Multi-layer plastic fuel tank

A multi-layer plastic fuel tank comprising (A) a gas barrier layer having on at least one side thereof (B) an adhesive layer and further thereon (C) a high-density polyethylene layer, the gas barrier layer (A) comprising a resin having gas barrier properties, the adhesive layer (B) comprising a resin having adhesiveness to both of the gas barrier layer (A) and the high-density polyethylene layer (C), the high-density polyethylene layer (C) comprising high-density polyethylene having an intrinsic viscosity of from 2 to 6 dl/g, a density of from 0.940 to 0.970 g/cm.sup.2, and a zero shear viscosity of from 2.0.times.10.sup.7 to 1.0.times.10.sup.8 poise at 190.degree. C.

FIELD OF THE INVENTION 
The present invention relates to a multi-layer plastic fuel tank and more 
particularly a multi-layer plastic fuel tank which exhibits satisfactory 
gasoline barrier properties and which can be recycled. 
BACKGROUND OF THE INVENTION 
In the field of automobile industry, application of plastics (synthetic 
resins) to various automotive parts has been eagerly studied with the 
recent tendencies toward weight reduction and energy saving. Polyolefin 
resins have generally been used as plastic materials for their cheapness, 
high strength, weather resistance and chemical resistance. 
High-molecular weight and high-density polyethylene has been proposed as a 
plastic material for a fuel tank, but it was reported that its gas barrier 
properties are not always sufficient so that gasoline evaporates to 
pollute the environment. 
A multi-layer container with improved gas barrier properties has been 
proposed in JP-B-61-42625, which is composed of a modified nylon resin 
layer having laminated on one side thereof a polyolefin resin layer via an 
adhesive layer. (The term "JP-B" as used herein means an "examined 
Japanese patent publication".) The modified nylon resin layer comprises 
nylon and a molten mixture of a modified copolymer having a maleic 
anhydride content of from 0.05 to 1% by weight prepared by grafting maleic 
anhydride to an ethylene-.alpha.-olefin copolymer having a degree of 
crystallinity of from 1 to 35% and a melt index of from 0.01 to 50 g/10 
min. The adhesive layer comprises a modified copolymer having a maleic 
anhydride content of from 0.01 to 1% by weight prepared by grafting maleic 
anhydride to an ethylene-.alpha.-olefin copolymer having a degree of 
crystallinity of from 2 to 30% and a melt index of from 0.01 to 50 g/10 
min. 
The polyolefin resin layer used in the above-mentioned multi-layer 
container specifically includes "Novatec BR300", a registered trade name 
of Mitsubishi Chemical Corp., which is high-density polyethylene having a 
zero shear viscosity of 1.25.times.10.sup.7 poise at 190.degree. C. 
However, the multi-layer container using high-density polyethylene having a 
zero shear viscosity of 1.25.times.10.sup.7 poise at 190.degree. C. as a 
polyolefin resin layer has a disadvantage of poor Izod impact strength 
particularly at low temperatures. Moreover, thin-walled parts are apt to 
be occur in the upper portion of the multi-layer container due to its poor 
resistance to drawdown, and the polyolefin resin layer is apt to become 
non-uniform due to poor uniform melt ductility. 
Recycling of molding flash or salvaged material has been considered for 
cost reduction of plastic fuel tanks. However, reuse of the flash or 
salvaged material of conventional multi-layer plastic fuel tanks involves 
a problem that the resulting fuel tanks have reduced impact resistance. 
In order to improve impact resistance, it has been suggested to knead 
high-density polyethylene and a part or the whole of salvaged multi-layer 
plastic fuel tanks (20 to 200 parts by weight per 100 parts by weight of 
the high-density polyethylene) in an extruder having an L/D ratio of 20 or 
more and a specially shaped screw at an extruding temperature of 
200.degree. to 250.degree. C., as described in JP-A-4-47918. (The term 
"JP-A" as used herein means an "unexamined published Japanese patent 
application"). 
The above-described process, however, requires to control the kneading 
temperature and to employ a specially shaped screw in a kneading machine. 
Further, it is difficult to produce a fuel tank retaining superiority in 
all aspects of barrier properties, impact resistance, weather resistance, 
and chemical resistance. Furthermore, it is not expected to inhibit 
reduction in impact resistance due to reuse of molding flash or salvaged 
material. 
