An organic oligomer binder produced by depolymerizing virgin, scrap, recycled or reclaimed polyethylene terephthalate via an alcoholysis reaction with branched glycols and esterifiing the resulting polyol oligomer with polybasic carboxylic acids and/or anhydrides.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The invention relates to energy curable coating resins made of 
poly(ethylene)terephthalate resin useful as binder materials in coating 
compositions and to a process for producing these compositions. 
2. Background of the Invention 
Material recycling and resource recovery are common practices in all but a 
few industries. Responding with passion and prudence to the new awareness 
of the fragility of our ecosystem, society has set about the rectification 
of past material excesses by falling upon the more ubiquitous materials 
used in modern civilization for corrective recovery. There is none more 
ubiquitous than plastics and no more ubiquitous plastics than polyolefins 
and polyesters such as polyethylene terephthalate (PET). 
PET is a high molecular weight linear polymer known in the fiber, film and 
plastic industries for more than forty years. The polymer is prepared from 
dimethyl terephthalate and ethylene glycol via a transesterification 
reaction, which is typically carried out with a basic catalyst such as 
antimony trioxide. The resulting material is a high melting solid 
exhibiting superior clarity, excellent mechanical properties, good thermal 
stability and resistance to common solvents. It can be readily melt spun 
to fiber, cast as film, extruded, blow or injection molded into a wide 
variety of high value articles. Compared to polyolefins, PET is a 
relatively expensive resin as the monomers are derived from para xylene 
and ethylene. Nonetheless, the properties of PET are so superior that the 
resin successfully challenges polyolefins as the material of choice for 
the manufacture of clothing, carpeting, industrial products, soft drink 
bottles, cast and injection molded articles. 
PET's utility and success places discarded PET materials high on the list 
of those discarded plastics and fibers that must be collected and 
recycled. But it is rare that reclaimed or recycled PET is used to replace 
virgin resin in processing plastic materials. This is because the process 
seldom can be carried out without some degree of degradation of the 
reclaimed polymer. This limits the amount of reclaimed PET that can be 
used to mold resins or film and all but eliminates the use of reclaimed 
PET in fibers. Consequently, the plastic industry has been hard at work to 
find better ways to employ reclaimed PET to take advantage of its superior 
mechanical and chemical properties. 
Of course, resins of many varieties such as solvent-borne, ultra-violet 
(UV) and electron beam (EB) energy curable resins, are used in enormous 
quantities for a multitude of applications in the organic coatings 
industries, i.e. as protective, barrier and insulating coatings, 
adhesives, sealants, dye and ink coatings, etc. However, virgin PET has 
garnered little of the coating market for resins because of its cost. The 
resins commonly used are vinyl polymers, particularly acrylates, polyvinyl 
chloride and polyvinyl acetate, epoxies, polyolefins, polyurethanes, 
aliphatic polyesters, phenolics, and the like. They are used in coating 
formulations as pre-formed high molecular weight polymers such as acrylate 
latex or, more typically, as low molecular weight oligomers which are 
crosslinked to form a matrix subsequent to being applied on a substrate. 
Despite its otherwise superior mechanical and chemical properties, virgin 
PET cannot compete with the foregoing resins of choice in price or 
availability. In the organic coatings industry it is desirable to have 
readily available UV/EB crosslinkable PET oligomers. 
At least with respect to price, reclaimed PET can compete with some of the 
more commonly used resins in coatings. For instance, the current price of 
reclaimed PET is far below the price of acrylates, particularly 
polymethylmethacrylate, which are commonly incorporated as the resin of 
choice for UV/EB curable coatings where high performance dictates the 
choice of resin. But for the absence of a readily UV/EB crosslinkable 
reclaimed PET oligomer, organic coatings would appear to be a viable 
market use for reclaimed or recycled PET. 
S. Lee et al., Polyurethanes Synthesized from Polyester Polyols Derived 
from PET Waste, Journal of Applied Polymer Science, Vol. 55, pgs. 1271-73 
(1995), teaches the depolymerization of PET waste by glycolysis to obtain 
oligomeric diols. 
