Material for packaging light-sensitive materials

A material for packaging light-sensitive materials composed of a composite sheet comprising a substrate coated with a middle layer(s) and a surface layer(s) is manufactured through melt co-extrusion, said surface layer(s) being of thermoplastic resins which have excellent heat seal properties yet have great neck-in, said middle layer(s) being of thermoplastic resins having small neck-in and excellent adhesion to a substrate, and any of layers of said composite sheet containing light-shielding material.

BACKGROUND 
The present invention relates to a material for packaging light-sensitive 
materials which deteriorate on exposure to light, in particular, to a 
material for packaging light-sensitive materials for photographic use. 
Heretofore, as the light-shielding paper for such packaging materials, for 
example as a backing sheet for photographic roll film, a composite sheet 
comprising a flexible substrate (a so-called "flexible sheet") such as 
paper coated with a thermoplastic resin layer has widely been used. A wide 
variety of resins have been used for the thermoplastic resin layer, all 
having both merits and demerits. 
For instance, low density polyethylene (hereinafter referred to as "LDPE") 
when used for the thermoplastic resin layer has the following demerits: 
various kinds of defects due to its insufficient flexibility tends to 
develop; heat seal temperature is high; no heat-sealability with a 
polystyrene spool for photographic film is obtained; when LDPE is 
heat-sealed with LDPE, heat-seal defects due to dusts, powders etc. (i.e. 
when powdery concomitants are present, heat-sealability is decreased) 
often occur; addition of a light-shielding material decreases strength of 
film and sealing strength. 
Similarly, to take the case of ethylene-vinyl acetate copolymer 
(hereinafter referred to as "EVA"), it has the following defects: water 
absorbability is too great; blocking tends to occur; carbon black is not 
uniformly dispersed; a substrate such as paper is not well adhered; 
neck-in is too great; film composed of EVA is not sharply and readily cut. 
Therefore, a composite sheet composed of a substrate coated with a single 
melt extruded EVA layer containing carbon black is not yet put to 
practical use as a light-shielding paper for the photographic roll film. 
In case that acrylic ester copolymer such as ethylene-ethylacrylate 
copolymer (hereinafter referred to as "EEA") is coated through melt 
extrusion, there also arise problems similar to those with the EVA coating 
such as too great neck-in, frequently occurring blocking, uneven 
dispersion of carbon black, poor adhesion to a substrate (Generally, EEA 
is inferior to LDPE) and a high cost. 
Consequently, most light-shielding paper has been manufactured by a process 
in which EVA is dissolved in a solvent and the resultant solution is 
coated to a substrate, which results in a high manufacturing cost. In case 
of EEA coating, the hot melt coating or the above-mentioned solution 
coating process has often been used for preparing a light-shielding paper 
for packaging powdered medicine or food such as chocolate, which leads to 
a high manufacturing cost. Since melt extrusion coating of EVA or EEA 
causes great neck-in and insufficient adhesion to a substrate, the 
solution coating process has been the only choice available. 
SUMMARY OF THE DISCLOSURE 
Accordingly, it is an object of the present invention to provide a novel 
and inexpensive material for packaging light-sensitive materials. 
It is another object of the present invention to provide a material for 
packaging light-sensitive materials having excellent heat seal properties 
and free from the above-mentioned disadvantages of the conventional 
products, especially such problems as insufficient adhesion to a substrate 
and too great neck-in. 
It is a further object of the present invention to provide a process for 
manufacturing a material for packaging light-sensitive materials having 
excellent heat seal properties and free from the above-mentioned drawbacks 
in the conventional products and manners. 
Still further objects of the present invention will become apparent in the 
following disclosure. 
Accordingly, the present invention provides a material for packaging 
light-sensitive materials composed of a composite sheet comprising a 
substrate coated with at least a middle layer and at least a surface layer 
through melt co-extrusion, said surface layer being of thermoplastic resin 
which has good heat seal properties yet has larger neck-in, said middle 
layer being of thermoplastic resin having small neck-in and good adhesion 
to a substrate, and one or more layers of said composite sheet containing 
light-shielding material. 
The present invention further provides a process for manufacturing the 
above-mentioned material for packaging light-sensitive materials by 
co-extruding and laminating said surface layer(s) and said middle layer(s) 
onto a substrate to form said composite sheet. 