The present invention has been accomplished in the light of the 
above-described circumstances. 
SUMMARY OF THE INVENTION 
An object of the present invention is to provide a multi-layer plastic fuel 
tank which exhibits satisfactory gasoline barrier properties and which can 
be recycled without relying on a special kneading or molding technique to 
produce fuel tanks while inhibiting a reduction in impact resistance. 
Other objects and effects of the present invention will be apparent from 
the following description. 
The present invention relates to a multi-layer plastic fuel tank comprising 
(A) a gas barrier layer having on at least one side thereof (B) an 
adhesive layer and further thereon (C) a high-density polyethylene layer, 
the gas barrier layer (A) comprising a resin having gas barrier properties, 
the adhesive layer (B) comprising a resin having adhesiveness to both of 
the gas barrier layer (A) and the high-density polyethylene layer (C), 
the high-density polyethylene layer (C) comprising high-density 
polyethylene having an intrinsic viscosity of from 2 to 6 dl/g, a density 
of from 0.940 to 0.970 g/cm.sup.3, and a zero shear viscosity of from 
2.0.times.10.sup.7 to 1.0.times.10.sup.8 poise at 190.degree. C. 
DETAILED DESCRIPTION OF THE INVENTION 
The multi-layer plastic fuel tank according to the present invention 
(hereinafter sometimes referred to as multi-layer fuel tank) comprises gas 
barrier layer (A) having laminated on at least one side thereof 
high-density polyethylene layer (C) via adhesive layer (B). 
The gas barrier layer (A) will be described in detail below. 
Resins with gas barrier properties are used in gas barrier layer (A). 
Examples thereof include a modified polyamide composition comprising a 
mixture of (1) an .alpha.,.beta.-unsaturated carboxylic acid-modified 
ethylene-.alpha.-olefin copolymer prepared by grafting an 
.alpha.,.beta.-unsaturated carboxylic acid or a derivative thereof to an 
ethylene-.alpha.-olefin copolymer at a grafting ratio of from 0.05 to 1% 
by weight, preferably from 0.2 to 0.6% by weight, based on the 
ethylene-.alpha.-olefin copolymer and (2) a polyamide. The 
ethylene-.alpha.-olefin copolymer, preferably has a degree of 
crystallinity of from 1 to 35%, more preferably from 1 to 30%, and a melt 
index of from 0.01 to 50 g/10 min, more preferably from 0.1 to 20 g/10 
min. Examples of the the .alpha.,.beta.-unsaturated carboxylic acid or a 
derivative thereof include monocarboxylic acids, such as acrylic acid and 
methacrylic acid, their derivatives, dicarboxylic acids, such as maleic 
acid, fumaric acid and citraconic acid, and their derivatives. Preferred 
examples of the .alpha.,.beta.-unsaturated carboxylic acid or a derivative 
thereof include maleic anhydride. 
The modified polyamide composition will be further described below in 
greater detail. 
Examples of the .alpha.-olefins in the ethylene-.alpha.-olefin copolymer 
(1) include propylene, butene-1, hexene-1, etc. The .alpha.-olefin is 
generally copolymerized with ethylene at a ratio of not more than 30% by 
weight, and preferably from 5 to 20% by weight, based on the total amount 
of the copolymer. 
The polyamide (2) generally has a relative viscosity of from about 1 to 6. 
Examples of the polyamide includes polyamide obtained by polycondensation 
of a diamine and a dicarboxylic acid, polyamide obtained by 
polycondensation of an aminocarboxylic acid, polyamide obtained by 
polycondensation of a lactam, and copolyamide thereof. 
Examples of the diamine includes aliphatic, alicyclic or aromatic diamines, 
such as hexamethylenediamine, decamethylenediamine, 
dodecamethylenediamine, trimethylhexamethylenediamine, 
1,3-bis(aminomethyl)cyclohexane, 1,4-bis(aminomethyl)cyclohexane, 
bis(p-aminocyclohexylmethane), m-xylylenediamine, and p-xylylenediamine. 
Examples of the dicarboxylic acid includes aliphatic, alicyclic or 
aromatic dicarboxylic acids, such as adipic acid, suberic acid, sebacic 
acid, cyclohexanedicarboxylic acid, terephthalic acid, and isophthalic 
acid. Examples of the aminocarboxylic acid includes .epsilon.-aminocaproic 
acid and 11-aminoundecanoic acid. Examples of the lactam includes 
.epsilon.-caprolactam and .epsilon.-laurolactam. 
