JP2674947B2 - Composition for cap seal - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a composition for cap seals, and more specifically, it does not generate chlorine gas during incineration, and is equal to or more than a conventional vinyl chloride paste resin. The present invention relates to an acrylic resin-based cap sealant composition having stress relaxation resistance, capable of being processed at a low temperature, and having a molded article having extremely low toxicity.

[0002]

2. Description of the Related Art Gaskets and liners used for sealing container lids and the like must have excellent fluidity, do not contain volatile components such as solvents, and be gelled by heating to form molded articles of a predetermined shape. Plastisol compositions are widely used because they have moderate flexibility and cushioning properties.

[0003] The plastisol is obtained by dispersing resin particles of an emulsion size or a suspension size in a liquid plasticizer as a dispersion medium, and this dispersion state is maintained at room temperature. By absorbing the plasticizer, the coalescence and plasticization of the resin particles are performed. Homopolymers and copolymers of vinyl chloride have been widely used as resins, but in order to prevent the release of hydrogen chloride into the atmosphere during incineration and to avoid the possibility of the generation of harmful substances such as dioxins. It has already been proposed to use acrylic resin plastisols.

For example, Japanese Examined Patent Publication No. 56-26263 includes particles of a single phase surfactant-free acrylic polymer or copolymer containing at least 60% by weight of alkyl acrylate or methacrylate units. And thus includes a compatible liquid plasticizer whose polymer or copolymer is non-volatile at room temperature and which is not a monomer having the same chemical structure as the monomer of said polymer or copolymer. A heat-bonding acrylic resin plastisol characterized in that it is dispersed in a surfactant-free medium is described.

[0005] Non-vinyl chloride resin-type reactive plastisols are also already known.
No. 72 discloses a reactive plastisol composed of a polyvinyl acetal resin which is insoluble in a plasticizer at room temperature and is plastic at a high temperature, an epoxy resin or a combination thereof with a polyester plasticizer, and a curing agent for the epoxy resin. ing.

Further, JP-A-62-161849 discloses a reactive plastisol comprising a polymethacrylate resin, a polyether or polyester type plasticizer modified with isocyanate or the like, and a thermal reaction initiator or a photoreaction initiator. Has been done.

More recently, RD344038-A (9
2, 11, 20), it is reported that a cross-linking agent is added to a plastisol composition, and the cross-linking agent reacts with an acrylic resin during gelation to form a cross-linked resin film or the like. .

[0008]

However, the known acrylic plastisols found in the former proposal have a drawback that they have a poor pot life as compared with vinyl chloride resin plastisol compositions, and flow during storage. However, it has the drawback that the gelling property is deteriorated and sufficient gelling performance is not obtained after storage. Furthermore, the creep resistance of the coating or molded product after gelling by heating, especially the creep resistance when heated. There is a drawback that the sex is not sufficient.

For example, a container or a container lid is provided with a gasket or a lining formed of a plastisol lining for the purpose of sealing, but one formed of an acrylic resin plastisol is formed of a vinyl chloride resin plastisol. Compared to the above, the creep resistance is significantly inferior, and due to the heat during hot filling and retort sterilization,
Troubles such as creep and rupture occur to cause leakage.

Further, as seen in the latter proposal, in the case of adding a crosslinking agent resin to an acrylic resin plastisol composition, the creep resistance of the molded product is certainly improved by the introduction of the crosslinked structure, The plastisol composition tends to cause premature gelation during storage and is not yet satisfactory in that it has a short pot life.

Therefore, the object of the present invention is to maintain the excellent fluidity required for coating, molding, etc. even during long-term storage, to exhibit excellent gelling performance at a relatively low temperature during heating, and to obtain the same. Another object of the present invention is to provide an acrylic resin-based cap sealant composition that exhibits stress relaxation resistance and creep resistance in which the coating or molded article is remarkably improved. It is another object of the present invention to provide an acrylic resin-based expandable cap sealant composition which, while being foamed, exhibits markedly improved stress relaxation resistance or creep resistance and pressure-resistant sealing performance.

[0012]

[Means for Solving the Problems] According to the present invention,
(A) Epoxy group-containing ethylenically unsaturated monomer 1
-50% by weight, the glass transition point is 5 when homopolymerized.
THF derived from 40% by weight or more of an acrylate or methacrylate monomer giving a polymer having a temperature of 0 ° C. or more, having a single particle size of 0.1-5 μm and 10-60% by weight.
100 parts by weight of insoluble resin particles, (b) 45 to 200 parts by weight of citric acid ester-based and / or glycol ester-based plasticizer, and (c) bisphenol A type and / or bisphenol F type epoxy resin 0 1 ~
10 parts by weight, and (d) a curing agent for epoxy resin 0.1 to 1
A cap sealant composition comprising 5 parts by weight is provided.

Also according to the present invention, (a) 1 to 50% by weight of an ethylenically unsaturated monomer containing an epoxy group,
Acrylate or methacrylate monomer 40 which gives a polymer having a glass transition point of 50 ° C. or more when homopolymerized
Derived from more than wt%, single particle size is 0.1-5μ
m and 100 to 100 parts by weight of resin particles having a THF insoluble content of 10 to 60% by weight, (b) 45 to 200 parts by weight of a citric acid ester-based and / or glycol ester-based plasticizer, and (c) bisphenol A Type and / or bisphenol F type epoxy resin 0.1 to 10 parts by weight,
(D) 0.1 to 15 parts by weight of a curing agent for epoxy resin,
(E) Azodicarbonamide and / or p, p′-oxybis (benzenesulfonylhydrazide) 0.1
A foamable cap sealant composition comprising 5 parts by weight is provided.

