CA1203650A

CA1203650A - Preparation of water-dilutable binder solutions, using monoalkyl glycol ethers

Info

Publication number: CA1203650A
Application number: CA000397569A
Authority: CA
Inventors: Heinz Nohe; Gerhard Neubert
Original assignee: BASF SE
Current assignee: BASF SE
Priority date: 1981-03-28
Filing date: 1982-03-04
Publication date: 1986-04-22
Also published as: DE3112429A1; DE3112429C2; EP0062226B1; DE3260767D1; EP0062226A1; ES510859A0; ATE9485T1; EP0062226B2; ES8303505A1

Abstract

Abstract of the disclosure: A process for the preparation of water-dilutable binder solutions, using a reaction pro-duct of isopropanol and propylene oxide as the solvent.
The solutions obtained may be used for coating and impregnation.

Description

~36~0 - 1 ~ O.Z. 0050/35051 Preparation of water-diluta~le binder solutions, using onoalkyl ~l~col ethers . . . _ . . . _ The present invention relates to a process for the preparation of water-dilutable binder solutions for coating and impregnation, using a monoalkyl glycol ether as the solvent.
The use of water-miscibie monoalkyl glycol ethers as solvents for water-dilutable coating agents and impreg-nants is known. For example, water-miscible organic solvents, especially l-butoxyethan-2-ol (butylglycol) and l-ethoxyethan-2-ol (ethylglycol) are used as constituents of heat-curable or oxidatively air-drying, water-dilutable paints based on resins having neutralized acidic or basic groups. These solvents lower the visccsity of the aqueous compositior!s by improving the sol~ation of the binder in the aqueous phase and also ensure better wetting of the substrate to be coated, and of the pigments con-tained in the compositions, as well as better levelling of the compositions.
For reasons of economy and minimization of sol vent pollution of the environment, it is desirable to minimize the content of organic solvents in these compo-sitions. However, this is only possible within limits.
With decreasing solvent content, the flow and processing characteristics of the aqueous compositions become less satisfactory, and ultimately the binder may become insoluble in the aqueous phase.

Moreover, such solvents are intended to speed up ~ b 365~) the surface drying, and ln-depth drying o:~ the aqueous coatings and impregnations at r0Om kemperature. In spite of the relatively high volatility which this requires, the concen-tration of solvent remaining in the dryiny film should neverthe-less at all times be such ~hat the proportion of water does not become so high as to interfere with film formation and cause damage to the filmr for example unsatisfactory levelling, reduced gloss, flaking, crazing and pitting, resulting in less good protection of the substrate.
~owever, the conventional monoalkyl glycol ethers each at best satisfy only some of these in part very contradictory requirements. This becomes particularly clear in the case of physically drying coating agents and impregnants, as described, for example, in DE-OS 3,022,870 (laid open on January 14, 1982 and in DE-OS 3,022,824 (laid open on January 7, 1982).
Thus it is true that butyglycol exhibits particularly good solvation o the neutralized copolymers described in the said publicakions and permits the preparation of aqueous coating compositions having a particularly low solvent content;
however, at room temperature butylglycol is so non-volatiIe that it remains too long in the coating and for a long time adversely effects the film hardness and water resistance o~ the coating.
More volatile conventional monoalkyl glycol ethers, for example ethylglycol, produce so little solvation of the water-dilutable resins mentioned th.at relatively high proportions of solvent must be used in the coating compo-sition if useful flow and processing characterlstics are ~3~
- 3 - O.Z. 0050/35051 to be attained.
It is true ~hat the combination of butylglycol with more volatile alcohols or conventional monoalkyl glycol ethers produces a usable compromise, but it still leaves much to be desired, since in such combinations the sol~ating power of the butylglycol is greatly reduced and, in some cases, compositiois constituting an increased fire hazard result.
It is an object of the present invention to provide solvents for the preparation of water-dilutable binders for coating compositions and impregnants, which do not suffer from the above disadvantages.
We have found that this object is achieved if, in a process for the preparation of water-dilutable binder solutions for coating agents and impregnants, using mono-alkyl glycol ethers as the solvent, the ethers used con-tain not less than 2 per cent by weight of a reaction pro-duct of isopropanol and propylene oxide.
Suitable reac-tion products of isopropanol with pro-pylene oxide are in general the equimolar reaction products,especially l-isopropoxypropan-2-ol or a mixture thereof with 2-isopropoxypropan-l-ol, which products may addition-ally contain small amounts, namely up to 20 per cent by weight, of reaction products of isopropanol with propylene oxide in the molar ratio of l:2, eg. l-diisopropoxypropan-

