Adhesive compositions

Linear saturated copolyesters of terephthalic acid, isophthalic acid, butanediol, and one or more aliphatic diols having at least 13 carbon atoms used as adhesives for the formation of wash-resistant bonds especially for temperature-sensitive materials. Preferably, the melting points of these adhesive compositions are from 50.degree. to 170.degree. C. and their relative viscosities, measured as 1% solutions in meta-cresol at 20.degree. C., are 1.40 to 1.80.

This application claims the priority of German Application P 37 38 495.3, 
filed Nov. 12, 1987. 
The present invention is directed to improved adhesive compositions, 
particularly those capable of providing bonds which are resistant to 
washing. 
BACKGROUND OF THE INVENTION 
Copolyesters derived from terephthalic acid and isophthalic acid with 
aliphatic diols having 2 to 12 carbon atoms are known as melt adhesives. 
In such compositions, it is also known to include aliphatic dicarboxylic 
acids. It has been found most desirable that, for such compositions, the 
melting point of the copolyester be between about 80.degree. and 
150.degree. C. Such melt adhesive compositions are described in 
EP-A-78889, DE-A-1920432, DE-A-2937946, U.S. Pat. No. 3,699,921, U.S. Pat. 
No. 4,094,721, and WO-A-83/2621. 
For example, U.S. Pat. No. 4,496,713 teaches copolyesters of terephthalic 
acid, butanediol, and other aliphatic diols having 6 to 20 carbon atoms. 
Such compositions are useful for injection molding or extrusion. However, 
the elevated melting points of these materials render them undesirable for 
use in connection with temperature sensitive substrates such as textiles. 
In U.S. Pat. No. 4,094,721, there are taught copolyesters of terephthalic 
acid, isophthalic acid, butanediol, and hexane diol. Optionally, one or 
more saturated dicarboxylic acids having 4 to 34 carbon atoms may also be 
included. These materials, however, have a substantial tendency to 
agglomerate, especially on milling and storage (see U.S. Pat. No. 
4,217,426). In addition, these compositions do not stand up to repeated 
washings at normal washing temperatures. 
It is also known to prepare copolyesters from terephthalic acid, adipic 
acid, ethylene glycol, and butanediol (see DE-A-1920432). However, the 
materials described in the foregoing reference have softening points in 
excess of 130.degree. C., at which temperature things as temperature 
sensitive fabrics cannot readily withstand. If the composition is selected 
so that the softening point is below 130.degree. C., it is too sticky to 
be useful in preparation of powdered coating materials as described in 
U.S. Pat. No. 4,094,721. 
Japanese 58-134 114 describes polyester hot-melt adhesives which are 
derived from terephthalic acid, isophthalic acid, butanediol, and an 
additional diol. The diols set forth have a maximum of 5 carbon atoms. 
There is no suggestion that a different carbon atom range would produce 
any improved results. 
Copolyesters based on terephthalic acid, adipic acid, ethylene glycol, and 
butanediol are also disclosed in U.S. Pat. No. 3,669,921. The 
agglomeration tendency of such compositions is so great that it is 
necessary to introduce substantial amounts of highly dispersed silicon 
dioxide in order to permit the granulate to be milled. Moreover, silicon 
dioxide must also be added to obtain a powder which would be suitable for 
coating, as described in WO-A-83/2621. 
The latter patent teaches the combination of terephthalic acid, butanediol, 
diethylene glycol, and at least one saturated dicarboxylic acid having 3 
to 12 carbon atoms. However, it has been found that the resistance to 
washing of such compositions is unacceptable. 
EP-A-78889 describes the combination of terephthalic acid, isophthalic 
acid, butanediol, an inorganic powder, and aliphatic diols having 5 to 12 
carbon atoms. While these compositions do not exhibit the tendency to 
agglomerate or to have poor storage stability, nonetheless, they are not 
really satisfactory for the purposes of the present invention. More 
specifically, their resistance to washing and dry cleaning is extremely 
poor and tends to the formation of undesirable bubbles. 
