Use of 1,3-dioxacyclopentane as a solvent for polyester resins

Polyester resins, comprising the polymerized residues of dibasic acids and diols, dibasic anhydrides and diols, and the lower alkyl esters of dibasic acids and diols, are soluble up to 40% by weight of solids in 1,3-dioxacyclopentane, and blends of 1,3-dioxacyclopentane with other relatively nontoxic solvents.

FIELD OF THE INVENTION 
This invention relates to solutions of crystalline polyesters for use in 
heat-sealable coating and adhesive applications. The polyesters were 
formerly known to be soluble only in highly toxic solvents, such as 
dioxane and chlorinated solvents, and are now known to be soluble in 
1,3-dioxacyclopentane and in solvent blends containing 
1,3-dioxacyclopentane and other relatively nontoxic cosolvents. 
BACKGROUND OF THE INVENTION 
Polyester resins, both branched and linear, are used in various 
heat-sealable adhesive and protective coating applications. Some of these 
applications require that the resins be dissolved or diluted with a 
solvent. The low molecular weight polyesters are readily soluble in common 
organic solvents. The high molecular weight and partially crystalline 
polyesters are not easily soluble. It has been disclosed in U.S. Pat. Nos. 
4,419,476, 4,298,724, 4,581,093, 4,486,508, and 4,487,909 that if high 
molecular weight polyesters are branched they can be made soluble in 
inexpensive, relatively nontoxic organic solvents. It is the linear 
polyesters, however, that impart improved chemical and heat resistance to 
the adhesives and coatings in which they are used, and these linear, 
crystalline polyesters are not soluble in the same relatively nontoxic 
solvents. 
Currently, the high molecular weight, linear polyesters are most commonly 
dissolved in dioxane and chlorinated solvents. Dioxane emits formaldehyde, 
a suspect carcinogen, and halogenated compounds are also considered 
suspect carcinogens, which makes their use as solvents environmentally 
questionable and potentially dangerous to health. Attempts to find 
innocuous substitutes have been hindered by marginal solubility of the 
linear polyester resins in the less toxic solvents, or by solvent 
evaporation rates that are either too fast or too slow to be functional in 
coating applications. Thus, there exists a need for solutions of high 
molecular weight, linear, partially crystalline polyesters in a solvent 
formulation that is low in toxicity, and consequently without the 
disadvantageous environmental and health related effects of the organic 
solvents commonly used for those polyester resins. 
SUMMARY OF THE INVENTION 
1,3-Dioxacyclopentane, also known as ethylene glycol methylene ether, 
formal glycol, or 1,3-dioxolane, has been found to be a suitable solvent 
for high molecular weight, crystalline, long chain, linear polyesters. 
This invention comprises a solution of a polyester resin for coating or 
adhesive application in 1,3-dioxacyclopentane as the sole organic solvent, 
or in a blend of cosolvents in which 1,3-dioxacyclopentane is present in 
an amount at least 25% of the solvent blend. 
The solution comprises, in a total of 100 parts by weight, (A) up to 40 
parts by weight of a polyester prepared from dibasic acids and diols, 
dibasic anhydrides and diols, the lower alkyl esters of dibasic acids and 
diols, and combinations of those, and (B) at least 60 parts by weight of 
solvent comprising (i) 1,3-dioxacyclopentane, present in an amount at 
least 25% by weight of the solvent, and (ii) optionally, a 
non-halogenated, cosolvent selected from the group consisting of C.sub.7 
-C.sub.10 aromatics, C.sub.3 -C.sub.8 ketones, ethers, and the lower alkyl 
esters of C.sub.2 -C.sub.4 carboxylic acids, and combinations of those, 
present in an amount from 0 to 75% by weight of the solvent.

