JP2001114310A - Plastic cap excellent in openability, closability and hermetical sealing - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a plastic cap which is excellent in combined capacities including openability, closability and hermetical sealing. SOLUTION: For a plastic cap which is characteristic of having excellent openability, closability and hermetical sealing while being integrally formed of a thermoplastic resin and equipped with a top part, a skirt part and a seal-up part formed at the inside of the top part for fitting to a mouth of a container, the surface at the inside of the top part including the seal-up part is made rough, and the surface roughness for the seal-up part is set in a range of 1 to 5 μm (according to the maximum height Rmax based on JIS B0601) while the surface roughness for the internal surface closer to the inside than the seal-up part is set at 5 μm or more and becomes more rough than the surface roughness at the seal-up part.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a plastic cap formed of one-piece plastic and having excellent opening, closing and sealing properties.

[0002]

2. Description of the Related Art Plastic caps used for beverage bottles and the like are common today, and olefin resins such as propylene polymers and ethylene polymers are generally widely used.

Japanese Utility Model Application Laid-Open No. 64-262 according to the proposal of the present applicant
No. 57 discloses a polypropylene resin cap having a screw portion on its inner surface for engaging with a container neck, wherein the surface of the screw portion has a surface roughness measured in accordance with JIS B 0651 of 2 to 6 μm. There has been proposed a resin cap made of polypropylene.

Japanese Patent Application Laid-Open No. 9-315451 discloses that, in a cap composed of a top surface and a skirt, at least the inner surface of the top surface in contact with the container opening has a density of 0.935 g / cm.
A cap characterized by being formed of a resin composition of a continuous phase of an ethylene-based polymer having a size of ³ cm or less and a dispersed phase of an ethylene-based polymer / organopolysiloxane copolymer is described.

[0005] The method of molding a plastic cap is roughly classified into an injection molding method and a compression molding method, each of which has advantages and disadvantages. The compression molding method has a shorter occupation time in a mold than the injection molding method. In addition, there is an advantage in terms of productivity and manufacturing equipment, such as a low required molding pressure.

[0006]

The plastic cap has a screw for fastening to the container mouth on the inner surface of the skirt, and a sealing portion for sealing with the container mouth on the inner surface of the top surface. On the other hand, cap plastics generally have a problem that they lack lubricity. In addition, the torque for opening and closing the plastic cap and the sealing performance (sealing performance) with the container mouth are generally in inverse proportion. However, there is a problem that the tightness is high and the stopper is difficult to open.

In order to solve this problem, means for incorporating a lubricant such as wax into the plastic molded into the cap is generally employed, however, there is still a limit in reducing or improving the opening or closing torque. At the same time, the wax has a problem of taste and smell, and the torque control by the wax has a remarkable change with time, has a large temperature dependency, and is difficult to handle.

In addition, when the cap is formed, it is particularly remarkable in the compression molding method. However, charge marks and welds are easily generated in the sealing portion on the top surface, and these charge marks and welds cause micro leaks. I have.
In order to reduce this, means such as raising the resin temperature during molding or changing the cooling water temperature are adopted, but due to the change in molding conditions, screw dripping occurs and productivity decreases. And other adverse effects.

Accordingly, it is an object of the present invention to provide a plastic cap which is excellent in a combination of an opening property, a closing property and a sealing property. Another object of the present invention is to provide a plastic cap which can be closed with a relatively small closing torque and with a reliable sealing property.

[0010]

According to the present invention, there is provided a sealing portion between a top surface portion integrally formed of a thermoplastic resin, a skirt portion, and a container opening formed on an inner surface of the top surface portion. In the plastic cap, the top surface portion is roughened at least on the inner surface side including the sealing portion, and the surface roughness (maximum height according to JIS B0601, Rmax) of the sealing portion is in the range of 1 to 5 μm, and the sealing portion is sealed. The surface roughness (maximum height according to JIS B0601; Rmax) of the inner surface inside the sealing portion is 5 μm or more and has a surface roughness larger than the surface roughness of the sealing portion, A plastic cap having excellent plugging and sealing properties is provided. In the present invention, the inner surface inside the sealing portion should have a surface roughness larger than the surface roughness of the sealing portion, and in particular, the surface roughness of the inner surface inside the sealing portion (JI
It is desirable that the maximum height (Rmax) based on SB0601 is larger than 5 μm. The thermoplastic resin used in the present invention has a flexural modulus (JIS K7203) of 800.
It is preferably an environmental stress crack resistant thermoplastic resin in the range of from 1600 MPa to 1600 MPa. Further, in the cap of the present invention, it is preferable that the inner surface of the skirt portion is a mirror surface.
In particular, the present invention includes a circumferential band connected to a lower end of the skirt portion via a breakable bridge, and includes an engaging portion on an inner surface of the circumferential band for engaging a jaw portion below an outer periphery of a container mouth. In this case, the surface of the engaging portion that comes into contact with the jaw portion when the plug is closed is provided with a surface roughness (a maximum height according to JIS B0601, Rma).
It is desirable that x) has a rough surface in the range of 1 to 50 μm. Suitable examples of the engaging portions provided on the inner surface of the circumferential band include a plurality of flap pieces which are arranged in a plurality of circumferential shapes and extend radially inward and obliquely upward.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A cap according to the present invention includes a top portion integrally formed of a thermoplastic resin, a skirt portion, and a sealing portion with a container opening formed on the inner surface of the top portion.
In the plastic cap of the present invention, the inner surface side of the top surface portion including at least the sealing portion is roughened, and the surface roughness of the sealing portion (maximum height according to JIS B0601, Rmax) is in the range of 1 to 5 μm. And the surface roughness of the inner surface inside the sealing part (JIS B0
601 is characterized by a combination of a maximum height (Rmax) of 5 μm or more and a surface roughness greater than the surface roughness of the sealing portion.

