JPH0924964A - Method for sealing container - Google Patents

Abstract

PURPOSE: To prevent plasticizer from transferring and eluting to contents in a container by putting a flexible polyolefin resin pre-molding between an opening of the container and a cap and by heating the cap until the pre-molding reaches its flex temperature or higher while the cap is being mounted or after the cap is mounted. CONSTITUTION: When a cap made of plastic more excellent in heat resistance than flexible polyolefin resin or metal such as tin is to be mounted on an opening of a container molded of rigid polyvinyl chloride or the like, a flexible polyolefin resin pre-molding is put between an opening of the container and the cap, and while the cap is being mounted on the opening or after it is mounted, the cap is heated until the pre-molding reaches its flex temperature or higher. Flexible polyolefin resin mainly containing ethylene-α-olefin copolymer of density less than 0.910 is preferably used, while chemical blowing agent is contained in the flexible polyolefin resin premolding if needed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for sealing a container. More specifically, the present invention has excellent sealing property,
The present invention relates to a container sealing method which is suitable for continuous production without the risk of elution of the plasticizer into the contents.

[0002]

2. Description of the Related Art Among lid materials for glass bottles, plastic containers, lid materials made of metal such as crowns, pull-up caps, tear-off caps, screw caps, etc. A sealing material for filling the space between the top surface and the inner surface of the lid material and absorbing a fall, vibration, and impact from the outside is used as an important member for sealing the container. This sealing material used to be cork in the old days, but in recent years low density polyethylene resin and soft polyvinyl chloride resin have been used. The method of sealing a container using these sealing materials is to coat the resin on the inner surface of the cap in advance, fill the container with the contents, and then clamp the skirt of the cap to the shape of the container tip while pressing it from above. It is common to attach the cap by a method such as squeezing along the side and crimping) or screwing. The method of coating the resin on the inner surface of the cap differs depending on the type of resin.For polyethylene resin, a fixed amount of molten resin is extruded onto the inner surface of the cap placed upside down and immediately cooled by pressing a mold of a predetermined shape. Perform shaping. In the case of polyvinyl chloride resin, a method is used in which a powdered polyvinyl chloride resin, a paste in which a plasticizer and other additives are mixed and dispersed, is applied to the inner surface of the cap, and then melted by heating to gel. There is.

[0003]

The method using a polyethylene resin is simple in process, inexpensive in material, and excellent in maintaining the purity of the contents because there is no migration or elution of the plasticizer. However, since it is inferior in hermeticity, it is limited to beer bottles having a small container opening such as a crown of beer and containers which are not required to be so hermetically sealed. On the other hand, the method using a polyvinyl chloride paste has good sealing properties and can be applied to wide mouth bottles with large openings and applications requiring high sealing performance, but the material is relatively expensive and The process is complicated. Further, the plasticizer in the paste may migrate to the contents and may be eluted, so that the purity retention of the contents is inferior to that of polyethylene. In recent years, from the viewpoint of environmental problems and food hygiene, a sealing method without migration and elution of the plasticizer is required, but a sealing method having excellent sealing performance comparable to the method using a polyvinyl chloride paste has not been devised. It was The present invention relates to a sealing method which has a high degree of sealing property, is free from the risk of migration and elution of the plasticizer into the contents, and has a simple process and is economical.

[0004]

That is, according to the present invention, a soft polyolefin resin preform is interposed between an opening of a container and a plastic or metal cap, and the cap is attached to the container opening by a method such as clamping. The present invention relates to a method for sealing a container, which comprises heating a plastic or metal cap until the soft polyolefin resin preform reaches a temperature equal to or higher than its softening point during or after the mounting process.

In the present invention, the container is a relatively hard container formed of glass, polypropylene, hard polyvinyl chloride, polystyrene, polyethylene terephthalate, etc., and is filled with food, pharmaceuticals, industrial chemicals, drinking water, etc. and transported. It is used for storage, subdivision, shaping for agar / jelly, etc. The shape thereof includes a small opening such as a beer bottle and a liquor bottle, a cylindrical container having a large opening such as a wide-mouthed bottle / cup container, and a rectangular container such as a lunch box.

