JPS6247706B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for thermally bonding plastic tape, and more particularly to a method for thermally bonding a folded portion of a plastic tape to the inner peripheral surface of an open end of a metal cylinder.

As shown in FIG. 1, the open ends 2a and 3a of a seamless upper can body 2 and a seamless lower can body 3 are fitted together via an adhesive layer 4,
A metal can 1 with a relatively thin body wall and having a bonded circumferential joint 5 is particularly suitable as a pressure-resistant can for storing beer, carbonated drinks, etc. (for example, an internal volume of about 1 to 10 liters). It is proposed as. In this case, the upper can body 2 and the lower can body 3 are usually made from blanks with a corrosion-resistant coating film (for example, a phenol epoxy coating film or an organosol coating) formed on the inner surface to prevent corrosion of the contents. Since it is formed by drawing, etc., the inner surface is protected by a coating film, but the metal is exposed at the end surface 3a ₁ (formed by cutting) of the inner open end 3a. . Therefore, in order to ensure corrosion resistance against the contents, it is desirable to cover the end surface 3a ₁ and the inner circumferential surface 3a ₂ near the end surface 3a ₁ with the adhesive layer 4 as shown in FIG.

On the other hand, as a method for forming the adhesive layer 4, it is possible to apply a liquid adhesive such as a thermosetting adhesive or a slurry adhesive, or electrostatically apply a powder adhesive. Heat-adhesive plastic tape is applied to the outer circumferential surface _3a3 of the portion 3a, leaving the protruding part, and then heat-bonding the protruding part to the end face _3a1 and the inner circumferential face _3a2 , and then attaching it to the open end of the upper can body 2. The method of fitting and thermally bonding the open end 2a
This is preferable in that it is easy to obtain an adhesive layer 4 having a uniform thickness and having no defects such as pores between the adhesive layer 4 and 3a.

As a method for thermally bonding the protruding portion of the plastic tape to the end surface _3a1 and the inner circumferential surface _3a2 , the present inventors previously proposed in Japanese Patent Application No. 57-42521 by folding the protruding portion approximately radially inward. Bend it so that the base of the protruding part touches the entire surface of the end face,
Next, a core is inserted into the open end, the protruding part is folded back, and the folded protruding part is pressed against the inner peripheral surface with the core, and in the pressed state, the open end is heated to a temperature higher than the temperature at which plastic can be thermally bonded. Heat it up,
We proposed a method for thermally bonding plastic tape to the open end of a metal cylinder, which is characterized by thermally bonding the protruding portion to the end face and inner peripheral surface.

The above heating of the opening end requires a short heating time;
It is preferable to use high-frequency induction heating for reasons such as ease of heating control, but in this case, depending on the induction heating conditions, especially the relative positional relationship between the high-frequency induction heating coil and the opening end. It has been found that problems such as scorching of the paint film and formation of bubbles and wrinkles in the adhesive layer are likely to occur.

The present invention aims to solve the above-mentioned technical problems.

In order to achieve the above object, the present invention heat-bonds the outer circumferential surface of the open end of a metal cylindrical body with a protruding part extending outward, and the protruding part is folded back to form the inside of the open end. A method of thermally bonding the folded portion of the plastic tape that is in contact with the circumferential surface to the inner circumferential surface, and electrically insulating the outer circumferential surface and the inner circumferential surface of the open end via the plastic tape. When pressed by the elastic member, a high-frequency induction heating coil is placed close to the open end so that the edge of the open end near the end surface is located approximately at the same position as the end surface in the axial direction. A plastic tape is placed on the inner circumferential surface of the open end of the metal cylindrical body, the heating coil being placed outside the end face and energizing the heating coil to heat the open end with high frequency induction. The present invention provides a method for thermal bonding.

The present invention will be described below with reference to the drawings.

In FIG. 2, 10 is a metal cylinder;
a is an open end. In this specification, the term "metal cylindrical body" refers to a cylindrical body having a pair of opposing open ends (without side seams or having a seam formed by welding, etc.), as well as a lower can shown in FIG. body 3
It also includes a cup-shaped cylinder with a bottom such as _{the one} shown in FIG. Further, the metal forming the metal cylinder includes tin-plated steel plate, stain-free steel (electrolytic chromic acid treated steel plate), aluminum (alloy) plate, and other arbitrary metals or alloys.

