Polyester adhesives

Disclosed is an adhesive composition comprising: PA1 (a) an amorphous or a crystallizable polyester having a melting point of about 80.degree. C. to about 230.degree. C. and a heat of fusion of 0 to about 18 calories per gram, and PA1 (b) from about 1 to about 35% by weight of a compound selected from the group consisting of ##STR1## wherein R.sub.1 is benzyl or phenyl and R.sub.2 is benzyl, phenyl or an alkyl group containing 1 to 10 carbon atoms, and ##STR2## wherein R.sub.3 is phenyl or benzyl, R.sub.4 is phenyl or benzyl and R.sub.5 is an alkyl group containing 1 to 10 carbon atoms.

DESCRIPTION 
Technical Field 
This invention relates to plasticized polyesters containing selected 
phthalate or phosphate plasticizers. The plasticized polyesters have 
substantially reduced melt viscosities, melting points, and glass 
transition temperatures as well as improved processing characteristics. 
These plasticized compositions are useful as adhesives in the form of 
powders, fibers, rods, and flexible films as well as for use in extruded 
flexible shapes such as tubing. 
Background 
A number of polyester polymers are known to be useful as hot-melt adhesives 
for structurally bonding metals, woods, plastics, and other materials. 
When these polyester polymers have molecular weights high enough to 
provide satisfactory cohesive and adhesive bond strength, their melt 
viscosities are so high that they cannot be applied by conventional 
application equipment, such as gear pumps or piston pumps, used widely in 
the packaging industry with conventional, low-viscosity, polyolefin-based 
adhesives. Reducing the molecular weight of the polyesters to lower levels 
severely reduces bond strength of the adhesives. 
In the manufacture of packaging adhesives based on ethylene-vinyl acetate 
copolymer, paraffin wax or other wax additives are used to reduce the melt 
viscosity of the adhesive blend. However, none of these usual 
viscosity-reducing waxes can be used with polyester polymers to provide 
the desired melt viscosity because they are highly incompatible with 
polyesters and separate out of the mixture as low-viscosity liquids in 
two-phase systems. 
U.S. Pat. No. 4,172,824 discloses blends of certain poly(ethylene 
terephthalate) copolymers containing adipic acid and 1,4-butanediol with 
selected benzoate ester plasticizers. 
These blends have melt viscosities low enough that they can be applied with 
conventional application equipment for hot-melt adhesives. However, the 
polyester portion of these blends has a tendency to decrease in inherent 
viscosity (I.V.) when the blends are heated. For example, these blends are 
typically found to decrease in inherent viscosity about 0.3-0.4 dl/g after 
being heated to typical application temperatures for eight hours. 
U.S. Pat. No. 4,094,721 relates to polyesters of terephthalic acid, 
1,4-butanediol and 1,6-hexanediol useful as adhesives. 
Benzoic acid esters are known for use in polymers. U.S. Pat. No. 3,186,961 
discloses the use of various aryl carboxylic acid esters, for example, 
diethylene glycol dibenzoate, triethylene glycol dibenzoate, etc., in 
aromatic polyesters of carbonic acid. U.S. Pat. No. 2,044,612 discloses 
the use of certain benzoates as plasticizers for plastics, including 
condensation products of polyhydric alcohols and polybasic acids. Canadian 
Pat. No. 919,190 and British Pat. No. 815,991 also disclose the use of 
benzoic acid esters as plasticizers for vinyl resins. 
U.S. Pat. No. 4,340,526 discloses certain terephthalate/isophthalate 
copolymers containing 1,4-butanediol and 1,6-hexanediol which are modified 
with diethyl phthalate or selected benzoate ester plasticizers. 
Ester plasticizers are effective in modifying the properties of poly(vinyl 
chloride) and cellulose esters so that they may be used in the form of 
molded objects, tubing, film, sheeting, and the like. These ester 
plasticizers are generally quite incompatible with polyesters. For 
example, a commonly used plasticizer like dioctyl phthalate is quite 
incompatible with polyesters. Thus, it has not been possible in the past 
to plasticize a wide range of polyesters in order to decrease melt 
viscosities, glass transition temperatures, and other fundamental 
properties so that they may be used in certain critical adhesive, film, or 
fiber forms. 
