Laid-Open No. 6-223672).
(See Japanese Patent Publication). The reason for this is that the contact of the contact part becomes a point contact due to these fine irregularities, the contact pressure per unit area of the contact part increases, and it becomes possible to electrically energize with a smaller pressing force, and This is because the contact electric resistance value can also be stabilized.

As a method for imparting a fine uneven surface (dull surface), that is, an appropriate surface roughness to the surface of a cold rolled steel plate or the like, the following method has been conventionally adopted. 1) A method of transferring the fine irregularities on the surface of the work roll to a steel plate by using a so-called dull roll having an appropriate surface roughness of the work roll. This method is widely used for rolling stainless steel sheets having excellent antiglare properties, rolling steel sheets for shadow masks, and the like.

2) During cold rolling, rolling oil, which is so-called oil pit, interposed between the surface of the work roll and the surface of the steel sheet as the material to be rolled is positively utilized to form fine irregularities on the surface of the steel sheet. (See Japanese Patent Application Laid-Open Nos. 8-103801 and 2001-58203).

In order to improve corrosion resistance and conductivity (to lower the contact electric resistance value) of ordinary stainless steel spring materials, especially switch spring materials,
A cold-rolled stainless steel plate or steel foil is provided with a nickel plating layer having a thickness of 1 μm or less as an undercoat, and a silver or gold plating layer is formed on the undercoat layer by electroplating.

[0011]

In the method of forming fine unevenness on the surface of a steel sheet or steel foil by cold rolling using a dull roll, the unevenness (surface roughness) of the surface of the rolled material is directional. Is likely to occur. That is, a difference in surface roughness between the rolling direction and the direction perpendicular to the rolling direction is likely to occur. The reason for this is
The surface of the work roll is made dull skin by polishing, shot blasting, electric discharge machining, etc., but this method cannot process the roll surface to a dull skin with uniform and fine irregularities, and This is because the surface roughness of the rolled material, which is directly transferred to the material to be rolled, has directionality. That is, in the material to be rolled that has been rolled using the dull roll, streaks are likely to be formed in the rolling direction.
Therefore, the surface roughness in the direction perpendicular to the rolling direction tends to be larger than the surface roughness in the rolling direction. If a stainless steel plate or steel foil with directional surface roughness is used as the spring material for switches, the contact electric resistance value of the contact part will become unstable and the durability of the spring material will be affected. Become.

Further, as described above, in the spring material made of stainless steel, particularly the spring material for switches, in order to improve corrosion resistance and conductivity, a coil material made of cold rolled coiled stainless steel foil is used. An electroplating layer of nickel, silver, gold, etc. is applied. However, even if the cold-rolled steel sheet or steel foil is not subjected to such electroplating, the electroplating step can be omitted if the conductivity is almost the same as that of the stainless steel spring material provided with the plated layer. However, the cost reduction effect is great.

Therefore, an object of the present invention is to provide a stainless steel plate,
In particular, the surface of ultra-thin plate-shaped steel foil has uniform surface roughness without directivity, and the contact electric resistance value is small and stable even without forming an electroplating layer of nickel, silver, gold, etc. Another object of the present invention is to provide various spring materials made of stainless steel foil for switches, which are low in manufacturing cost. The stainless steel foil spring material of the present invention is an ultrathin spring material having a thickness of 30 to 70 μm, and is particularly effective in reducing the manufacturing cost of various switches such as dome switches.

[0014]

The present invention relates to a stainless steel foil having a dull skin surface having a thickness of 30 to 70 μm, which is rolled by cold rolling and has a surface roughness Rz of this dull skin surface. A spring material made of stainless steel foil having a thickness of 0.3 to 1.0 μm. Furthermore, when the surface roughness Rz in the rolling direction is A and the surface roughness Rz in the direction perpendicular to the rolling direction is B, the present invention is made of a stainless steel foil having A / B of 0.8 to 1.1. It is a spring material.

Further, according to the present invention, when a current of 10 mA and a reciprocating contact load of 0 to 100 gf are applied to the dull skin surface, a stainless steel foil having a contact electric resistance value of 15 mΩ or less at a contact load of 50 to 100 gf. It is a spring material.

