Low viscosity hot-melt adhesives

Disclosed is a hot-melt adhesive composition capable of bonding paper to metal, glass and polyethylene terephthalate comprising an amorphous polymer selected from polypropylene or copoly(propylene-butene) having a propylene content of greater than 50%, a hydrocarbon tackifier resin, and a rosin tackifier. Preferably, the composition also contains a polyethylene wax.

TECHNICAL FIELD 
The present invention relates to hot-melt polymeric adhesives having good 
adhesion to substrates such as glass, metal, polymers, etc. This adhesive 
is especially useful in bonding labels, tapes and decals of conventional 
materials such as paper, plastic, etc. to such substrates. 
BACKGROUND OF THE INVENTION 
Hot-melt adhesives which are useful in such applications as the bonding of 
labels, tapes and decals to various substrates are well known in the art. 
Such adhesives are normally specially adapted for use on certain kinds of 
substrates. At the present time, however, I am unaware of amorphous 
olefin-based hot-melt adhesives which have the versatility of being useful 
in bonding to a variety of substrates such as glass, metal and polymers. 
Also, the hot-melt adhesives according to the present invention have a 
good balance of high and low temperature bond quality, and the combination 
of good tack and low viscosity for ease of application. Furthermore, the 
hot-melt adhesives according to the present inventin have low color, low 
odor when molten, good thermal stability and less tendency of 
bleed-through when compared to known conventional hot-melt adhesives. 
The adhesives according to this invention are generally applied by a 
hot-melt applicator which includes a reservoir for the adhesive, heating 
means for melting the adhesive and maintaining it in a molten state, and 
means for applying the adhesive for a particular end use. 
To be suitable for use on typical hot-melt labeling equipment, the adhesive 
should have several key characteristics. Among these are low viscosity at 
typical application temperatures of 150.degree.-180.degree. C., resistance 
to stringing, aggressive tack, long open time, and good specific adhesion 
to typical container and label substrates. Other desirable properties are 
low color and odor, low tendency to bleed through label stock, and good 
thermal stability. In the past, hot-melt adhesives useful for labeling 
have been commonly based on ethylene-vinyl acetate copolymers or synthetic 
block copolymer rubbers which are diluted with rosins, waxes, and 
plasticizers to yield the desired machining characteristics. Such 
formulations are generally high in color and odor, and exhibit significant 
changes in viscosity on exposure to heat for extended periods. While 
polyolefin-based adhesives exhibit low color and odor, and good thermal 
stability, those available to date generally lack the tack and adhesion 
necessary to bond a variety of label stocks to various substrates, and 
have not been available with the low viscosity necessary for machining on 
hot-melt labeling lines. Therefore, it would be an advance in the state of 
the art to provide a polyolefin-based adhesive having the necessary 
low-melt viscosity, good tack and specific adhesion, and low color and 
odor to be desirable in bonding or sealing labels, tapes, decals, etc., to 
provide bonds having good strengths at both low and high temperatures. 
One patent of interest is U.S. Pat. No. 4,567,223. This patent discloses a 
hot-melt adhesive comprising a blend of at least one modified (such as by 
reaction with an unsaturated polycarboxylic acid) propylene/C.sub.4 to 
C.sub.10 higher 1-olefin copolymer having an acid number of at least 5, a 
tackifying resin, and a high density, low viscosity polyethylene wax 
having a molecular weight of at least about 1000. The present inventin 
differs from the hot-melt adhesive of U.S. Pat. No. 4,567,223 in that the 
adhesive of the present invention uses an unmodified olefin polymer or 
copolymer. It further differs from this patent in that both a hydrocarbon 
tackifier and a rosin tackifier are required. The U.S. Pat. No. 4,567,223 
discloses in Example 8 that low density (i.e., 0.925) polyethylene wax is 
not satisfactory in that invention. 
DESCRIPTION OF THE INVENTION 
According to the present invention, there are provided hot-melt adhesive 
compositions useful for bonding paper and other substrates to metal, glass 
and polyethylene terephthalate comprising 
(a) about 30-60% by weight of an amorphous polymer selected from 
polypropylene or copoly(propylene-butene) having a propylene content of 
greater than 50%, the polymer having a melt viscosity of about 100-2000 
cps at 190.degree. C., a density of about 0.8 to 0.9 and a saponification 
number of about 0 to 5.0, 
(b) about 10-40% by weight of a saturated, polycyclic hydrocarbon tackifier 
resin having a Ring and Ball softening point (RBSP) of about 
70.degree.-130.degree. C. and a melt viscosity of about 100 to 2000 cps at 
190.degree. C., and 
(c) about 10-35% by weight of rosin tackifier having an acid number of 
about 130-170 and a RBSP of about 70.degree.-100.degree. C. 
