Bill Jeffries AOC,LLC and Richard Keeler AOC,LLC October 1-3, 2003

ABSTRACT methods of pigment addition can yield differences The solubility, CIELAB color, matrix viscosity, air in process time, consistency, matrix viscosity, flow release and leveling properties of highly filled un- and leveling, and cure time. saturated matrices made with different forms of Titanium dioxide colorant will be evaluat- Among composite manufacturers, particularly ed. A comparison of dry Titanium dioxide and col- when making non-reinforced composites such as or dispersions of TiO2 in various dispersion vehi- cultured marble, solid surface, centrifugal casting cles will be studied. With the advent of automated and “ concrete”, there is a growing de- casting machines, there is an increased demand mand for managing quality, color consistency and for liquid color dispersions. Liquid color disper- cost through the use of automated metering and sions can produce benefits when used in batch dispensing equipment. With resin heater options matrix processes. Dispersions can reduce mixing on this equipment, content can be taken to time, improve uniformity of color, reduce matrix higher levels (75-88%) than has traditionally been viscosity, assist air release, improve flow and lev- possible. Because the amount of Titanium dioxide eling, and decrease resin demand. The degree of being introduced into the composite matrix is typi- whiteness, as measured by CIELAB, is generally cally less than 2% by weight, liquid pigment dis- persions can be more accurately charged through considered to be a function of pigment concentra- automated equipment using metering pumps tion. This isn’t always true, not all Titanium diox- than by metering in dry powder Titanium dioxide. ide yields the same color at the same concentra- With the advent of this equipment, there has tion and liquid color dispersions vary in their influ- been an increase in demand for liquid pigment ence on matrix properties. Whiteness, air release, dispersions. flow and leveling, matrix viscosity and cure prop- erties may vary with various dispersions and dry Some of the differences and similarities in the pigments. A novel dispersion that reduces mixing properties of manufacturing composites using dry time, improves flow and leveling, aides air release Titanium dioxides versus liquid dispersions are to and reduces matrix viscosity will be presented be reviewed in this paper. The pigment type add- along with the comparison data of the matrix ed can influence the solubility, color uniformity, properties using different color vehicles. CIELAB color, matrix viscosity, air release, flow and leveling and cure properties of the composite INTRODUCTION matrix. The type and particle size of the Titanium While there are many specialty colors used in pol- dioxide and the chemistry of the “resin” the pig- yester composites, the mostly widely used color ment is dispersed in can impact these properties. by far is white. To make these composites white, For the purposes of this paper, the “resins” used dry Titanium dioxide is added to the composite to make these Titanium dioxide dispersions are matrix or Titanium dioxide is milled into a “resin” -free unsaturated . to make a liquid Titanium dioxide dispersion to be added. To achieve a consistent color in the part, These dispersions are typically 20-35% resin and dry Titanium dioxide is usually first dispersed into 65-80% Titanium dioxide with viscosity ranges the resin being used to make the part, the two from 2000 – 8000 cps. There are many variables

