Method of encapsulating an AC power type EL panel

An AC power type EL panel includes an AC power type EL element, thermoplastic adhesive layers formed on all surfaces of the AC power type EL element, and a pair of protective films adhered to cover substantially the entire surfaces of the the thermoplastic adhesive layers and having end portions to be fused to each other to seal the AC power type EL element. A thickness ratio of the protective film to the thermoplastic adhesive layer is within the range of 5:1 to 2:1. Since the thermocompression-bonded end portions of the thermoplastic adhesive layers having poor moisture barrier properties are not exposed between the protective films at the end portions of the AC power type EL panel, penetration of external moisture into the panel can be effectively prevented.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to an AC power type EL panel to be used as, 
e.g., a back light of a liquid crystal display device, an illumination 
light source, and a display element and a method of manufacturing the 
same. 
2. Description of the Related Art 
FIGS. 1A and 2 show the structure of a conventional AC power type EL panel. 
FIG. 1A is a sectional views perpendicular to a light-emitting surface of 
the AC power type EL panel, and FIG. 2 is a plan view showing the AC power 
type EL panel viewed from the above the light-emitting surface. Referring 
to FIG. 1A, a reflective insulating layer 2 is formed on a backplate 1 
consisting of an aluminum foil or the like, a light-emitting layer 3 is 
formed on the reflective insulating layer 2, and a transparent conductive 
film 4 is bonded by thermocompression on the light-emitting layer 3. The 
transparent conductive film 4 is constituted by a resin film 4b as a 
substrate consisting of, e.g., polyester and a transparent electrode 4a 
formed on the resin film 4b. The transparent film 4 is bonded by 
thermocompression on the light-emitting layer 3 so that the transparent 
electrode 4a faces down, thereby constituting the AC powder type EL 
element. The AC powder type EL panel is constituted by the AC powder type 
E element as described above, a pair of moisture-trapping films 5 formed 
on the upper and lower surfaces of the AC power type EL element and 
consisting of, e.g., nylon, thermoplastic adhesive layers 6b formed on the 
upper and lower surfaces of the moisture-trapping films 5, and a pair of 
protective films 6a having good moisture barrier properties and bonded by 
thermocompression from the above and below the pair of moisture-trapping 
films 5 via the thermoplastic adhesive layers 6b to seal the AC power type 
EL panel. 
As shown in FIG. 2, as the transparent electrode, a transparent conductive 
film 4 obtained by forming a thin film of a transparent electrode layer 4a 
on a resin film substrate 4b, and coating a silver paste of a bar-shape on 
the resulting thin film and baking it to form an auxiliary electrode 4c, 
can be used. Leads 7 consisting of phosphor bronze or aluminum a normally, 
externally led from the backplate 1 and the auxiliary electrode 4aformed 
on the conductive film 4. 
With the above arrangement, light emission can be obtained from the EL 
light-emitting element by applying an AC electric field having about 100 V 
and 100 to 1,000 Hz across the leads 7. In this state, however, the 
light-emitting layer 3 absorbs moisture to deteriorate the phosphor. 
Therefore, a method of manufacturing this AC power type EL element 
additionally requires a step of forming the protective films 6a as polymer 
films having good moisture barrier properties to seal the element and a 
step of forming the moisture-trapping layers 5 for trapping moisture 
permeating through the protective films 6a. 
As the moisture-trapping layers 5, a pair of moisture-trapping films 5 
having good moisture absorption characteristics such as nylon resin films 
are formed outside the AC power type EL element. An adhesive is coated on 
surface of each nylon resin film 5, and the films 5 are bonded to the AC 
power type EL element by thermocompression by a laminator with the AC 
power type EL element being sandwiched between the films 5 such that the 
adhesive faces inside. 
As the protective films 6a, films having good moisture barrier properties 
and small moisture permeability such as fluoroplastic films are used. The 
protective film 6a has a size larger than that of the AC power type EL 
element. The thermoplastic adhesive layer 6b is coated on one surface of 
each protective film 6a. The protective films 6a are bonded by 
thermocompression to sandwich the AC power type EL element such that the 
adhesive faces inside. The AC power type EL panel has a structure in which 
portions of the protective films 6a extending from the AC power type EL 
elements are bonded by thermocompression to each other by a laminator, 
thereby sealing the elements. A laminator used in thermocompression 
bonding of the protective films 6a and the thermoplastic adhesive layers 
6b is constituted by at least a pair of heat rollers having an internal 
heater. Sealing of the AC power type EL elements are performed as follows. 
