JP2545207B2 - How to make plastic caps - Google Patents

Abstract

A process for making a closure cap (2) provided with a gasket (5) from a polypropylene material for a container (1), said closure cap (2) comprising an end wall and a circumferential side wall (11), in which process the gasket (5) is formed in the closure cap via a melting and a cooling operation by applying in the closure cap an amount of plastisol which is shaped therein into a gasket configuration at an elevated temperature adjusted after the plastisol addition; causing the plastisol shaped into the gasket configuration to melt completely by further energy supply and then cooling same to form the gasket, whereby starting from an integral combination of the closure cap (2) with a sealing ring (13) which is connected with the closure cap by means of a number of frangible bridges (12) capable of being broken on the first opening of the container, and, to form the gasket (5), carrying out the melting operation by heating the closure cap after addition of the plastisol to a temperature of 50 to 110 DEG C and by exposing the resulting plastisol shaped into the gasket configuration subsequently, as is known per se, to microwave energy until the plastisol has been completely molten.

Description

TECHNICAL FIELD The present invention relates to a method for producing a plastic cap having a pill fur proof band (hereinafter, may be abbreviated as a PP band), and more specifically, to a hermetically sealed case. The present invention relates to a method for producing a plastic cap made of polyolefin (for example, polypropylene) equipped with a gasket for use by molding the gasket in a preformed cap body.

(Prior art) As a method of manufacturing a plastic cap with a gasket, after molding a plastic cap body by injection molding or the like, plastisol for forming a gasket is applied inside the cap body, and in this state, the plastisol is heated to form a flux, Then, there is known a method of cooling this and molding the gasket. This method has the advantage that the step of mounting the gasket in the cap is unnecessary,
It is industrially very useful in terms of productivity.

However, in this method, since the flux temperature of the plastisol is considerably high, when the plastisol is heated to flux by means such as ordinary oven heating, the plastic (for example, olefin resin) forming the cap body is deformed. I will end up. Particularly in a cap having a PP band, since the PP band is connected to the cap through a breakable bridge, the bridge is likely to break during heating. Therefore, it is necessary to employ a heating means capable of selectively heating the plastisol.

As a means for selectively heating the plastisol, there is a method by induction heating. In this case, conductive powder such as aluminum powder and iron powder must be mixed in the plastisol. For this reason, not only the conductive powder must be uniformly dispersed in plastisol, but the viscosity of plastisol becomes unnecessarily high, and the workability when plastisol is applied inside the cap body is significantly reduced. Cause problems.

Therefore, a method of heating plastisol by dielectric heating instead of induction heating has been proposed (for example, British Patent No. 1,327,583). This method is to selectively heat the plastisol by irradiating the plastisol with microwaves of a certain frequency (the plastic forming the cap body is microwave transparent), and the plastisol is electrically conductive. It is practically used without the need to mix powders. However, in this method, there is heat loss from the plastisol surface, so if the plastisol surface is sufficiently heated by microwaves to reach the specified flux temperature, the plastisol interior will overheat and become overheated. As a result, the vinyl chloride resin, which is the main component of plastisol, is thermally deteriorated, and the physical properties of the resulting gasket become unsatisfactory.

As a method for solving such a problem, British Patent No. 2,051,
No. 660 discloses that a plastic cap is preheated by oven heating prior to microwave heating. That is, by heating the plastic cap at a temperature lower than the melting point of the plastic constituting the cap and at a melting point of −35 ° C. or higher, and heating by the microwave in this state, heat loss from the plastisol surface is effectively made. It is possible to prevent it and to uniformly heat the entire plastisol to a constant flux temperature without overheating the inside of the plastisol.

(Problems to be Solved by the Invention) The method of British Patent No. 2,051,660 described above is PP
Even when applied to a cap provided with a band, it is extremely useful in that a bridge that connects the bands does not break when the plastisol is heated, and a gasket with no deterioration in physical properties can be effectively molded in the cap. Is the way.

However, in this method, after the plastisol is applied to the inside of the cap, preheating is performed prior to microwave heating, so that there is a drawback that the production rate is reduced by the amount of preheating. For example, in the above British patent specification,
When the cap is made of polypropylene resin (melting point 165 ° C), the preheating temperature is described as being at a temperature of 135 to 160 ° C for about 1 to 10 minutes.

Therefore, it is an object of the present invention to provide a method capable of molding a gasket having good physical properties in a plastic cap while shortening the preheating time as much as possible and effectively avoiding a decrease in production rate.