Pigment Influences on the Properties of Highly Filled Resin Systems, continued

that influence color and other properties of the by weight were used. Within an individual experi- composite. Many composite manufacturers per- ment, the same resin, catalyst types, catalyst lev- ceive the color consistency of their composite is a el, filler type and filler level was used. result of the liquid resin color. Good manufactur- ing practices do result in consistent liquid color, The mixing protocol for the solubility testing (Fig. but it is the cured resin color, (as measured by 3-6) was to first mix resin and catalyst for one mi- CIEL*a*b* or similar method, see Fig.1) that de- nute. This allows the most uniform distribution of termines the appearance and pigment demand catalyst because resin and catalyst are similar in for the composite. The higher the L* value, the viscosity and specific gravity and minimizes the brighter the composite, the closer to zero a* (red- possibility of catalyst absorption by pigmentation green) value and b* (blue-yellow) values are, the or fillers. Next, the background pigment (dark more neutral the color. From this data, the Delta E blue) was added and mixed a fixed number of cy- cles until homogeneous. Then the calcium car- (total color difference) from the desired color or bonate was added and mixed a fix number of cy- theoretical “brightest” can be calculated (ASTM cles until the matrix was homogeneous. Finally, D2244). Filler colors do vary greatly, but Titanium dry Titanium dioxide or liquid Titanium dioxide dioxide is very efficient at normalizing the color of dispersion was added to the catalyzed, blue col- a composite at relatively low doses. In Fig.2, the ored matrix and mixed the specified number of color variability of five types of Aluminum trihy- cycles, then immediately cast into the mold and drate and four types of calcium carbonate typical- allowed to gel and cure. Each sample represents ly used in highly filled (60-80% filler by weight) a different specimen, dry and dispersed, mixed composites was evaluated. The L*, a*, b* values for a specified number of cycles in a planetary were identified with each filler both with and with- mixer by the same process. Solubility, which influ- out pigment. Figure 2 demonstrates the variability ences the process time, color consistency and in filler contribution to composite color and the cure consistency, was compared by visual exami- normalizing effect of the pigment. The color dif- nation and photographs. ferences in the unpigmented composites vary sig- nificantly more than the pigmented composites (a The mixing protocol for the color testing (Fig. 7) delta E of less than 1.0 is considered indistin- was to first mix resin and catalyst for one minute. guishable to the naked eye). Next, the dry pigment or liquid dispersion was added and mixed a fixed number of cycles until Solubility influences mixing process time, color homogeneous. Then the calcium carbonate was consistency and cure consistency. Matrix viscosity added and mixed a fix number of cycles until the and thixotropy influence air release, flow and lev- mix was homogeneous. Finally, each sample was eling and uniformity of the part. Air release is in- cast into the mold, and allowed to gel and cure fluenced not only by viscosity but also by other overnight. The following day, the CIEL*a*b* color factors such as resin molecular weight, filler parti- values were read on a Data Color CS-5 spectro- cle size distribution, moisture, and gel time. In the photometer (ASTM E308). Color values were re- manufacture of highly filled composites, it is also ported for the L* value (darklight), a* value useful to cut cross sections of the part for visual (green-red) and b* value (blue-yellow) using the examination under a microscope or measure air daylight light source (D65 10 deg). The color re- by density per unit volume. sults reported in Fig. 2 were performed by the same procedure. The intent of this paper is to point out that Titani- um dioxide is not just a pigment to achieve aes- The mixing protocol for the viscosity testing was to thetic color. Various sources and vehicles of Tita- mix resin and pigment only for one minute. This nium dioxide can influence many properties of allowed more uniform dispersion of the dry pig- composite manufacturing and can be optimized ment and takes advantage of the solubility of the to a specific process. dispersion in the resin due to similar viscosities. Then the calcium carbonate filler was added and EXPERIMENTAL mixed until homogeneous. The number of mixing To make the composite test samples, standard cycles required for the matrix with the highest fill- orthophthalic unsaturated polyesters containing er content (highest viscosity) was determined first 29-31% styrene then the same number of mixing cycles was em-

