Process for preparing an aqueous dispersion containing hydroxyethyl cellulose

Abstract

The present invention relates to a process comprising the steps of a) recirculating a mixture of water, dispersant, neutralizing agent, and defoamer between a liquid process tank and a rotor stator assembly proximal to a powder tank; b) dispensing a first portion of inorganic opacifying pigment or extender from the powder tank into the rotor stator assembly; then c) dispensing hydroxyethyl cellulose and optionally a second portion of the inorganic opacifying pigment or extender from the powder tank into the rotor stator assembly. The process of the present invention efficiently provides pre-paints with desired viscosities and shelf stability.

Description

[0001] Process for Preparing an Aqueous Dispersion Containing Hydroxyethyl Cellulose of the Invention

[0002] The present invention relates to a process for preparing an aqueous dispersion containing hydroxyethyl cellulose (HEC), more particularly, an aqueous dispersion that contains HEC and extenders or opacifying pigments such as TiCh. Modular paint production can be used to create a full line of paints from stabilized mixtures of components (pre-paints) used to make the paints. This method of producing paint contrasts with the conventional paint making method of batch production of paint bases. The concept of modular paint has been around since 2000 and is based on limiting the number of raw materials and simplifying the overall paint production process. Furthermore, paints can be produced from modular components in places such as point of sale locations, warehouse locations, and fulfilment centers using paint dispensing machines.

[0003] Conventional paints are manufactured in a paint plant using a batch process. These paints are delivered to the point sale in a limited number of sheens (typically flat, matte, eggshell, satin, and semi-gloss) and tint bases (typically three to four tint bases to cover ultra deep colors to white) and there is limited to no flexibility to adjust the appearance (sheen) or color balance (base type) at the point of sale. (e.g. retail store).

[0004] Modular paint production, on the other hand, enables white paints with different, customized levels of TiO2and extender levels to fulfill customer requirements from a significantly smaller number of pre-paints and avoid building inventory of multiple base-sheen combinations.

[0005] A critical component for successful production of paint from pre-paints, which are components of a paint, but which are not by themselves fully formulated paints, is to deliver stabilized pre -paints, for example, binder or TiO2or extender combined with water, dispersant, neutralizing agent, rheology modifier, and defoamer, at the point of sale. Dispersion of powders in liquids using a rotor-stator enables faster production of TiO2or extender pre-paints. Nevertheless, combining a solid rheology modifier such as HEC with TiO2or extender in the rotor stator disadvantageously builds viscosity to an unacceptable level. It would therefore be desirable to find a way to control viscosity of an HEC-TiO2or HEC -extender pre -paint using a rotor stator for future use in a modular paint process. Summary of the Invention

[0006] The present invention addresses a need by providing a process comprising the steps of a) recirculating a mixture of water, dispersant, neutralizing agent, and defoamer between a liquid process tank and a rotor stator assembly proximal to a powder tank; b) dispensing a first portion of an inorganic opacifying pigment or extender from the powder tank into the rotor stator assembly; then c) dispensing hydroxyethyl cellulose and optionally a second portion of inorganic opacifying pigment or extender from the powder tank into the rotor stator mixer, wherein the ratio of total pigment or extender to hydroxyethyl cellulose is in the range of from 100:0.1 to 100:2; and wherein the proportion of pigment or extender dispensed in step b) to the proportion of optional pigment or extender dispensed in step c) is such that the KU viscosity of the resultant blend of the components is in the range of 80 KU to 120 Krebbs units at 25 °C. The process of the present invention efficiently provides pre-paints with desired viscosities and shelf stability.

[0007] Bried

[0008] FIG 1 illustrates the apparatus used in the process of the present invention.

[0009] Detailed Description of the Invention

[0010] The present invention is a process comprising the steps of a) recirculating a mixture of water, dispersant, neutralizing agent, and defoamer between a liquid process tank and a rotor stator assembly proximal to a powder tank; b) dispensing a first portion of an inorganic opacifying pigment or extender from the powder tank into the rotor stator assembly; then c) dispensing hydroxyethyl cellulose and optionally a second portion of inorganic opacifying pigment or extender from the powder tank into the rotor stator assembly, wherein the ratio of total pigment or extender to hydroxy ethyl cellulose is in the range of from 100:0. 1 to 100:2; and wherein the proportion of pigment or extender dispensed in step b) to the proportion of optional pigment or extender dispensed in step c) is such that the KU viscosity of the resultant blend of the components is in the range of 80 KU to 120 Krebbs units at 25 °C.

[0011] FIG. 1 illustrates an apparatus that can be used to prepare the dispersion by the process of the present invention. In a preferred process, a mixture of water, dispersant, neutralizing agent, defoamer, and optionally surfactant are placed in liquid process tank (10) optionally stirred with an overhead stirrer (20) and recirculated by way of conduit (30) through rotor stator assembly (40), which is a rotor stator contained in a mixer chamber. A first portion of inorganic opacifying pigment or extender particles are initially contained in powder tank (50). Valve (60) is opened causing particles to transfer from powder tank (50) into rotor stator assembly (40). The rotor stator spins at high speeds inside a slotted stator to reduce the particle size of the inorganic opacifying pigment or extender; the rapid spinning creates a powerful vortex that draws the solid particles into the rotor-stator, pumps the solid out against the slots, and mixes and recirculates the solids along with the aqueous mixture to form a dispersion. Hydroxyethyl cellulose (HEC) and optionally a second portion of the inorganic opacifying pigment or extender particles is then transferred from powder tank (50) into rotor stator assembly (40). The amount of inorganic opacifying pigment or extender dispensed in step b) compared with the amount dispensed in step c) is controlled to maintain a Krebs viscosity at 25 °C in the range of from 80 KU or from 85 KU, to 120 KU or to 100 KU or to 90 KU or to 95 KU. Viscosity is measured after the dispersion is dispensed from rotor stator assembly (40) through valve (70) and conduit (80) into a container, where Brookfield and KU viscosities are then measured. Preferably, the amount of inorganic opacifying pigment or extender dispensed in step b) is at least 60 wt% or at least 65 wt% or at least 70 wt% or at least 80 wt%, to 100 wt% or to 95 wt% of the total inorganic opacifying pigment or extender that is dispensed in steps b) and c). The total w / w ratio of the inorganic opacifying pigment or extender to the HEC in the final dispersion is preferably in the range of from 0.1 : 100 or from 0.2 : 100 to 2 : 100 or to 1 : 100. Preferably, the inorganic opacifying pigment or extender is TiCh. The total concentration of opacifying pigment or extender in the composition is preferably in the range of from 60 to 76 wt%, based on the weight of the composition. The process of the present invention excludes the addition of binder.

