Abstract:
A talc slurry and a method of producing the talc slurry. A talc product includes the talc slurry having total solids (TS) 40% or higher and a dispersant agent and/or a thickener.

Description:
FIELD OF THE INVENTION 
     The present invention relates to talc for paint products. The invention relates also to the method of producing said talc product. 
     BACKGROUND OF THE INVENTION 
     Talc products for paints are manufactured by milling specific talc ores in dry milling processes to the talc powders with desired particle size distribution. Typical median particle size for paint talc product is 1 to 25 μm and upper top cut is from 10 μm to 200 μm. Median particle size for talc powder used in paints cause different decorative properties to paints, e.g. high median particle size decreases gloss and low median size increases covering power. Median particle size also has influence on mechanical properties, e.g. on wet scrub resistance, of paints. 
     Dry powders are then dispersed in water during the production of water based paints. This causes problems because it is difficult to get homogenous dispersion of solid particles. Talc powders also cause dusting problems during storing and handling stages. 
     GENERAL DESCRIPTION OF THE INVENTION 
     It is the object of the present invention to improve the processability of talc for paint products. 
     For achieving this aim, the invention is characterized by features that are enlisted in the independent claims. Other claims represent preferred embodiments of the invention. 
     According to invention the talc product is talc slurry having total solids (TS) 40% and comprising a dispersant agent and/or a thickener. Said thickener improves the wetting of talc surfaces and improves the stability of talc slurry. Said dispersant agent improves the dispersing of talc in water. Said dispersant agent also makes grinding of talc easier. This kind of talc is ready dispersed in water and it makes a homogenous dispersion of talc in water. Users don&#39;t need to disperse the talc and so this new product is ready to use and can be added in any phase of the paint production, which increases the paint production capacity and makes the process more flexible. 
     The slurried talc also reduces the storage space needed compared with storing of same amount of dry powder. Talc slurry is also pumpable. The paint production process is thus easier to get automated by using talc slurry instead of dry power form talc. So it increases the production capacity of paint producers. Waste of packing material is also avoided by using talc slurry. When the talc is in slurry form, there is no dusting problem during storing and handling stages. 
     According to one aspect of the invention total solids (TS) of said talc slurry is 50% or higher. Advantageously total solids (TS) of said talc slurry is 60% or higher. This kind of talc slurry further reduces the storage space needed compared with storing of same amount of dry powder. 
     According to one aspect of the invention viscosity of talc slurry is 300 to 600 mPas (Brookfield Br100). This kind talc slurry is easy to pump. 
     According to one aspect of the invention storage stability of said talc product is 10%, which is measured as the sedimentation of talc particles in one month storing test in container where is no mixing. This kind of talc slurry is especially suitable talc for paint products. 
     In this document particle size of talc is expressed as an equivalent diameter of spherical particle that has the same falling rate in water as talc particles measured. 
     According to one aspect of the invention the talc slurry has unimodal PSD with average particle size (peak value) between 1-50 μm. This kind of talc is easy to pump and makes it possible to use unimodal, conventional or narrow PSD talc. Unimodal, narrow PSD talc has benefits in some specific application, for instance very fine talc (average PS between 1-3 μm) for thin film thickness coatings and lacquers to improve opacity, whiteness and sandability and adjust the gloss. Narrow and unimodal PSD of coarse talc (average PS between 10-30 μm) is beneficial in thick film protective coatings to achieve high enough film thickness (high solid content) without increasing the viscosity of paint. 
     According to one aspect of the invention talc slurry has multimodal particle size distribution between 1 to 50 μm. This improves the balance of paint properties. It also improves the stability of slurry compared to conventional unimodal or very narrow PSD talc. 
