Reinforced tape laminates

Fiber reinforced tape laminates characterized by superior strength properties are prepared utilizing a hot melt pressure sensitive adhesive comprising a styrene-butadiene block or multi-block copolymer, a tackifying resin and an oil.

BACKGROUND OF THE INVENTION 
The present invention relates to reinforced tape laminates and especially 
to glass fiber reinforced gummed tape laminates. 
The use of fibers, particularly glass fibers, to reinforce gummed tapes has 
long been accepted as a method for substantially increasing the tear 
strength of the tape. Such tape laminates are typically formed by applying 
an adhesive to the base sheet, laying on the fiber, then applying a top 
sheet and pressing the laminate through a pair of squeeze rolls. The tape 
is generally completed by applying an adhesive to one of the outer 
surfaces to form a gummed or prepasted coating although, in some 
instances, one of the sheets may be precoated prior to formation of the 
laminate. 
The requirements for the adhesive used in forming the laminate are 
stringent and include excellent paper adhesion as well as good specific 
adhesion to the fibers in order to give an overall strong construction. 
While the latter are the principal requirements, the adhesive must also 
possess heat and oxidation resistance, low temperature flexibility and 
must not bleed through the paper substrates. Originally, the adhesive used 
in producing the laminate were aqueous vinyl acetate based adhesive. More 
recently, however, tape manufacturers have switched to hot melt adhesives, 
most commonly those based on atactic polypropylene. 
SUMMARY OF THE INVENTION 
We have now found that pressure sensitive hot melt adhesives prepared from 
A--B--A type block and multi-block copolymers are particularly useful in 
the construction of reinforced gummed tape laminates. 
Thus, the present invention is directed to a reinforced gummed tape 
laminate comprising fibers bonded between two substrates, using a hot melt 
pressure sensitive adhesive composition comprising: 
(a) 10 to 35% by weight of an A--B--A block or multi-block copolymer where 
the A component is styrene and the B component is butadiene or 
hydrogenated butadiene and the A component comprises at least 28 parts per 
100 parts of the copolymer; 
(b) 45 to 70% by weight of a compatible tackifying resin; 
(c) 5 to 30% by weight of a plasticizing oil; 
(d) 0 to 5% by weight of a petroleum derived wax; and 
(e) 0.1 to 2% by weight of a stabilizer. 
More particularly, the present invention is directed to the use of a hot 
melt adhesive composition especially adapted for the above described 
laminate, the hot melt adhesives containing as the block copolymer, a 
multi-block styrene-butadiene copolymer containing at least 35 parts 
styrene per 100 parts copolymer. 
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The primary component of the adhesive compositions used in the present 
invention are block or multi-block copolymers having the general 
configuration: 
EQU A--B--A or A--B--A--B--A--B-- 
wherein the non-elastomeric polymer blocks A are styrene, while the 
elastomeric polymer blocks B are butadiene or butadiene which is partially 
or substantially hydrogenated. They may be linear or branched. Typical 
branched structures contain an elastomeric portion with at least three 
branches which can radiate out from a central hub or can be otherwise 
coupled together. 
The non-elastomeric styrene blocks should make up 28 to about 75% by weight 
of the block copolymer. The elastomeric block component making up the 
remainder of the copolymer is butadiene which may or may not be 
hydrogenated as taught, for example, in U.S. Pat. No. 3,700,633. This 
hydrogenation may be either partial or substantially complete. Selected 
conditions may be employed, for example, to hydrogenate the elastomeric 
butadiene block while not so modifying the vinyl arene polymer blocks. 
Other conditions may be chosen to hydrogenate substantially uniformly 
along the polymer chain, both the elastomeric and non-elastomeric blocks 
thereof being hydrogenated to practically the same extent, which may be 
either partially or substantially complete. 
Typical of the rubbery block copolymers useful herein are the 
polystyrene-polybutadiene-polystyrene, and e.g., 
polystyrene-poly-(ethylenebutylene)-polystyrene. These copolymers may be 
prepared using methods taught, for example, in U.S. Pat. Nos. 2,239,478; 
3,427,269; 3,700,633; 3,753,936; and 9,932,327. Alternatively, some may be 
obtained from Shell Chemical Co. under the trademarks Kraton 1101, 1102, 
1650, and 1652, and from Phillips Chemical Co. under trademarks Solprene 
418 and 423. These block copolymers are used at levels of 10 to 35% by 
weight of the adhesive, preferably 15 to 35% by weight. 
Most preferred for use herein are the linear A--B--A--B--A multi-block 
copolymers where the elastomeric block is butadiene and the 
non-elastomeric block is styrene and the latter is present in relatively 
high concentrations, i.e., at levels of 35% or above. Block copolymers 
marketed commercially at this time which meet the above described 
requirements are available from Firestone under the tradename Stereon 840A 
(57 parts butadiene and 43 parts styrene). Blends of these high styrene 
containing copolymers with other compatible block copolymers may also be 
employed. 
