JP3373085B2 - Conductive resin composition - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a conductive resin composition which is used as a resistance material or is used as a conductive material, in which a conductor (conductive particles) such as carbon black or graphite is mixed, and particularly humidity. The present invention relates to a conductive resin composition having a small change in electric resistance value due to a change.

[0002]

2. Description of the Related Art Conductive resins are, for example, resistance materials or
Used as a conductive material such as contact material. Generally, a thermosetting resin such as a phenol resin or a cresol resin is used as a binder resin, and a carbon-based material such as carbon black or graphite is mixed therein as conductive particles (filler). The electrical resistance value of the resin layer formed by curing is determined by the amount of conductive particles mixed therein. In addition, particles or particles of tin, silver, gold or the like may be mixed and used as the conductive particles.

[0003]

It is desired that the conductive resin of this type has a stable resistance value in the atmosphere of the use environment. In particular, when used as a resistance material for a semi-fixed resistor or as a resistance material for a strain-sensitive sensor, it is preferable that the resistance value does not fluctuate due to changes in the atmosphere of the usage environment. Further, recently, the above conductive resin may be used as a conductive material for covering the contacts of the switch. If a normal switch can only detect ON and OFF, contact resistance is not so important,
For example, in a circuit in which a plurality of switches and resistors having a plurality of resistance values are combined and the input is judged by detecting the resistance value of a circuit in which the switches are turned on, the switch may be changed due to a change in the atmosphere of the use environment. It is not desirable that the resistance value of the capacitor changes.

Humidity in the atmosphere of the above-mentioned use environment has the greatest effect on the fluctuation of the resistance value of the conductive resin. The fluctuation of the resistance value of the conductive resin due to the humidity change depends on the hygroscopicity of the binder resin.In general, when a resin having a high hygroscopicity is used as the binder resin, the fluctuation range of the resistance value with respect to the humidity change of the atmosphere. Grows larger.

In particular, among the above-mentioned conventional examples, in the case where the phenol resin is used as the binder resin, the fluctuation range of the resistance value with respect to the humidity change of the atmosphere becomes relatively large. As is well known, a phenol resin is obtained by condensation-polymerizing the phenol shown in Chemical formula 1 and formaldehyde (HCHO). However, since the hydroxyl group serving as a substituent of phenol is a hydrophilic functional group, it is hygroscopic. Is high, and therefore the range of fluctuation in resistance value due to changes in humidity is large.

[0006]

[Chemical 1]

In contrast, cresol resin such as m-
The cresol resin is obtained by condensation-polymerizing m-cresol shown in Chemical formula 2 and formaldehyde. However, since cresol has a methyl group, which is a hydrophobic functional group, as a substituent, The moisture absorption rate is low. However, since it also has a hydrophilic hydroxyl group, it also has hygroscopicity to a lesser degree than phenolic resin, and when used as a binder resin for conductive resin, the range of fluctuation in resistance value due to humidity changes is rather large. Will be things.

[0008]

[Chemical 2]

As described above, in a conductive resin using a phenol resin or a cresol resin as a binder resin, the resistance value fluctuates greatly due to changes in humidity, and as described above, resistors and other electronic devices that do not like the resistance value fluctuate. It is not suitable for use as an element. Furthermore, in the conductive resin in which a conductor such as carbon is mixed in the binder resin, the binder resin is a modified phenol resin obtained by condensation polymerization of phenol, methylbenzene and formaldehyde, or phenol and xylene ( There is a xylene-modified phenol resin obtained by condensation polymerization of dimethylbenzene) and formaldehyde.

As will be described later as Comparative Example (1),
The xylene-modified phenol resin in which the ratio of phenol to xylene is 7: 3 has a considerably lower moisture absorption rate than the phenol resin or m-cresol resin used as the conventional binder resin. According to the measurement, the saturated water absorption of the xylene-modified phenolic resin was 2.22 (% by weight). On the other hand, the saturated water absorption of the phenol resin is 3.90 (% by weight), and the saturated water absorption measured with two kinds of m-cresol resins is 2.96 (% by weight) and 2.
It is 84 (wt%). However, as shown in Comparative Example (1) of FIG. 1, the conductive resin using these resins as a binder has a resistance value variation of 4 to 1 due to humidity.
Since it is as large as 0% or more, it becomes unsuitable for use in, for example, resistors and other electronic devices that do not like fluctuations in resistance value.