Specific examples of the polyamide include nylon 6, nylon 66, nylon 610, 
nylon 9, nylon 11, nylon 12, nylon 6/66, nylon 66/610, and nylon 6/11. 
From the standpoint of moldability, a polyamide having a melting point of 
from 170.degree. to 280.degree. C., and particularly from 200.degree. to 
240.degree. C., is preferred. Nylon 6 is particularly preferred. 
The .alpha.,.beta.-unsaturated carboxylic acid-modified 
ethylene-.alpha.-olefin copolymer is generally mixed with the polyamide in 
an amount of from 10 to 50 parts by weight, and preferably from 10 to 30 
parts by weight, per 100 parts by weight of the polyamide. 
While the method of mixing is not particularly restricted, it is preferred 
to knead them in an extruder, etc. at a temperature of from 200.degree. to 
280.degree. C. 
The adhesive layer (B) will be described in detail below. 
The adhesive layer (B) comprises a resin having adhesiveness to both of the 
gas barrier layer (A) and the high-density polyethylene layer (C). 
Examples of the resin used in the adhesive layer (B) include a modified 
polyethylene prepared by grafting an unsaturated carboxylic acid or a 
derivative thereof to high-density polyethylene, preferably at a grafting 
ratio of from 0.01 to 1% by weight based on the high-density polyethylene. 
The modified polyethylene will be further described in detail below. 
High-density polyethylene having a density of from 0.940 to 0.970 
g/cm.sup.3 is preferably used in the above-mentioned modified 
polyethylene. Examples of the high-density polyethylene includes an 
ethylene homopolymer and a copolymer of ethylene and not more than 3% by 
weight, preferably from 0.05 to 0.5% by weight, of an .alpha.-olefin. 
Examples of the .alpha.-olefin includes propylene, butene-1, hexene-1, 
etc. Examples of the unsaturated carboxylic acid or a derivative thereof 
includes acrylic acid, methacrylic acid, maleic acid, fumaric acid, 
itaconic acid, citraconic acid, and an anhydride thereof, with maleic 
anhydride being particularly preferred. The amount of the unsaturated 
carboxylic acid or a derivative thereof to be grafted is preferably from 
0.02 to 0.06% by weight. 
The high-density polyethylene layer (C) will be described in detail below. 
The high-density polyethylene layer (C) comprises high-density polyethylene 
having an intrinsic viscosity of from 2 to 6 dl/g, preferably from 2.3 to 
5.5 dl/g, a density of from 0.940 to 0.970 g/cm.sup.3, preferably from 
0.950 to 0.965 g/cm.sup.3, and a zero shear viscosity of from 
2.0.times.10.sup.7 to 1.0.times.10.sup.8 poise, preferably from 
2.5.times.10.sup.7 to 9.0.times.10.sup.7 poise, at 190.degree. C. 
Examples of the high-density polyethylene include those of various species 
prepared by known processes, such as an ethylene homopolymer and a 
copolymer of ethylene and not more than 3% by weight, preferably from 0.05 
to 0.5% by weight, of an .alpha.-olefin. Examples of the .alpha.-olefin 
includes propylene, butene-1, hexane-1, etc. 
If the intrinsic viscosity or zero shear viscosity of the high-density 
polyethylene deviates from the above-specified respective range, molding 
properties, such as resistance to drawdown and uniform melt ductility, and 
impact resistance would be reduced. 
If desired, the high-density polyethylene layer may contain additives, such 
as pigments and thermal stabilizers, in an amount of not more than 1 part 
by weight per 100 parts by weight of the high-density polyethylene. 
The multi-layer fuel tank according to the present invention will be 
described in detail below. 
The multi-layer plastic fuel tank of the present invention comprises the 
gas barrier layer (A) having laminated on at least one side thereof 
high-density polyethylene layer (C) via adhesive layer (B). In particular, 
a 5-layered structure comprising 3 kinds of layers, in which gas barrier 
layer (A) has on both sides thereof high-density polyethylene layer (C) 
via adhesive layer (B), is preferred. 
