Functionalized silicas

Abstract

Functionalized silicas with 3-methacryloxypropylsilyl and/or glycidyloxypropylsilyl groups on the surface are prepared by mixing the silicas with the silane and heat-treating the mixture. The silicas are employed, for example, in solvent-containing coatings.

Description

INTRODUCTION AND BACKGROUND

[0001] The present invention relates to functionalized silicas, a process for their preparation and their use. It is known to react silicon dioxide obtained by flame hydrolysis and with a surface area of 40 to 200 m2/g with 3-methacryloxypropyltrimethoxysilane. The resulting silicon dioxide is then coated with a further shell of (meth)acrylate polymers and subsequently employed in dental compositions (EP 0 142 784 A1).

SUMMARY OF THE INVENTION

[0002] The present invention provides functionalized silicas, characterized by functional groups fixed on the surface, the groups being 3-methacryloxypropylsilyl and/or glycidyloxypropylsilyl.

[0003] The present invention also provides a process for the preparation of the functionalized silicas, which is characterized in that a silica is sprayed optionally first with water or dilute acid and then with a surface modification reagent or a mixture of several surface modification reagents in a suitable mixing vessel, with intensive mixing, the components are optionally re-mixed for 15 to 30 minutes and heat-treated at a temperature of 100 to 400° C. over a period of 1 to 6 h.

[0004] A silica prepared pyrogenically by the route of flame hydrolysis of SiCl4 can preferably be employed as the silica. Such pyrogenic silicas are known from Ullmanns Enzyklopädie der technischen Chemie [Ullmanns Encyclopaedia of Industrial Chemistry], 4th edition, volume 21, page 464 (1982).

[0005] In a preferred embodiment of the invention, a pyrogenic silica with a surface area of approx. 200 m2/g can be employed (Aerosil® 200).

[0006] Monomeric substances, such as 3-methacryloxypropyltrialkoxysilane and/or glycidyloxypropyltrialkoxysilane, wherein alkoxy can be methoxy, ethoxy and/or propoxy, can be employed as the surface modification reagent.

[0007] The amount of silane can be metered with respect to the silica such that no or only a small excess results. The excess silane can optionally be removed during the heat treatment.

[0008] The silica according to the invention can be employed in solvent-containing coatings, for example 2-component polyurethane coatings.

DETAILED DESCRIPTION OF INVENTION

[0009] The functionalized silicas according to the invention have the following advantages: When used in solvent-containing coatings, such as, 2-component polyurethane coatings, the scratch resistance of the coating surface is increased.

[0010] According to the invention, the pyrogenically prepared silicas according to table 1 can be employed as the silica for the silanization.

TABLE 1
Physico-chemical data of AEROSIL ®
	AEROSIL	AEROSIL	AEROSIL	AEROSIL	AEROSIL	AEROSIL	AEROSIL	AEROSIL
Test method	90	130	150	200	300	380	OX50	TT600
Behaviour towards	hydrophilic
water
Appearance	loose white powder
BET surface area1)	m2/g	90 ± 15	130 ± 25	150 ± 15	200 ± 25	300 ± 30	380 ± 30	50 ± 15	200 ± 50
Average primary	nm	20	16	14	12	7	7	40	40
particle size
Tamped density	g/l	80	50	50	50	50	50	130	60
approx. values2)
Compacted goods	g/l	120	120	120	120	120	120
(added “V”)
VV goods	g/l			50/75	50/75	50/75
(added “VV”)12)	g/l				120	120
Loss on drying3)	%	<1.0	<1.5	<0.59)	<1.5	<1.5	<2.0	<1.5	<2.5
(2 hours at 105° C.) on
leaving supply works
Loss on ignition4)7)	%	<1	<1	<1	<1	<2	<2.5	<1	<2.5
(2 hours at 1000° C.)
pH5)		3.7-4.7	3.7-4.7	3.7-4.7	3.7-4.7	3.7-4.7	3.7-4.7	3.8-4.8	3.6-4.5
SiO28)	%	>99.8	>99.8	>99.8	>99.8	>99.8	>99.8	>99.8	>99.8
Al2O28)	%	<0.05	<0.05	<0.05	<0.05	<0.05	<0.05	<0.08	<0.05
Fe2O38)	%	<0.003	<0.003	<0.003	<0.003	<0.003	<0.003	<0.01	<0.003
TiO28)	%	<0.03	<0.03	<0.03	<0.03	<0.03	<0.03	<0.03	<0.03
HCl8)10)	%	<0.025	<0.025	<0.025	<0.025	<0.025	<0.025	<0.025	<0.025
Sieve residue8)	%	<0.05	<0.05	<0.05	<0.05	<0.05	<0.05	<0.2	<0.05
(Mocker method, 45
μm)
Drum size (net)11)	kg	10	10	10	10	10	10	10	10
1)in accordance with DIN 66131
2)in accordance with DIN ISO 787/XI, JIS K 5101/18 (not sieved)
3)in accordance with DIN ISO 787/II, ASTM D 280. JIS K 5101/21
4)in accordance with DIN 55921, ASTM D 1208, JIS K 5101/23
5)in accordance with DIN ISO 787/IX, ASTM D 1208, JIS K 5101/24
6)in accordance with DIN ISO 787/XVIII, JIS K 5101/20
7)based on the substance dried for 2 hours at 105° C.
8)based on the substance ignited for 2 hours at 1000° C.
9)special packaging protecting against moisture
10)HCl content is a constituent of the loss on ignition
11)V goods are supplied in sacks of 20 kg
12)VV goods are currently supplied only from the Rheinfelden works

EXAMPLE 1

[0011] Aerosil® 200 is mixed with 4 parts water and 18 parts 3-methacryloxypropyltrimethoxysilane (for example DYNASILAN MEMO) and the mixture is heat-treated at 140° C. under an inert gas.