Heretofore, since a single melt extrusion coating layer (surface layer, 
i.e., heat seal layer) has both merits and demerits, it has been 
impossible to remove the demerits alone from the surface layer. The 
present invention resolves the aforementioned problem by laminating a 
middle layer of a thermoplastic resin (B) having small neck-in and good 
adhesion to a substrate, together with a surface layer (a heat seal layer) 
onto a substrate through a melt co-extrusion process. In addition, the 
material of the present invention meets all the other requirements for the 
material for packaging light-sensitive materials. Requisite properties for 
a material for packaging light-sensitive materials are as follows: small 
neck-in required for manufacturing the above-mentioned laminated sheet, 
superb heat seal properties necessary for making envelopes or bags, good 
light-shielding properties, uniform dispersion of light-shielding 
materials, superior sealability at low temperatures, excellent sealability 
when powdery concomitants are present, good hot tack, superior ability of 
being sharply and readily cut by cutters and the like, superb 
anti-blocking, and good water or moisture proofness. Other requirements 
relating to the manufacturing cost are fast laminating speed and reduced 
cost for film materials which lead to a low overall manufacturing cost. As 
a material for packaging photographic roll film, heat seal properties with 
polystyrene in addition to flexibility are required when the packaging 
material is heat-sealed with a polystyrene spool. The material for 
packaging light-sensitive materials of the present invention meets all the 
above requirements and is of great practical use. 
The material for packaging light-sensitive materials of the present 
invention can be used for photographic light-sensitive materials, 
medicines, dyes, foods and the like which change or deteriorate their 
characteristics on exposure to light. Especially it is most suitable for a 
light-shielding paper for photographic roll film.

The drawings are being presented for better illustration of the embodiments 
and not for the limitative purpose. Modifications suitable in the art may 
be entered without departing from the concept of the present invention. 
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The packaging material of the present invention is composed of at least 
three layers, i.e., a substrate, a middle layer and a surface layer. Of 
the layers, a substrate may be chosen from those which have been used for 
conventional packaging materials. Those having some flexibility, excellent 
light-shielding properties and high physical strengths are preferable, 
e.g., paper, bonded cloth, cellophane, synthetic paper, aluminum foil, 
thermoplastic film and the like. Thermoplastic resin film for a substrate 
encompasses high-density polyethylene, cross-laminated streched film made 
from high-density polyethylene of which the stretching axis is 
cross-laminated (crossing angle: 45-90 degrees), polyester, polyamide, 
polypropylene and the like. The substrate is not limited to one layer but 
may be made of lamination of several different material layers. In this 
case, various combinations of materials are possible in accordance with 
required light-shielding properties, moisture proofness, physical 
strengths, cost, thickness etc. In general, a combination of paper and 
thermoplastic resin film is used. Lamination of substrate layers can be 
made through melt extrusion coating of thermoplastic resins, with solvent 
type or solution type adhesives, or through the thermal bonding process or 
other known processes. A substrate may be provided with a printed layer 
and a protective layer on its surface(s). 
Neck-in herein used refers to a phenomenon that, in case that a 
thermoplastic resin is extruded from a slit like die to form a film or a 
coating layer, the resin film shrinks due to its surface tension 
immediately after it has come out from the die, which results in a 
narrower film width than the die width. Occurrence of neck-in not only 
makes it impossible to produce a film of a predetermined width, but also 
the margin portion of the film becomes thick due to its shrinkage so that 
film thickness becomes uneven entailing a big trimming loss. Besides the, 
thickened margin portion tends to stick to the pressure roll. 
Thermoplastic resins (B) having small neck-in and good adhesion to a 
substrate include low-density polyethylene (hereinafter referred to as 
"LDPE"), moderate-density polyethylene (hereinafter referred to as 
"MDPE"), high-density polyethylene (hereinafter referred to as "HDPE"), 
polypropylene; ethylene-acrylate copolymer [e.g. ethylene-alkylacrylate 
copolymer (EEA, EMA, etc.)], ethylene-methacrylate copolymer and 
ethylene-vinyl acetate copolymer (EVA), each of those three copolymers 
containing not less than 95 wt % of ethylene; and mixtures mainly composed 
of those resins. 