Pigment Influences on the Properties of Highly Filled Resin Systems, continued ployed with each subsequent sample. In the ex- trieved from the mixing vat and placed in polyeth- periment with Filler X (Fig. 8), a blend of calcium ylene bags. Samples were taken when the pig- carbonate and lightweight, the matrix viscosity ment loading equaled 0.5, 1.0, 1.5, 2.0, 2.5, and was measured by a Brookfield HB viscometer 3.0 percent. (ASTM D2196), using a T-C spindle at 2.5 rpm and 25 degrees C (77 F). In the subsequent ex- A computer study was initiated to measure the periment, using Filler Y (Fig. 9), a straight calcium brightness and overall color properties of the pig- carbonate, Brookfield RV viscosities were run us- mented matrix mixtures. Figure 3 has a listing of ing spindle #2 @ 2 and 20 rpm. This provides da- the Calcium Carbonate fillers. Table 4 has a list- ta on the thixotropic index between the dry and ing of Alumina Tri-Hydrate fillers, and Table 5 has dispersed pigment at various levels of filler. Vis- a listing of the hybrid fillers. cosity and thixotropy values are significant be- cause of their impact on air release and flow and Decoding L*-a*- b* values leveling properties.  This three-axis system is used by various in- Air release is influenced by many factors: viscosity dustries (especially the coatings and and thixotropy of the matrix resin, molecular segments) to communicate color and/or color weight, filler particles size distribution, moisture, differences. (For the testing presented in this and gel time. Of these, viscosity is the starting paper, the L* axis will be the primary axis for point to achieve proper air re ease. Composite measurements and discussion). manufacturers often wish to use the maximum amount of filler possible that achieves the desired A simple representation of this system comprised properties. For the purpose of this paper, air re- of the three axes L*, a*, and b*. lease or air content in the composite was not measured, but can be viewed in the photos (Fig 3-  L*: (Light-Dark) Higher L* values would be 6) used to illustrate the solubility of the pigments attributed to a lighter color, and lower num- and time-lapse photos (Fig 10-13) of the flow and bers would be attributed to a darker color. leveling.  a* : (Red-Green) Higher a* values indicate that the matrix color is more red (may appear Once the dry brightness and resin/filler matrix "pink"); lower a* values indicates that the ma- brightness studies were completed, we chose to trix color is more green. make a study of the effect of pigmentation versus  b* : (Yellow-Blue) Higher values for b* indi- changes in brightness and color. The experiments cate that the matrix color is more yellow, low- were designed to show the effect of pigment and er values for b* indicates that the matrix color its ability to change the L* lightness value when is more blue. combined with the overall color body of the resin/ filler matrix. Figure 1 illustrates the L* a* b* coordinate sys- tem. It is fairly common in our industry to use “ladder” type studies, where a variable, in this case the Results and Discussion pigment, will be tested in a step-wise fashion. We The dry L* lightness measurements for alumina know that generally these usage levels of Titani- tri-hydrate ranged between 99.2 (filler A40) and um Dioxide are below 3.0 percent based on the 99.8 (filler A50) when measured in the polyeth- matrix weight, but generally above 0.5 percent. ylene bags. The difference between the highest Thus a ladder study was initiated at levels of 0.5 and lowest alumina tri-hydrate dry values was 0.6 to 3.0 percent, in increments of 0.5 percent. units.

The pigment used in these studies was a liquid The matrix L* lightness measurements for alumi- dispersion of Titanium Dioxide (75% active sol- na trihydrate ranged from 90.8 (filler A20) and ids). We started with unpigmented matrix mixture 95.9 for (filler A50). The difference between the and added 0.5% pigment dispersion. After the highest and lowest alumina trihydrate matrix val- mixing process was completed, samples were re- ues was 5.1 units.

