JPH0234258B2 - - Google Patents

Description

[Detailed description of the invention]

Technical field to which the invention pertains The present invention relates to a method for manufacturing a double-wrapped can used for canning purposes, and more specifically, the double-sealed portion is filled with rubber foam having a closed cell structure, This invention relates to a method for manufacturing a double-wrapped can with particularly excellent leakage prevention properties. Conventional technology Conventionally, when producing canned goods, after filling the contents of the can body, the can end is covered,
Next, double seaming is performed between the can body flange and the peripheral edge of the can end to seal the can. In order to completely seal the double-sealed portion of the can body and can lid, a sealing compound is applied as a lining in the groove provided at the periphery of the can end, and the double-sealed portion is sealed. interpose an elastomer for Such a sealing compound is conventionally prepared by dissolving or dispersing styrene-butadiene rubber, adhesive, and filler in an organic solvent or water, along with an antiaging agent, thickener, or surfactant, if necessary. is commonly used. However, such rubber compositions for sealing cans have not yet been fully satisfactory in terms of complete prevention of leakage. In recent years, there has been a trend toward favoring beverages such as coffee and tea that are sterilized by pressure and heat after hot filling, and for these types of neutral beverages, leakage can cause serious problems such as deterioration of the contents. Therefore, it must have a higher degree of sealing performance than the sealant interposed in the seamed part. From this point of view, many proposals and improvements have been made regarding sealing rubber compositions that can be used as linings.
Publication No. 42669 proposes improving creep resistance by adding a modifier to styrene-butadiene rubber. Problems to be Solved by the Invention However, no matter how much the adhesion and creep resistance of the sealing rubber composition are improved in the double-sealed portion of such a case, It has been found that it is still difficult to completely prevent leakage. In other words, at the double seam part between the can body and the can lid,
The end of the can body is bent approximately 180 degrees and extends downward, and the area around the can lid is wrapped around the bent end of the can body. A lower clearance part is formed between the bottom edge and the can lid periphery, and an upper clearance part is formed between the can lid outermost edge and the can body end, but conventional sealing rubber is not used. In the composition lining method, the layer of the sealing rubber composition is present at most up to the lower clearance area, and it is impossible to sufficiently interpose the layer of the sealing rubber composition up to the upper clearance area. It's impossible.
Thus, with the conventional lining method, it is difficult to completely prevent leakage by filling the entire clearance area of the double seam with the sealing rubber composition. Furthermore, the part of the can body end where double seaming causes the most problems is the side seam of the can body, which requires severe machining, and cracks, gaps, etc. may occur at this seam. Since leakage is likely to occur, leakage passages are often formed in double-sealed areas where only the lower clearance area is filled with the sealing rubber composition. SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a method for manufacturing a double-wound can that effectively eliminates the above-mentioned drawbacks of conventional double-wound cans. Another object of the present invention is to provide a method for manufacturing a double-sealed can in which not only the lower clearance part of the seamed part but also the upper clearance part is filled with a sealing rubber composition without any delay. be. Still another object of the present invention is to provide a method for manufacturing a double-sealed can in which sealing rubber exists in a closed-cell structure in the clearance portion of the double-sealed portion. Means for Solving the Problems The present inventors lined the sealing periphery of a can end (can lid) member with a sealing rubber composition containing a foaming agent, and lined it between the sealing rubber composition containing a foaming agent and the flange of the can body member. By performing double seaming and then heating this seamed part or bringing an acidic solution into contact with the seamed part, a rubber foam with a closed cell structure can be formed in the clearance area of the seamed part, and the upper part can be It becomes possible to fill the clearance area with the rubber foam without any delay,
It has been found that the problem of leakage due to the causes mentioned above can be fundamentally solved. According to the present invention, the step of lining the sealing periphery of a can end member with a sealing rubber composition containing a foaming agent to form a lining layer of an unfoamed sealing rubber composition; and a can end member with the lining layer interposed between the flange portion of the can body member and the peripheral portion of the can end member, and a seaming portion of the resulting double-sealed can. There is provided a method for producing a double-wrapped can, comprising the steps of: heating the lining layer or bringing an acidic solution into contact with the seamed portion to make the lining layer into a rubber foam with a closed cell structure. . Function In FIG. 3, which shows an enlarged view of the double-sealed portion of a conventional can, this can is composed of a can body member 1 and a can end member 2, and a double-sealed portion 3 is formed between the two. Ru. In this double-sealed portion 3, the can body member 1 has an extended hook (sealed flange portion) 4;
This can body hook 4 is bent approximately 180 degrees downward from the root portion 5, and the extreme end 6 is located at the lowest position. On the other hand, the can end member 2 has a peripheral part 7, and this peripheral part 7 is connected to the hook 4 of the can body member 1.