Thermoplastic resins (A) forming a surface layer (a heat seal layer) and 
having good heat seal properties and larger neck-in encompass 
ethylene-vinyl acetate copolymer (EVA), ethylene-acrylate copolymer [e.g., 
ethylene-alkylacrylate copolymer (EEA, EMA, etc.)] and 
ethylene-methacrylate copolymer, each of those three copolymers containing 
not more than 93 wt % of ethylene (preferably 75-90 wt %); linear 
low-density polyethylene (hereinafter referred to as "L-LDPE); ionomer and 
the like; and a mixture of those resins. 
Neck-in values for such resins measured under below-mentioned conditions 
are shown in Table 1. Of the resins having large neck-in values, EVA and 
ionomer were measured at 280.degree. C. and L-LDPE, EEA and EMA at 
310.degree. C. Of the resins having small neck-in values, EVA containing 
not less than 95 wt % of ethylene was measured at 280.degree. C., EEA, 
EMA, LDPE, MDPE and HDPE were measured at 310.degree. C. 
Conditions 
An extruder made by Minamisenju Seisakusho Co., Ltd. of the following 
dimension was used. 
Diameter: 65 mm.phi., Screw: L/D 25 
Die Width: 550 mm, and Die (Slit) Openings: 0.7 mm 
Measuring Conditions 
Air Gap: 90 mm, Take-up Speed: 80 m/min 
A surface layer (a heat seal layer) (or layers) and a middle layer (or 
layers) are laminated onto either one or both surfaces of a substrate 
through melt co-extrusion. A material composed of a substrate, surface 
layers and middle layers which are laminated onto both surfaces of the 
substrate through melt co-extrusion is useful as a light-shielding paper 
for some kinds of packaging of photographic roll film. 
The above-mentioned thermoplastic resins (A) have excellent sealability at 
low temperatures, superior sealability even when powdery concomitants are 
present (hereinafter referred to as "good sealability with concomitants") 
and sufficient sealability with polystyrene (useful as a material for 
packaging photographic roll film) and are used for the surface layer (the 
heat seal layer) of the present invention. As hereinbefore mentioned, 
however, these resins have such drawbacks as large neck-in, easy cut-off 
or tear off, and insufficient sealability with a substrate (poor 
adhesion). Furthermore, since addition of carbon black (light-shielding 
material) makes such drawbacks more conspicuous, these resins have not 
been put to practical use as melt extrusion coating. As hereinbefore 
described, the surface layer (or layers) of the present invention may 
contain light-shielding material. 
Preferable combinations of the thermoplastic resins (A) for the surface 
layer and the thermoplastic resins (B) for the middle layer are as 
follows: 
______________________________________ 
(A) (B) 
______________________________________ 
Ethylene-vinyl acetate 
Low-density polyethylene 
Copolymer containing 
or moderate/high-density 
not more than 93 wt % 
polyethylene.fwdarw. 
of ethylene(EVA) 
Ethylene-acrylate copolymer 
Low-density polyethylene 
(EEA) containing not more 
or moderate/high-density 
than 93 wt % of ethylene 
polyethylene 
Linear low-density Low-density polyethylene 
polyethylene (L-LDPE) 
or moderate/high-density 
polyethylene 
Ionomer Low-density polyethylene 
or moderate/high-density 
polyethylene 
Ethylene-methacrylate 
Low-density polyethylene 
copolymer containing 
or moderate/ high-density 
not more than 93 wt % 
polyethylene.fwdarw. 
of ethylene 
______________________________________ 
Since such packaging materials are manufactured through the melt 
co-extrusion coating process, they can be produced faster and at a lower 
manufacturing cost than conventional ones made through the solution 
coating process using solutions obtained by dissolving EVA, EMA and/or EEA 
in solvents. 