Description of the Invention 
It has now been found that a very limited number of ester plasticizers are 
solvents for certain polyesters and that incorporation of these 
plasticizers in these polyesters can significantly reduce the melting 
point and glass transition temperatures of the polymers as well as to 
decrease the melt viscosity values of the blends. 
According to the present invention, there is provided an adhesive 
composition comprising: 
(a) an amorphous or a crystallizable polyester having a melting point of 
about 80.degree. C. to about 230.degree. C. and a heat of fusion of 0 to 
about 18 calories per gram, and 
(b) from about 1 to about 35% by weight of a compound selected from the 
group consisting of 
##STR3## 
wherein R.sub.1 is benzyl or phenyl and R.sub.2 is benzyl, phenyl or an 
alkyl group containing 1 to 10 carbon atoms, and 
##STR4## 
wherein R.sub.3 is phenyl or benzyl, R.sub.4 is phenyl or benzyl and 
R.sub.5 is an alkyl group containing 1 to 10 carbon atoms. 
Operable polyesters include both amorphous and crystallizable polyesters. 
Preferred polyesters include amorphous polyesters or relatively low 
melting polyesters with melting points up to about 230.degree. C. which 
have heats of fusion of less than about 18 calories per gram (cal./g.) of 
polymer. Very high melting polymers such as poly(ethylene terephthalate) 
and poly(1,4-cyclohexylenedimethylene terephthalate) are not generally 
operable in the practice of this invention because of the rather high 
temperatures (250.degree. C. and above) required for processing these 
blends. 
Some useful polyesters include poly(ethylene terephthalate) copolyesters 
modified with cyclohexanedimethanol or diethylene glycol, 
poly(tetramethylene terephthalate) copolymers modified with glutaric acid 
and diethylene glycol, poly(hexamethylene terephthalate) copolymers 
modified with glutaric acid and diethylene glycol, 
poly(1,4-cyclohexylenedimethylene 1,4-cyclohexanedicarboxylate) modified 
with trimellitic acid, and poly(tetramethylene glycol) and the like. 
The presence of the plasticizer provides significantly improved processing 
characteristics for the polyesters. For example, fibers and films may be 
extruded at temperatures lower than that required for the unmodified 
polyesters. The plasticized fibers may be used as a binder for nonwoven 
polyester fabrics and the bonding is conducted at relatively low 
temperatures. Plasticized films are readily used for laminating fabrics or 
attaching labels and emblems at low bonding temperatures. Generally, the 
plasticized films have better flexibility than the unmodified films and 
thus provide better hand for the bonded fabrics. Since the plasticizers 
are highly compatible with the polyesters, no exudation is noted on the 
surface of the films. 
Plasticized polyesters are readily reduced to powder by cryogenic grinding 
techniques using pinmill or hammermill grinders. These powders may be used 
on fusible interlining fabrics or used to bind nonwoven fabrics and 
bonding is achieved at relatively low temperatures. In the binding of 
nonwoven fabrics, the plasticized powders may be applied to the novwoven 
material from a water dispersion or by spraying the dry powders onto the 
fibers with an electrostatic spray gun. 
The plasticized polyesters are readily extruded into tubing and the tubing 
is much more flexible than the unmodified polyester. These flexible 
tubings are quite easy to wind onto a core. 
The concentration of the plasticizer can vary from about 1 to about 35% by 
weight. A preferred concentration range is from about 5 to about 25% by 
weight. 
The plasticizer may be incorporated into the polyester by heating the 
plasticizer and polymer at temperatures of about 75.degree. to about 
250.degree. C. using mixing rolls, Banbury mills, extruders and the like 
or the components may be dissolved in a mutual solvent followed by 
evaporation of the solvent. 
The polyester component of the invention is prepared by conventional 
techniques, for example, by ester interchange of one or more of the 
selected glycols with one or more of the selected dicarboxylic acids (see, 
for example, British Pat. No. 1,047,072). 
Many of the plasticizers described herein are commercially available.

The following examples are submitted for a better understanding of the 
invention. 