Preferably, the hot-melt adhesive composition further contains (d) an 
amount up to about 20% by weight of a polyethylene wax having a melt 
viscosity of about 100 to about 200 cps at 125.degree. C. and a RBSP of 
about 90.degree.-120.degree. C. Such hot-melt adhesive compositions are 
capable of forming peel strengths between paper and glass, metal or 
polymer of at least 500 gms/in width. Obviously, the adhesive compositions 
will total 100 weight % of (a) through (d) plus any minor quantities of 
conventional additives mentioned hereinafter. 
In a preferred embodiment of the present invention, the amorphous polymer 
is present in an amount of about 45-55% by weight, the hydrocarbon 
tackifier is present in an amount of about 15-25% by weight, the rosin 
tackifier is present in an amount of about 15-25% by weight and the 
polyethylene wax is present in an amount of about 5-15% by weight. 
Preferably, the viscosity of the amorphous polymer is about 200-500 cps at 
190.degree. C. and the RBSP of the hydrocarbon tackifier resin is about 
80.degree.-110.degree. C. Use of amorphous polymer of propylenebutene 
containing about 40% butent results in stronger bonds. Suitable 
commercially available amorphous polymers include Eastman M-5K polymer or 
Himont AFAX 250 polymer catalytically or thermally degraded to the desired 
viscosity. 
Suitable hydrocarbon tackifying resins can be a hydrocarbon resin such as 
DAC-B hydrocarbon resin prepared according to the process disclosed in 
U.S. Pat. No. 3,701,760 as well as other hydrocarbon resins, polyterpenes 
or synthetic polyterpenes, and the like. One such hydrocarbon tackifying 
resin is a hydrocarbon resin having a softening point of about 100.degree. 
C. and available commercially as Eastotac H-100 from Eastman Chemical 
Products, Inc. Other hydrocarbon tackifying resins can be prepared by the 
polymerization of monomers consisting primarily of olefins and diolefins 
and include, for example, the residual by-product monomers, resulting from 
the manufacture of isoprene. These hydrocarbon tackifying resins typically 
exhibit a Ring and Ball softening point of from about 80.degree. C. to 
about 135.degree. C.; an acid number of from about 0-2, a saponification 
value of less than about 1; and an iodine value of from about 30 to 100. 
Examples of such commercially available resins of this type are "Wingtack" 
95 and "Wingtack" 115 tackifying resins sold by the Goodyear Tire and 
Rubber Company, the Sta-Tac and Betaprene A or H resins sold by the 
Reichold Chemical Corporation. Arkon resins sold by Arakawa Forest 
Chemical Industires, and Escorez resins sold by Exxon Chemical Co. 
Also other suitable resins are the terpene polymers such as the polymeric, 
resinous materials obtained by polymerization and/or copolymerization of 
terepene hydrocarbons such as the alicyclic, monocyclic, and bicyclic 
monoterpenes and their mixtures, including allo-ocimene, carene, 
isomerized pinene, pinene, dipentene, terpinene, terpinolene, limonene, 
turpentine, a terpene cut or fraction, and various other terpenes. 
Particularly useful starting materials are terpene mixtures containing at 
least 20 percent beta-pinene and/or limonene or dipentene (racemic 
limonene), and the "sulfate turpentine" obtained as a by-product in the 
sulfate pulping process. Commercially available resins of the terpene type 
include the Zonarez terpene B-Series and 7000 Series resins from Arizona 
Chemical Corp. and Nirez resins from Reichhold Chemical Corp. The typical 
properties reported for the Zonarez Terpene Resins include Ring and Ball 
softening point of about 55.degree. to 125.degree. C. (ASTM E-28-67), 
Color of 2 to 3 (Gardner 1963, 50% in Heptane), Acid Number of less than 1 
(ASTM D465-59), Saponification Number of less than 1 (ASTM D464-59) and 
Specific Gravity at 25.degree. C. of 0.96 to 0.99 (ASTM D1963-61). 
Suitable rosin tackifiers are the tall oil rosin products having the 
specified Ring and Ball softening points and acid number. Suitable 
commercially available products include Acintol R and Polystix 85 rosins. 
The low viscosity polyethylene waxes useful in this invention are widely 
available articles of commerce and can be prepared by known techniques. 
