Solid colorant for tinting paint

Abstract

A solid colorant including a. 30-97 wt % of a pigment, b. less than 5 wt % of a solvent c. 3-40 wt % surfactants and wherein: the ratio S/A [Std dev of the particle size distribution/average particle size] of the solid colorant is <25%, preferably <22% and more preferably <20%, wherein wt % is relative to the total weight of the solid colorant, and wherein the particle size distribution is determined with light scattering with fully automated image analysis according to ISO 13322-1 Static image analysis First edition 2004 Dec. 1 by the use of the OCCHIO ZEPHYR ESR analyzer. A process for making the solid colorant, and the use of the solid colorant for tinting base paints by volumetric dosing of the solid colorant to the base paint.

Claims

1. A solid colorant comprising: a. 30-97 wt % of a pigment; b. less than 5 wt % of a solvent; c. 3-40 wt % surfactants; d. 0.1-2 wt % of defoaming agent; wherein a ratio S/A [Standard dev of the particle size distribution/average particle size] of the solid colorant is <25%, wherein wt % is relative to the total weight of the solid colorant and wherein the particle size distribution is determined with light scattering with fully automated image analysis according to ISO 13322-1 Static image analysis First edition 2004-12-01 by the use of an OCCHIO ZEPHYR ESR analyser; and wherein the solid colorant is suitable for dosing in a volumetric way.

2. The solid colorant according to claim 1, wherein the average particle size ranges between 400 and 1400 m.

3. The solid colorant according to claim 1, wherein the colorant comprises a. 50-90 wt % of a pigment; b. less than 3 wt % of a solvent; c. 5-30 wt % surfactants; d. 0.1-5 wt % additives; e. 0-20 wt % colorless filler; f. 0-10 wt % binder; wherein the solid colorant has an average particle size between 400 and 1400 m.

4. The solid colorant according to claim 1, wherein the colorant comprises 0.1 wt % to 5 wt % of an antioxidant based on the total weight of the solid colorant.

5. A process for making a solid colorant according to claim 1, wherein the process comprises the following steps: a. providing a liquid pigment dispersion containing 15-75 wt % of a pigment, 20-70 wt % of solvent and 5-30 wt % surfactant, wherein the wt % is relative to the total weight of the liquid pigment dispersion, b. spraying of the liquid pigment dispersion to obtain droplets of liquid pigment dispersion, c. freezing of the droplets of liquid pigment dispersion by a chilled flow of a gas having a temperature between 10 and 200 C. to obtain a frozen colorant, d. freeze drying the frozen colorant to obtain the solid colorant, wherein the spraying is performed by using a vibrating spray nozzle and wherein the vibrating spray nozzle operates with a vibration between 200 and 2000 Hz.

6. The process according to claim 5, wherein the liquid dispersion contains between 50 and 95 wt % solids, relative to the total of the liquid dispersion.

7. The process according to claim 5, wherein spraying is performed with a vibrating spray nozzle having a nozzle diameter between 0.1 and 0.4 mm.

8. A process comprising the steps of: tinting a paint composition with the solid colorant according to claim 1.

9. The process according to claim 8, wherein dosage of solid colorant is performed in a volumetric way.

10. A paint composition comprising a solid colorant according to claim 1.

11. A system for tinting base paint composition, comprising: a. at least one light-colored base paint composition packaged in a container with a volume of about 0.2 to 20 L equipped with and openable and reclosable lid, cap or other closure for an opening through which a colorant may be dispensed from an automated or manual colorant dispenser into the base paint composition; and b. an array of colorants being packaged in containers with a volume from 0.5 to 5 liters provided with a colorant dispenser from which colorant may be dispensed into the base paint composition, whereby the colorant is a solid colorant as defined in claim 1 and dispensing of the solid colorant is performed in a volumetric way.

12. The solid colorant according to claim 2, wherein the ratio of S/A of the solid colorant is less than 22%, wherein the average particle size ranges between 500 and 1300 m.

13. The solid colorant according to claim 2, wherein the ratio of S/A of the solid colorant is less than 20%, wherein the average particle size ranges between 600 and 1000 m.

14. The solid colorant according to claim 3, wherein the ratio of S/A of the solid colorant is less than 22%, wherein the average particle size ranges between 500 and 1300 m.