Sealing is performed in such a manner that the can body hook 4 is sandwiched between the outer annular portion 8 and the inner hook 9. In the peripheral part 7 of the can end member, the connecting part between the outer annular part 8 and the can lid hook 9 on the inner peripheral side or the downwardly curved part 10 is located below the lowermost end part 6 of the can body member 1. On the other hand, the tip 11 of the hook 9 on the inner peripheral side is located below the root portion 5 of the can body member 1 and the can body hook 4. As already explained, there is a lower clearance part (lower gap part) 1 between the lower curved part 10 of the can end member and the lowermost end part 6 of the can body member.
2, and an upper clearance portion (upper gap portion) 13 exists between the tip 11 of the can end member and the curved root portion 5 of the can body member. In the conventional double-wrapped can, the layer 14 of the sealing rubber composition is almost completely filled in the lower clearance part 12, but the upper clearance part 13 is not completely filled. , it can be seen that the structure has many voids. In such a structure, since the upper clearance part 13 does not have a sealing function, only the lower clearance part 12 is used for sealing, and there remains a possibility of leakage. FIG. 4 shows an enlarged view of the double seam portion at the side seam of the can body member 1, and the can body hook 4 corresponding to this seam portion has two can body metal material end portions 15a, 15b are joined via an adhesive layer 16. Thus, when subjected to severe processing such as flanging of the can body or double seaming with the can lid, the adhesive primer interposed between the adhesive layer 16 or between the adhesive layer 16 and the metal materials 15a, 15b. When cracks or breaks occur with a certain probability in a layer (not shown), the places where these cracks or breaks occur become leakage passages, and leakage occurs through the above-mentioned upper clearance portion of the gap. As shown in FIGS. 1 and 2, the double-wrapped can according to the present invention is characterized in that the sealing rubber composition layer 14 is made of a rubber foam having a closed cell structure, and that this rubber foam is attached to the base of the can end hook. 5 and the tip 11 of the can end hook, that is, the upper clearance section 13 is completely filled with no gaps, which is a novel and remarkable feature. That is, in the conventional can manufacturing method, it was not possible to fill the upper clearance part 13 with the sealing rubber composition without any gaps, whereas according to the present invention, the sealing rubber composition could not be filled in the upper clearance part 13 without any gaps. By foaming the rubber composition by heating or the like, the rubber composition expands in volume and flows outward from the seaming part due to the volume expansion, and as a result, the upper clearance part 13 is formed without any gaps. It becomes possible to fill it with rubber composition. Thus, according to the present invention, the sealing rubber composition is composed of a closed-cell foam having no air permeability;
Also, since the upper clearance part 13 closest to the air inside and outside the seamed part is filled with sealing rubber, the problem of leakage during packing is completely eliminated. The probability of leakage from the side joints in conventional double-wrapped cans is as low as 1 to 2 cans per million cans, but although this probability is quite low, it can be reduced to zero. It is impossible to do so, and there are no known effective measures to prevent this, and the only way to detect leaking cans is by conducting post-tests on cans and the like. On the other hand, according to the present invention, by employing the above-mentioned sealing structure, the occurrence of leaky cans can be fundamentally eliminated, and the industrial effects are extremely significant. Effects of Preferred Embodiments of the Invention The configuration of the present invention will be explained in more detail. Sealing Rubber Composition In the present invention, the sealing rubber composition includes:
Any composition that can be foamed by heating or contact with an acid and has excellent sealing performance can be used. This sealing rubber composition contains an elastomer polymer and a blowing agent as essential components, and further contains components such as a tackifier, a filler, a modifier, and a surfactant, as necessary. Examples of elastomer polymers include ethylene-propylene rubber, ethylene-propylene-diene rubber, polybutadiene rubber, polyisoprene rubber,
Any rubber can be used, such as butyl rubber, styrene-butadiene rubber (SBR), nitrile-butadiene rubber, chloroprene rubber, polyurethane rubber, acrylic rubber, epoxy rubber, etc. These elastomers line the can ends in the form of compositions dissolved or dispersed in a liquid medium. In the most preferred embodiment of the present invention, the rubber component has a styrene content ranging from 10 to 55% by weight (unless otherwise specified, all parts and percentages are by weight), particularly preferably from 23 to 55%. Some styrene-butadiene rubber is used. The above-mentioned styrene-butadiene rubber is known as SBR and has desirable creep resistance properties for sealants and excellent hygienic properties (extraction resistance) for food contents. The rubber used in the present invention has a Morny viscosity [ML ₁₊₄
(100℃)] is 20 to 150, particularly preferably 30 to 100
It is good that it is within the range of . When SBR has a Mooney viscosity higher than the above range, the hardness of the composition tends to increase, and as a result, it becomes difficult to obtain the desired expansion ratio when foaming is performed by heating or contact with an acid.