(Means for Solving the Problem) According to the present invention, the ceiling wall, the circumferential side wall hanging from the peripheral edge of the ceiling wall, and the lower end of the circumferential side wall provided with a breakable bridging portion are provided. And a pilfer proof band formed on the inner wall of the ceiling wall, and a circumferential projection is formed on the inner surface of the circumferential side wall. An annular space for a gasket is formed by these two projections. A microwave-transparent olefin resin plastic cap body is used, a gasket forming plastisol is applied to the annular space inside the cap body, and then the plastisol is irradiated with microwaves to be heated to form a gasket. In the method of manufacturing a plastic cap, the thickness of a portion of the ceiling wall located in the annular space as the cap body is Use the one that is set to 20 to 50% of the thickness of the ceiling wall of other parts, and place the plastisol-treated cap body in a heating atmosphere at a temperature lower than the melting point of the olefin resin that constitutes the cap body. There is provided a method for producing a plastic cap, characterized in that preheating is performed by holding for a predetermined time and then microwave heating is performed.

(Operation) In the present invention, the wall thickness of the gasket forming position (annular space for gasket) in the ceiling wall of the cap body is
It is extremely important to set the thickness to 20 to 50% of the thickness of other parts of the ceiling wall. That is, by making the wall thickness at the gasket forming position thin in this way, when the cap body on which the plastisol is applied is placed in a heating atmosphere, the temperature of the cap wall at the gasket forming position is It is heated to the temperature of the heating atmosphere (preheating temperature) more quickly than the portion. Therefore, the preheating time can be shortened as much as possible, and the production speed is improved. Further, when the preheating time is shortened, the thermal energy applied to the wall of the cap body other than the gasket forming position is also reduced, so that the deformation of the bridge portion in the preheating step can be effectively prevented.

The preheating is performed, for example, in a hot air oven, and the microwave heating is performed immediately after the preheating is completed, that is, after a predetermined time has elapsed. According to the present invention, since the plastisol is microwave-heated while the wall of the cap body at the gasket forming position is heated and held at a constant temperature, the heat loss of the plastisol surface, particularly the plastisol surface in contact with the cap body, is reduced. Effectively relaxed, the entire plastisol can be uniformly heated to a constant flux temperature without overheating the plastisol to an unnecessarily high temperature, so a gasket with good physical properties can be molded in the cap. it can. Further, since it is not necessary to compensate for the heat loss on the plastisol surface, the microwave heating time can be relatively short, and the heating time as a whole including the above-mentioned preheating time can be shortened and the production rate can be remarkably improved. .

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described below based on specific examples shown in the accompanying drawings.

Basic structure of the cap: An enlarged cross section of the gasket part of the plastic cap manufactured according to the present invention and an enlarged side cross section of the pill fur proof band (PP band) are shown in FIGS. 1 and 2 together with the container neck, respectively, and PP A part of the enlarged plane cross section of the band is shown in FIG.

In FIGS. 1 to 3, this plastic cap (generally designated by 10, see FIG. 2) is mounted on the upper end 1 of the neck of a container made of glass or the like. Especially the first
As is clear from the drawings and FIG. 2, the cap 10 has a ceiling wall 2 (see FIG. 1) and a circumferential side wall 11 (see FIG. 2) depending from the peripheral edge of the ceiling wall 2. A PP band 13 is provided at the lower end of the circumferential side wall 11 via a rupturable bridge portion 12.

Further, on the inner surface of the circumferential side wall 11, although not shown,
It is desirable to form a screw-like projection that can be screw-engaged with the neck of the container.

With particular reference to FIG. 1, a downward circumferential projection 3 is formed on the inner surface of the ceiling wall 2, and the lower circumferential projection 3 is formed on the inner surface of the circumferential side wall 11 near the base portion thereof. The circumferential protrusions 4 are formed so as to face each other. The plastisol is filled in the annular space formed by these circumferential protrusions 3 and 4, and the gasket 5 is formed.

Among the above-mentioned circumferential projections 3 and 4, the circumferential projection 3 formed on the inner surface of the ceiling wall 2 has a crescent-shaped cross section, and its tip is curved toward the circumferential side wall 11 and is tapered. Is desirable. That is, by having such a shape, the circumferential projection 3 has elasticity. As is apparent from FIG. 1, the circumferential projection 3 is arranged so that its tip contacts the upper end surface of the upper end 1 of the container neck. As a result, the twisting stress of the gasket 5 that occurs when the cap 10 is detached from the neck of the container can be effectively relieved by the elastic force of the tip of the circumferential protrusion 3. Further, when the contents contained in the container in which the cap 10 is mounted are subjected to heat sterilization treatment or the like, when the internal pressure of the container increases, the tip of the circumferential protrusion 3 elastically deforms and expands inside the container. Air escapes to the outside of the container through the space between the circumferential protrusion 3 and the upper surface of the container neck upper end 1. Therefore, the rise of the internal pressure of the container during the heat sterilization treatment is effectively alleviated, and the deformation of the container due to the increase of the internal pressure is effectively prevented. At the same time, due to the elastic deformation of the tip of the circumferential protrusion 3, the holding force of the gasket 5 is increased, and the gasket 5 is
It is stably held in the annular space formed by the circumferential protrusions 3 and 4.

