JPS62181343A - Sealant composition for lid of can - Google Patents

Abstract

PURPOSE:To obtain a sealant composition capable of filling a seamed part of a can in the form of closed cells when applied to a can lid as a lining and giving a can having excellent leak-proofness, by dispersing rubber latex particles and micro-encapsulated particles of solid foaming agent in an aqueous medium. CONSTITUTION:A composition containing rubber latex particles and microencapsulated particles of solid foaming agent in an aqueous medium in a dispersed state. The rubber latex particle is a styrene-butadiene copolymer rubber and the micro-encapsulated solid foaming agent is produced by using carnauba wax or beeswax as a shell and has a diameter of 0.05-500mum. The amount of the micro-encapsulated particle is 0.03-30pts.wt. per 100pts.wt. of the whole solid component. The composition is preferably further incorporated with a tackifier.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a sealant composition for can lids, and more particularly, it is applied to a can lid by lining and has a closed cell structure in the seamed part. The present invention relates to a sealant composition that can be filled with a rubber foam to produce a seamed part with excellent leakage prevention properties. Is the present invention still applicable to the above sealant composition? It also relates to improvements in bed life.

(Prior Art) Conventionally, in the production of canned goods, after filling the can body with the contents, a can end is placed on the can end, and then a can end is placed between the can body flange and the periphery of the can lid. Perform heavy seaming to seal. In order to completely seal the double-sealed portion between the can body and the can lid, a sealant is applied to the lining in a groove provided on the periphery of the can lid, and the double-sealed portion is sealed. A sealing nidistomer is interposed between the two. Conventionally, such sealants are prepared by dissolving or dispersing styrene-butadiene rubber, adhesive, and filler in an organic solvent or water, along with anti-aging agents, thickeners, or surfactants as necessary. are commonly used.

However, such rubber compositions for cans and elbows,
It has 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 neutral beverages with glazes, leakage can cause serious problems such as deterioration of the contents. Since there is a risk of this occurring, the sealant (n-land) present in the seamed portion must also have a higher degree of sealing performance. From this perspective, many proposals have been made regarding fM old DEM compositions that can be applied as linings.
Improvements have been made, for example, in Japanese Patent Publication No. 57-42669, it has been proposed to improve the creep resistance by adding a modifier to the styrene-butazoene copolymer.

(Problem to be Solved by the Invention) However, in such a double seam portion of a can body, no matter how much the adhesion and creep resistance of the sealing rubber composition are improved, the seam cannot be tightened. It has been found that it is difficult to completely prevent leakage from the

That is, from the viewpoint of strength, a can body with a lap joint on the side is used as a can body for canned beverages subjected to the above-mentioned pressure and heat sterilization process.
/7'yh joints always exist in the part of the flanz that is seamed to the can lid. There is a level difference in this lap joint, and cracks, etc., which are caused by cracking, occur in the lap joint during the severe winding and rolling process, and these steps and cracks become leakage paths. Leakage occurs frequently.

The inventors first applied a sealant composition containing rubber and a foaming agent to a can lid by lining it, sealed it with the can body, and then heated the seamed part. proposed that leakage from the seamed part could be prevented by filling the seamed part with closed-cell rubber foam (also pending application).

However, this acidic sealant has problems with its pot life, and the foaming agent tends to decompose during storage of the sealant composition, making it difficult to sufficiently foam the rubber composition after seaming. I run into the problem that.

Therefore, the technical disadvantage of the present invention is that it has excellent pot life, suppresses pre-foaming or decomposition during storage or drying of coating, and prevents foaming of the rubber composition within the seamed part after seaming. It is an object of the present invention to provide a sealant composition for a can lid, in which the closing portion is effectively filled with closed-cell rubber foam.

According to the present invention, the solid blowing agent is dispersed in the aqueous medium in the form of microencapsulated particles together with the rubber latex particles, so that the sealant composition can be stored or It is possible to suppress the pre-foaming and minute HD directions during coating and drying, and to effectively perform independent foaming of the rubber within the seaming portion.