The present invention solves the above-mentioned conventional problems by using a thermosetting resin as a binder resin,
Moreover, it is an object of the present invention to provide a conductive resin which has a low hygroscopic property and has a small variation in resistance value due to a change in environmental humidity.

[0012]

The present invention is a binder resin.
Odor of conductive resin composition in which conductor is mixed in fat
hand, The binder resin isToluene, xylene, mesh
Condensation polymerization of any of the ethylene and formaldehyde
A mixture of a resin and a thermosetting resinFormedAndPrevious
Thermosetting resins include phenol, methylbenzene, and phenol.
Modified phenolic resin obtained by condensation polymerization with maldehyde
With fatAnd the binder resin is benzene
The number of phenolic hydroxyl groups is 6 for 100 total ring nuclei
3 to 35It is characterized by being.

This invention uses a thermosetting resin, toluene,
With either xylene or mesitylene and formaldehyde
By mixing (blending) a resin obtained by condensation polymerization of the above, the hydrophobicity can be enhanced and the fluctuation of the resistance value due to the humidity change can be suppressed. The thermosetting resin contains, for example, phenol, and is a phenol resin, a cresol resin, a resorcinol resin, or the like.

Examples of the thermosetting resin include a modified phenol resin obtained by condensation polymerization of phenol, methylbenzene and formaldehyde, for example, a xylene modified phenol resin obtained by condensation polymerization of phenol, xylene and formaldehyde. This xylene-modified phenol resin has a hydrophobic property by containing xylene. The modified phenolic resin itself is highly hydrophobic, and therefore the modified phenolic resin and toluene, xylene
Condensation of either formaldehyde or mesitylene with formaldehyde
By mixing (blending) the polymerized resins,
Furthermore, the hydrophobicity can be increased, and a conductive resin having a small change in resistance value due to a change in humidity can be obtained.

[0015]

Chemical formula 3 shows an example of the structure of a straight type xylene resin obtained by condensation-polymerizing xylene (dimethylbenzene) and formaldehyde. Chemical formula 4 shows an example of the structure of a straight mesitylene resin obtained by condensation-polymerizing mesitylene (trimethylbenzene) and formaldehyde.

[0017]

[Chemical 3]

[0018]

[Chemical 4]

In the above, when the amount of methylbenzene in the binder resin is too large, the crosslink density is lowered and the mechanical strength is lowered, and at the same time, the amount of expansion (volume increase amount) due to the absorption of water becomes large and the conductivity is reduced. The arrangement density of the body is reduced. That is, the fluctuation range of the resistance value due to the humidity change becomes large. Further, when the amount of methylbenzene in the binder resin becomes excessively large, methylbenzene that cannot be completely dissolved in the binder resin will ooze on the resin surface and become sticky.

As described above, when the amount of methylbenzene in the binder resin exceeds the proper range, the mechanical strength is lowered, and the fluctuation range of the resistance value becomes large due to the humidity change,
Alternatively, the resin surface may become sticky. Therefore, there is a limit to increase the amount of methylbenzene in the binder resin. For example, as shown in the examples, when the binder resin is a xylene-modified phenol resin obtained by condensation-polymerizing 7: 3 phenol, xylene, and formaldehyde, as shown in FIG. 2, a xylene resin or a mesitylene resin is used. Mixing ratio (weight ratio) is 10
~ 50% range, relative humidity of 1% at a temperature of 40 ℃
The resistance change rate can be suppressed to a small value when the resistance is changed from 95% to 95%. Therefore, it is preferable that the number of hydroxyl groups of phenol is in the range of 63 to 35 with respect to 100 of the total number of benzene ring nuclei in the binder resin.

Furthermore, when a methylene resin is used as the methylbenzene of the binder resin, the mixture is uncured, the viscosity is high in the state where stirring force is not applied, and the complex viscosity coefficient is lowered during stirring. Since the binder resin of the printing ink contains the modified phenol resin and the mesitylene resin as the main components, the printing ink having a long pot life can be provided.