As is apparent from FIG. 1, in the present invention, the gasket forming portion (portion in which the annular space is formed) of the ceiling wall 2 of the cap is formed to be significantly thinner than other portions (ceiling wall). 20 to 50% of the thickness of the other parts of 2). This thinning causes the wall temperature at the gasket forming position to rise rapidly during preheating in a heating atmosphere described later, and thus the preheating time can be shortened. This point will be described in detail later. Moreover, since the flexibility of the container wall of the gasket forming portion is increased by the above-mentioned thinning, when the internal pressure of the container rises, the air inside the container can easily escape to the outside. Further, there is an additional advantage that the deformation of the container due to the increase of the internal pressure can be prevented more effectively.

Manufacture of Cap: In order to manufacture the plastic cap having the above structure according to the method of the present invention, first, a plastic cap body is molded using a microwave-transparent olefin resin. Here, the plastic cap main body means the cap 10 shown in FIGS. 1 and 2 described above, which does not have the gasket 5.

As the microwave permeable olefin resin, any olefin resin can be used as long as it is microwave permeable, but polypropylene resin is particularly preferably used. By using such an olefin resin,
It becomes possible to selectively heat the plastisol for forming the gasket during microwave heating described later. The plastic cap body can be molded by a known molding means such as injection molding.

After molding the plastic cap body, plastisol (liquid or semi-liquid) for forming a gasket is applied into the annular space formed by the circumferential projections 3 and 4 of the cap body. This is performed by a known means such as spin coating. That is, it can be easily performed by arranging the molded cap main body upward so that the ceiling wall 2 becomes the bottom, and injecting plastisol into the annular space while rotating this at high speed.

As the plastisol, those conventionally used for forming a gasket can be used. That is, a suspension prepared by blending a resin component such as vinyl chloride resin with a plasticizer, a stabilizer, a viscosity reducing agent, a torsion reducing agent and the like is used. In the present invention, plastisol having a low flux temperature is particularly suitable from the viewpoint of lowering the preheating temperature. As the flux temperature, that is, the temperature at which plastisol completely melts and becomes a solution,
The resin component is typically a vinyl chloride copolymer resin containing a vinyl acetate unit, and in the present invention, for example, a plastisol prepared using a vinyl chloride copolymer resin containing 5% of a vinyl acetate unit is used. Most preferably used.

According to the present invention, after the above-described plastisol is applied to the annular space in the cap body, preheating is performed by holding the cap body in a heating atmosphere using a heating oven or the like. This preheating is performed in order to control the heat loss from the plastisol surface during microwave heating, but the preheating temperature is the deformation of the cap body, especially the bridging part connecting the PP band 13. 12
In order to prevent the deformation or breakage of the above, it is essential that the melting point be lower than the melting point of the olefin resin forming the cap body. Generally, the melting point is 16 depending on the type of plastisol used (flux temperature of plastisol).
In the case of a polypropylene cap of 5 ° C, when a low flux temperature plastisol using a vinyl chloride copolymer resin containing vinyl acetate units is used, the preheating temperature (heating atmosphere temperature) is 50 to 110 ° C. Especially, it is better to set it to 100 ° C.

According to the present invention, the wall thickness of the gasket forming portion of the ceiling wall 2 of the cap is formed to be significantly thinner than other portions (20 to 50% of the thickness of other portions of the ceiling wall 2). ,
The heat transfer in this part is good, and the wall temperature at the gasket formation position rises more quickly than in other parts during preheating in the heating atmosphere. Reach sufficient temperature to prevent heat loss. Therefore, it becomes possible to shorten the preheating time and perform microwave heating in the next step,
The production speed can be increased. For example, in the case of using the plastisol having a low flux temperature described above, when the preheating temperature is set to 100 ° C., it may take about 15 to 30 seconds. In the method of British Patent No. 2,051,660 mentioned above, the preheating time is about 1 to 10 minutes, so it will be understood that the time required for preheating can be significantly shortened in the present invention.

