JPH0149608B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method of manufacturing a plastic cap, and more particularly to a method of manufacturing a threaded plastic cap used for sealing the mouth of a container such as a bottle by a compression method. Traditional plastic caps, i.e. glass,
Threaded plastic caps, which are used to seal the mouths of containers such as bottles made of plastic or metal, have mainly been made by injection molding. Injection molding is a method in which molten plastic is injected into a mold through a nozzle to form a molded product in a predetermined shape. However, good fluidity of the material is required, and therefore the melt flow index is usually low. A relatively low molecular weight plastic of approximately 10-20 g/10 min is used. Therefore, in order to ensure the necessary cap strength, it is necessary to make the top plate and the skirt portion relatively thick, which poses a problem of increasing material costs. Polyolefins, such as polyethylene or polypropylene, are preferred as plastic materials due to their low cost; however, caps made from polyolefins by injection molding are prone to stress cracks and have poor low-temperature impact strength. oxygen or _CO2
There was a problem that the contents were likely to change in quality because of their poor barrier properties. In response to this, a method of manufacturing plastic caps using a compression molding method has recently been proposed. In this method, a piece of molten plastic is placed into a cavity with a shape that corresponds to the external shape of the cap, and a plunger, which has a recess on the side surface that corresponds to the internal thread of the cap, is pushed into the cavity, and the cap is compression molded. It's a method. However, in this method, the end of the skirt is formed last, so in order to ensure an accurate profile at this end, the melt flow index with good fluidity is relatively large (injection molding method). This poses the problem of requiring the use of plastic (although to a lesser extent than in the case of 1) and requiring relatively high molding pressures. When manufacturing caps with a pilfer-proof band that connects the skirt section through a thin bridge section, the flow of resin at the bridge section is likely to become clogged due to solidification, and therefore the pilfer-proof band may be missing. Parts are likely to occur. Another problem is that it is difficult to form a pilfer-proof band with a complicated shape without creating a missing portion due to intermediate solidification. The above-mentioned difficulty is particularly severe when the skirt portion is high. Furthermore, since cavities are generally deeper, when molten plastic pieces are dropped and charged into the cavity, they tend to get caught on the side walls of the cavity, preventing satisfactory compression molding. Since the amount of air required is large, there is a problem in that special measures are required to bleed the air. It is an object of the present invention to solve the problems of the prior art described above. In order to achieve the above object, the present invention provides a method for manufacturing a plastic cap having a top plate and a skirt portion hanging down from the peripheral edge of the top plate, and a threaded protrusion formed on the inner surface of the skirt portion. , a first plunger having a threaded recess shaped like the threaded protrusion formed at the end of the side peripheral surface and having an end face shaped like the inner surface of the top plate, the first plunger corresponding to the outer surface of the top plate; Introducing the first plunger and the second plunger into a die cavity having an inner peripheral surface having a shape corresponding to the outer peripheral surface of the skirt portion while being compressed between the second plunger having a shaped end surface, The skirt portion is formed by a material of the plastic material flowing out from between the first plunger and the second plunger between the end of the side peripheral surface of the first plunger and the inner peripheral surface of the die cavity. The present invention provides a method for manufacturing a plastic cap having the following characteristics. The present invention also provides a method for manufacturing a plastic cap which has a top plate and a skirt portion hanging down from the peripheral edge of the top plate, and has a threaded protrusion formed on the inner surface of the skirt portion. a first plunger having a shape corresponding to the inner surface of the skirt portion, a threaded recess having a shape corresponding to the threaded protrusion, and a lower end surface having a shape corresponding to the inner surface of the top plate; The first plunger and the outer surface of the top plate are slid along the inner peripheral surface of the presser pad that is in contact with the upper surface of the die and whose inner diameter is substantially equal to the outer diameter of the first plunger. The first plunger and the second plunger are introduced into a die cavity having an inner peripheral surface having a shape corresponding to the outer peripheral surface of the skirt portion while being compressed between the second plunger having an end face having a corresponding shape. The skirt portion is formed by the material of the plastic material flowing out from between the first plunger and the second plunger between the end of the side peripheral surface of the first plunger and the inner peripheral surface of the die cavity. The present invention provides a method for manufacturing a plastic cap characterized by the following. Furthermore, the present invention has a top plate and a skirt part that hangs down from the peripheral edge of the top plate, a threaded protrusion is formed on the inner surface of the skirt part, and an end surface of the skirt part is formed into a short cylindrical shape through a plurality of bridge parts. In a method for manufacturing a plastic cap connected to a pilfer-proof band, the plastic material has a shape in which the lower end of the side circumferential surface corresponds to the inner surface of the skirt part,
a first plunger formed with a threaded recess having a shape corresponding to the threaded protrusion and whose lower end surface has a shape corresponding to the inner surface of the top plate, abutting against the upper surface of the die;
The inner diameter of the upper inner circumferential surface is substantially equal to the outer diameter of the first plunger, and the lower end of the lower inner circumferential surface has a plurality of thread-like recesses having a shape corresponding to the bridge portion, and a plurality of thread-like recesses connected to the thread-like recesses. A first plunger and a first plunger having an end surface having a shape corresponding to the outer surface of the top plate are slid along the inner circumferential surface of the upper part of the presser pad in which an annular recess having a shape corresponding to the pilfer-proof band is formed. While being compressed between the two plungers, the first plunger and the second plunger are introduced into a die cavity having an inner peripheral surface of a shape corresponding to the outer peripheral surface of the skirt portion, and the first plunger and the second plunger are compressed. The plastic cap is characterized in that the skirt portion is formed by the material of the plastic material flowing out from between the two plungers between the side circumferential end of the first plunger and the inner circumferential surface of the die cavity. A manufacturing method is provided. Next, the present invention has a top plate and a skirt part that hangs down from the peripheral edge of the top plate, a threaded protrusion is formed on the inner surface of the skirt part, and the end face of the skirt part is shortened through a plurality of bridge parts. In a method for manufacturing a plastic cap connected to a cylindrical pilfer-proof band and having a plurality of protrusions formed on the outer surface of the pilfer-proof band, a plastic material is attached such that the lower end of the side circumferential surface thereof is A first plunger having a shape corresponding to the inner surface, a threaded recess having a shape corresponding to the threaded protrusion, and a lower end surface having a shape corresponding to the inner surface of the top plate is brought into contact with the upper surface of the die. , the inner diameter of the upper inner circumferential surface is substantially equal to the outer diameter of the first plunger, and the lower end of the lower inner circumferential surface has a plurality of thread-like recesses having a shape corresponding to the bridge portion and connected to the thread-like recesses. While sliding along the inner circumferential surface of the upper part of the presser pad, an annular recess having a shape corresponding to the pilfer-proof band is formed, and the annular recess has a plurality of recesses having a shape corresponding to the flaky protrusion. , a first plunger;
