JP2003151459A - Method for manufacturing color cathode ray tube - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing color cathode ray tubes capable of controlling tension reduction of a color selection electrode by pressurizing a frame before spanning process. SOLUTION: A spanning process bonding the color selection electrode to a frame 10 under a condition that tension is applied on the color selection electrode is provided, and a frame pressurization process to pressurize the frame to a level that the frame 10 plastically deformed before the spanning process is included. Consequently, reduction of frame strength due to a high temperature heat treatment process is controlled by plastically deforming the frame 10 beforehand, and tension reduction of the color selection electrode can be controlled. Weight of the frame can be reduced as compared with a frame of a same structure without passing through the frame pressurizing process.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing a color cathode ray tube used for a display device such as a computer monitor and a television set.

[0002]

2. Description of the Related Art In recent years, in a color cathode ray tube, flattening of a panel has been promoted because it has the advantages that the range of reflected external light can be reduced and image distortion can be prevented. The color cathode ray tube plays a role of color selection for three electron beams emitted from an electron gun, and a plate-shaped color selection electrode (shadow mask) having a plurality of apertures is fixed to a frame to perform color selection. The electrode structure is formed. The color selection electrode structure is arranged so as to face the panel,
As the panel becomes flat, the color selection electrode also needs to be held in a state close to a flat surface. An iron material is generally used for the frame and the color selection electrode, but a Ni—Fe alloy may be used for the color selection electrode in order to reduce thermal expansion.

During operation of the cathode ray tube, thermal expansion due to electron beam bombardment displaces the apertures of the color selection electrode, and the electron beam passing through the apertures does not hit the prescribed phosphor correctly, resulting in uneven color. A doming phenomenon occurs. For this reason, a tensile force capable of absorbing thermal expansion due to a temperature rise of the color selection electrode is applied in advance to stretch and hold the color selection electrode on the support.
According to such stretching and holding, even if the temperature of the color selection electrode rises, it is possible to reduce the misalignment between the aperture of the color selection electrode and the phosphor stripe on the phosphor screen surface.

FIG. 8 shows a process chart of an example of a conventional method of manufacturing a color cathode ray tube using such a stretching method. In the frame assembling process, the short side frame and the long side frame are joined by welding to be integrated to form a frame-shaped frame.

In the next heat treatment step (heat treatment 1), this frame-like frame is heat-treated under the conditions of, for example, 550 ° C. or higher for 15 minutes in order to remove the processing strain during welding. Next, the process proceeds to a stretching step, and the color selection electrode is stretched and held in a frame-like frame to form a color selection electrode structure. As an example of stretching and holding, vertical direction (vertical direction of screen) is applied to the color selection electrode.
There is a method of welding and fixing to a frame-like frame with tension applied to the frame.

Next, a spring member which is a member for attaching to the panel is welded to the frame-shaped frame, and a damper which is a vibration absorbing member is attached to the color selection electrode. In this state, the heat treatment step (heat treatment 2) is performed. In this heat treatment process, before the glass frit process, the color selection electrode structure is previously heat treated under the same setting conditions as in the glass frit process. In this way, if the color selection electrode that has been subjected to the high temperature heat treatment is used to perform alignment with the phosphor screen surface, this state will be maintained even after the glass frit process. Therefore, it is possible to prevent the positional deviation between the color selection electrode and the phosphor screen surface.

Next, in the phosphor screen forming step, a phosphor screen is formed on the inner surface of the panel. This phosphor screen is formed by selectively exposing the photoresist applied to the inner surface of the panel to a desired position with the black matrix film and the red, green, and blue fluorescent coating films by using the color selection electrode as an exposure mask. By forming.

In the next glass frit step (heat treatment 3), the panel and the funnel are heat-treated and joined under the conditions of 440 to 470 ° C. and about 20 minutes.

[0009]

However, the conventional manufacturing method as described above has the following problems. When the color selection electrodes are stretched and held, a tension force is applied to the color selection electrodes and a compression force is applied to the frame to maintain a balanced state. Even if the stress applied to the frame at room temperature is within the elastic limit, if the process is transferred to the high temperature heat treatment step (heat treatment 2 in FIG. 8), the elastic limit of the frame is lowered and a creep phenomenon in which plastic deformation progresses occurs.