(Function) When a solid foaming agent is blended into rubber latex, decomposition of the solid foaming agent progresses at a slow but not negligible rate. That is, solid blowing agents are relatively stable in air at room temperature, but decompose more rapidly under conditions of contact with water than in air. In particular, Co-9 latex has a high value of around 10, and also contains components such as surfactants, so
The decomposition progresses much faster than in plain water. Rather than being unable to foam to the extent shown in diagram X after seaming due to the decomposition of the solid foaming agent, the rubber latex becomes dull with air bubbles in it, creating a uniform and dense rubber composition on each can lid. Forming layers becomes an office job.

According to the present invention, by dispersing the solid foaming agent in a microencapsulated state in the rubber latex, the solid foaming agent is prevented from coming into contact with water or with components dissolved or dispersed in an aqueous medium. Contact is blocked, and decomposition of the solid foaming agent during storage can be suppressed. This allows the rubber layer to foam to the desired degree after seaming, and also prevents air bubbles from forming in the lining composition. It is possible to form a dense rubber composition layer on the can lid while preventing generation and dulling.

As described above, a remarkable feature of the sealing rubber composition of the present invention is that the solid foaming agent selectively decomposes at the stage after seaming, and this is due to the fact that the shell of the microcapsules does not contain the solid foaming agent. There is a reason to protect the world, and the first fact is also closely related. That is, the can body flange and the can lid are tightened so that a layer of the sealing rubber composition is interposed between them, but the mechanical pressure applied to the layer of the rubber composition during tightening is υ, resulting in rupture of the capsule shell and exposure of the solid blowing agent. Exposure of the solid foaming agent due to the destruction of the capsule shell is noticeable in areas adjacent to the can body Franz wall and the can lid wall where leakage passages are likely to occur. Thus, the solid foaming agent is partially decomposed by the cooperative action of the auxiliary agent and heat or by the contact action with the acid decomposer, and the formation of closed foam cells causes the leakage passage to be blocked or blocked through the rubber. It is.

In addition, when the sealant composition of the present invention is used, it is possible to achieve a desired sealing area in terms of leakage prevention. - The effect that the clearance part can be filled with closed cell foam can be obtained.

In Fig. 3, which shows an enlarged view of the double seam part of a conventional can,
This can consists of a can body member 1 and a can end member 2, and a double seam portion 3 is formed between the two. In this double seaming part 3, the can body member 1 has an extended hook (a seamed part) 4 on the side, and this can body flap 4 has a root part 5.
It is bent approximately 180 degrees downward from the top end 6.
is located at the bottom. On the other hand, the can end member 2 has a peripheral portion 7
This peripheral portion 7 is in a shape that wraps around the hook 4 of the can body member 1, that is, the can body hook 4 is sandwiched between the outer peripheral annular portion 8 and the hook 9 on the inner peripheral side. Sealing is being done.

In the peripheral part 7 of the can end member, the connecting part between the outer peripheral 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 6 of the can body member l. On the other hand, the tip 11 of the hook 9 on the circumferential side is located below the root portion 5 of the can body member 1 and the can body hook 4. As already explained, the upper curved portion lO of the can end member and the lowermost end f of the can body member
There is a lower clearance part (lower gap part) I2 between the can end member 11 and the curved root part 5 of the can body member. exists. In a conventional double seam, the sealing rubber composition layer 14 fills the lower clearance portion 12 almost completely, but does not reach the upper clearance portion 13 completely. Not there,
It will be understood that the structure has many voids. In such a structure, Ara) 4-・Clearance part 13
Since it does not have a sealing function, it is necessary to seal only with the lower clearance part 12, and there remains a possibility that it will lead to leakage.