If the ceiling wall 2 of the cap or the entire wall of the cap body is made thin, the preheating time can be shortened as in the present invention. However, in that case, the strength of the cap is lowered, and the cap is easily deformed even by heating for a short time. According to the present invention, such inconvenience is effectively avoided by thinning only the gasket forming position.

The above-mentioned preheating is performed in the stage immediately before microwave heating after applying plastisol in the cap body, and is not for preheating the cap body before applying plastisol. It does not preheat. That is, in the device design, the step of applying plastisol inside the cap body and the microwave heating step are provided separately, so if preheating was performed in the step of applying plastisol or in the step before that, plastisol will not be applied. This is because the temperature of the cap body is lowered while the cap body is conveyed to the microwave heating step.

Preheating is performed for a predetermined time, and when the wall temperature at the gasket forming position of the cap body reaches a certain temperature, microwave heating is immediately performed, and plastisol is selectively heated and completely melted (that is, flux Will be). By cooling this, a gasket will be formed in the annular space in the cap body.

The microwave used for this microwave heating is not particularly limited as long as the selective heating of plastisol is effectively performed, but is generally 10 to 200 MHz, and particularly 27.10 to 2
A frequency of 7.15 MHz is suitable. In addition, this microwave heating is usually provided with a microwave transmitter in an oven for preheating, and after the start of preheating, after a lapse of a predetermined time,
It is better to heat by microwave immediately.

According to the present invention, as a result of performing preheating,
It is possible to effectively avoid heat loss from the plastisol surface during microwave heating. That is, if the heat loss from the plastisol surface is large, the inside of the plastisol is overheated until the plastisol surface reaches the flux temperature,
Deterioration of resin components such as vinyl chloride resin will result in unsatisfactory physical properties of the resulting gasket. According to the present invention, since the heat loss from the plastisol surface is effectively prevented, the entire plastisol is heated almost uniformly by the irradiation of microwaves, and the plastisol can be fluxed in a short time. Overheat is effectively prevented, and a gasket having good physical properties can be obtained. For example, when the microwave having the above-mentioned frequency is used, the microwave heating time may be about 3 to 15 seconds in the present invention.

As described above, according to the present invention, the time required for the entire heating process including the preheating time and the heating time by the microwave is significantly shortened, and the production efficiency is significantly improved.

After heating by microwaves, the gasket is molded in the annular space by cooling it.

Mounting of Cap: The plastic cap 10 obtained by the above-described method of the present invention is used by mounting it on the neck of the container by screwing or the like, and then sealing the PP band 13 on the outer surface of the neck of the container.

The above-mentioned FIG. 2 shows a state before the cap 10 is attached to the neck portion of the container and the PP band 13 is sealed. As can be understood from FIG. 2, the side wall 14 of the neck portion of the container is shown. A fastening collar (jaw) 17 is formed on the bridge band 12, and the bridging portion 12 is located just at the lower end of the fastening collar 17, and the PP band 13
The cap 10 so that it is located under the fastening collar 17.
The size of is set.

FIG. 4 shows a step of sealing the PP band 13 shown in FIG. 2, in which the PP band 13 is pressed against the outer surface of the side wall 14 of the container neck by the clamp 15 so as to be in close contact therewith. That is, the bridging portion 12 is deformed along the lower curved surface of the fastening collar 17, and the PP band 13 is in close contact with the outer surface of the side wall 14 of the container neck below the fastening collar 17.

FIG. 5 shows a cross section taken along the line VV in FIG. 4, but with reference to FIG. 5 together, as a result of the deformation of the bridging portion 12 and the PP band 13, the PP band 13 The diameter of
It will be appreciated that it is smaller than the maximum diameter of the fastening collar 17. Therefore, when the cap 10 is swung and opened from the neck of the container in this state, the cap 10 rises, whereas the PP band 13 is prevented from rising by the fastening collar 17. As a result, a large tension is applied to the bridging portion 12 connecting the PP band 13 and the cap 10 (circumferential side wall 11), and the bridging portion 12 is broken along the alternate long and short dash line 16 in FIG. To do. Thus, the PP band 13 is released from the cap 10,
This allows a third party to easily recognize that the opening operation has been performed.

In the sealing process of the PP band 13 described above, the bridge portion 12 and
It is preferable to perform pressing by the clamp 15 while heating the PP band 13. This heating is performed, for example, by holding the bridging portion 12 and the PP band 13 in a heating atmosphere of about 400 ° C. for about 2 seconds. In this case, as shown in FIG. 2, in the stage before sealing, the bridging portion
The 12 and the PP band 13 and the cap side wall 11 are preferably positioned so as not to contact the outer surface of the neck side wall 14 of the container. This is because if these are in contact with each other, heat is dissipated through the side wall 14 of the neck portion of the container and the plastic deformation of the PP band becomes insufficient.