a second end surface having a shape corresponding to the outer surface of the top plate;
The first plunger and the second plunger are introduced into a die cavity having an inner circumferential surface having a shape corresponding to the outer circumferential surface of the skirt portion while being compressed between the first plunger and the second plunger. manufacturing a plastic cap, characterized in that the skirt portion is formed by the material of the plastic material flowing out between the side circumferential ends of the first plunger and the inner circumferential surface of the die cavity from between the plungers. The present invention provides a method. The present invention will be described below with reference to the drawings. FIG. 1 shows an example of a plastic cap (hereinafter referred to as a cap) manufactured by the method of the present invention, in which the cap 1 is a top plate 2 and a peripheral edge 2a of the top plate 2. The skirt part 3 has a threaded protrusion (see 4 in Fig. 5) on its inner surface, and its outer circumferential surface 3a is designed to prevent slippage during sealing and opening. An axially extending knurling 3b is formed for a stop. FIGS. 2, 3, 4, and 5 show an example of the apparatus M and steps for manufacturing such a cap 1. As shown in FIG. The device M comprises an upper plunger 5, a lower plunger 6, a die 7 and a presser pad 8.
The upper plunger 5 has a screw-shaped recess 10 formed in the lower end _5a1 of the side circumferential surface, and has a screw-shaped recess 10 having a shape corresponding to the screw protrusion 4 of the cap 1.
is the inner surface 2b of the top plate 2 of the cap 1 (see Figure 5)
It has a shape corresponding to . The lower plunger 6 has an upper end surface 6a having a shape corresponding to the outer surface 2c of the top plate 2 of the cap 1, and a side circumferential surface 6b having a shape corresponding to the outer circumferential surface 3a of the skirt portion 3. The die 7 is configured to be slidable within the cavity 7a of the die 7, which has an inner circumferential surface _7a1 having a shape corresponding to the outer circumferential surface 3a of the die 7. Note that the dice 7 are fixed in a fixed position by a holding device (not shown). The presser pad 8 is attached to the side peripheral surface 5 of the upper plunger 5.
It is a ring-shaped body having an inner circumferential surface 8a that is slidable along the direction a. The inner diameter of the inner circumferential surface 8a is equal to the inner diameter of the end surface 3c (FIG. 4) of the skirt portion. Also, the inner peripheral surface 8a
The height is set to be larger than the height of the threaded recess 10, that is, the height h between the lowest point 10b and the highest point 10c (see FIG. 4). During compression molding, which will be described later, the plastic material forms a threaded recess 10.
This is to prevent it from rising through the air and escaping to the outside. The presser pad 8 is configured to be able to move up and down at a predetermined timing by a drive mechanism (not shown) via a vertical rod 11. In the above device M, first, the upper plunger 5
and raise the presser pad 8 above the die 7 and raise the lower plunger 6 into the die cavity 7a until its upper end surface 6a is located at a depth approximately equal to the height of the piece of plastic material 12 to be fed. When cap 1 is
A piece of plastic material 12 having an outer diameter approximately equal to the outer diameter of the cap 1 (its volume being substantially equal to the volume of the cap 1 to be formed) is placed on the upper end surface 6a of the lower plunger 6, as shown in FIG. . Therefore, the die cavity gap when charging the plastic material pieces 12 can be made shallow, so that charging can be carried out smoothly without causing problems such as the plastic material pieces 12 getting caught on the inner circumferential surface _7a1 of the die cavity during charging. can be done. Upper plunger 5 and presser pad 8 are then lowered to contact the upper surface of plastic blank 12 and die 7, respectively, as shown in FIG. The plastic constituting the plastic material piece 12 may be any thermoplastic, such as low density polyethylene, medium density polyethylene, high density polyethylene, linear low density polyethylene,
Polyolefins such as isotactic polypropylene, acrylic resins, nitrile resins, saturated polyester resins, etc., or copolymers or blends thereof, etc., are used, but in terms of cost,
If the melt index is relatively small (e.g. approx.
(0.3 to 10 g/10 min) Polyethylene and polypropylene plastics are particularly preferred. In this case, fillers such as colorants, lubricants, antistatic agents, and antioxidants are usually added. The plastic material piece 12 is made of these thermoplastics alone, or is made mainly of these thermoplastics and is coated with oxygen gas and CO ₂ barrier resin such as ethylene-vinyl alcohol copolymer, polyamide, polyvinylidene chloride, etc. Alternatively, it is formed by cutting a sheet or dropping a melt from a laminate or blend formed by laminating or blending polyvinyl alcohol or the like. Among others, water vapor, oxygen and _CO2
High-density polyethylene, linear low-density polyethylene, or polypropylene A, acid-modified polyolefin of A (B; functions as an adhesive), and ethylene-vinyl A five-layer laminate of alcohol copolymer, polyamide, or polyvinylidene chloride C having the structure ABCB-A is preferably used. Plastic blanks, either single plastics or blends, are generally formed by cutting melt extrudates, such as blank 12' shown in FIG. In the case of a material piece made of a laminate, generally a sheet-like laminate is cut into a diameter slightly smaller than the inner diameter of the inner circumferential surface _7a1 of the die cavity, such as the material piece 12 shown in FIG. is used. In this case, the material piece is preferably placed in a pan (pan; preferably, the inner surface of the recess is coated with a heat-resistant mold release agent such as fluororesin), and
The resin heated to a predetermined temperature (preferably a temperature slightly (approximately 3 to 20° C.) higher than the melting point of the resin) is charged into the die cavity 7a. In addition, by using, as the plastic material piece, a laminate having a layer made of relatively soft plastic on the upper plunger side and a layer made of relatively hard plastic on the lower plunger side, the above-described molding according to the present invention is carried out, Postscript 19th, 20th, 21st
As shown in the figure, it is also possible to simultaneously mold a cap having a liner layer (made of the above-mentioned soft plastic) as a sealing material. The temperature of the plastic material piece 12 (temperature when it is fed onto the lower plunger 6, or (temperature after being heated by an infrared heater, etc.), the lower end 5a ₁ of the side peripheral surface of the upper plunger,
The upper end surface 6a of the lower plunger, the inner circumferential surface 8a of the presser pad 8, and the inner circumferential surface 7a of the die cavity ₁
etc. temperature is determined. Therefore, the upper plunger 5, the lower plunger 6, and the die 7 have a built-in heater (not shown), and a built-in cooling pipe (not shown) as necessary to cool and solidify the cap after the molding is completed as described later. ing.
