Special SolventS for paintS and coatingS

Exactly Your Application

Special SolventS for paintS and coatingS

Formulations often contain a blend of slow and medium evaporation rate solvents to optimise the film properties and thus the final appearance. Evaporation rate can affect the drying time of the coatings or inks as well as the film appearance and durability. The evaporation profiles of Dipropylene glycol DME and Diethylene glycol dibutyl ether are given in Table 1:

The following figures show the effect of Dipropylene glycol DME on the Minimum Film For-mation Temperature (MFFT) (Figure 3) and on the Persoz Hardness (Figure 4):

Certainly it should be kept in mind that the evaporation rate of the pure solvent gives only a guide for the speed of drying of the coating. The evaporation of the solvent from a film depends strongly on the affinity of the solvent to the binder. A solvent or coalescent which is normally highly volatile but shows a strong affinity to the binder will evaporate slowly from the film. Industrial coatings usually have to meet short dry-times. As it can be generally stated that the more volatile the coalescing agent, the more the coalescing performance declines which lends to using a coalescent of medium volatility.

However, the best way to determine solvency is to simply test the solubility of typical coating resins in Clariant Special Solvents as shown in the following table:

coMpoUnd evaporation nUMber(n-bUac = 1)

Dipropylene glycol DME 0.13

Diethylene glycol dibutyl ether <0.01

coMpoUnd dipropylene glycol dMe

diethylene glycol dibUtyl ether

Acrylic (e.g. Acryloid™ B-66) + -

Alkyd (e.g. Plexal® P65) + -

Epoxy (e.g. D.E.R.™ 331) + +

Melamine (e.g. Cymel® 300) + +

Isocyanate (e.g. Desmodur® N100) + -

Polyester (e.g. Versamid® 930) - -

Polyester (e.g. Desmophen® 852) + -

Table 1. Evaporation numbers of Dipropylene glycol DME and Diethylene glycol dibutyl ether

Table 2. Solubility of typical resins in Clariant Special Solvents (+ = solubility >250 g/L)

Figure 1. Comparison of the MFFT of various solvents.

14

12

10

8

6

4

2

0

acrylic dM777

Styrene acrylic ldM6636

vinyl/versativ ldM2417

MFFT (°C)

Latex without solvent

Diprop. DME Ethyl Lactate Dowanol PM Butyl Diglycol

12,3 12,0 10,8

0,5 0,1 0,1 0,1 0,1 0,1

3,5 4,3 1,1

10,2 9,4 9,0

replacing nMp in pUd coatingS and paint Stripper forMUlationSAccording to REGULATION (EC) No. 1272/2008 N-Methyl pyrrolidone (NMP) is classified as CMR-substance (reprotoxic category 1B, H360D: May damage the unborn child); formulations containing more than 0.1% NMP have to be classified as toxic within the field of application of REACH. Additionally, CMR-substances are restricted to closed applications only by REACH to guarantee compliance with the substances´ DNEL- and PNECS-values.

Dipropylene glycol DME is not classified and lends itself as a suitable replacement for NMP in several cases.

pUd coatingSN-methylpyrrolidone (NMP) has been successfully used as a processing aid in the manufactur-ing of polyurethane dispersions (PUDs) for many years. However, the toxicity of NMP makes the presence of this solvent in the finished product undesirable.

A replacement candidate for NMP in the conventional process for the pre-polymer stage should have the following properties:• Inert, non-reactive solvent• Non-toxic and easy to handle• High solvating power• High chemical stability over a wide pH range• Mild odour• Low/moderate evaporation numbers

Clariant’s Dipropylene glycol DME fulfils all of these requirements.

dipropylene glycol dMe nMp

Melting Point -80 °C -24 °C

Boiling Point 175 °C 204 °C

Flash Point 65 °C 91 °C

Solubility in Water @ 20 °C

526 g/L miscible

Classification -

Figure 2. Comparison of the effect of various solvents on the Persoz Hardness.

