WO1992009992A1

WO1992009992A1 - Composition of electrically insulating polymers and electrically conductive fillers

Info

Publication number: WO1992009992A1
Application number: PCT/EP1991/002204
Authority: WO
Inventors: Horst Tamm; Manfred Leder
Original assignee: Henkel Kommanditgesellschaft Auf Aktien
Priority date: 1990-12-01
Filing date: 1991-11-22
Publication date: 1992-06-11

Abstract

The description relates to a composition for coating, sealing and adhesively securing which contains an aqueous dispersion of polymers with an electrical resistance of over 1010Φ, a bright conductive metal compound and carbon fibres and other additives which are important for coating, sealing and adhesively securing. For example, a bright adhesive bond with a resistivity of 5 x 106Φ is obtained with only 5 % of a pigment based in TiO¿2? and 0.25 % of a carbon fibre.

Description

"Composition of electrically insulating polymers and electrically conductive fillers"

The invention relates to compositions for coating, sealing and gluing with electrically non-conductive polymers and electrically conductive fillers, their production and use for the production of electrically conductive coatings, seals and adhesives.

It is known to make non-conductive organic polymers conductive by adding conductive fillers such as carbon black, graphite, metal powders and metal compounds and carbon fibers. If these fillers form a continuous network, the specific conductivity of the polymer is namely improved by several powers of ten, so that, for example, electrical charges are avoided, shielding against electromagnetic waves is made possible, and dangerous or even annoying electrostatically induced discharge processes are prevented. To form this percolation network, different amounts are necessary depending on the type and shape of the fillers. As a rule, one would like to add only a little conductive filler, since then the processing and the use properties of the polymeric composition are also changed only slightly. For carbon black and graphite, an addition of 8 to 15% by weight is necessary. The compositions are then black, they are pasty and difficult to apply. Depending on the base polymer, their viscosity can be reduced by adding solvents or water, but such dilutions also have disadvantages: They limit the storage stability (solvation of the soot micelles). Most of the time, the strength also decreases. Finally, dilution with organic solvents leads to flammability of the composition and further disadvantages such as instability of the set conductivity (rapid decrease in the set conductivity over time).

Bright, conductive, aqueous dispersion adhesives are known, e.g. THOMSIT K 112 and THOMSIT T 412 from Henkel Bautechnik GmbH, which contain 0.8 to 1.5% by weight of carbon fibers with a length of 3 mm. If you apply this to not too smooth underlays with pointed-toothed spatulas, you get bonds with an electrical resistance of less than 3 x 10º5 ohms, measured according to DIN 53276. This conductivity is required for dispersion PVC flooring materials from DIN 16860.

Bright (white and colored) conductive pigments are also known, which can also be used in an aqueous medium. The company Sachtleben Chemie GmbH describes in its brochure "Electrically conductive pigments" (11 / 1989-1000 / 8-014) inorganic pigments based on titanium oxide, zinc oxide and zinc sulfide with powder conductivities from 1 × 10 ^-2 to 6 × 10 ^{- 2} S / cm. For the antistatic finishing of, for example, adhesives, lacquers and paints, a minimum fill level of approx. These pigments cost about 25 to 60 DM / kg.

Finally, from JP 83/111559 electrically conductive floor coatings made of synthetic resins are known, which are electrically conductive fillers from 60 to 100 parts by weight / 100 Parts by weight of binder containing zinc oxide with 0.1 to 0.4 wt .-% aluminum. Conventional polymers are used on synthetic resins, which cross-link on contact with air, e.g. epoxy,

Polyamide, polyester or polyurethane resins. Fibers are added to improve the mechanical properties, for example carbon, steel, glass or synthetic organic fibers. A composition with 100 parts of binder, 2 parts of carbon fibers and 60 parts of zinc oxide with 0.4% aluminum gives a resistance of 1.6 × 10 ⁵ ohm cm. The formulation, which is only effective in the absence of water, is not suitable, for example, for large-scale use for conductive floor coverings, where dispersion-based adhesives have prevailed for economic, occupational hygiene and ecological reasons.