That is, a plurality of AC power type EL elements are aligned between two 
opposing elongated protective films such that distal end portions of their 
lead extend from the protective films, and the two protective films are 
bonded by thermocompression to each other. The upper and lower protective 
films and the thermoplastic adhesive layers integrated by sealing are cut 
into a predetermined size by a press cut method, thereby manufacturing an 
AC power type EL panel. 
The AC power type EL panel obtained by the above manufacturing method, 
however, has a problem of uneven deterioration of a light-emitting layer 
caused by penetration of moisture from a peripheral portion of the 
laminated protective film. When this uneven deterioration occurs, a 
distribution of brightness of the AC power type EL panel is significantly 
deteriorated within a short time period. Therefore, when the AC power type 
EL panel having the uneven deterioration is used as a back light of a 
liquid crystal display, it is difficult to read displayed characters. 
The uneven deterioration of the light-emitting layer is mainly caused by 
penetration of moisture from the thermoplastic adhesive layers formed on 
the protective films. As described above, the protective films are bonded 
by thermocompression from the above and below the AC power type EL 
elements via the thermoplastic adhesive layers to seal the elements and 
cut into a predetermined shape by a press cut method or the like. This cut 
surface is shown in an enlarged scale in FIG. 1B. As shown in FIG. 1B, the 
thermoplastic adhesive layers are exposed to the cut surface between the 
upper and lower protective films. External moisture permeates the exposed 
thermoplastic adhesive layers and penetrates into the panel. The 
light-emitting layer at the peripheral portion of the light-emitting 
surface is rapidly deteriorated by the penetrating moisture to cause 
uneven deterioration of the light-emitting surface. Therefore, a strong 
demand has arisen for development of an AC power type EL panel which 
improves moisture barrier properties of the protective films and the 
thermoplastic adhesive layers to prevent uneven deterioration of the 
light-emitting layers. 
As described above, according to a conventional AC power type EL panel 
obtained by vertically sandwiching AC power type EL elements by protective 
films having a larger size than that of the elements via thermoplastic 
adhesive layers, performing thermocompression bonding to seal the AC power 
type EL elements by a laminator, and cutting the protective films and the 
thermoplastic adhesive layers into a predetermined size, if cutting of the 
protective films and the thermoplastic adhesive layers is performed by a 
press cut method, the thermoplastic adhesive layers between the 
thermocompression-bonded protective films are exposed to the cut surface. 
Therefore, moisture outside the panel penetrates into the panel through 
the thermoplastic adhesive layers to cause uneven deterioration in the 
light-emitting layer from the peripheral portion of the light-emitting 
surface. 
SUMMARY OF THE INVENTION 
It is an object of the present invention to provide an AC power type EL 
panel which solves a problem of uneven deterioration in a light-emitting 
layer caused by moisture penetrating into the panel. 
It is another object of the present invention to provide a method of 
manufacturing an AC power type EL panel. 
An AC power type EL panel of the present invention comprises: 
an AC power type EL element including a transparent first electrode, a 
reflective insulating layer formed on the first electrode, a 
light-emitting layer formed on the reflective insulating layer, a second 
electrode provided on the light-emitting layer, and a pair of leads 
connected to the first and second electrodes; 
a thermoplastic adhesive layer formed on substantially the entire surfaces 
of the AC power E element; and 
a pair of protective films adhered to cover substantially the entire 
surface of the thermoplastic adhesive layer and having end portions to be 
fused to each other to seal the AC power type EL element. 
A thickness ratio of the protective film to the thermoplastic adhesive 
layer may be within the range of 5:1 to 2:1. 
According to the present invention, a pair of protective films having good 
moisture barrier properties are integrally fused at their end portions to 
seal the AC power type EL element and the thermoplastic adhesive layers. 
In the AC power type EL panel of the present invention, therefore, since 
the thermocompression-bonded end portions of the thermoplastic adhesive 
layers having poor moisture barrier properties are not exposed between a 
pair of protective films at the end portion of the AC power type EL panel, 
penetration of external moisture into the panel can be effectively 
prevented. 
