Finely divided precipitated silicas with a high structure, process for their preparation and their use.

The invention relates to a finely divided silica with a high structure, a process for producing the silica and the use of the silica as a matting agent in paint films.

It is known that the matting ability of a silica depends on various factors, such as, for example, the type of silica, the grain size, the refractive index and also the coating system. The particle shape and particle size distribution of the secondary particles and the overall effective specific particle volume are of particular importance.

In addition to high efficiency, expressed in terms of the reduction in the degree of gloss compared to the unmatted lacquer film, matting silicas also have a number of other requirements. For example, the drying behavior of the paint films should not be impaired, the paint system should not thicken excessively, and the scratch resistance of the paint films should not be reduced by the silica introduced.

An important point is the suspension behavior of the silica. The tendency of the silica to settle and to form hard soil bodies, which are difficult to stir up again, can be prevented or at least improved by a number of measures. For example, B. DE-AS 15 92 865 impregnation of silicas during the manufacturing process by means of wax emulsions.

It is known to use synthetic silicas as matting agents. Compare the pamphlets<ul id="ul0001" list-style="none"><li>EP-PS 0 008 613</li><li>DE-PS 24 14 478</li><li>DE-AS 17 67 332</li><li>DE-OS 1669 123</li><li>DE-AS 15 92 865</li></ul>

Numerous processes for the production of synthetic silicas are known (cf. Ferch in Chem.-Ing.-Techn. 48, 922-33 (1976).

According to DE-PS 24 14 478, airgel-like matting agents can be obtained by structuring pyrogenic silica. For this, pyrogenic silica is moistened with alkaline water, ground and dried. This procedure for producing matting agents is complex and expensive.

The matting agent according to DE-PS 24 14 478 is an excellent matting agent. It has the disadvantage that it thickens the paints too much. A solvent must therefore be added to work with the spray gun.

The object of the invention is to achieve the greatest possible savings in solvent requirements while maintaining the matting effect.

According to DE-PS 15 92 865, a wax-coated precipitated silica is produced and used as a matting agent.

This matting agent has the disadvantage that the paints produced with it have an undesirable blue haze on dark surfaces.

Another object of the invention is to produce a wax-coated matting agent that does not have a blue haze and has a better matting effect.

The invention relates to a fine-particle precipitated silica with a high structure<tables id="tabl0001" num="0001"><img file="EP0341383A2_D0001.tif" /></tables>

To determine the particle size with the Coulter Counter, approx. 0.5 g of silica in 50 ml of isotonic saline solution (0.5% NaCl and 0.089% Na₄P₂O₇ · 10 sts₂0 dispersed in distilled water) with a magnetic stirrer and then treated with ultrasound (200 watts) for 1 minute. This suspension is added to 200 ml of isotonic saline and stirred.

A measuring capillary is immersed in the stirred suspension and an electric field is applied to it. When the particles pass through the measuring capillary, the electric field changes depending on the particle size.

Another object of the invention is a method for producing the fine-particle precipitated silica with a high structure<tables id="tabl0002" num="0002"><img file="EP0341383A2_D0002.tif" /></tables>which is characterized in that a mixture of water and sodium silicate is heated to a temperature of 70 to 80 ° C with stirring, concentrated sulfuric acid is metered into this template until half of the alkali present is neutralized, the reaction mixture is treated by means of a shear unit and optionally at the same time the temperature increased to 86 t 5 ° C, after a period of 30 to 120 minutes concentrated sulfuric acid at a higher rate, Adds until the pH of the resulting silica suspension is 3.0 to 3.5, if necessary dilutes the silica suspension with water, optionally removes the coarse fraction using a centrifugal pump and a hydrocyclone, filters the silica using known filter devices, washes the silica filter cake sulfate-free, redispersed the silica filter cake with the addition of water by means of a stirrer to a suspension with a solids content of 80 ± 10 g / l, optionally adding alkyldimethylbenzylammonium chloride to this suspension, spray-drying the suspension thus obtained and optionally grinding the dried product.