DETAILED DESCRIPTION OF THE INVENTION 
The polyester solutions of this invention are made by dissolving a 
polyester resin, suitable for use in a coating or adhesive application, in 
1,3-dioxacyclopentane. This solvent, commercially available from Ferro 
Corporation, Grant Chemical Division, Baton Rouge, Louisiana, is 
relatively nontoxic and dissolves those high molecular weight, linear, 
crystalline polyesters that are virtually insoluble in other common, 
relatively nontoxic solvents. Although other common solvents cannot 
dissolve crystalline polyesters when they are used as the sole organic 
solvent, some, but not all, can be used with 1,3-dioxacyclopentane in a 
cosolvent blend that will dissolve the crystalline polyesters. The ability 
of the 1,3-dioxacyclopentane, and the ability of certain other solvents to 
act as cosolvents, was not discernible from the examination of standard 
solubility parameters. The data below show, for example, that 
tetrahydrofuran exhibited better solubility characteristics than methyl 
ethyl ketone, despite a contrary prediction with the use of solubility 
parameters. (Solubility parameters can be obtained in the Polymer 
Handbook, published by Wiley Interscience.) 
Suitable cosolvents with the 1,3-dioxacyclopentane are non-halogenated 
solvents and include C.sub.7 -C.sub.10 aromatics having a methyl group or 
groups attached to the ring in the ortho, meta, or para positions, and 
benzine naphthalenes (also known as VM&P, varnish makers' and painters' 
naphthalenes, which are not generally characterized and which are obtained 
from petroleum distillation process); C.sub.3 -C.sub.8 ketones; cyclic 
ethers, and ethers having the general formula R--O--R', in which R can be 
methyl, ethyl, propyl or butyl, and R' can be methyl, ethyl, propyl, 
butyl, ethylene glycol, and diethylene glycol; and the lower alkyl esters 
of C.sub.2 -C.sub.4 carboxylic acids, and combinations of those. 
Representative aromatics include toluene, aromatic naphthalene, xylene, and 
benzyl alcohol. Representative ketones include acetone, methyl ethyl 
ketone, methyl isobutyl ketone, isophorone, N-methyl pyrrolidone, 
cyclopentanone and cyclohexanone. Representative ethers are 
tetrahydrofuran, and ethylene glycol monoethyl ether, ethylene glycol 
monobutyl ether, diethylene glycol monomethyl ether, diethylene glycol 
monoethyl ether, diethylene glycol monobutyl ether, and their acetates. 
Representative esters of C.sub.2 -C.sub.4 carboxylic acids include methyl, 
ethyl, propyl, butyl, and amyl acetates, propionates, lactates and 
butyrates, and their isomers. These cosolvents can be used in combination 
with each other, provided that the 1,3-dioxacyclpentane is also a 
cosolvent. 
In general, the polyester solutions of this invention will consist by 
weight essentially of 15-40 parts, preferably 20-25 parts, of an 
appropriate polyester resin, preferably dissolved in at least 60 parts of 
1,3-dioxacyclopentane as the sole organic solvent, or dissolved in at 
least 60 parts of a solvent blend comprising 1,3-dioxacyclopentane present 
in an amount at least 25% by weight of the solvent blend, and of a 
suitable cosolvent. The more preferred cosolvents will be selected from 
the group consisting of tetrahydrofuran, methyl ethyl ketone, toluene, and 
ethyl acetate, and they will be present in an amount up to 75% by weight 
of the solvent blend, to make a total of 100 parts of polyester solution. 
These solvents have relatively low levels of toxicity, and have 
evaporation rates that are functional for coating and adhesive 
applications. 
Any polyester resin for a coating or adhesive application that has utility 
in solution and that is soluble in 1,3-dioxacyclopentane, may be used to 
formulate the polyester solutions of this invention. The precise 
formulation of the various types of polyesters will depend upon the 
specific end use. 
