JPS621316B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention prevents rusting of the can body joint and elution of metal into the contents of the can by applying nylon powder as an aqueous dispersion to the inner surface of the joint of the can body joined by welding and then heat-sealing the powder. The present invention relates to a method for protecting welds. Generally, a can body is manufactured by forming a metal plate such as a tin plate into a cylindrical shape and joining the ends with solder. However, this soldering method has problems such as lead pollution due to lead fume, heavy metal wastewater contamination due to washing with water, and rusting of the can due to residual etching material, so welding is increasingly being used to join the end faces of can bodies. In addition, an inexpensive metal material called stain-free steel that does not use tin has been developed to replace tinplate, but its characteristics make it impossible to solder, so thermoplastic resin is applied to the end of the can body for joining. , a method of joining by welding is adopted. Preventing the rusting of the joint parts of the can body and the elution of metal into the can contents by these joining methods is an essential condition, and various methods of protecting the joint parts are being studied. First, the can body joints joined using thermoplastic resin are coated with solvent-based vinyl paint, and the cut edges of the metal substrate are protected with tape-shaped thermoplastic resin, which serves both as adhesive and end surface protection. A method has been proposed in which a film is pressed onto the bonded end surface and heated and bonded using a roll. As with welded cans, solvent-based vinyl paint is applied to the welded can body joints. However, the drawbacks of this vinyl paint are that it has weak adhesion to the substrate, lacks solvent resistance, and whitening in boiling water.
For example, there are restrictions on the coating thickness. In particular, in the case of can body joints made by welding, unlike in the case of joining with thermoplastic resin, the exposed portion of the metal material is not only the cut end of the metal, but also mechanical scratches during joining, exposed parts of the metal base material due to welding, etc. It is necessary to protect the spots of joints, and the irregularities of the welding surface. In particular, when using stain-free steel as the material for cans, it is necessary to remove the chemically treated layer on the surface compared to joining by welding.
A wide range of metal materials will be exposed. In the present invention, nylon particles are applied as an aqueous dispersion to the inner surface of the can body joints formed by welding, and are heat-fused to provide sufficient adhesive strength and a coating thickness that can completely protect the welded parts. To provide a can body in which a protective film which is easily obtained and has good solvent resistance and boiling water resistance is formed to protect the welded portion from rusting and metal from melting into the contents. To join can bodies by welding, the surface treatment coating on the joint part of the can body plates (usually about 5 mm width) is removed by a conventional method, the joint is formed into a cylindrical or rectangular tube shape, and the joint parts are overlapped to make the entire length of the part. This is done by electric welding etc. over a period of time. Common surface treatment coatings include metal chemical treatment layers and primer treatment layers on stain-free steel. Metal materials that do not have such a surface treatment film can be electrically welded as they are. In the present invention, an aqueous dispersion of nylon particles with a melting point of 100 to 200°C and an average particle size of 100 μm or less is applied to the inner surface of the joint of the can body obtained by the above method, and is heat-fused. As the coating method, the following method is preferably employed. Using the nozzle method (a method using a normal lining machine in which the discharge amount can be adjusted arbitrarily by adjusting the nozzle diameter and pressure), the can body is fixed and the nozzle is moved, or the nozzle is fixed and the can body is moved. Spray on the torso. At this time, a uniform coating film can be obtained by linking the movement of the nozzle or the can body with the spraying.
In the case of a can body with a large diameter, coating can be performed using a roll coater that can be inserted into the can. The heating conditions are then the melting point of the nylon used, the thickness of the can material,
Conditions vary depending on the heating method, but it is preferable to heat the coated nylon powder so that the surface temperature is 20° C. or more higher than its melting point. For example, if the melting point of nylon is 200℃, high frequency or burner heating can be used for several seconds at a temperature of 220 to 280℃.