In summary, prior art compositions of this nature suffer from important 
drawbacks. These include tendency to agglomerate, difficulty in milling, 
and lack of resistance to repeated washings. The last generally manifests 
itself in the formation of bubbles which not only detracts from the smooth 
feel of the fabric, but also weakens the bond itself. 
SUMMARY OF THE INVENTION 
Therefore, it is among the objects of the present invention to provide 
adhesive compositions which do not tend to agglomerate. It is also among 
the objects of the present invention to provide adhesive compositions 
which can withstand numerous washings at high temperatures. It is further 
among the objects of the present invention to provide compositions of the 
foregoing type which are non-sticky when in powder form. 
The present invention comprises a careful tailoring of the monomers forming 
the copolyester adhesive composition so that all of the defects of the 
prior art are overcome. More specifically, such copolyesters are derived 
from a combination of terephthalic acid, isophthalic acid, butanediol, and 
higher aliphatic diols. The higher diols have at least 13 carbon atoms and 
are present in the amount of 1 to 30 mol %, based on the mixture of diols. 
It has been found that, by observing the foregoing parameters, compositions 
are produced which have excellent initial separation strengths, high 
washing resistance, excellent dry cleaning resistance, and exhibit little 
or no bubble formation. 
Moreover, such materials have markedly higher crystallization tendencies, 
probably due to the higher diols of which it is composed. This results in 
substantially reduced tendency to cohere compared with previously known 
compositions. These characteristics are particularly found when the higher 
diols have 13 to 20 carbon atoms. 
The result is a low softening temperature coupled with the absence of 
agglomeration, even without the introduction of any additives. These 
materials can be processed without difficulty to produce a storage stable, 
aggregate-free powder.

DETAILED DESCRIPTION OF THE INVENTION 
The copolyester adhesives of the present invention are produced in a manner 
analogous to the production of polybutylene-terephthalate as described in 
Kunststoffhandbuch, Volume 8, C. Hanser Verlag, Munich, 1973, Page 697. Of 
course, there are other ways of preparing these compositions which are 
well known to those of ordinary skill in the art. 
In a preferred form of the invention, the molar ratio of terephthalic acid 
to isophthalic acid is maintained between 75:25 and 40:60. More 
preferably, this ratio is from 65:35 to 45:55. The molar ratio of 
butanediol to the higher aliphatic diol (or mixture thereof) is 99:1 to 
70:30. In a particularly preferred form of the invention, this ratio is 
95:5 to 80:20. 
The higher diols contain 13 to 20, preferably 14 to 18, carbon atoms. They 
are advantageously used in an amount of 1 to 30 mol %, preferably 5 to 20 
mol %. 
It has been found that commercial mixtures of diols can be used in the 
present invention. For example, SR 100 diol has been found quite suitable. 
This is an aliphatic mixture of diols having 13 to 18 carbon atoms. The 
average chain length is 14 carbon atoms and the product is available from 
ARCO, Sartomer AG, Marshall Building, Westtown Road, West Chester, Pa. 
19380, U.S.A. 
It has also been found desirable that the compositions of the present 
invention have relative viscosities of 1.40 to 1.80. Preferably, the 
viscosity should be between 1.50 and 1.70. These viscosities are measured 
as a 1% m-cresol solution at 20.degree. C. The melting points of the 
compositions are preferably 90.degree. to 170.degree. C., more preferably 
100.degree. to 130.degree. C. Of course, the usual additives may also be 
included in the present compositions; e.g. processing agents, stabilizers, 
plasticizers, fillers, pigments, optical brighteners, etc. The 
compositions are pulverized in accordance with known methods. In 
particular, cold milling has been found suitable. 
The following examples are intended to illustrate the present invention, 
but are not limitative. 
EXAMPLES 1 to 3 
Terephthalic acid and isophthalic acid are esterified with butanediol and 
SR 100 diol, in accordance with the molar ratios given in Table 1, in the 
presence of titanium tetrabutylate. The reaction takes place at 
200.degree. C. to 230.degree. C., under nitrogen gas in an autoclave with 
stirring until the theoretical amount of water has been split off. The 
pressure is then reduced during an additional hour to about 1 mbar, 
followed by polycondensation at 250.degree. C., until the desired 
viscosity is reached. The autoclave contents are then removed through the 
bottom valve, cooled, and granulated. The dried granulate is cold milled 
under nitrogen, and the granular fraction, between 80 to 200 .mu.m, is 
sieved off. 
