JPH02263877A - Electrically conductive printing paste - Google Patents

Abstract

PURPOSE:To obtain an electrically conductive printing paste capable of keeping stable electrical conductivity and electrical contact over a long period by mixing a specific fine powder of a fluororesin to an electrically conductive printing paste containing a resin binder, electrically conductive powder and a solvent. CONSTITUTION:The objective paste can be produced by mixing (A) an electrically conductive printing paste composed mainly of a mixture of (i) a resin binder, (ii) electrically conductive powder and (m) a solvent with (B) 2-30 pts.wt. (based on the solid component of the component i) of a powdery fluororesin (e.g. polytetrafluoroethylene resin) having an average molecular weight of <=10,000, particle diameter of <=10mum and kinetic frictional coefficient of <=0.5.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a printed conductive paste used as various patterns formed on substrates of electronic components such as rotary variable resistors and slide switches. .

[Conventional technology]

Conventionally, electronic components such as rotary variable resistors, rotary switches, slide switches, and slide variable resistors have been produced by sliding a metal slider over a current collection pattern or resistor pattern formed on a substrate. By sliding the moving contacts, the resistance value of the electronic component and the on/off state of the switch are changed.

When a hard phenolic, epoxy, or ceramic substrate is used as the substrate for this type of electronic component, the resistor pattern formed on it requires a phenolic resin binder and silver.

A printed conductive paste made of a mixture of conductive powder such as carbon and a solvent such as a glycol derivative was used.

In addition, when a flexible polyester film or the like is used as a substrate for this type of electronic component, the pattern formed on it may contain a flexible resin binder such as polyester or polyurethane, and conductive powder such as silver or carbon. , a printed conductive paste made by mixing a solvent such as a glycol derivative was used.

The sliding contacts of the sliders come into sliding contact with the various patterns formed on these substrates.

Note that this sliding contact is often made of a metal such as silver-plated phosphor bronze.

[Problem to be solved by the invention]

However, in this type of conventional printed conductive paste, since the main component is basically an organic resin, it gradually wears out due to friction with the sliding contact of the metal slider, and eventually the required There was a problem that performance could not be maintained.

In particular, when a flexible material is used as the printed conductive paste, there is a problem in that the material is soft and is subject to severe wear.

The present invention has been made in view of the above-mentioned points, and an object of the present invention is to provide a printed conductive paste that is resistant to wear even when sliding contacts frequently come into sliding contact and whose conductivity or electrical contact is stable over a long period of time. be.

[Means to solve the problem]

In order to solve the above problems, the present invention has developed a printed conductive paste that has an average molecular weight of 10,000 to reduce friction.
Below, the particle size is 10t1m or less and the coefficient of kinetic friction is 0.
．． The powder of a fluororesin of 5 or less was blended in an amount of 2 parts by weight to 30 parts by weight based on the solid content of the resin binder.

Further, the present invention further includes adding metal carbide powder having a particle size of 10 μm or less and a Mohs hardness of 8 or more as a reinforcing agent to the above composition in an amount of 2 parts by weight to 30 parts by weight based on the solid content of the resin binder. It was composed of

[Effect]

By configuring the printed conductive paste as described above, it is possible to reduce the friction of various patterns on the substrate using the paste.
Even if the sliding contact of the slider frequently slides on these various patterns, the conductivity or electrical contact remains stable over a long period of time.

〔Example〕

Hereinafter, several embodiments of the present invention will be described in detail while comparing them with conventional examples.

(1) First, Examples 1 and 2 will be explained in comparison with Conventional Example A.

■Example 1 First, a method for manufacturing the printed conductive paste of Example 1 will be explained.

To produce this printed conductive paste, (1) 100 parts by weight of a butanol solution containing 50% xylene #1m (this xylene resin is the resin binder), (i) 2.8 parts by weight of acetylene black, 2.5 parts by weight of furnace black. 8
parts by weight, 0.6 parts by weight of graphite (the above is conductive powder), and (i) polytetrafluoroethylene resin powder (
Average molecular weight 5000. (Particle size: 10 μm or less) 2 parts by weight (Therefore, after volatilizing the nol based on the solid content of the xylene resin, (■) butyl cellosolve, ethyl carpitol acetate, methyl ethyl ketone (MEK) (composition ratio 5:4:1) 30 parts by weight of a solvent was added thereto and kneaded using a Miki roll mill.Thus, the printed conductive paste according to this example was completed.