On the other hand, in SBR whose Mooney viscosity is lower than the above range, physical properties such as creep resistance will deteriorate. As the blowing agent, any inorganic or organic blowing agent known per se that is conventionally used for foaming rubber can be used. Examples include, but are not limited to: a Inorganic blowing agent (1) Sodium bicarbonate (2) 50% dispersion of sodium bicarbonate in mineral oil (3) Paste of sodium bicarbonate (4) Ammonium bicarbonate (5) Ammonium carbonate b Nitroso compound (1) N,N ′-Dinitroso pentamethylene
Tetramine (DPT) (2) N,N'-dimethyl-N,N'-dinitroso terephthalamide (DMDNTA) c Azo compound (1) Azodicarbonamide (ABFA) (2) Complex containing azodicarbonamide as the main component Blowing agents (3) Azibis isobutyronitrile (AZDN) (4) Barium azodicarboxylate d Sulfonyl hydrazide (1) Benzene sulfonyl hydrazide (BSH) (2) P,P′-oxybis(benzenesulfonyl・Hydrazide) (3) Mixture of benzene-1,3-disulfonyl hydrazide and chlorinated paraffin (4) Toluene sulfonyl hydrazide (TSH) (5) Toluene sulfonyl hydrazide derivative e Other blowing agents (1) P-toluene sulfonyl semicarbazide (2) Trihydrazino triazine (3) Zinc-amine complex compound These blowing agents can be used alone or in combination with blowing aids to assist their decomposition or lower the decomposition temperature. Can be used in combination. Suitable examples of blowing aids are organic acids such as salicylic acid, citric acid, tartaric acid, stearic acid, lauric acid, phthalic acid, benzoic acid, and urea and urea derivatives. In the present invention, the blowing agent is used in an amount that ensures that a closed-cell rubber foam is formed in the double seam portion and that the upper clearance portion is filled with the rubber foam. in general,
0.03 to 30 parts of blowing agent per 100 parts of rubber solid content;
In particular, it is preferable to use it in an amount of 0.1 to 20 parts. That is,
If the amount of the blowing agent is less than the above range, it tends to be difficult to fill the rubber composition sufficiently into the upper clearance area, while if it is more than the above range, the bubbles may become enlarged or Alternatively, there is a tendency for a large number of open air bubbles to be generated, resulting in a decrease in sealing performance. A particularly suitable amount of the blowing agent to be used varies depending on the type of blowing agent, and is preferably determined in consideration of safety standards and the like. In order to improve the adhesion between the compound applied by lining and the can edge, the rubber composition of the present invention preferably contains a tackifier. Such tackifiers are well known per se, and those with good internal extraction resistance and flavor characteristics are selected and used. Suitable examples thereof are rosin resins such as rosin, hydrogenated rosin, hardened rosin, various esters of rosin or hydrogenated rosin; terbene resins;
Natural resin modified phenolic resin such as phenol-formaldehyde resin, rosin or terpene; Xylene-formaldehyde resin or its modified resin; Straight chain hydrocarbon resin (Piccopal resin)
etc. Furthermore, the sealing rubber composition of the present invention preferably contains a filler for the purpose of improving the rheological properties of the solution or dispersion and further adjusting the hardness of the dried film. As such fillers, many inorganic extender pigments and color pigments are used. A suitable example is colloidal silica,
Siliceous fillers such as anhydrous silicic acid, hydrous silicic acid, and synthetic silicates; light to heavy calcium carbonate, activated calcium carbonate; kaolin, calcined clay; alumina white; talcum powder; dolomite; alumina sulfate; barium sulfate ; magnesium carbonate, magnesium oxide, magnesium silicate; calcium sulfate; pumice powder; glass powder; asbestos powder; zinc oxide; titanium dioxide; carbon black. The rubber composition of the present invention may contain a thermoplastic elastomer as a modifier for the purpose of improving creep resistance and the like. Suitable examples of such modifiers are:
It consists of a vinyl aromatic compound and a conjugated diene, and the vinyl aromatic compound accounts for 40 to 90%, particularly preferably
