R101A Polyol-Modified Organosilicon: the Third Generation of Titanium Dioxide Organic Coating Agents

The organic coating agents for titanium dioxide have moved from NPG, TMP and TME through organosilicon to polyol-modified organosilicon. Using the measured data in the manual, this article sets the three generations — TMP, 7020 and R101A — side by side, to show what each generation solved and what it left behind.

Why rutile titanium dioxide must be organically coated

1

Rutile titanium dioxide is a premium white pigment with specific, strict requirements for physico-chemical indicators such as titanium dioxide content, pH value, resistivity, particle size, moisture and rutile content, and for pigment performance indicators such as weather resistance, tinting strength, whiteness, hiding power and brightness.

But beyond these indicators, processing performance now carries ever more weight. To obtain excellent pigment indicators and processing performance, titanium dioxide must be coated.

Coating is done in two stages: generally an inorganic coating (titanium, silicon, aluminium, etc.) first, then an organic coating.

The inorganic coating concentrates on pigment indicators, the organic coating on application and processing performance indicators; the two overlap and complement each other.

That is the skeleton of this article. Every comparison below takes place inside this division of labour.

The problem of the first generation: not heat-resistant, and it foams

The earliest organic coating agents were mainly NPG (neopentyl glycol), TMP (trimethylolpropane) and TME (trimethylolethane) — alcohols or alkanes that carry hydroxyl groups or generate them on hydrolysis.

Their common mechanism: hydrophilic polar groups are physically adsorbed on the titanium dioxide surface, while lipophilic non-polar groups point outward and interact with the organic dispersion medium, improving wetting.

The problem is just as clear: poor heat resistance, with yellowing and foaming readily appearing during use.

In concrete terms this comes down to two things:

• TMP causes yellowing in plastic applications
• TMP causes excessive foaming and similar defects when applied in pulp

A general-purpose rutile titanium dioxide must serve three systems at once: ordinary water-based systems (paper, coatings), ordinary oil-based systems (paints, inks) and high-temperature systems (rubbers, plastics and masterbatch).

TMP cannot serve both ends. Titanium dioxide producers need organic coating agents with better performance — exactly the problem the second and third generations set out to solve.

The second generation: organosilicon, and the problem it left behind

From the early 80s, overseas titanium dioxide companies began using organosilicon coating agents for the organic coating.

Titanium dioxide treated with an organosilicon coating can markedly improve compatibility in all kinds of media, raise tinting strength and whiteness, increase gloss and weather resistance, reduce oil absorption and improve adhesion to all kinds of resin and plastic media. Its temperature resistance is outstanding (over 300°C), the dosage is small and it is easy to use.

But it has one fatal drawback: it is hard to disperse, and agglomeration readily occurs.

That is where the problem sits. Organosilicon pushed heat resistance and generality up, and left dispersibility outside the door.

The third generation: R101A, polyol-modified organosilicon

The approach R101A takes is: use the excellent dispersing performance of polyols as an auxiliary material for the organosilicon coating agent, and thereby synthesise a polyol-modified organosilicon coating agent.

It belongs to the polyol-modified silicone emulsion family; the main components are polysiloxanes with active hydroxyl groups, polysiloxanes with active ether groups, and high-molecular-weight polyol. The molecule is an organic polymer centred on silicon atoms and carrying hydroxyl, ether, alcohol and similar groups.

Four structural features

① The abundant methyl groups on the Si atoms shield the high-energy polysiloxane backbone.

② The C-Si-Na bond is non-polar, which makes the intermolecular forces extremely weak.

③ The Si-O-OH bond is long and the bond angle in Si-O-OH-O-Si is large, so the Si-O-OH bond rotates very easily, and therefore R101A has good lubricity, flowability, weather resistance and abrasion resistance.

④ The Si-O-OH bond is a covalent bond with 75% ionic character (covalent bonds are directional, ionic bonds are not), and its bond energy is far greater than that of the C-O bond, so R101A has very good heat resistance and weather resistance compared with conventional organic compounds.

