Adhesive tape

An adhesive tape is provided which comprises a base paper material having a thickness of 30 to 150 g/m.sup.2, a film of high density polyethylene having a density of not less than 0.94 g/cc elongated at least six times only transversely to the longitudinal direction of the tape and having a thickness of 15 to 30.mu., said elongated film being attached to one side of said base paper material with a first layer of low density polyethylene of a thickness of 7 to 50.mu. being extruded between the base paper material and the elongated film, a second layer of low density polyethylene of a thickness of 7 to 50.mu. being extruded and attached to said elongated film so that the elongated film is sandwiched between the first and second layers of low density polyethylene, and a layer of pressure sensitive adhesive applied to the other side of said base paper material. The adhesive tape has a high tensile strength against a force applied in a direction transverse to the longitudinal direction of the tape. Nevertheless, the tape can be easily torn or cut by user's hand or hands exactly transversely to the longitudinal direction of the tape without being torn zigzag or in a slanting direction.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to an adhesive tape, and more particularly to an 
adhesive tape which may be conveniently used as a sealing tape for 
containers made of, for example, corrugated cardboard. 
2. Prior Art 
An adhesive tape for sealing, for example corrugated cardboard containers 
has been known in which paper, fabrics, a polypropylene film or a 
polyvinyl chloride film is used as a substrate, a pressure sensitive 
adhesive being applied to one side or both sides of the substrate. The 
adhesive sealing tape of the type in which paper is used as a substrate is 
not strong enough to seal containers filled with relatively heavy 
contents. Accordingly, a reinforced paper backed with various plastic 
films or fabrics has been used as a substrate material. However, the 
reinforced paper adhesive tape has drawbacks that it is quite difficult to 
cut by hand or hands and even if it can, the tape has a tendency to cut 
zigzag or in a slanting direction. Therefore, one has to utilize a special 
cutting device, which results in inefficient packing operation. In 
addition, when a reinforcing plastic film or fabric is adhered to the 
substrate paper, it is generally required to use a special adhesive or 
primer due to weak affinity between the reinforcing material and the 
substrate paper. Consequently, complicate steps for applying adhesives and 
for recovering solvents are necessarily involved for the production of 
such reinforced paper adhesive tape. In the meanwhile, the adhesive 
sealing tape of the type in which a polypropylene film or a polyvinyl film 
is used as a substrate, has inferior properties at low temperature such as 
brittleness. Furthermore, polyethylene or polyvinylchloride has large 
stiffness as shown by bending test as well as large coefficient of tensile 
elasticity at an elongation of 5%. Hence, when the tape comprising a film 
of these materials is used for sealing packages containing cold contents 
such as frozen food or used under low temperatures, the bent portions of 
the tape tends to stretch so that the tape gets turned or tucks up and 
peels off out of the packages. 
OBJECTS AND SUMMARY OF THE INVENTION 
It is an object of the present invention to provide an adhesive tape which 
can be easily cut by user's hand or hands exactly in a transverse 
direction to the longitudinal direction of the tape and which nevertheless 
has a high tensile strength against a force applied in the same direction. 
It is another object of the present invention to provide an adhesive tape 
having an outermost layer on which surface the tape can be adhered or 
applied so as to overlap one upon another. 
It is still another object of the present invention to provide an adhesive 
tape provided with an outermost layer which surface has appropriate 
releasing properties and frictional properties. 
It is yet another object of the present invention to provide an adhesive 
tape having an outermost layer on which markings such as figures or 
letters can be applied. 
It is a further object of the present invention to provide an adhesive tape 
which is cheap and therefore can be widely used. 
It is a further object of the invention to provide an adhesive tape which 
can be produced in a simple manner. 
It is a still further object of the invention to provide an adhesive tape 
which has excellent coldproof properties. 
These and other objects of the invention will become apparent with 
reference to the following description. 