It is a random copolymer containing an amount ranging from 55 to 80%. If desired, the sealing rubber composition of the present invention may contain compounding agents known per se according to known formulations. For example, the rubber composition of the present invention may contain amine-based, aldehyde-amine reaction product-based, ketone-amine reaction product-based, mixed amine-based, phenol-based, or other anti-aging agents or antioxidants or colorants. Agents can be added. In addition, the rubber composition in the form of a dispersion or latex may contain an emulsifying or dispersing stabilizer consisting of various surfactants; a hydrogen ion regulator; or sodium alginate, methyl cellulose, carboxymethyl cellulose, carboxymethyl starch, polyvinyl alcohol, A thickener such as sodium polyacrylate; or a preservative such as sorbic acid may be added. Details of these compounding agents are described in ``Handbook of Rubber and Plastic Compounded Chemicals'' published by Rubber Digest Co., Ltd. (June 15, 1966). In addition, an inorganic fine powder nucleating agent (nucleating agent) can be blended for the purpose of adjusting the bubble size, and an organic organosiloxane surfactant can be blended for the purpose of making the foam size uniform. A preferred formulation example of the sealing rubber composition is as follows. Prescription weight parts Rubber 100 Foaming agent 0.01~30 Foaming aid 0~20 Tackifier 5~200 Filler 30~200 Modifier 0~200 Surfactant 0~10 Each of these components is an organic solvent or It is dissolved or dispersed in a dispersing liquid medium such as water to form a lining composition. For example, in the case of a solvent type composition, aliphatic hydrocarbon liquids such as heptane and n-hexane; aromatic hydrocarbon liquids such as toluene and xylene; acetone; ketones such as MEK; ethers such as dioxane and tetrahydrofuran; An organic solvent such as esters such as ethyl acetate is used, and the above-mentioned rubber component and compounding components are dissolved or dispersed in this organic solvent. On the other hand, in the case of an aqueous dispersion type composition, the above-mentioned rubber component is combined with a compounding agent.
Emulsify and disperse using an emulsifier. In these solutions or dispersions, the solid content concentration at the time of application is between 20 and 90% in order to obtain a combination of appropriate spreadability suitable for lining and formation retention after lining.
Set to a desired value within the range of %. Among these, in the case of a solvent type composition, the solid content concentration should be 30 to 50%, and in the case of an aqueous dispersion type composition, the solid content concentration should be 30 to 70%. It is preferable to do so. Can body, can end, and double seaming The sealing rubber composition of the present invention is useful as a lining sealant for various cans.
As such a case, plastic steel,
Metal materials (planks) such as tin-plated steel sheets, stain-free steel, or aluminum are cut to the required size and side lap seams or hook seams are created by means such as soldering, adhesives, or welding. There are three-piece cans that use a can body formed with , or two-piece cans that use a seamless can body that is formed from the aforementioned metal material by drawing, drawing, ironing, or impact extrusion. ,
The rubber composition of the present invention can be applied to any of these containers to form a sealant interposed between the can body flange and the can end (can lid). The sealing rubber composition of the present invention can be applied to the groove on the periphery of the can end by various lining means. For example, rubber composition linings can be applied using a rotary chuck nozzle liner, in which the rubber composition is applied while rotating the punched can end, or a rotary nozzle liner, in which the can end is stopped and the rubber composition is applied while rotating the nozzle. This can be carried out using a nozzle liner or a die liner that transfers the rubber composition once to a die and then transfers it to the can end. The sealing rubber composition of the present invention is applied to the groove portion around the can end by the above-mentioned means and then, if necessary, dried to form a sealant layer. Double seaming of the can body and can end can be easily performed by a method known per se, for example, by using a seamer. In this case, the dimensions of the seaming part are:
Although it varies depending on the size of the can and the thickness of the can material, when the can plate thickness (defined as the average value of the flange thickness of the can body and the thickness of the can lid periphery) is t, the can body hook and Double seam so that the overlap length OL with the can end hook and the seaming part height W satisfy the following formulas: OL = 3t~10t......(1) W = 5t~15t......(2) It is desirable to carry out this procedure in order to fully realize the effects of the present invention. Foaming According to the present invention, the seam portion of the double seam can thus obtained is heated or brought into contact with acid to convert the aforementioned lining layer into a rubber foam having a closed cell structure. Of course, the heating temperature of the seaming part is sufficient to decompose the foaming agent contained in the lining layer, and this temperature is generally 50 to 350°C, particularly 80°C.