In addition, in the case of high-speed production (for example, several hundred pieces per minute), the temperature drop of the material piece 12 during molding is small, so
In order to speed up cooling and solidification after completion of molding, it is desirable to keep the temperature of the tool surface, such as the cavity inner peripheral surface _7a1 , as low as possible (for example, 20° C.). When the plastic material piece 12 is mainly made of polyolefin, stress cracks in the manufactured cap 1 (particularly when a container filled with a positive internal pressure liquid such as a carbonated drink is sealed, are likely to occur due to stress generated in the cap due to internal pressure). ) In order to prevent this, it is desirable that the polyolefin forming the cap 1 has molecular orientation, and for this purpose, it is necessary to perform the molding while the material is maintained at a temperature that allows molecular orientation. In the case of highly crystalline polyolefins, the temperature at which molecular orientation is possible is below 35°C above the melting point (defined as the peak temperature of the melting endotherm curve measured by differential thermal analysis under atmospheric pressure), and Possible temperature (the lower limit of the moldable temperature is approx.
130℃, approximately 110℃ for high-density polyethylene, and approximately 100℃ for linear low-density polyethylene)
means. In addition, in the case of a laminate mainly composed of a highly crystalline polyolefin and an ethylene-vinyl alcohol copolymer, if M is the vinyl alcohol content of the latter, the melting point of the polyolefin is lower than the melting point of the polyolefin.
It means a temperature below 35℃ higher and above (1.64M+20)℃. Further, in order to facilitate the formation of the threaded protrusion 4 and to ensure adhesion between the formed threaded protrusion 4 and the skirt portion 3, it is preferable to carry out the molding at a temperature that is higher than the melting point of the plastic and allows for molecular orientation. In addition, when the plastic is an amorphous plastic, it is preferable to perform the molding at a temperature at which molecular orientation is possible, which is higher than the liquid flow start temperature of the plastic. Here, the liquid flow start temperature is:
When heated at a constant speed under a plunger pressure of 160 kg/cm ² using a high-performance flow tester specified in JISK6719, the resin was heated to a diameter of 1 mm and a length of 10 mm.
It is defined as the temperature at which liquid flow starts to be discharged from a mm nozzle. First, from the state shown in Figure 2, remove plastic material piece 1.
2 is compressed between the upper plunger 5 and the lower plunger 6, and the upper plunger 5 and the lower plunger 6 are simultaneously introduced into the die cavity 7a (the introduction speed is usually 10 to 500 mm/sec). To enable compression (for compression at temperatures that allow molecular orientation, the compression force is typically around 200
~2000 Kg/cm ² , usually about 30 to 200 Kg/cm ² when compressed in a molten state higher than the molecular orientation temperature), so that the lowering speed of the upper plunger 5 is greater than that of the lower plunger, and The lowering speed of both plungers (not shown) is such that the upper end surface 3'a of the side wall 3' of the compact 1' during molding substantially contacts the corresponding lower surface 8b of the presser pad 8 (see FIG. 3). It is controlled by a drive control mechanism, such as a hydraulic mechanism or a cam mechanism. Particularly when a hydraulic mechanism is used, there is an advantage that even if there is some variation in the weight of the supplied material pieces 12, this variation is absorbed by variation in the thickness of the top plate. As shown in FIG. 3, the side wall portion 3' is formed in the direction of arrow F from the bottom wall portion 2' of the molded body 1' due to the above compression.
It is formed by the material flowing out between the lower end 5a ₁ of the side peripheral surface of the upper plunger and the inner peripheral surface 7a ₁ of the die cavity. At this time, a threaded protrusion 4 is formed in a portion of the upper plunger 5 corresponding to the threaded recess 10 while moving downward. During molding, the material also flows into the threaded recess 10 in the presser pad 8 up to the vicinity of the highest point 10c, but the material also flows into the inner circumferential surface 8a of the presser pad 8.
Since the height of is set higher than the above-mentioned h, there is no risk of the material escaping to the outside and producing defective products with insufficient quantity. In the drawing, the upper end 10a (see FIG. 4) of the threaded recess 10 is shown as
Air vent hole 1 formed in the upper plunger 5
Connected to 3. However, since the air in the threaded recess 10 also escapes from between the sliding surfaces of the upper plunger 5 and the holding pad 8, it is not necessarily necessary to provide the guide hole 13. When the upper plunger 5 and the lower plunger 6 reach the bottom dead center, as shown in FIG. is formed. Note that the end surface 3c of the skirt portion 3 is defined by the lower surface 8b of the presser pad 8, as described above. Then, if necessary, the upper plunger 5 and/or
or lower plunger 6 and/or die 7
Cap 1 can be formed by de-energizing the heater inside and energizing the cooling pipe (this is not necessary if the cooling pipe is energized from the beginning and the temperature of the inner surface of the die is low to begin with, as mentioned above). The upper plunger 5, as shown in FIG.
Lower plunger 6 and presser pad 8 are raised to eject cap 1 from die 7. Next, a guide hole 14 in the upper plunger 5 (a plug 16 is attached to the lower end by a spring 15, which is normally in close contact with the truncated conical lower end of the guide hole 14).