An adhesive tape of the invention comprises a base paper material having a 
thickness of 30 to 150 g/m.sup.2, a film of high density polyethylene 
having a density of not less than 0.94 g/cc elongated at least six times 
only transversely to the longitudinal direction of the tape and having a 
thickness of 15 to 30.mu., said elongated film being attached to one side 
of said base paper material with a first layer of low density polyethylene 
of a thickness of 7 to 50.mu. being extruded between the base paper 
material and the elongated film, a second layer of low density 
polyethylene of a thickness of 7 to 50 .mu. being extruded and attached to 
said elongated film so that the elongated film is sandwiched between the 
first and second layers of low density polyethylene, and a layer of 
pressure sensitive adhesive applied to the other side of said base paper 
material.

DESCRIPTION OF THE INVENTION 
Referring to FIG. 1, an adhesive tape of rolled type is generally indicated 
by reference numeral 10. It is, however, to be understood that the 
adhesive tape according to the invention is not limited only to the rolled 
type. In FIG. 2, an adhesive tape 20 comprises a base paper material 21, a 
film of high density polyethylene 22, a first layer 23 of low density 
polyethylene, a second layer 24 of low density polyethylene and a layer 25 
of pressure sensitive adhesive. 
In the adhesive tape of the invention it is of great importance that a film 
of high density polyethylene having a density of not less than 0.94 g/cc 
elongated at least six times, preferably ten times only transversely to 
the longitudinal direction of the tape be used. In this connection, it is 
to be noted that "transversely or a transverse direction" herein referred 
to means a direction a shown by an arrow in FIG. 1, whereas 
"longitudinally or a longitudinal direction" herein referred to means a 
direction b denoted by an arrow in FIG. 1 which crosses at a right angle 
with the arrow a. The reason why a high density polyethylene film of not 
less than 0.94 g/cc is used according to the invention is that a high 
strength against a transversely applied force is provided and that this 
characteristic does not disappear even at low temperatures. That is, the 
adhesive tape of high density polyethylene of not less than 0.94 g/cc has 
a stiffness of 8 to 16 g and a coefficient of tensile elasticity at an 
elongation of 5% of less than 90 kg/mm.sup.2. Therefore, such tape will 
not become brittle nor hardened under cold atmosphere so as to be 
intimately and yet firmly adhered to surfaces to be applied even to bent 
portions such as corners of a container. When a polyethylene film having a 
density of less than 0.94 g/cc is used, the advantages above mentioned 
cannot be obtained. 
Furthermore, when the aforementioned high density polyethylene film is 
elongated only transversely not less than six times, the elongated film 
has an improved tensile strength against a force applied in a transverse 
direction and at the same time a lowered tear strength against a force 
applied in the same direction. Accordingly, the adhesive tape comprising 
such polyethylene film can be easily torn or cut by user's hand or hands 
exactly transversely without using cutters. Nevertheless, the tape retains 
a high tensile strength so that even when a transverse stress acts on the 
tape, it will not break or peel off. If the high density polyethylene film 
is elongated not less than ten times, the characteristic properties as set 
forth can be further enhanced. However, it is not possible to produce an 
effective elongated film at an elongation above sixteen times. 
An adhesive tape having a density of less than 0.94 g/cc and/or elongated 
below six times in a transverse direction has not only insufficient 
transverse tensile strength but also high tear strength. Such tape, 
therefore, has to be cut by cutting devices. Still worse, when a 
transverse force is applied to the tape, it will easily split in a 
longitudinal direction. 
The film 22 of high density polyethylene has a thickness of 15 to 30.mu.. 
In a thickness of less than 15.mu., a predetermined strength cannot be 
obtained. On the contrary, above 30.mu., the film losses its flexibility. 
Accordingly, the adhesive tape cannot adhere intimately onto concaved or 
convexed surfaces to be applied. Particularly, when the tape is applied to 
corners of a container, it will peel off due to high restorable 
properties. 
In producing the film 22 of high density polyethylene, polyethylene of a 
density of not less than 0.94 g/cc is subjected to extrusion molding by 
means of an extruder equipped with a flat die and thereafter to elongation 
treatment at least six times in a transverse direction by means of, for 
example an elongating machine of tenter type. 
When producing the laminated adhesive tape 20 shown in FIG. 2, the 
following procedures may be conveniently used. 