Pigment Influences on the Properties of Highly Filled Resin Systems, continued

Figure 2 illustrates the differences in dry versus sample contained 70% by weight as much Titani- matrix measurements for the alumina trihydrate um dioxide as the dry sample. Fig. 7 demon- fillers. strates that the results were less than 0.17 delta E, meaning the difference was barely perceptible The dry L* lightness measurements for calcium to the spectrophotometer and could not be per- carbonate ranged between 96.7 (filler C35) and ceived by the naked eye. 98.0 (filler C25) when measured in the polyeth- ylene bags. The total difference between the high- Another critical area for comparison was matrix est and lowest calcium carbonate dry values was viscosity. For the experiment represented by Fig. 1.3 units.The ability of the material to flow across 8, in addition to the dry and dispersed pigments the mold and fill evaluated in the solubility experiment, an addi- the mold uniformly is a primary contributor to the tional source of Titanium dioxide (“Dry C”) was strength, cosmetics and process cycle time of added to the test. “Dry C” is an “equivalent” to making the composite. Flow and leveling is evalu- “Dry B” that was reported to have the same gen- ated by using a glass plate inclined between 30 eral particle size distribution, oil absorption, and and 45 degrees. To this plate is applied an equal color. The filler used in Figure 8, is a blend of cal- mass of dry and dispersed TiO2 formulations of cium carbonate and lightweight. These fillers the same diameter and thickness. Visual observa- tend to form very high matrix viscosities. The top tions and timed photographs can be used to cap- table is a comparison at 75% filler, 25% resin and ture their ability to flow; level and release en- 1.4 pph pigment. trained air (Fig. 10-13). At this dosing, both dispersed pigments result in CONCLUSION lower viscosity than the dry pigment samples. The The difference in the solubility of dry Titanium di- mix made with “Dry C” is much higher in viscosity oxide pigment as compared to a liquid Titanium than the other three. Reducing the filler to 71.5%, dioxide dispersion is represented in Fig. 3-6. In the results show that the matrix made with “Dry Figure 4, after 180 cycles under moderate inten- B” is lower in viscosity than the matrix made with sity mixing, the liquid pigment is sufficiently dis- the two dispersions, and again “Dry C” is signifi- persed that in a manufacturing operation, the cantly higher in viscosity. Another series of tests composite matrix could be poured into the mold. was performed to compare the viscosity and thix- The dry Titanium dioxide sample still contains otropy of matrix made with dry and liquid pig- some dry pigment at 360 cycles and even after ments. This is represented in Fig. 9. Samples 720 cycles there was one visible spec of undis- were created using 78%, 75% and 70% straight persed pigment. It should be noted that undis- calcium carbonate. The first observation is that in persed pigment creates an uncured area in a all cases, regardless of filler concentration and composite, if Titanium dioxide is used to brighten whether the viscosity is being measured at a high an already low color filler such as ATH, this could shear rate (20-rpm) or a low shear rate (2-rpm) be difficult to identify. the matrices made with dispersed pigment is low- er in viscosity. The results indicate that all matri- A common source of dry Titanium dioxide used in ces are in fact thixotropic, but as you reduce filler the composite industry was chosen for compari- (78%-70%) the thixotropic index drops (2.4 son to two different liquid dispersions. These dis- to 1.5). persions were made using this same dry Titanium dioxide, the difference being the chemistry of the The final test was to compare flow properties of “resin” the Titanium dioxide was dispersed in. Dis- the dispersions made from Dry B and Dispersed persion A is a widely sold Titanium dioxide disper- B. Equal formulations were made and poured on sion with a twelve-year performance history. Dis- glass plates positioned at approximately 35 de- persion B was a newer product being evaluated grees from horizontal. A photo was taken when for use in very highly filled composites made with the material was first poured (Fig. 10). Photos automated mixing and dispensing equipment. In (Fig. 11-13) were made every five minutes until the test, the same amount of dry titanium and the matrix actually gelled on the glass. The matrix dispersion was used, therefore each dispersion made with the liquid dispersion is more highly

Pigment Influences on the Properties of Highly Filled Resin Systems, continued

elongated than the matrix made from the dry ceptible to pigment type; various sources of Tita- TiO2, indicating more linear flow. What was also nium dioxide can yield vastly different viscosities. observed in real time but is difficult to see from Liquid dispersions can reduce matrix viscosity, the photographs is that as each matrix releases especially when the filler loading exceeds 75%. air, the dispersed matrix exhibits smaller divots The “resin” the pigment is dispersed in can also that tend to fill themselves as each bubble burst. influence the rheology of the matrix. Different liq- This phenomenon occurred more slowly with the uid color dispersions yield different viscosity, air dry pigment. release, flow and leveling properties. Dispersion A resulted in higher viscosity matrix than Dispersion CONCLUSIONS B, and when compared in flow tests (not shown) There is a significant difference in the solubility of performed more like the dry Titanium dioxide dis- liquid dispersions in highly filled composites. This persion. Several tests have been presented that makes dispersions ideal for use in automated would allow a composite manufacturer to opti- mixing and dispensing equipment where mixing mize their process for the parameters (such as time is minimal but can also be advantageous cycle time, color, consistency) that they wish to when batch mixing if process time is important. control. Most importantly, the Titanium dioxide Due to “wet” nature of liquid pigment dispersions, used to make composites is not a commodity. an equivalent dose by weight of dispersion, con- Through experimentation and product design it taining 20-30% less TiO2 can yield the same color can be used to influence many properties that with some highly filled composites. The working impact the appearance and performance of the viscosity of a highly filled matrix can be very sus- composite.