As described above, the plastic cap obtained by the method of the present invention is usually used as a cap having an inner diameter of 100 mm or less, but has the following three characteristics.

(A) After filling the contents, the container with the cap fastened can be subjected to compression or depressurization operation without any limitation.

(B) It can be reused even after the cap is once removed from the container.

(C) If the cap is once removed from the container, it is PP
Since the band has left, the fact can be recognized by a third party. Therefore, when it is used as a cap for a container of food or the like, the reliability of the warranty period of the contents shown in the container is extremely high.

(Effects of the Invention) According to the present invention, by making the gasket forming portion of the ceiling wall of the plastic cap thinner than other portions, the heating time required for forming the gasket in the cap is reduced. It was possible to shorten the time, and it became possible to improve productivity.

That is, plastisol is applied to the cap and preheated, and then the plastisol is selectively heated by microwave heating.However, by keeping the wall surface of the gasket forming part thin, the temperature of the wall surface is The temperature rises rapidly to a temperature where heat loss from the plastisol surface can be effectively prevented. Therefore, the microwave heating can be performed in a short time after starting the preheating. In this case, since only the gasket forming portion of the cap ceiling wall is thinned, the strength and the like of the plastic cap is not impaired. Further, during microwave heating, heat loss from the surface of plastisol is effectively prevented, so that the heating time by microwaves is shortened and the deterioration of physical properties of the gasket due to overheating inside plastisol can be prevented.

As described above, according to the present invention, since the heat treatment time including the preheating and the microwave heating is shortened, the productivity is improved, and the deformation of the plastic constituting the cap body is effectively prevented during the heat treatment. To be done. In particular, the plastic cap manufactured according to the present invention is provided with the pull fur proof band through the bridging portion which can be easily broken, so that the advantage of shortening the heat treatment time is extremely large. This is because the longer the heat treatment time, the more easily the bridge portion is deformed or broken.

[Brief description of drawings]

FIG. 1 shows an enlarged cross section of a gasket portion of a plastic cap manufactured by the method of the present invention. FIG. 2 shows an enlarged side cross section of a pill fur proof band provided on the cap of FIG. FIG. 3 shows a part of an enlarged plane section (section taken along line III-III in FIG. 2) of the pilfer proof band of FIG. FIG. 4 shows the step of sealing the pill fur proof band to the outer surface of the side wall of the container neck using the clamp in FIG. FIG. 5 shows a cross section (excluding the clamp and the container) taken along the line VV in FIG. 1 is the upper end of the neck of the container, 2 is the ceiling wall of the cap, 3 is the circumferential protrusions facing downward, 4 is the circumferential protrusion, 5 is the gasket, 10 is the plastic cap, 11 is the side wall of the cap, 12 is the bridging portion,
13 is a PP band, 14 is a side wall of a container neck, 15 is a clamp, and 17 is a fastening collar.

Claims (4)

(57) [Claims] 1. A ceiling wall, a peripheral side wall hanging down from a peripheral edge of the ceiling wall, and a pill fur proof band provided at a lower end of the peripheral side wall via a rupturable bridge portion. A microwave-transparent olefin resin plastic in which a downward circumferential projection is formed on the inner surface of the ceiling wall, a circumferential projection is formed on the inner surface of the circumferential side wall, and an annular space for a gasket is formed by these two projections. A method for producing a plastic cap, which comprises using a cap body, applying a gasket-forming plastisol in the annular space within the cap body, and then forming a gasket by irradiating the plastisol with microwaves to heat the plastisol. As the cap body, the thickness of the portion of the ceiling wall located in the annular space is 20 to 50% of the thickness of the ceiling wall of other portions. Using what is set, the plastisol-treated cap body is preheated by holding it in a heating atmosphere at a temperature lower than the melting point of the olefin resin constituting the cap body for a predetermined time, and then, A method of manufacturing a plastic cap, which is characterized in that microwave heating is performed. 2. The method according to claim 1, wherein the temperature of the heating atmosphere is maintained at 50 to 110 ° C. 3. The method according to claim 1, wherein the microwave heating is performed by microwave having a frequency of 10 to 200 MHz. 4. The preheating is performed in a heating atmosphere at 100 ° C.
Microwave heating for 5-30 seconds followed by 2
The method according to claim 1, wherein the method is performed by microwaves having a frequency of 7.10 to 27.15 MHz.