The temperature is preferably in the range of 250°C to 250°C. That is,
If this temperature is lower than the above range, the degree of decomposition of the foaming agent is low and it tends to be difficult to spread the foam sufficiently into the upper clearance area, and if it is higher than the above range for,
This is not preferable because it may cause the paint on the can body or lid to burn. The heating timing, heating means, etc. may be arbitrary as long as heating is performed after seaming. The lining layer can be heated by selectively heating the seamed portion with a high-frequency induction heating coil, by heating the seaming portion with a heating medium,
For example, a method of heating by contacting with hot water, hot steam, hot air, heated oil, a heated roll, a heated plate, a heated flame, etc. can be adopted without particular limitation. Foaming of the rubber composition for filling by heating is a step separate from heat sterilization or sterilization of the contents, and can be carried out before or after sterilization, or can be carried out simultaneously with heat sterilization. For example, heat sterilization of contents is generally
Since the heat treatment is carried out at a temperature of 80 to 130° C. for 5 to 120 minutes, the sealing rubber composition can be foamed at the same time under these heat treatment conditions, which is advantageous. When foaming is caused by contact with an acid, the double seam part may be immersed in an aqueous solution of an inorganic acid such as hydrochloric acid, sulfuric acid, phosphoric acid, nitric acid, or an organic acid such as citric acid or tartaric acid, but is not limited thereto. , a method such as spraying these aqueous solutions onto the double-sealed portion may be adopted. When foaming is caused by contact with acid,
After foaming is completed, it is preferable to wash thoroughly so that excess acid does not remain. In the present invention, the expansion ratio of the closed-cell rubber foam can be varied depending on the type of rubber and the use of the double-wrapped can, but generally speaking, the expansion ratio (per volume before foaming) (volume ratio after foaming) is
It is preferably in the range of 1.1 to 10 times, particularly 1.2 to 3 times. If this expansion ratio is lower than the above range, it is often difficult to fill the upper clearance area with sufficient rubber, while if it is higher than the above range, sealing performance tends to deteriorate. . The container or canned product formed according to the present invention does not leak even when stored for a long period of time, as well as during packaging processes such as heat sterilization (retort) and heating treatment. This advantage is similarly achieved in internal pressure cans for soft drinks containing a high concentration of carbon dioxide gas and in external pressure cans in which the inside of the can is in a highly vacuum state. Advantages and Examples of the Invention The excellent effects of the invention will be explained in detail by the following examples. In addition, unless otherwise specified, parts are expressed as parts per 100 parts by weight of rubber solid content. Example 1 Styrene-butadiene copolymer rubber (SBR;
Styrene content 35%, dry rubber Mooney viscosity
40, polymerization temperature: 50℃) Prepare latex (solid content in latex: 50%), clay (filler): 90
parts, titanium white (filler): 10 parts, carbon black (filler): 1 part, hydrogenated rosin (adhesive): 80 parts, Karaya gum (thickener): 2 parts, methylcellulose (thickener): 1 part of di-β-naphthylphenylenediamine (antiaging agent) and 2 parts of azodicarbonamide (foaming agent) were added and mixed with stirring to prepare sealing compound A. At that time, water and aqueous ammonia were added to adjust the solid content to 40% and pH to 11. On the other hand, Comparative Sample 1 was prepared in the same manner as Sealing Compound A, but the blowing agent azodicarbonamide was not added. These two types of sealing compounds were applied to a 200-diamond aluminum can lid and a TFS can lid, and dried at 90°C for 10 minutes. After double-sealing an aluminum can lid to one end of the 250ml 202 diamond side-lap seam adhesive can body (near the seaming part has been necked in to become 200 diamonds),
Fill the coffee beverage at 95℃ and TFS on the other end
The can lid was double-tightened. Canned these at 125℃
The product was prepared by subjecting it to retort sterilization for 40 minutes. After storing these canned products at room temperature for one month, they were submitted to a canning manufacturer for sealing inspection at the time of product shipment.