When only the upper plunger 5 is raised while the end surface 3c of the skirt portion is engaged with the lower surface 8b of the fixed presser pad 8 while sending pressurized air from a pressurized air source (not shown), the skirt Part 3
expands elastically, and the cap 1 is removed from the upper plunger 5. Alternatively, it may be removed by rotating the upper plunger 5 or the cap 1 and unscrewing it. FIG. 6 shows the state immediately before the plastic material piece 12' formed by cutting the melt-extruded body (see FIG. 22) is charged into the die cavity 7a and molding is started. . In this case, first the upper plunger 5 and presser pad 8 are raised, and the lower plunger 6 is raised within the die cavity 7a until its upper end surface 6a reaches a predetermined depth from the upper surface 7b of the die 7. A piece of molten plastic material 12', the weight of which is substantially equal to the weight of the cap 1 to be formed, is dropped onto the top surface 6a. The predetermined depth is determined by the die cavity gap 7 defined by the level of the upper end surface 6a and the die upper surface 7b.
Usually, the volume of a ₂ and the volume of the plastic material piece 12' are determined to be approximately equal. However, the side edge 6a ₁ of the upper end surface 6a may be at a level that substantially coincides with the die upper surface 7b. Therefore, the die cavity cavity _7a2 when the plastic material piece 12' is charged can be made shallow, so that the plastic material piece 12' can be loaded without causing problems such as getting stuck on the inner circumferential surface _7a1 of the die cavity. The entry is smooth. After that, the presser pad 8 is lowered, and its lower surface 8b is
is brought into contact with the upper surface 7b of the die, and with the lower plunger 6 stopped, the upper plunger 5 is lowered to crush the plastic material piece 12', and the material piece 12' fills the die cavity gap _7a2. As a result, a plate-like body similar to the material piece 12 shown in FIG. 2 is obtained. At this time, the piece of material 12' has hardly cooled down, so the shape of the portion 3c' corresponding to the end surface 3c of the skirt portion of the cap to be formed is as follows.
It is precisely defined by the portion _8b1 of the lower surface 8b of the presser pad which projects above the die cavity 7a. Thereafter, the plastic cap 1 is manufactured in the same manner as described above. In the above example, the die 7 was fixed and the piece of plastic material was introduced into the die cavity 7a while being compressed between the upper plunger 5 and the lower plunger 6. However, by fixing the lower plunger 6,
While the upper plunger 5 is lowered and the plastic material piece 2 is compressed between the upper plunger 5 and the lower plunger 6, the die 7 may be raised to introduce the plastic material piece 2 into the die cavity 7a. Alternatively, the upper plunger 5 may be fixed, the lower plunger 6 and the die 7 may be raised, and the piece of plastic material may be compressed between the upper and lower plungers 6 and introduced into the die cavity 7a. Further, the die 7, the upper plunger 5 and the lower plunger 6 may be moved up and down as appropriate to introduce the piece of plastic material into the die cavity 7a. The same applies to the following examples. Next, an example of manufacturing a pilfer-proof cap will be explained. FIG. 7 shows a heat-shrinkable pilfer-proof plastic cap 101, in which the end surface 103c of the skirt portion 103 is connected to a short cylindrical pilfer-proof band 105 via a plurality of thin bridge portions 106. There is. After screwing the cap 101 onto a container opening (not shown), the pilf-proof band 105 surrounding the jaws of the annular protrusion below the screw of the container opening is heated and shrunk. 105 can be engaged to the underside of the jaw. 8, 9, and 10 show the main parts of the apparatus N and the process for manufacturing the pilfer-proof cap 101, and the parts with the same symbols as those in FIGS. 2 to 4 are the same parts. shows. This also applies to the following drawings. At the lower part of the inner surface 108a of the presser pad 108, there is an annular recess 109 having a shape corresponding to the pilfer-proof band 105, and a plurality of annular recesses 109 having a shape corresponding to the bridge portion 106. The molding apparatus M is the same as the molding apparatus M described above except that a filamentous recess 110 reaching . The manufacturing method of the cap 101 is also almost the same as that of the cap 1. However, in this case, the upper end surface 6 of the lower plunger 6
a is kept as high as possible, preferably so that the side end surface 6a ₁ reaches the level of the die top surface 7b, as shown in FIG. After dropping the piece of molten plastic material 12' onto the lower plunger 6,
When the upper plunger 5 is lowered and compressed while the lower plunger 6 is stopped, the plastic material piece 12' is compressed into the annular recess 109 and the thread-like recess 110.
is almost filled. Subsequently, the material piece 12' is introduced into the die cavity 7a while being compressed between the upper plunger 5 and the lower plunger 6, and at the beginning of the introduction, as shown in FIG.
0, the annular recess 109 and the threaded recess 10 are completely filled. Since the above-mentioned filling occurs at the early stage of molding when the material has not yet cooled, the thin thread-like recesses 110 (the width in the circumferential direction is usually 0.3
~1.0 mm (however, the width of the recess corresponding to one unbreakable bridge is 2.0 to 5.0 mm)) is clogged with solidified material, resulting in an unfilled part in the annular recess 109, resulting in a defect where there is a missing part. There is no risk of producing a pilf-proof band 109. FIG. 10 shows a state in which the cap 101 is formed after the molding is completed, and shows a healthy pilfer-proof band 109 and a bridge portion 110.
is formed. The pilfu-proof cap 201 shown in FIG. 11 has a pilfu-proof band 205 and a bridge part 206 like the cap 101, but the inner surface of the pilfu-proof band 205 has a plurality of flaky protrusions 207. It differs from the cap 101 in that it is formed. The piece-like protrusion 207 is usually triangular in shape, and its upper end surface 207a is usually located on a plane perpendicular to the axis, but may be inclined with respect to the axis. When a container opening (not shown) is sealed with the cap 201, the lower surface of the chin of the container opening engages with the upper end surface 207a. When attempting to manufacture this type of pilfer-proof cap 201, a plurality of recesses in the shape corresponding to the flaky protrusions 207 are formed on the side wall of the upper plunger, and resin is filled into the recesses during molding to form the flaky protrusions. A protrusion 207 must be formed. However, when the cap 201 is pulled out after the molding is completed, the bridge portion 206 is easily cut off due to the resistance of the protrusion 207, and a satisfactory cap 2 can be obtained.