15. The solid colorant according to claim 3, wherein the ratio of S/A of the solid colorant is less than 20%, wherein the average particle size ranges between 600 and 1000 m.

16. The solid colorant according to claim 4, wherein the colorant comprises 0.1 wt % to 2 wt % of an antioxidant based on the total weight of the solid colorant, wherein colorant comprises between 0.1 and 1 wt % amount of defoaming agent.

17. The solid colorant according to claim 1, wherein the colorant comprises 0.1 and 0.5 wt % amount of defoaming agent.

18. The process of claim 5, wherein freezing of the droplets of liquid pigment dispersion is by a chilled flow of a gas having a temperature between 50 and 100 C., to obtain a frozen colorant.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 relates an example of a particles size distribution of particles prepared by a spray drying process.

(2) FIG. 2 relates to particles prepared with the process according to the invention.

(3) FIG. 3 shows testing equipment for volumetric dosing of solid pigment particles. The testing equipment contains a vessel 1, having an opening 2 for discharging solid particles, a plunger 3 which can be moved up and down to open or close opening 2 of vessel 1 in order to release solid particles 4.

DETAILED DESCRIPTION OF THE INVENTION

EXAMPLES

(4) A number of examples have been prepared to illustrate the invention. The compositions of the liquid pigment dispersion (LPD) to prepare solid colorants (SC) are summarized in table 1.

(5) TABLE-US-00001 TABLE 1 List of used materials and recipes Oxide Yellow Blue Green Red (3) (4) (5) (6) (7) (8) (9) (10) Raw material LPD SC LPD SC LPD SC LPD SC (1) Chemical PY42 PY42 PB PB PG7 PG7 PR PR Pigment constitution wt wt 15:3 15:3 wt wt 254 254 index (2) % % wt % wt % % % wt % wt % Water 41.4 1.35 61.3 1.74 39.4 1.67 36.8 1.86 Defoamer Silicone 0.15 0.14 0.38 0.37 0.49 0.51 0.24 0.22 Surfactants Di-Phosphate 11.94 10.37 13.64 11.85 15.38 14.49 5.87 4.91 ester Based on alcohol ethoxylate Pigment Phthalocyanine 23.97 46.28 PB15:3 Blue Pigment Yellow Iron 45.59 88.02 PY42 Oxide Pigment Phthalocyanine 39.71 83.13 PG7 Green Pigment Di-Keto- 50.0 92.96 PR254 Pyrrolo-Pyrrole (DPP) Biocide 0.58 0.11 0.73 0.14 0.95 0.20 0.25 0.05 LPD = Liquid pigment dispersion SC = Solid Colorant

Experiment 1: Preparation of a Liquid Pigment Dispersion

(6) The amounts of raw materials needed to prepare the liquid pigment dispersion are given in the recipes (table 1). First, the liquids are weighted into a 10 ltr vessel using a scale. The vessel is placed under a high shear dissolver. The solids materials (amounts weighted in on beforehand in a can) are added slowly using a spoon. The shear of the dissolver should be adjusted that a vortex is visible at all times during addition of the solids. After all solids are added the viscosity is measured on a Stormer rheometer and the viscosity is adjusted before the milling phase (typically between 70 and 120 Krebs Units (KU)) by addition of water. The dispersion is milled on a pearl mill till particle size typically <15 m. Measurement of the particle size is done with a Hegman gauge (according to SFS-ISO 1524). Viscosity, color strength and color shade (according to CIE lab) are measured and the liquid pigment dispersion is diluted to the required viscosity and color standard.

(7) TABLE-US-00002 TABLE 2 Measurements of the liquid pigment dispersions Oxide Yellow Blue Green Red (1) (2) (3) (4) (5) LPD LPD LPD LPD Pigment index PY42 PB15:3 PG7 PR254 Viscosity 62 KU 67 KU 65 KU 65 KU Fineness <15 m <15 m <15 m <15 m dE against std 0.35 0.52 0.19 0.26 CS against std 1.8 0.7 1.1 1.6

Experiment 2: Preparation of a Solid Colorant by Comparative Method A

(8) Production of Solid Colorants by Spray Drying:

(9) (a) atomization of a suspension with the aid of a one-material nozzle carried out in a spray tower;

(10) (b) bringing the droplets generated in step (a) in contact with air to dry the same to give granules with a given residual moisture content. The gas inlet temperature in the spray tower is 165 C. The gas outlet temperature is 70 C.