Item ④ is the molecular basis of the temperature resistance; item ③ is the source of the lubricity. The two properties are not a coincidence sitting side by side; they are two faces of the same structure.

Coating mechanism: more than physical adsorption

Traditional organic coating agents (NPG, TMP, TME) rely mainly on physical adsorption. R101A takes a different route.

Traditional organic coating agents (such as NPG, TMP, TME) are physically adsorbed on the surface of titanium dioxide through their hydrophilic polar groups, while their lipophilic non-polar groups point outward and interact with the organic dispersion medium, so as to enhance the wetting performance with the dispersion medium. R101A, by contrast, works mainly through the hydrogen-bond chemical adsorption between the siloxane groups in the polyol-modified silane polymer and the titanium dioxide, and through the chemical condensation reaction or substitution reaction between the hydroxyl/ether groups on the polyol-modified silane molecule and the hydroxyl groups on the surface of the titanium dioxide, forming on the surface of the titanium dioxide a very uniform, dense and firmly bonded polyol-modified silane film layer.

This layer does three things:

• It eliminates or weakens the polar adsorption between titanium dioxide particles
• It forms sterically hindering functional groups between the particles and prevents agglomeration
• It provides good lubricity, weather resistance, thermal stability and reactivity for subsequent reactions

The result: a marked improvement in the wetting and dispersion performance of titanium dioxide in all kinds of dispersion media, and an increase in the optical stability of the titanium dioxide.

Three generations side by side: TMP vs 7020 vs R101A

The comparison table given in the manual:

Because the testing systems and evaluation criteria differ from manufacturer to manufacturer, the results of this experiment are for reference only; we make no promise and no guarantee, and it is the responsibility of the user to verify whether the product meets its own requirements.

Row by row:

Tinting strength rises from 1860 to 2013, an increase of 8.2%.

is hard to disperse and readily agglomerates

reducing oil absorption

Best on four indicators (tinting strength, dispersibility, oil absorption, brightness), and level with 7020 on chroma resistance.

A further verification on carbon black

Moved from the bodyRe-tested on carbon black: eight indicators for Z111 with and without R101A (source text)

Parameter	Titanium dioxide version	Carbon black version
Appearance	White liquid	White paste-like liquid
Non-volatile content	23%	99.9%
Specific gravity g/mL	0.99	1.03
pH	6.8–7	6.8–7
Diluent	Water	Water
Dosage (based on powder weight)	0.1–3%	0.1–3%

2

The same R101A, switched to high-pigment carbon black Z111:

A further veri…

Indicator	Z111	Z111 + R101A
Blackness (≤)	16	15
Coloring strength (%≥)	125	130
Oil absorption (ml/g)	1.05	0.98
Volatiles (% 950°C)	8.0	8.3
Moisture (%≤)	5	4.5
PH	3.0	3.0
Flowability (35°C)	22	28
Sieve residue 10⁻⁶	50	20

Coloring strength 125 → 130, oil absorption 1.05 → 0.98, flowability 22 → 28, sieve residue 50 → 20.

Sieve residue falls from 50 to 20, down to four tenths of its original value.

the higher the blackness, the higher the coloring strength of the carbon black

How to use it: six steps for wet coating

Because of the limits of the laboratory equipment, dry coating is hard to disperse evenly, and the manual recommends wet coating.