In designing the multi-layer fuel tank of the present invention, the 
thickness of the gas barrier layer (A) is generally from 0.01 to 0.5 mm, 
preferably from 0.1 to 0.3 mm; that of adhesive layer (B) is generally 
from 0.01 to 0.5 mm, preferably from 0.1 to 0.3 mm; and that of 
high-density polyethylene layer (C) is generally from 1 to 10 mm, 
preferably from 1.5 to 5 mm. 
The multi-layer fuel tank of the present invention can be produced by a 
known blow molding method. 
For example, resins for each layer are separately plasticized in a 
plurality of extruders, introduced into the same die having concentric 
ring flow paths, laminated in the die while levelling each thickness to 
prepare an apparently one-layered parison. The parison is inflated in a 
mold by application of inner pressure of air to be brought into intimate 
contact with the mold and, at the same time, cooled to produce a 
multi-layer fuel tank. 
In the production of the multi-layer fuel tank, the molding flash resulting 
from the molding of the tank and/or salvaged fuel tanks may be reused as a 
part of the molding material. The flash or salvaged material is generally 
ground in a polymer grinder to particles or powder and mixed with pellets 
of the high-density polyethylene used for the high-density polyethylene 
layer (C). The mixing ratio of the flash or salvaged material is 
preferably not more than about 60 parts by weight, more preferably not 
more than 40 parts by weight, per 100 parts by weight of the high-density 
polyethylene. It is also preferred to dry the flash and salvaged material 
prior to mixing. 
The multi-layer fuel tank of the present invention, even when produced by 
reusing the molding flash and/or salvaged material, exhibits satisfactory 
adhesion between the high-density polyethylene layer and the gas barrier 
layer and undergoes no reduction in strength of the high-density 
polyethylene layer. 
The multi-layer fuel tank according to the present invention exhibits 
excellent gasoline barrier properties and is therefore suitable as a fuel 
tank, such as a gasoline tank. Even where molding flash resulting from the 
production step or salvaged tanks are mixed with the high-density 
polyethylene, fuel tanks with satisfactory impact resistance can be 
produced. 
The present invention will now be illustrated in greater detail by way of 
Examples, but the present invention is not limited thereto within the 
scope of the present invention. 
The raw materials used were as follows: 
(1) Hiqh-density polyethylene (HDPE): 
A: Ethylene-butene-1 copolymer (butene-1 content: 0.2 wt %); intrinsic 
viscosity: 2.41 dl/g; density: 0.953 g/cm.sup.3 ; zero shear viscosity: 
4.70.times.10.sup.7 poise 
B: Ethylene-butene-1 copolymer (butene-1 content: 0.18 wt %); intrinsic 
viscosity: 4.2 dl/g; density: 0.954 g/cm.sup.3 ; zero shear viscosity: 
4.48.times.10.sup.7 poise 
C: Ethylene-hexene-1 copolymer (hexene-1 content: 0.18 wt %); intrinsic 
viscosity: 5.3 dl/g; density: 0.954 g/cm.sup.3 ; zero shear viscosity: 
9.00.times.10.sup.7 poise 
D: Ethylene-hexene-1 copolymer (hexene-1 content: 0.2 wt %); intrinsic 
viscosity: 2.33 dl/g; density: 0.951 g/cm.sup.3 ; zero shear viscosity: 
1.47.times.10.sup.7 poise 
E: Novatec BR300 (a registered trade name of Mitsubishi Chemical Corp.); 
intrinsic viscosity: 2.80 dl/g; density: 0.947 g/cm.sup.3 ; zero shear 
viscosity: 1.25.times.10.sup.7 poise 
(2) Modified polyethylene (APO): 
F: Modified polyethylene prepared by grafting maleic anhydride (0.4 wt %) 
to high-density polyethylene having a density of 0.960 g/cm.sup.3 ; melt 
index (MI): 0.1 g/10 min 
(3) Modified polyamide composition (MPA): 
G: Modified polyamide composition prepared by mixing 80 parts by weight of 
nylon 6 having a relative viscosity of 4.0 and 20 parts by weight of an 
ethylene-butene-1 copolymer (butene-1 content: 13 mol %; degree of 
crystallinity: 20%; MI: 3.5 g/10 min) modified by 0.3 wt % of maleic 
anhydride 
(4) Polyamide (PA): 
H: Nylon 6 having a relative viscosity of 3.5 ("Novamid 1020" a registered 
trade name of Mitsubishi Chemical Corp.) 