[0014]

The cap sealant composition of the present invention comprises a dispersion medium containing a plasticizer as a main component and acrylic resin particles dispersed therein, and the acrylic resin particles are resin particles containing an epoxy group. It is a remarkable feature that the agent comprises a citric acid ester-based and / or glycol ester-based plasticizer. Acrylic resin particles containing an epoxy group are characterized in that they can be crosslinked at a relatively low temperature in a short time. Therefore, when the cap sealant composition of the present invention is heated to gel, it reacts with a curing agent or the like to form a reticulated crosslinked structure in the sealant composition, which significantly improves the creep resistance of the composition. Let

Liners and the like made from vinyl chloride resin plastisols are excellent in creep resistance, while liners and the like made from acrylic resin plastisols are inferior in creep resistance because, in the former case, they dissolve in the plasticizer during gelation. The amorphous portion and the crystalline portion which are not dissolved in the plasticizer have a network structure and exhibit rubber-like elasticity and creep resistance. This is probably because it is crystalline and compatible with the plasticizer, and no network structure is formed. On the other hand, in the acrylic resin plastisol of the present invention, the epoxy group in the acrylic resin reacts with the curing agent during gelation to generate a network structure, which becomes a factor for preventing stress relaxation. It seems that

The acrylic resin particles used in the present invention are also derived from 50% by weight or more of an acrylate or methacrylate monomer which gives a polymer having a glass transition point (Tg) of 70 ° C. or more when homopolymerized. It is particularly important for improving creep resistance during heating. In the present invention, the above-mentioned specific acrylate or methacrylate monomer as a main component, by using resin particles derived from a composition containing an ethylenically unsaturated monomer containing an epoxy group, hot filling or retort A sealant that can withstand sterilization is provided.

By the way, in the case of a plastisol containing an epoxy resin component, it is known that the viscosity increases during storage and the so-called pot life decreases. Epoxy group-containing acrylic resin used in the present invention, and citric acid ester-based and /
It was also found that the combination with a glycol ester-based plasticizer has exceptional viscosity stability and can significantly improve the pot life. This is a phenomenon peculiar only to citric acid ester-based and / or glycol ester-based plasticizers, and other plasticizers do not exhibit the viscosity stability that can be put to practical use.

In the present invention, the acrylic resin particles are 10 to 60% by weight of THF (tetrahydrofuran).
It is also important to have insoluble matter. That is, by allowing the resin particles to have a gel content in advance, crosslinking of grain boundaries can be completed in a short time and excellent creep resistance can be exhibited. If the THF insoluble content is less than the above range, it becomes difficult to crosslink the grain boundaries in a short time,
On the other hand, when the amount is more than the above range, it becomes difficult to crosslink the grain boundary itself, and none of them can exhibit excellent creep resistance.

Further in accordance with the present invention, the above composition and a specific blowing agent, namely azodicarbonamide and / or p,
p'-oxybis (benzenesulfonyl hydrazide)
It is possible to provide an acrylic resin-based foamable cap sealant composition that exhibits remarkably improved stress relaxation resistance, creep resistance, and pressure-resistant sealing performance while being foamed.

[0020]

Preferred Embodiment of the Invention

"Resin Particles" The acrylic resin particles of the dispersed phase used in the present invention include (a) 1 to 50% by weight of an ethylenically unsaturated monomer containing an epoxy group, and a glass transition point of 50 ° C or higher when homopolymerized, It is preferably derived from 40% by weight or more, preferably 50% by weight or more of an acrylate or methacrylate monomer giving a polymer at 70 ° C. or higher, and has a single particle size of 0.1-5 μm and 10-60% by weight of T.
It is a resin particle having an HF insoluble content. Resin particles containing less than 40% by weight of a polymer having a glass transition point of 50 ° C. or higher are not preferable because they tend to soften and form blocks during drying after the completion of the polymerization reaction.

[(I) Ethylenically Unsaturated Monomer Having Epoxy Group] Suitable examples of the ethylenically unsaturated monomer having an epoxy group include allyl glycidyl ether, glycidyl (meth) acrylate and methylglycidyl methacrylate. , Glycidyl-p-vinyl benzoate, methyl glycidyl itaconate, glycidyl ethyl maleate, glycidyl vinyl sulfonate, glycidyl (meth) allyl sulfonate, glycidyl esters, butadiene monooxide, vinyl cyclohexene monooxide, 2-methyl-5,6 And epoxy olefins such as epoxyhexene. However, the above (meth) acrylate means acrylate or methacrylate (the same applies hereinafter). Particularly useful monomers are
Allyl glycidyl ether and glycidyl (meth) acrylate.

[(II) (Meth) Acrylate that gives a homopolymer having a Tg of 70 ° C. or higher] In the present invention, an acrylic resin containing the above-mentioned (meth) acrylate as a main constituent monomer is used. The relationship between the (meth) acrylate monomer and the Tg of its homopolymer is as shown in Table 1 below.

[0023]

[Table 1]

[(III) Other Monomer Incorporated in Acrylic Resin] The acrylic resin particles used in the present invention essentially include the above-mentioned two-component monomers, but are copolymerized with them. The comonomer may be included, and examples of such a comonomer include the following.

