JPH03217466A - Nonflammable inorganic-based electroconductive paint composition having excellent resistance to moisture - Google Patents

Abstract

PURPOSE:To obtain the subject inorganic-based electroconductive paint composition having extremely excellent resistance to moisture and further low resistance, excellent adhesion and film-forming properties by mixing electroconductive powder and an aqueous solution of specific mixed water-soluble silicates in a fixed ratio. CONSTITUTION:The aimed paint composition is composed of (A) 0.4-1.0 pt.wt. electroconductive powder such as copper powder or nickel powder and (B) 1 pt.wt. aqueous solution of mixed water-soluble silicates containing at least Li-salt and Na-salt in mixed water-soluble silicates expressed by the formula (M is Li, Na or K; n is molar ratio). A molar ratio of the mixed water-soluble silicates is [0.40-0.75Li2O.0.25-0.60(Na2O-K2O)].3-5SiO2 (with a proviso that Na2O>K2O and Li2O+Na2O+K2O=1) and concentration of the aqueous solution is 25-35wt.%. Said composition is suitable as various electronic instruments or shielding materials for electromagnetic waves.

Description

Detailed Description of the Invention Field of industrial application: The present invention relates to a nonflammable inorganic conductive paint composition (hereinafter simply referred to as paint) with excellent moisture resistance, and is used in various electronic devices, electromagnetic waves, etc. Widely used as a coating for rolled wood, etc.

[Conventional technology]

Conventionally, organic conductive paints used water-soluble inorganic binders such as water-soluble silicates due to problems such as fires caused by solvent vapor during painting and the generation of toxic gas when the paint film burned. something is desired.

However, not many of these inorganic conductive paints are known due to the poor water resistance of the inorganic binder, but the following are known.

For example, a conductive paint with excellent heat resistance using graphite whose surface is coated with N
No. 8), conductive coating composition containing calcined coke (
JP-A No. 62-20573) is known.

2) Problems to be Solved by the Invention 2) However, the former conductive paint is intended to improve heat resistance, and the latter is intended to have high conductivity, not to improve moisture resistance. .

In addition, various water-soluble silicates are used as binders, but these binders generally have poor water resistance and wettability. etc. is not suitable. Therefore, methods such as adding additives such as curing agents and high-temperature heating can be considered, but adding a large amount of additives will make it difficult to mix the conductive powder, and high-temperature heating will make it difficult to mix the conductive powder. Because it leads to oxidation,
Any of these causes a decrease in the conductivity of the coating film. In addition, when a curing agent is used, it becomes a two-component type paint, which is inconvenient to handle and has a limited pot life. , properties as a binder such as adhesion and film-forming properties tend to deteriorate. Therefore, neither of them exhibits sufficient performance as a conductive paint.

The present invention is based on the above-mentioned viewpoint, and uses a water-soluble silicate, which is a water-soluble inorganic binder. ) conducted various research on conductive paints, and found and completed a composition that could maintain conductivity for a long time, especially under high humidity conditions. That is, an object of the present invention is to provide a nonflammable inorganic conductive paint with excellent moisture resistance.

[Means for solving the problems] The conductive paint of the present invention has excellent moisture resistance,
Conductive powder and general formula M2O・nSi○2 (M: Li, N
a, K, n: molar ratio), the mixed water-soluble silicate contains at least L1 salt and Na salt, and the molar composition of the mixed water-soluble silicate is C0. 40-0.75Li.

■・D. 25~060 (Na20"K2o)E
'3 ~5sio2 (however, Naz O>K2 0,
Li20tNaa 〇1K20=1), the concentration of the aqueous solution of the mixed water-soluble silicate is 25 to 35% by weight, and the blending ratio of the conductive powder to the aqueous solution is 04 to 1.0% by weight. It is characterized by

Examples of conductive materials include silver powder, nickel powder, copper powder, carbon powder, titanium nitride powder, surface-treated powders of these powders, and inorganic powders such as mica or sericite coated with highly conductive metals. Powder and other materials used in ordinary conductive paints can be used. Among these, copper powder, nickel powder, etc. are preferable in consideration of conductivity, economy, etc.