     Talc product having multimodal particle size distribution improves the paint property profile. It improves the paint quality compared to currently available product on the market. All the important decorative paint properties are either improved or kept constant compared to the conventional type of talc product. It makes also production of paints easier. The ready dispersed talc slurry can be added into the paint formulation in any phase of the paint production. 
     According to one aspect of the invention the talc product has at least two peaks of particle size distribution between 1 to 50 μm. According to one aspect of the invention the talc product has at least three peaks of particle size distribution between 1 to 50 μm. This bi-modal/multimodal particle size distribution improves the balance of paint properties and decreases gloss, increases covering power and/or increases mechanical properties of paint. 
     According to one aspect of the invention the talc product has multimodal PSD with two or more peaks between 1 to 50 μm. The multimodal PSD improves the balance of paint properties. According to one aspect of the invention one of the peaks of particle size distribution is between 1 to 5 μm. The fine particles, peaks between 1 to 5 μm, improve the balance between covering power and whiteness of the paint film. According to one aspect of the invention one of the peaks of particle size distribution is between 5 to 20 μm. The medium fine talc particles, peaks between 5 to 20 μm, improve the mechanical properties like wet scrub resistance and mud cracking resistance of paints. According to one aspect of the invention the slurry has at least one peak of particle size distribution being between 10 to 50 μm. Coarse talc particles, peaks between 10 to 50 μm, reduce the gloss (sheen) of paints. The multimodal (broad) PSD of talc allows the increase of talc content in the slurry without worsening of pumpability and stability of the slurry. 
     Talc slurry can be prepared in several different ways. Said talc slurry can be produced e.g. by using of semi-finished goods, e.g. talc concentrate or by milling talc ore and/or pre-slurry talc by wet milling process 
     Talc can be milled by using normal conventional type of dry milling techniques like ball mills, impact mills or jet mills (steam or compressed air), to get final fineness for talc. After the milling dry talc powder can be directly dispersed in water by using suitable chemicals or it can be first granulated after which dispersed in water. Finally the talc slurry is stabilized by using suitable stabilizers. 
     Another way is to prepare the slurry already during the milling phase. This method requires wet milling techniques like wet ball or pearl milling. This method requires the constant feed of chemicals to the mills together with talc raw material and water to get smooth milling and high enough solid content to the final slurry. After the milling the talc slurry is further stabilized, after which it is ready to be used for paint production. The particle size distribution (PSD) of talc is controlled by filling rate of milling pieces (balls or pearls) in the mills. Different size (diameter) of milling balls or pearls gives different size of talc. The PSD of talc wanted is achieved by adjusting the ratio of different size of grinding pieces. The residence time of talc slurry in mills affects also the particle size of talc. There can be several mills in series if needed. The wet milling is an advantageous technique to prepare talc slurry for paints because there is no need to dry the product during the manufacturing, which reduces the production costs. Thus the preparation of the talc product into slurry form is technically easy and thus production costs are low. Wet milling process also enables the production of the special type of products. 
     Advantageous wet milling is made by wet pearled mill. It has been also seen that wet pearl milling gives the possibility to prepare multi-modal PSD talc. The multi-modal PSD is beneficial for storage stability of talc slurry and it improves the balance or paint properties. 
     The multi-modal talc slurry product can be prepared also by using the normal unimodal, dry milled, products as a mixture in slurry preparation. 
     The talc slurry can be delivered either in reusable containers or by silo trucks, which reduces the amount of packing materials. 
     Production process of talc slurry comprises e.g. the steps:
         pregrinding of talc ore for producing talc,   wet milling of pregrinded talc to end products,   during the wet milling additives like dispersing and thickening agents and pH, regulator can be added,   stabilizing the slurry by cellulose based or synthetic thickener       