The invention is based on the task of producing silica particles with particle diameters in the grain size range from 1 to 6 μm. Particles smaller than 1 µm are ineffective for matting and usually cause undesirable thickening of the paints. On the other hand, particles that are too large lead to a disadvantageous roughness of the surface in the finished paints. The task is to set appropriate particle sizes during the precipitation and to preserve them through suitable measures to the finished product.

To ensure that all particles find the same growth conditions, the entire water glass is placed. Sulfuric acid is added in two steps. In the first step, the acid addition is measured so that after the end of the first stage of acid addition the silica begins to flocculate. During this growth phase, shear is added in addition to stirring to prevent excessive particle growth. The acid addition remains interrupted until the desired particle spectrum is reached. The remaining alkali content of the water glass is then neutralized in a second stage, while shearing continues. After a weakly acidic pH has been reached, the precipitation is complete.

The silica suspension is worked up in the usual way. There is a possibility that hard and coarse particles are formed by local acidification. These can be removed from the suspension using a hydrocyclone. The suspension is filtered, for example, with a frame filter press in which the filter cake is washed free of sulfate. The washed filter cake is redispersed in water, optionally a cationic surfactant is added and spray-dried. The cationic surfactant causes water to be displaced from the particle surface even in the aqueous phase, as a result of which the shrinkage process occurring during the drying process is largely prevented. In this way, it can be prevented that the particles accumulate to form larger, firm associations during drying. Depending on the desired fineness, the silica obtained can be used in this way or additionally ground. Due to the procedure described, light grinding is sufficient, ie only a small amount of grinding energy has to be used to deagglomerate the particles again.

The precipitated silica according to the invention can be used as a matting agent in paints.

It has the advantage that no additional solvent has to be used.

To improve the settling behavior of the silica products in paints, impregnation with emulsions is carried out in accordance with DE-PS 15 92 865.

Another object of the invention is a precipitated silica coated with an emulsion, which is produced from the precipitated silica according to the invention. The coating can be carried out by a known method according to DE-PS 15 92 865.

In addition to the same physico-chemical characteristics of the uncoated precipitated silica, the coated precipitated silica has a carbon content of 1 to 8% by weight.

In one embodiment of the invention, the precipitated silica can be coated using a silicone oil emulsion.

This precipitated silica can be used as a matting agent in paints.

In a special embodiment of the invention, the precipitated silica can have been coated by means of a polyethylene wax emulsion.

This precipitated silica can be used as a matting agent in paints.

It is particularly advantageous that the precipitated silicas coated with the wax emulsion do not produce a blue haze in the lacquer surfaces.

Examples

The process according to the invention is carried out in known apparatus.

The centerpiece of the precipitation apparatus is a hard-rubberized double jacket with a volume of 120 liters, which is equipped with an agitator. For example, anchor stirrers, bar stirrers or turbines are suitable as stirrers. The reaction vessel can be heated and thermostatted via the double jacket with oil as the heat transfer medium. At the bottom of the reaction vessel, a drain pipe is attached, which has a branch in front of the bottom outlet valve. This branch leads to a shear unit (Dispax reactor). with which the contents of the reaction vessel can be circulated. The recirculated precipitation suspension is reintroduced into the top of the reaction vessel through the pipeline attached to the pressure side of the shaving unit. Water glass is added either via a dosing pump from a storage vessel or directly from a barrel using a barrel pump. The sulfuric acid is dosed from a storage vessel using a dosing pump.

For the filtration, the precipitation suspension is pumped with the help of a positive displacement pump into a frame filter press, on which the filter cake formed is washed with sulfate-free water.

The washed filter cake is either placed on trays and dried in a drying cabinet or dispersed in water and spray dried.

The dried silica can then be ground. The product dried in the drying cabinet usually has to be pre-ground using a toothed disc mill before the fine grinding is carried out using a pin or air jet mill. The spray-dried product can either be used directly or subjected to fine grinding.