[0012] The silica obtained has the following properties:

BET [m2/g]           138
Tamped density [g/l] 52
pH                   4.6
C content            5.7
Loss on drying [%]   0.8
Loss on ignition [%] 9.7
DBP number [%]       228

EXAMPLE 2

[0013] Aerosil® 200 is mixed with 3 parts water and 16 parts 3-glycidyloxypropyltrimethoxysilane (for example DYNASILAN GLYMO) and the mixture is heat-treated at 140° C. under an inert gas.

[0014] The silica obtained has the following properties:

BET [m2/g]           165
Tamped density [g/l] 53
pH                   4.9
C content            5.5
Loss on drying [%]   1.5
Loss on ignition [%] 8.7
DBP number [%]       242

[0015] Experiment 1

[0016] A conventional 2-component polyurethane coating has been used to investigate the improvement in the scratch resistance. The recipe for the coating and the preparation, including the application, are summarized in the following:

	Parts by
Recipe:	wt.
Millbase	Setalux C 1152,	53.3
	XX - 51.50% (Akzo Nobel)
	Butyl acetate 98%	6.7
	Xylene	6.7
	AEROSIL (silica according to example 1)	5.0
Σ		71.7
Lacquer	Setalux C 1152,	1.1
constituents:	XX - 51.50% (Akzo Nobel)
	Xylene	12.2
	Ethoxypropyl acetate	1.5
	Butylglycol acetate	1.5
Hardener:	Desmodur N 75 (Bayer)	17.0
Σ		105.0
Binder concentration: 40%
AEROSIL ® calculated with respect to the milibase (SC): 18.8%
AEROSIL ® calculated with respect to the coating (total): 5%
AEROSIL ® calculated with respect to the coating (SC): 12,5%

[0017] Preparation and Application of the Coatings

[0018] The Setalux is mixed with the solvents. For predispersion, the AEROSIL® is then incorporated into this mixture with a dissolver (disc Ø 45 mm) and predispersed for 5 min at 2000 rpm. The mixture is dispersed in a laboratory bead mill for 30 min at 2500 rpm and a pump output of 60% using glass beads (Ø approx. 1 mm). The dispersing quality is checked with a grindometer, 25 μm, in accordance with DIN ISO 1524. It must be smaller than 10 μm.

[0019] The lacquer constituents are added to the millbase in accordance with the recipe, the components being mixed with a blade stirrer at 2000 rpm. The hardener is stirred into the mixture in the same manner.

[0020] After the coatings have been adjusted to the spray viscosity according to DIN 53411, the coatings are applied to black-lacquered metal sheets, for example DT 36 (Q-Panel), by means of spraying application (layer thickness about 40-50 μm). After the spraying, the metal sheets are dried for 24 h at room temperature and then for 2 h in a drying oven at 70° C.

[0021] Scratching Experiments:

[0022] The metal sheets are scoured with a quartz/water slurry (100 g water+1 g Marlon A 350, 0.25%+5 g Millicarb BG) with the aid of a scouring and washing resistance testing machine (Erichsen, brush with pig bristles). The shine before and 10 min after scouring is determined with a reflectometer (20° incident angle).

TABLE 2
Summary of the coating-relevant properties
of the liquid coatings and of the films applied and dried:
	AEROSIL	Silica/(example
	200	1)	Reference
Grindometer value	[μm]	<10	<10	—
Viscosity (millbase)	[mPas]
	6 rpm		1000	180
	60 rpm	464	600	143
Viscosity	[mPas]
(coating + hardener)	6 rpm	166	180	75
	60 rpm	141	147	62
Dilution (adjustment	[%]	11.5	8.5	1.7
to 20 s DIN 4 mm)
Scratch resistance
20° reflectometer value before	90.9	87.6	91.3
scratching
40 strokes with Sikron F 500	66.4	73.0	50.7
20° reflectometer value residual	73.0	83.3	55.5
shine
100 strokes with Millicarb	79.2	80.5	68.4
BG 20°
reflectometer value residual	87.1	91.9	74.9
shine [%]

[0023] Further variations and modifications of the foregoing will be apparent to those skilled in the art and are intended to be encompassed by the claims appended hereto.

[0024] European priority application 00 122 954.1 is relied on and incorporated herein by reference.

Claims

1. A functionalized silica, having at least one functional group fixed on the surface of said silica, the group being selected from the group consisting of 3-methacryloxypropylsilyl, glycidyloxypropylsilyl and mixtures thereof.

2. The functionalized silica according to claim 1 wherein the silica is produced by flame hydrolysis.

3. A process for the preparation of the functionalized silica according to claim 1, comprising spraying a silica optionally first with water or dilute acid and then with a surface modification reagent or a mixture of surface modification reagents in a mixing vessel, with intensive mixing, optionally re-mixing said silica for 15 to 30 minutes and heating at a temperature of 100 to 400° C. over a period of 1 to 6 h.

4. The process according to claim 3 wherein the surface modification agent is a member selected from the group consisting of 3-methacryltrialkoxysilane, glycidylotrialkoxysilane and mixtures thereof.

5. A surface coating with a coating containing the functionalized silica according to claim 1.

6. A coating composition comprising the functionalized silica of claim 1 and a solvent.

7. A coating composition for preparing a scratch resistant coating on a surface, comprising the functionalized silica according to claim 1 and a polyurethane.