FIG. 4 shows an enlarged view of the double seam portion at the side seam of the can body member 1, which corresponds to the seam portion of the can body 7. 4 has a structure in which two can body metal end portions 15a and 15b are joined via an adhesive layer 16. In this way, when undergoing severe processing such as flanging the can body or double seaming processing with the can lid, the adhesive layer 16 or the adhesive layer 1
If cracks or breaks occur in the adhesive primer layer (not shown) interposed between the metal material 6 and the metal materials 15a and 15b, the places where these cracks or breaks occur will become leakage paths, and the above-mentioned voids will become leakage paths. leakage will occur through the upper clearance section of the

The double-sealed part made using the sealant composition of the present invention has a seal shown in FIGS. 1 and 2, and the sealing rubber composition layer 14 is made of a rubber foam having a closed cell structure. 7. This rubber foam also forms the end of the can. Root 5 and can end hook tip 11
The clearance part between the upper clearance part 1 and the upper clearance part 1
3 is completely filled with no gaps, which is a novel and remarkable feature. That is, in the conventional can making 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 exists in the double seam part. 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 gap, base, and clearance part 13 It becomes possible to completely fill the rubber composition with the rubber composition without any gaps. in this way,
According to the unexploded IJI VC, the sealing rubber composition is made of a closed-cell foam with no air permeability, and the sealing rubber is filled in the upper clearance part 13 closest to the air inside and outside the seaming part. Therefore, the problem of leakage in canned foods is completely eliminated.

The probability of leakage from the side seam of conventional double-sealed cans is as low as 1 to 2 cans per million cans, but although this probability is extremely low, it is possible to reduce this to zero. It is impossible to do so, and there are no known effective measures to prevent this, and leakage cans have only been detected by post-tests of chairs, striking parts, etc. On the other hand, according to the present invention, by employing the above-mentioned sealing structure, the occurrence of leaking cans can be fundamentally eliminated, and the industrial effects are extremely significant.

(Operations and Effects of the Invention) According to the present invention, leakage from the seaming part of a can can be effectively prevented by a simple means of containing a solid foaming agent in a microencapsulated state in a sealant composition for can lids. It became possible to prevent this. In addition, by protecting the solid foaming agent contained in the microcapsule shell, it is possible to prevent pre-foaming and foaming during storage or application of the sealant composition, resulting in a uniform and dense rubber composition. By allowing the formation of
It was possible to effectively form a closed-cell foam that blocks the leakage path.

(Description of preferred embodiments of the invention) The configuration of the present invention will be explained in more detail.

In the present invention, as the sealing rubber composition, 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, polyisogrene rubber, butyl rubber, and styrene rubber.
Any rubber can be used, such as butadiene rubber (SBR), nitrile-butadiene rubber, chloroglene rubber, polyurethane rubber, acrylic rubber, epoxy rubber, and the like. These elastomers line can ends in the form of compositions dissolved or dispersed in a liquid medium.

In the most preferred embodiment of the present invention, the gum component has a styrene content of 10 to 55% by weight (unless otherwise specified, all parts and percentages are by weight), particularly preferably 23 to 55% styrene. Use styrene-butatsuene rubber in the range.

The above-mentioned styrene-butadiene rubber is known as so-called SBR and has desirable creep resistance properties for sealants and excellent sanitary properties (extraction resistance) for food contents.

The rubber used in the present invention has a Mooney viscosity [ML1+4(1
00℃] is 20 to 150, particularly preferably 30 to 1
It is better to be in the range of 00. 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 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.

Blowing Agent As the blowing agent, any inorganic or organic blowing agent known per se that is conventionally used for foaming rubber can be used in the form of microcapsules. Examples include, but are not limited to, the following passages:

a, inorganic blowing agent (1) M sodium carbonate (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, 1'/- dinitroso pentamethylene tetramine (DPT) (2) N, N'-dimethyl-N, manonitrone
Terephthalamide (DMDNTA) C, Azo compound (1) Azodicarbonamide (ABFA) (2) Patent blowing agent characterized by azodicarbonamide (3) Azobis isobutyronitrile (AZDN) (
4) Barium azodicargoxylate d, sulfonyl hydrazide (1) Benzene sulfonyl hydrazide r (BS
H) (2) P,? '-Oxybis(benzenesulfonyl hydranide) (3) Mixture of benzene-1,3-disulfonyl hydrazide and chlorinated paraffin (4) Toluene sulfonyl hydrazide (TSH) (
5) Toluene sulfonyl hydrazi) 94 body e,
Other blowing agents (1) P-) Luene-sulfonyl-sulfonate (2) Trihydrazino-triazine (3) Zinc-amine complex compounds These blowing agents can be used alone, or they can assist in their decomposition. Alternatively, it can be used in combination with a foaming aid for the purpose of lowering the decomposition temperature. 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.