     Production process of talc slurry produced from pregrined starting material or from ready milled end product comprises e.g. the steps:
         producing pre-slurry talc by adding of water and talc to process tank, and   adding of base, e.g. NaOH, to water or to pre-slurry talc in order to achieve pH-value 9.0 or higher   adding of a thickener to pre-slurry talc   adding of a dispersant to pre-slurry talc   milling said pre-slurry talc by wet milling process   sieving milled pre-slurry talc       

     An example of process flow sheet of the invention is shown in  FIG. 7 . 
     Wet grinding can reduce the whiteness of end product e.g. by 4-5 whiteness %-units compared if the same product is made by dry milling. So it is advantageous to use very high whiteness starting material, e.g. talc lumps, in wet pearl milling to get optimum product. 
     Talc product can be used in e.g. in following paint products:
         Interior and exterior flat emulsion paints   Multi purpose interior/exterior emulsion paints   Semigloss emulsion paints   Out door wood coatings   Wood primers   Textured paints   Silk and eggshell paints       

    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a graph displaying the mass population vs. particle size of the talc produced in Sample 1. 
         FIG. 2  is a graph displaying the mass population vs. particle size of the talc produced in Sample 2. 
         FIG. 3  is a graph displaying the mass population vs. particle size of the talc produced in Sample 3. 
         FIG. 4  is a graph displaying the mass population vs. particle size of the talc produced in Sample 4. 
         FIG. 5  is a graph displaying the mass population vs. particle size of the talc produced in Sample 5. 
         FIG. 6  is a graph displaying the mass population vs. particle size of the talc produced in Sample 6. 
         FIG. 7  is a flow diagram of an embodiment of a method for producing the talc slurry. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     An embodiment of the invention is explained in more detail below, with reference to the appended drawing. 
     Talc Slurry—milling and stabilisation trial 
     Materials 
     Talc—Finntalc P60 SL (d 50  around 84 μm). 
     Dispersing agent—specific dispersing agent where wetting property is also involved. 
     NaOH (Solvay, &gt;98%) at 10% in water was used to neutralise the dispersing agent. 
     Cellulose thickeners for the stabilization of the slurry: Celfow and Finnfix 2000G from CP Kelco. 
     Biocide—Thor MBF 28. 
     Initial Target Compositions 
     
       
         
               
             
               
               
               
             
               
               
               
             
           
               
                 TABLE 1 
               
             
             
               
                   
               
               
                 Composition with Celflow 
               
             
          
           
               
                 Component 
                 w-% 
                 Comments 
               
               
                   
               
             
          
           
               
                 1. Water 
                 38.40 
                   
               
               
                 2. Dispersing agent, 
                 0.96 
                 0.50% dry on dry 
               
               
                    (solids = 26 w-%) 
               
               
                 3. Biocide (Acticide BX) 
                 0.20 
               
               
                 4. NaOH (10 w-%) 
                 1.04 
                 =&gt; pH ~9.0 
               
               
                 5. Talc (Finntalc M20SL - 
                 50.10 
                 Mix by circumferential speed = 
               
               
                    lab trial) 
                   
                 15 m/s. 
               
               
                 6. Celflow S-50 Dry 
                 0.40 
                 0.8% dry on dry Mixing for 20 
               
               
                   
                   
                 minutes by circumferential speed = 
               
               
                   
                   
                 15 m/s 
               
               
                 7. Rest water 
                 8.90 
               
               
                 Total 
                 100.0 
               
               
                   
               
             
          
         
       
     
     
       
         
               
             
               
               
               
             
               
               
               
             
           
               
                 TABLE 2 
               
             
             
               
                   
               
               
                 Composition with Finnfix 2000G 
               
             
          
           
               
                 Component 
                 w-% 
                 Comments 
               
               
                   
               
             
          
           
               
                 1. Water 
                 38.4 
                   
               
               
                 2. Dispersing agent, (solid 
                 0.96 
                 0.50% dry on dry 
               
               
                    s = 26 w-%) 
               
               
                 3. Biocide (Acticide BX) 
                 0.2 
               
               
                 4. NaOH (10 w %) 
                 1.04 
                 =&gt; pH ~9.0 
               
               
                 5. Talc, (Finntalc M20SL - 
                 50.1 
                 Mix by circumferential speed = 
               
               
                    lab trial) 
                   
                 15 m/s. 
               