Further, the present invention is a switch provided with the above-mentioned stainless steel foil spring material. The switch of the present invention is a push button switch, a dome switch, a sheet-shaped metal contact, a multifunction input switch used in a mobile phone, or the like.

In the present invention, the dull surface formed on the rolled surface of the stainless steel foil spring material is formed by an oil pit during cold rolling using a multi-stage rolling mill. Further, it is desirable to use SUS301 as the stainless steel foil spring material of the present invention.
It is also possible to use a stainless steel foil obtained by cold rolling an austenitic stainless steel sheet such as S304. The surface hardness of the stainless steel foil spring material of the present invention is H.
It is preferably v450-600.

[0018]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below. The spring material made of stainless steel foil of the present invention can be manufactured from austenitic stainless steel sheets such as coiled SUS301, 304 by a multi-stage rolling mill having 12 or 20 stages and a plurality of rolling passes. That is,
By appropriately setting the reduction rate and the like for each of a plurality of rolling passes, work hardening is induced in the stainless steel foil to impart strength as a spring material. Furthermore, in each rolling pass, by interposing a suitable rolling oil between the work roll and the steel foil to be rolled, the so-called oil pit acts so that the rolled surface has no directionality and a uniform and fine dull. A stainless steel foil having a skin surface can be obtained.

In the stainless steel foil spring material of the present invention, it is desirable that the surface roughness Rz (ten-point average roughness) of the uniform and fine dull skin surface is at least 0.3 to 1.0 μm. The reason for this is that if the surface roughness Rz is less than 0.3 μm, the contact between the contacts becomes a surface contact when used as a spring material for various switches without forming a plating layer, and a contact pressure per unit area is increased. Is increased, and a comfortable click feeling cannot be obtained. Further, the surface roughness Rz is 1.
This is because if it is larger than 0 μm, dust is likely to enter the uneven portion for a long period of time, and corrosion and cracks are likely to occur from the uneven portion, resulting in a decrease in durability.

The stainless steel foil spring material of the present invention has a thickness of 3 by cold rolling using a multi-stage rolling mill.
It is desirable to set it to 0 to 70 μm. The reason is that when used as a spring material for dome switches, the thickness is 70
This is because if the thickness exceeds μm, a soft touch makes it impossible to perform a comfortable input operation, and if the thickness is less than 30 μm, the strength and durability of the spring material deteriorate.

In the stainless steel foil spring material of the present invention, when the surface roughness Rz in the rolling direction is A and the surface roughness Rz in the direction perpendicular to the rolling direction is B, A / B is 0.
The reason for limiting to 8 to 1.1 is as follows. When stainless steel foil is used as a spring material for switches, if the surface roughness of this steel foil is not uniform and has directionality, the contact pressure for operating each switch, that is, the contact per unit area between contacts There will be variations in pressure. In a mobile phone having a large number of operation switches, it is necessary to surely perform an input operation with a soft touch of a fingertip. Therefore, A / B is 0.8-
1.1, and more preferably 0.9 to 1.1. However, since the surface roughness Rz in the direction perpendicular to the rolling direction tends to be larger than the surface roughness Rz in the rolling direction,
It is necessary to set A / B to about 0.8 to 1.1 so that the surface roughness Rz is extremely non-directional.
Further, the coiled stainless steel foil spring material is cut into a size (piece) that can be used as a switch spring material by pressing. At this time, if the surface roughness is directional, it is necessary to consider the rolling direction of the coiled stainless steel foil that is cut during press working.

On the surface of the stainless steel foil, the oil pits during cold rolling are positively utilized to form a fine dull surface having no directionality and a surface roughness Rz of 0.3 to 1.0 μm. In order to do so, it is advisable to use a reverse type multi-high rolling mill and adopt the following rolling method. 1) A plurality of rolling passes (about 8 to 14 passes) are adopted, and a work roll having a fine surface roughness Ra is used toward the finishing rolling pass. The surface roughness Ra of the work roll used for the final finish rolling is 0.01 to 0.06 μ.
It is preferable to use a mirror-finished roll of m. 2) Rolling speed is 150 to 250 m / min, preferably 2
It is good to set it to 00-250 m / min. Then, when the finish rolling is completed, the rolled steel foil coil is degreased in the cleaning step, and then annealed to remove rolling distortion.