U. R. Vaidya et al., Unsaturated Polyesters from PET Waste, Journal of 
Applied Polymer Science, Vol. 34, pgs 235-46 (1987), teaches the 
glycolysis of PET waste with propylene glycol at different weight ratios. 
U.S. Pat. No. 5,552,478 teaches preparing oligomeric glycols from recycled 
PET by digesting a recyled PET feedstock with asymmetrical glycols then 
reacting the resulting mixture with acids having fewer than 12 carbon 
atoms. 
It is an object of the present invention to provide a low cost PET oligomer 
for use in coating formulations and as a binder in UV and EB curable 
coatings. 
Another objective of the invention is to produce the resin primarily from 
recycled or reclaimed PET. 
Other objects and advantages of the invention will become apparent from the 
following description of embodiments. 
SUMMARY OF THE INVENTION 
In one aspect the invention is a PET oligomer, having a number average 
molecular weight of about 850 to 5,000, a weight average molecular weight 
of about 4,000 to 25,000 and an acid value of about 5 to 50 mg KOH per 
gram comprised of about 40 to 70 weight percent recurring ethylene 
terephthalate units, recurring units of C.sub.3 + alpha alkylene 
terephthalate and hydroxy alkylene terephthalate, and pendant units of 
polybasic aliphatic alicyclic or aromatic polycarboxylate. 
In another aspect the invention is oligomeric PET polyol comprised of about 
40 to 70 weight percent recurring ethylene terephthalate units having the 
structure: 
##STR1## 
wherein R.sub.3 is alkyl; R.sub.1 and R.sub.2, alike or different, are 
hydrogen, aliphatic, alicyclic or aromatic carbonyl or carboxy carbonyl; x 
is an integer of 1 to 20, and y and z are integers of 1-10. 
In yet another aspect, the invention is a process for converting PET 
polymer into an organic binder oligomer having an acid value between 5 and 
50 mg KOH per gram comprising: 
a) contacting PET polymer particles with between 3 and 25 weight percent 
mixture of C.sub.3 + 1,2-alkylene glycol and polyhydric aliphatic alcohol 
in a 1:2 to 1:5 weight ratio, respectively, under alcoholysis conditions 
and in the presence of an alcoholysis catalyst for a time sufficient to 
convert said polymer to a oligomeric PET polyol 
b) contacting said polyol oligomer with between 5 and 40 weight percent of 
a polybasic aliphatic, alicyclic or aromatic organic acid or acid 
anhydride, under esterification conditions. 
DETAILED DESCRIPTION OF THE INVENTION 
The invention concerns a method of depolymerizing high molecular weight 
reclaimed, recycled or virgin PET into low molecular weight oligomers. The 
depolymerization is carried out by alcoholysis with certain glycols and 
polyhydric alcohols producing an oligomer having residual, derivatizable 
hydroxy functionality. This hydroxy functional oligomeric PET polyol is 
then esterified with polybasic carboxylic acids, anhydrides or acyl 
halides to produce a unique composition of a curable binder oligomer. The 
resin is deemed to be compatible with various coating formulations as a 
replacement for more expensive acrylate binders and other resinous 
materials in organic coatings. 
The derivatized PET compositions of the present invention achieve their 
unique compatibility with organic coating formulations by depolymerizing 
the reclaimed, recycled or virgin PET via an alcoholysis reaction using 
glycols and polyhydric alcohols that incorporate alkyl branching in the 
backbone of the oligomer. While not wishing to be bound by theory, it is 
believed that the branching disturbs the degree of crystalinity in the 
backbone and converts the oligomer to one that is more amenable to 
solvolysis by conventional components of organic coating systems. 
Preferably, the alcoholysis is carried out using a mixture of propylene 
glycol and glycerol. 
The degree of depolymerization of the reclaimed or virgin PET, which is a 
measure of the molecular weight of the resultant oligomer, can be 
controlled by a variety of process means or by adding depolymerization 
control agents. Also, the mole ratio of glycol used in depolymerization 
can serve as a means of securing the preferred range of molecular weights 
for the oligomer. 