All cans were inspected for sealing, and for acoustically defective cans, the degree of vacuum inside the can was measured, and those in which the degree of vacuum had decreased were identified as leaking cans. The test results are shown in Table 1. It can be seen that the double-wound can according to the present invention (using sealing compound A) has superior sealing performance compared to the conventional double-wound can (using comparative sample 1).

[Table] On the other hand, the presence of the sealing compound inside the double-sealed cans, especially the upper clearance, was observed. The can lid member near the double seam part is ground and removed leaving the hook 9, and the can body member is exposed. Furthermore, the coating film on the surface of the can body is polished to expose the iron surface, and in this state it is immersed in dilute nitric acid to dissolve and dissolve the iron.
Remove the chromate treatment film, paint film, etc. by treating with cat hydrochloric acid or concentrated sulfuric acid as necessary.
The compound of the upper clearance area and lower clearance area was exposed. As a result of observation, in the double-wound can of the present invention, the sealing compound (sealing compound A) foams approximately twice as much to form a closed cell structure, and both the upper and lower clearance areas are filled without any gaps. It was confirmed that On the other hand, in the conventional double-wound can (comparative sample 1 was used), no foaming of the sealing compound was observed, and the filling state of the compound in the upper clearance portion was incomplete. In addition, the aluminum can lid seam part and
No difference was observed in the presence of sealing compound in the TFS can lid seam area. Example 2 Using an adhesive can body made by double-sealing the aluminum can lid produced in Example 1 and a TFS can lid,
A can filled with a carbonated beverage (gas volume: approximately 4) was prepared. These canned products were passed through a water bath adjusted to pH 2.0 with hydrochloric acid for 1 minute and then washed with water to obtain canned products. For these canned products, a canned manufacturer conducted a sealing inspection at the time of product shipment. The sealing inspection was conducted visually, and any cans in which the contents of the canned product or its dried residue were found to be attached near the seaming part were considered to be leaky cans. The test results are shown in Table 2. It can be seen that the double-wrapped can according to the present invention (using sealing compound A) has superior sealing performance than the conventional double-wound can (using comparative sample 1).

[Table] Furthermore, according to the method shown in Example 1, the presence of the sealing compound in the upper clearance part and the lower clearance part was confirmed.
In the double-wrapped can using sealing compound A, as in Example 1, the sealing compound foams approximately twice as much to form a closed cell structure, with no gaps in both the upper and lower clearances. It was full. On the other hand, in the conventional double-wrapped can using Comparative Sample 1, no foaming of the sealing compound was observed, and the sealing compound was incompletely filled in the upper clearance area. Example 3 Sealing compound B was prepared as follows. Styrene-butadiene copolymer rubber (sterene content 23.5%, dry rubber Mooney viscosity 50, polymerization temperature 5°C) latex (solid content in latex 52%), clay (filler): 80 parts, titanium white (filler) agent): 10 parts, rosin (adhesive): 60 parts,
Karaya gum (thickener): 2 parts, methyl cellulose (thickener): 1 part, di-β-naphthylphenylenediamine (anti-aging agent): 1 part, sodium bicarbonate (foaming agent): 10 parts are stirred and mixed. did. At this time, water and aqueous ammonia were added so that the solid content was 40% and the pH was 11. Sealing compound C was prepared in the following manner. Solid rubber of styrene-butadiene copolymer rubber (styrene content 35%, dry rubber Mooney viscosity 35, polymerization temperature 50°C), clay (filler):
100 parts, titanium white (filler): 15 parts, G-β
- Naphthylphenylenediamine (anti-aging agent):
Add 1 part and knead with a Banbury mixer, and then add rosin (adhesive): 100 parts, Karaya gum (thickener): 2 parts, methylcellulose (thickener): 1 part,
Rosin soap (surfactant): 5 parts and p,p'-oxybis(benzenesulfonyl hydrazide)
(Foaming agent): 3 parts were added and dispersed in water using a high speed mixer. At this time, ammonia water was added so that the solid content was 40% and the pH was 11. Sealing compound D was prepared in the following manner. Solid rubber of styrene-butadiene copolymer rubber (styrene content 35%, dry rubber Mooney viscosity 35, polymerization temperature 50°C), clay (filler):
60 parts, titanium white (filler): 20 parts, di-β
- Naphthylphenylenediamine (anti-aging agent):
Add 1 part and mix with a Banbury mixer,
Furthermore, rosin (adhesive): 80 parts and N,N'-gintroso pentamethylene tetramine (foaming agent):
5 parts and 1 part of salicylic acid (foaming aid) were dissolved and decomposed in hexane. At this time, the solid content was adjusted to 40%. These three types of sealing compounds were applied to a 200 diamond aluminum can lid and a TFS can lid.