2-ol and/or 2-diisopropoxypropan-l-ol.
The monoalkyl glycol ethers used preferentially accordingly consist of, or contain, l-isopropoxypropan-2-ol. However, in a particular embodiment of the process ~3~

according to the invention, a h;.yher proportion of the reaction products of isopropanol with 2 moles of propylene oxide, or even such reaction products alone, may be employed.
l-Isopropoxypropan-2-ol is more volatile than ethy]-glycol. Amongst materials of such relative volatility, it is distinguished by particularly good solvating power for numerous water-dilutable resins, such as are descri~ed, for example, in DE-OS 3,022,870 (laid open on January 14, 1982) and in DE-OS 3,022~824 (laid open on January 7, 1982).
~ccordingly, it permits the preparation of aqueous coating compositions and impregnants, having a low solvent content, which exhibit more rapid surface drying and in-depth drying.
Moreover, compared with similar volatile glycol ethers, eg.
ethylglycol, it more effectively assists wetting of the substrates, as well as film Eormation, and levelling of the coatings. As a result, the coatings also provide better protection against corrosion.
A further important advantaye is that as a resul-t o~ the use of l-isopropoxypropan-2-ol resins having a lower content of salt groups and accordingly a more hydrophobic character and better water resistance and alkali resistance can be used in water-dilutable fast-drying ~ormulations.
Moreover, l-isopropoxypropan-2-ol has the advan-tage of a particularly beneficial effec-t on the flow of water-dilutable coating compositions compared with the effect of similar volatile glycol ethers. Extremely high viscosities, and a sudden drop to extremely low viscosities, as is particularly pronounced when diluting neutralized ~3~
_ 5 _ O.Z. 0050/35051 resin solutions, having a low content of salt groups and of solvent, with water, can be substantially or entirely avoided.
Accordingly, the use, according to the invention, of l-isopropoxypropan-2-ol permits the preparation of water-diluta~le coating compositions and impregnants which at one and the same time exhibit a particularly low solvent con-tent, improved flow, rapid surface drying, early develop-ment of water repellency of the drying layer, rapid in-depth drying, high water-swelling resistance and alkali resistance of the fully dried coatings, good wetting of the substrate, good levelling and strong adhesion.
l-Isopropoxypropan-2~ol is moreover more easily biodegradable, and physiologically safer, than most other monoalkyl glycol ethers.
l-Isopropoxypropan-2-ol can be extensively used as the sole auxiliary solvent for aqueous coating compo-sitions and impregnants. However, other partially or completely water-miscible solvents, for example n-butanol, sec.-butanol, isopropanol, methoxypropanol and butylglycol, can additionally be present if, for example, the sur~ace drying of the coating is to be acceleratd further or film formation and levelling are to be improved further.
However, the use of mixtures with dipropylene glyol monoisopropyl ethers and especially with 2-isopropoxypro-pan-l-ol, which are formed as by-products in the preparation of l-isopropoxypropan--2-ol, is preferred. In particular, a combination of l-isopropoxypropan~2-ol with a small proportion, namely from about 2 to 20%, of 2-isopropoxy-~{336~