The open end 10a of the metal cylindrical body 10 shown in FIG. 2 corresponds to the open end 3a of the lower can 3 shown in FIG. It is becoming. Although not shown,
An anticorrosive coating (preferably with excellent thermal adhesion to plastic tape 11 described later) is formed on the inner surface. A primer coating film (not shown) excellent in thermal adhesion to the plastic tape 11 is formed on the outer surface, particularly on the outer circumferential surface _10a3 of the opening end, as required. Note that the end surface 10 of the opening end 10a
a ₁ is usually left cut so that the metal is exposed.

A plastic tape 11 is thermally bonded along the entire circumference to surround the outer circumferential surface _10a3 of the open end 10a, and a portion of the plastic tape 11 is not thermally bonded and extends outward to form the protruding portion 11a. It is becoming. The width of the portion thermally bonded to the outer peripheral surface is usually about 4 to 10 mm, which is longer than the width of the protruding portion 11a. Examples of the plastic forming the plastic tape 11 include thermoplastics having a relatively low melting point or softening point and having polar groups, such as modified linear polyester, nylon 11 or nylon 12, or acid-modified polyolefin.

Plastic tape 1 surrounding the outer peripheral surface _10a3
For example, as previously proposed by the present inventors, thermal bonding is performed using a plastic tape having a length substantially equal to the circumferential length of the outer circumferential surface _10a3 held by vacuum adsorption on the circumferential surface of an adhesive roll. The open end 10a, which is heated to a temperature that allows thermal bonding and whose interior is supported by a mandrel, is moved onto the outer peripheral surface _10a3 under pressure while rotating at the same peripheral speed as the adhesive roll. It is done by twisting.

The open end 10a is inserted into the die 12 shown in FIG. 3 so that the base 11a ₁ of the protruding portion 11a (width is usually about 0.5 to 3 mm) comes into contact with the entire surface of the end surface 10a ₁ . It is bent approximately radially inward. The die 12 has an open end insertion hole 13
(hereinafter referred to as opening end side hole), opening end side hole 1
a stepped portion 14 connected to 3 and extending radially inward;
and a hole 15 (hereinafter referred to as core side hole) for inserting a core 16 (see FIG. 4) connected to the stepped portion 14.

The opening end side hole portion 13 has a truncated conical guide surface 13.
a and a short cylindrical guide surface 13b, and the inner diameter of the short cylindrical guide surface _13b is (D ₁ +2t ), that is, the opening end 10a to which the plastic tape 11 is thermally bonded to the outer peripheral surface _10a3 can be loosely inserted. The length of the short cylindrical guide surface 13b in the axial direction is shorter than the length of the open end 10a, and preferably is approximately equal to the length of the folded protrusion 11a.

The radial width of the stepped portion 14 is determined to be substantially equal to the sum of the thickness of the open end 10a and the thickness t of the plastic tape 11. Therefore, the open end 1
When 0a is inserted into the die 12 through the open end side hole 13, it hits the stepped part 14 and the protruding part 11a
is bent almost radially inward, and the protruding portion 1
The base portion 11a ₁ of 1a is clamped between the stepped portion 14 and the end surface 10a ₁ .

The core side hole portion 15 has a short cylindrical guide surface 15a and a frusto-conical guide surface 15b for guiding the core 16 connected to the stepped portion 14. The inner diameter of the short cylindrical guide surface 15a is substantially equal to the inner diameter D of the open end 10a.

The die 12 has a built-in high-frequency induction heating coil 17 (hereinafter referred to as a heating coil) close to and surrounding the short cylindrical guide surface 13b. Part 10a
can be heated to a temperature higher than the temperature at which the plastic forming the plastic tape 11 can be thermally bonded (ie, higher than the melting point or softening point). For this reason, the die 12 is made of a material that is electrically insulating, does not undergo induction heating, and has strength and heat resistance, such as ceramics, Bakelite, fluororesin, and the like.

The heating coil 17 has an open end 10a that is connected to the die 12.
In the inserted state, the edge 17a of the open end closer to the end surface _10a1 is aligned with the end surface 11 in the axial direction.
The open end 10 is located at approximately the same position as a ₁ or outside the end surface 11a ₁ (in the case of FIG. 3).
It is important that it is provided close to a.
The reason will be explained later.