Styrene, vinyltoluene, acrylonitrile, methacrylonitrile, vinyl acetate. Ethylenically unsaturated carboxylic acids or their anhydrides; eg acrylic acid,
Methacrylic acid, crotonic acid, maleic acid, fumaric acid, itaconic acid, citraconic acid, maleic anhydride, itaconic anhydride, etc. Amide group-containing monomers; for example (meth) acrylamide. Hydroxyl group-containing monomer; for example, (meth) acrylic acid hydroxyethyl ester, (meth) acrylic acid hydroxypropyl ester, acrylic acid propylene glycol monoester. Amino group-containing monomer; for example, dimethylaminoethyl (meth) acrylate, t-butylaminoethyl (meth) acrylate, vinylpyridine, 2-vinyl-5-ethylpyridine, oxazolylethyl (meth) acrylate, (meth ) Hydroxyethyl aminoethyl acrylate. Monomers containing methylol groups and etherified methylol groups; dimethylol compounds of (meth) acrylamide and etherified products thereof, for example, ethyl ether compounds or butyl ether compounds. In addition, a polyfunctional monomer described below may be used for the purpose of adjusting the THF-insoluble content to a specific range.

[(IV) Method for producing resin particles] The acrylic resin particles used in the present invention have a single particle diameter of 0.1 to 5 μm.
In the production thereof, an emulsion polymerization method, an emulsion seeding polymerization method, and a fine suspension polymerization method are used.

Generally, a composition containing a monomer or a crosslinking agent resin is emulsified or suspended in water as an oil phase, and polymerization is carried out in the presence of a polymerization initiator. The aqueous medium is preferably used in an amount of 0.6 to 3.5 times by weight, particularly 0.9 to 2.5 times by weight, based on the total amount of the monomer components.

In the emulsion polymerization method, the monomer or cross-linking agent resin-containing composition is solubilized in the surfactant micelle, and polymerization is carried out using a water-soluble polymerization initiator. The size of the obtained emulsion particles is generally 0.1 to 0.2 μm, and it is usually adjusted to a desired particle size in combination with a seed polymerization method. The amount of the surfactant used is 0.
Suitably 5 to 5 parts by weight. The emulsion polymerization method is
It is effective when the monomer has low viscosity.

In the fine suspension polymerization method, a surfactant, a monomer-containing polymerizable composition, a polymerization initiator soluble in the composition,
After homogenizing other polymerization aids and, if necessary, a suspension stabilizer under high shear, a fine suspension having an oil phase particle size of 0.1 to 5 μm is prepared, and then transferred to a polymerization container. Polymerization is performed under stirring.

For homogenizing treatment, generally known one-stage or two-stage pressurizing high-pressure pumps, homomixers, spiral pin mixers, colloid mills, vibrating stirrers, high-pressure jets from nozzles or orifices, and homogenizers such as ultrasonic waves. Is used. Since it is possible to forcibly atomize the mixture under high shear, it is possible to apply the fine suspension polymerization method even if the mixed solution before homogenization is viscous.

The amount of the surfactant used is usually 0.1 to 5 parts by weight per 100 parts by weight of the monomer component.

The seeded polymerization method is used to adjust the particle size as described above. Polymerization is carried out by adding appropriate amounts of a new monomer or a crosslinkable monomer, a polymerization initiator and a surfactant all at once in a divided or continuous manner using the particles obtained by emulsion or fine suspension polymerization as a seed. Polymerization proceeds by adjusting the reaction environment so that new particles are not generated during the seeding polymerization operation.

[Method of giving acrylic resin particles a THF insoluble content] In the cap sealant composition of the present invention, the acrylic resin particles contain 5 to 80% by weight, preferably 10 to 60% by weight of THF insoluble matter. It has dissolved components. If the insoluble content is less than 5% by weight, the stress relaxation property of the molded product will be insufficient, and if it exceeds 80% by weight, the molded product will be hard and the cap sealing property will be deteriorated. The following method is used to provide this insoluble matter.

The first method is a method of interposing a monomer or oligomer which causes a crosslinking reaction in the polymerizable composition. 1. Use of polyfunctional monomers: -Divinylbenzene, trivinylbenzene. .A monomer or oligomer having two or more acryloyl groups or methacryloyl groups at the terminal or side chain of the molecule,
Generally as used for UV and EB curable acrylic paints. -Polyol polyacrylate-Modified polyol polyacrylate. -Epoxy acrylate. -Urethane acrylate. -Polyester acrylate. -A polyfunctional arylate which is a condensation product of a polyvalent organic acid and allyl alcohol. Acrylic resin particles having a THF insoluble content are prepared by mixing the above polyfunctional monomer with an acrylic monomer and polymerizing the mixture.

2. When polymerizing a (meth) acrylate having an epoxy group, resin particles containing a solvent-insoluble gel component can be synthesized depending on the conditions without taking a special action such as blending a polyfunctional vinyl. This is because a reaction between epoxy groups occurs. For example, when a redox type initiator is used as the polymerization initiator, it is recognized that the one used as the reducing agent accelerates the ring opening of the epoxy.

In the production of acrylic resin particles, as the polymerization initiator, azo compounds such as azobisisobutyronitrile, methyl azobisisobutyrate, azobiscyclohexanecarbonitrile and azobis-2,4-dimethylvaleronitrile, cumene hydro are used. Hydroperoxides such as peroxide and t-butyl hydroperoxide, di-t-
Dialkyl peroxides such as butyl peroxide and dicumyl peroxide, diacyl peroxides such as benzoyl peroxide and lauroyl peroxide, t-butylperoxypivalate, t-butylperoxylaurate, di-
Peroxyesters such as t-butyldiperoxyfurarate, ketone peroxides such as methylethylketone peroxide, peroxydicarbonates such as diisopropylperoxydicarbonate, persulfates such as ammonium persulfate and potassium persulfate, hydrogen peroxide solution. Inorganic peroxides such as can be used depending on the polymerization method.
Further, the peroxide-based initiator can be used as a redox-based low-temperature initiator in combination with an appropriate reducing agent. In addition, a combination of ionizing radiation such as γ-ray or accelerated electron beam or ultraviolet light and various sensitizers can be used.
The amount of the polymerization initiator is 0.01 to 100 parts by weight of the monomer.
It is preferable to use it in an amount of 3 parts by weight.