These waxes are made by direct synthesis or by degradating polyethylene to 
the desired viscosity. Polyethylene waxes normally have, and should have 
for the present invention, melting points in the range of 80.degree. to 
120.degree. C., and preferably in the range of 105.degree. to 115.degree. 
C., preferably about 110.degree. C., a penetration hardness at 23.degree. 
C. of about 3 dmm, and a melt viscosity preferably of about 100 to about 
200 cp. at 125.degree. C. Suitable commercially available waxes include 
Epolene N-14 and Epolene N-11 Waxes, products of Eastman Kodak Company, 
both of which have densities of about 0.92. 
The adhesive compositions of this invention are prepared by blending 
together the adhesive components in the melt at a temperature of about 
160.degree. C. to about 200.degree. C. until a homogeneous mixture is 
obtained. Various methods of blending materials of this type are known to 
the art and any method that produces a homogeneous mixture is 
satisfactory. These components blend easily in the melt and a heated 
vessel equipped with a stirrer is all that is required. For example, a 
Cowles stirrer provides effective mixing for preparing these compositions. 
Solvents such as hexane, heptane, mineral spirits, xylene, toluene, 
benzene, chlorinated hydrocarbons, etc., are not needed to prepare the 
compositions of this invention; however, they can be used if desired. 
In addition to the adhesive components, it is desirable for the adhesive 
compositions to contain about 0.1 percent to about 1.5 percent by weight, 
of one or more antioxidants. Antioxidants that are effective include, for 
example, tris (di-t-butyl-p-hydroxybenzyl)-trimethylbenzene (Lonox 330), 
alkylated bisphenol (Naugawhite), zinc dibutyl dithiocarbamate (Butyl 
Zimate), and 4.4'-methylene bis(2,6-di-tert-butylphenol) (Ethyl 702), 
tetrakis[methylene(3,5-di-tert-butyl-4-hydroxyhydrocinnamate)methane] 
(Irganox 1010), lauryl stearyl thiodipropionate (Plastanox 1212), and 
dilauryl 3,3'-thiodipropionate (Plastanox LTDP), 
2,6-di-tert-butyl-p-cresol (BHT) and the like. 
Additives such as nucleating agents, pigments, colorants, fillers, 
solvents, and the like can also be added to the adhesive compositions of 
the present invention. 
The adhesive compositions of this invention, which are essentially 100 
percent solids, have a melt viscosity in the range of 100 to 800 
centipoise at 177.degree. C. and a RBSP of 80.degree.-120.degree. C. 
The following examples are submitted for a better understanding of the 
invention. 
In the examples, the various compositions are melt blended in a beaker at 
190.degree. C. by stirring until a homogeneous mixture is obtained. The 
adhesive is put in a hot-melt applicator for application to a substrate. 
Adhesion at various temperatures is determined by applying a 1/8 inch wide 
bead of adhesive lengthwise to a single sample of label stock, and 
immediately bringing the desired container, such as a glass jar in contact 
with moderate hand pressure. Application temperature is 177.degree. C. The 
label stock is polypropylene coated kraft paper. The bonded specimens are 
placed in a controlled environment at the desired condition, and allowed 
to age for 24 hours. Five test specimens are made with each adhesive. The 
bonds are separated by hand and a determination made as to the type of 
failure. An adhesive having good bonding capabilities will exhibit fiber 
tear (FT) of the label stock. An adhesive having poor or no bonding 
capabilities will exhibit no fiber tear (NFT) of the label, and generally 
fails adhesively from the container. 
This same test can also be used to estimate relative degree of tack by 
noting the ability of the label to readily affix itself to the container; 
likewise open times can be compared by simply timing the longest open time 
at which a bond is obtained.

EXAMPLE 1 
______________________________________ 
Composition: 
50% Eastman APP M-5K amorphous 
polypropylene degraded to 
.about.700 cps at 190.degree. C. 
20% Eastotac H-100 hydrocarbon 
resin tackifier 
20% Polystix 85 rosin 
tackifier (Hercules) 
9.1% Epolene N-14 Polyethylene wax 
0.7% DLTDP 
0.2% hindered phenol antioxidant 
(Irganox 1010) 
______________________________________ 
Viscosity: 390 cps at 177.degree. C. 
RBSP: 96.degree. C. 
Color: Gardner 8 
______________________________________ 
Adhesion: (Polypropylene coated labels to glass): 
100% fiber tear at 23.degree. C. 