EXAMPLE 1 (Control) 
Polyester A powder (1.5 g.; Polyester A is a copolyester containing 
terephthalic acid, 69 mol % ethylene glycol, and 31 mole % 
1,4-cyclohexanedimethanol; I.V.=0.78, Tg=74.degree. C., amorphous; 
.DELTA.H.sub.f O cal./g.) is placed in a pyrex test tube with 30 mL of 
dioctyl phthalate plasticizer and the mixture is heated to 200.degree. C. 
with stirring. The polyester melts and forms a liquid layer in the bottom 
of the test tube but it does not dissolve or mix with the dioctyl 
phthalate. When cooled to 23.degree. C., the polymer solidifies and the 
plasticizer remains above the solid as a clear layer. This example 
demonstrates that Polyester A is completely insoluble in dioctyl phthalate 
in the 23.degree. to 200.degree. C. temperature range. 
Similar results are obtained when dinonyl phthalate, diisononyl phthalate, 
diisodecyl phthalate, Santicizer 610 (phthalate esters based on alcohols 
containing 6 to 10 carbon atoms) or Santicizer 711 (phthalate esters based 
on alcohols containing 7 to 11 carbon atoms) are used instead of dioctyl 
phthalate. 
EXAMPLE 2 (Control) 
Solubility tests are conducted in dioctyl phthalate according to the 
procedure of Example 1 using the following polyesters: 
Polyester B (a copolyester containing terephthalic acid, 70 mol % ethylene 
glycol, and 30 mol % 1,4-cyclohexanedimethanol; I.V.=0.62; Tg=75.degree. 
C., amorphous; .DELTA.H.sub.f =O cal./g.). 
Polyester C (a copolyester containing terephthalic acid, 68 mol % ethylene 
glycol, and 32 mol % 1,4-cyclohexanedimethanol; I.V.=0.45; Tg=74.degree. 
C., amorphous; .DELTA.H.sub.f =O Cal./g.). 
Polyester D (a copolyester containing terephthalic acid, 60 mol % 
1,4-cyclohexanedimethanol, and 40 mol % ethylene glycol; I.V.=0.72; 
Tm=220.degree. C.; .DELTA.H.sub.f =0.9 cal./g., Tg=81.degree. C.). 
Polyester E (a copolyester containing terephthalic acid, 63 mol % ethylene 
glycol, and 37 mol % diethylene glycol; I.V.=0.66; Tm=184.degree. C.; 
.DELTA.H.sub.f =1.6 cal./g.; Tg=54.degree. C.). 
Polyester F (a copolyester containing 72 mol % terephthalic acid, 28 mol % 
glutaric acid, 55 mol % 1,4-butanediol and 45 mol % diethylene glycol; 
.DELTA.H.sub.f =3.5 cal./g.; I.V.=0.83; Tm=110.degree. C., Tg=6.degree. 
C.). 
Polyester G (a copolyester containing 81 mol % terephthalic acid, 19 mol % 
glutaric acid, 55 mol % 1,4-butanediol and 45 mol % diethylene glycol; 
.DELTA.H.sub.f =3.6 cal./g.; I.V.=0.81; Tm=126.degree. C.; Tg=10.degree. 
C.). 
Polyester H (a copolyester containing 79 mol % terephthalic acid, 21 mol % 
glutaric acid, 80 mol % 1,6-hexanediol, an 20 mol % diethylene glycol; 
.DELTA.H.sub.f =6.2 cal./g.; I.V.=0.72; Tm=100.degree. C.; Tg=-1.degree. 
C.). 
Polyester I (a copolyester containing 76 mol % 
trans-1,4-cyclohexanedicarboxylic acid, 24 mol % glutaric acid, 75 mol % 
1,4-butanediol and 25 mol % diethylene glycol; I.V.=0.82; Tm=108.degree. 
C.; .DELTA.H.sub.f =2.9 cal./g.; Tg=13.degree. C.). 
Polyester J (a copolyester containing 99.5 mol % 
trans-1,4-cyclohexanedicarboxylic acid, 0.5 mol % trimellitic anhydride, 
1,4-cyclohexanedimethanol, and 25 wt. % of polytetramethylene glycol with 
MW 1000; .DELTA.H.sub.f =3.4 cal./g.; I.V.=1.05; Tm=200.degree. C.; 
Tg=-5.degree. C.). 