The oligomer's hydroxyls (polyol) units are reacted with any appropriate 
reagent having a functionality greater than 1 and capable of converting 
the oligomer to one capable of forming an organic coating matrix by curing 
and crosslinking. This may be conveniently realized with agents such as 
polycarboxylic acids, esters, anhydrides or acyl halides to form a binder 
resin. The residual acid functionality can be used for subsequent 
reactions for example forming an Al.sup.++ salt by employing aluminum 
chelating agents. Of course, other agents may be used, including 
polyisocyanates. 
An important consideration in the preparation of the derivatized oligomer 
of the present invention is the requirement that the oligomeric polyol be 
derivatized in such a manner as to provide a sufficient, but not 
excessive, amount of branching. Insufficient or excessive branching 
negatively affects the utility of the any matrix formed. Carboxylic acids 
can be used to render the acid value of the oligomer between 5 and 50 mg 
KOH per gram and produce an oligomeric binder that is compatible with 
organic coating formulations. 
The PET oligomer of the present invention is useful for preparing 
oligomeric binder for organic coatings. The oligomer comprises between 40 
and 70 weight percent of ethylene terephthalate and includes recurring 
units of C.sub.3 + alpha alkylene terephthalate, hydroxy alkylene 
terephthalate and polybasic aliphatic, alicyclic or aromatic carboxylate 
moieties. The oligomer has a number average molecular weight between 850 
and 5000, a weight average molecular weight between 4,000 and 25,000 and 
an acid value between 5 and 50 mg KOH per gram. 
The oligomer may contain up to 20 weight percent of aliphatic or aromatic 
monocarboxylate moieties, such as benzoic acid. The oligomer may also 
contain between 4 and 8 weight percent of C.sub.3.sup.+ alpha alkylene 
terephthalate, between 7 and 11 weight percent of hydroxy alkylene 
terephthalate, and between 23 and 28 weight percent of polybasic 
aliphatic, alicyclic or aromatic carboxylate. 
The PET oligomer preferably has a number average molecular weight between 
1000 and 2000, a weight average molecular weight between 6,000 and 12,000 
and an acid value between 27 and 30 mg KOH per gram. 
PET polymer suitable for use in the process of this invention is preferably 
gathered from scrap, recycled or reclaimed PET sources. These sources 
provide PET at a cost sufficiently low to compete with ordinary coating 
resin sources. However, other than cost, there is nothing intrinsically 
limiting the process of the present invention to scrap, recycled or 
reclaimed PET and competitively priced virgin PET could also be used as 
feedstock in the process. Reclaimed or recycled PET is available in 
abundance from waste film, fiber, injection molded and blow molded 
articles and may be used in the process in the form of chips, flake or 
powder. The process readily converts virgin, scrap, recycled or reclaimed 
PET into value added energy curable organic coating resins. Due to the 
excellent film properties obtained from using PET, e.g. higher degree of 
strength, stiffness, toughness and gloss, the resin offers an economic and 
performance alternative to multi-functional acrylated oligomers used in 
energy curable organic coating formulations. 
The process of the present invention may be carried out batch or continuous 
mode wherein solid, reclaimed, high molecular weight PET particles, 
preferably in the form of chips or flake, are mixed with at least one 
branched C.sub.3 + glycol, preferably propylene glycol, and optionally, at 
least one polyhydric alcohol containing at least one secondary hydroxyl 
group and two primary hydroxyl groups. Glycerol is the preferred 
polyhydric alcohol. The mixture is then placed in contact with a 
transesterification or alcoholysis catalyst to produce a reclaimed 
oligomeric polyol PET having branching secondary hydroxyl groups. 
The oligomerization reaction is carried out at a temperature between 150 
and 250.degree. C., preferably between 190 and 225.degree. C. and most 
preferably between 215 and 220.degree. C. for about 2 to 12 hours, 
preferably 3 hours, or even more preferably until the solid PET, glycol, 
glycerol mixture converts to a clear or homogeneous mixture or 
melt-solution that contains no visible PET particles. The resulting 
oligomeric PET polyol should have a hydroxyl number between 48 and 412. 
The depolymerization reaction can be carried out at atmospheric, 
subatmospheric or supra-atmospheric pressures, but preferably is carried 
out at atmospheric pressure. The alcoholysis step is preferably carried 
out without removing the ethylene glycol or branched glycol from the 
reaction mixture in an effort to promote depolymerization of PET to an 
oligomer. 