As shown in FIG. 4, the core 16 includes a rigid core 16a and a sleeve 16b made of heat-resistant elastic rubber.
It is equipped with The sleeve 16b consists of a tapered part _16b1 formed at the tip and _a cylindrical part _16b2 .
It is easy to push into the inside of 5. Cylindrical part 16b ₂
The outer diameter of the opening end 10a is determined to be at least the value obtained by subtracting twice the thickness t of the plastic tape from the inner diameter D of the open end 10a, that is, at least (D-2t), and as shown in FIG. Push the core 16 into the die 12 through the core side hole 15, and use the sleeve 16b to
The protruding part 11a extending approximately radially inward is folded back, and the folded protruding part 11a is clamped between the inner circumferential surface _10a2 of the open end and the sleeve 16b, so that it can be elastically pressed. There is.
At this time, the portion of the plastic tape ₁₁ adhered to the outer peripheral surface 10a3 is supported by the short cylindrical guide surface 13b of the opening end side hole 13.

The elastic rubber forming the sleeve 16b includes:
It is desirable to use a material that has electrical insulation properties, excellent heat resistance and abrasion resistance, and excellent removability from the plastic tape 11 that has been melted or softened and solidified, such as fluororubber or silicone rubber. In addition, the hardness of the rubber (shore A) is preferably 30 to 90 degrees, and more preferably 60 degrees.
~80 degrees is more preferred. If it is lower than 30 degrees, it will be too soft and it will be difficult to apply sufficient elastic pressing force, and if it is higher than 90 degrees, it will be too hard and difficult to insert into the folded protrusion 11a.

As shown in FIG. 5, after the insertion of the core 16 is completed, when the heating coil 17 is energized, the open end 10
a is heated by induction to a temperature higher than the temperature at which the plastic can be thermally bonded, and the base portion 11a ₁ of the protruding portion 11a is heated to the end surface 10a ₁ and the remaining portion of the protruding portion 11a is heated to the inner peripheral surface 10a ₂ under pressure. Glued.
The heating temperature and pressing force are controlled to such an extent that the thickness of the plastic tape 11 does not substantially change during thermal bonding. After thermal bonding, the heating coil 17 is deenergized, and after the plastic tape 11 is cooled and solidified,
The core 16 and the metal cylinder 10 are extracted from the die 12.

Curve a in FIG. 6 shows an example of the heating temperature distribution along the opening end 10a, and shows the heating temperature distribution in the region from the end 11a' of the folded protrusion 11a to the end surface 10a ₁ of the opening end. A relatively gentle temperature gradient can be seen along the line. Curve b represents the open end 10a.
This figure shows the temperature distribution when high-frequency induction heating is performed under similar conditions when is a free end, that is, when the die 12 and core ₁₆ are not attached. On the other hand, the temperature rises at a steep slope, probably due to the edge effect.

When the die 12 and the core 16 are attached, the temperature gradient becomes relatively gentle as shown by the curve a, probably because heat is removed by conduction to the sleeve 16b of the die 12 and the core 16. Therefore, by adjusting the current supplied to the heating coil 17 and the energization time so that the temperature of the curved part a between the end portion 11a' and the end surface _10a1 reaches a predetermined thermal bonding temperature, the protruding portion can be removed. 11a
is thermally bonded to the end surface 10a ₁ and the inner circumferential surface 10a ₂ of the open end, so that the end surface 10a ₁ can be reliably protected without creating pores or the like.

Since the plastic tape portion thermally bonded to the outer circumferential surface _10a3 is not overheated, its surface condition remains unchanged, so that fitting in the subsequent process can be carried out smoothly. In addition, in the above example,
Since the outer peripheral surface of the opening end 10a is fixed,
During heating, the open end 10a cannot expand due to thermal expansion, and therefore the distance between the heating coils 17 is constant along the entire circumference, so that uniform heating is performed along the entire circumference.

For comparison, the a' curve in FIG. 8 shows that the edge 17a of the open end of the heating coil 17 closer to the end surface _11a1 is located inside along the axis line than the end surface _11a1 , as shown in FIG. 3 shows an example of the heating temperature distribution along the opening end 10a in the case of FIG. In this case, the heating temperature rapidly decreases from the end 11a' of the protruding portion toward the end surface _10a1 of the open end 10a.

This is considered to be due to the fact that the b' curve showing the temperature distribution when the open end 10a is a free end is almost horizontal, and the heat absorption by the core 16 and the die 12. Therefore, if the heating coil current and energization time are set so that the end surface 10a ₁ reaches an appropriate thermal bonding temperature, the vicinity of the protruding end 11a' is likely to be overheated. As a result, the coating film in that area is likely to burn, or bubbles or wrinkles may occur in the plastic tape 11 on the outer circumferential surface _10a3 , which tends to cause problems during fitting in subsequent steps.
On the other hand, if the output of the heating coil 17 is lowered in an attempt to prevent the above-mentioned overheating, the vicinity of the end surface _10a1 will not reach a sufficient temperature for thermal bonding, and therefore thermal bonding will not be performed.
Or even if it is done, it will be incomplete and it will be difficult to obtain a satisfactory anti-corrosion effect.

In order to prevent the above-mentioned overheating, it is conceivable to air-cool the vicinity of the end portion 11a', but this would complicate the equipment and operation. It is also conceivable to lengthen the short cylindrical guide surface 13b of the die 12, but this is likely to cause trouble when bending the protruding portion 11a inward.

The present invention is not limited to the above examples; for example, if the heating coil is ring-shaped along the circumference of the open end and satisfies the above conditions, It may be arranged inside or outside opposite the end surface.

According to the present invention, the high-frequency induction heating coil is arranged such that the edge of the open end near the end face is located at approximately the same position as the end face in the axial direction, or is located outside the end face, and With the outer and inner circumferential surfaces of the end portion pressed by an electrically insulating member through the plastic tape, the protruding portion of the folded plastic tape is thermally bonded to the inner circumferential surface of the open end. Therefore, the opening end portion corresponding to the folded-back protruding portion is heated almost uniformly and efficiently by induction, thereby preventing scorching of the paint film due to overheating, generation of bubbles or wrinkles in the adhesive layer, or unresolved defects due to insufficient heating. This has the effect that a sound thermally bonded portion can be obtained without the risk of causing problems such as the occurrence of adhesive portions.

[Brief explanation of the drawing]

FIG. 1 is a longitudinal cross-sectional view of an example of a metal container in which a metal cylinder to which plastic tape is thermally bonded by the method of the present invention is assembled as a lower can body, and FIG. FIG. 3 is a vertical cross-sectional view of a main part of an example of a metal cylinder with plastic tape thermally bonded to the outer circumferential surface of the open end. A vertical cross-sectional view showing a state in which the protruding portion of the plastic tape is folded inward after being inserted into a die arranged according to the invention. A partially cutaway front view of an example of the core, FIG. 5 is a longitudinal cross-sectional view showing the state in which the core in FIG. 4 is inserted into the open end of FIG. 3 and the protruding portion is folded back, and FIG. Diagram 7 showing an example of induction heating temperature distribution along the opening edge in the case of
The figure is a longitudinal sectional view showing an example of the relative positional relationship between the heating coil and the opening end in the comparative example, and FIG. 8 is a diagram showing an example of the induction heating temperature distribution along the opening end in the comparative example. be. 10... Metal cylindrical body, 10a... Open end, 10a ₁ ...
End face, 10a ₂ ...inner peripheral surface, 10a ₃ ...outer peripheral surface, 11...
Plastic tape, 11a... protrusion, 12
...Die (electrical insulating member), 16... Core (electrical insulating member), 17... High frequency induction heating coil, 17
a... End face near the end face.

Claims (1)

[Claims] 1 Plastic tape is thermally bonded to the outer circumferential surface of the open end of a metal cylinder, leaving an outwardly extending protrusion, and the protruding portion is folded back to abut the inner circumferential surface of the open end. , a method of thermally bonding the folded portion to the inner circumferential surface, in which the outer circumferential surface and the inner circumferential surface of the open end are pressed by an electrically insulating member via the plastic tape. A high-frequency induction heating coil is arranged close to the open end so that the edge of the open end closer to the end face is located at approximately the same position as the end face in the axial direction or outside the end face. 1. A method for thermally bonding a plastic tape to an inner circumferential surface of an open end of a metal cylinder, the method comprising: installing a heating coil, applying electricity to the heating coil, and heating the open end with high frequency induction.