100% fiber tear at 0.degree. C. 
100% fiber tear at 50.degree. C. 
______________________________________ 
Tack: Very good 
Open time: 30 sec. 
Thermal Stability (viscosity after 100 hrs at 177.degree. C. in air):&lt;10% 
change in viscosity 
Peel Strength (Kraft to Kraft): 600 gms/in width. 
EXAMPLE 2 Control 
______________________________________ 
Composition: 50% Eastman M-5K Polymer 
49.5% Polystix 85 rosin tackifier 
0.25% BHT 
0.25% Irganox 1010 antioxidant 
______________________________________ 
Viscosity: 590 cps at 177.degree. C. 
Color: Gardner 11 
______________________________________ 
Adhesion: .about.75% Fiber tear at 23.degree. C. 
100% fiber tear at 0.degree. C. 
.about.75% fiber tear at 50.degree. C. 
______________________________________ 
Tack: Very good 
Open time and stability not measured. 
EXAMPLE 3 
______________________________________ 
Composition: 
50% Amorphous propylene-butene 
copolymer, 40% butene, 
viscosity is 525 cps at 190.degree. C. 
20% Eastotac H-100 hydrocarbon 
resin tackifier 
20% Polystix 85 rosin tackifier 
9.1% Epolene N-14 polyethylene wax 
0.7% DLTDP 
0.2% Irganox 1010 antioxidant 
______________________________________ 
Viscosity: 350 cps at 177.degree. C. 
Color: Gardner 8 
Ring and Ball Softening Point: 96.degree. C. 
Tack: good 
Adhesion: 100% fiber tear at 0.degree. C., 23.degree. C. and 50.degree. C. 
EXAMPLE 4 (Control) 
______________________________________ 
A B 
______________________________________ 
Eastman M-5K 50% 50% 
polymer 
Polystix 85 rosin 
10% 30% 
tackifier 
Eastotac H-100 hydro- 
30% -- 
carbon tackifier 
Epolene N-14 wax 
9.1% 19.1% 
Irganox 1010 0.2% 0.2% 
antioxidant 
DLTDP 0.7% 0.7% 
Viscosity at 177.degree. C.: 
680 cps 490 cps 
Adhesion: 23.degree. C.: 
.about.25% 
fiber .about.25% 
fiber 
tear tear 
______________________________________ 
In the above examples, Example 2 illustrates poor color and adhesion at 
higher temperatures obtained when the hydrocarbon tackifier and wax are 
omitted. Example 4, A and B, illustrate loss of fiber tear when the level 
of rosin tackifier is at the lower limit, or level of polyethylene wax is 
near the higher limit. 
In the examples, Eastman M-5K polymer is an amorphous polypropylene having 
a melt viscosity of 2400 at 190.degree. C., a density of 0.86 and a SAP 
No. of 0. It is degraded to a viscosity of about 700 cps at 190.degree. C. 
Density is about 0.86 and SAP No. is 0. 
Eastotac H-100 resin is a hydrocarbon resin tackifier having a RBSP of 
100.degree. C., and a melt viscosity of 175 cps t 190.degree. C. 
Polystix 85 is a rosin tackifier having an acid number of 156 and a RBSP of 
80.degree. C. 
Eastman N-14 is a low viscosity polyethylene wax having a melt viscosity of 
157 cps at 125.degree. C., a RBSP of 106.degree. C., and a density of 
0.92. 
The compound designated DLTDP is dilaurylthiodipropionate and BHT is 
butylated hydroxy toluene. 
Himont AFAX 250 polymer is an amorphous polymer having a viscosity of 300 
cps at 190.degree. C. 
Acintol R rosin is a rosin tackifier having an acid number of 155 and a 
RBSP of 80.degree. C. 
Unless otherwise specified, saponification (SAP) numbers used herein are 
determined according to ASTM D-1387 for waxes and ASTM D-464 for rosins. 
Acid numbers are determined according to ASTM D-1386-59. Peel strengths 
are determined according to ASTM D-903. 
Melt viscosities are determined on a Brookfield Model RTV Thermosel 
Viscometer using a No. 27 spindle. RBSP is determined in .degree.C. using 
ASTM E-28, and densities are determined using a density gradient tube 
(ASTM Method D-1505). 
Unless otherwise stated, all parts, percentages, ratios, etc., are by 
weight. 
While the invention has been described in detail with particular reference 
to preferred embodiments thereof, it will be understood that variations 
and modifications can be effected within the spirit and scope of the 
invention.