The mixed water-soluble silicate contains at least L salt and Na salt. This is due to the following reasons. That is, a dried coating film of a paint made of a Na salt or a K salt, or a mixture of the two as a binder and a conductive powder mixed therein, rapidly loses its conductivity under wet conditions. In addition, when only L1 salt is used as a binder, the moisture resistance is high, but as the test time increases, the surface electrical resistance value (hereinafter referred to as "resistance value" in J:J.) rapidly increases, and furthermore, the coating resistance increases. While the surface of the film is rough and prone to cracking and peeling, a mixed aqueous silicate binder containing L1 salt in Na salt or a mixture of Na salt and K salt improves the adhesion and film formability of the coating film. At the same time, the ability to maintain conductivity under wet conditions is also improved.

Moreover, the reason why Na, ○>K20 is set is due to the following reason j. That is, in the L1 salt composition, K salt is inferior to Na salt in suppressing the increase in resistance under wet conditions, but it is effective in preventing paint film whitening (efflorescence), so it may be added depending on the application. is preferable. From the above, in order to maintain the anti-whitening effect and improve moisture resistance, Na20
>K2 0 is required.

The molar ratio (n) of Sin2 is in the range of 3-5. Within this range, moisture resistance, adhesiveness, and film-forming properties can be achieved at the same time. The concentration of the aqueous solution is 25-35%. This is because within this range, it is easy to mix with the conductive powder, the fluidity necessary for the paint can be obtained, and there is little change in resistance under moisture resistance. Moreover, the mixing ratio of the conductive powder to this aqueous solution is 0.4 to 1.0 in terms of weight ratio. If this is less than 0.4, the conductive powder in the coating film becomes diluted and a paint with good conductivity cannot be obtained.1. If it exceeds 0, the apparent viscosity of the paint increases, making it difficult to apply, and furthermore, the conductivity of the resulting paint film also deteriorates. This is thought to be because the adhesion between the conductive powders deteriorates due to an insufficient amount of binder relative to the conductive powders.

The method for preparing the aqueous solution having the above composition is not particularly limited, but usually a lithium silicate aqueous solution, a sodium silicate aqueous solution, or a potassium silicate aqueous solution is mixed as appropriate. Further, the drying temperature of this paint is usually above the temperature necessary to evaporate water and strengthen the silicic acid skeleton, and below the temperature at which conductivity decreases due to oxidation of the conductive powder. Note that this temperature is usually about 120°C to 180°C.

In order to maintain the stability of the paint, this paint contains organic thickeners such as sodium alginate and sodium polyacrylate in an amount of 2% by weight or less (hereinafter referred to as %), which does not affect nonflammability, or which does not affect conductivity. Anti-settling agents such as bentonite (for example, 5% or less) and clay minerals (10% or less), dispersants, etc., which do not affect the composition can be added. In order to ensure wettability, we also need water resistance improvers that do not significantly reduce conductivity, adhesion, film forming properties, etc., curing agents that are added before use, and improvements to the properties of the coating film. Therefore, synthetic resins and emulsions thereof can be blended within a range that maintains nonflammability.

[Function] The properties of the water-soluble silicate differ mainly depending on the type and molar ratio (n) of the alkali metal (M). For example, the order of water resistance is Li20>K20≧Na20, and the order of adhesiveness and film formability is Na20>K20>LisO.

In the present invention, because of the mixed water-soluble silicate, not only the resistance value under wet conditions is smaller than that of the K salt alone, but also the rapid resistance value that occurs when the test time is increased as seen in the case of the L1 salt alone. No increase occurs either. In other words, long-term conductivity can be maintained, which is not expected from the change in resistance of a single water-soluble silicate when wet. This is L
This is thought to occur due to the synergistic effect of the conductivity retention ability of the coating film under wet conditions of the i-salt, the adhesion and film-forming properties of the Na salt, and the adhesion and film-forming properties of the K salt added as necessary. In addition, for the same alkali metal, the higher the molar ratio n of S102, the better the water resistance, but if this n becomes too large, the adhesion and film formability will decrease, which will also affect the moisture resistance, etc. It also becomes difficult. In the present invention, this n is 3 to 5
Therefore, it has excellent moisture resistance.

Further, in the present invention, since the concentration of the aqueous solution and the blending ratio of the conductive powder to the aqueous solution are also predetermined values, an appropriate resistance value can be maintained, and film formability and moisture resistance are also excellent.

〔Example〕

The present invention will be specifically explained below using Examples.