The above-mentioned solid foaming agent is generally in the form of powder or granules, and is used as microencapsulated particles. The shell material of the microcapsule particles must be non-water permeable and pressure sensitive since the microcapsules are used by being dispersed in an aqueous medium and the core material is easily decomposed on contact with water. A film-forming material is used that is easily destructible.

Suitable examples of shell materials include, for example, carnauba wax,
Animal and vegetable waxes such as cotton wax, beeswax, wool wax, montan wax, rough-in wax, microcrystalline wax, polyethylene wax, polyethylene wax, mineral wax or synthetic waxes, low molecular weight olefin resin, low molecular weight styrene resin, Petroleum resins, rosins, phenolic resins, xylene resins, amino resins,
These are various hydrophobic resins such as epoxy resins.

For microencapsulation, the above-mentioned core material is dispersed in a melt of the shell material, and the melt is sprayed into the air or dispersed into the air by a rotating body to granulate the shell material. A method is used in which the core material is dispersed in an organic solvent solution and the dispersion is sprayed and granulated.

For the purposes of the present invention, the diameter of the microcapsule particles is 0.
05 to s 00 tsn, 0.1 to 100 in %
.mu.m range, while the shell material, when used in an amount of 1 to 100%, especially 10 to 50% by weight, based on the core material, is advantageous in terms of protection of the solid blowing agent and crushability under pressure. Satisfactory results are obtained.

Any means may be employed to impart water dispersibility to the microcapsule particles. For example, by subjecting microcapsule particles to a corona discharge treatment, hydrophilicity can be imparted to the surface to the extent that they can be water-dispersed.
Alternatively, water dispersibility can be imparted by surface treatment with alcohol or the like.

Note that 1. The blowing agent and the auxiliary agent may be microencapsulated in the form of a mixture, only the blowing agent may be microencapsulated and the auxiliary agent may be added to the latex, or both may be microencapsulated independently. Te ・Moyoi.

In the present invention, the microencapsulated foaming agent is used to ensure that a closed-cell foam is formed in the double seam area and that the foam is filled in the gap, clearance, and clearance areas. used in large quantities. In general, the microencapsulated blowing agent may be used in an amount of 0.03 to 30 parts, particularly 0.1 to 20 parts, per 100 parts of comb solids. 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, whereas if the amount is more than the above range, air bubbles may form. There is a tendency for the formation of enlarged υ or open air bubbles to increase, and the sealing performance may deteriorate. 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 sealant applied to the lining and the can lid, 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 flaker properties are selected and used. A suitable example is rosin,
Rosin resin such as hydrogenated rosin, hardened rosin, rosin or various esters of hydrogenated non-ester; Terpene resin: Natural resin such as phenol-formaldehyde resin, rosin or terpene; Modified phenol resin: xylene-formaldehyde resin or its modified resin. ; Straight chain hydrocarbon resins (Piccopales & fats) and the like.

Furthermore, it is desirable that the sealing rubber composition of the present invention contains a filler for the purpose of improving the rheological properties of the dispersion and further adjusting the hardness of the dried film. As such fillers, many inorganic pigments and color pigments are used. A suitable example is colloidal silica,
Siliceous fillers such as anhydrous silicic acid, hydrated silicic acid, and synthetic silicates; light to heavy calcium carbonate, activated calcium carbonate: carllion, calcined clay: alumina white; talcum powder; dolomite; sulfuric acid alumina: sulfuric acid Barium: magnesium carbonate, magnesium oxide, magnesium silicate; calcium sulfate: pumice powder; lath powder; asbestos powder; zinc oxide: titanium dioxide; carpin 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 is a random copolymer consisting of a vinyl aromatic compound and a conjugated diene and containing the vinyl aromatic compound in an amount ranging from 40 to 90%, particularly preferably from 55 to 80%.