Between the film 22 of high density polyethylene produced in the manner as 
hereinabove described and the base paper material 21, a first layer 23 of 
low density polyethylene which serves as an adhesive is extruded through 
an extruder in the known manners and conditions so that the layer 23 is 
sandwiched between the paper material 21 and the film 22. While passing 
through laminate rollers, the three layers 21, 22, 23 are adhered one 
another under pressure to form a three-layer laminate sheet 26. The second 
layer 24 of low density polyethylene is then extruded through another 
extruder in the known manners and conditions and adhered onto the surface 
27 of the sheet 26 while passing through laminate rollers to form a 
four-layer laminate sheet 28. Finally, the layer 25 of pressure sensitive 
adhesive is applied to the base paper material 21. 
As the base paper material, kraft paper such as clupak kraft paper may 
preferably be used although any other paper known in the art can be 
utilized. The thickness of the paper may be between 30 and 150 g/m.sup.2, 
preferably 40 and 100 g/m.sup.2. 
Commercially available low density polyethylene may be conveniently 
utilized for materials of the first and second layers 23 and 24. The first 
layer 23 functions as an adhesive for the paper material 21 and a film 22 
of high density polyethylene and may have a thickness of 7 to 50.mu., 
preferably 10 to 35.mu.. The second layer 24 forms an outermost layer of 
the adhesive tape 20 according to the invention. Since low density 
polyethylene is used, the outermost or second layer 24 has appropriate 
releasing properties. Hence, when the tape is in the form of a roll as 
shown in FIG. 1, the tape 20 can be easily peeled off from the roll 10. 
Nevertheless, the tape may be applied or adhered by overlapping one upon 
another since the second layer 24 has also appropriate adhering 
properties. Therefore, containers can be firmly sealed. Furthermore, the 
layer 24 has proper frictional properties so that when applied to 
containers, they may be stacked without the danger of being fallen down. 
In addition, if desired, markings such as figures or letters may be 
applied to the outer surface of the second layer 24. The second layer 24 
may have a thickness of 7 to 50.mu., preferably 10 to 35.mu.. 
The pressure sensitive adhesive 25 which is used according to the invention 
includes a solvent type such as rubber system or acryl system, an emulsion 
type such as acryl system or vinylacetate system and a hot-melting type 
such as EVA systems (ethylenevinyl acetate system), rubber system or 
rubber polyamide resin system. The adhesive may be directly applied to the 
base paper material 21 whether the solvent type or emulsion type adhesive 
may be used if applied at a temperature below 120.degree. C. In case of 
adhesive which cannot be adhered above 120.degree. C., the transferring 
method can preferably be used whether the adhesive is of the solvent type, 
the emulsion type or of the hot-melting type above referred to. Of the 
hot-melting type adhesives, the rubber system consisting of the following 
commercially available products may be preferred; 
______________________________________ 
Cariflex TR 110 7 
(Shell Chemical) 
Polybutene LV-100 
(Nisseki Resin Chemical) 
Arkon M 100 (Arakawa Rinsan Chemical) 
Shellflex 371 (Shell Chemical) 
Anti-Oxidant BZ (Ouchishinkoh Chemical) 
______________________________________ 
The acryl system of the emulsion type adhesive such as sold under the trade 
name "Nikasol TS TB 3" by Nippon Garbide Kogyo K.K. including polyacrylate 
system may be most preferably used, utilizing the transferring method. The 
thickness of the pressure sensitive adhesive layer 25 may preferably be 
between 5.mu. and 200.mu.. 
The adhesive tape according to the invention may be used for teaching 
materials such as coloured paper if the base paper material 21 is coloured 
while the first and second layers 23, 24 and the film 22 are transparent 
or translucent or if the base paper material 21 is white while the film 22 
is coloured. In any form, pigments are not exposed on the surface so that 
the adhesive tape or modified coloured paper is suitable for children's 
use from sanitary standpoint of view. The adhesive tape can also be 
utilized for labels if the base paper material 21 is printed to form 
patterns, figures, letters or a combination thereof on its surface. 
THE EXAMPLES OF THE INVENTION 
EXAMPLE 1 
High density polyethylene having a density of 0.94 g/cc was extruded 
through a flat die and then elongated transversely eight times by means of 
an elongating machine of the tender type to obtain a film having a 
thickness of 18.mu.. 