Heating with a hot air stove takes about 1 to 5 minutes at a temperature of 200 to 250°C. The coating thickness of the aqueous dispersion of nylon powder in the present invention is particularly preferably 10 to 500μ,
If it is less than 10μ, pinholes may occur, while if it exceeds 500μ, surface irregularities and foaming may occur during heating and melting. The most important feature of the present invention is that since it uses an aqueous dispersion of nylon powder, a uniform coating film of any thickness can be created on the joint area, and the liquid viscosity can be adjusted to suit the coating process. Moreover, it is possible to avoid environmental pollution and the risk of ignition, which are problems associated with solvent-based systems. Depending on the coating substrate, in order to improve the flowability of the coating liquid at the end faces and joints, this dispersion may be
It is also possible to add appropriate amounts of solvent. Other features of the present invention are that, since nylon powder is mainly used, a film with good solvent resistance and adhesion to the substrate, which is not found in solvent-based paints, can be obtained, there is little contamination of the contents, and nylon powder A protective film with good boiling water resistance and retort resistance can be obtained by adjusting the melting point of the powder and selecting other additives. The metal materials used in the present invention include chemically treated steel sheets called so-called stain-free steel, such as Cansuper (Nippon Steel) and Hitop (Toyo Kobe), which are commercially available as chromium-treated steel sheets, as well as ultrathin steel sheets such as nickel and aluminum. It is also possible to use various steel plates such as galvanized steel plates, tin plates, untreated cold-rolled steel plates, and non-ferrous materials such as aluminum. Furthermore, it is also possible to use a metal material coated with a metal baking paint for the purpose of protecting the inner surface of the can body. Here, the metal baking paints include epoxy-phenol paints, epoxy-polyisocyanate paints, epoxy-amino resin paints,
Epoxy resin - polybasic acid paint, epoxy resin -
Commonly known paints such as aminosilane primers are useful, and can be freely selected depending on the metal material used and conditions of use. As the nylon used in the present invention, nylon 8 (melting point: 199°C)

[Formula] Nylon 10 (melting point 189℃, (−NH(CH ₂ ) ₉ −CO)−
_o ), nylon 11 (melting point 189℃,

[Formula] Nylon 12 (melting point 176 °C,

[Formula] Nylon 13 (melting point 168℃, omega-lactam ring-opening polymerization type nylon such as (-NH( _-CH2 ) _-12CO ) _-o , nylon 10-12
(Melting point 195℃, (−CO(−CH ₂ )− ₁₀ −CONH(−
_CH2 ) ₁₀ , -NH) _-o ), nylon 12-10 (melting point 171
℃, (−CO(−CH ₂ )− ₈ CONH(−CH ₂ )− ₁₂ NH)− _o ),
Nylon 12-12 (melting point 182℃, (-CO( _-CH2 ) _-10 CO
-NH( _-CH2 ) _-12NH ) _-o ), nylon 13-13 (melting point
171℃,

Introducing homopolymers such as [formula]), repeating units of these nylons and homonylons with a melting point of 280°C or higher (e.g. nylon 9, nylon 6-10, nylon 6-9, nylon 6-13, nylon 12-6) Copolymerized nylon can be used. Copolymerized nylons include nylon 6/66/12 (ε-caprolactam (6), 1-6 hexamethylene diamine and adipic acid nylon salt (6.6), and ω-laurinlactam (12), hereinafter the same indications ) Nylon 6/12, Nylon 6/66/6-
10, Nylon 6/66/11, Nylon 6/11, Nylon 6/66/6-12, Nylon 6/6-10/12,
Various combinations such as nylon 11/12, nylon 6/6-12/12 nylon 6/(trimethylhexamethylenediamine and adipate), nylon consisting of a combination of dimer acid and diamine of C ₅ or more, and various By changing the composition ratio, the melting point can be freely adjusted to a preferred range. Various copolymerized nylons with different melting points are already commercially available, such as Platamide H150 (melting point 121°C) and H005 (melting point 121°C) manufactured by Pratebon.