A method of manufacturing an AC power type EL panel of the present 
invention comprises the steps of: 
forming a reflective insulating layer on a first electrode; 
forming a light-emitting layer on the reflective insulating layer; 
providing a second electrode on the light-emitting layer; 
connecting leads from the first and second electrodes to obtain an AC power 
type EL element; 
forming thermoplastic adhesive layers on a pair of protective films having 
a size larger than that of the first and second electrodes; 
bonding one protective film to upper surface of said AC power type EL 
element and the other protective film to lower surface of said AC power 
type EL element by thermocompression from the above and below by the 
protective films to seal the AC power type EL element; and 
cutting the end portions of the thermocompression-bonded protective films 
into a predetermined shape by using a laser, thus fusing the end portions 
of said protecting layers, 
wherein a thickness ratio of the protective film to the thermoplastic 
adhesive layer falls within the range of 5:1 to 2:1. 
According to the method of the present invention, thermocompression bonding 
is performed by limiting the ratio of the thickness of the protective film 
to that of the thermoplastic resin layer, and the thermocompression-bonded 
protective films are cut by using a laser. Therefore, since the protective 
films having good moisture barrier properties are integrally fused at the 
cut surfaces of the protective films, the thermoplastic adhesive layers 
having poor moisture barrier properties can be sealed into the protective 
films. In the AC power type EL panel manufactured in this manner, the 
thermoplastic resin layers are not exposed to the cut surface. 
Additional objects and advantages of the invention will be set forth in the 
description which follows, and in part will be obvious from the 
description, or may be learned by practice of the invention. The objects 
and advantages of the invention may be realized and obtained by means of 
the instrumentalities and combinations particularly pointed out in the 
appended claims.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
A preferred embodiment of the present invention will be described below 
with reference to the accompanying drawings. FIG. 3A is a sectional view 
showing an AC power type EL panel according to one embodiment of the 
present invention. Referring to FIG. 3A, a reflective insulating layer is 
formed on a first electrode 1, a light-emitting layer 3 is formed on the 
reflective insulating layer 2, a second electrode 4 is formed on the 
reflective insulating layer 3, and leads are led from both the electrodes 
1 and 4, thereby constituting the AC power type EL element. 
As a material of the first electrode 1, aluminum, copper, or nickel, for 
example, can be used. 
As a material of the second electrode 4, indium oxide or ITO, for example, 
can be used. 
As a phosphor for us in the light-emitting layer 2, a conventional EL lamp 
phosphor can be used. Examples of the phosphor are ZnS:Cu,Cl, ZnS:Cu,I, 
and ZnS:Cu,Mn,Cl. 
Thermoplastic resin layers 6b and a pair of protective films adhered on the 
thermoplastic resin layers 6b are formed on the surfaces of the AC powder 
type EL element described above. The end portions of the pair of 
protective films are fused to each other to seal the AC power type EL 
element. A ratio of the thickness of the protective film to that of the 
thermoplastic adhesive layer is limited to within the range of 5:1 to 2:1. 
Although this thickness ratio varies in accordance wit the types of 
protective film and thermoplastic adhesive, it is preferably within the 
range of 4:1 to 3:1. 
Since the end portion of the AC power type EL panel having the above 
arrangement is airtightly covered with a molten product of the protective 
films 6a, the thermoplastic adhesive layers 6b having poor moisture 
barrier properties are not exposed between the protective films at the end 
portion of the AC power type EL panel. Therefore, penetration of external 
moisture into the panel can be effectively prevented. 
Examples of the material of the protective film used in the present 
invention are polychlorotrifluoroethylene (to be referred to as PCTFE 
hereinafter), a combination of polyethylene terephthalate (PET) and butyl 
rubber, and a combination of high-density polyethylene and PET. The 
material of the film, however, is not limited to these examples as long as 
the film is transparent and has low water permeability and good moisture 
barrier properties. Although the thickness of the protective film is not 
particularly limited, it is 100 to 300 .mu.m, and preferably, 150 to 200 
.mu.m in consideration of processability, cost, permeability, and moisture 
barrier properties. 
The thermoplastic adhesive used in the present invention is a polymer layer 
which can be adhered upon heating or pressurization, e.g., an olefin 
resin, an acrylic resin, a vinyl acetate resin, and polyester. 