That is, the plastic cap of the present invention
The top surface is characterized in that the inner surface is roughened, and the roughening is performed by sealing the surface with a surface roughness (maximum height according to JIS B0601, Rmax) of 1 to 5 μm, and the surface roughness ( Maximum height based on JIS B0601, Rma
It is characterized in that the roughening is performed separately from the surface inside the sealing portion having x) of 5 μm or more and having a surface roughness larger than the surface roughness of the sealing portion.

According to the present invention, by performing the above-described roughening on the inner surface of the top surface including the sealing portion, charge marks and welds that often appear on the sealing portion are almost completely eliminated, and the occurrence of micro leak is effectively prevented. Can be prevented. still,
The above-mentioned charge mark is a surface defect caused by rapid solidification of the resin in the mold, while a weld is a surface defect caused by air remaining in the mold at the junction of the resin flows without escape. It is. It will be easily understood that the formation of these surface defects in the sealing portion causes micro-leakage. See the example below. That is, in a conventional plastic cap in which the inner surface of the top surface including the sealing portion is a mirror surface, water is filled at room temperature, and capping is performed at a torque of 18 kgfcm.
When the occurrence of micro leak was tested under the condition of inverting for 48 hours in the atmosphere of No. 5, it was found that 5 out of 10 micro leaks occurred, whereas the cap of the present invention in which the inner surface of the top surface including the sealing portion was roughened, Under the same test conditions, the number of micro leaks was 0 out of 10, and it is understood that roughening of the inner surface of the top surface is effective in preventing the micro leak.

The fact that the sealing portion is roughened to improve the sealing performance may give a rather strange feeling. The following may be considered as a reason for this. That is, the surface roughening of the cap top surface is achieved by roughening the mold, but when the mold is roughened, the resin surface when the mold surface comes into contact with the molten resin is reduced. There is little cooling, and the air escape during molding is also good, which seems to have led to the disappearance of charge marks and welds which cause micro leaks. That is, the surface defect due to the charge mark or the weld exceeds the degree of surface roughening of the sealing portion in the present invention, and the disappearance of the charge mark or the weld leads to an improvement in the sealing performance.

In the present invention, the opening torque is controlled to a certain area called easy-opening property by further setting the surface roughness of the sealing portion with the container opening provided on the inner surface of the top surface within a certain range. In addition, it is possible to completely prevent the occurrence of poor sealing due to incomplete winding when closing.

As shown in an example to be described later, in a conventional plastic cap having a mirror surface on the inner surface of the top surface including the sealing portion, when the opening torque is measured under the condition of two weeks at room temperature, the average is 11 kgf-cm. On the other hand, in the cap of the present invention in which the surface roughness of the sealing portion is set in the range of 1 to 5 μm, the opening torque is 8 kgf-c.
It can be reduced to the order of m.

Further, according to the present invention, by setting the surface roughness of the sealing portion within the specific range described above, it is possible to effectively prevent the occurrence of poor sealing due to incomplete tightening of the cap at the time of closing. Can be. The capping operation (closing operation) on the container mouth is generally performed by a chuck provided with an electromagnetic coupling means, and when the closing torque reaches a certain value, transmission of rotational torque to the cap is interrupted. . Therefore, if there is an abnormal increase in torque when the cap is closed, the tightening of the cap does not completely proceed, and the cap is tightly sealed to the container opening in a state of poor sealing, that is, a loose state. On the other hand, in the present invention, an abnormal increase in torque at the time of plugging is also suppressed,
The tightening of the cap completely proceeds to the designed final stage, and the occurrence of poor sealing due to incomplete tightening is prevented.