01 is difficult to manufacture. As a countermeasure against this, it is possible to eliminate the gap 2 between the bridge parts 206 without forming the bridge parts 206.
04, that is, the skirt portion 20
3 and the pilfer-proof band 205 are formed continuously along the entire circumference (using a presser pad that is capable of such forming), and the obtained cap is printed, for example, in Japanese Patent Publication No. 1439/1983. Open the void 204 using a kerf knife as described.
There is a method of forming the gap 204 and the bridge portion 206 by cutting the portion where the gap 204 is to be formed. However, in this case, there is a problem in that a post-processing process called drilling is required. A method for solving such problems will be described below. As shown in FIG. 12, thin wall portions 324a and 32 extend downward from the lower end of the skirt portion 323.
4b elongated (e.g. 4mm (length) x 1mm
×0.6mm) Connected to the skirt portion 323 via a plurality of bridge portions 324, is ring-shaped and has an inner diameter approximately equal to that of the inner surface of the skirt portion 323 where no threaded protrusion is formed, and has a height. Almost equal to the height of the bridge portion 324 (for example, 4 mm),
Alternatively, the cap 321 is slightly lower than that and has a pilfer-proof band 325 formed with a plurality of thin-walled protrusions 326 on the outer surface, and a bridge portion 324, a pilfer-proof band 325 and a strip-like protrusion on the inner surface as described later. It can be formed in the same manner as described above except for using a presser pad 328 having a recess formed therein corresponding to the protrusion 326. The cap 321 connects the pilfer-proof band 325 to the bridge portion 324 as shown in FIG.
By inverting the pilfer-proof band 325 inwardly in the A direction, the piece-like protrusion 326
Pilf-proof cap 32 located on the inner surface of
1a. Similarly, as shown in FIG. 14, the cap 321 is made by inverting the pilfer-proof band 325 outward in the direction B with respect to the bridge portion 324, so that the strip-shaped protrusion 326 is attached to the pilfer-proof band 325. A pilfer-proof cap 321b located on the inner surface can be formed. In the case of either cap 321a or 321b,
When the container mouth (not shown) is sealed, the piece-shaped projection 326 engages with the outer surface of the annular projection located below the threaded part of the container mouth or the lower surface of its jaw (not shown). , when opening the cap, the pilfer-proof band does not rise together with the skirt portion 323, and the bridge portion 324 moves to the thin wall portion 3.
It is cut at 24b to ensure pilfer-proof properties. 15 and 16 are drawings showing a method of forming the cap 321, in which parts with the same reference numerals as those in FIG. 8 indicate similar parts. The presser pad 328 has a concave portion 334 having a shape corresponding to the bridge portion 324, and a thin wall portion 3.
24a, 324b, and a recess 335 having a shape corresponding to the pilfer-proof band 325 are formed. A plurality of recesses 336 shaped like
is connected. In the above apparatus Q, in the same way as when manufacturing the cap 101, with the presser pad 328 in contact with the upper surface of the die 7, the die cavity is pressed while the plastic material piece 12' is pressed by the upper plunger 5 and the lower plunger 6. 7
As shown in FIG. 16, a cap 321 having a bridge portion 324, a thin wall portion 324a, a luff-proof band 325, and a piece-like protrusion portion 326 can be formed by introducing the cap 321 into a portion a. To remove the formed cap 321, move up the upper plunger and remove the pilf-proof band 32.
By providing relief on the inside of the presser pad 3
28 can be easily raised without damaging the protrusion 326. 17 and 18 show polypropylene layer A1
2″a ₁ , maleic anhydride modified polypropylene layer (adhesive layer: B) 12″b ₁ , ethylene/vinyl alcohol copolymer layer C12″c, maleic anhydride modified polypropylene layer 12″b ₂ B and polypropylene layer A12 ″A laminate consisting of ₂ (A layer, B layer,
This is an example in which a cap 1'' with excellent gas barrier properties was formed using a piece of material 12'' with a C layer thickness ratio of 93:3:4. 19, 20, and 21 show a low density polyethylene layer 12a and a polypropylene layer 12b.
With the low-density polyethylene layer 12a of the laminate material piece 12 facing upward, the cap 1 is opened using the upper plunger 405, which has a recess 405a in a shape corresponding to the liner layer 408 to be formed on the lower end surface. In the same way as when forming
4 shows a process for manufacturing a cap 401 having a liner layer 408. In this case, material piece 1
The diameter of the recess 405a is slightly smaller than the inner diameter of the recess 405a, and the volume of the polyethylene layer 12a and the recess 4
It is desirable that the volumes of 05a be approximately equal. According to the method of manufacturing plastic caps of the present invention, plastic caps can be molded without requiring as much fluidity of the material as in conventional injection molding or compression molding methods. Therefore, it can be applied to materials with a relatively low melt index and high molecular weight, and therefore has the effect of realizing thinning while maintaining the necessary strength. It also has the advantage of producing plastic caps with skirt ends with accurate profiles and pilfer-proof plastic caps with no missing parts. Furthermore, when the plastic material is mainly composed of polyolefin, it has the advantage that stress cracks can be prevented and low-temperature impact strength can be improved by molding preferably at a temperature higher than the melting point that allows for molecular orientation. Furthermore, by molding a laminate mainly composed of polyolefin and oxygen and CO ₂ barrier plastic at a temperature that allows molecular orientation, it has the advantage that a cap with excellent barrier properties against water vapor, oxygen and CO ₂ can be produced. Examples will be described below. Example 1 An isotactic material with a density (20°C) of 0.90 g/cm ³ , a melting point measured by differential thermal analysis of 160°C, and a melt flow index measured at 230°C under a load of 2160 g of 0.6 g/10 min. Polypropylene, diameter 40
mm, using an extruder incorporating a full-flight screw with an effective length of 880 mm, a T-die sheet extruder with an adapter and a single manifold T-die, and a sheet forming device with a cooling roll and a travel link cutter. Thickness is 4mm
It was formed into a plate-like sheet. This sheet was punched into a disc-shaped blank with a diameter of 29.0 mm using a punching press. Next, this blank was placed in a metal pan having a circular recess with an inner diameter of 29.1 mm and a depth of 4.2 mm, the inner surface of which was coated with Teflon resin. The bread was placed on a conveyor and passed through an infrared tunnel oven to keep the blank at exactly 164°C. while the upper plunger of a device of the type shown in FIG. 2 (having a diameter of 28.0 mm and the shape shown in FIG. 2);
The lower plunger (diameter 29.95 mm) and cavity (inner diameter 30.0 mm) were preheated by an internal heater so that their surface temperature was 65°C. The bread that came out of the oven was then mechanically transferred to the upper part of the lower plunger of the apparatus, and the bread was immediately inverted and the molten blank inside the pan was placed on top of the lower plunger. .