In the AC power type EL panel, moisture-trapping layers 5 can be formed 
between the EL light-emitting element and the thermoplastic adhesive 
layers. Examples of the moisture-trapping layer of the present invention 
are films consisting of nylon 6, or nylon 6,6 having thermoplastic resin 
layers on one side of the films. 
A method of manufacturing the AC power type EL panel shown in FIG. 3A will 
be described below. 
The reflective insulating layer 2, the light-emitting layer 3, and the 
second electrode 4 are sequentially formed on the first electrode 1, and 
the leads 7 are formed to be led from both the electrodes 1 and 4, thereby 
manufacturing the AC power type EL element. The manufactured AC power type 
EL element is sandwiched between a pair of moisture-trapping films having 
thermoplastic resin layers, and the moisture-trapping films are bonded by 
thermocompression to the AC power type EL element. The AC power type EL 
element which is sandwiched between a pair of moisture-trapping films is 
sandwiched between a pair of protective films having thermoplastic resin 
layers having the size larger than that of the EL element, and the 
protective films are bonded by thermocompression to seal the AC power type 
EL element. An AC power type EL panel can be obtained by cutting the end 
portions of the thermocompression-bonded protective films 6b into a 
predetermined shape by using a laser. 
In a thermocompression bonding step, a heating temperature is preferably 
80.degree. C. to 170.degree. C., and more preferably, 100.degree. C. to 
150.degree. C., and a linear pressure is preferably 4 to 48 kg/cm, and 
more preferably, 5 to 40 kg/cm. 
In formation of the reflective insulating layer and the light-emitting 
layer on the backplate, a binder prepared by dissolving an organic high 
dielectric such as cyanoethylprulan or cyanoethylpolyvinylalcohol into an 
organic solvent such as N,N-dimethylformamide can be used. The reflective 
insulating layer can be formed by coating a reflective insulating material 
paste prepared by dispersing a white powder having a high dielectric 
constant such as barium titanate into the binder, on the back plate using 
doctor roll method or screen printing method and heating and drying the 
reflective insulating material paste. The light-emitting layer can be 
formed following the same procedures as for the reflective insulating 
layer except that a phosphor such as ZnS:Cu,Cl is dispersed in the binder 
to prepare a light-emitting material paste and this light-emitting 
material paste is used in place of the reflective insulating material 
paste. In this manner, the reflective insulating layer and the 
light-emitting layer are sequentially formed on the backplate. 
As the transparent electrode on the light-emitting layer, a thin film as a 
transparent electrode layer consisting of, e.g., ITO or indium oxide can 
be formed on a resin film substrate consisting of, e.g., polyester or 
polyethylene terephthalate by sputtering or vapor deposition. In addition, 
a transparent conductive film obtained by coating and baking a silver 
paste in the form of a bar on the resulting thin film to form an auxiliary 
electrode can be used. This transparent conductive film can be overlapped 
and bonded by thermocompression with the transparent and auxiliary 
electrodes facing down. Leads consisting of, e.g., phosphor bronze or 
aluminum can be externally led from the backplate 1 and the auxiliary 
electrode on the conductive film. 
The thermoplastic adhesive can be formed on the protective film in the form 
of a layer. Examples of a method of forming the thermoplastic adhesive 
layer on the protective film are a method of dissolving a thermoplastic 
adhesive component in an organic solvent and coating the resultant 
solution and a method of melting and extrusion-laminating a thermoplastic 
adhesive component. 
A step of sealing the AC power type EL element by bonding the protective 
films and the thermoplastic adhesive layers to element by 
thermocompression is generally performed by using a laminator. A laminator 
is generally constituted by a pair of heat rolls having an internal 
infrared heater or a pair of induction-heating type heat rolls. Two films 
having the thermoplastic adhesive layers on the protective films are 
opposed each other such that the thermoplastic adhesive layers are 
arranged inside, the AC power type EL element is sandwiched between the 
two opposing films, and the two films are fed between rotating heat rolls. 