The sheet resistance value of this printed conductive paste was about 80 Ω/hole.

Then, as shown in FIG. 1, this printed conductive paste 1 is printed as a resistor pattern into a horse-shaped shape by screen printing on a phenol laminate board 3, and is baked at 190°C for 15 minutes to create a rotary variable resistor pattern. I created a resistor board.

In addition, 5 shown in FIG. 1 is a silver paste, and 7 is a slider made of phosphor bronze plated with silver.

Example 2 Next, a method for producing a printed conductive paste of Example 2 will be described.

To produce this printed conductive paste, (i) 100 parts by weight of a butanol solution containing 50% xylene resin is mixed with (i)
2.8 parts by weight of acetylene black, 2.8 parts by weight of furnace black, 0.6 parts by weight of graphite, and (i)
2 parts by weight of polytetrafluoroethylene resin powder (therefore, 30 parts by weight of a solvent consisting of the above-mentioned xylene (iv) butyl cellosolve, ethyl carpitol acetate, and MEK (composition ratio 5:4:1) was added thereto using a three-roll mill. Knead.

Furthermore, in this example, a 5/100 amount was taken out of the composition kneaded as described above, and (v)
5 parts by weight of titanium carbide (Tic) (therefore, 10 parts by weight based on the solid content of the xylene resin), and (vi) the remaining amount of the composition before and after 95 parts by weight.
/100 and dispersed for 1 hour.

This completes the printed conductive paste according to this example.

In this example, (V) titanium carbide (T
i C) is metal carbide powder as reinforcing material.

The sheet resistance value of this printed conductive paste was also about 80 Ω/hole.

Then, as shown in FIG. 1, this printed conductive paste was baked at 190° C. for 15 minutes to produce a substrate for a rotary variable resistor.

Comparative Example A Next, for comparison with Examples 1 and 2, a conventional printed conductive paste containing no polytetrafluoroethylene resin powder or titanium carbide (TiC) was also prepared.

To produce this printed conductive paste, (i) 100 parts by weight of a butanol solution containing 50% xylene
2.8 parts by weight of acetylene black, 2.8 parts by weight of furnace black, and 0.6 parts by weight of graphite are blended.

Next, this was stirred in a Raikai machine for a day and night to volatilize the butanol, and then (i) butyl cellosolve, ethyl carpitol acetate, MEK (composition ratio 5:4:1)
30 parts by weight of a solvent consisting of the following ingredients were added and kneaded using a three-roll mill. This completes the printed conductive paste according to this comparative example.

Even with this printed conductive paste, the sheet resistance value was about 80Ω/hole.

Then, as shown in FIG. 1, this printed conductive paste was baked at 190° C. for 15 minutes to produce a substrate for a rotary variable resistor.

Next, the present inventor created Example 1 as described above.
Example 2. The sliding contact of the slider 7 as shown in FIG. 1 was brought into sliding contact with each substrate of Comparative Example A, and the number of times of sliding and the rate of change in resistance value (maximum resistance value at both ends of the resistor pattern) were measured. We measured the relationship between

FIG. 2 is a diagram showing the measurement results.

As shown in the figure, in Comparative Example A, the resistance value decreased significantly at one point and then increased significantly again. This increase in resistance value indicates that this resistor pattern has deteriorated.

On the other hand, Example 1 in which polytetrafluoroethylene resin was blended,
The resistance value decreases a little and then increases again, deteriorating the resistor pattern.
ES'? In Example 2, in which titanium carbide (TiC) was also added to -+, the resistance value gradually decreased and then increased only slightly, indicating that there was almost no deterioration of the resistor pattern.

Next, the present inventor described the above-mentioned Example 1. Example 2. A sliding contact of a slider as shown in FIG.
2615,8 method B) was determined.

FIG. 3 is a diagram showing the measurement results.

As shown in the figure, in Comparative Example A, the more the number of times of sliding increases, the higher the concentrated contact resistance increases.