In the present invention, the cap is essentially made of plastic or metal having a heat resistance higher than that of the soft polyolefin resin. Polypropylene, hard polyvinyl chloride, polystyrene, polyethylene terephthalate, polycarbonate, etc. are used as plastics with better heat resistance than the soft polyolefin resin, which has better heat resistance than the soft polyolefin resin used as the sealing material and can open the container. It is essential that the soft polyolefin resin itself does not soften and melt at a temperature at which the soft polyolefin resin softens and melts when heated during or after the step of mounting on the part. As a metal cap, tin plate,
Clamp-type caps such as crowns, pull-up caps, tear-off caps used in cup-shaped liquor containers, screw-type screw caps, lug caps, etc. made of stainless steel, aluminum, etc. are used.
Anticorrosion coating or printing may be applied. In that case, it is preferable to use a coating material or ink having particularly high heat resistance.

As the soft polyolefin resin, a high pressure method is used.
Branched polyethylene, coexistence of ethylene and vinyl esters
Polymers, ethylene and unsaturated carboxylic acids and their esters
Copolymer with ters, Copolymerization of ethylene and acid anhydride
Body, ionomer resin, ethylene and α-olefins
Copolymer of propylene and ethylene or butene-1
Bending rigidity of copolymers with
Is about 1000 kg / cm ^TwoThe following are preferred, bending
Rigidity is 500kg / cm^TwoThe following are more preferred
Yes. The softening temperature is the load specified in ASTM D1525.
1 kg Vicat softening point of 100 ° C or less is preferable.
Those having a temperature of 80 ° C. or lower are more preferable. Ethylene and α-o
Among the copolymers of reffin, α-olefin is butene-
1, hexene-1, 4-methylpentene-1, octene
-1, decene -1, and a plurality of these, the density
The so-called ultra-low density polyethylene having a value of less than 0.910 is
It has excellent sealing performance and great resistance to shock.
Therefore, it is particularly preferable as the soft polyolefin resin. This
These ultra low density polyethylenes usually have a temperature of 30 to 300 ° C.
Normal pressure to 3000 kg / cm under the polymerization temperature of^TwoPolymerization of
Under pressure, in the presence or absence of solvent, gas-solid phase, liquid
-It is polymerized in the solid phase or under a uniform liquid layer and is not suitable as a catalyst.
Representative of homogeneous transition metal catalysts and metallocene catalysts
Homogeneous catalysts are used. The ethylene-α-olefin
The content of α-olefin in the vinyl copolymer is 10
The amount is at least%, preferably at least 15% by weight.

The soft polyolefin resin includes other commonly used known compounding agents such as antioxidants, neutralizing agents, lubricants, fatty acids, metal soaps, silicone oils, silicone gums, silicone resins and fluorine compounds. A releasing agent, an antistatic agent, a pigment, an inorganic or organic filler or the like may be added within a range that does not impair the object of the present invention.

The soft polyolefin resin is molded in advance into a shape that is smaller than the inner diameter of the cap (inner margin in the case of something other than a circular shape) and conforms to the top surface of the container opening, and then the cap and the container opening. And then a cap is attached to the container opening. Although the thickness of the preform varies depending on the size and shape of the cap, it is 1 to 2 mm in the portion that comes into contact with the top surface of the opening of the container and is substantially used for sealing. In addition, a double ring-shaped rib having a height of about 1 mm may be provided.

Even if the top surface of the container opening is molded by the same mold, it may be slightly different for each lot or for each container due to variations in molding conditions and materials. . Although this slight difference in shape is absorbed by the deformation of the sealing material when the cap is attached or after it is attached, a high degree of sealing performance can be obtained, but compared to soft vinyl chloride containing a large amount of plasticizer, In the case of resin, the deformation was small and the sealing property was poor. The present invention interposes a soft polyolefin resin preform between the container opening and a plastic or metal cap, and during or after the step of attaching the cap to the container opening, the soft polyolefin resin preform is By heating the cap until it reaches a temperature equal to or higher than the softening point, a high degree of sealing performance comparable to the conventional sealing method using a soft vinyl chloride paste is obtained.