The thermoplastic adhesive layers are heated and pressurized between the 
heat rolls to fuse the thermoplastic adhesive layers so that the AC power 
type EL element is sealed by the protective films and the thermoplastic 
adhesive layers. In order to produce a pressure between the heat rolls, a 
force is generally applied on both end portions of the roll by two 
cylindrical hydraulic or pneumatic cylinders. A linear pressure P between 
the two heat rolls to be applied on the AC power type EL element is 
defined by the following equation (1): 
EQU P (kg/cm)=2.multidot..pi..multidot.D.sup.2 .multidot.P.sub.O /L/4 (1) 
D : cylinder inner diameter (cm) 
P.sub.O : cylinder pressure (kg/cm.sup.2) 
L : AC power type EL element width (cm) 
Sealing of the AC power type EL element by the protective films is 
generally performed by applying the linear pressure and the heat defined 
as described above on the AC power type EL element. If, however, an AC 
power type panel having a comparatively small light-emitting area, sealing 
can be performed by uniformly applying a pressure and heat on the entire 
surface of the AC power type EL element by using a hot press in 
consideration of a production efficiency and manufacturing cost. In this 
case, a pressure P' required for sealing is defined by the following 
equation (2) assuming that the pressure is applied on the surface to be 
pressed by using N cylinders. Note that a thermocompression bonding 
direction, a width L, and a length W are shown in FIG. 2: 
EQU P'(kg/cm.sup.2)=N.multidot..pi..multidot.D.sup.2 .multidot.P.sub.O /L/W/4 
(2) 
D : cylinder inner diameter (cm) 
PO : Cylinder pressure (kg/cm.sup.2) 
L : AC powder type EL element width (cm) 
W : AC powder type EL element length (cm) 
N : Number of cylinder 
In the present invention, since P is limited to 5 (kg/cm) .ltoreq.P 
.ltoreq.40 (kg/cm), the pressure P' is represented by the following 
equation (3): 
EQU (5.multidot.N)/(2.multidot.W) (kg/cm.sup.2) 
.ltoreq.P'.ltoreq.(40.multidot.N)/(2.multidot.W)(kg/cm.sup.2) 
Therefore, by performing the thermocompression bonding step by setting N, 
W, and P' to satisfy the above equation (3), the effect of the present 
invention can be obtained regardless of a linear pressure. 
Examples of a laser used in the present invention are a carbon dioxide gas 
laser and an excimer laser. The type of laser, however, is not limited to 
these examples as long as the laser can cut the films but does not cut the 
metal. 
In the AC power type EL panel of the present invention, when the AC power 
type EL element is to be sealed by the protective films via the 
thermoplastic adhesive layers, a ratio of the thickness of the protective 
film to that of the thermoplastic adhesive layer falls within the range of 
5:1 to 2:1. After the protective films are bonded by thermocompression to 
seal the element, the protective films are melted and cut by using a laser 
to airtightly cover peripheral portions of the thermoplastic adhesive 
layers by a molten product of the protective films. As a result, a 
moisture vapor resistance of the protective films can be significantly 
improved. Therefore, an AC power type EL panel which does not cause uneven 
deterioration even after it is used over a long time period. 
The present invention will be described in more detail below by way of its 
examples. 
EXAMPLES 1-3 
A reflective insulating layer paste prepared by dispersing a barium 
titanate powder in a binder solution in which cyanoethylprulan and 
cyanoethy polyvinylalcohol in N,N-dimethylformamide (to be referred to as 
DMF hereinafter) was coated on a backplate 1 consisting of an aluminum 
foil by a screen printing method. Thereafter, the coated reflective 
insulating layer paste was dried at 120.degree. C. to remove DMF, thereby 
forming a reflective insulating layer 2 having a thickness of 30 to 40 
.mu.m. 
A light-emitting layer paste prepared by dispersing a ZnS:Cu,Cl phosphor 
and an organic fluorescent pigment in the above binder solution was coated 
on the reflective insulating layer 2. Thereafter, the coated 
light-emitting layer paste was dried at 120.degree. C. to remove DMF, 
thereby forming a light-emitting layer 3 having a thickness of 30 to 40 
.mu.m. 
A transparent conductive film 4 was formed by depositing ITO as a 
transparent electrode 4a on a PET film 4b. A thermosetting silver paste 
was printed on the transparent electrode 4a by a screen printing method. 
Thereafter, the printed silver paste was baked and thermoset at 
150.degree. C. for 30 minutes to form an auxiliary electrode 4c on the 
transparent conductive film 4. Leads 7 consisting of phosphor bronze were 
temporarily fixed by a PET tape at predetermined positions of the 
auxiliary electrode 4c and the backplate 1. 