When the creep phenomenon occurs, even if the temperature is returned to room temperature, the plastically deformed portion is not restored, and as a result, the initial tensile force of the color selection electrode is reduced to about 70 to 40%. When the tensile force is lowered, it may cause vibration, and there is a problem that the above-mentioned doming phenomenon may not be sufficiently prevented. Also, along with the decrease in tensile force, the distribution state of the tensile force of the color selection electrode at room temperature also fluctuates,
There is a problem that wrinkles easily occur on the color selection electrode.

In order to prevent the decrease in tensile force as described above,
It is possible to apply a sufficient tensile force in advance, but since it is stretched with a tension in the region close to the yield stress of the color selection electrode before heat treatment, it is necessary to increase the tensile force from the viewpoint of material strength. There was a limit. Further, it is conceivable to increase the rigidity of the frame, but in this case, there is a problem that the frame weight increases and the cost increases.

The present invention is to solve the above-mentioned conventional problems, and by pre-pressurizing the frame before the stretching step, it is possible to suppress a decrease in the tensile force of the color selection electrode. An object of the present invention is to provide a method of manufacturing a color cathode ray tube that can be used.

[0013]

In order to achieve the above object, a method of manufacturing a color cathode ray tube according to the present invention is a frame for joining a color selection electrode to a frame while applying a tensile force to the color selection electrode. It is characterized by comprising a tensioning step, and before the stretching step, there is a frame pressure step of pressurizing the frame to plastically deform the frame. According to the manufacturing method of the color cathode ray tube as described above, by plastically deforming the frame before the stretching step, it is possible to suppress a decrease in the frame strength in the high temperature heat treatment step, and to reduce the tensile force of the color selection electrode. The decrease can be suppressed. As a result, the weight of the frame can be reduced as compared with the case where the frame having the same structure is used and the frame pressing step is not performed.

In the method of manufacturing a color cathode ray tube, the pressurization of the frame is performed by heating the frame in a state where at least a part of the frame is held so as to restrain the positional fluctuation of the frame. It is preferable to carry out.

Further, it comprises a frame assembling step of assembling the frame before the stretching step, and a heat treatment step of removing the distortion of the frame after the frame assembling step. It is preferable to perform the heat treatment step. According to the manufacturing method of the color cathode ray tube as described above, the frame pressure can be applied simultaneously with the heat treatment during the heat treatment step, which is advantageous for improving the productivity.

Further, it is preferable that a cutting step of cutting the mounting surface of the color selection electrode in the frame is performed after the frame pressing step. According to the manufacturing method of the color cathode ray tube as described above, since it is not necessary to perform a cutting process in consideration of a change in the mounting surface of the color selection electrode due to the pressurization of the frame, when the cathode ray tube is completed,
Variations in the distance between the color selection electrode and the phosphor surface can be reduced.

After the frame pressurizing step, it is preferable to proceed to the tensioning step. According to the manufacturing method of the color cathode ray tube as described above, the pressurizing equipment for pressurizing the frame can be used also as the pressurizing equipment in the stretching step.

[0018]

DETAILED DESCRIPTION OF THE INVENTION An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 shows a sectional view of a color cathode ray tube according to an embodiment of the present invention. The color cathode-ray tube 1 shown in this figure has a substantially rectangular face panel 2 having a phosphor screen surface 2a formed on the inner surface thereof, and a funnel 3 connected to the rear of the face panel 2 to form an envelope. Has been formed. An electron gun 4 that emits three electron beams is built in the neck portion 3 a of the funnel 3, and the electron beam emitted from the electron gun 4 is generated by a deflection yoke 5 arranged on the outer peripheral surface of the funnel 3. , Is deflected and reaches the screen surface 2a.

Inside the face panel 2, a color selection electrode (shadow mask) 6 provided so as to face the phosphor screen surface 2a is arranged. The color selection electrode 6 plays a role of color selection for the three electron beams emitted from the electron gun 4. A indicates the electron beam trajectory. In the color selection electrode 6 according to this embodiment, a large number of substantially slot-shaped apertures, which are electron beam passage apertures, are formed in a flat plate by etching. Further, the color selection electrode 6 is fixed to the frame 7 which is a support, and the color selection electrode 6 and the frame 7 form a color selection electrode structure. The color selection electrode structure is hooked on panel pins 9 of the face panel 2 by spring members 8 provided on the frame 7.