The object of the invention is to find an economically justifiable bright composition for coating, sealing and gluing, which has an electrical resistance of preferably <3 · 10 ⁵ Ohm, but at most 1 · 10 ⁷ Ohm and its processability and achievable adhesive strength compared to non-conductive Adhesives is practically unchanged.

The solution according to the invention can be found in the patent claims. It is based essentially on the synergistic effect of conductive pigments and carbon fibers. Even very small amounts of carbon fibers and small amounts of conductive pigments lead to a sudden reduction in electrical resistance by a factor of up to 10 ^. This effect is surprising since neither the conductive pigments nor the carbon fibers have such an effect in the stated concentrations, not even as the sum of the individual effects. The resistance of an acrylate adhesive becomes 5% by weight of a conductive titanium oxide and 0.25% by weight of one Carbon fiber reduced to 5 x 10 ⁶ ohms. The resistance of the adhesive with 5% titanium oxide alone is approximately 1 x 10 ¹¹ ohms. If 0.25% by weight of carbon fibers is added to the adhesive, the resistance is more than 10 ¹⁰ .

The light-colored metal compounds mentioned are white, yellow, orange or other light-colored pigments, which allow a light setting of products made from them and are fundamentally different from previously known dark (carbon black, graphite, finest metal powder) or metallic (aluminum "powder", bronze "powder) "and the like) distinguish conductive feedstocks. Examples of these new conductive pigments are pigments based on titanium dioxide, zinc oxide,

Zinc sulfide, barium sulfate and pigments based on mica / metal oxide. The titanium oxide according to the following specification from Sachtleben Chemie GmbH is preferably used:

Table 1: TiO ₂ (rutile mixed phase solution) properties Typ

yellow orange / brown

Powder conductivity 1 · 10 ^-2 S / cm 5 · 10 ^-2 S / cm

Particle shape sphere sphere

Average grain size (d ₅₀ ) 2.0 μm 1.5 μm

Specific surface area 19.1 m ² / g 16.0 m ² / g

Density 4.9 g / cm ⁿ 4.9 g / cm ⁿ

Bulk volume 110 ml / 100 g 120 ml / 100 g

Oil absorption 36.9 g / 100 g 40 g / 100 g

Dry loss 105 ° C 0.3% 0.3%

pH in water 3.5 3.1

Conductivity in water 0.3 mS / cm 0.18 mS / cm

L ^* 85.3 74.2

a ^* - 16.2 10.4

b ^* 54.3 64.7

Brightness Y 66 47

This titanium oxide is a mixed phase pigment made of titanium, chromium and antimony oxide. The zinc oxide from the same company also shows above-average values. It is characterized by the following table.

Table 2: ZnO

Characteristics type

light gray light gray

Powder conductivity 3 · 10 ^-2 S / cm 2 · 10 ^-2 S / cm

Particle shape needle ball

Average grain size (dsg) (7.8) μm 1.0 μm

Specific surface area 6.5 m ² / g 7.3 m ² / g

Density 5.7 g / cm ⁿ 5.7 g / cm ⁿ

Bulk volume 200 ml / 100 g 120 ml / 100 g

Oil absorption 49.8 g / 100 g 22 g / 100 g

Dry loss 105 ° C 0.18% 0.23% pH in water 7.4 7.0

Conductivity in water 0.06 mS / cm 0.4 mS / cm

L ^* 84.6 85.4

a ^* - 0.4 - 2.46

b ^* 4.8 6.34

Brightness Y 65 67

It can also be obtained from Sachtleben Chemie GmbH.