- 6 - O.Z. 0050/35051 propan l-ol ~akes it possible further to improve the sol-vating power for water-dilutable resins7 and the levelling and gloss of aqueous coating compositions, wi-thout sub-stantially reducing the rate of evaporation o~ the glycol ether.
In special cases, for example if the solvent con tent of the coating compositions is to be very low and at the same time delayed drying and good levelling and gloss are desired, a higher proportion of dipropylene glycol monoisopropyl ethers can be employed, or these ethers may even be used as the sole solvent. In such cases, for example, l-diisopropoxypropan-2-ol, and its mixtures with a small proportion, namely up to about 10 per cent by weight, of 2-diisopropoxypropan-1-ol are preferred.
These dipropylene glycol monoisopropyl ethers have par-ticularly good solvating power for water-dilutable resins.
It is true that their rate of evaporation is low, but it suffices even for drying at room temperature, so that particularly low-solvent coating compositions can be pre-pared.
Water~dilutable coating compositions in which l-iso-propoxypropan-2-ol is used according to the inventlon are in particular those where water-dilutability is attributable to the neutralization of basic or acidic groups in the binder. Examples of such binders are carboxyl-containing polymers and polycondensates, which are neutralized with bases and which are crosslinked, and become water-resistant, through oxidative drying or by combination with resins with which they react, for example epoxy resins, aziridine ~L2~36~i~
O.Z. 0050/35051 derivatives or heat-curable aminoplasts.
The use of the ethers in water~dilutable, physically drying and air-drying coating compositions, especially as described in the two German patent applications cited above, is particularly preferred. In these cases, the mono-alkyl glycol ethers described prove particularly effective (cf. the Examples3.
For these applications, l-isopropoxypropan-2-ol is advantageously ~mployed in amounts of from 20 to 300, preferably from 40 to lO0, % by weight based on the binder containing salt groups.
In contrast, the diisopropoxypropanols, which evaporate more slowly, are in general employed in amounts of only from about lO to 40% by weight, based on binder.
A further use, according to the invention, of these g~ycol ethers is to add them to coating compositions and impregnants based on aqueous dispersions. With the glycol ethers used accordlng to the invention, more rapid in-depth drying is achieved, and the minimum film-forming temperature is lowered, without significantly a~fecting the shelf life of tihe dispersions. Thus, once again, coatings can be produced which attain their ultimate film properties, for example hardness and non-blocking, within a substantially shorter time than when using conventional film-forming assistants. For this purpose, the glvcol ethers described are generally employed in an amount of from about 3 to ~0%, based on dispersedpolymerO
The coating compositions and impregnants pre~ared from the binder solutions according to the invention may