[0022]

EXAMPLES Comparative Example (1) and Examples (1) to (9) shown in Table 1 show the compounding ratio of the resin solution. The xylene-modified phenol resin is obtained by condensation-polymerizing xylene, phenol, and formaldehyde, and the weight ratio of xylene to phenol is 7/3. The xylene resin is obtained by reacting m-xylene and formaldehyde in the presence of a strong acidic catalyst to cause condensation polymerization.
It is a straight type xylene resin having the structure shown in. The mesitylene resin is obtained by reacting mesitylene and formaldehyde in the presence of a strongly acidic catalyst for condensation polymerization, and is, for example, a straight mesitylene resin having a structure shown in Chemical formula 4. In Table 1, xylene resin (ii) and xylene resin (ii) are shown, but these xylene resins (ii) and (ii) have different molecular weights and oxygen contents.

[0023]

[Table 1]

In Comparative Example (1) and each Example, each resin was weighed and mixed in the weight parts shown in Table 1, and the solvent was added and stirred. Those with slow dissolution were stirred while heating at 100 ° C or lower. Carbon black was added to each resin solution as a conductor so that the solid content ratio was 21 (volume%).
After further adding a diluent and making it wet, it was kneaded with a three-roll to form a paste. The solid content ratio is (resin volume +
The ratio of (volume of carbon black) to (volume of carbon black) is expressed as a percentage.

The above-mentioned paste was formed for each of Comparative Example (1) and each Example, and this was screen-printed on a ceramic substrate using a mask of Tetron 200 mesh, and heated at 200 ° C. for 20 minutes to cure. Then, a resistor was produced. With respect to the resistors produced in Comparative Example (1) and each example, the resistance value was measured after being left in an environment of a temperature of 40 ° C. and a relative humidity of 1% for 24 hours, and then a temperature of 40 ° C. and a relative humidity of 95%. The sample was left in the environment for 24 hours, and then the resistance value was measured. The ratio of the resistance value when the relative humidity was 95% to the resistance value when the relative humidity was 1% was expressed as a percentage, which was defined as the resistance value change rate with respect to the humidity change. Table 2 shows the rate of change of the resistance value for each of the resistors using the resin solutions of Comparative Example (1) and Examples shown in Table 1.

[0026]

[Table 2]

When the fixed ratio of carbon black is 21 (volume%), the resistance change rate is 3.53 in the resistor using the xylene-modified phenol resin as the binder resin as in Comparative Example (1). %, But as shown in FIG. 1 described later, when the amount of carbon black is about 5 to 18 vol% and about 20% or more, the resistance change rate exceeds 5% and further 12%. Will be exceeded.

On the other hand, each of Examples (1) to (6) in which the xylene-modified phenolic resin is mixed with 25 to 50 parts by weight of the xylene resin (a) or the xylene resin (b), and In Examples (7) to (9) in which 25 to 50 parts by weight of the mesitylene resin was mixed, the resistance value change rate was the same as that of the resistor formed of only the xylene-modified phenol resin of Comparative Example (1). The resistance value change becomes equal to or less than the resistance value change, and as shown in FIG. 1 described later, the resistance value change rate becomes 5% or less in a wide range of the carbon black amount of 5 to 35 vol%, and the carbon black amount further decreases. If it is about 6 vol% or more, the resistance change rate is 4
% Or less, and particularly in the range of 13 to 21 vol%, it is understood that the resistance value change rate is 2% or less, which is extremely small.

By the way, in Example (6), the rate of change in resistance was equivalent to that of Comparative Example (1), and other Examples (1) to (5) and (7) in which xylene resin or mesitylene resin was mixed. In (9) to (9), the resistance value change rate is lower than that in Comparative Example (1). The rate of change in resistance of Example (6) is
The reason why it is equivalent to that of Comparative Example (1) is considered as follows. When the mixing ratio of the xylene resin to the xylene-modified phenol resin is increased, the number of hydroxyl groups of phenol decreases and conversely the number of methyl groups increases, resulting in higher hydrophobicity and lower hygroscopicity. When the amount is large, the thermosetting property is lowered and the crosslink density is lowered. As a result, the volume increase increases due to the absorption of less water,
It is believed that the carbon black becomes longer and the resistance value decreases.

By the way, although the mixing ratio of the xylene resin to the xylene-modified phenol resin of Example (3) was the same as that of Example (6), the rate of change in resistance was 3.18%. Although different from that of (6), this difference is considered to be influenced by the difference in the molecular structure of methylbenzene.