Immediately lower the presser pad onto the upper end of the cavity, and then use the upper plunger and lower plunger to compress the disc-shaped blank by applying a pressure of approximately 220 kg/cm ² to it until the distance from the upper end of the cavity to the upper end of the lower plunger is 16 mm. The upper and lower plungers were introduced into the cavity until they were in position. Immediately thereafter, raise the presser foot pad by 30mm, and while rotating the upper plunger to the left,
It was raised to 20mm above the lower end of the presser foot pad. In this way, the 2.38 g plastic cap 1-A molded on the side surface of the upper plunger is prevented from rising upward by the lower end of the presser pad.
By rotating the upper plunger to the left, it was removed from the upper plunger, and immediately after the upper plunger was raised, it was dropped onto the upper surface of the lower plunger, which had been raised. For comparison, the melt flow index is 0.6.
g/10 minutes, using the same polypropylene as above with a melting point of 160°C, using a screw in-line injection molding machine at a resin temperature of 220°C and an injection pressure of 80 kg/cm ² , a cavity inner diameter of 30 mm, a core outer diameter of 28 mm, A plastic cap 1'-B was molded by injection into a mold with a cavity length of 16 mm corresponding to the cap height. In addition, isotactic polypropylene with a melting point of 162℃ and a melt flow index of 15.0g/10 minutes was added at an injection temperature of 222℃ and an injection pressure of 50℃.
Kg/cm ² was injected into a mold in the same manner as described above to form a plastic cap 1'-C. Table 1 shows the measurement results of the dimensions and weight of the above three types of polypropylene plastic caps, and the measurement results of stress crack resistance. Stress cracks were measured in the following manner. Gently fill a glass bottle with carbonated water containing about 4 volumes of carbon dioxide gas at 15.6℃ at low temperature (3℃), close the above three types of caps, and pour it into the surfactant solution heated to 50℃. Cracks occurring in the cap after being left for a week were visually measured. As is clear from Table 1, the plastic cap according to the present invention has extremely excellent stress crack resistance.

[Table] Example 2 Density is 0.90g/cm ³ and melting point by differential thermal analysis is
160℃ polypropylene (PP) as the outermost layer,
The ethylene content is 40 mol%, the vinyl alcohol content is 60 mol%, the melting point is 164°C, and the oxygen permeability coefficient at 35°C and 60% relative humidity is 2.5 × 10 ^-13 cc・cm/
^The intermediate layer is an ethylene-vinyl alcohol copolymer (EE) with a density of 0.90 g/cm 3 and a density of 0.90 g/cm ³ .
Modified with maleic anhydride with a melting point of 159°C (degree of modification 0.35)
Weight %) Polypropylene (MP) is used as the adhesive layer between the outermost layer and the intermediate layer, an extruder for the outermost layer has a built-in full-flight screw with a diameter of 90 mm, and an adhesive with a built-in full-flight screw with a diameter of 40 mm. A combination of an extruder for the agent layer and an intermediate extruder with a built-in full-flight screw with a diameter of 40 mm, a feed pipe, a 5-layer feed block, a single manifold T-die, a cooling roll, a nip roll, a traveling cutter,
Using a plate-shaped sheet forming device consisting of a suction cutter, PP-MP with a width of 250 mm and a thickness of 3.74 mm is produced.
A plate-like sheet having a multilayer structure of three types and five layers of the structure -EE-MP-PP was molded. The extrusion rate of each extruder was adjusted so that the composition ratio of the outermost layer: adhesive layer: intermediate layer of the obtained sheet was as close as possible to 93:3:4 in terms of thickness ratio, and the plate-like sheet was formed. I went. Next, this plate-like sheet is punched out using a punching press to make the diameter
A 29 mm disk-shaped blank was cut out and the blank was heated to 166° C. in exactly the same manner as in Example 1. Using the same compression molding equipment as in Example 1, Example 1 was cut out.
A plastic cap 1-B having the same shape was molded. Plastic cap 1 molded in Example 1
The following tests were conducted on three types of caps: -A and 1'-C, and cap 1-B molded in this example. A saline solution is placed in a biaxially oriented polyethylene terephthalate bottle with an internal volume of 1.5 liters, and the above three types of plastic caps are attached. Next, after storing these saline-filled and sealed bottles in a freezer set to 0℃ overnight, an inverted drop test was performed with the plastic caps hitting the concrete surface from a height of 1.5 m, and the number of broken plastic caps was calculated. It was measured. Next, carbonated water containing 2.5 volumes of carbon dioxide at 15.6°C was filled into a 170ml glass bottle, and immediately the three types of plastic caps 1-A, 1'-C,
and 1-B, and measured the amount of carbon dioxide loss, which is the sum of the leakage of carbon dioxide from the cap and the amount of permeation through the cap top plate wall, at 25℃ using a carbon dioxide leak measuring device and a gas chromatograph. It was measured. These results are shown in Table 2.