The sealing rubber composition of the present invention may contain, if desired, compounding agents that are known per se in accordance with 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 and colorants. Agents can be added. Also, Dis A? The rubber composition in the form of rubber or latex may contain an emulsifying or dispersing stabilizer consisting of various surfactants; a hydrogen ion regulator; or sodium alginate, methyl cellulose, calcium hydroxide, oxymethylcellulose, carboxymethyl starch, holvinyl alcohol,
A thickener such as sodium polyacrylate; or a preservative such as rubic acid may be added. Details of these compounds are described in "Handbook of Rubber and Plastic Compound Chemicals" published by Rubber Digest (June 15, 1966). In addition, inorganic fine powder nucleating agents are used to adjust the bubble size.
An organic organosiloxane surfactant may be added for the purpose of making the foam size uniform.

A preferred formulation example of the sealing rubber composition is as follows.

Rubber 100 Foaming aid O~20 Tackifier 5~200 Filler 30~200 Modification
Agent 0~200 Surfactant O~
10 Each of these components is dispersed in a liquid dispersion medium to prepare a lining composition. That is, the above-mentioned rubber component is emulsified and dispersed together with the compounding agent using an emulsifier. In these dispersions, the solid content concentration at the time of application is within the range of 20 to 90% so as to obtain a combination of appropriate spreadability suitable for lining and shape retention after lining.
Set to desired value. Among these, the sealing rubber composition of the present invention is suitable for use in O can bodies, can lids, and double-sealed seals having a solid content concentration of 30 to 70 cm. Useful as a sealant - To make such a can body, cut metal materials (Zrank) such as black steel, tin-plated steel plate, tin-free steel, or aluminum into the required size, and apply solder, adhesive, welding, etc. Three-piece cans using a can body with a side lap seam or hook seam formed by the means of - Two-piece cans using seamless can bodies formed by extrusion processing are known, but the rubber composition of the present invention can be applied to any of these can bodies without intervening between the can body flange and the can lid. It can be applied to form a sealant.

The sealing rubber composition of the present invention can be applied to the peripheral groove of a can lid by various lining means. For example, rubber composition linings can be applied using chuck-rotating nozzle liners, which are applied while rotating a stamped can lid;
This can be done using a rotating nozzle nozzle liner, in which the rubber composition is applied while the can lid is stopped and the nozzle is rotated, or a guiliner, in which the rubber composition is first transferred to a die and then transferred to the can lid. .

The sealing rubber composition of the present invention is applied to the groove portion around the can lid by the above-mentioned means and then, if necessary, dried to form a sealant layer.

Double seaming of the can body and can lid can be easily performed by a method known per se, for example, by using a seamer. It also varies depending on the thickness.

When the thickness of the can (defined as the average value of the flange thickness of the can body and the thickness of the can lid periphery) is 1-1, the overlap length OL between the can body hook and the can lid hook and the height of the seaming part It is desirable to perform double seaming so that W satisfies the following formula (% formula % (1)) in order to fully realize the effects of the present invention.

Foaming According to the present invention, the seam portion of the double seam portion 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 desirably in the range of 50 to 350°C, particularly 80 to 250°C.

That is, if this temperature is lower than the above range, the degree of decomposition of the foaming agent will be low, and it will tend to be difficult to spread the foam sufficiently into the upper clearance area; If it is too high, the paint on the can body or lid may become scorched, which is not preferable.

The heating timing, heating means, etc. may be arbitrary, as long as the heating properties can be achieved after seaming. The lining layer can be heated by selectively heating the seamed part with a high-frequency induction heating coil. A method of heating by contacting with a frame or the like can be adopted without particular restriction. 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, since heat sterilization of the contents is generally carried out by heat treatment at a temperature of 80 to 130°C for 5 to 120 minutes, foaming of the sealing rubber composition can be carried out simultaneously under these heat treatment conditions, which is advantageous. .

When foaming is caused by contact with an acid, the double seam may be treated with an inorganic acid such as, but not limited to, hydrochloric acid, sulfuric acid, phosphoric acid, nitric acid, or an organic acid such as citric acid.