As shown in an example to be described later, when the sealing portion is mirror-finished, if the closing operation of the container mouth portion is performed under the condition of the fastening torque of 18 kgfcm, the rate of occurrence of poor sealing becomes 0.01. %, Whereas a cap provided with a sealing portion having a surface roughness in the above range can suppress the occurrence rate of sealing failure due to incomplete winding to zero, and the excellent effect of the present invention can be achieved. it is obvious.

According to the present invention, by forming a rough surface having a specific range of surface roughness in the sealing portion on the inner surface of the cap top surface, the sealing performance is improved without lowering the sealing performance. It is possible to improve the opening and closing properties, which is presumably because the contact area with the container mouth is reduced.

In the present invention, the surface roughness (J
It is also important that the maximum height (Rmax) based on IS B0601 be in the range of 1 to 5 μm described above. When the surface roughness of the sealing portion falls below the above range, the effect of improving the openability and pluggability is not sufficient. On the other hand, when the surface roughness of the sealing portion exceeds the above range, the tendency of occurrence of micro leak increases. Not preferred.

As already pointed out, in the cap of the present invention, the inner surface of the top surface including the sealing portion is roughened, but the degree of roughening of the inner surface inside the sealing portion is also constant. There is a range, and the surface roughness of this part (JIS B
The maximum height according to 0601, Rmax) should be at least 5 μm and have a surface roughness greater than the surface roughness of the seal. Because the inner surface inside the sealed part is the part that is strongly compressed in compression molding and the part where the flow of resin occurs most severely in injection molding, it is necessary to roughen this part Has a very effective effect on the disappearance of charge marks and welds.

When the surface roughness of the inner surface of the portion inside the sealing portion is lower than the above range, the effect of eliminating charge marks and welds is reduced as compared with the case where the surface roughness is within the above range. The surface roughness of the inner surface of the portion inside the sealing portion is preferably larger than 5 μm and smaller than 30 μm. If this surface roughness is larger than this range,
For the prevention of microphone leak, an increase in the effect is not expected as compared with the case where it is in the above range, and the surface roughness becomes conspicuous to the naked eye, which is undesirable in terms of appearance characteristics.

The thermoplastic resin used in the present invention is preferably an environmental stress crack resistant thermoplastic resin having a flexural modulus in the range of 800 to 1600 MPa. It has been found that the effect of roughening the inner surface of the cap top surface according to the present invention is also related to the flexural modulus of the plastic used. That is, when the flexural modulus of the plastic falls below the above range, the above-described effects due to the surface roughening tend to be reduced. On the other hand, when the flexural modulus exceeds the above range, the torque adjustment is not affected. It tends to be less effective at preventing micro leaks.

It is also important that the plastic used has resistance to environmental stress cracking. Environmental stress cracking is one of the defects often seen in polyethylene molded products. Water, organic solvents such as alcohols, surfactants, or their vapors come into contact with stressed polyethylene molded products. Then, it is known as a phenomenon that generates a crack. In the case of a cap, a sealing pressure (seal pressure) with the container mouth is always applied to the sealing portion of the cap, and furthermore, the contents and its vapor come into contact with the sealing portion, so that environmental stress cracks occur. It will be understood that the environment is easy to do. In the cap of the present invention, it has already been pointed out that the occurrence of micro-leakage is prevented by roughening the inner surface of the top surface portion, as described above. Even micro-cracks cause leakage and poor sealing, so that a resin having excellent environmental stress crack resistance must be used. Further, in the cap of the present invention, it is preferable that the inner surface of the skirt portion is a mirror surface. In other words, by making the inner surface of the skirt portion of the cap a mirror surface, it is easy to remove the mold at the time of manufacturing the cap, and workability at the time of manufacturing is improved.

According to the present invention, there is provided a circumferential band connected to a lower end of a skirt portion via a breakable bridge, and an engaging portion which engages with a jaw portion below the outer periphery of a container mouth is provided on an inner surface of the circumferential band. Can be advantageously applied to the provided cap,
In this case, the surface of the engaging portion that comes into contact with the jaw portion when the plug is closed may have a rough surface having a surface roughness (maximum height based on JIS B0601; Rmax) in the range of 1 to 50 μm. It is desirable to prevent the occurrence of poor sealing due to complete winding. That is, as already pointed out, if there is an abnormal increase in the closing torque at the time of plugging, the tightening of the cap does not proceed completely, which causes a poor sealing, as already pointed out. In addition to the engagement torque between the container mouth and the cap seal,
There is a torque when the engaging part gets over the jaw of the container. In the present invention, the surface of the engaging portion that comes into contact with the jaw portion at the time of plugging has a surface roughness (Rmax) of 1 to 50 μm.
By setting the rough surface in the range, the torque when the engaging portion gets over the jaw portion of the container can be reduced, the cap can be securely tightened, and the sealing performance can be maintained.