Polymer K (a copolyester of terephthalic acid and 1,4-butanediol, I.V.=0.7, 
Tm=225.degree. C., Tg=25.degree. C., and .DELTA.H.sub.f =18.0 cal./g. 
Polyesters B, C, D, E, F, G, H, I, J, and K are found to be insoluble in 
dioctyl phthalate. 
EXAMPLE 3 
The solubility test of Example 1 is repeated using butyl benzyl phthalate 
instead of dioctyl phthalate. Polymers A, B, C, D, E, F, G, H, I, J, and K 
are found to dissolve in butyl benzyl phthalate at a temperature of about 
70.degree. C. or higher and completely clear solutions are obtained. 
Similarly good solubility results are obtained when methyl benzyl 
phthalate, ethyl benzyl phthalate, propyl benzyl phthalate, isobutyl 
benzyl phthalate, hexyl benzyl phthalate, dibenzyl phthalate, and phenyl 
benzyl phthalate are used instead of butyl benzyl phthalate. 
EXAMPLE 4 
The solubility test of Example 1 is repeated except that isodecyl diphenyl 
phosphate is used instead of dioctyl phthalate. Polymers A, B, C, D, E, F, 
G, H, I, and J are found to dissolve readily in hot isodecyl diphenyl 
phosphate and completely clear solutions are obtained. Similarly good 
solubility results are obtained when octyl phenyl benzyl phosphate, butyl 
diphenyl phosphate, ethyl diphenyl phosphate, and isobutyl dibenzyl 
phosphate are used instead of isodecyl diphenyl phosphate. 
EXAMPLE 5 
Polyester A (47.5 g.) is heated with butyl benzyl phthalate (2.5 g.) in a 
Brabender Plastograph mixer at 170.degree. C. for five minutes in the melt 
phase to provide a blend containing 5 wt. % plasticizer. The plasticized 
polyester has a melt viscosity of 4,125,000 cp. at 190.degree. C. (Melt 
Index Method; melt index=2 g./10 minutes) and a glass transition 
temperature of 57.degree. C. The modulus of a 3 mil (0.08 mm) compression 
molded film is 200,000 psi (14090 kg./cm..sup.2 (by ASTM-882). For 
comparative purposes the unplasticized polyester has zero melt flow at 
190.degree. C. and a glass transition temperature of 74.degree. C. The 
modulus of a 3 mil (0.08 mm) film of the unplasticized polyester is 
187,000 psi (13175 kg./cm..sup.2). Similar results are obtained with 
isodecyl diphenyl phosphate. T-peel bonds (4.times.4 inches) (10.times.10 
cm.) are made on a Sentinel heat sealer with 3 mil (0.08 mm) compression 
molded films of unplasticized polyester as well as with plasticized 
polyester using polyester/cotton twill fabric using three second bonding 
time, 20 psig (1.4 kg./cm..sup.2 gage) pressure and the temperatures shown 
below. The bonds are cooled on a stone bench top, 1/2 inch (1.27 mm) is 
trimmed from each side and three one-inch (2.54 cm.) T-peel bonds are cut 
from each specimen. Bonds are tested at 23.degree. C. on an Instron 
tester at a crosshead speed of two in./min. (5.1 cm./min.) with the 
following results: 
______________________________________ 
Bonding T-Peel Bond Strength, Pli 
Temperature (Kg./linear cm.) 
.degree.F., (.degree.C.) 
Unplasticized 
Plasticized 
______________________________________ 
300 (149) 0 1.1 (0.196) 
350 (177) 1.3 (0.23) 2.4 (0.42) 
400 (204) 6.5 (1.16) 10.6 (1.89) 
______________________________________ 
Bonding temperatures above 400.degree. F. (204.degree. C.) scorch and 
degrade the fabric. This example illustrates that adding only 5% of the 
soluble plasticizer to the polyester lowers bonding temperature and 
increases bond strength. Bonds made with the plasticized polyester show 
excellent resistance to five cycles of commercial laundering and dry 
cleaning. 
EXAMPLE 6 
The procedure of Example 5 is repeated except that Polyester A is blended 
with 25 wt. % butyl benzyl phthalate. The plasticized polyester has a melt 
viscosity of 493,000 cps at 190.degree. C. (melt index=17 g./10 minutes at 
190.degree. C.) and a glass transition temperature of 23.degree. C. The 
modulus of a 3 mil (0.08 mm) compression molded film by ASTM-882 is 1,000 
psi (70.5 kg./cm..sup.2). 