FIG. 2 is a process chart of a method of manufacturing a color cathode ray tube according to an embodiment of the present invention. In the frame assembling process, the short side frame and the long side frame are joined by welding and integrated to form a frame-shaped frame. FIG. 3 shows a perspective view of a frame-shaped frame according to an embodiment of the present invention. The lower surface of the long side frame 11 is joined to the upper surface of the short side frame 12 by welding to form the frame-shaped frame 10.
(Corresponding to the frame 7 in FIG. 1) is formed.

The long side frame 11 has a plate thickness of 1.4 to 1.8.
It is a press-punched material having a size of about mm that is bent. Further, in order to increase rigidity and ensure a predetermined strength, there is a bent portion 11a having a triangular cross section. Further, the end portion 11b of the bent portion is welded along the longitudinal direction. Like the long-side frame 11, the short-side frame 12 is made by bending a press-punched material having a plate thickness of 1.4 to 1.8 mm. Reference numeral 13 is a mounting plate for the spring material 14 (FIG. 7).

In the next frame heat treatment step (heat treatment 1), the frame-like frame 10 is heat-treated under conditions of, for example, 550 ° C. or higher for 15 minutes in order to remove work strain during welding.

Next, the frame pressurizing step is performed. Figure 4
(A) is a schematic perspective view for explaining a frame pressurizing step. In the frame pressurizing step, the pressurizing plate 14 is pressed against the side surface of the long side frame 11, and as shown by the arrow,
A force is applied to the frame-shaped frame 10 in the compression direction. The applied force in this step is a force applied to the frame in the heat treatment step (heat treatment 2) after the stretching step described later or a force higher than that.

By applying a compressive force to the frame-shaped frame 10 in this step, the frame-shaped frame 10 is plastically deformed.
FIG. 4B shows an example of the frame shape before and after pressurization. This figure is a schematic view of the frame-shaped frame 10 as viewed from above. The broken line shows the state before pressurization, and the solid line shows the state after pressurization. When the compressive force is released, the elastically deformed portion returns to the original state, but the plastically deformed portion does not return to the state before the application, and the long side frame 11 after the compressive force is released.
Does not match the position of the dashed line. This also applies to the short-side frame 12, and if the short-side frame 12 bends due to plastic deformation, the bending remains the same even when the compressive force is released.

The pressurization of the frame may be carried out by directly pressing the frame using the pressurizing plate as described above, or by pressing the frame while heating. Figure 5
It is a schematic perspective view of an example of such heating and pressurization. The tip portion 15a of the jig 15 is in contact with the upper portion of the side surface of the long-side frame 11 at the central portion in the longitudinal direction. Jig 15
Since it is a rigid body, the portion of the side surface of the long side frame 11 with which the tip portion 15a of the jig 15 is in contact is restrained from moving in the direction in which the long side frame 11 spreads.

When heated at a high temperature in such a state, the short side frame 12 tends to expand in the longitudinal direction due to thermal expansion, but the restriction due to the jig 15 suppresses the expansion due to thermal expansion. Therefore, the frame-shaped frame 10
A compressive force is applied to, and as shown in FIG. 4, the same effect as directly pressurizing the frame can be obtained.

Such heating and pressurizing may be performed by a separate heat treatment step, but if the heat treatment step of the frame (heat treatment 1 in FIG. 2) is used, it is advantageous in terms of productivity. is there. Further, in such a high temperature atmosphere, the frame may be directly pressed by using a pressure plate. in this case,
Since the applied pressure is smaller than the pressurization at room temperature, it is advantageous in terms of simplification and downsizing of equipment.

In any case, by pressurizing in a high temperature atmosphere, a desired effect can be obtained with a pressurizing force which is about half the pressurizing force required at the pressurizing step at room temperature, so that the equipment can be simplified. , Which is advantageous in terms of downsizing.

In the next milling process, the long side frame 1
The upper surface 11c of 1 (bonding surface of the color selection electrode) is cut so as to obtain a predetermined radius of curvature. The upper surface portion 11c of the long-side frame 11 is distorted due to the frame assembly process, the heat treatment process, and the frame pressure process. For this reason, even if the long side frame 11 alone has a regular radius of curvature, the radius of curvature also changes through these steps.