As the surfactants, alkyl sulphates such as sodium lauryl sulfate and sodium myristyl sulphate, alkyl allyl sulphonates such as sodium dodecylbenzene sulphonate, alkyl dialkyls such as sodium dioctyl sulfosuccinate and sodium dihexyl sulfosuccinate. Sulfosuccinates, fatty acid salts such as potassium stearate, alkyl phosphates, polyoxyethylene alkyl ether sulfates, anionic surfactants such as acyl sarcosine salts, sorbitan monolaurate, sorbitan monostearate and other sorbitan fatty acid esters , Glycerin fatty acid esters, polyoxyethylene sorbitan fatty acid esters, polyoxyethylene alkyl ethers, polyethylene glycol fatty acid esters, Nonionic surfactants such as polyoxyethylene polyoxypropylene alkyl ethers, etc. can be used conventionally known.

As the suspension stabilizer, polyvinyl alcohol, partially saponified polyvinyl acetate, polyacrylic acid, polymethacryl acid, polyvinylpyrrolidone, polymethacrylamide and other synthetic polymers, gelatin, tragacanth, starch, methylcellulose and other cellulose derivatives. Natural polymers such as barium sulfate, calcium sulfate, barium carbonate,
A hardly water-soluble inorganic fine powder such as magnesium carbonate, calcium phosphate, talc or bentonite can be used.

Other polymerization aids include higher alcohols such as cetyl alcohol and lauryl alcohol, higher fatty acids such as lauric acid, palmitic acid and stearic acid or esters thereof, aromatic hydrocarbons, higher aliphatic hydrocarbons. And inorganic salts such as sodium chloride, potassium chloride, sodium sulfate and sodium bicarbonate. Further, in order to control the polymer molecular weight, 1-
It is possible to use mercaptans such as butanethiol, thiophenol, ethyl mercaptoacetate, 2-mercaptoethanol, 2-naphthalenethiol, n-dodecyl mercaptan, t-dodecyl mercaptan, disulfides such as diisopropyl xanthogen disulfide, and diazothioether. it can.

The above-mentioned polymerization reaction is carried out under anoxic conditions such as substitution with an inert gas in a temperature range of 25 to 100 ° C., particularly 40 to 85 ° C., with stirring.

As a method for recovering the powder of the acrylic resin particle composition from the emulsion or emulsion prepared according to the present invention, a usual method for drying a vinyl chloride resin for plastisol can be adopted. As the drying method, multi-blade rotary disc type, disc type rotary disc type, spray drying such as nozzle type, centrifugal dehydration drying of the acrylic resin composition through coagulation destruction of the emulsion with inorganic salt or alcohol, milk Direct filtration dehydration of the suspension may be mentioned. Depending on the case, crushing with a hammer mill, a pin mill or the like may be added thereafter.

[Plasticizer] In the present invention, as a plasticizer, a citric acid ester-based and / or glycol ester-based plasticizer is added in an amount of 45 to 200 parts by weight, preferably 60 to 150 parts by weight, per 100 parts by weight of the resin particles. It is important to use in quantity. If it is less than 45 parts by weight, the viscosity of the prepared plastisol is too high and it is difficult to process it. If it exceeds 200 parts by weight, the mechanical strength of the molded product is lowered. Suitable examples of this plasticizer are:

Citrate type: triethyl citrate, tributyl citrate, acetyl triethyl citrate, tributyl acetyl citrate, tri-2-ethylhexyl acetyl citrate, n-octyl decyl acetyl citrate, distearyl citrate, tristearyl citrate. etc. Glycol ester type: ethylphthalylethyl glycolate, methylphthalylethyl glycolate, butylphthalylbutyl glycolate, etc.

Useful among the above plasticizers are triethyl citrate, acetyl citrate triethyl, acetyl citrate tributyl, ethylphthalylethyl glycolate, butylphthalylbutyl glycolate and the like.

[Epoxy Resin] In the cap sealing composition of the present invention, 0.1 to 10 parts by weight, particularly 0.3 to 10 parts by weight of bisphenol A type and / or bisphenol F type epoxy resin is used per 100 parts by weight of acrylic resin particles. It is recommended to use in an amount of parts by weight. If the amount is less than 0.1 parts by weight, the cross-linking of the molded product is insufficient and the stress relaxation property is insufficient, and if it exceeds 10 parts by weight, the molded product becomes too hard and the cap sealing property deteriorates. Suitable examples of epoxy resins are as follows. Bisphenol A type epoxy resin: The one shown in Table 2 below is used.

[0046]

[Table 2]

Bisphenol F type epoxy resin: The one shown in Table 3 below is used.

[0048]

[Table 3] Although Epicoat is an epoxy resin manufactured by Yuka Shell Epoxy Co., Ltd., the epoxy resin that can be used is not limited to the above.

Among the above epoxy resins, useful for the present invention are low molecular weight epoxy resins having a number average molecular weight of 300 to 1700, particularly 300 to 1000.
Epoxy resins are useful.