The effectiveness of the uncoated precipitated silicas produced according to Examples 1-6 is compared in a black stoving lacquer with the product produced according to DE-PS 24 14 478. In addition to the solvent requirement, the gloss level according to Lange at a reflection angle of 60 and the grindometer value according to Hegman are assessed.

The gloss meter according to B. Lange, widely used in Germany, is used to determine the degree of gloss, which is a measure of the matting power of the tested matting silica. The Lange gloss meter uses a 45 ° angle of incidence and reflection. The measured gloss levels are given in percent. The smaller its value, the better the matting ability of the tested silica or, in other words, the less matting agent has to be used in order to achieve a specific degree of gloss.

The grindometer value is determined using a grindometer. The grindometer value, which in u. is measured is a measure of the coarsest particles that are in the finished, sprayable paint mixture after the matting silica has been stirred in. It can be related to the formation of specks in the dry paint film. With the help of the grindometer, the dreaded, unwanted "spray grain" can be recognized.

The paint used has the following composition:<tables id="tabl0003" num="0003"><img file="EP0341383A2_D0003.tif" /></tables>

2.6 parts by weight are incorporated. Product. The incorporation takes place by stirring for 10 minutes with a paddle stirrer at 2000 rpm. The paint is sprayed onto sheet metal in a 30 µm thick dry layer. air dried and baked at 180 C for 30 min.

The values ​​determined can be found in Table 2.

example 1

66 kg water and 21 kg soda water glass (d = 1.35 g / cm³; SiO module₂, : N / A₂0 = 3.3) and the mixture is heated to 75 ° C. with stirring. Concentrated sulfuric acid (d = 1.83) is metered into this precipitation template at a rate of 1.45 l / h in 30 minutes. After 25 minutes of precipitation, the shaving unit (Dispax reactor) is switched on. Shortly after the end of the acid addition, silica begins to flocculate and the temperature of the precipitation is raised to 85 ° C. The acid supply remains interrupted for 20 minutes (waiting stage). After 50 minutes, the further acid is added at 1.8 l over a period of 15 minutes. The resulting silica suspension then has a pH of 3.4. The shaving unit is switched off.

The suspension is diluted with 28 l of water and applied to a hydrocyclone by means of a centrifugal pump with an inlet pressure of 4.5 bar. The ratio of coarse to fine suspension is 1:12.

The fine material suspension is passed through a frame filter press and washed free of sulfate.

The washed filter cake is redispersed with an Ultra-Turrax with the addition of water so that a suspension of 80 g / l is formed. An alkyldimethylbenzylammonium chloride (BARQUAT @) is added to the suspension so that 0.8 g / l of active ingredient are present in the suspension.

This suspension passes through a sieve with a mesh size of 120 μm, whereby coarse foreign particles are retained. Immediately afterwards the suspension is spray dried. The atomization takes place using a two-substance nozzle.

The dried product has the following physicochemical properties:<tables id="tabl0004" num="0004"><img file="EP0341383A2_D0004.tif" /></tables>

Example 2-5

Precipitated silicas are produced as described in Example 1, with the only difference that the duration of the interruption of the acid addition (= waiting stage) is varied.

The physico-chemical data of the products obtained are listed in Table 1.

Example 6

A precipitated silica is produced as described in Example 1. In contrast to Example 1, heating to 85 ° C. is dispensed with during the second phase of acid addition. The waiting time is 30 minutes.

The physico-chemical data of the precipitated silica obtained are listed in Table 1.

Example 7 (coating with silicone oil emulsion)

A precipitated silica, as described in Example 1, is produced. In contrast to example 1, the waiting time is 60 minutes. After the end of the precipitation, 3.4 kg of an emulsion of silicone oil are added to the precipitated silica suspension.

The emulsion is made as follows:<ul id="ul0002" list-style="none"><li>0.24 parts by weight of Emulan AF are dissolved in 80 parts by weight of water. 20 parts by weight of Baysifon-Oil® AC 3031 are added while dispersing with an Ultra-Turrax.</li></ul>

The precipitation silica suspension is worked up as described in Example 1. The spray-dried precipitated silica is then ground in an air jet mill.