When foaming is caused by contact with zero acid, methods such as immersion in an aqueous solution such as tartaric acid or spraying of these aqueous solutions onto the double-sealed part should be taken so that no excess acid remains after foaming is complete. It is preferable to wash thoroughly.

In the present invention, the expansion ratio of the closed cell rubber foam is
Although it can vary depending on the type of rubber and the purpose of the double-sealed can, generally speaking, the expansion ratio (ratio of foam diameter volume to volume before foaming) is 1.1 to 10 times, especially 1. ．．
It is preferably in the range of 2 to 3 times. If the foaming ratio is lower than the above range, it is often difficult to sufficiently fill the upper clearance area with rubber, while if it is higher than the above range, the sealing performance tends to deteriorate. .

The can bodies or canned goods formed according to the present invention can be used in canning processes such as heat sterilization (retort) and heating treatment, as well as
No leakage occurs even when stored for long periods of time, and this advantage applies to internal pressure cans for soft drinks that contain carbon dioxide at high temperatures, as well as external pressure cans where the inside of the can is in a highly vacuum state. achieved.

(Example) In the following examples, microcapsules and sealants were manufactured in the following manner. Unless otherwise specified, parts are expressed as parts by weight, and the composition of the sealant refers to elastomer (rubber).
Expressed as 1 part by weight per 100 parts by weight of solid content.
Regardless of the type of core material (solid foaming agent), it was produced in the following manner.

Shell material f, ;l! A solid foaming agent that has been dissolved in a solvent and crushed and classified to a particle size slightly smaller than the particle size of the microcapsules to be obtained is added.

Stir and mix until evenly distributed. At this time, the concentration of the shell material is adjusted so that the viscosity of the dispersion is 500 to 1000 ep. Further, a solvent is selected that is a good solvent for the shell material and a non-solvent or a poor solvent for the core material. This dispersion was sprayed into the air and the falling microencapsulated particles were collected to obtain a microencapsulated solid foaming agent.

In the examples, sealants were manufactured in the following manner.

Prepare elastomer latex with a solid content of about 50 parts,
For 100 parts by weight of elastomer solid content, clay (filler): 90 parts, titanium white (filler) = 10 parts,
Cargon black (filler): 1 part, hydrogenated rosin:
(Tackifier): 80 parts, Karaya gum (thickener) = 2
1 part of methylcellulose (thickener) and 1 part of di-β-naphthylphenylenediamine (antiaging agent) were added and stirred and mixed. The type and properties of the elastomer differ for each sample. Microencapsulated solid blowing agent particles were added to this mixture and further stirred and mixed.
The shell material of the microencapsulated solid foaming agent particles, the glaze and amount ratio of the core material (weight of the shell material/weight of the core material - 1X100), particle size, and amount added to the sealant are different for each sample. . At that time, water and aqueous ammonia were added to adjust the solid content to 40% and -11.

Example 1 Sample A contained styrene as the elastomer latex.
Latex of butadiene copolymer rubber (styrene content: 335%, dry rubber Mooney viscosity: 40, polymerization temperature: 50° C.) was used. In addition, as a microencapsulated solid foaming agent, the shell material is low molecular weight polystyrene, the core material is azodicarbonamide, the ratio of the amount of the shell material to the core material is about 30, and the average particle size is about 20 μm. The amount added to the sealant is 100 parts by weight of total solids.
There were 5 parts. On the other hand, comparative sample A was made using the same elastomer latex as sample A, but no microencapsulated solid blowing agent was added. Apply this two-layer sealant to a 200-year aluminum can lid and a T.
It was applied to an FSW can lid and dried at 90°C for 10 minutes. After double-sealing an aluminum can lid with one end of a 250 m 1202 diamond side-drug seam adhesive can body (necked-in processing is performed near the seam to make it 200 diamonds), a coffee beverage at 95°C is filled. , T at the other end
The FS can lid was double-sealed. Furthermore, 1 of these canned foods
Products were prepared by subjecting them to a retort killing process at 25°C for 40 minutes. After storing these canned products at room temperature for one month, they were subjected to a sealing inspection by a can manufacturer at the time of product shipment.