Compared to the unplasticized polyester the plasticized composition is 
easily extruded into film and tubing and injection molded into shaped 
articles at much lower pressures and shorter cycle times. 
T-peel bonds 4.times.4 inches (10.times.10 cm.) are made with 3-mil (0.08 
mm.) compression molded film of unplasticized polyester as well as with 
plasticized polyester samples using polyester/cotton twill fabric on a 
Sentinel heat sealer at the temperatures shown below (three second bonding 
time; 20 psig (1.4 kg./cm..sup.2 gage) bonding pressure). Immediately after 
bonding, the bonds are quenched by placing the bonds on the stone bench top 
(temperature .about.23.degree. C.) until the bonds have cooled to room 
temperature. One-half inch (1.27 cm.) is trimmed for each side and three 
one-inch (2.54 cm.) T-peel bonds are cut from each specimen. Bonds are 
tested at 23.degree. C. on an Instron tester at a crosshead speed of two 
inches/minute (5.1 cm./min.) with the following results. 
______________________________________ 
Unplasticized Polyester 
Plastcized Polyester 
Bonding T-Peel Bond Bonding T-Peel Bond 
Temp., .degree.F. 
Strength, Pli Temp., .degree.F. 
Strength, Pli 
(.degree.C.) 
(kg/linear cm) 
(.degree.C.) 
(kg/linear cm) 
______________________________________ 
300 (149) 
0 250 (121) 6.6 (1.18) 
350 (177) 
1.3 (0.23) 300 (149) 15.5 (2.77) 
400 (204) 
6.5 (1.16) 350 (177) 9.7 (1.73) 
______________________________________ 
The addition of 25 wt. % butyl benzyl phthalate to Polyester A caused a 
reduction of at least 100 F..degree. (37.7 C..degree.) in its bonding 
temperature and provided a significant increase in bond strength compared 
to the control (15.5 vs. 0 pli (2.77 vs. 0 kg./cm.) at a bonding 
temperature of 149.degree. C.). 
Similarly good results are obtained when the Polyester A is plasticized 
with isodecyl diphenyl phosphate. 
EXAMPLE 7 
Polyester B (4.25 pounds or 1.93 kg.) and 0.75 pounds (0.34 kg.) of butyl 
benzyl phthalate are melt blended in a 3/4 inch (1.9-cm.) Brabender 
extruder at .about.175.degree. C. and pelletized. The blend is 
cryogenically ground in a Mikro Pulverizer with liquid nitrogen using a 
0.08-in. (2 mm) screen. After drying the powder at 40.degree. C. overnight 
under vacuum (25 inches of water; 635 kg./m..sup.2) the powder is 
classified by screening through 70 and 200 U.S. mesh screens by shaking 
for 15 minutes on a mechanical vibrator. 
A polyester nonwoven web is formed by passing polyester staple fiber 
through a textile card machine to give a web weight of 4 ounces/yard.sup.2 
(136.3 gm./m..sup.2). Medium powder (70-200 mesh) of the plasticized 
polyester is fluidized with nitrogen and sprayed on the web with an 
electrostatic gun to give a uniform coating. The web is passed through a 
heating chamber of infrared heaters to fuse the adhesive powder and then 
through calendering rolls. The weight of adhesive in the web is 15 wt. %. 
The web has a nice soft hand and is strong and uniformly bonded in both 
the machine and transverse directions. Bonding of a nonwoven web with 
70-200 mesh powder of the unplasticized polyester in a similar manner gave 
a very weak web probably because of the high melt viscosity of the 
polyester and its inability to flow out. 
EXAMPLE 8 
The procedure of Example 7 is repeated except that Polyester F is melt 
blended with 10 wt. % of butyl benzyl phthalate. A nonwoven web bonded 
with medium powder (70-200 mesh) of this plasticized polyester has a nice 
soft hand and good strength in both the machine and transverse directions. 
EXAMPLE 9 
Polyester B is dissolved in methylene chloride with 10 wt. % butyl benzyl 
phthalate (based on the weight of polyester). The methylene chloride is 
evaporated and the resultant blend is granulated and dried at 40.degree. 