The transparent electrode 4a and the light-emitting layer 3 were bonded by 
using a laminator at a heating temperature of 170.degree. C., a linear 
pressure of 20 to 40 kg/cm, a feed speed of 10 to 50 cm/min. In addition, 
moisture-trapping films 5 constituted by a nylon 6 film and a 
thermoplastic adhesive adhered on the nylon 6 film was bonded to the outer 
surfaces of the transparent electrode 4a and the backplate 1 by using a 
laminator at a heating temperature of 130.degree. C., a linear pressure of 
20 to 30 kg/cm, and a feed speed of 30 to 50 cm/min. 
Films obtained by forming thermoplastic adhesive layers 6b on protective 
films 6a consisting of PCTFE were bonded by thermocompression on the outer 
surfaces of the moisture-trapping films 5 by using a laminator at a 
heating temperature of 130.degree. C., a linear pressure of 20 kg/cm, and 
a feed speed of 30 cm/min. while the thickness ratio of the protective 
film to the thermoplastic adhesive was changed to be 5:1, 4:1, and 2:1, 
thereby sealing an AC power type EL element. Thereafter, the projecting 
protective films were cut by a carbon dioxide gas laser to obtain AC power 
type EL panels, and the characteristics of the panels were compared and 
evaluated. Practical processing conditions for cutting the protective 
films and the thermoplastic adhesive layers by using a carbon dioxide gas 
laser are summarized in the following Table. 
TABLE 
______________________________________ 
Carbon Dioxide Gas Laser Output 
17.5 W 
Lens-Sample Interval 90.0 mm 
Assist Gas Ar 
Assist Gas Supply Amount 20.0 l/min. 
Cutting Speed 20.0 m/sec. 
______________________________________ 
As Controls 1 to 3, panels were manufactured following the same procedures 
as in Examples 1 to 3 except that the thickness ratio of the protective 
film to the thermoplastic adhesive were changed to 8:1, 6:1, and 1:1. In 
addition, Controls 4 to 10 were manufactured following the same procedures 
as in Examples 1 to 3 except that the thickness ratio was changed to be 
8:1, 6:1, 5:1, 4:1, 2:1, and 1:1 and cutting was performed by a press cut 
method. 
The thickness of the protective film was set to be 200/.mu.m in all the 
examples. Half life of brightness as brightness of the AC power type EL 
panel and decrement time of distribution of brightness as its distribution 
of brightness were measured for each AC power type EL panels of the 
present invention and the controls. FIGS. 4 and 5 are a graph showing a 
relationship between the distribution of brightness and a thickness ratio 
of the protective film to the thermopastic adhesive layer and a 
relationship between the half life of brightness and the thickness ratio, 
respectively, according to the measurement results of the distribution of 
brightness and the decrement time of distribution of brightness obtained 
at room temperature of 25.degree. C. and a relative humidity of 60% when 
an AC voltage of 100 V and 400 Hz was applied. Distribution of brightness 
was defined as a value obtained by dividing maximum brightness of the 
light-emitting surface by its minimum brightness, and the decrement time 
of distribution of brightness is defined as a light emission time required 
for the distribution of brightness to exceed 1.2. As is apparent from FIG. 
3, the AC power type EL panels having the thickness ratio of the 
protective film to the thermoplastic adhesive layer falling within the 
range of 5:1 to 2:1 has good decrement time of distribution of brightness 
exceeding 3,000 hours, while the distributions of brightness of the AC 
power type EL panels of other conditions were rapidly degraded as a time 
passed. To contrary to this, the decrement time of distribution of 
brightness of each control was 1,000 hours regardless of the thickness 
ratio. As is apparent from FIG. 5, the half time of brightness indicating 
the life of panel of each AC power type EL panel having the thickness 
ratio according to the present invention wa three to four times those of 
the controls. 
The similar experiment was conducted by changing the laminating conditions 
of sealing such that the heating temperature of 100.degree. C. to 
150.degree. C. and the linear pressure of 5 to 40 kg/cm. As a result, the 
brightness and the distribution of brightness were significantly improved 
when the thickness ratio of the protective film to the thermoplastic 
adhesive layer fell within the range of 5:1 to 2:1 as compared with other 
ranges. In addition, it was found that this effect appeared regardless of 
the feed speed upon thermocompression bonding. 
