WO1999051692A1

WO1999051692A1 - Matting agents based on coated silicon dioxide

Info

Publication number: WO1999051692A1
Application number: PCT/EP1999/002160
Authority: WO
Inventors: Ute Pospesch; Horst Schneider; Georg Lüers
Original assignee: Grace Gmbh
Priority date: 1998-04-03
Filing date: 1999-03-30
Publication date: 1999-10-14
Also published as: AU3418799A; DE19816362A1; TW500779B

Abstract

The invention relates to a matting agent based on silicon dioxide, the silicon dioxide particles having a particle size of 2.5 to 20 νm and a moisture content of 0 to 65 wt.%, based on the matting agent, and being coated with 0.2 to 10 wt.% of a urea-urethane derivative or a mixture of urea-urethane derivatives.

Description

Matting agents based on coated silicon dioxide

The present invention relates to coated matting agents, processes for their preparation and their use in paints and lacquers.

Silicon dioxide particles or silica gel particles are used, inter alia, as matting agents to achieve a micro-rough surface on coatings. However, in most solvent- or water-based paints and lacquers, untreated silica gel particles often form hard sediments during storage. Attempts to redisperse these matting agents are usually difficult, and in many cases unsuccessful. This then often means that the gloss of coatings produced with such paints varies as the paint is used up, since some of the matting agent accumulates on the bottom of the container in which the paint or lacquer is stored. To avoid this undesirable effect, additives such as bentonites , which form thixotropic structures and prevent sedimentation of the particles, are added by the paint manufacturer. Another possibility is that the manufacturer modifies the matting agents themselves, i.e. for example coats them with a wax chosen from the group consisting of polyolefins, mineral waxes, paraffins and the like. 5 to 10 wt.% wax, based on the matting agent, is usually used to form a matting agent which gives, in conventional paints and lacquers, soft sediments which can easily be redispersed. - 2 -

DE 10 06 100 thus discloses a process for the preparation of silica gel matting agents in which dried and ground silica gel is impregnated with microcrystalline wax which is insoluble in solvents for lacquers and the like. The process is carried out at temperatures above the melting point of the wax.

Another process for the preparation of matting agents is known from DE 15 92 865. In this process, an aqueous emulsion or dispersion of an inert colourless high-melting wax or synthetic substances which is insoluble in lacquer solvents at room temperature is employed for modification of the silicic acids.

WO 95/31508 discloses a matting agent based on an amorphous silica gel having a certain pore size distribution, which is coated with specific waxes and has good matting properties, and a process for the preparation thereof.

EP-A-0 348 226 discloses a matting agent based on an inorganic hydrogel having a certain pore volume and content of volatile substances, and a specific average particle size and particle size distribution, so that a certain grinding fineness is obtained when it is dispersed in a coating composition.

EP-A-0 003 627 discloses a process for the preparation of a hydrophilic composition of urea, formaldehyde and an aqueous colloidal dispersion of silica particles, in which various mixing stages are carried out at certain pH values and the silica particles have an average size of 1 to 8 μm. The compositions obtained by the process disclosed are used in photographic photosensitive silver halide material.

WO 97/12942 discloses a coating material which can be cured by irradiation or heat and consists of a composition which comprises chemically modified silicon dioxide particles. The silicon dioxide particles are modified to the effect that organic compounds which contain polymeric unsaturated groups, (thio)urea - 3 -

groups and ( thio)urethane groups are bonded chemically to their surface via a silyloxy group.

The abovementioned processes for coating silicon dioxide particles have the disadvantage of consuming relatively large amounts of wax (5 to 10 wt.%). Furthermore, they cannot be used with hydrogel matting agents for the following reasons. Silicon dioxide xerogel particles are usually coated with wax in a jet mill at temperatures above the melting point of the wax. During this operation, the molten wax is distributed homogeneously on the silicon dioxide particles. If the wax is added during the micronization of a hydrogel, which is carried out at relatively low temperatures, this does not lead to coating of the particles because the melting point of the wax is not reached (the maximum possible temperature during grinding of the hydrogel in the jet mill is 505C, and increasing the heat supplied would have the effect only of evaporating the water from the silica gel, and not of increasing the temperature) . The use of such a mixture of silicic acid hydrogel and wax particles in water-based paints or lacquers therefore leads to the formation of hard sediments. The wax therefore has no effect.

The object of the present invention is thus to provide an efficient matting agent which, during storage in water-based paints and lacquers, forms soft sediments which can readily be redispersed. It is also an object of the present invention to provide a more efficient coating process for silicon dioxide particles, which is superior to the coating with wax known from the prior art.