140

120

100

80

60

40

20

0

acrylic dM777

Styrene acrylic ldM6636

vinyl/versativ ldM2417

MFFT (°C)

Latex without solvent

Diprop. DME Ethyl Lactate Dowanol PM Butyl Diglycol

97 47 59

36 18 17 36 27 19

66 35 25

92 48 48

The results show that Dipropylene glycol DME usually lowers the MFFT and function as a softener in latex formulations. Further comparisons of Dipropylene glycol DME with common latex and acrylic resin binders for a wide variety of applications can be found in the literature.

As it is not completely water-soluble and still has a strong affinity for hydrophobic compounds, it will aid in coupling the polyisocyanate into the water phase. Compared to other solvents, Dipropylene glycol DME is a more effective solvent for reducing the viscosity of polyisocyanate resins. And since it is not especially hygroscopic (compared to NMP), resin formulators can be sure that little moisture will be present to cause early CO2 formation by the reaction of water with isocyanate. The surface tension of Dipropylene glycol DME is lower (26.3 mN/m at 25 °C) than that of many other solvents and therefore helpful to reduce the formation of microblisters caused by CO2 trapped in the film during the drying circle. The effectiveness and benefits of Dipropylene glycol DME usage in PUDs has been proven during the last 20 years.

In coating formulations, Dipropylene glycol DME can also be used as a co-solvent in combina-tion with propylene glycol methyl ether acetate (PMA) as an alternative to ethylene glycol ethyl ether acetate (EEA), which has been identified as a CMR-substance. Experimental results sug-gest that the use of Dipropylene glycol DME as solvent additive to PMA provides film hardness development rates and final film hardness that are comparable to formulations based on EEA and superior to those based on PMA alone. The disadvantage of Dipropylene glycol DME – showing a lower solubility for 2,2-di(hydroxymethyl)-propionic acid (DMPA) in comparison with NMP, can be offset by adding a surfactant such as Tegomer® D3403, for instance, to the prepolymer.

paint Stripper forMUlationSThe removal of old or unwanted (e.g. graffiti) paint is often needed before applying new layers of coatings. The wide range of paint types means that specific paint strippers have to be formu-lated for particular applications.

In the past, NMP was successfully used in paint stripping formulations, but its toxicity presents a health risk and drives the efforts to develop NMP-free formulations. Water-based paint strip-per formulations containing Dipropylene glycol DME exhibit good solvency and enhanced stripping times over a range of paint types.

Table 3 compares the stripping times in minutes of formulations made with NMP versus Dipropylene glycol DME (Diprop DME):

additive pva paint alkyd paint polyeSter paint

NMP (100%) 30 30 10

NMP + H2O (85:15) 90 160 50

NMP + PEG (85:15) 45 45 20

Diprop DME (100%) >120 45 30

Diprop DME+ H2O (85:15) 45 25 11

Diprop DME+ PEG (85:15) 30 15 15

The addition of water or another protic solvent like a polyethylene glycol (e.g. PEG 1200) has a marked positive effect on Dipropylene glycol DME formulations, enhancing their performance by decreasing stripping times.

This information corresponds to the present state of our knowledge and is intended as a general description of our products and their possible applications. Clariant makes no warranties, express or implied, as to the information’s accu-racy, adequacy, sufficiency or freedom from defect and assumes no liability in connection with any use of this infor-mation. Any user of this product is responsible for determi-ning the suitability of Clariant’s products for its particular application. * Nothing included in this information waives any of Clariant’s General Terms and Conditions of Sale, which control unless it agrees otherwise in writing. Any existing intellectual/industrial property rights must be ob-served. Due to possible changes in our products and appli-cable national and international regulations and laws, the status of our products could change. Material Safety Data Sheets providing safety precautions, that should be obser-ved when handling or storing Clariant products, are available upon request and are provided in compliance with appli-cable law. You should obtain and review the applicable Ma-terial Safety Data Sheet information before handling any of these products. For additional information, please contact Clariant.

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