(11) (c) separation of the granules from the gas stream.

(12) Irregular granules have been formed having a large particle size distribution and low porosity (BET values generally 15 m.sup.2/g, and especially 10 m.sup.2/g). The S/A typically ranges between 40 and 60 (see table 4).

Experiment 3: Preparation of a Solid Colorant by Method B

(13) With a vibrating nozzle droplets of the liquid pigment dispersion are formed, which are immediately cooled in a tube containing chilled nitrogen gas stream (in counterflow to the particles) having a temperature between about 78 C. and 70 C. The frozen droplets are collected in a container and freeze dried in a freeze drier (pressure 0.1 mbar and temperature 25 C.)

(14) The vibrating nozzle preferably has a diameter of 0.3 mm. A typical used frequency of 500 Hz, amplitude 400 mV and pressure 110 mbar. Nice well defined solid colorant particles are obtained, having a narrow particle size distribution with S/A between 5 and 20 (see table 4).

Experiment 4: Difference in Solubility Due to Particle Size of the Spheres

(15) To use the solid colorants in practice, the maximum shaking time (using a paint shaker) to develop full color strength in the paint is 2 minutes. The size of the spheres might have an influence on the solubility of the solid colorant.

(16) A liquid pigment dispersion of Oxide Yellow pigment has been made according to experiment 1, using the recipe given in table 1 (column 3). From this liquid pigment dispersion solid colorants have been made using method B as described in experiment 3, resulting in a solid colorants with recipe as given in table 1 (column 4). Depending on the size of the vibrating nozzle different fractions have been obtained.

(17) The solid colorant has been divided in fractions with different particle size (0-250, 250-500, 500-710, 710-1000, 1000-1400, 1400-2000 m) using sieves with different mesh.

(18) From each fraction 1.3 grams was added to 100 grams of an acrylic white paint in a 120 ml plastic can (height 70 mm, diameter 50 mm). These mixtures were shaken for different times (t=1, 2, 3, 4, 5 and 6 min) in a vibrational paint shaker (e.g. Vibro ST from Corob). After every shaking time the samples were opened, a part of the paint was taken out and a draw-down on a black-white card was made using a block-applicator of 150 m.

(19) The color strength of all samples has been measured using a spectrophotometer (measurement on Z-axis, according to LAB Color Space). The sample with the smallest particle size (0-250 m) and shaken for 6 minutes has been used as standard. All other samples have been measured against this standard. The color strength between the standard and the samples is measured and the difference is presented in % in table 2. When the difference in color strength between the standard and the sample <2% the particles are considered as being dissolved.

(20) TABLE-US-00003 TABLE 3 Color strength development at different particle size Color strength development [Fz %], Std 0-250 m, 6 min shaking time Fraction size Mixing 0-250 250-500 500-710 710-1000 1000-1400 1400-2000 2000-2500 time m m m m m m m 1 min 2.79 17.24 73.2 90.73 93.84 95.45 95.53 2 min 1.32 0.2 0.13 0.02 0.87 34.39 58.22 3 min 0.87 0 0.55 0.86 0.69 1.61 1.76 4 min 0.4 0.62 0.99 0.95 0.82 2.17 3.74 5 min 0.12 0.46 0.91 1.62 1.27 2.08 3.77 6 min STD 0.76 1.44 1.44 1.53 2.57 4.19

(21) The particle size of the spheres has an influence on the solubility of the spheres in the paint. Particle size of the largest spheres should be <1400 m to prevent particle size having influence on the solubility of the spheres into the paint within the required max shaking time of 2 minutes.

Experiment 5: Difference in PSD Due to the Used Production Method for the Solid Colorants

(22) An important factor for accurate volumetric dosing of the dispenser or specifically the dosing unit, is the variation in powder particle size.

(23) To determine particle size and particle distribution an OCCHIO ZEPHYR ESR analyzer has been used. The analyzer gives accurate size and shape analysis of free flowing powders with a particle size from 20 m to 30 mm. The OCCHIO ZEPHYR ESR analyzer works according to the ISO 13322-1 Static image analysis First edition 2004-12-01 standard.