The physicochemical data are listed in Table 3.

Example 8 (coating with polyethylene wax emulsion)

The precipitated silica is produced as described in Example 1. The waiting time is 90 minutes. 45 I of the fine suspension obtained are mixed with 625 g of a wax emulsion with stirring. The wax emulsion is produced in an autoclave which can be heated with steam and equipped with a disperser. In this, 4.8 parts by weight of an alkyl polyglycol ether (Marlowet® GFW) are first dissolved in 81.0 parts by weight of water at 100 ° C. at about 100 ° C.

14.2 parts by weight of low-pressure polyethylene wax are then added and the mixture is heated to 130.degree. When 130 ° C is reached, the disperser is switched on and dispersed for 30 minutes. During this time the temperature is kept between 130 ° C and 140 ° C. After switching off the disperser and cooling to around 110 ° C, the finished emulsion is drained.

The polyethylene wax used is characterized by the following key figures:<tables id="tabl0005" num="0005"><img file="EP0341383A2_D0005.tif" /></tables>

The precipitation silica suspension is worked up as described in Example 1. The spray-dried precipitated silica is then ground in an air jet mill.

The physicochemical data are listed in Table 3.

Example 9 (coating with polyethylene wax emulsion)

The precipitated silica is produced as described in Example 1. The waiting time is 90 minutes. From the fine suspension obtained, 45 l are mixed with 860 g of a wax emulsion with stirring. The wax emulsion is produced in an autoclave which can be heated with steam and equipped with a disperser. In this, 4.8 parts by weight of an alkyl polyglycol ether (Marlowet® GFW) are first dissolved in 81.0 parts by weight of water at 100 ° C. at 100 ° C.

14.2 parts by weight of low-pressure polyethylene wax are then added and the mixture is heated to 130.degree. When 130 ° C is reached, the disperser is switched on and dispersed for 30 minutes. During this time the temperature is kept between 130 ° C and 140 ° C. After switching off the disperser and cooling to around 110 ° C, the finished emulsion is drained.

The polyethylene wax used is characterized by the following key figures:<tables id="tabl0006" num="0006"><img file="EP0341383A2_D0006.tif" /></tables>

The precipitation silica suspension is worked up as described in Example 1. The spray-dried precipitated silica is then ground in an air jet mill.

The physico-chemical data are listed in Table 3.

Example 10

The performance properties of the precipitated silicas obtained according to Examples 7, 8 and 9 are compared in three test lacquer formulations with a matting agent prepared according to DE-PS 15 92 865. The data are summarized in Table 4.

The degree of gloss is determined using gloss meters according to Lange or Gardner (ASTM D 523 - 53 T). According to Lange, the angles of incidence and reflection are 45 °, according to Gardner 60 and 85 °. The grindometer value is determined according to ISO 1524 in the black stove enamel.

The test lacquer formulations and the procedure are described below.

A) Black stove enamel

<tables id="tabl0007" num="0007"><img file="EP0341383A2_D0007.tif" /></tables>

5 g of precipitated silica or matting agent are stirred into 100 g of lacquer with a paddle stirrer at 2000 rpm for 8 minutes. The viscosity of the mixture is adjusted with xylene to an outflow time of 20 seconds (Ford cup, DIN 4 mm nozzle).

The varnish is sprayed onto sheet metal in a 30 μm thick dry layer, air dried and 30 min. Baked at 180 ° C.

B) polyester lacquer (UP lacquer)

<tables id="tabl0008" num="0008"><img file="EP0341383A2_D0008.tif" /></tables>

6.5 g of precipitated silica or matting agent are introduced into 100 g of this lacquer mixture before processing and dispersed for 8 minutes at 2000 rpm using a paddle stirrer. The viscosity of the mixture is adjusted to an outlet time of 20 seconds (Ford cup, DIN 4 mm nozzle) with ethyl acetate. The paint mixture is applied in layers of approx. 80 µm.