On the other hand, in Example 1 in which poly(4-fluoroethylene) resin was blended, the concentrated contact resistance increased by 1 degree, but the degree of increase was smaller than that in Comparative Example A. In Example 2, which also contained a mixture of 1 and 2, the concentrated contact resistance hardly changed.

(2) Next, Example 3 will be explained in comparison with Conventional Example B.

■Example 3 First, a method for manufacturing the printed conductive paste of Example 3 will be explained.

In order to produce this printed conductive paste, (1) a polyurethane flexible printed conductive paste (a commercially available product with a resin binder content of about 20 to 25%); (i) titanium carbide (TiC), and (i) titanium carbide (TiC),
iv) 95 parts by weight of the printed conductive paste of (i) and 2 parts by weight of polytetrafluoroethylene resin, where the solid content of the resin binder in the polyurethane flexible printed conductive paste of (1) is about 20 to 25%. Therefore, the amount of titanium carbide (Tic) in (i) based on the solid content of the resin binder is 20 to 25 parts by weight. The amount of the polytetrafluoroethylene resin (iv) based on the solid content of the resin/ininder is 8 to 10 parts by weight.

This completes the printed conductive paste according to this example.

Then, print this printed conductive paste as shown in Figure 1,
By baking this at 150° C. for 20 minutes, a flexible substrate for a rotary variable resistor was created.

Comparative Example B Next, in order to compare with Example 3, a conventional printed conductive paste containing no polytetrafluoroethylene resin powder or titanium carbide (TiC) was also prepared.

That is, in order to produce this printed conductive paste, (i) a polyurethane flexible printed conductive paste (commercially available, with a resin binder content of about 20 to 25%), which is the same as (1) shown in Example 3 above; A flexible substrate of a variable resistor was prepared by printing a horse-like shape by screen printing onto a polyester film 3' and baking it at 150° C. for 20 minutes.

Next, the present inventor created Example 3 as described above.
A sliding contact of a slider as shown in Fig. 1 was brought into sliding contact with each board of Comparative Example B, and the number of times of sliding and the rate of change in resistance value (maximum resistance value at both ends of the resistor pattern) were measured. We measured the relationship between

FIG. 4 is a diagram showing the measurement results.

As shown in the figure, in Comparative Example B, as the number of times the slider slides increases, its resistance value increases significantly, and the resistor pattern deteriorates more severely.

On the other hand, polytetrafluoroethylene resin and titanium carbide (T
In Example 3 containing iC), the resistance value increases as the number of times the slider slides increases, but the degree of increase is considerably lower than in Conventional Example B, and the resistance value of the resistor pattern increases. Less deterioration.

Next, the inventor of the present invention described the above-mentioned Example 3. A sliding contact of a slider as shown in FIG. 1 was brought into sliding contact with each substrate of Comparative Example A,
Its sliding number and concentrated contact resistance (JIS C52615,
8 method B) was measured.

FIG. 5 is a diagram showing the measurement results.

As shown in the figure, in Comparative Example B, the more the number of times of sliding increases, the higher the concentrated contact resistance increases.

On the other hand, it was found that in Example 3, in which polytetrafluoroethylene resin and titanium carbide (TiC) were blended, the concentrated contact resistance increased only slightly.

(3) Next, Example 4 will be explained in comparison with Conventional Example C.

■Example 4 First, a method for manufacturing the printed conductive paste of Example 4 will be explained.

In order to produce this printed conductive paste, (1) polyurethane flexible printed conductive paste (a commercially available product with a resin binder content of about 20 to 25%). 5 parts by weight of (using the same material as in (i)), (i) 5 parts by weight of titanium carbide (TiC)
Weight Then, (iv) the printed conductive paste 9 of the above (i)
5 parts by weight and 5 parts by weight of polytetrafluoroethylene resin.This completes the printing groove 1 paste according to this example.

Here, since the (+) polyurethane-based flexible printed conductive paste contains about 20 to 25% resin binder solid content, the blending amount of (i) titanium carbide (Tic) relative to the resin binder solid content. This means 20 to 25 parts by weight. In addition, the blending amount of the polytetrafluoroethylene resin (iv) with respect to the solid content of the resin binder is also 20 to 2.
This means 5 parts by weight.