C. under vacuum (135 mm. mercury) overnight. The blend is melt spun at 
220.degree. C. using a 1.5 inch (3.8 cm.) extruder equipped with a gear 
pump and a 45-hole spinnerette (0.5 mm diameter holes). The filaments 
coming out of the spinnerette are air cooled and wound on a take-up roll. 
The filaments are subsequently drafted 3x at 70.degree.-100.degree. C., 
crimped at 23.degree. C. with 12 crimps/inch (4.7 crimps/cm.) in a stuffer 
box and cut into 11/2 inch staple fiber. A nonwoven web is prepared by 
mixing 20 wt. % of this binder fiber with polyester staple fiber, passing 
the blend of fibers through a Shirley textile card machine and then 
through a bank of infrared heaters to fuse the binder fibers and bond the 
web. The nonwoven web has a nice soft hand and good strength in both the 
machine and transverse direction. 
Unmodified Polyester B is not spinnable into fibers at temperatures less 
than 300.degree. C. 
EXAMPLE 10 
Polyester A is melt blended with 15 wt. % butyl benzyl phthalate in a 13/4 
inch extruder at a melt temperature of .about.225.degree. C. The extruded 
blend is passed through a water cooling bath and pelletized. The pellets 
are dried under vacuum at 40.degree. C. overnight. The blend has a melt 
viscosity of 1,550,000 cp a 190.degree. C. (melt indexer; 2160 g. weight) 
and a Tg of .about.50.degree. C. by DSC analysis. The blend is injection 
molded on a New Britain molding machine at a melt temperature of 
230.degree. C. into a spiral mold. The plasticized polyester flowed 90 mm 
at a pressure of 700 psi (49.2 kg./cm..sup.2) compared to 58 mm for the 
unplasticized polyester. 
EXAMPLE 11 
The addition of 25 wt. % butyl benzyl phthalate to Polyester B caused 
induced crystallization and a Tm of 157.degree. C. with a .DELTA.H.sub.f 
of 0.63 cal/g. This polymer is normally considered to be completely 
amorphous showing only a Tg by DSC analysis. 
The term "polyester" is used herein in a generic sense to include 
copolyesters. Also, esters of the acids rather than the acids themselves 
may be used in preparing the polyesters. For example, dimethyl 
terephthalic may be used in place of terephthalic acid if desired. 
Although not required in the practice of this invention, small amounts of 
stabilizers, pigments, colorants, anticaking agents, fluorescent agents or 
other additives may be used if desired. 
Whenever the term "inherent viscosity" (I.V.) is used in this application, 
it will be understood to refer to viscosity determinations made at 
25.degree. C. using 0.50 gram of polymer per 100 ml. of a solvent composed 
of 60 percent phenol and 40 percent tetrachloroethane. 
For purpose herein, "melting point" (Tm) is measured by a differential 
scanning calorimeter using standard, well-known techniques. 
The "heat of fusion" .DELTA.H.sub.f of polymers is the amount of heat 
absorbed when crystallizable polymers are melted. .DELTA.H.sub.f values 
are readily obtained using differential scanning calorimeters 
(Perkin-Elmer). For example, one method for determining .DELTA.H.sub.f is 
described in Journal of Applied Polymer Science, 20, 1209 (1976). 
Measurement of .DELTA.H.sub.f is also described in duPont Thermal Analysis 
Bulletin No. 900-8 (1965). Qualitatively, it is possible to compare the 
degree of crystallinity of polymers by comparing their .DELTA.H.sub.f 
values. 
As indicated above, when copolyesters prepared as described above are 
employed as melt adhesives to laminate various fabric systems, metal 
strips and the like, excellent bonds result. The strength of the bonds is 
determined by the so-called "peel test" based on a modification of the 
ASTM "T-Peel Test" set forth on pages 63 and 64 on the 1964 edition of the 
BOOK OF ASTM STANDARDS, published by the American Society for Testing 
Materials, and more specifically identified as Test Number D-1876-61-T. 
The invention has been described in detail with particular reference to 
preferred embodiments thereof but it will be understood that variations 
and modifications can be effected within the spirit and scope of the 
invention.