They can be produced according to the teachings of DE 39 29 056, DE 39 29 057 and EP 404087 from Metallgesellschaft AG, Frankfurt. Thus, the electrically conductive rutile mixed-phase pigment is produced essentially by adding a mineral-acidic aqueous dispersion of a rutile-mixed-phase pigment to a solution containing mineral-acid hydrolyzable tin compounds and a solution containing mineral-acid hydrolyzable antimony compounds, with constant stirring, the hydrolyzable compounds by increasing the pH -Values are hydrolyzed and that coated with the hydroxide precipitates Rutile mixed-phase pigment, if appropriate after aging, is separated off, dried and calcined. For example, 100 g of a rutile mixed-phase pigment containing (Ti, Ni, Sb) oxide (Sicotan Yellow L 1010 from BASF AG) (specific surface area 3 m ² / g) are suspended in 400 ml of water at 70 ° C. and adjusted to pH 2 with hydrochloric acid. Then 500 ml of water are suspended at 70 ° C and adjusted to pH 2 with hydrochloric acid. Then 500 ml of water at 70 ° C, 1 ml of SnCl ₄ and 1 ml of HCl (conc.) Are added. The resulting yellow suspension is stirred at pH 1.5 for 60 min. Subsequently, 800 ml of 10% NaOH and 31 ml of SnCl4, dissolved in 100 ml of 2 molar HCl, are added simultaneously and the mixture is stirred for a further 30 min. The total time of this step is 120 min, the temperature is 70 ° C. Within the next 90 min, the pH is reduced to 2.5 with HCl and 5.3 g of SbCl ₃ , dissolved in 100 ml of 2 molar HCl and 170 ml of 10% NaOH, are simultaneously added dropwise. The yellow suspension is left at 70 ° C. for 20 h. The solid is then separated and dried. The specific powder conductivity after annealing at 500 ° C (1) or 600 ° C (2) is 1.4 x 10 ^-4 x (Ohm cm) ^-1 (1) or 5.1 x 10 ^-3 (Ohm cm) ^{- 1} ( 2). (Example 1 of DE 39 29 057).

The electrically conductive zinc sulfide particles are essentially prepared by combining an aqueous solution or suspension of a copper salt with a pH of 2 to 12 and zinc sulfide particles with vigorous stirring and separating the zinc sulfide particles provided with a copper sulfide coating by surface reaction and worked up. For example, 29.2 g of CUSO ₄ x 5 H ₂ O are dissolved in 800 ml of H ₂ O and the pH is adjusted to 9 with concentrated ammonia solution. Then 100 g of ZnS in powder form (d ₅₀ ¹ ) 0.37 μm; specific surface area 6.8 m ² / g BET method) with stirring within one minute. The resulting copper sulfide represents 11% of the product. The suspension is 30 min at room temperature and a further 85 min at 60 ° C. touched. The solid obtained after solid / liquid separation is dried at 110 ° C. It has a specific electrical powder conductivity of 1.9 x 10 ^-2 (Ohm cm) ^-1 . If ZnS powder is added to the Cu (II) solution, there is almost no S ion in the reaction solution. S-ions, which detach themselves from the ZnS surface upon contact with the reaction solution in accordance with the solubility product of the ZnS, are immediately noticed again (and thus almost at the ZnS surface) as CuS. If a ZnS suspension is used, there are a few dissolved S ions following the ZnS solubility product. After their precipitation as CuS, the conditions correspond to those when using ZnS powder (Example 1 of DE 3929056).