Then, as shown in FIG. 6, the printed conductive paste 11 thus obtained is linearly screen-printed onto the polyester film 13 on which the silver paste 15 has been printed and dried so as to cover the silver paste 15. And this is 15
By baking at 0° C. for 20 minutes, a flexible substrate for the slide type switch shown in the figure was created.

Note that 17 is a metal slider whose sliding contact slides on the conductive paste 11.

Comparative Example C Next, for comparison with Example 4, a conventional printed conductive paste containing no polytetrafluoroethylene resin powder or titanium carbide (TiC) was also prepared.

That is, in order to manufacture this printed conductive paste, (i) a polyurethane flexible printed conductive paste (commercially available, with a resin binder content of about 20 to 25%), which is the same as (1) shown in Example 4 above; Polyester film 1 is prepared by printing silver paste 15 on it and drying it.
3, by printing in a straight line so as to cover the silver paste 15 and baking this at 150 ° C. for 20 minutes,
A flexible substrate for a sliding switch as shown in FIG. 6 was prepared.

Next, the present inventor created Example 4 as described above.
A slider 17 as shown in FIG. 6 was placed on each substrate of Comparative Example C.
The number of sliding contacts and the contact resistance (O
(contact resistance at N) was measured.

FIG. 7 is a diagram showing the measurement results.

As shown in the figure, in Comparative Example C, as the number of times the slider slides increases, its resistance value increases significantly, and the resistor pattern deteriorates more severely.

On the other hand, in Example 4 in which polytetrafluoroethylene resin and titanium carbide (TiC) were blended, the resistance value increased as the number of times the slider slid increased; It was found that the degree of increase was considerably lower than that of the previous example, and that the deterioration of the resistor pattern was small.

Although the printed conductive paste according to the present invention has been described above using several examples, the present invention is not limited thereto, and the materials to be blended and their ratios can be changed within a predetermined range.

That is, in the above embodiment, a case was explained in which polytetrafluoroethylene resin was used as the fluororesin, but the present invention is not limited thereto. ether resin, polyfluoroalkoxyethylene resin, polytetrafluoroethylene hexafluoropropylene co-assembly resin, etc.),
It was confirmed that any fluororesin produced the same effect as the above example.

Note that the above dynamic friction coefficient will be defined here.

FIG. 8 is a diagram showing a method of measuring the coefficient of dynamic friction. As shown in Figure 5, in order to measure the coefficient of dynamic friction, the sample fluororesin powder is spread on an aluminum rotary table 91, and the inner radius r, = 1 (1) and the outer radius r, = 112.
A copper cylinder 92 with a diameter of 1.2 cm is pressed against the cylinder 92 with a load of 3 kg. An arm 93 is attached to this cylinder 92 at right angles to the central axis.

After that, the rotary table 91 is allowed to rotate at a speed of 60 revolutions per minute, and the torque F transmitted to the cylinder 92 at this time is applied to the arm 93 at a distance of 9-4 cm from the central axis of the cylinder 92.
Measure at the top.

Then, by substituting these values into the formula below, the dynamic friction coefficient μ can be obtained.

In each of the above embodiments, titanium carbide (TiC) is used as the metal carbide powder, but the metal carbide powder is not limited to this, and other materials such as tungsten carbide (WC) and silicon carbide (SiC) are also used. It was confirmed that the same effects as those of the above-mentioned Examples could be obtained using various metal carbide powders.

In addition to the above-mentioned examples, the inventor of the present invention also prepared various printed conductive pastes with different mixing ratios of a predetermined fluororesin and metal carbide powder, and measured their performance.

As a result, ・In order to reduce friction, fluororesin powder with an average molecular weight of 10,000 or less, a particle size of 10 μm or less, and a coefficient of dynamic friction of 0.5 or less is added to the printed conductive paste, which mainly consists of a resin binder, conductive powder, and solvent. If it is blended in a range of 2 parts by weight to 30 parts by weight (more preferably in a range of 4 parts by weight to 25 parts by weight) based on the solid content of the resin binder, what is the ratio of the blending? It turned out to be good too.