[0023]

EXAMPLES Example 1 Examples of the present invention will be described below. SUS30 having a thickness of 54 to 92 μm before rolling
For 7 types of stainless steel coils consisting of 1 (test numbers 1 to 7 shown in Table 1), using a 12-high rolling mill, 8
After 14 to 14 rolling passes, a steel foil having a thickness of 30 to 70 μm having a fine dull surface (fine uneven surface) on the surface of the material to be rolled was rolled by an oil pit. Then, the surface roughness Rz of the rolled steel foil in the rolling direction (direction a) and the surface roughness Rz in the direction perpendicular to the rolling direction (direction b) were measured.
In this rolling test, the work rolls were changed 4 to 5 times during the entire rolling pass. As for the surface roughness of the work roll used for this rolling, a rough roll having a surface roughness Ra of about 0.8 to 1 μm is used in the first and second passes, and the surface roughness Ra is set in the finishing rolling pass. 0.01-0.
A high speed work roll of 08 μm was used. Further, the rolling speed of each rolling pass is within a range of 150 to 250 m / min, and the rolling speed of the final finishing rolling pass is 200 to 250.
m / min. The rolling oil used is a mineral oil rolling oil. Thickness before and after rolling of the stainless steel foil used in this rolling test, number of rolling passes, surface roughness Rz (A) in the rolling direction (direction a) of the rolled steel foil, direction perpendicular to the rolling direction Table 1 shows the surface roughness Rz (B) in the (b direction) and its ratio (A / B). In addition, in order to compare the test numbers 8 and 9 shown in Table 1 with the test numbers 1 to 7, the surface roughness Ra was 0.10 μm and 0.20 μm, respectively, by polishing the surface of the work roll in finish rolling. An example of rolling in which this polishing grain is transferred to a steel foil using a dull roll is shown.

From the results of test numbers 1 to 7 shown in Table 1,
The final rolling pass has a work roll surface roughness Ra of 0.0.
Set to a very smooth mirror surface state of 1 to 0.06 μm, 2
When finish rolling is performed at a rolling speed of 0 to 250 m / min, the surface roughness Rz is 0.3 to 1.0 due to the oil pit.
It was found that a stainless steel foil having a dull surface of about μm can be obtained. FIG. 2 (a) shows a micrograph (magnification: 200) of the surface of the rolled stainless steel foil when rolled under the conditions shown in test number 2. By rolling under the condition of test number 2 shown in FIG. 2 (a), it was possible to obtain a uniform dull surface with no directionality on the surface of the material to be rolled. In contrast, FIG. 2B shows a micrograph (magnification: 200) of the surface of the rolled stainless steel foil when rolled under the condition of test number 9 using a dull roll. As shown in FIG. 2 (b), when a work roll is rolled using a dull roll having coarse polishing, a streak pattern is easily transferred to the material to be rolled in the rolling direction. Similarly, a striped pattern was also transferred in the rolling direction on the steel foil rolled in test number 8.

[0025]

[Table 1]

Example 2 The stainless steel foil coil rolled in Example 1 was washed in a washing process, and subsequently at a temperature of 410.
Strain relief annealing was performed at ˜420 ° C. Then, in a state in which the steel foil is not plated, the contact electric resistance value in the rolling direction (a direction) of the steel foil and the direction (b direction) perpendicular to the rolling direction is measured by a contact electric resistance meter (Yamazaki Co., Ltd.). It was measured using a precision machine research laboratory CRS-113-AU type), and the relationship between the surface roughness Rz of the steel foil and the contact electric resistance value was investigated. In addition, the measurement of the contact electric resistance value was performed by making a test piece (planar) of 10 mm × 10 mm in length and width from annealed steel foil, and reciprocating it while applying a contact load of 0 to 100 gf in a linear distance of 1.04 mm. In other words, the contact electric resistance value when a reciprocating contact load was applied was measured. In addition,
The applied current value at the time of measurement is 10 mA, and the moving speed of the test piece is 1.
mm / min, the probe used the pure gold wire. FIG. 1 shows a contact load region where the contact electric resistance value is stable at 15 mΩ or less in this measurement.