The film thus obtained was adhered to a base paper material with a layer of 
low density polyethylene (0.918 g/cc) having a thickness of 20.mu. being 
sandwiched between the base paper material and the film and laminated by 
rollers to obtain a three-layer laminate sheet. As the base paper 
material, clupak kraft paper having a weight per m.sup.2 of 78 g/m.sup.2 
was used. 
A layer of low density polyethylene (0.918 g/cc) having a thickness of 
20.mu. was extruded and adhered onto the high density polyethylene film of 
the three-layer laminate sheet to obtain a four-layer laminate sheet. 
Then on the paper material of the four-layer laminate sheet a pressure 
sensitive adhesive was applied by means of the transferring method to have 
a thickness of 80 g/m.sup.2 and dried at 135.degree. to 160.degree. C. The 
tapes obtained was wound up to form a roll and cut to have a width of 
50mm. As the pressure sensitive adhesive, the acryl system of the emulsion 
type adhesive having the following composition was used: 
______________________________________ 
Parts by wt. 
______________________________________ 
50% solution of polyacrylate emulsion 
100 
Cumarone resin 5 
Ester gum 5 
Benzohexatoluene 2 
______________________________________ 
The adhesive tapes thus obtained were subjected to various experiments. The 
result is given in Table I. 
Table I 
__________________________________________________________________________ 
The adhesive 
Known Known reinforced 
Known 
tape according 
kraft adhesive 
paper adhesive 
fabric adhesive 
Test to the invention 
tape tape tape 
__________________________________________________________________________ 
Temperature 
20 -20 20 20 20 
(.degree.C.) 
Transverse 
tensile 
strength 
13.1 
13.9 
4.7 6.8 7.8 
(kg/10mm 
in width) 
Transverse 
elongation 
19.0 
15.0 
5.0 10.9 6.8 
(%) 
Transverse 
tear strength 
300 313 280 550 720 
(g) 
The conditions 
of cut edges 
Good 
Good 
Poor Poor Good 
__________________________________________________________________________ 
In the experiments in Table I, the transverse tensile strength and the 
transverse elongation were determined according to Japanese Industrial 
Standard (Hereinafter referred to as JIS)Z-1523. The transverse tear 
strength was determined according to JIS L-1004. The conditions of cut 
edges were determined by observing the edges of the tapes torn at a rate 
of 30 m/mm, each tape having had a notch of 3mm in a transverse direction 
from the edge. "Good" means that the tape was torn exactly transversely, 
whereas "Poor" means that the tape was almost not torn transversely. 
For the purpose of comparison, a kraft adhesive tape, a reinforced paper 
adhesive tape and a fabric adhesive tape commercially available under 
trade names "Nittoch Kraft Tape 7100", "Krapack 7150" and "Nittoh Nuno 
Tape" (Each produced by Nittoh Denki Kogyo K.K.), respectively were used. 
From Table I it can be seen that the adhesive tape of the invention has 
transverse tensile strength several times as strong as the known kraft 
adhesive tape. Furthermore, the paper adhesive tape of the invention has 
larger transverse tensile strength than the known reinforced paper 
adhesive tape which are used for sealing containers containing heavy 
contents. The transverse tear strength of the paper adhesive tape 
according to the invention can be torn exactly in a transverse direction 
with a force almost equal to that required for the kraft adhesive tape of 
the known type. In addition, the strengths at room temperature are almost 
the same as those at -20.degree. C. 
EXAMPLE 2 
The adhesive tapes were made in the same manner as in Example 1 except that 
the high density polyethylene films were elongated at various 
magnification. 
The result is given in Table II. 
Table II 
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Magnification 
Transverse Transverse The 
of transverse 
tensile strength 
tear conditions of 
elongation 
(kg/10mm in width) 
strength cut edges 
______________________________________ 
0 5.4 535 Poor 
4 6.7 585 * 
6 9.8 317 Good 
8 11.7 292 " 
10 12.9 298 " 
12 13.2 282 " 
14 13.9 288 " 
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Note: 
* 10% of the test samples were not torn in a transverse direction. The 
conditions of the cut edges were determined in accordance with Example 1. 