If the molecular weight of the fluororesin exceeds 10,000, dispersion in the printed conductive paste will be inhibited, and the fluidity and smoothness of the printed conductive paste will be impaired, which is disadvantageous. Note that if the particle size of this fluororesin exceeds 10 μm, when this printed conductive paste is printed on a substrate, too many fluororesin particles will be exposed on the surface, which may impede electrical contact. This is inconvenient. On the other hand, if the amount of the fluororesin blended is less than 2 parts by weight based on the solid content of the resin binder, the effect of reducing friction cannot be sufficiently exhibited.

Furthermore, if the amount of the fluororesin added is 30 parts by weight or more based on the solid content of the resin binder, the electrical properties of the printed conductive paste will be impaired and the mechanical properties will also be degraded.

In addition, when metal carbide powder is further added as a reinforcing agent to the printed conductive paste containing the fluororesin in the above range,
The blending ratio is 2 to 30 parts by weight (preferably 4 to 25 parts by weight) of particles with a particle size of 10 μm or less and a Mohs hardness of 8 or more based on the solid content of the resin binder. It was also found that when blended, the abrasion resistance was considerably improved compared to the case of a printed conductive paste containing only the above-mentioned fluororesin.

If the particle size of the metal carbide powder exceeds 10 μm, when this printed conductive paste is printed on the substrate, too many metal ash powder particles will be exposed on the surface, inhibiting electrical contact. This causes a disturbance in the smoothness of its surface. On the other hand, if the amount of metal carbide powder is less than 2 parts by weight based on the solid content of the resin binder, the effect of reinforcing the printed conductive paste cannot be sufficiently exhibited. If the amount of metal carbide powder is 30 parts by weight or more based on the solid content of the resin binder, the electrical properties of the printed conductive paste will be impaired and the mechanical properties of the printed conductive paste will also be degraded.

〔Effect of the invention〕

As explained in detail above, according to the printed conductive paste of the present invention, even if the sliding contact of the slider frequently comes into sliding contact with various patterns using the paste, it is difficult to wear out, and the conductivity or electrical It has the excellent effect of maintaining stable contact over a long period of time.

[Brief explanation of drawings]

FIG. 1 is a plan view showing a substrate of a rotary variable resistor using a printed conductive paste according to the present invention, and FIG. 2 is a plan view showing a substrate of a rotary variable resistor using printed conductive paste according to the present invention.
Example 2. FIG. 3 is a diagram showing the relationship between the number of times the slider slides on each substrate of Comparative Example A and the rate of change in resistance value. Example 2. A diagram showing the relationship between the number of times the slider slides on each substrate of Comparative Example A and the concentrated contact resistance, and FIG. 4 shows the slider sliding on each substrate of Example 3 and Comparative Example B. FIG. 5 is a diagram showing the relationship between the number of times of sliding and the rate of change in resistance value. A diagram showing the relationship between the number of times the slider slides on each substrate of Comparative Example B and concentrated contact resistance, and FIG. 6 shows a substrate of a sliding switch using the printed conductive paste according to the present invention. The plan view and FIG. 7 are of Example 4. FIG. 8 is a diagram showing the relationship between the number of times the sliding contact of the slider slides on each substrate of Comparative Example C and the contact resistance, and FIG. 8 is a diagram showing the method for measuring the coefficient of dynamic friction. In the figure, 1, 11 are printed conductive pastes.

Claims (4)

[Claims] (1) A printed conductive paste whose main component is a mixture of a resin binder, a conductive powder, and a solvent is mixed with a fluororesin having an average molecular weight of 10,000 or less, a particle size of 10 μm or less, and a dynamic friction coefficient of 0.5 or less. A printed conductive paste characterized in that the powder is mixed in an amount of 2 parts by weight to 30 parts by weight based on the solid content of the resin binder. (2) The fluororesin is polytetrafluoroethylene resin,
The printed conductive paste according to claim 1, wherein the printed conductive paste is a polyfluorinated ethylene propylene ether resin, a polyfluorinated alkoxyethylene resin, or a polytetrafluorinated ethylene hexafluorinated propylene copolymer resin. (3) A metal carbide powder having a particle size of 10 μm or less and a Mohs hardness of 8 or more is mixed in the printed conductive paste in an amount of 2 parts by weight to 30 parts by weight based on the solid content of the resin binder. The printed conductive paste according to claim (1) or (2). (4) The printed conductive paste according to claim 3, wherein the metal carbide powder is titanium carbide, tungsten carbide, or silicon carbide.