The following was found from Example 2. 1) As shown in test numbers 1 to 4 in FIG. 1, surface roughness Rz of rolled stainless steel foil in the rolling direction (direction a).
When the ratio of (A) and the surface roughness Rz (B) in the direction (b direction) perpendicular to the rolling direction, A / B is in the range of 0.8 to 1.1, the contact load is 50 to 100 gf. In the range, a stable contact resistance value with a contact electric resistance value of 15 mΩ or less can be obtained. Especially test number 2 with A / B value of 0.98
, The contact load is 3 even if the a and b directions are taken into consideration.
A stable contact resistance value of 15 mΩ or less was obtained in a wide range of 3 to 100 gf. 2) In the test numbers 8 and 9 rolled using the dull roll, since the directionality is generated in the surface roughness Rz of the rolled steel foil, the contact load region where the contact electric resistance value is stable at 15 mΩ or less is It became extremely narrow. That is, considering the a and b directions, in the test number 8, the contact load is 8
The contact electric resistance value was 15 mΩ or less in the narrow region of 2 to 100 gf and the test number 9 of 83 to 100 gf. 3) Compared with test numbers 1 to 4, test numbers 5 to 7,
The reason why the area of the contact load where the contact electric resistance value is stable at 15 mΩ or less is narrowed is that the surface roughness Rz of the rolled steel foil is a fine dull skin surface outside the range of 0.3 to 1.0 μm, or It is speculated that the contact electric resistance value became unstable due to the formation of the rough dull skin surface.

FIGS. 3 (a) and 3 (b) are diagrams showing the results of measuring the contact electric resistance value for the test number 3 which is the example of the present invention shown in FIG. 1, and also FIGS. 5 (a) and 5 (b). (B)
The diagram of the result of having measured the contact electric resistance value about the test number 6 which is a comparative example is shown in FIG. As is clear from FIGS. 3 (a) and 3 (b), in the test number 3 which is an example of the present invention, the rolling load is 15 mΩ or less in the region where the contact load is 50 to 100 gf in the direction perpendicular to the rolling direction. 30 to 10
A contact electric resistance value of 20 mΩ or less was obtained in a wide region of 0 gf. On the other hand, in the test number 6 which is the comparative example shown in FIGS. 5A and 5B, the variation in the contact electric resistance value in the direction perpendicular to the rolling direction was large.

(Example 3) The test piece whose contact electric resistance value was measured in Example 2 was wrapped in neutral paper and stored in a room at room temperature of 25 to 28 ° C and humidity of 50 to 70% for about 30 days, and then again. The contact electric resistance value was measured, and it was confirmed whether the contact electric resistance value changed with time. The method of measuring the contact electric resistance value is the same as in the second embodiment.

An example of the measurement result of the contact electric resistance value in Example 3 is shown in FIGS. 4 and 6. 4 (a) and 4
(B) is the contact resistance of the steel foil shown in test number 3 which is the example of the present invention shown in FIG. 1, and FIG. 6 (a) and 6 (b) is the contact electricity of the steel foil shown in test number 6 which is also the comparative example. It is a diagram which shows the measurement result of resistance value. As is clear from FIGS. 3 to 6,
The stainless steel foil spring material of the present invention did not show a large change in the contact electric resistance value even after 30 days. On the other hand, in Test No. 6 as a comparative example, as shown in FIG. 6, an extreme decrease in the contact electric resistance value and a variation in the contact electric resistance value due to the contact load were confirmed.

Example 4 With respect to SUS301 stainless steel foil, after forming a nickel plating layer as a base,
A gold plating layer having a thickness of 0.08 μm was formed, and
The contact electric resistance value was measured by the same procedure. The contact electric resistance value at this time is 2 to 5 when the contact load is 10 to 100 gf.
It was mΩ. Similarly, a silver plating layer having a thickness of 0.61 μm was formed on the nickel plating layer as a base, and the contact electric resistance value was measured. The contact electric resistance value at this time was 5 to 10 mΩ at a contact load of 10 to 100 gf.