Example 1 Lithium silicate aqueous solution (n = 3.6, concentration 23%) and sodium silicate (n = 3.0, concentration 39%) were mixed,
(0.48Ll20・0.52Naz O)' 3.4
A mixed silicate aqueous solution having a composition of 3 io and a concentration of 29% was prepared. This aqueous solution and a conductive powder (electrolytic copper powder FCC-115A manufactured by Fukuda Metal Foil & Powder Industry Co., Ltd.) were mixed at a weight ratio of 6:4 (ratio: 4/6=0,67) to prepare a paint. This paint was bar coated onto a glass plate and dried at 160°C for 30 minutes to produce a test piece. The thickness of the paint was approximately 70 μm.

This test piece was left to stand at a temperature of 50° C. and a relative humidity of 99% or more using a humidity tester, and the change in surface resistance was measured. The results are shown in the table and figure.

For resistance measurement, a Loresta FP type 4-needle resistance meter manufactured by Mitsubishi Yuka ■ was used. No abnormalities such as cracks or peeling were observed in the coating film after the test.

Example 2 In this example, the mixed silicate aqueous solution composition was changed to (0.71Li
．． O・0.29NazO)・3.3Si○2,
The same procedure as in Example 1 was carried out except that the aqueous solution concentration was 25%, and the results are also shown in the table and figure. The specimen after the test was slightly blackish, but no abnormalities such as cracks or peeling were observed.

Example 3 In this example, potassium silicate (n=3.1, concentration 4
(0%), (0.48Li20・0.52Na2
0.0.12K. O) ・Other than using a 3-component aqueous solution with a composition of 3.33lO2 and an aqueous solution concentration of 30%,
It was carried out in the same manner as in Example 1. The results are also shown in the table and figure. No abnormalities such as cracks or peeling were observed in the test piece after the test.

Practical Example 4 This example was carried out in the same manner as in Example 1, except that carbon nickel powder was used instead of electrolytic copper powder as the conductive powder, and the results are shown in the tables and figures. No abnormalities such as cracks or peeling were observed in the test piece after the test.

Example 5 In this example, a calcium silicate board for interior use was used as the object to be coated, and the paint having the composition used in Example 3 was applied by spraying, dried at 130°C for 30 minutes, and the results are shown. and shown in the figure. No abnormalities such as cracks or peeling were observed in the test piece after the test.

Example 6 In this example, the aqueous solution composition was (0.65L120.
0.35Na20) ・Using 3.4S+Oa,
The same procedure as in Example 1 was carried out except that the concentration was 27%, and the results are shown in the table and figure. The specimen after the test was slightly blackish, but no abnormalities such as cracks or peeling were observed.

Example 7 In this example, the aqueous solution composition was (0.43Ll20.
The procedure was carried out in the same manner as in Example 1, except that 0.57Na,○)・3.68102 was used, its concentration was 29%, the drying temperature was 130°C, and the drying time was 30 minutes. The results are shown in the table and figure. No abnormalities such as cracks or H separation were observed in the test piece after the test.

Comparative Example 1 This comparative example was carried out in the same manner as in Example 1, except that only a lithium silicate solution (n = 3.6, concentration 23%) was used instead of the mixed silicate aqueous solution, and the results are shown below. and shown in the figure. After the test, the test piece showed some peeling. Furthermore, in some cases, the entire coating film fell off.

Comparative Example 2 In this comparative example, the aqueous solution composition was changed to (0.29Li, 0 ・0
．． 7 1Naa O) ・3.2 S +02,
L] Salt and Na salt are out of the range of the present invention, and the concentration is reduced to 3.
The same procedure as in Example 1 was carried out except that the concentration was 3%, and the results are shown in the table and figure.

Comparative Example 3 In this comparative example, a lithium silicate aqueous solution (n = 7.6, concentration 22%) and a sodium silicate aqueous solution (n - 3.0, concentration 3
(9%) was prepared by mixing (0.5 4 L l 20
・0.46NazO) ・5.5SiO2 The same procedure as in Example 1 was carried out except that the 3i02 composition exceeded the range of the present invention and the concentration was 25%, and the results were obtained. are shown in the table and figure. The surface of the coating film after drying was rough, and some of the test pieces after the test were peeled off.

Comparative Example 4 In this comparative example, 0.41LizO was prepared by mixing a lithium silicate aqueous solution (n=3.6, concentration 23%) and a sodium silicate aqueous solution (n=2.0, concentration 46%). −
0.59Na20>・2.73i0. Using a mixed aqueous silicic acid solution with a composition of 8102, the composition is below the range of the present invention,
The same procedure as in Example 1 was carried out except that the concentration was 31%, and the results are shown in the table and figure.