[Curing Agent for Epoxy Resin] The curing agent used in the composition for a cap seal of the present invention is to cure the epoxy resin component contained in the acrylic resin particles or further contained in the plastisol. is there. The amount used is 0.1 to 15 per 100 parts by weight of acrylic resin particles.
Parts by weight, preferably 0.3 to 10 parts by weight. 0.1
If it is less than 15 parts by weight, the cross-linking of the molded product is insufficient and the stress relaxation property is insufficient, and if it exceeds 15 parts by weight, the molded product becomes too hard and the cap sealing property deteriorates. As the curing agent, any known one can be used, but the following ones are preferable.

A methylolated or ether methylolated amino resin, a modified or unmodified polyamine, a modified or unmodified polyamidoamine, a methylolated or ether methylolated phenolic resin and the like.

[Composition] The composition for cap seal of the present invention contains a resin compound known per se, such as a filler,
A colorant, a heat stabilizer, a foaming agent, a cross-linking agent, an antioxidant, a thickener, a thinning agent, an oxygen absorber and the like can be added according to a known method. Each of these components should be non-toxic or low-toxic.

The composition of the present invention is useful as a foam cap sealant having excellent creep resistance. For this purpose, a foaming agent known per se is used. Among them, azodicarbonamide and / or p, p′-oxybis (benzenesulfonylhydrazide) is preferable in view of creep resistance and sealing performance. is there. The foaming agent is preferably used in an amount of 0.1 to 5 parts by weight per 100 parts by weight of the acrylic resin particles.

[Use] The acrylic resin plastisol composition of the present invention has an excellent pot life and gelation performance, and the obtained coating or molded article has excellent creep resistance. Therefore, PVC plastisol has been widely used in various applications as a sealant for caps, such as crowns, white caps, etc.
It can be widely used for packing or gaskets such as pill fur proof caps and tear-off caps.

For molding, means such as slush molding, rotational molding, casting, and dip molding can be used. For coating, spread method, dipping method, spin coating method, gravure coating method, spray coating method, A screen coating method or the like is employed. The acrylic resin plastisol of the present invention is particularly useful for forming a sealing gasket or liner for various container lids by spin coating.

In general, the acrylic resin plastisol composition of the present invention preferably has a viscosity of 5 to 1000 poise at room temperature from the viewpoint of workability at the time of coating and molding, while the hardness at the time of gelation is foaming or Although it is different even if it is not foamed,
For applications such as the above-mentioned sealing gasket or liner,
It preferably has a hardness (JIS-A) of 30 to 75.
Curing of the plastisol can be easily performed by heating to a temperature of 100 to 230 ° C.

[0057]

The present invention will be described in detail below with reference to examples. The measurement in the examples was carried out by the following method.

[THF-insoluble matter] Acrylic resin powder having a sample weight of W ₁ is placed in an Erlenmeyer flask, and the THF-soluble matter is extracted at room temperature overnight while stirring in THF. Then, solid-liquid separation is performed with a centrifuge, the supernatant is removed, and then THF is added to wash the THF insoluble matter. Solid-liquid separation is performed again, the supernatant is removed, and TH
The total amount of the F insoluble matter is placed in a container of known weight, dried sufficiently in a vacuum dryer, and the weight W ₂ of the THF insoluble matter is weighed. As a result, the THF insoluble matter is 100 W ₂
It can be calculated as / W ₁ % by weight.

[Gelling Performance] A certain amount of the composition for cap sealing was weighed in an aluminum pan and heat treated at 220 ° C. for 60 seconds to evaluate the state of the gelled sheet.
The gelling performance is indicated by ◯ when a flexible and tough gelled sheet is obtained, Δ when the sheet is a flexible sheet but slightly weakened, and x when the sheet is not flexible.

[Creep resistance test] The creep resistance was evaluated by stress relaxation measurement. The stress relaxation property and the creep property are in a one-sided relationship, and the creep resistance of the sample can be easily evaluated from the stress relaxation behavior.
Specifically, a sample piece having a width of 7 mm and a thickness of about 1 mm is prepared, and the sample is sandwiched between two chucks arranged at an interval of 20 mm, and a tensile strain of 50% is instantaneously applied to the sample. It was observed that the stress relaxed with time from the moment the strain was applied to. The ambient temperature of the sample was controlled, and the measurement was carried out at 120 ° C. for about 1 hour.

After the application of strain, the stress 0.1 seconds later is defined as the initial stress σ.
₀ and the stress after t time is σ _t , σ _t / σ ₀
The relaxation time is the time t at which e ⁻¹ (= 0.368). To provide a composition for a cap seal that does not cause creep deformation during use as a gasket or a liner, retains excellent sealing properties for a long period of time, and can withstand severe use conditions such as retort treatment. For 120 ℃
It is necessary that the relaxation time is at least 40 minutes or longer. When the sample is broken at 120 ° C for 1 hour, it cannot be used as a gasket or a liner.

In the examples, unless otherwise specified,
A gelled sheet was prepared from plastisol under the heating condition of 220 ° C. for 60 seconds and used for the creep resistance test.

[Sealing Test] A white cap shell having a diameter of 63 mm was lined with a composition for cap sealing, and heat treated at 220 ° C. for 60 seconds to obtain 1.3 m.
The liner portion was formed with a thickness of m. A thick glass bottle having an inner volume of 185 cc was filled with hot water at 90 ° C. so that the head space was 10 cc, and the liner was sealed under the condition of giving a compressive strain of 40%. Then, the sample was subjected to retort treatment at 120 ° C. for 30 minutes, and the sealing property was evaluated.