As a method of interposing the preform, the preform may be placed on the top surface of the container opening immediately before the cap is attached to the container, and the cap may be immediately attached to the container by a method such as clamping or screwing. However, the preformed body may be fitted on the inner surface in advance, or a cap that has been heat-bonded may be attached to the container. Alternatively, the cap and the soft polyolefin resin preform may be integrated into a container by a method in which the inner surface of the cap is the bottom surface and the melted soft polyolefin resin is placed on the inner surface of the cap.

As a method of heating the cap until the soft polyolefin resin preform reaches a temperature above its softening point, there are indirect methods using hot air, infrared rays, electric heaters, etc. Although the method of contacting is adopted, it is essential that the heating of the cap can be easily adjusted to a certain degree in order to control the softening and melting of the soft polyolefin resin preform to a certain degree. The method in which the cap is made of metal and heated by an inductor that generates an alternating magnetic field, so-called induction heating, has a fast heating rate and can be connected to a non-contact temperature sensor to ensure reliable temperature control. It is particularly preferable because it is possible. The extent to which the cap is heated is until the soft polyolefin resin of the sealant softens and melts and deforms following the subtle difference in shape of the top surface of the container opening to completely fill the gap between the cap and the top surface of the container. It is desirable to do.
The heating temperature and time vary depending on the size and shape of the cap and the thickness of the sealing material, so the optimum value should be selected accordingly.

When the soft polyolefin resin contains a foaming agent and is foamed in the space between the cap and the top of the container opening by being heated above the softening point and foaming temperature of the resin through the cap, the container It is more preferable that the voids can be filled more faithfully and quickly by following the shape of the top surface of the opening, and that the shock absorption after completion of sealing is improved. In this case, the foaming agent may be either an inorganic or organic decomposable foaming agent or a volatile foaming agent, but an inorganic or organic decomposable foaming agent is preferred because it is easily compounded. Examples of the inorganic decomposable foaming agent include ammonium carbonate, sodium bicarbonate, sodium boron hydride, silicon oxyhydride and the like. Examples of the organic decomposable foaming agent include azodicarbonamide (ADCA), azobisisobutylnitrile (AIBN), pp'-oxybisbenzenesulfonylhydrazide (OBSH),
And the like. As the decomposition aid for lowering the foaming initiation temperature, for example, urea compounds, zinc white, inorganic metal salts such as tribasic lead sulfate, and metal soaps such as zinc stearate and calcium stearate are used.

[0014]

The present invention will be described below with reference to examples. The evaluation method and the physical property measurement method are as follows. (1) Density According to JIS-K6760, it measured at 23 degreeC. (2) Softening point According to ASTM-D1525, the temperature was increased at a rate of 50 ° C / hr under conditions of a needle tip area of 1 mm ² and a load of 1 kg, and the temperature when the penetrating needle was sunk by 1 mm was measured. (3) Bending rigidity rate It measured at 23 degreeC according to JIS-K7106.

Example 1 Density 0.890 g / cm ³ , MFR 4.0 g / 10 minutes,
Ultra low density polyethylene resin with flexural rigidity of 350 kg / cm ² (Excellen EUL43 manufactured by Sumitomo Chemical Co., Ltd.)
0), thickness 1.5 mm, inner diameter 30 mm, outer diameter 37
A ring-shaped sheet having a height of 2 mm on the surface of the sheet.
mm, 0.8 mm thick vertical preform having two ring-shaped ribs is manufactured by a press molding method using male and female dies, and the ribs are mounted on the inner surface of the aluminum pull-up cap having a diameter of 38 mm. I put it in. Next, after filling a glass bottle with an internal volume of 180 ml with distilled water at 80 ° C.,
The above pull-up cap was capped with a clamp device, and the aluminum pull-up cap was heated to a temperature of 200 ° C. with an induction heating device manufactured by Sankyo Electric Co., Ltd. At this time, the time required for heating was 26 seconds. When the preform of ultra-low density polyethylene resin was observed after cooling, it was found that it was softly deformed following the tip shape of the top surface of the glass bottle and completely filled the void between the cap and the top surface of the glass bottle top surface. This glass bottle with the cap down, height 3
It was dropped once from the position of 0 cm, and immediately the presence or absence of leakage of distilled water was observed. Then, it was allowed to stand for 48 hours, and the degree of vacuum inside the glass bottle was measured. The vacuum degree was measured using a vacuum can tester. The results are shown in Table 1 together with other examples and comparative examples.

Example 2 AD was previously added as a chemical foaming agent to ultra-low density polyethylene resin.
CA-based foaming agent SELMIC C-121 (Sankyo Kasei Co., Ltd.)
The capping and sealing properties were evaluated in the same manner as in Example 1 except that 1 PHR was added to give foamability.

Comparative Example 1 In Example 1, capping and sealing performance were evaluated in the same manner as in Example 1 except that the cap was not subjected to induction heating.

Comparative Example 2 Polyvinyl chloride paste was used as a sealing material. 100 parts by weight of polyvinyl chloride (powder), DOP80
By weight, 30 parts by weight of calcium carbonate, 3 parts by weight of a stabilizer and 1 part by weight of a foaming agent were mixed and dispersed by a Henschel mixer, and then defoamed and stirred to obtain a paste. 0.5 g of this paste was poured onto the inner surface of the same aluminum pull-up cap as in Example 1, and heated in an oven at 200 ° C. for 2 minutes to foam and cure (gel) to obtain a sample lid. This sample lid was capped in the same manner as in Example 1 and the hermeticity was evaluated.

[0019]

[Table 1] ----------------------------------------- Examples Comparative Example 1 2 1 2 Total number of samples (pieces) 50 50 50 50 Number of samples passed drop test (pieces) * 1 50 50 0 50 Number of samples passed vacuum test (pieces) * 2 50 50 10 50 −−−−−−−−−−−−−−−−−− −−−−−−−−−−−−− * 1 Number of samples that passed the drop test: Number of samples that did not leak after the drop test (pieces) * 2 Number of samples that passed the vacuum test: Specified vacuum (25 cm · Hg or more) The number of samples that maintained

[0020]

Industrial Applicability As described above, according to the present invention, it has excellent sealing property comparable to the method of using a paste of soft vinyl chloride resin as a sealing agent, and migration of a plasticizer into the contents of a container is eluted. A fear-free sealing method was obtained.

Front Page Continuation (72) Inventor Mr. Kino Akira 1212-1 Nakashinda, Ebina City, Kanagawa Japan Institute of Chemical Research (72) Inventor Yuji Dohara 1212-1, Nakashinda, Ebina City, Kanagawa Prefecture Stock Company Inside the Japan Institute for Chemical Research

Claims (4)

[Claims] 1. A soft polyolefin resin preform during or after the step of inserting a soft polyolefin resin preform between the opening of the container and a plastic or metal cap and attaching the cap to the container opening. A method for sealing a container, wherein the cap is heated until the temperature reaches a temperature above its softening point. 2. The soft polyolefin resin preform contains a chemical foaming agent, and the preform reaches a softening point or higher and a foaming start temperature or higher during or after the step of mounting the preform on the container. The method for sealing a container according to claim 1, wherein a plastic or metal cap is heated. 3. The soft polyolefin resin has a density of 0.9.
The method for sealing a container according to claim 1 or 2, wherein the main component is an ethylene-α-olefin copolymer of less than 10. 4. The method for sealing a container according to claim 1, wherein heating of the metal cap is performed by electromagnetic induction.