The second step of the process involves converting, via an esterification 
reaction, the oligomer PET polyol produced by depolymerization. The 
oligomeric PET polyol's secondary hydroxyl groups are reacted with a di- 
or polybasic aliphatic, alicyclic or aromatic carboxylic acid or 
derivative thereof. The esterification reaction may be carried out under 
conventional esterification methods and conditions. A preferred acid 
derivative is a di-carboxy aromatic carboxylic acid anhydride, while more 
preferred is phthalic acid anhydride (PAA). Methylhexahydrophthalic acid 
anhydride (MHHPA) may also be used as a preferred acid derivative. The 
esterification reaction produces a predominantly linear saturated 
polyester oligomer having an acid value between 5 and 50 mg KOH per gram 
and more preferably between 20 and 30 mg KOH per gram. 
Catalysts which are useful in the depolymerization reaction include any 
catalysts employed in the conventional synthesis of PET and includes, for 
example, antimony trioxide, tetraalkyl titanates, alkyl metal hydroxides 
and methoxides and alkaline earth metal oxide and hydroxides. 
An important consideration in the process of the present invention is the 
selection of glycol employed in the depolymerization. It has been 
suprisingly discovered that depolymerized PET is most compatible with 
known organic coating formulations when the PET is depolymerized using 
alkyl branched or substituted 1,2-glycols. As previously mentioned, it is 
believed that branched glycols, when incorporated into the PET polymer 
backbone, disturb the crystalinity of the resulting polyol oligomer and 
enhance solubility. While propylene glycol, for example 1,2-dihydroxy 
propane, is preferred, other alkyl and aromatic branched compounds can be 
used such as alicyclic or aromatic compounds bearing a substituent 
1,2-glycol group such as styrene glycol. 
The branched glycol, when used as the sole depolymerizing agent, is 
employed in a weight ratio of 3:25 glycol to PET, but preferably between 
4:8. When a polyhydric alcohol is included, the weight ratio of glycol to 
polyhydric alcohol is between 1:2 to 1:5. 
The binder resin of the invention is a PET oligomer comprising between 40 
and 70 weight percent recurring ethylene terephthalate units and that in 
turn have recurring units of C.sub.3 + alpha alkylene terephthalate, 
hydroxy alkylene terephthalate and polybasic aliphatic, alicyclic or 
aromatic carboxylate. The resin has a number average molecular weight 
between 850 and 5000, a weight average molecular weight between 4,000 and 
25,000 and an acid value between 5 and 50 mg KOH per gram. Optionally, the 
resin may contain up to 20 weight percent of monocarboxylate, and 
preferably between 3 and 10 weight percent benzoate. 
Preferably, the C.sub.3.sup.+ alpha alkylene terephthalate selected is 
propylene terephthate and the hydroxy alkylene terephthalate selected is 
2-hydroxypropylene terephthalate. 
The polybasic aliphatic, alicyclic or aromatic carboxylate contained in the 
binder resin is preferably a dicarboxylic acid carboxylate which may be 
contained as a dicarboxylate in the oligomer backbone, as a pendant group, 
or as an end carboxy carboxylate group wherein a single carboxy group is 
esterified with residual hydroxy group to form a moiety having an ester 
link to the oligomer and a free carboxylic acid group. Preferably, the 
polybasic alicyclic carboxylate is selected from 
methylcyclohexane-1-carboxy-2-carboxylate or 
methylcyclohexane-1,2-dicarboxylate. The most preferred carboxylate is 
that derived by reaction of residual hydroxyl groups in the oligomer with 
phthalic anhydride to produce benzene 1-carboxy-2-carboxylate. 
The preferred oligomeric binder contains between 4 and 8 weight percent of 
C.sub.3 + alpha alkylene terephthalate, between 7 and 11 weight percent of 
hydroxy alkylene terephthalate, between 23 and 28 weight percent of 
polybasic aliphatic, alicyclic or aromatic carboxylate moieties. The resin 
has a preferred number average molecular weight between 1000 and 2000, a 
weight average molecular weight between 6,000 and 12,000 and an acid value 
between 27 and 30 mg KOH per gram. 