[Table] Example 3 showing the number of caps produced A heat-shrinkable pilfer-proof plastic cap was supplied by melting and dropping the material, and was molded using the molding method according to the present invention and the compression molding method according to the prior art for comparison. The resin used as the material has a density (20℃) of 0.90g/cm ³ ,
Melting point by differential thermal analysis is 162℃, 230℃, 2160g
The melt flow under load was 0.31 g/10 min for isotactic polypropylene. Diameter 40mm effective length 880 for melting and dripping feeding of material
Portable extruder 500, which has a built-in full-flight screw of mm and is equipped with a rotary cutter in the nozzle section, which can cut and drip extruded molten resin into a fixed amount.
(Fig. 22) was used. The configuration of the molding apparatus N is shown in FIG. The diameter of the upper plunger is 28 mm, and the thread forming recess is machined for 1.5 turns at a pitch of 8 threads/inch from a position whose center line is 3.5 mm from the lower end surface of the upper plunger. The height of the presser pad is 10 mm, and the height of the recess that forms the pilfer-proof band is 4 mm.
0.6mm, concave part 11 for forming a bridge part connected to it
0 has a height of 1 mm, a depth of 0.6 mm, a width of 0.5 mm, and a knurling in the axial direction corresponding to the knurling 3b is provided inside the cavity 7, and its inscribed circle diameter is 30 mm.
A knurling corresponding to the knurling of the cavity 7 is applied to the outer periphery of the lower plunger so that it is almost in close contact with the inside of the cavity 7 and can slide. In addition, in order to enable each method according to the present invention and the conventional compression molding method, the upper plunger 5, lower plunger 6, die 7, and presser pad 8 can be driven or fixed by a hydraulic circuit independently or in conjunction with each other. I'm starting to be able to do it. The entire system combining the material supply device R and the molding device N is constructed as shown in FIG. 22. The molten resin lump 12a (170°C) extruded from the portable extruder 500 of the material supply device R to the nozzle part is transferred to the rotary cutter 5 rotated at a constant speed by a constant speed motor 501.
A certain amount (2.58 g) is cut at 02 and dropped onto the upper surface of the lower plunger of the molding device. Immediately after dropping the material, the material supply device R is moved back in the direction A to be located in a place where it does not interfere with molding. The molding device N is set to start molding in conjunction with the completion of this retraction. Using this system, the die 7 was first fixed, and the presser pad 8, upper plunger 5, and lower plunger 6 could be driven so that the surface temperature of each was 30°C. The lower plunger 6 is set in advance at a position directly below the lower end surface of the presser pad 8, and molten resin (2.58 g) is dripped onto the upper surface of the lower plunger 6, and the upper plunger 5 is immediately lowered to compress the material and maintain the pressure to a predetermined level. The movement of the lower plunger was controlled so as to maintain the lower plunger at a value of . At this time, the lowering speed of the upper plunger is 50mm/
In seconds, the lower plunger starts descending when a pressure of 130Kg/cm ² is applied to the material piece, and slightly slower than the upper plunger in order to maintain that pressure and not to interfere with the lowering of the upper plunger. lowered it. When the lower plunger 6 was lowered by 16 mm, the operation of each part was stopped. The obtained molded article 3-A was taken out in the same manner as in Example 1. Next, the lower plunger was fixed and the upper plunger and die holding pad could be driven. The surface temperature of each of these was maintained at 30°C. The die and the presser pad were brought into contact with each other in advance, and the presser pad was set so as to be located directly above the upper end surface of the lower plunger. While dropping the molten resin (25.8 g) onto the upper surface of the lower plunger of the device made in this way and lowering the upper plunger to compress the material piece,
The movements of the die and presser pad were controlled to maintain the pressure at a predetermined value. The lowering speed of the upper plunger at that time was 50 mm/sec, and the die and presser pad started to rise when a pressure of 130 kg/cm ² was applied to the material piece, and the pressure was maintained while rising. When the die and presser pad rose 16 mm, the operation of each part was stopped. The obtained molded article 3-B was taken out in the same manner as in Example 1. Finally, in order to perform the conventional compression molding method, the lower plunger, die, and presser pad are fixed so that the top of the lower plunger is located 16 mm below the lower end surface of the presser pad and the die is in close contact with the presser pad.
As a result, these parts do not move until the molding is completed. Molten resin (2.58 g) at 170° C. was dropped onto the upper surface of the lower plunger of the apparatus thus set, and the upper plunger was immediately lowered. The lowering speed of the upper plunger is 50 mm/s and the final pressure is 130
Kg/cm ² or 200Kg/cm ² or 250Kg/cm ² . Molded products 3-C ₁ , 3-C ₂ , 3- obtained at each final pressure
C ₃ was taken out in the same manner as in Example 1. Molded products 3-A, 3- obtained as above
B, 3-C ₁ , 3-C ₂ , and 3-C ₃ were examined for molded product shape and heat shrinkability of pilfer-proof bands. Regarding the shape of the molded product, the shape of the pilfu-proof band, the presence or absence of residual air bubbles in the molded product, and the heat shrinkability of the pilfu-proof band were determined by immersing the cut pilfu-proof band in an oil bath at 140°C for 10 seconds. The actual cord collection rate and the shape after shrinkage were investigated. The results obtained are shown in Table 3.

【table】 [Brief explanation of drawings]

FIG. 1 is a perspective view of a first example of a cap manufactured by the method of the present invention, FIGS. 2, 3, and 4.
5 and 6 are longitudinal sectional views showing an example of the process of the manufacturing method of the present invention for manufacturing the cap shown in FIG. 1, and FIG. Figure 3 is a diagram showing the state immediately before molding, Figure 4 is a diagram showing the state after molding, and Figure 5 is just before the cap is pulled out from the upper plunger. 6 is a drawing showing the state immediately after charging the plastic material piece formed by melt extrusion and cutting, and FIG. 7 is a drawing showing the second state of the cap manufactured by the method of the present invention. FIGS. 8, 9, and 10 are longitudinal cross-sectional views showing an example of the manufacturing process of the cap shown in FIG. 7, and FIG. FIG. 9 is a diagram showing the state at the initial stage of molding; FIG. 10 is a diagram showing the state after molding is completed; FIG. 11 is a diagram showing the third state of the cap manufactured by the method of the present invention. FIG. 12 is a perspective view of a fourth example of the cap manufactured by the method of the present invention, and FIGS. 13 and 14 are respectively views of the cap of FIG. 12. Place the pilfer-proof band on the inside of the bridge.