These objects are achieved by a matting agent based on silicon dioxide, which is characterized in that it comprises silicon dioxide particles which have a particle size of 2.5 to 20 μm and a moisture content of 0 to 65 wt.%, based on the matting agent, and are coated with 0.2 to 10 wt . % of a urea-urethane derivative or a mixture of urea-urethane derivatives of the general formula: - 4 -

R¹-0-CO-NH-R³-NH-CO-NH-R⁵-NH-CO-NH-R⁴-NH-CO-OR² ( I )

in which R 1 and R2 independently of one another are C_nH_2n+1- or C_mH_2m+1(C_pH_2pO)_r-, n = 4 to 22, m = 1 to 18, p = 2 to 4, r = 1 to 10, R and R independently of one another are

-Q-CH₃, - H₃, HQ- H₂HQ- _or __(CH₂)₆-

and

R⁵ =

H

*1 CΛ»Ht, ** C ≠ πu

CH„-

O hO- ^■ -O- CH-O, -

CH--

-CH₂-CH₂-, -(CH₂)₆- or -(CH₂)₁₂-.

The invention furthermore relates to a process for the preparation of a matting agent, which is characterized in that the urea-urethane derivative ( s ) of the formula (I) is/are added to the silicon dioxide during the micronization thereof.

The sub-claims relate to preferred embodiments of the invention.

The urea-urethane derivatives according to the invention are also called the organic component or additive in the following.

The organic additive is thus in general a urea-urethane compound of low molecular weight.

In a preferred embodiment of the invention, in the urea-urethane derivative of the formula (I), independently of one another, n = 4 - 18, in particular 4 - 14, preferably 4 - 8, m = 1 - 15, in particular 1 - 12, preferably 4 - 8, p = 2 or 3, in particular - 5 -

2, and r = 1 - 8, in particular 3 - 8, preferably 4 - 6. R and R independently of one another are preferably

-Q > j--a ' or

-Ov©-

and R is preferably

0,-0- or

Examples of urea-urethane derivatives which are particularly preferred according to the invention are: . — . o o

CH-JCHJICHJCHJO),— C ^NH— ^T^^^I— ^NH— ^C-^NH (QV^{" H}* \0) ^NH_C~ ^NH~ f_f^l ^NH_C ~^" '∞^^CH^,^^

CHj CHj C1 , CHV

or

O O

C₄H_a(CH₂CH₂0)_s — C— l H — r^~^| — NH— C — t- H ( j) — ^{a i}2 ( ~ ) NH— C— NH — r^N"! NH— C— (OCH_jCHgJ^Hg CHj CHj

CHj'

wherein s+t = 6 to 9 and s and t are greater than or equal to 3

The silicon dioxide component is preferably chosen from silicic acid hydrogels and/or silicic acid xerogels. These can be prepared by the sol-gel process or by the precipitation process. The size of the silicon dioxide particles is preferably 5 to 15 μm, in particular 5 to 10 μm.

Depending on whether hydrogels or xerogels are used for the preparation of the matting agents according to the invention, the silicon dioxide particles have a moisture content of 0 to 10 wt.%, in particular 0 to 5 wt.%, and preferably 1 to 3 wt . % , or 5 a moisture content of 30 to 65 wt.%, in particular 40 to 60 wt.%, and preferably about 50 wt.%, based on the matting agent. They - 6 -

are preferably coated with 0.3 to 8 wt.%, in particular 0.5 to 3 wt . % urea-urethane derivative of the formula (I), based on the matting agent.

It is known from the prior art that the bipolar structure of urea-urethane derivatives in solvents of a certain polarity leads to the formation of three-dimensional networks . This effect is utilized to generate a thixotropic effect in lacquers and paints, which e.g. prevents silica gel particles from forming hard sediments. However, the three-dimensional structure is formed only in systems of a certain, i.e. moderate, polarity. Thus, according to the manufacturer' s specification, the commercial product BYK-410 from BYK Chemie GmbH, which falls under the above formula (I), shows no thixotropic effect in alcohol and water.

Surprisingly, the formation of hard sediments in water-based lacquers and paints is avoided if silicon dioxide particles or silica gel particles which act as the matting agent are coated with the urea-urethane derivatives according to formula (I).

The matting agents according to the invention are in general prepared by adding the urea derivatives according to the invention to the silicon dioxide during comminution thereof. This can be carried out, for example, in a jet mill or in high-speed mixers (e.g. in a Henschel mixer). The jet mill is preferably operated with a hot air supply. As a result, the organic component is distributed in the form of very fine particles on the silica gel particles.