[0026]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention is applicable to an arbitrary plastic cap having a top portion integrally formed of a thermoplastic resin, a skirt portion, and a sealing portion with a container opening formed on the inner surface of the top portion. can do. This cap can be any known tamper-evident feature (tamper-evidence feature)
Can be provided. Further, the sealing portion provided on the inner surface of the top surface portion may be a flat seal contacting the top surface of the container mouth portion, a seal by an outer ring contacting the outer peripheral surface of the container mouth portion, or the inner peripheral surface of the container mouth portion. A seal with an inner ring in contact may be used, or a combination of two or more of these may be used.

In FIGS. 1 (partial cross-sectional side view), FIG. 2 (bottom view) and FIG. 3 (partial cross-sectional side view together with the container mouth) showing an example of the cap of the present invention, the plastic cap is a container. It has a substantially cylindrical shape according to the shape of the mouth portion 5 and is formed by a top surface portion 1 and a skirt portion 2 hanging down from a peripheral portion of the top surface portion 1.

An inner surface of the top surface portion 1 includes a sealing engagement portion 11 with the container opening 5 and a portion 12 inside the sealing engagement portion. At least the inner surface of the part that contributes to sealing with the container has a surface roughness (Rmax)
Is roughened to the above-mentioned range of 1 to 5 μm. On the other hand, the portion inside the sealing portion roughened to 1 to 5 μm has a surface roughness (Rmax) including the portion 12 of 5 μm or more and a surface roughness larger than the surface roughness of the sealing portion. It is flattened.

In the cap of this specific example, the sealing engagement portion 11 includes the outer ring 13 and the inner ring 1.
5 and an intermediate portion 14, and the outer ring 1
3 is provided with a radially inward projection 16 that engages with the outer periphery 51 of the container mouth. The inner ring 15 serves as a guide for correctly centering the cap on the container mouth when the cap is fastened to the container mouth 5, and the sealing portion between the container mouth 5 and the outer ring 13 has a shoulder shape. And an intermediate portion 14. That is, the seal with the container mouth is
This is performed exclusively by the radial engagement between the outer ring 13 and the outer peripheral portion 51 of the container opening and the vertical engagement between the intermediate portion 14 and the top surface 50 of the container opening.

In this case, the outer ring 13 and the shoulder-like intermediate portion 14 are roughened to a range of 1 to 5 μm, and the inner portion thereof has a surface roughness of 5 μm or more, and The surface may be roughened so as to have a larger surface roughness than the above, or the entire sealing engagement portion 11 may be roughened to a range of 1 to 5 μm, and the inner portion 12 has a surface roughness of 5 μm or more and is sealed. The part may be roughened so as to have a surface roughness larger than the surface roughness of the part. In the cap of the present invention, excellent sealing properties such as prevention of micro leaks are achieved by double roughening the sealing portion and the portion inside the sealing portion.

A knurl groove 21 is formed on the outer surface of the skirt portion 2 to facilitate gripping of the cap, while a screw 5 of the container opening is formed on the inner surface side of the skirt portion 2.
3 is formed with a screw 22 that engages with the screw 3. A gas vent groove 23 is formed in places of the screw 22 to quickly release gas when opening the plug and to prevent the cap from flying. In the cap of the present invention, the inner surface of the skirt portion 2 is preferably mirror-finished to improve the releasability.

The cap of FIGS. 1 to 3 is also provided with a cap opening / clearing mechanism. That is,
On the lower side of the skirt portion 2 of the cap, a circumferential band 4 for indicating opening is provided via an annular cut surface 3. The lower end of the skirt portion 2 of the cap and the peripheral band 4 are divided by the annular cut surface 3, and the bridges 3 are distributed in a circumferential manner so as to be located inside the inner periphery of the cut surface 3.
They are connected by one.

The circumferential band 4 is provided with a large number of piece-shaped fins 41 which extend in a radially inward and oblique direction and are arranged circumferentially for locking to the container mouth. ,
At the time of closure, it is designed to engage with the jaw 54 below the outer periphery of the container mouth. When the cap is closed in the container, when the cap is rotated in the closing direction, the screw 53 on the container mouth and the screw 22 on the inner surface of the skirt are engaged, and the capping proceeds. In this case, since the extending direction of the fins 41 of the circumferential band 4 and the plugging direction match, the fins 41 climb over the chin of the container mouth and reach the lower portion thereof, and the fins 41 Retention is ensured. In the cap of the present invention, since the sealing portion is roughened to a certain surface roughness, an abnormal increase in the closing torque is suppressed, and the outer ring 13 and the outer peripheral portion of the container opening in the radial direction have a sealing engagement and a step. The sealing engagement in the vertical direction between the shoulder-shaped intermediate portion 14 and the top surface of the container mouth is ensured, and complete tightening without loosening is possible.