Representative polyester resins suitable for use as heat sealable coatings 
include those made from dibasic acids and diols (higher polyols act as 
branching agents). Suitable dibasic acids include, but are not limited to, 
succinic acid, adipic acid, glutaric acid, azelaic acid, sebacic acid, 
phthalic acid, isophthalic and terephthalic acids. Suitable diols have 
2-14 carbons in the chain and include, but are not limited to, ethylene 
glycol, 1,4-butanediol, 1,2-propanediol, 1,3-propanediol, 
1,4-cyclohexanedimethanol, and polyethylene glycol. The polyesters may 
also be derived from the anhydrides of the dibasic acids, or from a 
transesterification from the lower alkyl ester of the acid. 
Alternatively, linear polyester resins suitable for coating and adhesive 
applications can be obtained commercially, for example, from Morton 
Chemical, Elk Grove, Ill. under the tradenames Morester.RTM. 49000 and 
Morester.RTM. 49002; and from Goodyear, Akron, Ohio, under the tradenames 
Resin Vitels.RTM. 1700 and Resin Vitels.RTM. 1900. 
When these polyesters are used in coating compositions, additives 
conventionally used with these polyesters in coating compositions may be 
employed in the conventional amounts. Examples of additives in 
representative amounts used are crosslinking agents, long chain fatty acid 
amides, petrolatum, polyethylene wax, and paraffin, used alone or in 
combination, in amounts from 0.05-10 parts of the total weight of solids. 
When heat sealing is done in-line with the coating process, crosslinking 
agents usually are added to impart additional heat resistance and chemical 
resistance. Examples of conventional crosslinking agents in representative 
amounts used are isocyanate crosslinkers, such as toluene diisocyanate, 
4,4'-methylene-bis(diphenyl diisocyanate), the 5/2 molar adduct of toluene 
diisocyanate and trimethylolpropane, the 2/lmolaradduct of toluene 
diisocyanate and diethylene glycol, and 1,6-hexamethylene diisocyanate, in 
amounts up to about 15 parts of the total weight of solids; and polymeric 
diisocyanates based on isophoronediisocyanate, and optional 
trimethoxysilane coupling agents containing amino, epoxy, ether, or 
mercapto groups, in amounts not to exceed 3 parts of the total weight of 
solids. 
The resultant coating compositions, when appropriately formulated and 
coated, may be used, for example, as heat-seal lidding for food products, 
such as butter, yoghurt, and jelly; as packaging for foods to be 
microwaved or oven heated; and as industrial laminates, such as, in sail 
cloth, cable wrap, flexible circuitry, and solar protection film. 
When these compositions are used in adhesive applications, the 
abovementioned crosslinking agents may be used to impart additional bond 
strength, and chemical and heat resistance. 
EXAMPLES 
The following examples show the solubility at varying solids contents by 
weight of four commercially available and substantially linear polyester 
resin compositions in 1,3-dioxacyclopentane and in 1,3-dioxacyclopentane 
with cosolvents, and the insolubility of the same resins in other 
available and commonly used nontoxic organic solvents. 
The resins tested were Morester.RTM. 49000 and Morester.RTM. 49002 from 
Morton Chemical, and Vitel.RTM. 1900 from Goodyear. All four of the resins 
are substantially linear and have some degree of crystallinity, the 49002 
and the 1900 being more crystalline than 49000 and 1700, respectively. 
The resins and solvents were placed in sealed jars on a roller mill and 
mixed for 24 hours at room temperature. The resins were considered soluble 
if at the end of 24 hours the contents of the jar were clear, and they 
were considered insoluble if the contents showed gelling or phasing. 
The results are set out in the following tables. 