The sealing property is whether or not the negative pressure is maintained when the sample is returned to room temperature (when the negative pressure is reached, the top surface of the cap is pulled inward) and the change in weight before and after the test. It was evaluated by. Immediately after the retort, the one having the hermeticity was followed up for one month. In addition, the state of the liner portion was also observed immediately after the retort and one month later. If the liner part is in poor condition, creep flow occurs so that the cap metal surface can be seen through the part where the bottle mouth was in contact, or the liner is completely divided along the bottle mouth and the cap metal surface is There are things that are exposed. In particular, the former defect is referred to as creep and the latter defect is referred to as cut-through.

Examples 1 to 3 In a stainless steel premix tank equipped with a stirrer, methyl methacrylate monomer (M
MA) (95-X) parts by weight, glycidyl methacrylate (GMA) 5 parts by weight, ethylene glycol dimethacrylate (EGDMA) X parts by weight, t-butyl peroxypivalate 0.2 parts by weight, lauryl alcohol 2.3 parts by weight, 1 part by weight of sodium lauryl sulfate and 122 parts by weight of water were charged, and after deaeration and nitrogen substitution were repeated, a droplet of the monomer composition was formed by stirring at room temperature for 20 minutes.

Then, the mixture was passed through a pressure homogenizer to form fine droplets of the monomer composition having a uniform diameter, which were introduced into a degassed stainless steel autoclave equipped with a stirrer. While stirring, raise the temperature to 60 ° C,
The temperature was maintained for 5 hours to complete the reaction. The single particle size of the seven kinds of acrylic resin emulsions polymerized here was measured by a centrifugal sedimentation type particle sizer, and the average particle size was 1.
It was in the range of 0 ± 0.5 μm. Further, these were spray dried to prepare an acrylic resin powder.

In an Ishikawa type crusher, 100 parts by weight of the above acrylic resin powder, 80 parts by weight of acetyl tributyl citrate, 4 parts by weight of Epicoat 834 (bisphenol A type epoxy resin manufactured by Yuka Shell Epoxy Co., Ltd.), Cymel 303
(Mitsui Cyanamid Co. melamine fat) 3.5 parts by weight,
Then, 0.1 parts by weight of Catalyst 600 (aromatic sulfonic acid catalyst manufactured by Mitsui Cyanamid Co., Ltd.) was charged, kneaded for 20 minutes, and then degassed in vacuum for 10 minutes to prepare a paste-like composition for cap sealing.

In Examples 1 to 3, acrylic resin particles having various THF-insoluble components were prepared by changing the amount of EGDMA which is a bifunctional vinyl monomer in the above composition. Table 4 shows the specific composition and THF insoluble matter.
As shown in FIG. Table 4 also shows the results of the gelation performance, creep resistance test, and sealability test.

The creep resistance test sample was prepared by spreading the cap sealing composition on a tin plate with a knife coater and subjecting it to heat treatment at 220 ° C. for 60 seconds.
As a result of stress relaxation measurement at 120 ° C, 2 for each sample
It was confirmed that the sample had a relaxation time of 5 minutes or more, and no breakage of the sample during the measurement was observed. Even in the sealability test, it was confirmed that the sealability was maintained for one month after the retort treatment, and the liner was in good condition.
No remarkable progress of creep was observed in months.

[0070]

[Table 4]

Comparative Example 1 99.8 parts by weight of MMA, EG
An acrylic resin and powder were prepared by the same polymerization prescription as in Examples 1 to 3 except that 0.2 part by weight of DMA was used as the acrylic monomer. Further, 100 parts by weight of this acrylic powder, 80 parts by weight of ATBC, 8344 parts by weight of Epicoat,
Cymel 303 3.5 parts by weight, and Catalyst 600.
1 part by weight was charged into an Ishikawa type crusher, and a paste-like composition for a cap seal was prepared in the same manner as in the above-mentioned Examples.

The THF insoluble content of the acrylic powder prepared here was 15.7%, and the composition for a cap seal was
A soft and tough gelled sheet was formed at 220 ° C. for 60 seconds, but the composition for a cap seal of this comparative example was inferior in creep resistance and hermeticity. In the creep resistance test, the relaxation time at 120 ° C. was 5.7 minutes, and sample breakage was also observed. Also, in the test of hermeticity, 120 ° C-
It was confirmed that cut-through occurred in the liner portion after the retort treatment for 30 minutes, and the heat resistance and creep resistance that could withstand the retort were not provided.

From the above-mentioned examples and this comparative example, it can be understood that it is important that the acrylic resin has an epoxy group in order to provide a cap sealant composition having retort resistance. .

Comparative Example 2 100 parts by weight of the powder of Example 2 was mixed with 80 parts by weight of ATBC to prepare a paste-like cap sealing composition without an epoxy resin and a cross-linking agent for epoxy resin. It was a composition.

The THF insoluble content of the acrylic powder was determined in Example 2.
As shown in the above, from the composition for a cap seal,
A soft and tough gelled sheet was obtained by heat treatment at 220 ° C. for 60 seconds. In the creep resistance test, the relaxation time at 120 ° C. was 3.9 minutes, and sample breakage was also observed.
Further, in the test of sealing property, it was confirmed that cut-through was generated in the liner portion in the retort treatment at 120 ° C. for 30 minutes, and that it did not have the heat resistance and creep resistance at a level capable of withstanding the retort.

In order to provide a cap sealant composition having retort resistance from the above-described Examples and Comparative Examples, an epoxy resin and an epoxy resin are cross-linked with respect to an acrylic resin having an epoxy group. It can be appreciated that it is important to combine the agents.