Comparative Example 5 In this comparative example, the three types of aqueous solutions used in Example 3 were mixed and prepared (0.42Li=0.026Na20
・0.32K20) ・Using an aqueous solution with a 3.3SiO2 composition, the process was carried out in the same manner as in Example 1, except that the concentration was set to 31% because it became a Na salt and a K salt, which was outside the range of the present invention, and the results were as follows. are shown in the table and figure.

Comparative Example 6 In this comparative example, the blending ratio (weight ratio) of the aqueous solution and electrolytic copper powder in Example 1 was changed from 6:4 to 7.5:25 (ratio; 2.5
/7.5=0.33). As a result, since the amount of copper powder was small, the surface resistance of this coating film after drying was on the order of KΩ/sq, resulting in a high resistance.

Comparative Example 7 This comparative example was carried out in the same manner as in Example 1 except that the mixing ratio of the aqueous solution and electrolytic copper powder in Example 1 was changed from 6゛4 to 4.6 (ratio; 6/4 = 15). . As a result, even though the amount of copper powder was increased, the surface resistance of this coating film after drying was on the order of KΩ/sq, indicating a high resistance. This is because the paint is non-uniform and clumps, making it impossible to apply it evenly and resulting in insufficient contact between the conductive particles.

Comparative Example 8 Using the water-soluble silicate of Example 1, the silicate concentration was reduced to 20
If it is as small as %, the paint does not exhibit adequate fluidity and the adhesion between the conductive powders becomes weak, resulting in high resistance.

On the other hand, if the silicate concentration is similarly increased to 40%, the viscosity of the paint increases and coating becomes difficult. Furthermore, if the weight ratio of the silicate aqueous solution and the conductive powder is 1:1.2, the coating will not be uniform and cannot be applied uniformly. on the other hand,
If the ratio is less than 0.4, the contact between the conductive powders will be insufficient, resulting in high resistance.

In any of the above cases, a coating film cannot be formed with sufficient adhesion to the object to be coated (and the adhesion between the conductive powders is also not sufficiently good), so even if a coating film cannot be formed. However, the resistance of the coating film changes with the passage of wet time, and the wet resistance is very low. Even when exposed to high humidity for a long time of 1,500 hours, there is very little change in surface resistance, and the moisture resistance is significantly superior to that of the comparative example. In particular, as in Comparative Example 2, L
Simply removing the 5102 composition as shown in Comparative Examples 3 and 4 results in a marked decrease in moisture resistance. The same thing is true even if only 200 hours have passed, and the resistance increases significantly. Further, in all of the above examples, there was no abnormality in the coating film after the test, and all showed good adhesion and film formability.

Furthermore, in all cases of this example, the surface resistance value is about 1 to 2 Ω/sq or less even when exposed to moisture for a long time,
Especially in Examples 1, 3 to 5, even after 1500 hours, 184
˜1.8 or less, all of them have extremely excellent performance as shielding materials.

:Effects of the Invention] As shown in the above effects, the present conductive paint has a predetermined mixed alkali silicate composition, a predetermined concentration of its aqueous solution, and contains a predetermined amount of conductive powder. So,
In other words, due to the synergistic effect of these elements, it has excellent moisture resistance, low resistance, and adhesive properties. It also has excellent film-forming properties, making it an excellent nonflammable conductive paint and exhibiting well-balanced performance. Therefore, it is extremely useful for various electronic devices, electromagnetic shielding materials, etc.

[Brief explanation of drawings]

The figure is a graph showing the relationship between test time and surface resistance in Examples and Comparative Examples.

Claims (1)

[Claims] (1) Conductive powder and general formula M_2O・nSiO_2(M
: Li, Na, K, n: molar ratio) containing at least a Li salt and a Na salt of a mixed water-soluble silicate represented by
The molar composition of the mixed water-soluble silicate is [0.40 to 0.75
Li_2O・0.25~0.60(Na_2O+K_2
O)]・3~5SiO_2 (however, Na_2O>K_2
O, Li_2O+Na_2O+K_2O=1),
The concentration of the aqueous solution of the mixed water-soluble silicate is 25 to 35% by weight.
A nonflammable inorganic conductive coating composition with excellent moisture resistance, further comprising a weight ratio of conductive powder to the aqueous solution of 0.4 to 1.0.