L-LDPE, as well as the other aforementioned resins, may effectively be 
utilized for the surface layer by employing the process of the present 
invention. L-LDPE is a low-density polyethylene copolymer obtainable by 
copolymerizing ethylene and 0.5 to 10 wt % .alpha.-olefin having 4 to 10 
carbons through a low pressure process. It is commercially available in 
the following trade names: Unipol (U.C.C.), Dowlex (Dow Chemical Co., 
Ltd.), Sclair (Du-Pont de Nemour Canada), Marlex (Phillips Co., Ltd.) and 
Ultzex (Mitsui Petrochemical Industries Co., Ltd.). L-LDPE is excellent in 
hot tack, sealability with concomitants and tear strength, and in 
addition, it has such an advantage that the aforementioned excellent 
characteristics are not impaired even when a large quantity of carbon 
black is incorporated. By co-extruding L-LDPE with other thermoplastic 
resins (B) having small neck-in through the melt extrusion process, a 
packaging material with desirable neck-in and improved cutting readiness 
and unsealing properties can be obtained. Especially preferable 
thermoplastic resins (B) for use in combination with L-LDPE are 
low-density polyethylene (LDPE), moderate-density polyethylene (MDPE), 
high-density polyethylene (HDPE), polypropylene and the like. 
It is desirable that some considerations should be taken into account when 
thickness of a surface layer (or layers) or a middle layer (or layers) to 
be co-extruded are determined. 
It is preferable that the thickness of the surface layer is smaller than 
that of the middle layer. 
Heretofore, it has been difficult to make a thin surface layer (heat seal 
layer) independently and stably due to neck-in. The process of melt 
co-extrusion of the surface layer (or-layers) and a middle layer (or 
layers) of the present invention permits a choice of even a smallest 
thickness required for the surface layer. 
The required thickness of the surface layer varies according to a use or 
other conditions. In general, it ranges from 1 to 30 microns, preferably 
from 3 to 20 microns. The combined thickness of the surface layer and the 
co-extruded middle layer is approximately 7 to 100 microns, preferably 
about 10 to 50 microns. 
For preventing neck-in, the surface layer is thinner than the middle layer. 
Preferable thickness ratio between the heat seal layer and the middle 
layer range from 1:1.2 to 1:25, more preferably from 1:2 to 1:15. The 
lower limit of thickness of each layer to be co-extruded is determined by 
such factors as film formation ability and neck-in of each layer, and the 
combined total thickness of the two layers. When the aforementioned lower 
limit of the combined thickness of the two kinds of layers is less than 7 
microns film formation from thermoplastic resins through extrusion would 
be difficult, whereas when the combined thickness exceeds the upper limit, 
100 microns the manufacturing cost becomes too high. 
Since the material of the present invention is a material for packaging 
light-sensitive materials, at least one layer necessarily contains 
light-shielding material. The light-shielding material may be mixed into 
and dispersed in a substrate and/or co-extruded resin layers. It may also 
be adhered to surfaces of layers (usually to a surface or surfaces of a 
substrate) through printing, impregnation, coating or deposition. The 
light-shielding material used herein refers to the material which does not 
transmit ultraviolet and visible rays of light and is available in the 
form of film such as aluminum deposited film, metal foil such as aluminum 
foil or particulate or powdery material dispersed in the layers. 
Particularly, the light-shielding material encompasses inorganic and 
organic pigments such as carbon black, iron oxide, zinc oxide, titanium 
oxide, aluminum powder, aluminum paste, calcium carbonate, barium sulfate, 
cadmium pigments, chrome yellow pigments, red oxide, cobalt blue, copper 
phthalocyanine pigments, monoazo or polyazo pigments, aniline black and 
other various pigments and mixtures thereof. 
The light-shielding material may be contained in an adhesive layer or 
layers in a substrate. 
The substrate herein used includes one to which a light-shielding layer (or 
layers) in the form of film or foil is adhered. In the examples to be 
described hereinafter, however, the substrate is expressed separately from 
the light-shielding layer for the sake of convenience. Aluminum foil, in 
general, is used not only as a light shielding layer but is often 
preferred also for its antistatic properties. 
The packaging material of the present invention having the aforementioned 
structure is not only advantageous in the manufacturing process, but is 
useful as an excellent material for packaging light-sensitive materials 
which is suitable for a wide variety of uses. 
The light-sensitive materials herein described encompass not only 
photosensitive materials for photographic use but all materials which 
undergo deterioration on exposure to light. Hence, they include not only 
various kinds of photosensitive materials for photographic use such as 
silver halide photosensitive materials for color and monochrome films, 
printing and X-ray, and diazo photosensitive materials, but foods such as 
chocolate, margarine, fermentation products such as Miso, wine, beer and 
the like, pharmaceutical articles and dyes which deteriorate when exposed 
to light. 