3 6 ~ ~
- 8 - O.Z. 0050/35051 ~dditionally con~ain the conventional surface-coating additives and assistants, for example pigments, fillers, plasticizers, anti-sedi~entation agentS,thickeners, anti-foam agents, wetting agents and lubricants.
The Examples which follow illustrate the subject of the present invention without restricting the invention thereto. Parts and percentages are by weight 9 unless stated otherwise.

lOO parts of a mass polymer prepared in a conven-tional manner from 47 parts of styrene, 45 parts of isobutyl acrylate, 8 parts of acrylic acid and 1.5 parts of tert.-butyl perbenzoate as the initiator, and having a K value of 28, measured on a 3% strength acetone solution by the method of DIN 53,726, are dissolved in 100 parts of the glycol ether shown in Table 1 and neutralized with the amount of 25% strength aqueous ammonia equivalent to the carboxyl groups, and the solution is then diluted with 135 parts of demineralized water and brought to pH 8.7 by further addition of 25% strength ammonia.
To assist the film-forming characteristics and drying speeds, these clear finishes are coated onto a glass plate by means of a film spreader with a gap of 0.10 mm. The results are shown in Table 1.

:~2~36~
O . Z . 0050/3505 1 h a~

, U~ ~ O
O O
~1 ~ O O
~O.~ ~ ~
O ~ ~ O
~ m oq ,- ~ ~ o X ~1 ~ ~ ~ ~0 0 3 ::~
~ O S:: O ~1 a) 3 ~ O ,a o Q a~ C
h ~0 ~ ~ 0 o o ~ a~
V C) .,_ ~, S ~ ~
,~ 3 ,_, . o ~0 eo h 3 3 C
~ ~ ~ O ~ C~ ~1 c~ ~ ~ ~ O ~ ~ ~-1 ~1 .h S ~ rl C O O
~ .,~ ~ O r~
r-l ~ D ~ Q. Q.
~ "_ E~
~_ O S~
t~
~I
O
O ~ 0 ._ .
~.
X O a~
O O ~ _ R. O ~ O
~;t O O ~
Q, ~1 O O O
O ~ J~ 0 ~1 ~1 0 U~ . a) 3 3 0 ~0 ~: O
O ~ O
~1 1:t~ 0 !~
.~ ,~
~ S O O
a, ~-- o ~ ~ t~
D u~ ~ ~ ~ 3 E~ .. . ~ ~ E I O ~ S~
0~ ~ ~ ~ o o S:: O~ ~ 3 .,~ ~ - o 5~
h ~ . !;:~c ~r1 ~ ~r~ ~ C ~ 3 a) ~0 a.~C O 0~_ ~ 0 o ~o ~ ~-- ~ 0 ~a) 1 ;~; ~~1~1 ~I r-i ~ ~ ~ ~ s 3 0 ~ ~o ~ o ~ ~ ~ 3 ~ 0r~
11 ~1 S ~r~ X_~ ~r~ ~ 4 ~r1 C O 11) Ln ~ri 0 ~ ~ ~.r~ ~ 0 S-Q~ OO S ~ S,~ ~ ) O c~ 0 ~ 1 X O
G Z; ~ ~ 3 0 a~ S ~ C~ Ul D~
H S ~ O a~ ~ r--I
X r~ V ~ r~ ~r~
0 V V ~ ~ 3 ~ ~ D ~\J

~LZ~36~t - 10 - O Z. 0050/35051 The results in Table 1 show that l-isopropoxypro-pan-2-ol has a be-tter solvating action than ethylglycol and moreover permits the preparation of aqueous finishes which exhibit good wetting, good levelling and relatively rapid drying.
EXAMP~E 2 100 parts of the resin of Example 1 are dissolved hot in 50 parts of the glycol ether shown in Table 2, and after complete neutralization with ammonia the solution is diluted, similarly to Example 1, to 25% polymer con-centration by means o~ water. Using these clear finishes, films are spread on glass and sheet metal by means of a film spreader (0.2 mm gap). The results are shown in Table 2. All these clear finishes can be diluted with excess water without thereby causing the binder to floccu-late. Ail of them efficiently wet glass, iron, alu-minum and zinc and dry to give clear ~ilms with good levelling. The clear finishes 2.3, 2.4, 2.5, 2.6 and 2.7 give films with improved gloss (? compared to 2.1 and 2.2?).
COMPARATIVE EXAMPI,E C
This is carried out like Example 2, except that ethylglycol is used as the glycol ether. On adding water to the neutralized solution, the binder becomes insoluble and precipitates. The same result is obtained i~ the proportion of ethylglycol is increased to 75 parts.