After heating and drying for a minute, Sealing Compound D was left as it was for one day and then tested. These can lids were double-sealed to a 250ml 202-diamond side-lap seam adhesive can body (the area near the seam was necked in to become 200-diamond).
Sixty samples were prepared for each of three types of sealing compounds, aluminum can lids, and TFS can lids. Of these, each of 20 cans was heated in the vicinity of the seaming part by high-frequency induction heating to reach approximately 300°C in approximately 5 seconds. Each of the other 20 cans was placed in an air heated oven set at 150°C for 10 minutes. For each of the other 20 cans, an acetic acid aqueous solution adjusted to pH 2.0 was sprayed from the outside of the can to the vicinity of the seaming part, and washed with water after 2 minutes. Regarding these samples, the presence state of the sealing compound inside the seamed portion was observed according to the method shown in Example 1. As a result, for all samples, the sealing compound expanded to about twice its size and formed a closed cell structure.
Both the upper and lower clearance areas were filled with no gaps. Example 4 Latex of styrene-butadiene copolymer rubber (styrene content 35%, dry rubber Morney viscosity 30, polymerization temperature 50°C) (solid content in latex 50%)
%), clay (filler): 100 parts, titanium white (filler): 10 parts, carbon black (filler):
1 part, hydrogenated rosin (adhesive): 70 parts, Karaya gum (thickener): 2 parts, methylcellulose (thickener): 1 part, di-β-naphthylphenylenediamine (antiaging agent): 1 part and rosin soap (surfactant): 2 parts were added and mixed with stirring to prepare an intermediate product of a sealing compound. At that time, water and aqueous ammonia were added to adjust the solid content to 40% and pH to 11. To this intermediate product, azodicarbonamide in the amount shown in Table 3 was added and mixed with stirring to prepare five types of sample sealing compounds. These sealing compounds were applied to a 202-diamond aluminum can lid, dried, double wrapped around the same type of can body as used in Example 1, and then sealed by heat steam sterilization at 125°C for 40 minutes. The compound was foamed. As a result of observing the presence of the sealing compound inside the seam of these cans using the method shown in Example 1, foaming of the sealing compound was observed in all samples. The foaming ratio is also shown in Table 3. The sealing compound was completely filled with the sealing compound in both the upper and lower clearances inside the seaming section. In addition, it was confirmed that sealing compounds E, F, G, and H formed closed cell structures, but in the sealing compounds, the cells were continuous in some areas and did not form a closed cell structure.

【table】 [Brief explanation of drawings]

FIG. 1 is an enlarged cross-sectional view showing the seaming part of the double-wrap can according to the present invention, FIG. 2 is an enlarged cross-sectional view showing the seaming part corresponding to the can body overlap joint of the can of FIG. 3
The figure is an enlarged sectional view showing a seaming part of a conventional double seam can, and FIG. 4 is an enlarged sectional view showing a seaming part corresponding to the overlapping seam of the can shown in FIG. 1 is a can body member, 2 is a can end member, 3 is a double seam part, 4 is a can body hook, 9 is a can end hook, 12 is a lower clearance, 13 is an upper clearance, 14 is a rubber composition layer. represent

Claims (1)

[Scope of Claims] 1. A step of lining the sealing periphery of the can end member with a sealing rubber composition containing a foaming agent to form a lining layer of an unfoamed sealing rubber composition, and a can body. A step of double seaming the member and the can end member with the lining layer interposed between the flange portion of the can body member and the peripheral portion of the can end member, and seaming the resulting double seamed can. A method for manufacturing a double-wrapped can, comprising the step of heating the lining layer to form a closed-cell rubber foam. 2. A step of lining the sealing periphery of the can end member with a sealing rubber composition containing a foaming agent to form a lining layer of an unfoamed sealing rubber composition; and a can body member and a can end member. double seaming with the lining layer interposed between the flange part of the can body member and the peripheral part of the can end member, and contacting the seamed part of the resulting double seamed can with an acidic solution. A method for manufacturing a double-wound can, comprising the step of: forming the lining layer into a rubber foam having a closed cell structure.