The electrically conductive zinc oxide is produced by a process in which an aqueous alkali solution is reacted with a solution which contains a water-soluble zinc compound and at least one water-soluble metal compound which is selected from the group consisting of the tin, There are gallium, indium and aluminum compounds, the amount determined after calcining the mixed precipitates of at least one of the members of the group consisting of tin oxide, gallium oxide, indium oxide and aluminum oxide in the range from 0.005 to 5.0 parts by weight per 100 parts by weight of zinc oxide , and wherein these two solutions are simultaneously fed to a reaction zone in such a way that the reaction solution is kept at a desired pH in the range from 6 to 12.5, whereupon the mixed precipitates thus obtained are calcined in a reducing atmosphere. For example, 11.17 kg of 96% pure zinc chloride, 71.76 g of 98% pure tin (IV) chloride, the amount of which corresponds to an amount of 0.593% by weight of SnO ₂ based on zinc oxide, and 64.72 g of 99.9% pure gallium chloride, the amount of which corresponds to an amount of 0.545% by weight of Ga ₂ O ₃ , based on zinc oxide, in 400 ml of 36% hydrochloric acid and enough water to dissolve 15 l of solution A. Solution A and a solution of 240 g / 1 NaOH are simultaneously fed to a reaction system for 180 minutes, the reaction solution being kept at a pH of 10 and a reaction temperature of 60.degree. The resulting mixed precipitates are filtered off in the usual manner and then washed with water until the electrical conductivity of the filtrate is only a maximum of 300 μS / cm. Then they are air dried at 105 ° C. The product thus obtained in the form of approximately 2 to 30 mm large lumps is calcined as such in a hydrogen gas atmosphere at 500 ° C. for 60 minutes, where

6.3 kg of electroconductive zinc white powder can be obtained, which has a specific electrical resistance of 1.8 × 10 ° Ohm · cm.

The conductive pigments based on mica / metal oxide are produced by Merck from an aqueous tin and antimony salt solution by adding a base with the precipitation of a SnO ₂ / Sb ₂ O ₃ oxide hydrate mixture. In the subsequent annealing process, the bound water is removed and the antimony is oxidized to a higher valence level. The pigment is now conductive (for details see Glausch, Brückner and Maisch, färbe + lack, 96. (1990), pages 412-415).

They are characterized by good conductivity, e.g. for the gl-based pigment EM 140537L from Merck is (as resistance) <50 Ohm / cm or for the barium sulfate-based pigment (in aqueous suspension) is 0.33 mS / cm.

According to the invention, the conductive fillers are used in a concentration of 2 to 10, preferably 5 to 8% by weight, based on the composition. The carbon fibers can have a high or low modulus of elasticity. They can be unsized or sized, for example epoxy or glycerine sized. Preferably, their fiber length should be approximately 3 mm in the initial state. However, shorter fiber lengths can also be used. Fibers are understood to mean elongated aggregates whose length is at least 10 times as large as their diameter, which usually ranges from 5 to 20 μm, preferably 7 to 15 μm.

All aqueous dispersions of polymers with an electrical resistance of more than 10 ^ ohms, measured in accordance with DIN 53 274, can be used as binders, e.g. Polyacrylates, polyvinyl acetate, polyethylene vinyl acetates, copolymers from the compound classes mentioned, polystyrene acrylates, polystyrene butadiene latices.

However, copolymers of esters of acrylic acid with C 1 -C 6 alcohols and vinyl acetate and optionally acrylic acid and / or other copolymerizable carboxylic acids such as methacrylic acid and crotonic acid are preferably used. Specific monomers are: butyl acrylate, ethylhexyl acrylate, vinyl acetate, small amounts of free acrylic acid.

The polyacrylate dispersion ACRONAL V 303 (manufacturer: BASF) is very preferred.

The binders are used as an aqueous dispersion with a solids content of preferably 50 to 65% by weight.

Finally, the compositions contain further additives which improve their processing and their performance properties. These primarily include natural or synthetic resins, solubilizers, dispersion aids, preservatives, defoamers, antifreeze.

Depending on the area of application, these additives are used in different concentrations. The concentration of the resin is 0 up to 20 wt .-%, based on the composition. The concentration of non-conductive fillers such as chalk and quartz powder

is 0 to 45%, the total filler concentration should not exceed 50% by weight. The water content of the composition is 15 to 35% by weight. Organic solvents are max. 7 wt .-% included.