All cans were inspected for sealing, and for cans with poor acoustics, the degree of vacuum inside the can was measured, and those with a reduced degree of vacuum were identified as leaking mortars.

The test results are shown in Table 1. The sealant according to the present invention (sealant composition for can lids, sample A) 1&: It can be seen that the cans used had better sealing performance than the cans using the conventional sealant (comparative sample A).

Table 1 On the other hand, the presence of sealant N in the double-sealed interior of these canned goods, mainly in the upper clearance area, was observed. Grind and remove the can lid member near the double seam part, leaving the hook 9, to expose the can body member. The iron is dissolved and removed by immersing it in dilute nitric acid, and if necessary, it is further treated with concentrated hydrochloric acid or concentrated sulfuric acid to remove the chromate treatment breakage and paint film.

Results of an in-depth inspection that exposed the sealant in the upper and lower clearance areas 1. In cans using the sealant according to the present invention (sample A), the sealant foams approximately 2.5 times and has a closed cell structure. It forms a ! - Both the clearance area and the lower clearance area were filled with sealant without any gaps. It is thought that the foaming occurred as a result of the foaming agent decomposing due to heating during retort sterilization treatment. On the other hand, conventional sealant (comparative sample A)? In the cans used, the sealant foamed and the sealant was insufficiently filled into the clearance areas, and it was observed that there were gaps. In addition, there was no difference in the filling state of sealant between the aluminum can lid seam part and the TFS *can lid seam part. It was prepared by directly adding the same amount of azodicarbonamide as that added to Sample A and stirring and mixing without adding an encapsulated solid blowing agent.

The viscosity of Sample A, Comparative Sample A, and Comparative Sample B was measured using a Brookfield viscometer (low shear region) and a Mopars viscometer (high shear region), and changes in viscosity over time were investigated.◎3 months at room temperature The viscosity of the sealant stored for a period of time did not change much in Sample A containing microencapsulated solid blowing agent and Comparative Sample A containing no solid blowing agent, but when the solid blowing agent was directly added. Comparative sample B had increased viscosity and turned into a liquid, making it impossible to line it.

Example 3 Sealants were prepared containing microencapsulated solid blowing agents in amounts as shown in Table 2.

Here, low molecular weight polyethylene is used as the shell material, azodicarbonamide is used as the solid foaming agent, citric acid is used as the foaming aid, and the microcaggulated particles are mixed to form the core material. The surface was modified by subjecting it to electrical discharge treatment. The average particle size of the microencapsulated particles is approximately 5
0 μm, and the amount ratio of shell material to core material was 10%.

Table 2 These sealants were applied to the can lid and wrapped around the can body in the same manner as in Example 1, and after the canned coffee beverage was retorted.

As a result of observing the filling state of the sealant inside the seam according to the procedure shown in Example 1, it was found that in samples B, C, D, E, and F, the sealant foamed in a closed cell state and
・Although the clearance part was completely filled, in sample G, there were parts where bubbles were continuous, and it was found that it was in a state where it was easy to form a leakage path. ◎ Example 4゜ As shown in Table 3 A sealant was prepared containing 10 parts per 100 parts total solids of a microencapsulated solid blowing agent having a particle size. Here, the shell material is low molecular weight polystyrene and the core material is Noahzocal? The other components were the same as in Example 1.

Table 3 These sealants were lined on the can lid and wrapped around the can body in the same manner as in Example 1 to produce canned coffee beverages. □ After retorting the canned goods, following the procedure shown in Example 1, As a result of observing the filling state of sealant inside the seam,
Which sealant? Even in the cans used, the sealant foamed in a closed-cell state and completely filled the clearance area. In addition, the stability of the viscosity of these sealants over time was investigated using the method shown in Example 2. However,
In Sample M, the microencapsulated solid foaming agent tended to settle and separate after 3 months, and the viscosity after redispersion decreased and the lining property deteriorated, but in other samples, There was little change in viscosity, and lining was possible.