               
                 6. CMC Finnfix 2000G Dry 
                 0.54 
                 1.08% dry on dry Mixing for 
               
               
                   
                   
                 20 minutes by circumferential 
               
               
                   
                   
                 speed = 15 m/s 
               
               
                 7. Rest water 
                 8.8 
               
               
                   
               
             
          
         
       
     
     In the industrial test was used 0.7% of the dispersing agent. 
     Industrial Trial 
     Pre-slurry was made in a 3 m 3  tank equipped with a cutting type agitator. To make the pre-slurry, water was added first, then NaOH (10%), dispersing agent and finally the talc P60 SL. All the dispersant was added in the pre-slurry—no addition of dispersant was made to the mills. The quantity of dispersant was always 0.7% (d/d). 
     The flow sheet of the process is shown in  FIG. 7 . 
     The pH of the final pre-slurry was measured and was corrected when necessary, to achieve a value above 9. During the trial, several mixes of pre-slurry were made to make it available for the milling process. 
     In the first trial, the pre-slurry was introduced in a first mill. The product from the first mill was then introduced in a second mill. After the second mill, no other actions were performed to the slurry. 
     Samples were taken from the first (samples 1 and 2) and the second mill (sample 3). 
     A second trial was performed with pre-slurry at 60% of solid content. Samples were taken from the first (sample 5) and the second mill (sample 6). 
     A third test was done with similar conditions to the first one. The difference was that the slurry after the mill was sieved using 100 μm nets. The rejected was going back to the mill, with some losses due to the high flow rate and viscosity of the rejected product. 
     The sieving presented severe problems, with the rejected product from the sieves being about 70% of the feeding. The dispersant does not permit an efficient sieving of the slurry. A sample of the sieved slurry was taken (sample 6). 
     Talc slurry samples were stabilized. 
     Table 3 shows the final composition of the samples, after stabilisation. 
     The making of each sample is described in Appendix 1, with the actions described by chronological order. 
     Conclusions: 
     
         
         
           
             Talc slurries with d 50  between 1.45 and 7.36 μm and solids content between 40.3 and 60.1% were made. 
             The making of the pre-slurry presented no major problems, although corrections of the pH had to be performed. 
             The operation of the mills was stable after solving some initial problems. Even at 60% solids, the mills presented no problems. 
             Samples were taken from the mills at 50 and 60% solids content. 
             The samples of the slurries were stabilized with two cellulose thickeners. The Celflow product shown a good effect on increasing viscosity at low shear rates and decreasing it at high shear rates. 
           
         
       
    
                                                                                                                 TABLE 3                   Talc slurry samples                    Solids           NaOH       Finnfix           Particles           Slurry   content   d 50     Biocide   (10%)   Celflow   2000G   η 10 rpm     η 100 rpm     above 63       Sample   (kg)   (%)   (μm)   (%)   (%)   (%)   (%)   (cP)   (cP)   μm (%)                    1   120   51.7   3.1   0.2   0.08   0.3   —   930   260   13.1       2   120   51.7   3.2   0.2   0.04   —   0.5   1320   310   13.1       3   200   55.0   1.6   0.2   0.03   —   —   1440   1248   3.8       4   260   58.6   8.4   0.2   0.04    0.15   —   680   412   21.9       5   200   60.1   3.3   0.2   0.05   —   —   930   995   10.2       6   545   40.3   2.4   0.2   —   0.2   —   360   110   2.4                    
Sample 1
 
     Description: sample from the first mill, with pre-slurry at 50% solid content. 
     120 kg of slurry. 
     Mass population vs. particle size of talc in sample 1 is expressed in  FIG. 1 . Said talc product has following peaks of particle size distribution:
         1.5 μm   3.8 μm   9.3 μm   19.5 μm   37 μm       

     Solids content: 51.7% 
     Granulometry: 
     d 50 =3.09 μm 
     Viscosity at 25° C.: 
     η 10 rpm =200 cP η 100 rpm =386 cP 
     Celflow—125 g (0.1% of talc) 
     η 10 rpm =900 cP η 100 rpm =265 cP 
     pH=8.6 
     NaOH (10%)—100 mL 
     η 10 rpm =200 cP η 100 rpm =160 cP 
     pH=9.5 
     Thor MBF28—0.2 kg 
     Celflow—0.0625 kg 
     η 10 rpm =930 cP η 100 rpm =260 cP. 
     Sample 2 
     Description: sample from the first mill, with pre-slurry at 50% solid content. 
     120 kg of slurry. Characteristics equal to sample 1. 
     Mass population vs. particle size of talc in sample 2 is expressed in  FIG. 2 . Said talc product has following peaks of particle size distribution:
         2.4 μm   5.2 μm   13 μm   28 μm       

