JPH0138832B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to an adhesive for metal cans that is used to manufacture metal cans and has excellent adhesive properties, sealing properties, sanitary properties, resistance to contents, etc. Conventionally, when manufacturing metal cans, the can body has been joined by soldering, nylon resin adhesive, or welding, and the can body, top, and bottom lids have been joined by soldering, nylon resin adhesive, or welding.
They are joined by double seaming and then adhering with solder, or by fusing nylon adhesive to the can body and then double seaming. As described above, various methods have been used to maintain adhesive strength and sealing properties for joining the can body and the top and bottom lids of metal cans, but solder bonding has mainly been used. With solder bonding, regardless of the type of content, its sealing performance,
It had excellent adhesive strength. However, it was not necessarily an advantageous bonding method because of problems such as the soaring price of solder, the sanitary nature of lead as a solder component, washing cans with water after soldering, and inability to apply to stain-free steel plates. In addition, adhesion using nylon requires primer treatment, and
Since the adhesive is in the form of a film, it is necessary to heat the adhesive portion to adhere the adhesive, and this method cannot be called an advantageous method due to the difficulty of adhesion and the high cost of nylon film. On the other hand, various resins have been proposed to improve these drawbacks. Examples include synthetic rubber adhesives and modified polyolefin-urethane adhesives, but these are not always satisfactory in terms of adhesiveness, sealing properties, sanitary properties, etc. Namely, butadiene-acrylonitrile, butadiene-acrylonitrile-styrene, butadiene-
Rubber adhesives such as styrene, neoprene, polyisobutylene, and chlorinated rubber have good sealing properties, but
There were problems with seaming strength, solvent resistance, etc., and there was a limit to its use in food-related applications or as an adhesive for metal cans filled with organic solvents. As a result of intensive research, the present inventors have found that while maintaining the same sealing performance as solder-bonded cans and nylon-bonded cans, they have excellent adhesion to metals and organic coatings, seaming properties, solvent resistance, hot water resistance, Apply an adhesive with excellent safety and hygiene properties to the can body joint and the joint between the can body and can lid.
By coating to a film thickness of 70μ, preferably 40 to 60μ, it is possible to produce improved metal cans. That is, in the present invention, 0.5 parts by weight of at least one metal compound selected from calcium, magnesium, zinc, aluminum, and sodium is added to 100 parts by weight of the carboxyl group-containing polyolefin.
The present invention relates to an adhesive for metal cans, characterized in that it is made by mixing 100 parts by weight of a modified polyolefin containing 100 parts by weight with 100 to 300 parts by weight of an acrylic resin obtained by emulsion polymerization. Metal cans using the adhesive of the present invention can withstand the contents even when filled with edible oil, soybean oil, etc., paints, thinners, various solvents, industrial oils, etc., with almost no reduction in adhesive strength. It has excellent sealing properties. Therefore, it is hygienic like a solder can, and the can can be washed with water.
Problems with aesthetics have been resolved, and compared to nylon adhesive cans, the process is simpler and workability is better.
Moreover, it can be provided at low cost. Furthermore, the adhesive of the present invention has good adhesion to ordinary can materials, and therefore can be widely applied. For example, solder-bonded cans are generally limited to tinplate as the material for the can, but the adhesive of the present invention can be applied not only to tinplate but also to materials other than tinplate, such as zinc or chromium-plated steel sheets, phosphoric acid or chromic acid treatment. Metal materials such as steel plates and aluminum plates, as well as phenolic resins, epoxy resins,
It exhibits good adhesion and sealing properties to boards coated or laminated with urea resin, vinyl resin, alkyd resin, amino resin, polyolefin resin, etc. The carboxyl group-containing polyolefin according to the present invention includes a copolymer of an olefin and an ethylenically unsaturated carboxylic acid, a graft polymer of a polyolefin and an ethylenically unsaturated carboxylic acid, and the like. Ethylene is mainly used as the olefin for copolymers, but propylene, etc.
Any copolymerizable olefin can be used. Further, as the ethylenically unsaturated carboxylic acid, acrylic acid, methacrylic acid, maleic anhydride, etc. can be used, and any copolymerizable ethylenically unsaturated carboxylic acid can be used. In addition, the copolymer of olefin and ethylenically unsaturated carboxylic acid can be obtained by radical polymerizing olefin and ethylenically unsaturated carboxylic acid alkyl ester, and then using an alkali. It may also be hydrolyzed to form a carboxyl group-containing polyolefin. Furthermore, other monomers such as vinyl acetate and styrene may be copolymerized. In addition, graft polymers include polyethylene, polypropylene, ethylene-propylene copolymer, polybutene, etc., and acrylic acid, methacrylic acid, maleic acid, maleic anhydride, itaconic acid,