[0012] It has been discovered that the viscosity of a paint containing HEC and an inorganic opacifying pigment or an extender can be controlled around a very narrow desired viscosity range using the process of the present invention.

[0013] Examples

[0014] General Procedure for Preparing Paint with HEC and TiCh

[0015] A KYNEPILOT Disperser was used to prepare the paints. Water, dispersant, neutralizing agent, defoamer, and optionally surfactant were added to a liquid process tank fitted with an overhead stirrer, and TiO? was loaded into the powder tank. The water-additive mixture was circulated through the rotor stator set at 1500 rpm to 2000 rpm for 2 min, after which time stirring was initiated. The rotor stator speed was increased to 3000 rpm to 3500 rpm, the TiCh was dispensed from the powder tank to the rotor stator assembly. After completion of from 50 to 100 wt% of the total TiCh that was added, HEC and from 0 to 50 wt% of the remaining TiCh was added in a separate dispensing step. Recirculation was continued for 5 to 15 min, after which time the speed was reduced to 1500 rpm to 2500 rpm. The powder tank was rinsed to remove any residual TiCh, and recirculation was continued for up to 10 min. The dispersion was collected.

[0016] Table 1 shows the amounts of materials used to make the paint. Dispersant refers to TAMOL™ 1124 Dispersant; Defoamer refers to FoamStar St 2434 Defoamer; TiO2 refers to Ti-Pure R-706 TiOj: AMP-95 refers to AMP-95 Multifunctional Amino Alcohol (2-amino-2- methyl-1 -propanol in a 5% aqueous solution); and HEC refers to CELLOSIZE™ QP-4400H Hydroxyethyl Cellulose. (TAMOL and CELLOSIZE are Trademarks of The Dow Chemical Company or its Affiliates.)

[0017] Table 1 - Materials and Amounts used to Prepare Paints

[0018] Table 2 illustrates the impact of initial TiO2 addition (TiO2o) and final TiO2f on initial and 14-d KU and Brookfield viscosities (centipoise (cP)) at 30 rpm (KU0and KUr; BFOand BFO) and shelf stabilities. All the HEC (50 g) was added in final addition step. KU viscosity was measured with a Model KU-1+ viscometer from Brookfield by placing a paddle in the container with the pre-paint and spinning the paddle at a 200 RPM until stability of the Kreb Unit (KU) is reached.

[0019] Brookfield viscosity was measured with a spindle number 4 using a Model DV-II+ Pro viscometer from Brookfield. Brookfield viscosity was measured at 30 rpm for 15 s (spindle 4) using Brookfield viscometer. The targeted initial and final Brookfield viscosities were in the range of from 1500 cP to 10,000 cP.

[0020] Table 2 - Effect of Initial TiCE Addition on Viscosity and Shelf Stability

[0021] Samples prepared by the process of the present invention met criteria for KU and Brookfield viscosity and shelf stability. If has been discovered that when the initial charge of TiCh was 50 wt% or less, the targeted viscosities were not met.

[0022] KU and Brookfield viscosities for the comparative example were not measurable because the rotor stator clogged under the experimental conditions. A substantial amount of water was required to unclog the system, resulting in unacceptably low viscosities.

Claims

Claims:

1. A process comprising the steps of a) recirculating a mixture of water, dispersant, neutralizing agent, and defoamer between a liquid process tank and a rotor stator assembly proximal to a powder tank; b) dispensing a first portion of inorganic opacifying pigment or extender from the powder tank into the rotor stator assembly; then c) dispensing hydroxyethyl cellulose and optionally a second portion of inorganic opacifying pigment or extender from the powder tank into the rotor stator assembly, wherein the ratio of total pigment or extender to hydroxyethyl cellulose is in the range of from 100:

0. 1 to 100:2; and wherein the proportion of pigment or extender dispensed in step b) to the proportion of optional pigment or extender dispensed in step c) is such that the KU viscosity of the resultant blend of the components is in the range of 80 KU to 120 Krebbs units at 25 °C.

2. The process of Claim 1 wherein the inorganic opacifying pigment is TiCh, wherein the process excludes the addition of binder.

3. The process of Claim 1 wherein the amount of TiCh dispensed in step b) is from 60 wt% to 100 wt% of the total TiCh that is dispensed in steps b) and c).

4. The process of Claim 3 wherein the amount of TiCh dispensed in step b) is from 70 wt% to 100 wt% of the total UO2 that is dispensed in steps b) and c).

5. The process of Claim 3 wherein the amount of TiCU dispensed in step b) is from 80 wt% to 95 wt% of the total TiCh that is dispensed in steps b) and c).

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