From the results shown in Table 2, a xylene-modified phenol resin having a phenol / xylene ratio of 7: 3 was used, and the xylene-modified phenol resin and the xylene resin or mesitylene resin were contained in a weight ratio of 75:25 to 50. It can be seen that, when the ratio is 50, the ratio can be suppressed to a range equal to or lower than the rate of change in resistance of the xylene-modified phenol resin in which the ratio of phenol to xylene is 7: 3, that is, 3.53% or less. From the above, it is preferable that the number of hydroxyl groups of phenol is between 70 and 35 when the total number of benzene rings of the resin binder is 100, because the rate of change in resistance can be suppressed.

Next, the amount of carbon black which is a conductor in the binder resin and the relative humidity of 1% at a temperature of 40 ° C.
From 95% to 95% was investigated. In this measurement, the fixed ratio of carbon black to the resin solutions shown in Table 1 (Comparative Example (1) and Example (8)) was changed, and the kneaded paste was screened on a ceramic substrate. Print and print at 200 ℃ 2
A resistor cured by heating for 0 minutes was used. In FIG. 1, the horizontal axis represents the solid content ratio (volume%) of carbon black, and the vertical axis represents the resistance value change rate.

From FIG. 1, when the xylene-modified phenol resin mixed with the mesitylene resin (resin solution of Example (8)) was used, the rate of change in resistance value was extremely high irrespective of the solid content ratio of carbon black. It can be suppressed to a low range of about 1 to 5%, and carbon black is about 1%.
It has been found that the resistance change rate can be suppressed to 2% or less in the range of 3 to 20%. Therefore, in the case of a resistor (conductive resin) in which a mixture of mesitylene resin or xylene resin in xylene-modified phenol resin was used as a binder resin, when the resistance value was set in a wide range by changing the carbon content. In any of the resistance value settings, the resistance value change rate with respect to the humidity change is low.

As described above, in the resistor (conductive resin) using the xylene-modified phenol resin and the binder resin in which the xylene resin or the mesitylene resin is mixed, the resistance value change rate with respect to the humidity change becomes small. However, the reason is that the hygroscopicity of these resins is low as described above. Therefore, the saturated moisture absorption rate of each resin was investigated. In this measurement, as shown in Table 3,
m- which is the condensation polymerization of m-cresol and formaldehyde
Cresol resins (a) and (b) were used as comparative examples.
The molecular weight and oxygen content are different between (a) and (b).

Further, a resin solution prepared by mixing 25 parts by weight of the xylene resin (b) with 75 parts by weight of the m-cresol resin (a) is set as Example (10). Comparative examples (3) and (4) are m-cresol resins (a) and (b), respectively. Further, a comparative example (2) is a phenol resin obtained by condensation polymerization of phenol and formaldehyde.

[0036]

[Table 3]

The resin solutions of Comparative Examples (1), (2), (3) and (4) and Examples (1) to (10) were heat-cured without mixing carbon black. The conditions for heat curing are as follows. Each resin solution was heated from room temperature to 130 ° C. over 96 hours and kept at 130 ° C. for 24 hours. After that, it was gradually cooled to room temperature over 10 hours. It was heated in a constant temperature bath of 150 ° C. for 1 hour, further heated in a constant temperature bath of 200 ° C. for 1 hour, and then stored at room temperature.

Each of the above samples was heated and dried at 120 ° C. for 3 hours and then weighed. Then 70
The sample was placed in a thermo-hygrostat having a relative humidity of 95% and absorbed. The weight of each sample was measured in a state where moisture absorption was saturated, and the saturated moisture absorption rate of the resin was calculated from the weight immediately after drying and the weight after moisture absorption saturation. The results are shown in Table 4.

[0039]

[Table 4]

From Table 4, the resins obtained by heating and curing the resin solutions of Comparative Examples (1), (2), (3) and (4) have a saturated moisture absorption of 2.22%, 3.90% and 2.96%. And 2.8
In contrast to the high value of 4%, the resin obtained by heating and curing the resin solutions of Examples (1) to (9) in which the xylene-modified phenol resin is mixed with the xylene resin or the mesitylene resin has a saturated moisture absorption rate. It is extremely low, less than 1.64%. Further, the resin obtained by heating and curing the resin solution of Example (10) in which the xylene resin is mixed with the m-cresol resin also has a low saturated moisture absorption rate of 1.89%.