The conductive adhesives of the composition according to the invention are usually produced by mixing the constituents, the procedure being generally such that the polymer dispersion is initially introduced. After the additives have been added, the pH is adjusted, which is generally close to the neutral point (pH 6 to 7.5). With latices (e.g. styrene-butadiene latices), the pH is adjusted in the more alkaline range (pH 8 to 10). Alkalies such as ammonia, dilute sodium hydroxide solution, aminomethyl propanol are used to adjust the pH. After the fillers have been stirred in and smooth, the conductive pigment is added in the specified concentration. Then the resin is added, e.g. as a concentrated resin solution in organic solvents. Finally, the carbon fibers are added, care must be taken to ensure that an even distribution is ensured and, on the other hand, the addition of carbon fibers is not reduced by stirring for too long or too violently.

The composition according to the invention is used for coating, sealing and gluing by applying it in the desired layer thickness. For this purpose, pointed toothed spatula, for example with a tooth gap width of 4.5 mm and a tooth gap depth of 3.5 mm, are advantageously used. Combing the rag several times should be avoided. If the product according to the invention is to be used as an adhesive, the covering to be conductively bonded is inserted after a flash-off time (which is 10 to 15 minutes under normal conditions), depending on the temperature, air humidity and substrate absorbency. Then it is rolled on.

If the product according to the invention is to be used as a coating, the rheology should be set so that the grooved application runs to a layer that is as uniform as possible. Even drying ensures that the application dries without tension and cracking.

example

An adhesive was produced from the following components: 29% by weight of a 60% dispersion of copolyacrylates

(ACRONAL V 303 from BASF),

22% by weight of chalk,

18% by weight quartz flour,

23% by weight of a 70% solution of a balsam resin in toluene, 4.4% by weight of water and

3.6% by weight additives.

The added carbon fiber "SIGRAFIL SSC 3 GLB" from Sigri had an elastic modulus of 230 kN / mm ² and a length of 3 mm. It was sized with glycerin.

The following were used as conductive fillers and, at higher additions, as indicated in the table below, a corresponding amount of filler (chalk and quartz powder) or quartz powder was deducted:

I: rutile mixed phase pigment, orange,

II: zinc oxide, light gray,

III: zinc sulfide, green,

IV: barium sulfate and

V: mica / metal oxide.

The fillers I to IV come from the company Sachtleben Chemie GmbH and the filler V from the company Merck.

These ingredients were mixed in the order listed above, taking into account the precautions listed. The adhesive had the following physical properties: viscosity approx. 15000 mPas, liter weight: approx. 1.35, pH value: approx. 6.5. The adhesive was applied to a chipboard that was densely coated with a polyurethane matting using a pointed toothed spatula (tooth gap width 4.5 mm, tooth gap depth 3.5 mm) and the adhesive film applied was dried for 24 hours at room temperature (23 ° C., 55% relative air) . The resistance was measured in accordance with DIN 53 276. The results obtained are summarized in the following table.

Table 3: Electrical resistance as a function of electrically conductive fillers Current adhesive filler C-fiber resistance

No. Type% by weight% by weight Ohm

1.corresponds to - - - 1 x 10 ¹¹ description

2. "- - 0.25> 10 ¹⁰

3. "- - 0.5> 10 ¹⁰

4. "- - 1 <3 x 10 ⁵

5. "I 5 - 1 x 10 ¹¹

6. "II 5 - 1 x 10 ¹¹

7 "III 5 - 1 x 10 ¹¹

8. (less I 5)

Quartz) II 5) 15 -> 10 ¹⁰

III 5)

9. (less I 20 - 1.4 x 10 ⁷ filler)