℃), H101 (melting point 107℃), H103 (melting point 84℃),
H104 (melting point 131°C), H106 (melting point 112°C), Dupont Zytel 63 (melting point 153°C), Toray CM-
4000 (melting point 146℃) is a typical commercially available product. Among these nylons, it is selected depending on the usage conditions and required physical properties. However, nylon with a melting point of over 200℃ tends to discolor the base material under melting conditions, leading to melting of tin in tinplate, and nylon with a melting point of 100℃ or less may soften and melt when filled at high temperatures after sterilizing foods, etc. There is. In addition, the definition of the melting point of nylon in the present invention is determined by differential scanning calorimetry (DSC) for a sample of nylon that has been sufficiently annealed to confirm crystallinity.
It is defined as the apex of the endothermic peak of the crystal melting curve when the temperature is raised at a rate of °C/min, and when there are two or more endothermic peaks in a blend composition of two or more types of nylon, it is the endotherm that has the largest endothermic area. The apex of the peak defines the melting point. For nylon that does not contain any crystalline parts, the softening point determined by the JIS K2425 ring and ball method converts to the melting point. These nylon raw materials are freeze-pulverized or granulated by other methods, sized into particles of 100 microns or less, and used as an aqueous dispersion. Nylon powder, which has a specific gravity greater than that of water, is uniformly dispersed in the aqueous dispersion, eliminating sedimentation and keeping it stable. It can be evenly applied to the welded can body joints without flickering, and can be applied evenly to the can body joints by welding, drying, and heating. In order to provide a uniform film after melting and to have sufficient adhesion to the substrate, the average particle size of the nylon powder must be 100 μm or less. Further, the amount of nylon powder in the aqueous dispersion is preferably 15 to 40% by weight, and preferably 25 to 40% by weight.
35% by weight is more preferred. When the amount is less than 1.5% by weight, precipitation tends to occur unless the amount of dispersant exceeds 3%, and when it exceeds 40% by weight, fluidity tends to be poor and coating becomes difficult. When making a dispersion, one or more thickening and dispersing agents selected from water-soluble salts of polymers or copolymers of acrylic acid or methacrylic acid, polyethylene oxide, and ammonium salts of higher fatty acids are used. Ru. The amount of these thickeners can be adjusted freely depending on the type of nylon used, the particle size, the amount used, the coating substrate and its usage conditions, but it depends on the sedimentation stability of the dispersion and the adhesion to the substrate. In consideration of wettability, adhesion to the substrate, etc., the amount is most preferably 0.1 to 3 parts by weight. In addition to those mentioned above, fine powder resins other than nylon, benzenesulfonic acid amide, toluenesulfonic acid amide, cyclohexane sulfonic acid amide, hydroxybenzoic acid ester, bisphenol A and other ordinary nylon plasticizers, dyes,
It is also possible to add fine powders of titanium oxide, silicon dioxide, bentonite, etc., if necessary. Furthermore, depending on the metal material, for this aqueous dispersion, alcohols that are liquid at room temperature such as methanol and ethanol, ethylene glycol and its derivatives such as methyl cellosolve, ethyl cellosolve, butyl cellosolve, and even its acetate derivatives may be used. By adding certain methyl cellosolve acetate, ethyl cellosolve acetate, or butyl cellosolve acetate, it is possible to improve the wetting characteristics to the substrate. In the present invention, the average particle size of the nylon powder is
If it is larger than 100μ, sedimentation will occur in the dispersion, not only will uniform dispersion not be obtained.
After heating and melting, the coating surface becomes uneven and pinholes are likely to occur in the coating. Next, in order to further facilitate understanding of the present invention, specific examples will be explained. Reference example 1 Electric tinplate manufactured by Nippon Steel (ET#25, 0.24
mm, material A), electrolytic chrome-plated steel sheet manufactured by Toyo Kohan Co., Ltd. (height top, 0.2 mm, material B) and electrolytic chrome plated steel sheet manufactured by Toyo Kohan Co., Ltd. (high top, 0.2
mm) with a known epoxyphenol paint to a thickness of 5 mm.
Copolymerized nylon manufactured by Pratebon Co., Ltd. was applied as a dispersion of nylon powder on the surface of the plate material (Material C), which was coated with μ and dried and cured at 200℃ for 10 minutes.