Figure 1

Pigment Influences on the Properties of Highly Filled Resin Systems, continued

Figure 2

ATH FILLER ONLY: @ 1.00% TiO2 L* a* b* Delta E L* a* b* Delta E ATH “A” 82.93 -0.23 4.41 STD 95.52 -0.78 2.16 STD ATH “B” 76.87 -1.01 5.55 6.22 94.84 -1.13 2.98 1.12 ATH “C” 76.16 -0.91 5.81 6.95 94.81 -1.06 2.51 0.84 ATH “D” 75.97 -1.59 6.14 7.3 95.17 -1.18 2.79 0.82 ATH “E” 77.69 -1.24 4.17 5.34 94.14 -1.19 2.87 1.61 average 77.92 -0.996 5.216 6.45 94.9 -1.07 2.66 1.10

Calcium Carbonate FILLER ONLY: @ 1.00% TiO2

L* a* b* Delta E L* a* b* Delta E CaCO3 “A” 85.48 -0.71 6.27 STD 94.56 -0.79 3.09 STD CaCO3 “B” 81.09 -0.42 7.04 4.47 92.86 -0.68 2.51 1.80 CaCO3 “C” 81.49 -0.31 5.83 4.03 92.78 -0.71 3.07 1.78 CaCO3 “D” 82.56 -0.26 4.71 3.34 93.39 -0.77 2.65 1.25 Average 82.66 -0.43 5.96 3.95 93.40 -0.74 2.83 1.61

ATH FILLER ONLY: @ 1.00% TiO2

L* a* b* Delta E L* a* b* Delta E ATH “A” 82.93 -0.23 4.41 STD 95.52 -0.78 2.16 STD ATH “B” 76.87 -1.01 5.55 6.22 94.84 -1.13 2.98 1.12 ATH “C” 76.16 -0.91 5.81 6.95 94.81 -1.06 2.51 0.84 ATH “D” 75.97 -1.59 6.14 7.3 95.17 -1.18 2.79 0.82 ATH “E” 77.69 -1.24 4.17 5.34 94.14 -1.19 2.87 1.61 average 77.92 -0.996 5.216 6.45 94.9 -1.07 2.66 1.10

Calcium Carbonate FILLER ONLY: @ 1.00% TiO2

L* a* b* Delta E L* a* b* Delta E CaCO3 “A” 85.48 -0.71 6.27 STD 94.56 -0.79 3.09 STD CaCO3 “B” 81.09 -0.42 7.04 4.47 92.86 -0.68 2.51 1.80 CaCO3 “C” 81.49 -0.31 5.83 4.03 92.78 -0.71 3.07 1.78 CaCO3 “D” 82.56 -0.26 4.71 3.34 93.39 -0.77 2.65 1.25 Average 82.66 -0.43 5.96 3.95 93.40 -0.74 2.83 1.61

Pigment Influences on the Properties of Highly Filled Resin Systems, continued

Figure 3 Figure 4

Figure 5 Figure 6

Pigment Influences on the Properties of Highly Filled Resin Systems, continued

Figure 7

Color Comparison of Dry and Dispersed [email protected] pph L* a* b* Delta E Dry TiO2 93.84 -0.33 2.52 0 Dispersion A 93.84 -0.32 2.53 0.01 Dispersion B 93.71 -0.28 2.42 0.17

Figure 8

TiO2 Viscosity Comparison @ 75% Filler X Sample Resin Filler X Pigment Viscosity, cps Dry C 150 450 8.4 2624000 Dry B 150 450 8.4 2080000 Disp A 150 450 8.4 1720000 Disp B 150 450 8.4 1696000

TiO2 Viscosity Comparison @ 71.5% Filler X Sample Resin Filler X Pigment Viscosity, cps Dry C 171 429 8.4 736000 Dry B 171 429 8.4 556800 Disp A 171 429 8.4 640000 Disp B 171 429 8.4 619200

Figure 9

Viscosities of Dry TiO2 B and Dispersed TiO2 B in Filler Y Sample Resin Filler Y Dry TiO2 Viscosity Viscosity Thix S.D. @ 2 rpm’s S.D. @ 20 rpm’s Index Dry B 110 390 7.5 3330000 1390000 2.4 Dry B 125 375 7.5 1230000 604000 2.04 Dry B 150 350 7.5 410000 282000 1.45

Viscosities of Dry TiO2 B and Dispersed TiO2 B in Filler Y Sample Resin Filler Dispersed Viscosity Viscosity Thix TiO2 S.D. @ 2 rpm’s S.D. @ 20 rpm’s Index

Disp B 110 390 7.5 2150000 886000 2.43 Disp B 125 375 7.5 1020000 492000 2.07 Pigment Influences on the Properties of Highly Filled Resin Systems, continued

Figure 10 Figure 11

Figure 12 Figure 13