TABLE 1 
______________________________________ 
SOLUBILITY OF LINEAR POLYESTERS AT 15% SOLIDS 
RESINS 
SOLVENTS 49000 49002 1700 1900 
______________________________________ 
(DOCP) 1,3-dioxacyclopentane 
+ + + + 
(THF) tetrahydrofuran 
+ - + - 
(IOPH) isopropanol 
- - - - 
(HEP) heptane - - - - 
(MEK) methyl ethyl ketone 
- - - - 
(TOL) toluene - - - - 
(ETAC) ethyl acetate 
- - - - 
(ACE) acetone - - 
(CYHX) cyclohexanone - - 
______________________________________ 
+ indicates soluble 
- indicates insoluble 
An examination of the solubility parameters from the Polymer Handbook, 
Wiley Interscience, would lead to the prediction that methyl ethyl ketone, 
acetone, and cyclohexanone would have dissolved the polyesters as readily 
as 1,3-dioxcyclopentane, but in fact, Table 1 shows that resins 49002 and 
1900, having the greater degree of crystallinity compared to the other two 
resins, 49000 and 1700, respectively, were obstinatelly insoluble in 
common organic solvents and were soluble at 15% solids only in 
1,3-dioxacyclopentane. 
TABLE 2 
______________________________________ 
SOLUBILITY OF LINEAR POLYESTERS 
AT 15% SOLIDS IN SOLVENT BLENDS 
RESINS 
SOLVENT BLENDS (%) 
49000 49002 1700 1900 
______________________________________ 
75 DOCP: 25 THF 
+ + + + 
75 DOCP: 25 MEK 
+ + + - 
75 DOCP: 25 TOL 
+ + + + 
75 DOCP: 25 ETAC 
+ - + - 
75 DOCP: 25 IPOH 
+ - + - 
75 DOCP: 25 HEP 
- - - - 
75 DOCP: 25 ACE + - 
75 DOCP: 25 CYHX + + 
50 DOCP: 50 THF 
+ + + - 
50 DOCP: 50 MEK 
+ - + - 
50 DOCP: 50 TOL 
+ - + - 
50 DOCP: 50 ETAC 
+ - + - 
25 DOCP: 75 THF 
+ + + - 
25 DOCP: 75 MEK 
+ - + - 
25 DOCP: 75 TOL 
+ - + - 
25 DOCP: 75 ETAC 
+ - + - 
25 DOCP: 75 IPOH 
- - - - 
______________________________________ 
+ indicates soluble 
- indicates insoluble 
Table 2 show that solvent blends consisting of 75% 1,3-dioxacyclopentane 
with tetrahydrofuran, methyl ethyl ketone, cyclohexanone, acetone and 
toluene, can be used to dissolve the 49002 resin at 15% solids, and 
solvent blends consisting of 75% 1,3-dioxacyclopentane with 
tetrahydrofuran, cyclohexanone, and toluene can be used to dissolve the 
1900 resin, at 15% solids. The solubility parameters of these cosolvents 
would have predicted that acetone and methyl ethyl ketone would have been 
more suitable cosolvents for the 1900 resin than tetrahydrofuran, but in 
fact, they were not. 
TABLE 3 
______________________________________ 
SOLUBILITY OF LINEAR POLYESTER RESINS 
AT 15-50% SOLIDS 
RESINS 
SOLVENT SOLIDS 49000 49002 1700 1900 
______________________________________ 
THF 15 + - + - 
20 + - + - 
25 + - + - 
30 + - + - 
35 + - + - 
40 + - + - 
45 + - - - 
50 - - - - 
DOCP 15 + + + + 
20 + + + - 
25 + - + - 
30 + - + - 
35 + - + - 
40 + - + - 
45 - - - - 
50 - - - - 
______________________________________ 
Table 3 shows that the 49000 and 1700 resins can be dissolved in 
1,3-dioxacyclopentane and in tetrahydrofuran up to 40% solids, and that 
the resins with greater crystallinity, 49002 and 1900, can be dissolved at 
20% and 15% solids respectively, only in 1,3-dioxacyclopentane, and not in 
tetrahydrofuran. 
The data show that 1,3-dioxacyclopentane can be used as a solvent for 
linear, crystalline polyesters that are not soluble in other common, 
relatively nontoxic solvents.