A powder mixture of 1000 g of H104P (0 to 80 μ) (melting point 131°C) and 50 g of polyethyl UF20 manufactured by Tetsusei Kagaku Co., Ltd. was prepared in advance with 143 g of a 1% aqueous solution of sodium polyacrylate, Aron A-20P manufactured by Toagosei Chemical Co., Ltd. and 5.3 g of ammonium stearate. g in 1710 g of water, stirred and dispersed in an aqueous dispersion, and coated to a thickness of 50 to 100 μ (resin content equivalent).
Subsequently, it was heated in a hot air dryer at 180°C for 5 minutes to obtain a uniform coating film. Similarly, nylon 11 (melting point 189°C) was applied to the above plate material, prepared with a dispersion of the same composition, and heated for 5 minutes in a hot air dryer at 210°C.
A uniform coating of ~100μ was obtained. As Comparative Reference Example 1, the above-mentioned
H104 powder (0~80μ) and nylon 11 powder (0
~63μ) was sprayed to form a film under the same conditions at a film thickness of 50 to 100μ. Similarly, polyvinyl chloride paint (solid concentration 20%)
was applied and dried with hot air at 150°C for 5 minutes to produce a film with an average coating thickness of 20 μm. Boards coated with these coatings were tested with a pinhole test (immersed in a 1% CuSo ₄ aqueous solution for 30 minutes to check for pinholes), and a goblin test (untreated film and film treated by immersion in 100°C boiling water for 30 minutes). , cut 100 squares into 1 mm squares and peeled off with Nichiban cellophane tape), and tested the appearance of the film (presence or absence of whitening) after immersion in boiling water at 100°C to evaluate adhesion to the substrate, uniformity of the film, and We investigated boiling water resistance. As shown in Table 1, it was confirmed that the product can be used to protect can body joints. Example 1 An electrolytic chrome-plated steel plate (high top, 0.2 mm) manufactured by Toyo Kohan Co., Ltd. was cut into 210 mm x 125 mm, and a known epoxy-phenol paint was applied to a thickness of 5 μm at both ends of the 125 mm length, except for the 5 mm width at each end. Using a plate that had been dried and cured at 200°C for 10 minutes, both sides of the coated plate were joined by electric welding in a conventional manner and formed into a tube. H104 dispersion and nylon 11 dispersion produced by the same method as in Reference Example 1 were applied to the internal joints of the can body using a conventional spray method to a coating width of 10mm and a film thickness of 50 to 100μ. After heating in an oven at 150℃ for 5 minutes and 210℃ for 5 minutes, the bottom lid was double-sealed using the usual method, the contents shown in Table 2 were filled, and the top lid was double-sealed using the usual method to make canned goods. . As comparative example 1,
H104 powder (0~80μ), nylon 11 powder (0~63
μ) was applied to the same pipe body to a film thickness of approximately 50 to 100 μ, heated in an oven at 180℃ for 5 minutes and 210℃ for 5 minutes, and polyvinyl chloride paint (solid content concentration 20%) was applied. The mixture was applied to a film thickness of 20 μm, heated in an oven at 150° C. for 5 minutes, and then canned in the same manner as above. The canned food was stored at 500°C for 20 days, the amount of iron eluted was measured, and the canned food was stored at 100°C for 2 hours to observe peeling and whitening on the protective surface of the joint. The results are shown in Table 2. Table 2 shows that in the cans of the present invention, iron elution into the contents is extremely small, and the welded joints are protected. The amount of iron eluted was measured in accordance with JIS K 0102.

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Claims (1)

[Claims] 1 Nylon powder with a melting point of 100 to 200°C and an average particle size of 100μ or less selected from water-soluble salts of polymers or copolymers of acrylic acid or methacrylic acid, polyethylene oxide, and ammonium salts of higher fatty acids 1
An aqueous dispersion dispersed using seeds or two or more thickening dispersants is applied to the joint part of the inner surface of the can body joined by welding, and then heated to fuse the nylon powder to the joint part. A method for protecting a can body joint, characterized by: