JP6470951B2 - Method for producing resin cap having sealing material made of hot melt composition - Google Patents

Description

  The present invention relates to a method of manufacturing a resin cap having a seal material, and more specifically, a seal material formed by forming a seal material made of a hot melt composition on a resin cap by spin lining is formed. The manufacturing method of the resin cap which consists of.

Resin sealing materials made of various resins are provided on the inner surface side of the top plate portion of the container lid so as to be in close contact with the tip of the container mouth and improve the sealing performance of the container.
The method of forming the resin liner differs depending on the material constituting the sealing material. For example, in the case of a sealing material made of a thermoplastic resin such as polyethylene, a molten resin made of a thermoplastic resin supplied into the cap is embossed. An in-shell molding method, or an insert molding method in which a thermoplastic resin is injection-molded using a cap as a part of a mold has been proposed.
In the case of a sealing material made of vinyl chloride resin, a method in which vinyl plastisol is supplied by spin lining, and in the case of a liner made of natural rubber, an aqueous dispersion latex such as natural rubber is used. In the case of a sealing material made of urethane elastomer, it is formed by mixing the isocyanate component and the polyol component and then cross-linking.

  The sealing material made of thermoplastic resin is excellent in water resistance, but the sealing material by in-shell molding or insert molding requires a dedicated mold to form the sealing material, and the sealing material using plastisol In this case, a plasticizer is indispensable, the odor derived from the plasticizer is a problem, and an oven for baking during plasticization is necessary, and certain equipment is required. In addition, when rubber latex is used, a long drying process is required to dry the moisture in the material. Furthermore, a sealing material made of a urethane elastomer has a low moisture barrier property and needs to be heated in an oven for crosslinking in forming.

From this point of view, there are no problems such as odor and moisture barrier properties, and it can be supplied to the cap shell in a ring shape by a spin lining device, and there is no need for baking. As a sealing material excellent in property and economy, a sealing material made of a hot melt composition has also been proposed (Patent Document 1).
Since the sealing material made of the hot melt composition has higher hardness than the general sealing material described above, the sealing is performed at the corner on the outer peripheral side of the container mouth rather than sealing at the top surface of the container mouth. In order to form a sealing material on the outer periphery of the inner surface of the top plate portion of the cap shell, after applying the hot melt composition as a liner material to the cap shell by spin lining, Further, afterspinning is performed, the liner material is caused to flow toward the outer peripheral edge and the liner surface is smoothed.

JP 2013-203476 A

However, when the sealing material is formed on the outer peripheral edge of the cap shell in this way, there arises a problem that the sealing material protrudes outside from a portion where the sealing material of the cap shell is to be formed during after-spin.
Such protrusion of the sealing material impairs the smoothness of the sealing surface and is inferior in appearance characteristics. In addition, if the protruding portion is detached from the sealing material, it may be mixed into the contents, so it is necessary to manage the occurrence of such a shape defect, and stable continuous production cannot be performed. .
Accordingly, an object of the present invention is to provide a cap manufacturing method that can effectively prevent the seal material from protruding in a cap manufacturing method having a sealing material made of a hot melt composition.

According to the present invention, the annular sealing material made of the hot melt composition is formed by spin lining on the outer peripheral edge of the top plate portion inner surface of the polypropylene cap shell consisting of the top plate portion and the skirt portion depending from the peripheral edge of the top plate portion. In the method of manufacturing a cap, an annular inclined surface that increases in axial thickness toward the outer diameter side of the cap is formed at the boundary between the inner surface of the top plate portion and the inner surface of the skirt portion of the polypropylene cap shell. An annular projection that protrudes inward from the inner surface of the skirt portion is formed below the annular inclined surface, and a flat portion that is continuous with the annular inclined surface is formed on the inner surface of the top plate portion, and the cap is located more than the flat portion. An annular ridge projecting downward from the inside is formed, and at least a side surface of the annular ridge on the flat portion side has an axial thickness toward the outer diameter of the cap. A inclined surface small, the upward and annular inclined surface and the flat portion above the annular projection is sealing material forming position, prior to the spin lining process to cap shell inner surface of the hot melt composition, the cap shell top plate by providing the plasma surface treatment process on at least the sealing member forming position of the portion surface, the manufacturing method of the cap, characterized by the wetting tension of the sealing material located above 32 mN / m is provided.

In the manufacturing method of the cap of the present invention,
1. The hot melt composition has a viscosity at 180 ° C. by a B-type viscometer in the range of 500 to 5000 mPa · sec,
2. The hot melt composition is a hot melt composition based on an ethylene vinyl acetate copolymer;
3. The hot melt composition contains a lubricant,
4). The spin lining process is performed by rotating the cap shell under a condition of 100 to 600 rpm;
Is preferred.

In the present invention, a plasma surface treatment is performed on the inner surface of the cap shell top plate portion at a position where a seal material made of the hot melt composition is formed, and the wetting tension is set to 32 mN / m or more, whereby the seal material made of the hot melt composition. The fluidity of the sealing material can be controlled, the sealing material spreads while adhering to the sealing material forming position, and the formation of the protruding portion of the sealing material can be suppressed.
Further, since the sticking out of the sealing material is effectively prevented, the continuous production can be stably performed, and the productivity and economy are excellent.
The excellent effects of the present invention are also apparent from the results of Examples described later.
In other words, after the plasma surface treatment is performed on the cap shell sealing material forming position, a sealing material made of a hot melt composition is applied by spin lining, and after-spin is performed to form the sealing material surface at a desired position. There was no protrusion of the sealing material, the outer peripheral edge of the sealing material formed a uniform arc, and the sealing performance was excellent (Examples 1 to 5).
On the other hand, when the sealing material is formed in the same manner as in the embodiment except that the plasma surface treatment is not performed, a protruding portion in which a part of the outer peripheral edge of the sealing material protrudes outward is formed. In addition to being inferior, the sealing performance was not satisfactory as compared with the examples (Comparative Examples 1 to 3). Further, even when the plasma treatment was performed, when the wetting tension on the surface where the seal was formed was less than 32 mN / m, the protrusion was formed (Comparative Example 4).
When the flame treatment is performed instead of the plasma treatment, the flame treatment cannot be accurately performed at the sealing material forming position, and the cap shell hem portion and a part of the inner surface (screw portion) are melted and deformed. The cap shell could not be used as a product (Comparative Examples 5 and 6).

It is an expanded sectional view of the part which forms the sealing material of an example of the cap manufactured by the method of this invention.

In the cap manufacturing method of the present invention, a polypropylene cap shell comprising a top plate portion and a skirt portion depending from the periphery of the top plate portion is used, and a sealing material is formed as an annular portion on the outer peripheral edge of the top plate portion inner surface of the cap shell. The sealing material which consists of a hot-melt composition is formed in a position by spin lining.
At this time, it is an important feature that, prior to supplying the sealing material, a plasma surface treatment process is performed at the sealing material forming position so that the wetting tension at the sealing material forming position is 32 mN / m or more. According to the plasma treatment, the surface treatment can be performed efficiently on a limited surface of the inner surface of the cap top plate portion without damaging the cap. This improves the wettability of the surface of the seal formation position, and the hot melt composition spreads while adhering to the surface of the seal formation position at the time of spin lining or after spin, so that it can be effectively prevented from protruding from the seal formation position. .

FIG. 1 is a view showing an example of a cap shell used in the present invention. A cap shell 1 is composed of a top plate portion 2 and a skirt portion 3 depending from the periphery of the top plate portion 2. A screw portion 4 that can be engaged with the screw portion 31 of the container mouth portion 30 is formed.
On the inner surface side of the top plate portion 2 of the cap shell 1, an annular inclined surface 5 is formed at a boundary portion between the top plate portion 2 and the skirt portion 3, and an annular ridge 6 is formed on the inner side of the annular inclined surface 5. Is formed. The annular ridge 6 is formed so that the diameter at the distal end portion 6a is smaller than the inner diameter of the container mouth portion 30 to which the cap is applied.
In the specific example shown in the figure, the sealing material 20 made of a hot melt composition is composed of an annular inclined surface 5, an annular ridge 6, and a flat portion 7 formed between the annular inclined surface 5 and the annular ridge 6. Since it is formed in the annular portion (sealing material forming position) on the inner surface of the cap top plate portion to be configured, the plasma surface treatment is applied to the sealing material forming position.

(Plasma surface treatment)
As long as the wetting tension at the sealing material forming position is 32 mN / m or more, particularly 38 to 60 mN / m, the plasma surface treatment is performed by a conventionally known plasma treatment such as vacuum plasma treatment, reduced pressure plasma treatment, atmospheric pressure plasma treatment, etc. Although it can be used, it is particularly preferable to use atmospheric pressure plasma treatment. Since atmospheric pressure plasma treatment does not require a constant pressure chamber, it can be easily incorporated into existing lines, and the equipment cost is advantageous compared to other plasma treatments.

As the apparatus used for the atmospheric pressure plasma treatment, a conventionally known commercial product can be used. As a suitable treatment condition for setting the wetting tension at the sealing material forming position of the cap shell made of polypropylene within the above range, atmospheric pressure is used. It is preferable to set a pressure in the vicinity of 100 to 800 Torr, a processing time of 0.4 to 10 seconds, a temperature of 5 to 40 ° C., and an output of 400 W. The atmosphere gas includes inert gases such as helium, argon, krypton, xenon, neon, radon, nitrogen, oxygen, air, carbon monoxide, carbon dioxide, carbon tetrachloride, chloroform, hydrogen, ammonia, carbon tetra Fluoride, trichlorofluoroethane, trifluoromethane, acetone, silane and the like can be suitably used. A known fluorinated gas or a mixed gas of the above gases can also be used.
Atmospheric pressure plasma treatment can be carried out under the above-described conditions by discharging the plasma jet electronically to excite the plasma jet electronically and bringing it into contact with the material to be treated (sealing material forming position surface).

(Hot melt composition)
The sealing material composed of the hot melt composition used for the resin cap of the present invention has a thermoplasticity measured at B-type viscometer and having a viscosity at 180 ° C. of 500 to 5000 mPa · sec, particularly 500 to 3000 mPa · sec. It consists of a resin or a thermoplastic resin composition, and can be selected from those generally marketed as hot melt compositions.
The hot melt composition is formed by blending a thermoplastic resin such as an olefin resin or a thermoplastic elastomer such as a styrene with a wax or a plasticizer for viscosity adjustment as necessary. Among the melt compositions, a hot melt composition having a viscosity in a B-type viscometer in the above range and a JIS A hardness in the range of 70 to 95 at the time of liner formation can be suitably used. The softening point (R & B formula) is preferably in the range of 70 to 110 ° C.
Preferably, a hot melt composition based on an ethylene vinyl acetate copolymer can be used.

  Further, the hot melt composition of the present invention can contain a conventionally known lubricant such as erucic acid amide, although not limited thereto. In other words, blending a lubricant can reduce the opening torque in the screw cap and improve the unplugging property. On the other hand, blending a lubricant increases the flow of the sealing material and suppresses the protrusion. In the present invention, the wet tension at the sealing material forming position is adjusted by plasma treatment, and the sticking out of the sealing material made of the hot melt composition is effectively prevented. There is no problem.

(Cap shell)
As the cap shell used for the resin cap of the present invention, it is desirable to use one made of polypropylene.
In order to prevent the seal material from sticking out, it is desirable that the wetting tension on the surface of the cap shell where the seal is formed is larger than the wetting tension of the sealing material. In addition, polypropylene that can form a cap shell with excellent appearance characteristics has a lower wetting tension than the sealing material, and therefore, the sticking out of the hot melt composition becomes particularly prominent. However, in the present invention, since the wetting tension at the sealing material forming position can be adjusted to the above-described range by performing the plasma treatment, it is particularly preferable to use a polypropylene cap shell having excellent heat resistance. It is consistent with the purpose.

Moreover, in the cap of this invention, since the sealing material surface is smooth | blunted and a static friction coefficient is 0.10 or less, a plug opening torque can be reduced. Therefore, even when a cap having a screw portion is used, the opening torque can be reduced without blending a lubricant, and the sticking out of the sealing material can be effectively prevented. Of course, the cap is not limited to the screw cap, and may be a cap of a type that fits into the container mouth.
In addition, the shape of the cap shell top plate part inner surface is not limited to the specific example shown in the figure. For example, in the specific example shown in the figure, the sealing material forming position is defined by forming the annular ridge 6, but the sealing material is located near the outer peripheral edge of the inner surface of the cap shell top plate portion by the centrifugal force by spin lining. Since it is formed, the annular ridge does not necessarily have to be formed.
In addition, since the vicinity of the boundary between the top plate portion and the skirt portion of the cap shell is formed as the annular inclined surface 5, the fluidity of the sealing material is controlled by reducing the amount of the sealing material and facilitating the cooling of the sealing material. Although the protrusion can be effectively suppressed, in the present invention, since the fluidity of the sealing material can be controlled by controlling the wettability of the sealing material forming position by plasma treatment, it is not always necessary to use an inclined surface.
Further, as shown in FIG. 1, although not essential, an annular projection 8 projecting downward from the inner surface of the skirt portion may be formed below the annular inclined surface 5, thereby further protruding the seal portion. Can be suppressed.

(Formation of sealing material)
In the present invention, first, the above-described surface treatment process by plasma treatment is applied to the sealing material forming position on the inner surface of the cap shell top plate portion.
Next, the sealing material in a molten state composed of the above-described hot melt composition is subjected to a spin lining process in which the sealing material is applied by spin lining to the sealing material forming position subjected to the plasma surface treatment. At this time, it is particularly preferable to rotate the cap shell under the condition of 100 to 600 rpm. Thereafter, if necessary, the cap shell is further rotated, the surface of the sealing material is spread outward by centrifugal force, the surface is smoothed, naturally cooled and solidified to complete the sealing material. In addition, as shown in the figure, when an annular inclined surface is formed at the sealing material forming position, the sealing material at the location corresponding to the annular inclined surface is crimped to the outer corner of the container mouth to ensure sealing performance. Possible sealing materials are formed.

Example 1
Plasma was irradiated for 1 second using a wettability improving plasma irradiator “ST-7000” manufactured by Keyence Corporation at the position where the sealing material was formed on the inner surface of the top plate portion of the polypropylene cap shell with an inner diameter of 38 mm. The wetting tension at the sealing material forming position after plasma irradiation was 56 mN / m.
Next, while the cap shell is rotated at a speed of 400 rpm, a hot melt composition made of an ethylene vinyl acetate copolymer and having a viscosity of 560 mPa · s as measured by a B-type viscometer is supplied. , 30 caps were evaluated. The results are shown in Table 1.

(Examples 2 to 4)
The hot melt composition was the same as in Example 1, except that the viscosity of the hot melt composition was 1150 mPa · s (Example 2), 2100 mPa · s (Example 3), and 2950 mPa · s (Example 4). The protrusion of the was evaluated. The results are shown in Table 1.

(Example 5)
Extrusion of the hot melt composition was evaluated in the same manner as in Example 1 except that the viscosity of the hot melt composition was 4700 mPa · s and the rotation speed of the cap was 600 rpm. The results are shown in Table 1.

(Comparative Examples 1-3)
Extrusion of the hot melt composition was evaluated in the same manner as in Examples 1 to 3, except that the plasma treatment was not performed. The results are shown in Table 1.

(Examples 6 to 10 and Comparative Example 4)
For the cap shell used in Example 1, the wetting tension was measured while changing the plasma irradiation time, and the continuous lining property was evaluated using the hot melt composition used in Example 1 for the cap shell after the plasma irradiation. did. The results are shown in Table 2. Conditions for continuous lining evaluation are as follows.
While rotating the cap shell at a speed of 400 rpm, a hot melt composition made of an ethylene vinyl acetate copolymer and having a viscosity of 560 mPa · s as measured by a B-type viscometer is supplied. The composition was evaluated for protrusion and chipping.

(Comparative Examples 5 and 6)
Continuous lining properties were measured in the same manner as in Example 6 except that flame treatment (surface treatment of the inner surface of the cap with a gas burner at 0.16 s / once) was performed instead of plasma treatment. The results are shown in Table 2.

(Example 11)
In the same manner as in Example 1, a hot melt composition having a viscosity of 560 mPa · s was supplied, and the smoothness of the hot melt composition was evaluated. The rotational speed of the cap shell was changed as shown in Table 3, and the smoothness of the formed sealing material was measured. The results are shown in Table 3.
The method for measuring the smoothness is as follows.
Using the ROUNDTEST RA-2200 roundness / cylindrical shape measuring machine manufactured by Mitutoyo Corporation, the position where the cap comes into contact with the bottle is measured at a rotational speed of 6 rpm. The difference was taken as the smoothness of the sealing material.

In the resin cap manufacturing method of the present invention, the fluidity of the sealing material made of the hot-melt composition can be controlled by improving the wettability of the sealing material forming position of the cap shell by plasma treatment, and the sealing material is not protruded. Since it is effectively suppressed and can be stably produced continuously, it can be suitably used for the production of mass-produced products.
Moreover, it is excellent in sealing performance and has a small opening torque, and can be suitably used particularly as a cap having a screw portion.

  DESCRIPTION OF SYMBOLS 1 Cap shell, 2 Top board part, 3 Skirt part, 5 Annular inclined surface, 6 Annular protrusion, 7 Flat part, 8 Annular protrusion, 20 Seal material, 30 Container mouth part.

Claims (5)

This is a cap manufacturing method in which an annular sealing material made of a hot melt composition is formed by spin lining on the outer peripheral edge of the inner surface of the top plate portion of a polypropylene cap shell consisting of a top plate portion and a skirt portion depending from the peripheral edge of the top plate portion. And
An annular inclined surface whose axial thickness increases toward the outer diameter of the cap is formed at the boundary between the inner surface of the top plate portion and the inner surface of the skirt portion of the polypropylene cap shell, and below the annular inclined surface. Is formed with an annular protrusion that protrudes from the inner surface of the skirt to the inside of the cap,
The inner surface of the top plate portion is formed with a flat portion continuous with the annular inclined surface and an annular ridge protruding downward from the inside of the cap with respect to the flat portion, and at least the flat portion side of the annular ridge The side surface is an inclined surface in which the axial thickness decreases toward the outer diameter of the cap,
Above the annular protrusion, and on the annular inclined surface and the flat portion are the sealing material forming position,
Before spin lining process to cap shell inner surface of the hot melt composition, by providing a plasma surface treatment process on at least the sealing member forming position of the cap shell top panel inner surface, 32 mN the wetting tension of the seal material forming position / M or more, The manufacturing method of the cap characterized by the above-mentioned.   The method for producing a cap according to claim 1, wherein the hot melt composition has a viscosity at 180 ° C measured by a B-type viscometer in the range of 500 to 5000 mPa · sec.   The method for producing a cap according to claim 1 or 2, wherein the hot melt composition is a hot melt composition mainly composed of an ethylene vinyl acetate copolymer.   The method for producing a cap according to claim 1, wherein the hot melt composition contains a lubricant.   The cap manufacturing method according to claim 1, wherein the spin lining step is performed by rotating the cap shell under a condition of 100 to 600 rpm.