On the other hand, when the cap is opened, the circumferential band 4 is positioned below the jaw of the container mouth by the fins 41, and the opening direction is opposite to the direction in which the fins extend. Therefore, the cap 31 is fixed so as not to rotate, and only the cap body (the top surface 1 and the skirt 2) rotates in the opening direction, so that the bridge 31 is broken by the shearing force. Due to this rupture, the cap body and the peripheral band 4 are separated and the plug is opened. At this time, in the cap of the present invention, since the sealing portion is roughened to a certain surface roughness (Rmax), the opening torque is suppressed to a low value, and opening by hand is easy.

In FIGS. 4 (partial cross-sectional side view), FIG. 5 (bottom view) and FIG. 6 (partial cross-sectional side view showing together with the container mouth) showing other examples of the cap of the present invention, , The overall configuration is the same as that shown in FIG. 1, and common members are indicated by common reference numerals.

In the cap of this embodiment, as in the examples of FIGS.
3, an inner ring 15, and an intermediate portion 14. The inner ring 15 is formed with a radially outward projection 17 that engages with the inner peripheral portion of the container opening. When the cap is fastened to the container mouth, the outer ring 13 regulates the position of the outer periphery of the container mouth to ensure the sealing engagement between the inner ring and the inner periphery 52 of the container mouth. The sealing part with the container mouth part 5 is composed of an inner ring 15 and a stepped intermediate part 14. That is, sealing with the container mouth portion is performed exclusively by radial engagement between the inner ring 15 and the container mouth inner peripheral portion 52 and vertical engagement between the flat portion 14 and the container mouth top surface 50. It is. Needless to say, the outer ring 13 and the inner ring 15 may be hermetically engaged with each other, or the outer ring 13, the flat portion 14 and the inner ring 15 may be hermetically engaged. It can also be done.

In the case of the cap of the specific example shown in FIGS. 4 to 6, the engagement and fixing of the peripheral band 4 to the opening of the container are performed by the flap pieces 42.
It is performed by The flap piece 42 extends obliquely upward, and is provided so as to be capable of being deformed in a direction in which the diameter of the tip increases. Thus, in the cap shown in FIGS. 4 to 6 as well, the flap piece 42 can ride over the jaw 54 below the outer periphery of the container mouth and engage with the lower part thereof when the cap is closed, so that the circumferential band 4 can be fixed to the container mouth. In this specific example, the surface of the flap piece 42 that comes into contact with the jaw 54 at the time of closure is a rough surface having a surface roughness (Rmax) in the range of 1 to 50 μm. It is possible to reduce the torque at the time of getting over, securely tighten the cap, and prevent poor sealing. The reduction of the closing torque by roughening the flap piece 42 can be achieved not only in the sealing engagement portion shown in FIGS. 4 to 6 but also in the combination with the sealing engagement portion in FIGS. Should be understood.

In the cap shown in FIGS. 4 to 6, the capping and unsealing are performed according to the same principle as that shown in FIGS.

FIG. 7 shows still another example of the cap of the present invention.
In (side sectional view), FIG. 8 (bottom view) and FIG. 9 (partial sectional view shown together with the container mouth), the overall configuration of this plastic cap is the same as that shown in FIGS. , Common members are indicated by common reference numerals.

In the cap of this specific example, as in the examples of FIGS. 1 to 3, the sealing engagement portion 11 includes an outer ring 13, an inner ring 15, and a small projection-like intermediate portion 14.
Consists of The outer ring 13 is used to restrict the position of the outer peripheral portion 51 of the container mouth to secure the sealing engagement between the inner ring 15 and the inner periphery 52 of the container mouth when the cap is fastened to the container mouth. The sealing portion with the container mouth 5 is formed by an inner ring 15 and a small projection-like intermediate portion 14.
It is composed of That is, the sealing with the container mouth is achieved by the radial engagement between the inner ring 15 and the container inner peripheral portion 52 and the vertical engagement between the small projection intermediate portion 14 and the container mouth top surface 50. It is done exclusively. Needless to say, the outer ring 13 and the inner ring 15 may be hermetically engaged with each other, or the outer ring 13, the intermediate portion 14 and the inner ring 15 may be hermetically engaged. It can also be done.

In the case of the cap of the specific example shown in FIGS. 7 to 9, the engagement and fixing of the circumferential band 4 to the container
It is performed by The ratchet 43 is used for the circumferential band 4
A large number are attached to the inner surface at regular intervals via a root, and the tips extend inward in the radial direction and in the opening direction. It should be understood that a space 44 is formed between the distal end portion and the circumferential band 4 to allow the distal end portion to be deformed radially outward. On the other hand, the container mouth 5 for fastening the cap has a ratchet 55 below and on the outer periphery of the jaw 54. Thus, in the cap shown in FIGS. 7 to 9, the ratchet 43 can rotate over the jaw 54 and the ratchet 55 on the outer periphery of the container mouth when the cap is closed, so that the circumferential band can be rotated with the proper fastening torque. It can be fastened to the container mouth. Also,
At the time of opening, the tip of the ratchet 43 of the cap engages with the ratchet 55 of the container mouth, and is fixed so as not to rotate, and only the cap body (top surface 1 and skirt portion 2) rotates in the opening direction. The bridge 3
1 breaks. Due to this rupture, the cap body and the peripheral band 4 are separated and the plug is opened.

In the cap shown in FIGS. 7 to 9, the peripheral band 4 remaining in the container opening 5 after opening is prevented from dropping out of the container opening when the contents are poured out.
A drop prevention projection 45 is provided, and the projection 45 engages with the jaw 54 of the container mouth to achieve this object.

Also, in the cap shown in FIGS. 7 to 9, in order to protect the bridge 31 from breaking when the cap is closed, the circumferential band 4 is formed with a protruding portion 46 with one side standing upright, and the lower end of the skirt portion 2 is also formed. The stepped shoulder 32 is formed, and at the time of plugging, the projection 46 and the stepped shoulder 32 come into contact with each other, so that the closing torque can be smoothly transmitted to the circumferential band 4 without breaking the bridge. ing.

Also in the caps shown in FIGS. 7 to 9, since the sealing portion is roughened to a certain surface roughness (maximum height according to JIS B0601, Rmax), it is possible to perform tight tightening without micro-leakage. Is prevented, the opening torque is suppressed to a low value, and opening by hand is easy.

[Plastic] The plastic constituting the cap of the present invention must be an environmental stress crack resistant thermoplastic resin having a flexural modulus in the range of 800 to 1600 MPa for the reasons described above. Examples of the resin satisfying the above conditions include a polypropylene resin and a high-density polyethylene having a branched chain structure.

The polypropylene used is crystalline,
It may be a homopolypropylene under the condition that a small amount of a comonomer may be copolymerized, a block copolymerized polypropylene or a random copolymerized polypropylene. The melt flow rate (JIS K7210) of the polypropylene used is generally 2 to 30 g /
It is better to be in the range of 10 min. Polypropylene is
It has excellent resistance to environmental stress cracking and is effective in preventing the occurrence of micro leaks.

The high-density polyethylene having a branched chain structure has the advantage that, while having a flexural modulus in the above-mentioned range, the polyethylene is exceptionally excellent in environmental stress cracking resistance. The high-density polyethylene is a copolymer of ethylene and an α-olefin having 3 to 12 carbon atoms, and has a melt flow rate (MFR) of 2.
0 to 10 g / 10 minutes, and the density is 0.945 to
High density polyethylene with 0.960 g / cm ³ is suitable.

In the high-density polyethylene, the α-olefin to be copolymerized with ethylene is particularly an α-olefin having a C number of 3 to 12, specifically, propylene,
Butene-1, hexene-1, octene-1, 4-methyl-1-pentene, nonene-1, decene-1, dodecene-1 and the like are used alone or in combination of two or more.
These α-olefin comonomer improve the environmental stress cracking resistance of high density polyethylene. The above α
-Among the olefins, butene-1 and hexene-1 are preferred. Generally, the density of the ethylene / α-olefin copolymer tends to decrease as the amount of the α-olefin comonomer increases. In the high-density polyethylene used in the present invention, the density is 0.94 as described above.
Α- as in the range of 5 to 0.960 g / cm ^3.
The olefin is preferably copolymerized. The content of the α-olefin in the high-density polyethylene varies depending on the polymerization method, but is generally in the range of 1 to 15% by weight, preferably 1 to 10% by weight. The high-density polyethylene used in the present invention is 0.945 to 0.960 g /
It should have a density of cm ³ , especially 0.950 to 0.955 g / cm ³ . When the density is lower than the above range, the rigidity of the resin container lid is insufficient, and the sealing property tends to decrease due to, for example, bulging deformation of the top surface. On the other hand, when the density exceeds the above range, environmental stress cracks and the like tend to occur easily.

In the present invention, plastics used for the production of caps include fillers, colorants, heat stabilizers, weather stabilizers, antioxidants, antioxidants, light stabilizers, ultraviolet absorbers, antistatic agents, Lubricants such as metal soaps and waxes,
A known resin compounding agent such as a modifying resin or rubber can be compounded according to a known formulation.

[Manufacturing Method of Cap] The cap of the present invention is obtained by converting the above-mentioned thermoplastic resin into a mold comprising a core mold having a roughened surface corresponding to the inner surface of the cap top surface, and a cavity mold. It can be produced by injection or by compression molding a molten resin mass of a thermoplastic resin using the above-mentioned mold.

The core mold used in the present invention forms the inner surface of the cap. The portion corresponding to the inner surface of the top surface is roughened as described above, and the portion corresponding to the sealing portion is formed. Has a surface roughness (maximum height based on JIS B0601; Rmax) of 1 to 5 μm, and the surface inside the portion corresponding to the sealed portion has a surface roughness (Rmax) of 5 μm. As described above, the surface is roughened to have a surface roughness greater than the surface roughness of the sealing portion. The surface roughening of the mold surface is performed by means known per se such as electric discharge machining or sand blasting, and the degree of surface roughness is controlled by means known per se. On the other hand, the portion corresponding to the skirt portion of the core mold is mirror-finished.

In the case of compression molding, a large number of core dies and cavity dies are arranged around a rotary turret as a pair capable of moving up and down. In the rotation direction of the rotary turret, a supply region for a molten resin, a compression molding region, and a removal region for a molded cap are provided in this order.

The plastic used for molding the cap is
It is kneaded in an extruder and quantitatively extruded from an orifice or die. The extruded molten resin is cut by a cutter, and the cut molten resin mass is supplied into an open mold by rotation of the cutter and air. At this time, since the inner surface of the mold is roughened, generation of charge marks due to rapid cooling of the resin is prevented. Thus, when the mold is opened, the cap formed by compression molding is removed from the mold and becomes a cap product.

The cap according to the invention has the advantage of having, in a very simple manner, a combination of excellent opening, closing and sealing properties.

[Experimental Examples] The following experimental examples will be shown in order to specifically show the excellent effects of the present invention. (1) Preparation of Sample The surface of the mold formed on the sealed portion was mirror-finished, and Comparative Example 1 was prepared. The surface of the mold formed on the sealed portion is subjected to mechanical polishing and sand blasting, and the surface roughness of the sealed portion is from 1 to 12 μm (maximum height based on JIS B0601, Rma).
Comparative Examples 1 to 5 having x) were prepared. Further, Examples 1 to 3 having a surface roughness (Rmax) of 10 μm on the inner surface inside the sealed portion were prepared. Mirror finish buffing, sandblasting # 120, # 135, # 150, # 1
80, # 220 glass beads with air pressure of 4 kg / cm
² for 10 seconds.

Melt flow rate 20 and block copolymer of polyethylene and polypropylene having a flexural modulus of 1440 MPa were added to the molds treated in Comparative Examples and Examples.
゜ Injection molding at 100 MPa, C, mirror surface ~ 12
One-piece plastic caps with a surface roughness (Rmax) of up to μ were produced.

(2) Evaluation of Cap Performance Instantaneous pressure resistance test: A 500 ml PET bottle was filled with water at room temperature, and the cap prepared in (1) was capped at 18 kgfcm. At this time, the angle formed by the threading start position of the bottle and the threading start position of the cap was defined as a tightening angle. Next, after standing at room temperature for one day, nitrogen gas was injected into the bottle in water, and the pressure at which bubbles were generated from the sealed portion between the cap and the bottle was defined as the instantaneous pressure resistance value. Liquid leakage test: Fill a 500 ml PET bottle with colored room temperature water, cap the cap prepared in (1) with a torque of 18 kgfcm, invert it in an atmosphere of 40 ° C. for 48 hours. The number of leaked liquids was confirmed. Opening torque test: A 500 ml PET bottle was filled with water at room temperature, the cap prepared in (1) was capped with a torque of 18 kgfcm, left at room temperature for 2 weeks, and then the opening torque was measured.

Table 1 shows the evaluation results. From the above results, as is clear from the present invention, when the surface of the sealing portion of the cap is a mirror surface, by setting the surface roughness (Rmax) of the portion to 1 μ or more, the tightening angle increases, The breakdown voltage increased between 1 and 5 μm of surface roughness (Rmax). In addition, a decrease in the opening torque after standing at room temperature for 2 weeks was observed. Further, by setting the surface roughness (Rmax) of the inner surface inside the sealing portion to 10 μm, the water filling is performed at 40 ° C.
The liquid leakage in the inverted 48 hours was 0/10.

[0059]

[Table 1] Mold surface treatment of sealing part Tightening from sealing part Instantaneous water filling Room temperature Inner mold angle Withstand pressure value 40 ° C 2 weeks Surface finish Surface roughness Surface processing N = 5 N = 5 Opening after inverted Surface roughness 48 Time Torque μm μm PSI Leakage / N Kgfcm Comparative Example 1 Mirror Finish Mirror Surface 339 57.0 5/10 11.0 Comparative Example 2 # 150 8 Mirror Surface 357 62.0 2/10 8.5 Blast Comparative Example 3 # 120 12 Mirror Surface 353 50.6 3/10 8.5 Blast Comparative Example 4 Mechanical polishing 1 Mirror surface 354 69.6 1/10 8.0 Comparative Example 5 # 220 3 Mirror surface 359 67.0 1/10 8.1 Blast Comparative Example 6 # 180 5 Mirror surface 351 69.6 1/10 8.0 Blast Example 1 Mechanical polishing 1 10 354 69.6 0/10 8.0 Example 2 # 220 3 10 359 67.0 0/10 8.1 Blast Example 3 # 180 5 10 351 69.6 0/10 8.0 Blast

[0060]

According to the present invention, the inner surface of the top surface including the sealing portion is roughened to a specific surface roughness (maximum height based on JIS B0601, Rmax), so that the inner surface of the top surface often appears in the sealing portion. The charge mark and the weld disappear almost completely, and the occurrence of micro leak can be effectively prevented. Further, in the present invention, by forming a rough surface having a specific range of surface roughness in the sealing portion on the inner surface of the cap top surface portion, the sealing performance can be improved while improving the sealing performance without deteriorating the sealing performance. The pluggability and the pluggability can be improved. The present invention provides a cap including a circumferential band connected to a lower end of a skirt portion via a breakable bridge, and an engaging portion on an inner surface of the circumferential band for engaging a jaw below an outer periphery of a container mouth. In this case, the surface of the engaging portion that comes into contact with the jaw portion at the time of plugging is roughened with a surface roughness (maximum height according to JIS B0601, Rmax) in the range of 1 to 50 μm. By using the surface, it is possible to more effectively prevent the occurrence of poor sealing due to incomplete winding when closing.

[Brief description of the drawings]

FIG. 1 is a partially sectional side view showing an example of a cap of the present invention.

FIG. 2 is a bottom view of the cap of FIG.

FIG. 3 is a partially sectional side view showing the cap of FIG. 1 together with a container mouth.

FIG. 4 is a partially sectional side view showing another example of the cap of the present invention.

FIG. 5 is a bottom view of the cap of FIG. 4;

FIG. 6 is a partial cross-sectional side view showing the cap of FIG. 4 together with a container mouth.

FIG. 7 is a side sectional view showing still another example of the cap of the present invention.

FIG. 8 is a bottom view of the cap of FIG. 7;

9 is a partial sectional view showing the cap of FIG. 7 together with a container mouth.

 ────────────────────────────────────────────────── ─── Continued on the front page F term (reference) 3E084 AA04 AA12 AB01 BA01 CA01 CC04 CC05 DA01 DB05 DB12 DC04 DC05 FA09 FB01 GA04 GB04 GB08 HA03 HB02 HC03 HD01 HD03 HD04 KA13 KB01 LA05 LA17

Claims (5)

[Claims] 1. A plastic cap comprising: a top surface portion integrally formed of a thermoplastic resin; a skirt portion; and a sealing portion with a container opening formed on an inner surface of the top surface portion.
At least the inner surface side of the top surface including the sealing portion is roughened, and the surface roughness (maximum height according to JIS B0601; Rmax) of the sealing portion is in the range of 1 to 5 μm, and the inside of the sealing portion is inside. Surface roughness of inner surface (JIS B06
A plastic cap excellent in opening, closing and sealing properties, having a maximum height (Rmax) of 5 μm or more and a surface roughness greater than the surface roughness of the sealing part. 2. The method according to claim 1, wherein the thermoplastic resin has a flexural modulus (JIS).
The plastic cap according to any one of claims 1 to 3, wherein K7203 is an environmental stress crack resistant thermoplastic resin having a range of 800 to 1600 MPa. 3. The plastic cap according to claim 1, wherein the inner surface of the skirt portion is a mirror surface. 4. A peripheral band connected to a lower end of the skirt portion via a breakable bridge, and an inner surface of the peripheral band is provided with an engaging portion which engages with a jaw portion below an outer periphery of a container mouth. The surface of the engaging portion that comes into contact with the jaw portion when the plug is closed is a rough surface having a surface roughness (maximum height according to JIS B0601, Rmax) in the range of 1 to 50 μm. Item 4. The cap according to any one of Items 1 to 3. 5. The cap according to claim 4, wherein the engaging portions are formed of a plurality of flap pieces arranged in a circumferential shape and extending in a radially inward and obliquely upward direction.