The physical properties of the raw materials were measured according to the 
following methods: 
1) Intrinsic Viscosity (.eta.): 
Measured at 130.degree. C. in tetralin. 
2) Density: 
Measured in accordance with JIS K6760. 
3) Zero Shear Viscosity (.eta..sub.0): 
Stress rheometer "RSR-M" manufactured by Rheometrics Co. was used for 
measurement. This apparatus enables measurement of a melt shear viscosity 
in a low shear rate region from creep characteristics. 
In general, a shear viscosity of a molten polymer reaches a stationary 
value at a low shear rate (not more than 10.sup.3 sec.sup.-1) and becomes 
smaller as the shear rate increases. The term "zero shear viscosity 
(.eta..sub.0)" is the above-mentioned stationary value. 
The fixture was a cone-disc type having a diameter of 25 mm at an angle of 
0.1 rad between the cone and the disc. 
The test specimens were prepared by pressing pellets in a press molding 
machine into a sheet having a thickness of about 1 mm. The measuring 
temperature was 190.degree. C.

EXAMPLES 1 TO 3 AND COMATIVE EXAMPLES 1 TO 3 
Preparation of Multi-layer Fuel Tank: 
Multi-layer fuel tanks having the layer structure (5-ply laminate of 3 
kinds of layers) shown in Tables 2 and 3 below were prepared as follows. 
Resins for each layer as shown in Tables 2 and 3 were separately melted in 
the respective extruder, introduced into the same die with concentric ring 
flow paths, laminated in the die (die temperature: 235.degree. C.), and 
coextruded to form a molten tube (parison). 
The resulting parison was clamped in a mold (mold temperature: 20.degree. 
C.), and air was fed into the parison at a pressure of 6 kg/cm.sup.2 to 
obtain a 60 l-volume multi-layer fuel tank having the layer structure and 
layer thickness as shown in Table 2. 
The cylinder temperature in each extruder was as shown in Table 1. 
TABLE 1 
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High-density polyethylene (HDPE) 
185-215.degree. C. 
Modified polyethylene (APO) 
170-230.degree. C. 
Modified polyamide (MPA) 
240-245.degree. C. 
Polyamide (PA) 240-245.degree. C. 
______________________________________ 
TABLE 2 
______________________________________ 
Thickness 
Layer Resin (.mu.m) 
______________________________________ 
Outer HDPE layer 
HDPE 2,600 
Outer Adhesive layer 
APO 100 
Barrier layer MPA or PA 100 
Inner Adhesive layer 
APO 100 
Inner HDPE layer 
HDPE 2,600 
______________________________________ 
TABLE 3 
______________________________________ 
Example Comparative Example 
Layer 1 2 3 1 2 3 
______________________________________ 
Inner and 
HDPE HDPE HDPE HDPE HDPE HDPE 
Outer HDPE 
A B C D E A 
Layer 
Inner and 
APO APO APO APO APO APO 
Outer F F F F F F 
Adhesive 
Layer 
Barrier MPA MPA MPA MPA MPA PA 
Layer G G G G G H 
______________________________________ 
Where HDPE E was used as the high-density polyethylene layer, the extruded 
parison underwent drawdown while being clamped in a mold, which appeared 
as thin-walled part in the upper portion of the resulting molded article 
(fuel tank). Further, the high-density polyolefin layer had poor 
uniformity due to insufficient melt ductility. 
Strength Test of Multi-layer Fuel Tank: 
Each of the multi-layer fuel tanks produced in Examples 1 to 3 and 
Comparative Examples 1 to 3 was filled up with water or antifreeze. The 
tank was dropped from the height shown in Table 4 at the temperature shown 
in Table 4. The strength was evaluated by any crack produced. The results 
are shown in Table 4. 