The material of the present invention can be used for packaging all the 
aforementioned light-sensitive materials. In particular, it is very useful 
as a light-shielding paper for photographic roll film. The light-shielding 
paper used in the form of a backing sheet for the photographic roll film 
is used in such manners that it is wound upon a spool superposed on a 
given length of a photographic film or wound within a hollow drum, e.g., a 
magazine of a given size. Accordingly, the maximum thickness of the 
light-shielding paper is limited since the length of such paper is given. 
In general, it is fixed in a range of 50 to 150 microns, preferably in a 
range of 90 to 120 microns. 
The main drawbacks in properties of the conventional materials for 
packaging photographic roll film are counted as follows: (1) Poor moisture 
proofness may cause adhesion of the light-shielding paper to film under 
high temperatures and humidities. (2) Fog may arise due to permeated 
gases. (3) Instability in dimensions may be caused by water absorption. 
The material of the present invention is excellent in light-shielding 
properties as well as in flexibility, moisture proofness, gas-shielding 
properties and stability in dimensions even when it is formed in a thin 
layer. From the viewpoint of moisture proofness, it is recommended that 
the substrate has, in addition to paper, an aluminum layer such as 3-30 
microns thick aluminum foil, 5-100 microns thick aluminum paste, 0.01-0.2 
microns thick aluminum deposited layer and 5-100 microns thick aluminum 
powder-dispersed layer. The surface layer (heat seal layer) or layers and 
the middle layer or layers of the present invention can easily be adhered 
to the surface (or surfaces) of such a substrate through melt co-extrusion 
coating. 
EXAMPLES 
The present invention will be described by way of embodiments with 
reference to drawings. However, the embodiments and examples are presented 
for better understanding of the invention but not for limitation thereof 
and any modifications apparent in the art would be made without departing 
from the concept and scope of the Claims of the present invention. 
FIGS. 1 to 4 are sectional views showing conventional packaging material. 
FIGS. 5 to 15 are sectional views showing embodiments of the material 
according to the present invention. 
FIG. 1 shows a packaging material comprising a substrate 1, a 
light-shielding layer 2 (such as an aluminum deposited layer, a purified 
layer or a light-shielding coating film layer), and a thermoplastic resin 
layer 3. This kind of material is widely used for packaging diazo 
photosensitive materials, low sensitive silver halide photosensitive 
materials, foods such as chocolate and Miso, dyes, medicines and the like. 
FIG. 2 shows a packaging material consisting of the substrate 1 and a 
thermoplastic layer 3a containing light-shielding material which is 
laminated directly onto the surface of the substrate 1. 
FIG. 3 shows a packaging material produced by adhering on aluminum foil 5 
to a substrate 1a containing light-shielding material by means of an 
adhesive layer 4 and by coating the thermoplastic resin layer 3 to the 
aluminum layer. 
FIG. 4 shows an example structurally similar to that of FIG. 3 except that 
the thermoplastic resin layer 3a contains light-shielding material and the 
layer 3a is adhered to the aluminum foil 5 by means of an adhesive, for 
example by melt extrusion coating of LDPE. This material is good in 
moisture proofness, gas shielding properties and light-shielding 
properties and is most widely used for packaging silver halide 
photosensitive materials. 
FIG. 5 shows an embodiment of the present invention corresponding to the 
example in FIG. 1 of the conventional material. In lieu of the 
thermoplastic resin layer 3, a surface layer (a heat seal layer) 7 and a 
middle layer 6 are laminated through the melt co-extrusion process. This 
embodiment can eliminate such problems as neck-in and insufficient 
adhesion to the substrate, and have excellent heat seal properties, hot 
tack and sealability with concomitants. 
FIG. 6 shows an embodiment identical with the embodiment of FIG. 5 except 
that a middle layer 6a contains light-shielding material. 
FIG. 7 shows an embodiment identical with the embodiment of FIG. 5 except 
that a surface layer (a heat seal layer) 7a contains light-shielding 
material which corresponds to the surface layer 7. 
FIG. 8 shows an embodiment similar to the embodiment of FIG. 5 except that 
the middle layer 6a and the surface layer (the heat seal layer) 7a both 
contain light-shielding material. This embodiment has improved 
light-shielding properties. 