The urea derivatives themselves can be prepared as disclosed in EP-A-0 006 252. They can advantageously be added in the form of organic solutions which contain 10 to 75 wt.%, preferably 30 to 60 wt.%, and in particular 45 to 55 wt.% urea-urethane derivative. N-Methylpyrrolidone, for example, can be used as the solvent. Thus, for example, the commercial product BYK-410 from BYK Chemie GmbH, Wesel, which comprises the urea-urethanes of the - 7 -

general formula I in the form of an up to 65 wt.% solution in N- methylpyrrolidone can be particularly advantageously employed.

The silicon dioxide or silica gel used in the process according to the invention can be prepared by the sol-gel process, as described, for example, in EP-A-0 384 226.

Hydrogels are employed according to the invention in particular. Hydrogel matting agents have the advantage that they do not form dusts, because the pores are filled with water. Small amounts of surface water cause an adhesion of the particles to one another. In the process according to the invention, for example, the hydrogel is micronized with hot air in a jet mill, dried to a moisture content of 30 to 65 wt.%, preferably 40 to 60 wt.%, in particular about 50 wt.%, and coated with the urea derivative.

If a xerogel is employed, this is preferably micronized with hot air in a jet mill, adjusted to a moisture content of 0 to 10 wt.%, preferably 0 to 5 wt.%, in particular 1 to 3 wt.%, and coated with the urea derivative.

The new coating process as a rule requires only about 1 wt.% organic material, based on the matting agent, although less or more organic material can be employed according to the invention for the coating. Considerably lower concentrations of organic additive are therefore needed to allow the formation of soft sediments, which can readily be redissolved, in paints and lacquers. In contrast, in the case of wax coatings, 5 to 10 wt.% wax is needed to prevent the formation of hard sediments in water-based systems to a sufficient extent. The process according to the invention therefore not only gives a cost advantage due to saving of material and lower process temperatures, but also increases the efficiency of the matting agent. The efficiency of the material is higher, because the silicon dioxide content, which causes the matting, is higher. - 8 -

It is assumed that in the case of the matting agents according to the invention, the formation of hard sediments is avoided by the following mechanism: The urea-urethane derivative must in general be separated into individual molecules so that it has the maximum activity. This is typically achieved by dissolving it in solvents of moderate polarity. The addition of the additive to the silica gel particles in the jet mill, however, leads to deaggregation to very fine particles, regardless of the solvent. These very fine particles of the organic component are bonded to the silica gel particles. This causes an inhomogeneous polarity of the particle surface and consequently only a loose agglomeration ( flocculation) during sediment formation. The flocks are large enough to withstand the gravimetric forces in the sediment, and remain soft and, even after storage, readily dissolvable.

The matting agents according to the invention can therefore advantageously be used in water-based coatings, paints and lacquers and aqueous radiation-curing lacquer systems .

Examples

The pore volume of the particles was measured by adsorption of nitrogen using an ASAP 2400 nitrogen adsorption measuring instrument from Micro eritics . The particle sizes were determined with the aid of the Malvern Mastersizer from Malvern Instruments Ltd. The moisture content of the hydrogel was determined via the weight loss at a temperature of 160°C. The moisture content of the xerogel was measured using a Karl-Fischer device. The percentages by weight stated relate to the weight of the end product (matting agent).

The carbon content was measured using a Leco SC 440 apparatus (Dύsseldorf) and stated in per cent by weight, based on the silicon dioxide content in the end product. - 9 -

The sedimentation experiments were carried out in two lacquer systems: a) Senosol-Hydro-Glanzlack, a clear water-based coating from Weilburger Lackfabrik, and b) WACOCELL S 689 from Lackchemie Mannheim, Wagner GmbH.

Example 1

Using the sol-gel process, a silicic acid hydrogel having a moisture content of 65 wt.% was prepared and micronized in a jet mill operated with hot air. The hot air temperature was 220°C and the amount introduced was 720 kg/h. At the same time, 2.6 1/h urea-urethane derivative BYK-410 (commercial product from BYK Chemie GmbH Wesel) were introduced into the jet mill via an inlet nozzle. The resulting product had a particle size of 8 μm, a water content of 54.5% and a carbon content of 0.56 wt.% (corresponding to an additive concentration of about 0.7 wt.%).

Comparison example 1

As in example 1, using the sol-gel process, a silicic acid hydrogel having a moisture content of 65 wt.% was micronized to a particle size of 8.0 μm and a water content of 56.3 wt.% in a jet mill with a hot air supply. In contrast to example 1, however, no coating was carried out.