(24) Each sample was given to a vibrating feeder where it was transported to a drop shaft to obtain gravity dispersion of the sample in the OCCHIO ZEPHYR ESR analyzer. Thereafter the camera took pictures from all particles in the focus. For each sample the particle size of 50000 particles was analyzed. The statistical evaluation was performed with the use of CALLISTO-software.

(25) Liquid pigment dispersions of Oxide Yellow, Blue, Green and Red pigment have been made according to experiment 1, using the recipes given in table 1 (columns 3, 5, 7 and 9). From this liquid pigment dispersions solid colorants have been made using method A and method B as described in experiment 2 and 3, resulting in solid colorants with recipes as given in table 1 (columns 4, 6, 8 and 10).

(26) In table 4 a summary of the results of the PSD measurements are given. The Min-Max and the factor S/A [standard deviation of the particle size distribution/average particle size] (%) are a measure for the homogeneity in size and distribution of the solid colorant, which is an important indication of the flowability. A perfect flowability is required for optimal volumetric dispensing of the spheres. FIGS. 1 and 2 are examples of the difference in PSD using different methods to produce the spheres.

(27) The results show that method A solid colorant spheres are relatively very small in size compared to method B solid colorant spheres. Furthermore, method B spheres show much less size variation than method A spheres. The homogeneity in size (S/A <25%, preferably <20%) seen in method B spheres is an important indication of the excellent flow ability of these spheres.

(28) TABLE-US-00004 TABLE 4 Sphere colorant (ISO diameter) data for different types of spheres and solid colorants Sphere size (ISO Inner diameter) (m) S/A (%) Std. Dev./ Produc- Std. Dev. Average tion Average (3) S/A Solid Colorant Method Min-Max (A) (S) (%) Blue PB15:3 A 22.5-561 198 106 53% B .sup.560-1350 890 146 16% Oxide Yellow A 22.5-645 329 132 40% PY42 B .sup.593-1375 978 141 14% Green PG7 A 22.5-921 347 162 47% B .sup.225-1221 783 160 20% Red PR254 A 22.5-645 190 112 59%

Experiment 6: Testing of Volumetric Dosing of Solid Colorants

(29) A testing device is constructed for testing volumetric dosing of solid particles. The device is schematically illustrated in FIG. 3. The testing unit contains a vessel or container 1 which has an opening 2 for dosing solid particles. The opening can be opened or closed by means of a plunger 3, which can move up and down. During the time that the plunger is opened, a certain volume of solid colorant will be dosed by gravity.

(30) The volumetric dosage of two samples has been tested with the device as illustrated in FIG. 3.

(31) The following test method has been used:

(32) The plunger is moved down, which means the dosing unit is closed. The container 1 is partially filled with solid spheres. The plunger is moved upwards, which starts the dosing of solid colorant through opening 2 for a determined period of time. The plunger is moved down again in order to close the dosing unit. The amount of spheres is measured by weight, using the tap density to determine the volume.

(33) In the first test the funnel was filled with Oxide Yellow PY42, produced with production method B (see experiment 5, table 4). The particle size ranges between 593-1375 m, with a narrow particle size distribution (S/A is 14%). With a closed plunger there was no leaking of particles. When filling the funnel the sample looked homogenous; there was no difference in particle size noticed between the top and bottom of the sample.

(34) In the second (comparative) test the funnel was filled with Oxide Yellow PY42 solid spheres, produced with production method A (see experiment 5, table 4). The particle size ranges between 22.5 and 645 m and S/A is 40%, which means that the particle size distribution is very broad. Even when the plunger 3 was closed, the fraction small particles started to fall through the (small) opening between plunger 3 and opening 2.

(35) Due to leakage of small particles, and the inhomogeneity of the particles in container 1, the dosing of the particles was inaccurate and unreliable. Further it was noticed that during filling of the funnel the bigger particles came to the surface, while the smaller particles moved to the bottom. It is expected that this will result in inaccuracy of volumetric dosing.

(36) From above tests it can be concluded that a small particle size distribution is needed for accurate volumetric dosing. And that volumetric dosing becomes impossible when the particle size of the solid colorants is too small.