From the results of the above examples, the contact electric resistance value of the stainless steel foil spring material of the present invention is inferior to that of the stainless steel foil spring material provided with the silver plating layer, Even if a plating layer of nickel, silver, gold or the like is not provided, the contact electric resistance value can be stabilized at an extremely low value of 15 mΩ or less in a low contact load region of 50 to 100 gf, and changes with time. It can be said that the decrease in the contact electric resistance value due to is small. Therefore, the spring material made of stainless steel foil according to the present invention is widely used in various switch spring materials such as push button switches, dome switches, and mobile phones even if they are not plated with gold or silver. It can be used very effectively as a function input switch.

In order to use the stainless steel foil spring material of the present invention as a spring material for various dome switches, the steel foil spring material (coil shape) is pressed into an arc-shaped spring material as shown in FIG. 4, and cut into an appropriate size to obtain a switch spring material. Then, the switch spring material is supplied to the assembly process of the dome switch or the electronic device and assembled into the switch or the electronic device.

In the above description of the embodiments of the present invention, an example in which the present invention is applied to SUS301 which is austenitic stainless steel has been described, but the present invention can also be applied to SUS304.

[0035]

The present invention described above has the following effects. 1) The contact electric resistance value is extremely low, and the contact electric resistance value is stable in the low load region, so it is possible to perform stable on / off of current by soft touch, and for various durable switches. A spring material can be provided. 2) A spring material for a switch having a low contact electric resistance value can be provided without forming an electroplating layer of nickel, silver, gold or the like on the surface. Therefore, the manufacturing cost can be reduced by 20 to 30% as compared with the conventional spring material for switches plated with nickel, silver, and gold, which can contribute to the provision of various inexpensive switches. .

[Brief description of drawings]

FIG. 1 is a diagram for explaining a relationship between a surface roughness Rz and a contact electric resistance value in a rolling direction of a stainless steel foil spring material and a direction perpendicular to the rolling direction.

2A and 2B are microscopic photographs of a dull skin surface of a spring material made of a stainless steel foil, FIG. 2A is an example of the present invention, and FIG. 2B is a photograph showing a state when dull roll is used.

FIG. 3 is a diagram when a relationship between a contact electric resistance value and a contact load is measured for test number 3 which is an example of the present invention shown in FIG. 1, and (a) is a diagram when measured in a rolling direction. , (B) are diagrams when measured in a direction perpendicular to the rolling direction.

FIG. 4 is a diagram when the relationship between the contact electric resistance value and the contact load after 30 days has been measured for the spring material made of stainless steel foil of test number 3 shown in FIG. 3, (a) is the rolling direction And (b) is a diagram when measured in a direction perpendicular to the rolling direction.

5 is a diagram when a relationship between a contact load and a contact electric resistance value is measured for test number 6 which is a comparative example shown in FIG. 1, and (a) is a diagram when measured in a rolling direction,
(B) is a diagram when measured in a direction perpendicular to the rolling direction.

FIG. 6 is a diagram when the relationship between the contact electric resistance value and the contact load after 30 days has been measured for the spring material made of stainless steel foil of test number 6 shown in FIG. 5, (a) is the rolling direction And (b) is a diagram when measured in a direction perpendicular to the rolling direction.

FIG. 7 is a cross-sectional view for explaining the configuration of a dome switch.

[Explanation of symbols]

1: Circuit board 2: First fixed contact 3: Second fixed contact 4: Arc spring material 7: Push button

Claims (4)

[Claims] 1. A thickness of 30 to 70 μm obtained by cold rolling.
A stainless steel foil which is rolled to m and has a dull surface on its surface, wherein the dull surface has a surface roughness Rz of 0.3 to
A spring material made of stainless steel foil having a thickness of 1.0 μm. 2. The surface roughness Rz of the dull surface in the rolling direction.
Is A and the surface roughness Rz in the direction perpendicular to the rolling direction is B, A / B is 0.8 to 1.1, and the stainless steel foil spring according to claim 1. Material. 3. An applied current of 10 mA on the dull skin surface, 0
When a reciprocating contact load of up to 100 gf is applied, the contact electric resistance value is 15 m when the contact load is 50 to 100 gf.
Ω or less, Claim 1 or Claim 2 characterized by the above-mentioned.
Spring material made of stainless steel foil described in. 4. A switch comprising the stainless steel foil spring material according to any one of claims 1 to 3.