     Finnfix 2000G—0.125 kg 
     η 10 rpm =215 cP η 100 rpm =173 cP 
     Finnfix 2000G—0.0625 kg 
     η 10 rpm =450 cP η 100 rpm =190 cP 
     Finnfix 2000G—0.0625 kg 
     η 10 rpm =1020 cP η 100 rpm =272 cP 
     Thor MBF 28—0.2 kg 
     pH=9.0 
     NaOH (10%)—50 mL 
     pH=9.5 
     η 10 rpm =430 cP η 100 rpm =176 cP 
     Finnfix 2000G—0.0625 kg 
     η 10 rpm =1320 cP η 100 rpm =310 cP. 
     Sample 3 
     Description: sample from the second mill, with pre-slurry at 50% solid content. 
     200 kg of slurry. 
     Mass population vs. particle size of talc in sample 3 is expressed in  FIG. 3 . Said talc product has following peaks of particle size distribution:
         3.8 μm   8.0 μm   18 μm       

     Solids content: 55.0% 
     Granulometry: 
     d 50 =1.45 μm 
     Thor MBF 28—0.4 kg 
     pH=9.3 
     NaOH (10%)—50 mL 
     pH=9.5 
     Viscosity at 25° C. (spl 4): 
     η 10 rpm =1440 cP η 100 rpm =1248 cP 
     No cellulose was added to this slurry. 
     Sample 4 
     Description: sample from the first mill, with pre-slurry at 60% solid content. 
     260 kg of slurry. 
     Mass population vs. particle size of talc in sample 4 is expressed in  FIG. 4 . Said talc product has following peaks of particle size distribution:
         1.5 μm   9.6 μm   20 μm   38 μm       

     Solids content: 58.6% 
     Granulometry: 
     d 50 =7.36 μm 
     Thor MBF 28—0.5 kg 
     pH=9.1 
     NaOH (10%)—100 mL 
     pH=9.5 
     NaOH (10%)—15 mL 
     pH=9.5 
     Viscosity at 25° C.: 
     η 10 rpm =400 cP η 100 rpm =510 cP 
     Celfow—0.1300 kg 
     η 10 rpm =620 cP η 100 rpm =386 cP 
     Celflow—0.0650 kg 
     η 10 rpm =680 cP η 100 rpm =412 cP. 
     Sample 5 
     Description: sample from the second mill, with pre-slurry at 60% solid content. 
     200 kg of slurry. 
     Mass population vs. particle size of talc in sample 5 is expressed in  FIG. 5 . Said talc product has following peaks of particle size distribution:
         1.3 μm   3.8 μm   8.5 μm   16 μm   27 μm       

     Solids content: 60.1% 
     Granulometry: 
     d 50 =3.30 μm 
     Viscosity at 25° C. (spl 6): 
     η 10 rpm =1200 cP η 100 rpm =1840 cP 
     Thor MBF 28—0.4 kg 
     pH=8.9 
     NaOH (10%)—100 mL 
     pH=9.4 
     Viscosity at 25° C. (spl 3): 
     η 10 rpm =930 cP η 100 rpm =995 cP 
     No cellulose was added to this sample. 
     Sample 6 
     Description: Sieved sample from the mill, with pre-slurry at 50% solid content. 
     545 kg of slurry. 
     Mass population vs. particle size of talc in sample 6 is expressed in  FIG. 6 . Said talc product has following peaks of particle size distribution:
         4.0 μm   9.0 μm       

     Solids content: 40.3% 
     Granulometry: 
     d 50 =2.83 μm 
     Thor MBF 28—1.1 kg 
     pH=9.4 
     Celflow—218 g 
     η 10 rpm =130 cP η 100 rpm =81 cP 
     Celflow—218 g 
     η 10 rpm =360 cP η 100 rpm =110 cP.