15 and 16 are longitudinal cross-sectional views showing the initial state of forming the cap shown in FIG. 12 and the state immediately after the cap is formed, respectively. FIG. 17 , FIG. 18 is a longitudinal sectional view showing the process of manufacturing a cap of the type shown in FIG. 1 from a material piece made of a laminate, and FIG. 17 is a drawing showing the state before molding.
Figure 18 is a drawing showing the state after molding is completed, Figure 19
21 are longitudinal sectional views showing an example of the process of manufacturing a cap having a liner layer by the method of the present invention, and FIG. 19 is a drawing showing the state before molding;
FIG. 20 is a diagram showing the initial state of molding, FIG. 21 is a diagram showing the state after molding is completed, and FIG. 22 is a perspective view of an example of a system including a material supply device and a molding device used in carrying out the present invention. It is a diagram. 1,1″,101,201,321,321a,
321b...Plastic cap, 2...Top plate, 2
a...Peripheral part, 3...Skirt part, 4...Threaded protrusion part,
5... Upper (first) plunger, 6... Lower (second) plunger.
) Plunger, 7a...Die cavity, 10
...Threaded recess, 12, 12'...Plastic material piece.

Claims (1)

[Claims] 1. A method for manufacturing a plastic cap having a top plate and a skirt portion hanging down from the peripheral edge of the top plate, and a threaded projection formed on the inner surface of the skirt portion, wherein a plastic material is A first plunger having a threaded recess shaped like the protrusion formed at the end of the side peripheral surface and having an end face shaped like the inner surface of the top plate, and an end face shaped like the outer face of the top plate. The first plunger and the second plunger are introduced into a die cavity having an inner circumferential surface having a shape corresponding to the outer circumferential surface of the skirt portion while being compressed between the second plunger having a The skirt portion is formed by a material of the plastic material flowing out from between the plunger and the second plunger between the end of the side peripheral surface of the first plunger and the inner peripheral surface of the die cavity. Method of manufacturing plastic caps. 2. In a method for manufacturing a plastic cap having a top plate and a skirt part hanging down from the peripheral edge of the top plate, and a threaded protrusion formed on the inner surface of the skirt part, the plastic material is A first plunger having a shape corresponding to the inner surface of the top plate, a threaded recess shaped like the threaded protrusion, and a lower end surface corresponding to the inner surface of the top plate is attached to the top surface of the die. the first plunger while sliding along the inner peripheral surface of the presser pad that is in contact with the first plunger and whose inner diameter is substantially equal to the outer diameter of the first plunger.
and a second plunger having an end face having a shape corresponding to the outer surface of the top plate, the first plunger and the second plunger are compressed between the first plunger and the second plunger having an end face having a shape corresponding to the outer peripheral surface of the skirt portion. The plastic is introduced into a die cavity having an inner peripheral surface and flows out from between the first plunger and the second plunger between the end of the side peripheral surface of the first plunger and the inner peripheral surface of the die cavity. A method for manufacturing a plastic cap, characterized in that the skirt portion is formed from a raw material. 3 It has a top plate and a skirt part that hangs down from the peripheral edge of the top plate, a threaded protrusion is formed on the inner surface of the skirt part, and the end surface of the skirt part is connected to a short cylindrical pillar via a plurality of bridge parts. In a method of manufacturing a plastic cap connected to a proof band,
A plastic material is formed such that the lower end of the side circumferential surface has a shape corresponding to the inner surface of the skirt portion, a threaded recess shaped like the threaded protrusion is formed, and the lower end surface corresponds to the inner surface of the top plate. A first plunger having a shape is brought into contact with the upper surface of the die, the inner diameter of the upper inner peripheral surface is substantially equal to the outer diameter of the first plunger,
The upper part of the presser pad is formed with a plurality of thread-like recesses having a shape corresponding to the bridge part and an annular recess having a shape corresponding to the pilfer-proof band connected to the thread-like recesses at the lower end of the lower inner peripheral surface. While sliding along the inner peripheral surface, the first plunger and the second plunger are compressed between the first plunger and the second plunger having an end surface having a shape corresponding to the outer surface of the top plate. , into a die cavity having an inner circumferential surface of a shape corresponding to the outer circumferential surface of the skirt portion, and from between the first plunger and the second plunger, the end portion of the side circumferential surface of the first plunger and the end portion of the side circumferential surface of the first plunger. A method for manufacturing a plastic cap, characterized in that the skirt portion is formed by the material of the plastic material flowing between the inner peripheral surfaces of the die cavity. 4 It has a top plate and a skirt part that hangs down from the peripheral edge of the top plate, a threaded protrusion is formed on the inner surface of the skirt part, and the end surface of the skirt part is connected to a short cylindrical pillar via a plurality of bridge parts. A method for manufacturing a plastic cap connected to a proof band and having a plurality of protrusions formed on the outer surface of the pilfer-proof band, wherein the plastic material is shaped so that the lower end of the side circumferential surface corresponds to the inner surface of the skirt portion. A first plunger, which has a screw-shaped recess with a shape corresponding to the screw protrusion, and whose lower end surface has a shape corresponding to the inner surface of the top plate, is brought into contact with the upper surface of the die, and the upper inner peripheral surface The inner diameter of the first plunger is substantially equal to the outer diameter of the first plunger, and the lower end of the lower inner peripheral surface has a plurality of thread-like recesses having a shape corresponding to the bridge part, and the pilfer-proof band is connected to the thread-like recesses. An annular recess having a shape corresponding to the shape of the first plunger is formed, and the annular recess has a plurality of recesses having a shape corresponding to the piece-shaped protrusion. and a second plunger having an end surface having a shape corresponding to the outer surface of the top plate, while compressing the first plunger and the second plunger between the inner periphery having a shape corresponding to the outer periphery of the skirt portion. The plastic material is introduced into a die cavity having a surface and flows out from between the first plunger and the second plunger between the end of the side peripheral surface of the first plunger and the inner peripheral surface of the die cavity. A method for manufacturing a plastic cap, characterized in that the skirt portion is formed of a material.