From the above, in the resistors using Examples (1) to (9) as shown in Table 2, the reason why the resistance value change rate with respect to the humidity change was low was that the saturated moisture absorption rate was low. I know that there is. Furthermore, the resin of Example (10) obtained by mixing 25 parts of xylene resin (b) with 75 parts of m-cresol resin (a) obtained by condensation polymerization of m-cresol and formaldehyde had a saturated moisture absorption rate of Example (1). )
It is easily predicted that the resistance value (conductive resin) using this as a binder resin can lower the rate of change in resistance value with respect to humidity change, as in Example (1). It In addition, in the resin in which 75 parts by weight of the m-cresol resin and 25 parts by weight of the xylene resin are mixed, the number of hydroxyl groups of phenol is 75 with respect to the total number of nuclides of the benzene ring of 100.

Next, in the case where the xylene resin or the mesitylene resin is mixed with the xylene-modified phenol resin, the change in the weight ratio of the xylene resin or the mesitylene resin and the change in the resistance value at the relative humidity of 1% and the relative humidity of 95%. I investigated the relationship with the rate. In Table 5, resin solutions in which the mixing ratio (weight ratio) of the mesitylene resin to the xylene-modified phenol resin is changed are shown in Examples (11) to (14).

[0043]

[Table 5]

Resin solutions of Examples (11) and (12), and further Examples (1) (2) (3) (7) (8).
The same resistor as shown in Table 2 was formed for each resin solution of (9). That is, carbon black as a conductor was added to each resin solution so that the solid content ratio was 21 (volume%). After adding more diluent and wetting, 3
This roll is kneaded into a paste, which is used as Tetron 20.
Screen printing was performed on a ceramic substrate using a 0-mesh mask, and heating was performed at 200 ° C. for 20 minutes to cure, and a resistor was produced. Temperature of 40 ℃ for each resistor
The resistance value was measured after leaving it in an environment with a relative humidity of 1% for 24 hours.
After standing for 4 hours, the resistance value was measured and the rate of change in resistance value at both humidity was examined.

In FIG. 2, the horizontal axis represents the mixing ratio (weight ratio) of the xylene resin or the mesitylene resin, and the vertical axis represents the rate of change in resistance value. In FIG. 2, a mesitylene resin (Examples (7), (8), (9)) is used rather than a resistor using a resin mixed with xylene resin (Examples (1) to (3)) as a binder.
It is understood that the resistance value change rate due to the humidity change is smaller in the resistor using the resin mixed with (11) and (12)) as the binder. It is predicted that this is because mesitylene has more methyl groups, which are hydrophobic functional groups, than xylene.

Further, in the case where the mesitylene resin is mixed, the resistance value change rate is very low even when the mixing ratio is about 10% by weight. Even if a xylene resin is mixed, it is expected that the resistance change rate can be sufficiently reduced when the mixing ratio is about 10% by weight. From FIG. 2, the mixing ratio of mesitylene resin or xylene resin is 1
It is preferably in the range of 0 to 50% by weight. The xylene-modified phenolic resin in these examples has a ratio of phenol to xylene of 7/3. Therefore, it is understood that the number of hydroxyl groups is preferably in the range of 63 to 35 when the total number of benzene rings of the mixed resin is 100.

Further, when the mesitylene resin is mixed, the resistance change rate is low when the mixing ratio of the mesitylene resin is between 15% and 33%, and is minimal at 25%. Therefore, it is most preferable to set the mixing ratio of the mesitylene resin to the xylene-modified phenol resin in the range of 15 to 33%.
That is, when the total number of benzene ring nuclei in the resin mixed with mesitylene resin is 100, the number of hydroxyl groups is 60 to 4
A range of 7 is most preferred.

By the way, Example (3) and Example (6)
Then, when the weight part of methylbenzene such as xylene resin or mesitylene resin with respect to the xylene-modified phenol resin exceeds 50 parts by weight, in the cured product, methylbenzene that is not completely dissolved in the cured product oozes out to the surface of the cured product. , From the problem of stickiness,
In the present invention, the amount of methylbenzene mixed in the xylene-modified phenol resin is preferably 50 parts by weight or less, more preferably 33 parts by weight or less from the viewpoint of mechanical properties.