One or more types of fumaric acid etc. are used. Although carboxyl group-containing polyolefins have excellent adhesion to metal materials and resistance to contents, they have problems such as low softening points and high temperature dependence of viscosity. Therefore, during can manufacturing, when heating is applied to fuse the can body to the top and bottom, problems may occur such as protrusion from the double seam, poor sealing (leakage), and a decrease in seam strength. Therefore, it cannot be said that it is necessarily a good adhesive for metal cans. In the present invention, it has been found that it is effective to blend a metal compound into the carboxyl group-containing polyolefin in order to eliminate protrusion from the double-sealed portion while maintaining adhesiveness and content resistance. That is, metal compounds such as acetates, carbonates, hydroxides, and oxides of calcium, magnesium, zinc, aluminum, sodium, etc. are blended. The blending is preferably carried out at a temperature equal to or higher than the softening point of the carboxyl group-containing polyolefin.
The blending ratio usually varies depending on the type of carboxyl group-containing polyolefin, but 0.5 to 10 parts by weight of the metal compound is blended per 100 parts by weight. 0.5
If it is less than 10 parts by weight, the desired softening point will not be raised and it will not be possible to eliminate the protrusion from the double seaming part, and if it is more than 10 parts by weight, the film will become too hard and the double seaming property will be insufficient. , the sealing performance deteriorates. The blending of the metal compound includes cases in which all or part of the carboxyl groups of the carboxyl group-containing polyolefin form a metal salt or a metal ion crosslinked product, as well as cases in which they are simply mixed. Commercially available modified polyolefins can be used. For example, Chemipearl manufactured by Mitsui Petrochemical Industries, Corporen L manufactured by Asahi Dow Co., Ltd.
2000, L-4000, L-6000, and Surlyn manufactured by DuPont in the United States. In the present invention, it is preferable to use an acrylic resin in combination in order to improve the performance as an adhesive. In other words, when manufacturing metal cans using synthetic resin, for example, in the process of seaming the can body, top, and bottom lid, if the resin is too hard, there will be less overlap between the double seams and the adhesive strength will deteriorate. This results in an adverse effect on the seal. Therefore, in the seaming process, the resin needs to be soft enough to sufficiently fill the seam gap at room temperature. For this reason, while maintaining polyolefin's excellent adhesion to metal substrates and organic coatings, it also counteracts its shortcomings, such as poor sealing properties due to the hardness of the coatings and poor sealing properties caused by drafts. For flexibility, elongation,
It is effective to use an acrylic resin with excellent solvent resistance and hot water resistance. Monomers used in the acrylic resin synthesis of the present invention include acrylic acid and its esters such as methyl, ethyl, butyl, isobutyl, 2-ethylhexyl, and 2-hydroxyethyl, methacrylic acid and its methyl, ethyl, butyl, isobutyl, Examples include esters such as 2-ethylhexyl and 2-hydroxyethyl, styrene, maleic acid, itaconic acid, and fumaric acid. Preferably, the hydroxyl group-containing (meth)acrylic acid alkyl ester is used in an amount of 1 to 20% by weight. By using an acrylic resin containing a hydroxyl group-containing (meth)acrylic acid alkyl ester, it has good adhesion to metal materials and organic coatings, and exhibits better seaming strength. The amount of hydroxyl group-containing (meth)acrylic acid alkyl ester used is 1% by weight in the monomer.
If it is less than 20% by weight, there will be no adhesive effect, and if it exceeds 20% by weight, hot water resistance etc. will decrease. Acrylic resins can be easily produced by solution polymerization, emulsion polymerization, etc., but from the viewpoint of solvent resistance, elongation, etc., it is desirable that they have a high molecular weight. That is, manufacturing by emulsion polymerization method meets this purpose. The acrylic resin of the present invention is a modified polyolefin
The effect can be confirmed by adding 100 to 300 parts by weight to 100 parts by weight. Less than 100 parts by weight,
It is insufficient to give the adhesive the flexibility required during seaming, and if it exceeds 300 parts by weight,
Properties such as solvent resistance and hot water resistance are significantly reduced. The most significant feature of the adhesive for metal cans according to the present invention is that heating and curing after seaming can be completed in a relatively short time, thereby reducing equipment costs and energy costs. For example, the specific curing conditions for tinplate are approximately 180 to 200℃ for 2 to 5 seconds, and for chromic acid treated steel sheets (TFS) where melting of the metal coating layer is not a problem, higher temperatures are required. For example, it is possible to heat up to about 250℃,