As shown in Table II, with a magnification of transverse elongation of not 
less than six, satisfactory results are obtained. 
Further experiments were effected using the same adhesive tapes. However, 
the thickness of the high density polyethylene film was varied. The result 
is shown in Table III. 
Table III 
______________________________________ 
Transverse tensile strength (kg/10mm in width) 
Magnification of 
Thickness 
tensile 
(mm) elongation 6 8 10 12 
______________________________________ 
0.008 5.5 6.0 6.2 -- 
0.010 6.8 7.7 7.9 8.4 
0.020 9.8 11.7 12.9 13.7 
0.030 9.7 12.5 12.7 14.4 
0.040 10.4 14.1 14.9 16.4 
0.060 11.2 15.4 16.2 17.7 
______________________________________ 
Note: The tensile strength was determined according to JIS Z1523. 
With the adhesive tape comprising a film of a thickness of less than 
0.010mm, a satisfactory transverse tensile strength was not obtained. On 
the other hand, with the adhesive tape having a film of a thickness of 
more than 0.050mm, favourable flexibility was not attained. 
EXAMPLE 3 
The adhesive tapes each having a width of 50mm were made in the same manner 
as in Example 1. The adhesive tapes were applied to a whole upper surface 
(41.times. 43 cm) of a corrugated cardboard container having a height of 
25 cm. To a whole bottom surface (41.times. 43 cm) of another container of 
the same size and material, the adhesive tapes were applied. The two 
containers were stacked so that the upper surface contacts with the bottom 
surface. Each container was loaded to weigh 25 kg. 
The two vertically stacked containers were inclined gradually and the 
angles at which the upper stacked container starts to slide down were 
measured. The result is given in Table IV. 
Table IV 
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Tape applied Angle (.degree.) 
______________________________________ 
Without tape 32.6 
Known Kraft 
adhesive tape 9.4 
Known fabric 
adhesive tape 27.4 
Adhesive tape 
of the Invention 31.9 
______________________________________ 
Note: Known Kraft adhesive tape and fabric adhesive tape are the same as 
used in Example 1. 
From Table IV it will be understood that the adhesive tapes of the 
invention have good frictional properties. 
EXAMPLE 4 
An adhesive tape having no second layer of low density polyethylene was 
made for the purpose of the comparison as follows: 
High density polyethylene having a density of 0.96 g/cc was extruded 
through a flat die and then elongated transversely ten times by means of 
an elongating machine of the tenter type to obtain a film having a 
thickness of 20.mu.. 
The film thus obtained was adhered to a bass paper material with a layer of 
low density polyethylene having a thickness of 15.mu. being sandwiched 
between the base paper material and the film and laminated by rollers. As 
the base paper material, clupak kraft paper having a weight per m.sup.2 of 
73 g/m.sup.2 was used. 
Then on the other side of the paper material a pressure sensitive adhesive 
was applied by means of a coating machine to have thickness of 40.mu. and 
dried at 110.degree. to 130.degree. C. The tapes thus obtained was wound 
up to form a roll and cut to have a width of 10 mm. The pressure sensitive 
adhesive has the following compositions: 
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Natural rubber - MMA-AN graftpolymer 
4.1 parts 
by wt. 
Terpene resin 1.8 parts 
by wt. 
Zinc white 0.15 parts 
by wt. 
Trimethylthiuram disulfide 
0.06 parts 
by wt. 
Toluene 6.0 parts 
by wt. 
______________________________________ 
The adhesive tapes of the invention were made in the same manner as in 
Example 1 except that the roll was cut to have a width of 10 mm. 
The strengths required for peeling the tapes off the rolls were measured. 
The result is given in Table V. 
Table V 
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Tape Strength for peeling (g) 
______________________________________ 
Com. Ex. Impossible to peel off 
Tape according 220 
to the Invention 
______________________________________ 
From Table V it will be noted that the adhesive tapes of the present 
invention have appropriate releasing properties. 
Although the present invention has been described with reference to 
preferred embodiments and examples, various modifications and variations 
can be made without departing from the spirit of the invention. It is 
intended that all these modifications and variations be included.