Further, since the radius of curvature also varies in the subsequent tensioning process, the degree of cutting in the milling process should be in consideration of the variation of the radius of curvature in the tensioning process. By the cutting process of this step, the distance between the color selection electrode surface and the phosphor screen surface 2a (FIG. 1) can be set to an appropriate value, and the color shift due to the position shift of the electron beam can be prevented. Moreover, since the upper surface 11a is smoothed by such a cutting process, the subsequent welding with the color selection electrode becomes easy.

After undergoing such a treatment, the process goes to the stretching step. FIG. 6 shows a schematic perspective view in the stretching step. In the stretching step, the color selection electrode 16 in which the opening 17 which is the electron beam passage hole is formed by etching,
The frame-shaped frame 10 is joined in a state where a tensile force is applied. The color selection electrode 16 is joined to the frame upper surface 11c by welding in a state where a tensile force is applied in the direction of arrow A and a compressive force is applied to the frame 10 in the direction of arrow B. Welding is performed, for example, on the frame upper surface 11
It is performed while rotating the roller electrode on c.

After joining by this welding, the color selection electrode is cut into a predetermined length, and the color selection electrode 16 and the frame-shaped frame 10 are cut.
A color selection electrode assembly, which is a joined body with the, is formed. Figure 7
[Fig. 3] shows a perspective view of a color selection electrode assembly. In the state of this figure, the restoring force of the color selecting electrode 16 (the contracting direction) and the restoring force of the frame-shaped frame 10 (the extending direction) are balanced, and the color selecting electrode 16 is applied with a tensile force in the arrow C direction. In this state, the frame-shaped frame 10 is fixed.

Here, it is preferable that the tension applied to the color selection electrode is set such that the peripheral tension is smaller than the central tension. For example, the central tension is 100% and the peripheral tension is in the range of 90% to 65%. In addition to such tension distribution, by attaching a damper for preventing vibration to the non-hole portion 16a of the color selection electrode (damper mounting step in FIG. 2), vibration of the color selection electrode can be suppressed and color misregistration can be prevented. Can be prevented.

As an example of the damper, a frame-shaped body obtained by bending a rod-shaped body can be used. By inserting the frame-shaped body into the hole formed in the color selection electrode and attaching it, the frame-shaped body and the color selection electrode can be attached. Vibration between the color selection electrodes can be absorbed by sliding between the color selection electrodes. In addition to the mounting of the damper, the four-corner mounting plate 13 of the frame 10
The spring member 14 is welded.

Although the frame pressurization is performed before the milling step as shown in FIG. 2, the frame pressurization may be performed after the milling step. The cutting process in this case is performed by pressing the frame to the upper surface 11 of the long side frame.
It suffices to perform the cutting process in anticipation of the variation in the radius of curvature of c. As a result, the frame pressurizing process can be continued in the stretching step, so that the frame pressurizing equipment can also be used as the pressurizing equipment in the stretching step.

Next, the heat treatment step (heat treatment 2 in FIG. 2) is performed. In this heat treatment process, before the glass frit process, the color selection electrode structure is previously heat treated under the same setting conditions as in the glass frit process. Through this heat treatment step, the elastic limit of the frame is lowered, a creep phenomenon in which plastic deformation progresses occurs, and when the temperature is returned to room temperature, the initial tensile force of the color selection electrode is lowered. However, once the high-temperature heat treatment is performed, the creep phenomenon does not newly progress in the next high-temperature heat treatment in the glass frit process, and the decrease in the tensile force of the color selection electrode in the glass frit process can be prevented.

By using the color selection electrode that has been subjected to this high temperature heat treatment to perform alignment with the phosphor screen surface, this state will be maintained even after the glass frit process. Therefore, it is possible to prevent the positional displacement between the color selection electrode and the phosphor screen surface when the temperature is returned to room temperature due to the plastic deformation in the glass frit process.