As the heating temperature increases, the heating time can be made shorter than the above range. In addition to the above-mentioned two components, the adhesive for metal cans of the present invention may contain other resins, thickeners, antifoam fillers, etc., as necessary. The adhesive of the present invention can be used in the form of a solution, film, tape, powder, aqueous dispersion, etc., but in the present invention, an aqueous dispersion is preferred for workability and process efficiency. From a management perspective, it is advantageous. Furthermore, an alcohol-based solvent, an ester-based solvent, or the like can be added to the water dispersion adhesive as necessary to improve drying properties, coatability, etc. Thus, the present invention is an adhesive for metal can bodies, can bodies, tops, and bottom covers that has excellent seaming properties, adhesion properties, solvent resistance, etc., and can be used in a wide variety of applications. The invention is illustrated by the following examples and comparative examples. Here, parts represent parts by weight. Production example 1 Put 50.4 parts of distilled water in a flask with a stirrer, and add 70.
Warm to ℃. Add to this 31.5 parts of distilled water, 28.6 parts of 2-ethylhexyl acrylate, 25.0 parts of ethyl acrylate, and 2-hydroxyethyl methacrylate.
A mixture of 6.3 parts of acrylic acid, 3.1 parts of acrylic acid, 0.01 part of benzoyl peroxide, and 1.0 part of a surfactant was added dropwise over 3 hours to react. Thus the solid content is 40
An emulsion of acrylic resin A having a weight percent and a viscosity of 10 cps was obtained. Production example 2 Put 50.4 parts of distilled water into a flask with a stirrer, and add 70.
Warm to ℃. A mixture of 31.5 parts of distilled water, 47.3 parts of butyl acrylate, 12.6 parts of 2-hydroxyethyl acrylate, 3.1 parts of acrylic acid, 0.01 part of benzoyl peroxide, and 1.0 part of surfactant was added dropwise to this over a period of 3 hours, and the mixture was allowed to react. Ta. In this way, an emulsion of acrylic resin B having a solid content of 40% by weight and a viscosity of 10 cps was obtained. Production example 3 Put 50.4 parts of distilled water in a flask with a stirrer, and add 70.
Warm to ℃. To this was added a mixture of 31.5 parts of distilled water, 25.1 parts of ethyl acrylate, 34.8 parts of 2-ethylhexyl acrylate, 3.1 parts of acrylic acid, 0.01 part of benzoyl peroxide, and 1.0 parts of a surfactant.
It took some time to drip and react. In this way, an emulsion of acrylic resin C having a solid content of 40% by weight and a viscosity of 10 cps was obtained. Production Example 4 100 parts of ethylene-methacrylic acid copolymer (methacrylic acid content: 20% by weight) and 5 parts of aluminum hydroxide were melt-mixed using a ruder, and then pelletized. Next, add the above pellets to a flask with a stirrer.
100 parts of xylene and 100 parts of xylene were added, heated and dissolved, and then dropped into cold xylene to precipitate a resin, which was filtered and taken out. Next, 40 parts of the obtained modified resin powder was mixed with 60 parts of water and stirred with a homogenizer to obtain a modified polyethylene resin (a) aqueous dispersion with a solid content of 40% by weight. Production Example 5 In Production Example 4, the amount of aluminum hydroxide was reduced to 1
A modified polyethylene resin (b) aqueous dispersion having a solid content of 40% by weight was obtained by the same operation except that the amount was changed. Production Example 6 A modified polyethylene resin (c) aqueous dispersion having a solid content of 40% by weight was obtained by the same procedure as in Production Example 4 except that calcium hydroxide was used instead of aluminum hydroxide. Production Example 7 Put 100 parts of ethylene-methacrylic acid copolymer (methacrylic acid content 20% by weight), 8 parts of magnesium acetate, and 50 parts of water into an autoclave equipped with a stirrer, heat to 140°C with stirring, and keep at this temperature. After holding the mixture for 20 minutes, 107 parts of water was gradually added to uniformly disperse the mixture, and the mixture was cooled to room temperature to obtain a modified polyethylene resin (d) aqueous dispersion having a solid content of 40% by weight. Production Example 8 In Production Example 4, a modified polyethylene resin (e) aqueous dispersion with a solid content of 40% by weight was prepared in the same manner as in Example 4, except that 15 parts of sodium hydroxide was used instead of 5 parts of aluminum hydroxide. Obtained. Examples 1 to 5 45 parts of the acrylic resin emulsion obtained in Production Examples 1 to 3, an aqueous dispersion of commercially available modified polyethylene resin (Chemipearl S-100, Copolene L-4000)
29 parts, 21 parts of distilled water, and 5 parts of isopropyl alcohol were mixed to prepare an adhesive having the resin composition shown in Table 1. Chemipearl S-100: An aqueous dispersion made by blending 9 parts of sodium hydroxide with 100 parts of a graft copolymer of polyethylene and methacrylic acid (solid content 30% by weight) Copolene L-4000: Polyethylene and methacrylic acid An aqueous dispersion obtained by blending 9 parts of sodium hydroxide with 100 parts of acrylic acid graft copolymer (solid content 40% by weight) Examples 6 to 10 Acrylic resin A and production examples 4 to 7 Adhesives were prepared using the modified polyethylene resins (a) to (d) as shown in Table 2 in terms of solid content.