Next, Comparative Example (1) and Example (9)
Each of the resin solutions (11), (12), (13) and (14) was used, and carbon black as a conductor was added to each resin solution so that the solid content ratio was 6 (volume%). After further adding a diluent and making it wet, it was kneaded with a three-roll to form a paste. The dynamic viscoelasticity of each paste was measured using a fluid spectrometer RFSII manufactured by Rheometrics. The result is shown in FIG. The measurement was performed at an ambient temperature of 25 ° C. The horizontal axis of FIG. 3 represents the angular velocity ω (rad / s) of 0.2% sinusoidal distortion applied to each paste,
The vertical axis shows the complex viscosity coefficient η * (P: Poise).

According to the results shown in FIG. 3, in the comparative example (1) containing only the xylene-modified phenol resin, the complex viscosity coefficient is substantially constant without depending on the angular velocity of the sine wave distortion. On the other hand, Examples (9) (11) (12) (1) in which mesitylene resin was mixed
3) In (14), the complex viscosity coefficient decreases as the angular velocity increases logarithmically. That is, when the mesitylene resin is mixed, the viscosity is high and the conductive material such as carbon black or graphite is unlikely to settle in the storage state where the stirring force is not applied, and it is stable, and when stirred, it is similar to Comparative Example (1). The viscosity can be reduced to the value of, and screen printing can be performed in an appropriate viscosity state. In terms of such a viscosity change, it is preferable to use a mixture of a xylene-modified phenol resin and a mesitylene resin.

In the above embodiments, the resistor in which carbon is mixed in the binder resin is used as an example of the conductive resin. However, as the conductive filler in the binder resin, conductive particles or particles such as tin, gold and silver are used. It is possible to carry out the present invention with respect to a conductive resin in which is used.

[0052]

As described above, according to the present invention, in the conductive resin in which the conductor is mixed with the thermosetting resin, the binder resin is the mixture of the modified phenol resin and methylbenzene. Since it is possible to suppress the property to be low, it is possible to provide an electronic element such as a conductive resin and a switch in which the variation of the resistance value due to the variation of the environmental humidity is further reduced. Further, when the mixing ratio of methylbenzene to the modified phenolic resin is about 15 to 33% by weight, the rate of change in resistance value can be suppressed to 2% or less, and the solid surface is not sticky and has excellent mechanical properties. A resin and an electronic element can be provided.

Further, when a methylene resin is used as the methylbenzene of the binder resin, the viscosity is high when the mixture is uncured and the stirring force is not applied, and the complex viscosity coefficient decreases during stirring. Therefore, when the binder resin of the printing ink contains the modified phenol resin and the mesitylene resin as the main components, the printing ink having a long pot life can be provided, which is remarkably cured.

[Brief description of drawings]

FIG. 1 is a diagram showing the relationship between the amount of carbon black and the resistance value change rate due to humidity change in a resistor having a binder resin made of a xylene-modified phenol resin or a mesitylene resin mixed therein.

FIG. 2 is a line showing the relationship between the ratio of xylene resin or mesitylene resin and the rate of change in resistance value due to humidity change in a resistor having a binder resin made of xylene-modified phenol resin mixed with xylene resin or mesitylene resin. Figure,

FIG. 3 is a diagram showing the relationship between the angular velocity of sinusoidal strain and the complex viscosity coefficient of a paste in which carbon black is mixed in the resin solution of each example,

Claims (2)

(57) [Claims] 1. A conductor is mixed in a binder resin.
In the conductive resin composition, The binder resin isToluene, xylene, mesitile
Of condensation-polymerized formaldehyde with either
With a mixture of fat and thermosetting resinFormedAnd The thermosetting resin is phenol, methylbenzene,
Modified phenol obtained by condensation polymerization with lumaldehyde
With resinHas been formed, The binder resin has a total number of benzene ring nuclei of 100.
In contrast, the number of phenolic hydroxyl groups is 63 to 35 To be
A characteristic conductive resin composition. Wherein the conductor is carbon, conductive resin composition according to claim 1, wherein the ratio of the carbon of the volume to the sum of the volume of the binder resin and the carbon is from 15 to 35%.