~2~36~
O . Z . 00 5 0 / 3 5 05 1 o o o o ~ 2 ~ o~ ~ 3 ~a) ~ ~

.
o o n ~ ~ S ~
O C~ ~ O

Ln o a) ~

o o ~ ~ æ æ ~ ~
0 ~ ~ ~-~ O
Q
t) O
~ ~n ~ æ ~: ~
N C\`~ a~ ~ ,1 0 ~ D
m o cc LO
E~ . ,1 o ~qo o u~ ~
i s~o c~ ~

X O
.,1 I p., ~: R. ~

H ~, S~ S~
~ Q. C~
s ~ Q, O ~L X X ~ ~ ~
O O :~ O O E~ ~ ~' -O ~ ~ O O O O

. CO ~ X ~ O~ ~ ~ ~ O U~
~1 0 0 ~ S~ O O --I O t~
~ O ^ S~ O '~ 1 'C) O
S~ O O ~ ~ I I I :~ O
O, U~ m ~ ~ V
^ ^
¢

3~5~
- 12 - O.Z. 0050/35051 EXAMP~E 3 100 parts of a mass polymer having a lower acid number than the polymer of Example 1, and pr~epared from 48.5 parts of styrene, 45 parts of isobutyl acrylate and 6.5 parts of acrylic acid, aredissolved in 100 parts of glycol ether, neutralized with ammonia and diluted with water, all as described ln Example 1. The glycol ether used is one of the mixtures in Table 2. The finishes obtained are free from clouding, and the films have, inter alia, increased resistance to long-term exposure to alkali, eg. 1 N sodium hydroxide solution, compared to the films of Example 1.
COMPARATIV~E EXAMPLE D
This is carried out like Example 3, but using ethylglycol instead of the glycol ethers proposed in the present invention. On adding water to the ~eutralized ethylglycol solution, the copolymer becomes insoluble and precipitates.

100 parts of a mass polymer prepared from 50 parts of methyl methacrylateg 47 parts of isobutyl acrylate and 3 parts of acrylic acid and having a K value, measured on a 3% strength solution in acetone, of 29, are dissolved hot in 75 parts of the isopropoxypropanol mixture 2.1 (cf.
Table 2) and the solution is neutralized as in Example 1.
On dilution with 225 parts of demineralized water, a finish which is virtually free from clouding and has a pH of 8.7 is obtainéd.
This finish can be diluted with water in all ~2~36~;~
- 13 - -Z. 0050/35051 proportions, without causing the copolymer to precipitate.
It exhibits very good wettlng of a great variety of sub-strates, such as glass, iron, aluminum, zinc and numerous plastics, as well as very good levelling and rapid drying.
_ COMPARATI~'E EXAMPLE E
This is carried out like Example 4, but replacing the 75 parts of isopropylpropanol mixture by 75 parts of ethylglcyol. On dilution with water, the neutralized solutions become extremely viscous and milky. They are not capable of being diluted with water in all proportions.

Claims

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A process for the preparation of a water-dilutable binder solution for coating compositions and impregnants, using a monoalkyl glycol ether as the solvent, wherein the monoalkyl glycol ether used contains not less than 2 per cent by weight of the reaction product of isopropanol and propylene oxide.

2. A process as claimed in claim 1, wherein the reaction product of isopropanol and propylene oxide is 1-isopropoxypropan-2-ol or a mixture of 1-isopropoxypropan-2-ol and 2-isopropoxypropan-1-ol.

3. A process as claimed in claim 1, wherein the reaction product of isopropanol and propylene oxide is 1-diisopropoxypropan-2-ol or a mixture of 1-diisopropoxy-propan-2-ol and 2-diisopropoxypropan-1-ol.

4. A process as claimed in claim 1 or 2, wherein the reaction product of isopropanol and propylene oxide contains up to 20 per cent by weight of 1-diisopropoxypropan-2-ol and/or 2-diisopropoxypropan-1-ol.

5. A process as claimed in claim 1, wherein additional partially or completely water miscible solvents are used.

6. A process as claimed in claim 1, wherein the binder used is a carboxyl-containing polymer or polycondensate which is neutralized with a base and crosslinked by oxydative drying or by combination with resins with which they react.

7. A process as claimed in claim 5, wherein the binder used is a carboxyl-containing polymer or polycondensate which is neutralized with a base and crosslinked by oxidative drying or by combination with resins with which they react.