FIGS. 9 and 12 show embodiments corresponding to the example of FIG. 2. The 
middle layer 6 or 6a and the surface layer 7 or 7a are laminated to the 
substrate 1a or 1, respectively, through the melt co-extrusion coating 
process. The embodiments of FIG. 9 and FIG. 12 include at least one layer 
containing light-shielding material. FIG. 10 shows an embodiment in which 
the substrate 1a consists of two layers (1', 1'a). FIG. 11 shows an 
embodiment wherein the light-shielding layer 2 of FIG. 5 is laminated to 
the surface of the packaging material. 
FIGS. 13 to 15 show embodiments corresponding to conventional examples of 
FIGS. 3 and 4. These embodiments are especially useful for packaging high 
photosensitive materials. Addition of light-sensitive material either to 
substrate as shown in FIG. 13 or to the middle layer as shown in FIG. 14 
depends upon the material of each layer and the application of the 
packaging material. If middle layers (6a, 6'a) and surface layers (heat 
seal layers) (7, 7') are applied onto both surfaces of the aluminum foil 5 
as shown in FIG. 15, no adhesive is necessary. The material of FIG. 15 is 
most suitable for applications where high Gelbo test strength and a great 
extent of impact perforation are especially required. 
EXAMPLE 1 
Tests were conducted to compare the properties of a light-shielding paper 
of the present invention having a structure as shown in FIG. 5 and a 
conventional paper as shown in FIG. 1. 
Each substrate 1 was a bleached kraft paper having a basis weight of 30 
g/cm.sup.2 and a thickness of 30 microns, and including a 0.08 micron 
thick aluminum-deposited layer. The thermoplastic resin layer 3 of FIG. 1 
was produced through melt extrusion coating of EEA containing 82% by 
weight of ethylene (NUC 6170 manufactured by Nippon Unicar Co., Ltd.) to 
form a layer of a thickness of 50 microns. Instead of the thermoplastic 
resin layer 3 of FIG. 1, a surface layer (heat seal layer) 7 of EEA having 
a thickness of 10 microns and containing 82% by weight of ethylene and a 
middle layer 6 of EEA having a thickness of 40 microns and containing 
96.5% by weight of ethylene were used in FIG. 5. 
The results in Table 1 show that the inventive light-shielding paper is 
more excellent in adhesion to the substrate, neck-in, cutting readiness, 
laminating speed, anti-blocking and manufacturing cost than the 
conventional light-shielding paper. 
EXAMPLE 2 
Similarly, tests were made to compare the properties of an inventive 
material for packaging light-sensitive materials as shown in FIG. 12 and a 
conventional material as shown in FIG. 2. 
The conventional material of FIG. 2 had the thermoplastic resin layer 3a of 
EEA having a thickness of 20 microns and containing 82% by weight of 
ethylene and 4.5% by weight of carbon black, whereas the inventive 
material had a surface layer (heat seal layer) 7a of EEA having a 
thickness of 5 microns and containing 82% by weight of ethylene and 4.5% 
by weight of carbon black and the middle layer 6a of LDPE having a 
thickness of 15 microns and a density of 0.923 g/cm.sup.3 and containing 
4.5% by weight of carbon black. 
The results in Table 1 reveal that the inventive material is more excellent 
in adhesion to substrate, neck-in, cutting readiness, laminating speed, 
anti-blocking, manufacturing cost as well as carbon black dispersion than 
the conventional material. 
EXAMPLE 3 
In the similar manner, properties of an inventive material as shown in FIG. 
13 and a conventional material as shown in FIG. 3 were compared. 
The substrate 1a of each material was a bleached kraft paper having a 
thickness of 40 microns and a basis weight of 35 g/cm.sup.2 and containing 
5% by weight of carbon black, and an aluminum foil 5 having a thickness of 
9 microns was laminated to the substrate by means of a melt extruded LDPE 
adhesive having a thickness of 13 microns. The conventional material had a 
thermoplastic resin layer 3 of L-LDPE (Ultzex 2080C manufactured by Mitsui 
Petrochemical Industries, Ltd.) having a thickness of 50 microns, while 
the inventive material had a surface layer (heat seal layer) 7 of L-LDPE 
(Ultzex 2080C manufactured by Mitsui Petrochemical Industries, Ltd.) 
having a thickness of 7 microns and a middle layer 6 of LDPE having a 
thickness of 43 microns and a density of 0.920 g/cm.sup.3, both layers 
having been melt co-extruded. 