[Comparative Example 3] MM as an acrylic monomer
Acrylic resin particles and powder were prepared by the same polymerization prescription as in Examples 1 to 3, except that 95 parts by weight of A and 5 parts by weight of GMA were used as 0.01 parts by weight of 1-butanethiol as a polymerization degree adjusting agent. Further, 100 parts by weight of this acrylic powder, 80 parts by weight of ATBC, 44.4 parts by weight of Epicoat 834,
Cymel 303 3.5 parts by weight, and Catalyst 600.
1 part by weight was charged into an Ishikawa type crusher, and a paste-like composition for a cap seal was prepared in the same manner as in the above-mentioned Examples.

The THF insoluble content of the acrylic powder prepared here was 7.5%, and the composition for cap sealing was 2%.
A flexible and tough gelled sheet was formed at 20 ° C. for 60 seconds. In the creep resistance test, the relaxation time at 120 ° C is 1
Although it was 3 minutes, no sample fracture was observed. Sealability test shows 120 ° C-30 minutes retort treatment 1
Although the sealing property was maintained even after a month, it was confirmed that creep flow was progressing in the opened liner portion after a month, and the sealing was about to be impaired from the state of the liner. Therefore, it cannot be said that the composition for a cap seal of this comparative example has heat resistance and creep resistance that can withstand the retort.

From the above-mentioned examples and this comparative example, in order to provide the composition for a cap seal having the retort resistance, the acrylic resin having an epoxy group has a THF insoluble content of a certain level or more. Understand that what you are doing is important.

[Comparative Example 4] MMA 94.6 parts by weight, GM
Acrylic resins and powders were prepared by the same polymerization prescription as in Examples 1 to 3 except that 5 parts by weight of A and 0.4 parts by weight of EGDMA were used as the acrylic monomer. 80 parts by weight of ATBC and Epicoat for 100 parts by weight of this acrylic powder
834 4 parts by weight, Cymel 303 3.5 parts by weight, and Catalyst 600 0.1 parts by weight were mixed to prepare paste-like cap seal compositions as in Examples 1 to 3.

TH of acrylic resin prepared in this comparative example
The F insoluble content was 62.1%, and the composition for cap sealing did not form a flexible gelled sheet at 220 ° C. for 60 seconds. A flexible gelled sheet was obtained by changing the heating condition to 180 ° C. for 180 seconds, but in the creep resistance test, the sample was instantaneously broken at the same time as the strain was applied to the sample.

From the above-mentioned examples and this comparative example, in order to provide a composition for a cap seal excellent in gelling performance, an acrylic resin having an epoxy group has a THF insoluble content of a certain level or less. Understand that what you are doing is important.

Comparative Example 5 To 100 parts by weight of the acrylic resin particles of Example 2, 80 parts by weight of ATBC, 11 parts by weight of Epicoat 834, 16 parts by weight of Cymel 303, and 0.1 part by weight of Catalyst 600 were blended. A paste-like composition for cap sealing was prepared as in Examples 1-3.

Although a soft gelled sheet was obtained by heat treatment at 220 ° C. for 60 seconds, a sample rupture occurred within 1 minute in the creep resistance test, and a cut-through occurred in the liner in the sealability test. Occurred.

From the above-mentioned examples and this comparative example, in order to provide a cap sealant composition having retort resistance, acrylic resin particles having an epoxy group were prepared.
It can be understood that it is important to combine a certain level or less of the epoxy resin and the crosslinking agent for the epoxy resin.

[Example 4] 90 parts by weight of MMA, GMA1
An acrylic resin and its powder were prepared by the same polymerization formulation as in Examples 1 to 3 except that 0 part by weight was used as the acrylic monomer. The single particle size of this acrylic resin is 0.9μ
m, and the THF insoluble content was 24.3% by weight.

Acrylic resin particles 100 prepared here
80 parts by weight of ATBC, Epikote 8284 with respect to parts by weight
Parts by weight, Cymel 325 3 parts by weight, and Catalyst 600
0.1 part by weight was compounded and a paste-like composition for a cap seal was prepared in the same manner as in Examples 1 to 3.

A soft and tough gelled sheet was obtained by heat treatment at 220 ° C. for 60 seconds, and in the creep resistance test, it was 1
The result was that the relaxation time at 20 ° C. was 1 hour or more, and the sample did not break. In the sealability test, it was confirmed from the retort that the seal was maintained for one month, and the liner was in a good condition. The composition for a cap seal of this example has heat resistance and creep resistance capable of withstanding a retort.

[Example 5] In the composition for cap sealing of Example 2, the cap seal was prepared by the same composition and method as in Example 2, except that the plasticizer was changed from ATBC to butylphthalylbutyl glycolate (BPBG). A composition for use was prepared.

A soft and tough gelled sheet was obtained by heat treatment at 220 ° C. for 60 seconds, and it was 1 in the creep resistance test.
The result was that the relaxation time at 20 ° C. was 1 hour or longer.
From the sealability test, it was confirmed that the composition for a cap seal of this example had heat resistance and creep resistance capable of withstanding a retort.

[Example 6] In the composition for a cap seal of Example 2, Cymel 303 was used as ADEKA EH331.
A composition for cap sealing was prepared by the same composition and method as in Example 2, except that the modified polyamide amine cross-linking agent manufactured by Asahi Denka Co., Ltd. was used.

A soft and tough gelled sheet was obtained by heat treatment at 220 ° C. for 60 seconds, and a creep resistance test showed 1
The result was that the relaxation time at 20 ° C. was 1 hour or longer.
From the sealability test, it was confirmed that the composition for a cap seal of this example had heat resistance and creep resistance capable of withstanding a retort.