The above effect can be obtained when the thickness ratio of the protective 
film to the thermoplastic adhesive layer falls within the range of 5:1 to 
2:1 for the following reason. That is, if the thickness ratio is smaller 
than 2:1, since an amount of the melted protective films is absolutely 
insufficient during laser cutting, the thermoplastic adhesive layers 
cannot be covered. If the thickness ratio is larger than 5:1, since the 
melted protective films sag downward by a gravitational force, the 
thermoplastic adhesive layers are exposed to the cut surface. If, however, 
the thickness ratio falls within the range of 5:1 to 2:1, since the melted 
protective films air-tightly cover the thermoplastic adhesive layers upon 
laser cutting, no thermoplastic adhesive layers are exposed to the cut 
surface to prevent penetration of moisture into the AC power type EL 
panel. 
EXAMPLES 4-27 
AC power type EL panels were manufactured by cutting protective films and 
thermoplastic adhesive layers by using a carbon dioxide gas laser 
following the same procedures as in Example 1 except that a protective 
film is of 200-.mu.m thick and a thermoplastic adhesive layer is of 
50-.mu.m thick and thermocompression bonding was performed under various 
conditions, and decrement time of distribution of brightness and half life 
of brightness were measured following the same procedures as in the above 
experiment. 
FIGS. 6 and 7 are graphs showing a relationship between the decrement time 
of distribution of brightness and a heating temperature upon 
thermocompression bonding and a relationship between the half life of 
brightness and the heating temperature of the AC power type EL panels 
obtained by thermocompression bonding at various heating temperatures 
under the conditions of a linear pressure of 25 kg/cm and a feed speed of 
30 cm/min. as Examples 4 to 13 and Controls 10 to 19. As is apparent from 
FIGS. 6 and 7, good decrement time of distribution of brightness and half 
life of brightness of 3,000 and 3,500 hours, respectively, were obtained 
within the heating temperature range of 100.degree. C. to 150.degree. C. 
FIGS. 8 and 9 are graphs showing a relationship between decrement time of 
distribution of brightness and a linear pressure and a relationship 
between half life of distribution and the linear pressure of AC power type 
EL panels manufactured by cutting the protective films and the 
thermoplastic adhesive layers by a carbon dioxide gas laser after 
thermocompression bonding was performed by various linear pressures under 
the conditions of heating temperature of 130.degree. C. and a feed speed 
of 30 cm/min. as Examples 14 to 27 and Controls 20 to 32. As is apparent 
from FIGS. 8 and 9, the decrement time of distribution of brightness and 
the half life of brightness of the AC power type EL panel manufactured 
within the linear pressure range of 5 to 40 kg/cm were 3,000 to 3,500 
hours, while the decrement time of distribution of brightness and the half 
life of brightness were 2,000 hours under the conditions of the linear 
pressure of 4 kg/cm or less and more than 40 kg/cm. 
When the heating temperature and the linear pressure are increased, it is 
difficult to uniformly perform thermocompression bonding since flowability 
of the thermoplastic adhesive is largely increased. When the thickness 
ratio of the protective film to the thermoplastic adhesive layer has a 
distribution, a region in which the ratio of the two is very large 
partially appears. To contrary to this, when the heating temperature and 
the linear pressure are decreased, the flowability of the thermoplastic 
adhesive is decreased. Therefore, since the thermoplastic adhesive is not 
airtightly filled in edge and corner portions of the AC power type EL 
element but produces bubbles, sealing of the AC power type EL element 
becomes imperfect. 
As described above, the AC power type EL panel can be uniformly and 
airtightly sealed by performing thermocompression bonding under the 
conditions of preferably a heating temperature of 100.degree. C. to 
150.degree. C. and a linear pressure of 5 to 40 kg/cm. By cutting the 
resultant panel by using a laser, the thermoplastic adhesive at the cut 
surface can be airtightly covered with the protective films to realize an 
AC power type EL panel free from uneven deterioration. 
Additional advantages and modifications will readily occur to those skilled 
in the art. Therefore, the invention in its broader aspects is not limited 
to the specific details, representative devices, and illustrated examples 
shown and described herein. Accordingly, various modifications may be made 
without departing from the spirit or scope of the general inventive 
concept as defined by the appended claims and their equivalents.