In each case 3 g of the products prepared in example 1 and comparison example 1 were incorporated into 100 g Senosol Hydro- Glanzlack, type 07-1415-405.314 (Weilburger Lackfabrik, Weilburg) by stirring with a dissolver (dispersing unit) for 10 minutes at 3,000 rpm (revolutions per minute). The lacquer was then introduced into 100 ml vessels and the closed vessels were stored in the laboratory at room temperature for 6 weeks . After this period of time, the consistency of the sediments formed from the matting agent particles was investigated. - 10 -

The non-coated hydrogel matting agents (comparison example 1) formed a hard sediment which could no longer be dispersed by shaking. It was possible to remove the sediment from the bottom of the vessel only by using a spatula. The hydrogel coated with BYK-410 (example 1) formed a sediment which could be redispersed very easily. The sediment already became detached from the bottom of the vessel by merely turning the vessel over.

Example 2

A silica acid xerogel prepared by the sol-gel process and having a moisture content of about 1 wt . % and a particle size of 0.1 to 3 mm was mixed with BYK-410 in a Henschel mixer of the type FM 10L. 7.5 g of the organic compound were added to 750 g silica gel while stirring at 1,000 rpm for 10 minutes. When the addition had ended, mixing was continued for 10 minutes at 2,500 rpm. The mixture was micronized to a particle size of 5 μm in a fluidized bed jet mill of the type Alpine AFG 100. The grinding conditions used here were:

Grinding pressure: 5.0 bar

Air consumption: 26 m /h

Temperature in the grinding chamber: 163°C

Sifter: 15,050 rpm

A product having a particle size of 5.49 μm, a carbon content of 0.66 wt.% and a moisture content of 2.7 wt.% was obtained.

Comparison example 2

Starting from the same xerogel as in example 2, a non-coated comparison material was prepared in the same mill as in example 2 under the following conditions: - 1 1 -

Grinding pressure: 5.0 bar

Air consumption: 19 m /h

Temperature in the grinding chamber: 19 °C

Sifter: 15,170 rpm

The product thus obtained had a particle size of 5.5 μm, a carbon content of < 0.2 wt.% and a moisture content of 1.34 wt.%.

Comparison example 3

A wax-coated comparison material was prepared on a production scale by grinding silicic acid xerogel in an air jet mill with simultaneous addition of wax into the jet mill. The silica gel was fed in at 350 kg/h and the wax at 30 kg/h. The other grinding conditions were:

Grinding pressure: 7.5 bar

Air consumption: 1,780 m /h

Temperature in the grinding chamber: 138°C

A product having a particle size of 5.56 μm, a carbon content of 7.5 wt.% and a moisture content of 1.3 wt.% was obtained.

In each case 3 g of the products obtained in example 2, comparison example 2 and comparison example 3 were incorporated into 100 g Senosol Hydro-Glanzlack in the same manner as described under example 1 and comparison example 1. The sedimentation of the particles was also investigated as in example 1. After 6 weeks, the consistency of the sediments was evaluated as follows .

Example 2 : The product according to the invention formed a sediment which could be redispersed very easily. The sediment could already be detached from the bottom merely by turning the vessel over. - 12 -

Comparison example 2 : The non-coated product formed a hard sediment which could be detached from the bottom again only using a spatula.

Comparison example 3: The product coated with wax formed a hard sediment which could be redispersed by vigorously shaking the vessel .

The comparison shows the clearly improved properties of a coating with 1 wt . % BYK-410 compared with a coating with 10 wt.% wax and non-coated matting agent.

Comparison example 4

The products from example 2, comparison example 2 and comparison example 3 were incorporated into a conventional nitrocellulose paint (WACOCELL S 689). In each case 2 g of the matting agent were incorporated into 100 g nitrocellulose paint using a dissolver at 3,000 rpm for 10 minutes, the mixture was introduced into 100 ml vessels and these were closed and stored in the laboratory at room temperature for 6 weeks. After this time, the consistency of the sediments formed from the matting agent particles was investigated:

Example 2 : The product coated according to the invention formed a hard sediment which was comparable to that of the product from comparison example 2.

Comparison example 2 : The non-coated matting agent formed a hard sediment which could be dispersed only with great difficulty.

Comparison example 3 : The dispersing agent coated with wax formed a sediment which could be redispersed very easily. The sediment could already be detached from the bottom by turning the vessel over. - 13 -

This comparison shows that the effect according to the invention, i.e. the avoidance of the formation of hard sediments by coating with urea-urethane derivatives, can be achieved only in water- based paints .