Example 5 Microencapsulated particles of a solid blowing agent having the ratio of shell material to core material as shown in Table 4 were prepared. Here, graphine wax was used as the shell material, and habenzene sulfonyl hydrazide was used as the core material, and the average particle size was about 5 μm.

Table 4 Using the same elastomer as used in Sample A of Example 1, six types of sealants were prepared with the amount of microencapsulated solid blowing agent added at 3 parts per 100 parts by weight of total solids.

In the same manner as in Example 1, these sealants were applied to the can lid and wrapped around the can body to produce canned coffee beverages. After the cans were retorted, the filling state of the sealant inside the sear was observed according to the procedure shown in Example 1. As a result, in all cans using the sealant according to the present invention, the sealant foamed in a closed cell state and completely filled the upper clearance area, but in comparison sample C.
In the cans using 0, there was very little foaming of the sealant, and the area in the armpit and clearance area was incompletely filled.
It is presumed that this is because the shell material of Comparative Sample C was too thick and the microcapsules were not destroyed during double seaming. In addition, when the stability of the viscosity of these sealants over time was investigated using the method shown in Example 2, all samples showed little change in viscosity and were in a state where they could be fully lined.Example 6゜See Table 5. Four sealants were made using the same solid blowing agent as shown in the table, the amounts of microencapsulated particles shown in the table, and the same elastomeric latex used in Sample A.

Table 5 These sealants were used to line the can lid and wrap around the can body in the same manner as in Example 1 to produce canned coffee beverages. After retorting the cans, we observed the filling state of the sealant inside the seam using the procedure shown in Example 1. As a result, the sealant was foamed in a closed cell state in any of the cans used with sealant H. , completely filling the upper clearance area. Furthermore, when the stability of the viscosity of these sealants over time was investigated using the method shown in Example 2, all samples showed little change in viscosity and were in a state that could be used for sufficient lining.

Example 7 Four types of microencapsulated solid blowing agent particles were prepared using polyethylene wax, epoxy resin, phenolic resin, and rosin as the resin materials and noajicarbonamide kumquat as the core material, 4 using these microencapsulated particles and the same elastomer latex and other additives used for Sample A.
A seed sealant was made.

These sealants were used to line the can lid and wrapped around the can body to produce canned coffee beverages in the same manner as the actual MigAJl. After all the cans were retorted, the filling state of the sealant inside the seam was observed using the procedure shown in Example 1. As a result, the sealant foamed in a closed-cell state in any of the cans using the sealant. Example 2 The upper clearance area was completely filled with fCo.
When we investigated the stability of the viscosity of these sealants over time using the method described in
The condition was sufficient for lining.

Example 8 Using an elastomeric latex as shown in Table 6 and the same microencapsulated particles used in Sample A,
These sealants were used to line a can lid and wrapped around a can body in the same manner as in Example 1 to produce canned coffee beverages. After the canned food was retorted, the filling state of the sealant inside the first seam was observed using the procedure shown in Example 1. As a result, in all cans using sealant, the sealant foamed in a closed cell state, completely filling the upper clearance area. Furthermore, when the stability of the viscosity of these sealants over time was investigated using the method shown in Example 2, all samples showed little change in viscosity and were in a state that could be used for sufficient lining.

[Brief explanation of drawings]

Figure 1 is an enlarged sectional view showing the seamed part of the double seamed part obtained using the composition of the present invention, and Figure 2 is the seamed part corresponding to the overlapping seam of the can body of the can shown in Figure 1. FIG. FIG. 3 is an enlarged sectional view showing the seaming part of the conventional double seaming part, and FIG. 4 is an enlarged sectional view showing the 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 Represents a layer.

Claims (3)

[Claims] (1) A sealant composition for can lids used for lining can lids and sealing the seam, characterized by containing rubber latex particles and microencapsulated solid foaming agent particles in a dispersed state in an aqueous medium. thing. (2) The composition according to claim 1, wherein the rubber latex particles are latex particles of styrene-butadiene copolymer rubber. (3) Microcapsule particles of solid blowing agent have a total solid content of 1
The composition according to claim 1, wherein the composition is contained in an amount of 0.03 to 30 parts by weight per 00 parts by weight.