The tackifying resins useful in the adhesive compositions can be 
hydrocarbon resins, synthetic polyterpenes, rosin esters, natural 
terpenes, and the like. More particularly, the useful tackifying resins 
include any compatible resins or mixtures thereof such as (1) natural and 
modified rosins such, for example, as gum rosin, wood resin, tall-oil 
rosin, distilled rosin, hydrogenated rosin, dimerized rosin, and 
polymerized rosin; (2) glycerol and pentaerythritol esters of natural and 
modified rosins, such for example as the glycerol ester of pale, wood 
rosin, the glycerol ester of hydrogenated rosin, the glycerol ester of 
polymerized rosin, the pentaerythritol ester of hydrogenated rosin, and 
the phenolic-modified pentaerythritol ester of rosin; (3) copolymers and 
terpolymers of natured terpenes, e.g., styrene/terpene and alpha methyl 
styrene/terpene; (4) polyterpene resins having a softening point, as 
determined by ASTM method E28-58T, of from about 80.degree. to 150.degree. 
C.; the latter polyterpene resins generally resulting from the 
polymerization of terpene hydrocarbons, such as the cicyclic monoterpene 
known as pinene, in the presence of Friedel-Crafts catalysts at moderately 
low temperatures; also included are hydrogenated polyterpene resins; (5) 
phenolic modified terpene resins and hydrogenated derivatives thereof 
such, for example, as the resin product resulting from the condensation, 
in an acidic medium, of a bicyclic terpene and a phenol; (6) aliphatic 
petroleum hydrocarbon resins having a Ball and Ring softening point of 
from about 70.degree. to 135.degree. C.; the latter resins resulting from 
the polymerization of monomers consisting primarily of olefins and 
diolefins; also included are the hydrogenated aliphatic petroleum 
hydrocarbon resins; (7) aromatic petroleum hydrocarbon resins and the 
hydrogenated derivatives thereof; and (8) alicyclic petroleum hydrocarbon 
resins and the hydrogenated derivatives thereof. Mixtures of two or more 
of the above described tackifying resins may be required for some 
formulations. 
The selection of the particular tackifying agent is, in large part, 
dependent upon the specific block copolymer employed. The preferred 
adhesive formulations for use herein which employ the linear multi-block 
Stereon type copolymers provide optimum properties when tackifiers of 
modified terpene having ring and ball softening point of about 
100.degree.-120.degree. C. such as Zonatac 105, are employed. 
Among the applicable stabilizers or antioxidants utilized herein are 
included high molecular weight hindered phenols and multifunctional 
phenols such as sulfur and phosphorous-containing phenols. Hindered 
phenols are well known to those skilled in the art and may be 
characterized as phenolic compounds which also contain sterically bulky 
radicals in close proximity to the phenolic hydroxyl group thereof. In 
particular, tertiary butyl groups generally are substituted into the 
benzene ring in at least one of the ortho positions relative to the 
phenolic hydroxy group. The presence of these sterically bulky substituted 
radicals in the vicinity of the hydroxyl group serves to retard its 
stretching frequency, and correspondingly, its reactivity; this steric 
hindrance thus providing the phenolic compound with its stabilizing 
properties. Representative hindered phenols include: 1,3,5-trimethyl 
2,4,6-tris (3,5-di-tert-butyl-4-hydroxybenzyl)benzene; pentaerythrityl 
tetrakis-3(3,5-di-tert-butyl-4-hydroxyphenyl)propionate; 
n-octadecyl-3(3,5-di-tert-butyl-4-hydroxyphenyl)-propionate; 
4,4'-methylenebis (2,6-tert-butylphenol); 4,4'-thiobis 
(6-tert-butyl-o-cresol); 2,6-di-tertbutylphenol; 
6-(4-hydroxyphenoxy)-2,4-bis(n-octyl-thio)-1,3,5-triazine; di-n-octadecyl 
3,5-di-tert-butyl-4-hydroxy-benzylphosphonate; 2-(n-octylthio)ethyl 
3,5-di-tert-butyl-4-hydroxy-benzoate; and sorbitol 
hexa[3-(3,5,-di-tert-butyl-4 -hydroxyphenyl)-propionate]. 
The performance of these antioxidants may be further enhanced by utilizing, 
in conjunction therewith, known synergists such, for example, as 
thiodipropionate esters and phosphites. Particularly useful is 
distearylthiodipropionate. 
These stabilizers, if used, are generally present in amounts of about 0.1 
to 1.5 weight percent, preferably 0.25 to 1.0%. 
Various placticizing or extending oils are also present in the composition 
in amounts of 5% to about 30%, preferably 5 to 25% by weight in order to 
provide wetting action and/or viscosity control. The above broadly 
includes not only the usual plasticizing oils but also contemplates the 
use of olefin oligomers and low molecular weight polymers as well as 
vegetable and animal oil and their derivatives. The petroleum derived oils 
which may be employed, are relatively high boiling materials containing 
only a minor proportion of aromatic hydrocarbons (preferably less than 30% 
and, more particularly, less than 15% by weight of the oil). 
Alternatively, the oil may be totally non-aromatic. The oligomers may be 
polypropylenes, polybutenes, hydrogenaged polyisoprene, hydrogenated 
polybutadiene, or the like, having average molecular weights between about 
350 and about 10,000. Vegetable and animal oils include glyceryl esters of 
the usual fatty acids and polymerization products thereof. 