Claims

- 14 -

Patent claims

Matting agent based on silicon dioxide, characterized in that it comprises silicon dioxide particles which have a particle size of 2.5 to 20 μm and a moisture content of 0 to 65 wt.%, based on the matting agent, and are coated with 0.2 to 10 wt.% of a urea-urethane derivative or a mixture of urea-urethane derivatives of the general formula:

R¹-0-CO-NH-R³-NH-CO-NH-R⁵-NH-CO-NH-R-NH-CO-OR² ( I )

in which R 1 and R2 independently of one another are C_nH_2n+1- or C_mH_2m+1(C_pH_2pO)_r-, n = 4 to 22, m = 1 to 18, p = 2 to 4, r = 1 to 10,

R and R independently of one another are

- -^CH- >-CH, or -(CH₂)₆-

-o-^∞-< ^■o- and

R

-O-ϊ H-O- • - CQH. iQ CH-,

CH,-

-o-to- - -otp- • ό^

-CH₂-CH₂-, -(CH₂)₆- or -(CH₂)₁₂-.

2. Matting agent according to claim 1, characterized in that it comprises silicon dioxide particles having a particle size of 5 to 15 μm, in particular 5 to 10 μm. - 15 -

3. Matting agent according to claim 1 or claim 2, characterized in that the silicon dioxide particles have a moisture content of 0 to 10 wt.%, in particular 0 to 5 wt.%, and preferably 1 to 3 wt.%, based on the matting agent .

4. Matting agent according to claim 1 or claim 2, characterized in that the silicon dioxide particles have a moisture content of 30 to 65 wt.%, in particular 40 to 60 wt.%, and preferably about 50 wt.% , based on the matting agent .

5. Matting agent according to one of the preceding claims, characterized in that the silicon dioxide particles are coated with 0.3 to 8 wt.%, preferably 0.5 to 3 wt.% urea- urethane derivative of the formula (I), based on the matting agent.

6. Matting agent according to one of the preceding claims, characterized in that the silicon dioxide is chosen from silicic acid hydrogels and/or silicic acid xerogels.

7. Matting agent according to one of the preceding claims, characterized in that, in the urea-urethane derivative of the formula (I), independently of one another, n = 4 - 18, in particular 4 - 14, preferably 4 - 8, m = l - 15, in particular 1 - 12, preferably 4 - 8, p = 2 or 3, in particular 2, and r = 1 - 8 , in particular 3 - 8, pprreeffeerraabbllyy 4 - 6, R and R independently of one another are preferably

^•Q -CH, ,

-T O- and R = H _ _ H

Ot ^H-O or C -QH f ^H Q CH-₃ - 16 -

8. Matting agent according to one of the preceding claims, characterized in that the urea-urethane derivative has the formula

O

II

CH. j^CH₂ ^,-^-^NH-^t^ ^»^ (O/ ^N N^H— C^_—^NN^HHπ ^-^:^_rr_^" _NH_C-(C H₂CH₂,,CH₂CH₃

CH, CHj' CH, CHV or

O II

3₄H_g(CH₂CH₂0)_s-C— N IlH— ^\Y— NH-C-NF ^-o 1H-C— NH— r-^sY— NH-C— (CCH_jC+Lj^H-,

_Q ^"CH_j CHj CHj CH^j in which s + t = 6 - 9 and s and t are greater than or equal to 3.

Process for the preparation of a matting agent, according 5 to one of claims 1 to 8 , characterized in that the urea- urethane derivative( s) of the formula (I) is/are added to the silicon dioxide during micronization thereof.

10. Process according to claim 9, characterized in that the 0 urea-urethane derivative is added in the form of an organic solution which comprises 10 to 75 wt.%, preferably 30 to 60 wt.%, and in particular 45 to 55 wt.% of the urea-urethane derivative .

5 11. Process according to claim 10, characterized in that the organic solvent is N-methylpyrrolidone .

12. Process according to one of claims 9 to 11, characterized in that the micronization is carried out with hot air in a 0 jet mill.

13. Process according to one of claims 9 to 12, characterized in that silicic acid hydrogel is micronized with hot air in a jet mill and dried to a moisture content of 30 to 5 65 wt.%, preferably 40 to 60 wt.%, in particular about 50 wt.%. - 17 -

14. Process according to one of claims 9 to 13, characterized in that silicic acid xerogel is micronized with hot air in a jet mill and adjusted to a moisture content of 0 to 10 wt.%, preferably 0 to 5 wt.%, in particular 1 to 3 wt.%.

15. Use of a matting agent according to one of claims 1 to 8 or prepared according to one of claims 9 to 14 in water-based coatings, paints or lacquers.

16. Use of a matting agent according to one of claims 1 to 8 or prepared according to one of claims 9 to 14 in aqueous radiation-curing lacquer systems .