Taking the treatment of 200 g of titanium dioxide at an addition level of 0.5% as an example:

1. 01Add a suitable amount of purified water to a glass beaker fitted with a mechanical stirrer (about 20–50 mL of purified water, enough to wet the titanium dioxide completely and to slurry it uniformly), and start the stirrer
2. 02Add 1 g of R101A polyol-modified silane coating agent to the beaker
3. 03Slowly add the 200 g of titanium dioxide to be treated into the beaker and slurry for 30 min
4. 04Stop the stirrer, transfer the titanium dioxide from the beaker into an evaporating dish, cover it with clean filter paper and place it in an oven with fume extraction and constant-temperature control, drying at 105°C for about 6–8 h until completely dry
5. 05Take out the dried titanium dioxide and pulverise it with a small air-jet mill
6. 06Test the relevant pigment indicators of the titanium dioxide (such as dispersibility and oil absorption) and the application indicators (temperature resistance, dry powder flowability)

Two addition methods that can be used directly on the production line

Slurry method: add the R101A slurry directly to the homogeniser or mixing tank of the crude rutile titanium dioxide, and carry out air-jet pulverisation once the coating has been made fully uniform.

Air-jet synchronised method: R101A is added in proportion directly with the screw feed during the air-jet pulverisation step, or sprayed into the air-jet mill chamber.

Water cooling method for carbon black plants: pigment carbon black producers can add it directly into the water of the second cooling stage (water : R101A = 5 : 1) and spray-coat directly, which preserves the original particle size, improves the dispersing performance in subsequent applications and lowers the oil absorption of the carbon black.

Indicators and dosage

R101A is not only for titanium dioxide: activating dispersive coating can be applied across whole powder series such as oxidised carbon black, carbon black, calcium carbonate, talc, lithopone, barium sulphate, sodium sulphate, and organic or inorganic pigments. Its main role is to improve oxidation resistance, temperature resistance, organic compatibility with the material, dispersibility and anti-agglomeration performance.

One disclaimer and three reminders

Disclaimer: because the testing systems and evaluation criteria differ from manufacturer to manufacturer, the results of this experiment are for reference only and carry no promise or guarantee, and it is the responsibility of the user to verify whether the product meets its own requirements.

Reminder one: universality is not free. R101A is presented as one brand with universal applicability — it covers water, oil and high-temperature systems alike. But “universal” refers to the broad compatibility of the coating agent itself, not to its being optimal for every powder. The dosage still has to be adjusted for each powder according to oil absorption and fineness.

the limits of the laboratory equipment

Frequently asked questions

Q: Where do 7020 and R101A differ? A: They are level on chroma resistance (both 150°C); on the remaining indicators R101A is ahead — dispersibility from 5.3 up to 6.50, oil absorption from 18.56 down to 16.30 g/100g, tinting strength from 1930 up to 2013, brightness from 94.6 up to 96.2. The manual gives only the grade designation and the corresponding values; it does not state which generation 7020 belongs to.

Q: Why must the wet process be used — can the dry process not work? A: The manual’s own words are “Because of the limits of the laboratory equipment, dry coating is hard to disperse evenly, and wet coating is recommended.” What is limited is the laboratory equipment, not the dry process itself.

Q: What is the denominator of the 0.1%–3% dosage? A: The powder weight. The manual writes “dosage 0.1-3% (based on powder weight)”, and another place also states “the addition level of R101A in titanium dioxide is 0.1%-3%”.

Q: What unit is the dispersibility value of 6.50 in? A: The manual specifies no dimension. 4.5 / 5.3 / 6.50 are relative rating values under the same evaluation system; they can only be compared against one another and cannot be used as absolute values.

Q: Can this coating agent be used only on titanium dioxide? A: No. The manual ran a verification with high-pigment carbon black Z111 from Shanghai Coking (200 g, addition level 0.5%), and the carbon black version has corresponding data for indicators such as blackness, coloring strength, oil absorption and sieve residue.

In one sentence

Organic coating for titanium dioxide has gone through three generations: TMP is not heat-resistant and foams, organosilicon is heat-resistant but hard to disperse, and R101A uses polyols to make up for the shortfalls of both — dispersibility from 4.5 up to 6.50, oil absorption down 14.6%, chroma resistance from 110°C up to 150°C. When selecting, remember one thing: if you want generality, use R101A; for the process, follow the six wet-coating steps given in the manual.