【table】 Chemipearl S-100: Manufactured by Mitsui Petrochemical Co., Ltd. Corporen L-4000: Manufactured by Asahi Dow Co., Ltd.

[Table] Comparative Examples 1 to 7 Table 3 was used instead of acrylic resin A in Example 1.
An adhesive was prepared using an aqueous dispersion (solid content: 30% by weight) of the resin shown in .

【table】

[Table] Comparative Example 8 Example 4 except that an aqueous dispersion of modified polyethylene resin (e) was used instead of corpolene in Example 4.
Adhesive was prepared in the same manner. The adhesives of the above Examples and Comparative Examples were coated on a tin plate so that the dry film thickness was 30μ, and the adhesives were heated at 80°C.
After drying for 10 minutes, it was heat treated at 200°C for 2 minutes and tested for coatability, elongation, and solvent resistance. At the same time, each adhesive was applied to the top and bottom lid of a 5-gallon can to a film thickness of 30 μm.
After drying at ℃ for 10 minutes, it was double seamed with the can body, and the seamed portion was further heat-treated at 200°C for 3 seconds using a gas burner to prepare a test can. The strength of the seamed portion of this can was measured. These results are shown in Table 4.

【table】

[Table] Comparative Example 7 was applied to the top and bottom lids of a five-gallon can, and an actual can test (water content) was performed.
A leak has occurred. Furthermore, the seaming strength of Example 5 was approximately 30% lower than that of the other Examples. As shown in Table 4, Examples 1 to 10 are considered to meet the required performance as an adhesive. Furthermore, in Example 1, a dry coating of 30 μm was applied to the top and gutter of the bottom lid of a five-gallon can made of tin plate, and after drying at 80°C for 10 minutes, the can body and top were coated. Then, the ground cover was wrapped twice and further heated at 200°C for 3 seconds using a gas burner. Regarding this, double-sealing and sealing tests were conducted. The results are shown in Table 5.

【table】

[Table] Example 11 Graft polymer of polypropylene and acrylic acid (acrylic acid grafting rate 2% by weight) 0.5 to 100 parts
100 parts of modified polyolefin prepared by melting and mixing 100 parts of calcium hydroxide and 150 parts of solidified acrylic resin A were each made into pellets, made into a film using a ruder, and adhered to the top and bottom parts of the body of a five-gallon can. I let it happen. Using this, the top and bottom lids were double-sealed and heat treated at 200°C for 3 seconds to create a can. This can was filled 18 times with water and stored for one month, but no leakage was observed. Example 12 In Example 1, chromic acid treated steel sheet (TFS) was used as the metal material for the five-gallon can, the seaming part was heated at 230°C for 2 seconds, and the dry adhesive film thickness was 50μ. A 5-gallon can was manufactured in the same manner as in Example 1 except for this. When the five-gallon can was subjected to a leakage test, a water test, a drop test, and a seam strength measurement, almost the same results as in Example 1 were obtained.

Claims (1)

[Claims] 1 Calcium, magnesium, zinc,
100 parts by weight of a modified polyolefin blended with 0.5 to 10 parts by weight of a metal compound which is an acetate, carbonate, hydroxide or oxide of at least one metal selected from aluminum and sodium, and 100 parts by weight of an acrylic resin obtained by emulsion polymerization. An adhesive for metal cans, characterized in that it is made by mixing ~300 parts by weight. 2 Claim 1 using an acrylic resin obtained by polymerizing one type selected from hydroxyl group-containing acrylic acid alkyl ester and hydroxyl group-containing methacrylic acid alkyl ester and other monomers
Adhesive for metal cans as described in section. 3 1 to 20% by weight of one type selected from hydroxyl group-containing acrylic acid alkyl ester and hydroxyl group-containing methacrylic acid alkyl ester based on the total monomers.
3. The adhesive for metal cans according to claim 2, which uses an acrylic resin obtained by using the acrylic resin. 4. The adhesive for metal cans according to any one of claims 1 to 3, which uses a modified polyolefin in which a metal compound is blended with a copolymer of ethylene and one type selected from acrylic acid and methacrylic acid. 5. The adhesive for metal cans according to any one of claims 1 to 3, which uses a modified polyolefin in which a metal compound is blended with a graft polymer of polyolefin and ethylenically unsaturated carboxylic acid. 6. The adhesive for metal cans according to any one of claims 1 to 5, comprising an aqueous dispersion of modified polyolefin and acrylic resin.