Here, although the initial tensile force of the color selection electrode is lowered by passing through the high temperature heat treatment step, in the present embodiment, a frame pressure step is provided before the high temperature heat treatment step, The frame is plastically deformed. The effect of this will be described using experimental results. In Table 1 below, one sample according to the comparative example (No. 1) that has not been subjected to the frame pressure treatment and four samples (No. 2 to 5) according to the example that has undergone the pressure treatment.
For, the measured values of the tensile force (N) before and after the heat treatment step are shown. The frame structure was the same for all the samples, and in the stretching step, seven locations along the longitudinal direction of the long side frame were pressed in a direction in which the distance between the opposing long side frames was reduced. The distribution of each pressure value (N) at 7 locations is
Left-right symmetry, from end to end 882N, 1568N, 16
66N, 1568N, 1666N, 1568N, 882N. In this case, each central pressure value (N) is the fourth from the end, 1568N. The long side of the sample is about 60
0 mm, the distance (pitch) between pressure points is 100 m
m. About the pulling force of the color selection electrode, 2940N
And

For the four samples (Nos. 2 to 5) which were subjected to the pressure treatment before the stretching step, 440 ° C. and 40
The pressure treatment was performed in a high temperature atmosphere for 3 minutes, and the pressure point and the pressure value distribution were the same as those in the stretching step. The heat treatment conditions (heat treatment 2 in FIG. 2) were the same for all samples, and the conditions were 440 ° C. and 40 minutes. As the material of each part, the long side frame was made of high tensile steel, the short side frame was made of stainless steel, and the color selection electrode was made of iron.

[0040]

[Table 1]

For each sample, T₁(N) is a stretch
The tensile force of the color selection electrode after that,₂(N) is
It is the tensile force after the heat treatment step. Each value is color selected
It corresponds to each position of the electrode. Position in table (m
m) is the horizontal position of the color selection electrode,
0 is the center of the color selection electrode, and a positive value is the color selection electrode.
When viewed from above, the middle part on the right side with respect to the center
Distance from center, negative value means left side of center
Is the distance from the center of. Table 1, T in the bottom column ₁(flat
Average) (N), T₂(Average) (N) is that
No. 2-5 T₁, T₂Is the average value of
It Table 2 below was calculated based on the experimental results of Table 1.
Shows the data.

[0042]

[Table 2]

In Table 2, the retention rate is the heat treatment step.
After (corresponding to heat treatment 2 in FIG. 2), color selection before heat treatment
It shows how much the pulling force of another electrode is maintained.
It R ₁~ R_Five(%) Is T of each sample in Table 1.₂/ T₁×
Calculated as 100. Also, there is R (average) (%)
Is an example. 2 to 5 R₂~ R_FiveAverage of (%)
It is a value. R (average) -R in the bottom column₁Is the average protection of the example.
It is the difference between the holding ratio and the holding ratio of the comparative example.

Comparative Example No. The retention rate R _{1 of 1} is 64 to 7
The range of 6% (the average of 9 locations is 71.1%), while the retention rate R (average) of the example is in the range of 73 to 83% (the average of 9 locations is 78.7%). Thus, when viewed as the entire color selection electrode, the retention rate of the example exceeds the retention rate of the comparative example. Also, as to the retention rate at each position of the color selection electrode, as can be seen from the values in the bottom column, the retention rate R (average) of the example is the retention rate R ₁ of the comparative example at any position. It is higher.

That is, by plastically deforming the frame before the stretching step, it is possible to suppress the decrease in the frame strength in the high temperature heat treatment step and to suppress the decrease in the tensile force of the color selection electrode. Can be improved. As described above, the reason why the retention rate of this embodiment is excellent is that the rigidity of the frame is improved due to work hardening by plastically deforming the frame in advance.

The comparative example No. In Example 1, Example N
o. In order to secure the retention rate equivalent to 2 to 5, it is necessary to increase the rigidity of the frame, which increases the weight of the frame. In this embodiment, since the holding ratio can be improved without increasing the special rigidity, the weight of the frame can be reduced as compared with the case where the frame having the same structure is used and the frame pressurizing step is not performed. .

Further, after the heat treatment step, Comparative Example N
o. In Example 1, the unevenness of the color selection electrode was about 10 to 20 μm, whereas in Example No. 2-5, 10 μm
Below, the examples also had the effect of reducing the occurrence of wrinkles.