Various petroleum derived waxes may also be used in amounts less than about 
15% by weight of the composition in order to impart fluidity in the molten 
condition of the adhesive and flexibility to the set adhesive, and to 
serve as a wetting agent for bonding cellulosic fibers. The term 
"petroleum derived wax" includes both paraffin and microcrystalline waxes 
having melting points within the range of 130.degree.-225.degree. F. as 
well as synthetic waxes such as low molecular weight polyethylene or 
Fisher-Tropsch waxes. 
Other additives conventionally used in hot melt adhesives for reinforced 
tape laminates including clay, diatomaceous earth, barium sulfate, calcium 
carbonate, talc, colloidal silica, etc. may also be present in these 
adhesives. 
The adhesive compositions are prepared by blending the components in the 
melt at a temperature of about 130.degree.-200.degree. C. until a 
homogeneous blend is obtained, approximately two hours. Various methods of 
blending are known to the art and any method that produces a homogeneous 
blend is satisfactory. 
The resultant adhesives are then used to bond the fibers between the two 
substrates using conventional techniques. Most commonly the reinforcing 
fibers are glass fibers which, in some cases, may be starch coated. The 
fibers may be laid directly in random or predetermined configurations on 
the adhesive coated base substrate or they may be laid on in the form of a 
prefabricated scrim web. The base substrates are usually formed from kraft 
paper having a weight of 30 to 40 pounds per 300 sq. ft. ream. 
The laminate is generally formed by applying the hot melt adhesive to a 
continuous layer of the base sheet at a temperature of about 250.degree. 
to 350.degree. F. and a coating thickness of 0.001 to 0.002 inches 
(equivalent to a coating weight of approximately 15-30 pounds per 3000 sq. 
ft. ream). This coating is performed on a roll or extrusion coater run at 
a speed of about 200-1000 feet per minute. The fibers or scrim are laid 
down on the coated substrate and a top sheet applied therein. The 
resultant laminate is then pressed to form a board, usually by passing 
through a pair of squeeze rolls. 
If desired, one surface of one of the substrates may be precoated with an 
adhesive prior to lamination. Alternatively, an adhesive coating may be 
applied to one of the outer surfaces after formation of the laminate. Any 
remoistenable or pressure sensitive adhesive used in conventional gummed 
tape manufacture may be utilized. 
This invention can be further illustrated by the following examples or 
preferred embodiments thereof, although it will be understood that these 
examples are included merely for purposes of illustration and are not 
intended to limit the scope of the invention unless otherwise specifically 
indicated. 
Testing Procedures 
Studies on reinforced tapes have indicated that two of the most stringent 
requirements for the adhesive are the ability to adhere the two substrates 
as well as the ability to adhere the fibers. Therefore, in testing the 
tapes of the present invention, the following tests were performed: 
180.degree. Peel Test (Kraft to Kraft): A thin coating of adhesive was 
applied to one kraft substrate and a second kraft substrate laminated 
thereon. Uncoated tabs left at one end of each substrate, were screwed 
into the jaws of an Instrom tester and the laminate peeled at a crosshead 
separation speed of two inches per minute. The force required to pull the 
substrates apart was recorded. 
FIber Retention Strength: Glass fibers were laminated lengthwise between 
two layers of kraft with a portion of the fibers extending beyond the 
laminated construction. The laminated portion was cut to one inch. The 
fibers were then pulled out, one at a time, using a tensile tester with 
jaw separation speed of two inches per minute. The force required to pull 
out each one inch bonded length of fiber was recorded.

EXAMPLE I 
Ten parts process oil (Shellflex 371N) and 0.5 parts trionylphenyl 
phosphite oxidant were blended with 20 parts Stereon 840A at 325.degree. 
F. When the blend was homogeneous, 20 additional parts oil were added 
followed by 50 parts Permalyn 105, a pentaerythritol ester of rosin 
tackifier. The resulting pressure sensitive adhesive was designated 
Adhesive A. 
The adhesive was compared, using the tests described above, with a 
tackifying resin fortified atactic polypropylene adhesive presently 
employed in the commercial production of reinforced tapes. 
The peel strength of Adhesive A was 3.5 pounds per linear inch per mil of 
adhesive compared with 2.9 pounds for the atactic polypropylene. The fiber 
retention test gave a strength value of 8.0 pounds per linear inch for 
Adhesive A contrasted with 6.2 pounds for the atactic polypropylene. 
In a similar manner, other adhesives can be prepared utilizing, for 
example, Kraton G 1652, Kraton 1102. Kraton 1101, and Kraton 1650 as well 
as a variety of other tackifying resins. In all cases, the resultant 
adhesives should be useful in prepared fiber reinforced gummed tape 
laminates characterized by superior tensile strength property. 
Now that the preferred embodiments of the present invention have been 
described in detail, various modifications and improvements thereon will 
become readily apparent to those skilled in the art. Accordingly, the 
spirit and scope of the present invention is to be limited only by 
appended claims, and not by the foregoing disclosure.