10.As 9 II 20 - 6 x 10 ¹⁰

11. "III 20 - 4 x 10 ¹⁰

02. "I 20 0.25 2 x 10 ⁴

13. "II 20 0.25 3 x 10 ⁸

14. "III 20 0.25 2 x 10 ⁹

15. "I 15 0.25 9 x 10 ⁴

16. "I 10 0.25 1 x 10 ⁵

17.As 8 I 5 0.25 5 x 10 ⁵

18. "I 4 0.25 2 x 10 ⁷

19. "I 3 0.25 5 x 10 ⁷

20. "I 2 0.25 5 x 10 ⁸ Continued Table 3 running adhesive filler C-fibers resistance

No. Type% by weight% by weight Ohm

21. as 8 Ia, II, III 1.67; 1, 67; 0.25 5 x 10 ⁹

1.67

22.As 9 I 5 0.5 3 x 106

23. "II 5 0.5 1 x 10 ⁶

24. "III 5 0.5 4 x 10 ⁸

25. "II 5 0.25 1.5 x 10 ⁹

26. "III 5 0.25 3 x 10 ⁹

27 as per no. 1 IV 5 - 1.5 x 10 ¹⁰

28 "IV 5 0.25 6 x 10 ⁸

29 "IV 10 - 1.5 x 10 ¹⁰

30 "IV 10 0.25 5 x 10 ⁹

31 "V 5 - 5 x 10 ¹⁰

02 "V 5 0.25 2 x 10 ⁹

33 "V 10 - 5 x 10 ¹⁰

34 "V 10 0.25 6 x 10 ⁸

The adhesive strength was determined by means of the peel resistance determination of a PVC bond in accordance with DIN 16860. After storage at room temperature (14 days at 23 ° C., 55% rel. Air humidity) or at 70 ° C. (7 d RT, 5 d 70 ° C, 2 d RT; as specified in DIN 16860) the following peel resistance values were found:

The results show that the adhesive according to the invention has a strength which is approximately 50% higher than that of the co-conductive material, which contains only the conductive pigment as a conductivity additive.

Claims

1. Composition for coating, sealing and adhesive containing

A an aqueous dispersion of polymers with an electrical resistance of more than 10 ¹⁰ ohms,

B bright conductive pigments and

C other additives such as non-conductive fillers, pigments, preservatives, dispersion aids, solubilizers, natural or synthetic resins and film aids,

marked by

B1) 2 to 15% by weight of bright metal compounds with a

Conductivity of more than 1 · 10 ^-2 ohm ^-1 cm ^-1 and

B2) 0.2 to 0.5% by weight of carbon fibers, based on the

entire composition, as an electrically conductive

Fillers.

2. Composition according to claim 1, characterized by one or more bright conductive pigments from the group titanium oxide, zinc oxide, zinc sulfide, barium sulfate and mica, with titanium oxide being preferred.

3. Composition according to claim 1, characterized by polymers

a) esters of acrylic acid with C ₁ -C ₈ alcohols,

b) vinyl acetate and optionally

c) acrylic acid and / or other copolymerizable

Carboxylic acids, especially methacrylic acid and crotonic acid.

4. Composition according to claim 1, characterized by 0 to 45 wt .-%, based on the total composition non-conductive fillers, the total concentration of fillers should not exceed 50% by weight.

Composition according to claim 1, characterized by 0 to 20% by weight, based on the total composition of resins, e.g. Balsam resin, as an additive.

6. Production of the composition according to at least one of claims 1 to 5, characterized in that the carbon fibers are mixed in evenly and gently.

7. Use of the composition according to at least one of claims 1 to 5 for the production of coatings, seals and bonds with an electrical resistance of <1 · 10 ⁷ ohms, measured according to DIN 53276.

8. Use according to claim 7, characterized by the application of the composition with a notched trowel with a tooth gap width of 4.5 mm, a tooth gap depth of 3.5 mm and with pointed dental bridges.

9. Use according to claim 7, characterized by the composition of titanium oxide in the form of a rutile mixed-phase pigment and of carbon fibers of 3 mm in length.

10. Use according to claim 7 for the production of electrically conductive bonds of floor coverings with a resistance of approximately 10 ⁷ ohms and less.