C) DD varnish

<tables id="tabl0009" num="0009"><img file="EP0341383A2_D0009.tif" /></tables>

10.8 g of matting agent and 36 g of Desmodur® L / 75% in ethyl acetate are added to 100 g of the above mixture and dispersed for 8 minutes at 2000 rpm using a paddle stirrer. The mixture is adjusted to an outlet time of 18 seconds with ethyl acetate (DIN cup, 4 mm nozzle according to DIN 53211). The application takes place in layer thicknesses of 30 - 40 µm.

As can be seen from Table 4, a significant improvement in the matting effect can be found in all test lacquer formulations compared to the prior art.<tables id="tabl0010" num="0010"><img file="EP0341383A2_D0010.tif" /></tables><tables id="tabl0011" num="0011"><img file="EP0341383A2_D0011.tif" /></tables><tables id="tabl0012" num="0012"><img file="EP0341383A2_D0012.tif" /></tables><tables id="tabl0013" num="0013"><img file="EP0341383A2_D0013.tif" /></tables>The trade names used in the examples gave the following meanings:

Varnish pre-paste Tack® 1

<tables id="tabl0014" num="0014"><img file="EP0341383A2_D0014.tif" /></tables>

Alftalat AR 481 m

Characteristics: Short or medium oil, drying alkyd resins. Type of oil: castor oil

Areas of application: stove enamels and primers for metal surfaces. Acid-curing paints. Combination nitrocellulose varnishes.<tables id="tabl0015" num="0015"><img file="EP0341383A2_D0015.tif" /></tables><tables id="tabl0016" num="0016"><img file="EP0341383A2_D0016.tif" /></tables>

Maprenal MF 800

Characteristics: Unplasticized, isobutyl etherified melamine formaldehyde resins.<tables id="tabl0017" num="0017"><img file="EP0341383A2_D0017.tif" /></tables>

Baysilone paint additive OL 17

<tables id="tabl0018" num="0018"><img file="EP0341383A2_D0018.tif" /></tables>

Baysilon-Oil® AC 3031

<tables id="tabl0019" num="0019"><img file="EP0341383A2_D0019.tif" /></tables>

Emulan AF

<tables id="tabl0020" num="0020"><img file="EP0341383A2_D0020.tif" /></tables>

Alkydal R 40

<tables id="tabl0021" num="0021"><img file="EP0341383A2_D0021.tif" /></tables>

Roskydal 500 A.

<tables id="tabl0022" num="0022"><img file="EP0341383A2_D0022.tif" /></tables>

Roskydal tix 18th

<tables id="tabl0023" num="0023"><img file="EP0341383A2_D0023.tif" /></tables><tables id="tabl0024" num="0024"><img file="EP0341383A2_D0024.tif" /></tables>

Pigment green 6001

<tables id="tabl0025" num="0025"><img file="EP0341383A2_D0025.tif" /></tables><tables id="tabl0026" num="0026"><img file="EP0341383A2_D0026.tif" /></tables>

Octa-Solingen-Cobalt

Octa-Solingen cobalt is a dry substance which, in addition to 2-n ethylhexanoic acid (C₈H₁₆O₂) Contains 16% Co.

Desmophen 800

<tables id="tabl0027" num="0027"><img file="EP0341383A2_D0027.tif" /></tables>

Aerosil

R

200

Aerosil^R 200 is a fumed silica with the following physico-chemical characteristics:<tables id="tabl0028" num="0028"><img file="EP0341383A2_D0028.tif" /></tables>

Desmophen 1700

<tables id="tabl0029" num="0029"><img file="EP0341383A2_D0029.tif" /></tables>

NC chips E 730

NC-Chips E 730 is a collodion wool

Shellsol® A

Shellsol® A is an aromatic-rich carbon solvent with the following data:<tables id="tabl0030" num="0030"><img file="EP0341383A2_D0030.tif" /></tables>

Desmodur L

<tables id="tabl0031" num="0031"><img file="EP0341383A2_D0031.tif" /></tables>