COMATIVE EXAMPLES 
Comparative Examples A, B, C, D, E and F are prepared from compositions 
according to Table 1, in the same manner as Examples 1 to 3. The results 
are given in Table 2. The parameters for all the Examples are determined 
as follows: 
.eta. rel: the relative viscosity is determined as a 1% solution in 
m-cresol at 20.degree. C. 
Tm: melting point is the maximum of the melt peak obtained by differential 
scanning calorimetry at a heating rate of 20.degree. C./min. 
Processability: the powder was judged for processability on a scale of 1 
(good), 2 (satisfactory) and 3 (poor). 
Separation strength/Bubble formation: powder having a particle size of 80 
to 200 .mu.m is coated on a conventional carrier material using a powder 
point coating apparatus having a 17 mesh gravure roller at a coating 
weight of 17.+-.2 g/m.sup.2. This is then adhered to a conventional upper 
material using a continuous press at 130.degree. C. under a pressure of 
350 g/cm.sup.2. At the adhered parts, the bonding is measured initially, 
after 10 washes at 60.degree. C., after 10 washes at 95.degree. C., and 
after 10 dry cleanings. The separation strength is calculated according to 
DIN 54310. After 10 washes, the tests are evaluated on a scale of 1 to 5 
on the upper material for bubble formation according to the following 
scale: 
1. Very good, no bubbles 
2. Good, very few, barely visible bubbles 
3. Few, but clearly visible small bubbles (&lt;2 mm) 
4. Many small and large bubbles 
5. Very large long bubbles. 
TABLE 1 
__________________________________________________________________________ 
Composition (Mol %) 
Example 
TPA 
IPA 
ADA BD HD DDD SR100 
Additive (wt. %) 
__________________________________________________________________________ 
1 50 50 -- 90 -- -- 10 -- 
2 50 50 -- 80 -- -- 20 -- 
3 62 38 -- 70 -- -- 30 -- 
A 75 25 -- 45 55 -- -- 0.15 talc 
B 85 15 -- 60 -- 40 -- 0.15 talc 
C 70 30 -- 50 50 -- -- -- 
D 50 50 -- 100 
-- -- -- -- 
E 60 -- 40 75 -- 25 -- -- 
F 85 15 -- 50 50 -- -- -- 
__________________________________________________________________________ 
TPA = terephthalic acid 
IPA = isophthalic acid 
ADA = adipic acid 
BD = butanediol 
HD = hexanediol 
DDD = dodecanediol 
TABLE 2 
__________________________________________________________________________ 
Example 1 2 3 A B C D E F 
__________________________________________________________________________ 
Tm (.degree.C.) 
120 98 122 120 100 110 125 112 110 
.eta. rel 1.55 
1.63 
1.64 
1.67 
1.64 
1.58 
1.67 
1.61 
1.62 
Processability of 
1 1 1 1 1 3 2 1 2 
powder 
Separation strength 
(N/5 cm) 
Without treatment 
13 14 13 12 11 8 10 10 10 
after 10 .times. 60.degree. C. washes 
11.5 
13 11 8 9 5 4 7 9 
after 10 .times. 95.degree. C. washes 
9 10 9 6 4 3 0 6 7 
after 10 .times. dry clean. 
10 12 10 8 6 5 2 7 6 
Bubble formation 
after 10 .times. 60.degree. C. washes 
1 1 1 3 3 4 3 2 2 
after 10 .times. 95.degree. C. washes 
2 2 2 4 5 4 -- 3 3 
__________________________________________________________________________ 
Adhesive compositions which exhibit bubble formation values of 3 to 5 are 
not acceptable adhesives. In general, the compositions of Examples 1 to 3 
(the present invention) have surprising superior properties to those of 
the five Comparative Examples. 
As is apparent from the foregoing, the present invention is to be broadly 
construed and not to be limited except by the character of the claims 
appended hereto.