The results are shown in Table 1. 
EXAMPLE 4 
The packaging material of the present invention as shown in FIG. 15 and a 
conventional material as shown in FIG. 4 were compared. The conventional 
material was produced by laminating an LDPE layer containing 5% by weight 
of carbon black and having a thickness of 37 microns and a density of 
0.923 g/cm.sup.3 onto an aluminum foil 5 by means of an adhesive 4. The 
substrate 1, the aluminum foil 5 and the adhesive 4 equivalent to those 
used for Example 3 were used. The material of FIG. 15 had the surface 
layers (heat seal layers) 7, 7' of EEA containing 88 wt % of ethylene and 
each having a thickness of 5 microns and the middle layers 6a', 6a of LDPE 
containing 5% by weight of carbon black and having a density of 0.923 
g/cm.sup.3 and each layer having a thickness of 8 and 45 microns, 
respectively. 
The heat seal layer 7' and the middle layer 6a' were beforehand melt 
co-extruded between the substrate 1 (in the narrow sense) and the aluminum 
foil 5 in the arrangement as shown in FIG. 15 to form a laminate (i.e., a 
substrate in the broad sense), then the middle layer 6a and the surface 
layer 7 were melt co-extruded to laminate onto the aluminum foil 5 of this 
laminate resulting in a composite sheet. 
The results are shown in Table 1. 
EXAMPLE 5 
Tests were conducted to compare properties of the inventive and 
conventional packaging materials identical with those used in Example 2 
except that instead of EEA, EVA containing 90% by weight of ethylene was 
used for the thermoplastic resin layer 3 and the surface layer 7a. 
The results obtained were almost similar to those of Example 2. 
EXAMPLE 6 
Tests were conducted to compare properties of an inventive and conventional 
packaging materials identical with those used in Example 5 except that 
ionomer (Surlyn 1652 manufactured by E. I. Du Pont de Nemours & Co. 
(Inc.)), in lieu of EVA, was used for the thermoplastic resin layer 3 and 
the surface layer 7a. 
The results were almost similar to those obtained in Example 5. The neck-in 
of the inventive material (FIG. 12) was 22 mm, much better than 35 mm for 
the conventional material. Besides the cost of resins for the inventive 
material was reduced to less than 60% of that for the conventional 
material. 
TABLE 1 
__________________________________________________________________________ 
Example 1 
Example 2 
Example 3 
Example 4 
Example 5 
Drawing No. 
FIG. 1 
FIG. 5 
FIG. 2 
FIG. 12 
FIG. 3 
FIG. 13 
FIG. 4 
FIG. 14 
FIG. 2 
FIG. 12 
Conv. 
Inv. 
Conv. 
Inv. 
Conv. 
Inv. 
Conv. 
Inv. 
Conv. 
Inv. 
Neck-in 
large 
small 
large 
small 
large 
small 
small 
small 
large 
small 
37 mm 
25 mm 
32 mm 
22 mm 
33 mm 
20 mm 
19 mm 
20 mm 
36 mm 
23 mm 
__________________________________________________________________________ 
Light-shielding 
C C C A A A A A B A 
Properties 
Sealability at Low 
A A A A B B D A A A 
Temperatures 
Hot Tack A A A A A A D A A A 
Cutting Readiness 
D B D B D B B B D B 
Dipersion of 
-- -- D B -- -- B B D B 
Carbon Black 
Laminating Speed 
D B D B D B B B D B 
Anti-blocking(EEA) 
E C E C C B B C E C 
Resin Material 
D B D B C B B B D B 
Cost 
Ratio of 1.5 1.0 1.5 1.0 1.2 1.0 0.9 1.0 1.4 1.0 
Manufacturing Cost 
Adhesion to 
D B D B C B B B D B 
Substrate 
Heat Sealability 
A A A A E E E B A A 
with Polystyrene 
__________________________________________________________________________ 
*Conv. = Conventional Material 
**Inv. = Inventive Material 
A = Excellent 
B = Sufficiently practical 
C = Practical 
D = Hardly usable 
E = Unusable (Improvements required) 
Cutting readiness: Cutting readiness of a material upon being cut with a 
cutter, perforating machine, or the like. 
Antiblocking: difficulty of interlayer adherence when load is applied to 
sheets.