TABLE 4 
__________________________________________________________________________ 
Temperature 
Example Comparative Example 
and height 
1 2 3 1 2 3 
__________________________________________________________________________ 
Room temp., 
no no no no no no 
16 m crack 
crack 
crack 
crack 
crack 
crack 
-40.degree. C., 6 m 
no no no no no no 
crack 
crack 
crack 
crack 
crack 
crack 
-40.degree. C., 9 m 
no no no no no no 
crack 
crack 
crack 
crack 
crack 
crack 
-40.degree. C., 16 m 
no no no cracked 
cracked 
cracked 
crack 
crack 
crack 
__________________________________________________________________________ 
EXAMPLES 4 AND 5 AND COMATIVE EXAMPLES 4 TO 6 
Each of the multi-layer fuel tanks produced in Examples 1 and 3 and 
Comparative Examples 1 to 3 was ground in a crusher having a punching 
plate hole diameter of 8 mm. The grinds were kneaded in a single-screw 
extruder or a twin-screw extruder under the conditions shown in Table 5 to 
obtain chips. A 60 l-volume 5-layered fuel tank comprising 3 kinds of 
layers was produced in the same manner as in Example 1, except that the 
high-density polyethylene layer was composed of the high-density 
polyethylene mixed with the resulting chips in an amount of 40% by weight 
based on the amount of the mixture. 
TABLE 5 
______________________________________ 
(1) Single-screw extruder: 
A product of Union Plastics K.K. ("30 .0.") 
L/D: 20; Compression ratio: 3.2 
Full-flighed screw 
Resin temperature: 240.degree. C. 
(2) Twin-screw extruder: 
A product of Japan Steel Works, Ltd. ("TEX44HCT") 
L/D: 24.5 
Kneading part: kneading disc 
Resin temperature: 240.degree. C. 
______________________________________ 
Strength Test of Multi-layer Fuel Tank: 
Each of the multi-layer fuel tanks produced in Examples 4 and 5 and 
Comparative Examples 4 to 6 was tested for its strength in the same manner 
as in Example 1. The results obtained are shown in Table 6. 
TABLE 6 
______________________________________ 
Comparative 
Temperature 
Example Example 
and height 
4 5 4 5 6 
______________________________________ 
Room temp., 
no no no no no 
16 m crack crack crack crack crack 
-40.degree. C., 6 m 
no no no no no 
crack crack crack crack crack 
-40.degree. C., 9 m 
no no no no cracked 
crack crack crack crack 
-40.degree. C., 12 m 
no no cracked 
cracked 
cracked 
crack crack 
______________________________________ 
Evaluation of Material Characteristics: 
In Examples 4 and 5 and Comparative Examples 4 to 6, the chips obtained 
were measured for a specific energy Esp in each extruder and the particle 
diameter of polyamide (NY). The results obtained are shown in Tables 7 and 
8. Further, the chips were pressed at 230.degree. C. to prepare an Izod 
test specimen, and an Izod strength was measured at 23.degree. C. or 
-40.degree. C. according to JIS K 7110. The results obtained are shown in 
Tables 7 and 8 together with an Izod strength retention with respect to an 
Izod test specimen comprising HDPE alone. 
TABLE 7 
______________________________________ 
(Single-Screw Extruder) 
Comparative 
Example Example 
4 5 4 5 6 
______________________________________ 
Specific Energy 
0.2 0.2 0.2 0.2 0.2 
Esp 
Particle Diameter 
25 25 30 30 30 
of NY (.mu.m) 
Izod Strength 
23 NB 22 14 20 
(23.degree. C.) 
Retention (%) 
100 100 100 100 87 
Izod Strength 
19 NB 6 8 12 
(-40.degree. C.) 
Retention (%) 
100 100 100 100 63 
______________________________________ 
Note: Specific energy EsP: kg .multidot. h/kw 
Izod strength: kg .multidot. cm/cm 
TABLE 8 
______________________________________ 
(Twin-Screw Extruder) 
Example 4 
______________________________________ 
Specific Energy Esp 
0.25 
Particle Diameter of 
20 
NY (.mu.m) 
Izod Strength (23.degree. C.) 
23 
Retention (%) 100 
Izod Strength (-40.degree. C.) 
19 
Retention (%) 100 
______________________________________ 
As described above, the present invention provides a multi-layer plastic 
fuel tank which exhibits satisfactory gasoline barrier properties and 
which can be recycled without requiring a special kneading or molding 
technique to produce fuel tanks while inhibiting a reduction in impact 
resistance. 
While the invention has been described in detail and with reference to 
specific examples thereof, it will be apparent to one skilled in the art 
that various changes and modifications can be made therein without 
departing from the spirit and scope thereof.