Here, when a tensile force is applied to the color selection electrode in the vertical direction, a compressive force corresponding to the Poisson's ratio is also applied in the horizontal direction. Wrinkles occur in the vertical direction of the color selection electrode,
The compressive force in the lateral direction of the color selection electrode is likely to occur in a portion where the change is abrupt. When the applied pressure before the stretching step is set so that the pressure value of the adjacent portion changes abruptly, the degree of plastic deformation of the long side frame also changes abruptly.

In this case, the degree of plastic deformation of the long-side frame has already drastically changed, even if the pressure applied to the long-side frame in the straddling step does not have a large difference at the adjacent application points. Therefore, since the lateral compressive force of the color selection electrode changes abruptly, a portion where the lateral compressive force of the color selection electrode changes abruptly occurs after the heat treatment process, and wrinkles easily occur. Become.

From this, in the present embodiment, the occurrence of wrinkles is reduced because the holding rate of the tensile force is high and the difference in pressure value between adjacent portions is small, that is, It is considered that the applied pressure before the stretching process was set so that the pressure value changed smoothly.

As described above, after the heat treatment of the color selection electrode assembly is completed, the phosphor screen is formed on the inner surface of the face panel in the phosphor screen forming step. This phosphor screen is formed by selectively exposing the photoresist applied to the inner surface of the panel to a desired position with the black matrix film and the red, green, and blue fluorescent coating films by using the color selection electrode as an exposure mask. By forming.

After the fluorescent screen is formed, the glass frit process (heat treatment 3 in FIG. 2) is carried out, and the face panel and the funnel are heat-treated and joined under the condition of 440 to 470 ° C. for about 20 minutes to form the color. The envelope of the cathode ray tube is completed.

[0053]

As described above, according to the present invention, by plastically deforming the frame before the stretching step, it is possible to suppress the decrease in the frame strength in the high temperature heat treatment step, and to reduce the color selection electrode. It is possible to suppress a decrease in tensile force. As a result, the weight of the frame can be reduced as compared with the case where the frame having the same structure is used and the frame pressing step is not performed.

[Brief description of drawings]

FIG. 1 is an overall sectional view of a color cathode ray tube according to an embodiment of the present invention.

FIG. 2 is a process diagram of a method of manufacturing a color cathode ray tube according to an embodiment of the present invention.

FIG. 3 is a perspective view of a frame-shaped frame according to an embodiment of the present invention.

FIG. 4 is a perspective view illustrating a frame pressurizing step according to an embodiment of the present invention.

FIG. 5 is a perspective view illustrating a frame pressurizing step according to another embodiment of the present invention.

FIG. 6 is a perspective view illustrating a stretching step according to an embodiment of the present invention.

FIG. 7 is a perspective view of a color selection structure according to an embodiment of the present invention.

FIG. 8 is a process chart of an example of a conventional method for manufacturing a color cathode ray tube.

[Explanation of symbols] 1 color cathode ray tube 2 face panel 3 funnel 6,16 color selection electrode 7,10 Frame-shaped frame 8,14 Spring material 11 long side frame 12 short side frames 13 Mounting plate 14 Pressure plate 15 jigs

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Toshifumi Nakatani             1006 Kadoma, Kadoma-shi, Osaka Matsushita Electric             Sangyo Co., Ltd. F term (reference) 5C031 EE08 EE11

Claims (5)

[Claims] 1. In a state in which a tensile force is applied to the color selection electrode,
A step of joining the color selection electrodes to a frame,
A method of manufacturing a color cathode ray tube comprising a frame pressurizing step of pressurizing the frame to plastically deform the frame before the stretching step. 2. The color according to claim 1, wherein the pressurization of the frame is performed by heating the frame while holding at least a part of the frame so as to restrain the positional fluctuation of the frame. Method for manufacturing cathode ray tube. 3. A frame assembling step of assembling the frame before the stretching step, and a heat treatment step of removing distortion of the frame after the frame assembling step, wherein the heating of the frame comprises: The method for manufacturing a color cathode ray tube according to claim 2, wherein the method is performed in the heat treatment step. 4. The method of manufacturing a color cathode ray tube according to claim 1, further comprising a cutting step of cutting the mounting surface of the color selection electrode in the frame after the frame pressing step. 5. The method of manufacturing a color cathode ray tube according to claim 1, wherein after the step of pressurizing the frame, the step of continuing to the step of stretching is continued.