The PET oligomer of the invention has between 40 and 70 weight percent 
recurring ethylene terephthalate units and depicted structurally as 
follows: 
##STR2## 
wherein R.sub.3 is alkyl; R.sub.1 and R.sub.2, alike or different, are 
hydrogen, aliphatic, alicyclic or aromatic carbonyl or carboxy carbonyl; x 
is an integer of 1 to 20, and y and z are integers of 1-10. 
The following examples illustrate specific aspects of the present invention 
and are not intended to limit the scoipe thereof in any respect and should 
not be so construed. All parts are in units of parts per 100 parts of 
product.

EXAMPLE 1 
Preparation of a Oligomeric Binder 
Scrap PET (35.9 parts, available from Tennessee Eastman Corporation), 
1,2-propanediol (4.0 parts, available from Ashland Corporation), glycerol 
(6.6 parts, available from Ashland Corporation) and Tyzor TBT catalyst 
(0.3 parts, available from DuPont Company, Tyzor.RTM. TBT is a trademark 
of DuPont Company) were charged to a dry reactor. The mixture was agitated 
and heated to between 215 and 220.degree. C. under nitrogen and held at 
this temperature for about 6 hours wherein the PET dissolved. Methyl 
hexahydrophthalic anhydride (17.7 parts, available from Lonza, 
Incorporated) was added to the mixture over a 1 hour period while the 
temperature was increased to 230.degree. C. and water was removed. Benzoic 
acid (6.0 parts) was added and the temperature was again raised and 
maintained at 240.degree. C. until the acid number of the binder resin was 
no longer decreasing linearly with time. 
EXAMPLE 2 
Preparation of UV Curable Coating 
The product of Example 1 was cooled to 210.degree. C. and sparged with air. 
Next, 4-methoxy phenol (0.1 parts, MEHQ available from Eastman Chemicals 
Corporation) and benzophenone (6.8 parts) were added. The mixture was 
cooled to 120.degree. C. or less and tripropylene glycol diacrylate (23.0 
parts TPGDA, available from RadCure Corporation) was added. The mixture 
was then cooled to 95.degree. C. and its viscosity was adjusted as 
necessary by addiing additional TPGDA until a Haake viscosity (Eta 4th 
point) of 7-10 PaS was acheived. The resulting coating was filtered, 
collected and cured. The coating exhibited superior rub and solvent 
resistance compared to an epoxy acrylic derived coating. 
EXAMPLE 3 
Preparation of a Oligomeric Binder 
Reclaimed or scrap PET (52.5 parts), 1,2-propanediol (4.0 parts), glycerol 
(9.6 parts) and Tyzor TBT catalyst (0.4 parts, available from DuPont 
Company, Tyzor.RTM. TBT is a trademark of DuPont Company) were charged to 
a dry reactor. The mixture was agitated and heated to between 215 and 
220.degree. C. under nitrogen and held at that temperature for about 4 
hours whereby all the PET dissolved. Benzoic acid (8.8 parts) and phthalic 
anhydride (22.8 parts) were added over a 1 hour period and the temperature 
was increased to 230.degree. C. The temperature was further increased to 
240.degree. C. and maintained until the acid number no longer was 
decreasing linearly with time. The binder resin had a softening point of 
93.degree. C. and an acid value of 26.8 mg KOH per gram. 
EXAMPLE 4 
Preparation of UV Curable Coating Vehicle 
The product of Example 3 (63.7 parts) was cooled to 205.degree. C. and 
sparged with air. Benzoflex 400 (6.4 parts, Velsicol) and MEHQ (0.1 parts) 
were added and the mixture was cooled to 100.degree. C. Tripropylene 
glycol diacrylate (parts 29.8) was added and the viscosity was adjusted 
with tripropylene glycol diacrylate (TPGDA, available from RadCure 
Corporation) to achieve a Haake viscosity (4th point) of 8 to 11 PaS. The 
coating was filtered and collected. The performance of the coating was 
superior to the epoxy-acrylic derived standard. 
The present invention has been described in detail, including the preferred 
embodiments thereof. However, it will be appreciated that those skilled in 
the art, upon consideration of the present disclosure, may make 
modifications and/or improvements on this invention that fall within the 
scope and spirit of the invention as set forth in the following claims.