[Examples 7 to 11] Acrylic resin particles having the resin composition, particle size, and THF-insoluble content shown in Table 5 were prepared by the fine suspension polymerization method according to Examples 1 to 3. Then, a cap sealant composition was prepared by further combining the composition shown in Table 5 with a plasticizer, an epoxy resin, and a crosslinking agent for an epoxy resin.

For these cap sealing compositions,
The same test as in Examples 1 to 3 was performed. The results are as shown in Table 6.

The cap sealing compositions of Examples 7 to 11 were all excellent in creep resistance and could withstand retort treatment.

[0096]

[Table 5]

[0097]

[Table 6]

[0098]

[Table 7]

[0099]

The composition for cap seals of the present invention comprises:
Acrylic resin particles containing epoxy groups as dispersed particles,
By using a citric acid ester-based and / or glycol ester-based plasticizer as the dispersion medium, excellent fluidity necessary for coating, molding, etc. can be maintained even during long-term storage,
When heated, it shows excellent gelling performance at relatively low temperatures,
Moreover, the obtained coating or molded product exhibits significantly improved stress relaxation resistance or creep resistance.

First, the acrylic resin particles containing an epoxy group are characterized in that they can be crosslinked at a relatively low temperature in a short time. Therefore, when the cap sealant composition of the present invention is heated to gel, it reacts with a curing agent or the like to form a reticulated crosslinked structure in the sealant composition, which significantly improves the creep resistance of the composition. Let

The reason why a liner or the like made of an acrylic resin plastisol is inferior in creep resistance is that, in the case of a vinyl chloride resin plastisol, an amorphous portion dissolved in the plasticizer during gelation and a crystalline portion not dissolved in the plasticizer. And are present in a network structure and exhibit rubber-like elasticity and creep resistance, whereas in the case of acrylic resin, most of them are amorphous and compatible with the plasticizer to form a network structure. It is believed that the cause is that the plastisol of the acrylic resin of the present invention, the epoxy group in the acrylic resin at the time of gelation, and the curing agent and the like to cause a network structure, which causes stress. It is a factor that prevents mitigation.

In the present invention, a composition mainly containing an acrylate or methacrylate monomer that gives a polymer having a glass transition point (Tg) of 70 ° C. or more when homopolymerized, and containing an ethylenically unsaturated monomer containing an epoxy group. By using resin particles derived from a product, a sealant that can withstand hot filling and retort sterilization can be provided.

In the case of a plastisol containing an epoxy resin component, the viscosity increases during storage and the so-called pot life decreases, but with the epoxy group-containing acrylic resin used in the present invention,
In combination with a citric acid ester-based and / or glycol ester-based plasticizer, it has exceptional viscosity stability and can significantly improve pot life.

In the present invention, the acrylic resin particles are 10 to 60% by weight of THF (tetrahydrofuran).
By having an insoluble content, that is, by having a gel content in the resin particles in advance, it is possible to complete the cross-linking of the grain boundaries in a short time and to exhibit excellent creep resistance.

Further, according to the present invention, an acrylic resin-based resin exhibiting remarkably improved stress relaxation resistance or creep resistance and pressure-resistant sealing performance by being foamed by the combined use of the above composition and a specific foaming agent. The foamable cap sealant composition can be provided.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical display location C08L 63/00 C08L 63/00 C // C08J 9/06 CEY C08J 9/06 CEY C09J 163/00 C09J 163/00 C09K 3/10 C09K 3/10 L (72) Inventor Takeo Kobayashi 2-6-1, Marunouchi, Chiyoda-ku, Tokyo Zeon Co., Ltd. (56) Reference JP-A-55-120681 (JP, A) JP-A-4-332722 (JP, A) JP-A-4-189887 (JP, A) JP-A-4-275338 (JP, A) JP-A-7-157622 (JP, A) JP-A-5 -194781 (JP, A)

Claims (2)

(57) [Claims] 1. (a) 1 to 50% by weight of an ethylenically unsaturated monomer containing an epoxy group and 40% by weight of an acrylate or methacrylate monomer giving a polymer having a glass transition point of 50 ° C. or higher when homopolymerized. Derived from the above, the single particle size is 0.1 to 5 μm and 10 to 60
Acrylic resin particles having a THF insoluble content of 1% by weight
00 parts by weight and (b) 45 to 200 parts by weight of a citric acid ester-based and / or glycol ester-based plasticizer,
A composition for a cap seal, which comprises (c) 0.1 to 10 parts by weight of a bisphenol A type and / or bisphenol F type epoxy resin, and (d) 0.1 to 15 parts by weight of a curing agent for an epoxy resin. 2. (a) 1 to 50% by weight of an ethylenically unsaturated monomer containing an epoxy group and 40% by weight of an acrylate or methacrylate monomer giving a polymer having a glass transition point of 50 ° C. or higher when homopolymerized. Derived from the above, the single particle size is 0.1 to 5 μm and 10 to 60
Acrylic resin particles having a THF insoluble content of 1% by weight
00 parts by weight and (b) 45 to 200 parts by weight of a citric acid ester-based and / or glycol ester-based plasticizer,
(C) 0.1 to 10 parts by weight of bisphenol A type and / or bisphenol F type epoxy resin, (d) 0.1 to 15 parts by weight of curing agent for epoxy resin, (e) azodicarbonamide and / or A foamable cap sealant composition comprising 0.1 to 5 parts by weight of p, p'-oxybis (benzenesulfonylhydrazide).