JPH04312843A - Metal-resin laminate having excellent desulfurizing property - Google Patents

Abstract

PURPOSE:To prevent sulfur staining and the offensive odor of hydrogen sulfide getting trouble in the canning of food containing protein containing sulfur such as fishes, meats, beer or the like without changing the properties of content and contamination by a heavy metal. CONSTITUTION:A volatile sulfide and a substance forming a stable sulfide with sulfide ions are mixed into a coating layer between the metallic material of a metal-resin laminate, in which the coating layer having permeability to the volatile sulfide and water is laminated on the surface of the metallic material, and the coating layer. According to the method, a sulfide in canned food is taken into a can vessel, thus preventing the generation of sulfur staining and an offensive odor. Metallic salt, monosaccharide, fumaric acid salt, furfural, D-glucuronolactone and potassium bromate are cited as a substance forming the stable sulfide.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention relates to materials for sealed containers for storing contents such as beverage cans and food cans that contain sulfur-containing proteins and are likely to generate unpleasant odors such as hydrogen sulfide. The present invention provides a laminate with excellent desulfurization properties that can be used in whole or in part.

0002

[Prior Art] When fish, meat, etc. are packed in ordinary tin-plated cans, the sulfur-containing proteins contained in these foods decompose and the sulfur compounds produced react with the tin plating and the iron underlying the tin plating. As a result, black sulfur sulfides such as tin sulfide and iron sulfide are produced, some of which are accompanied by hydrogen sulfide and emit a foul odor.

[0003] For this purpose, chemical conversion treatment of tinplate is effective, and methods have been used to prevent the base metal from coming into contact with sulfur-containing proteins by painting.

Further, paints containing aluminum flakes or zinc white (C enamel) have also been used.

On the other hand, there are food additives that suppress the production of sulfides, such as sugars such as glucose, maltose, galactose, lactose, ribose, fructose, and sorbose, fumaric acid and its salts, amino acids such as glutamic acid, furfural, and D-glutamic acid. Chronolactone, potassium bromate, sodium sulfite, etc. are said to be effective.

[0006]

[Problem to be solved by the invention] These techniques alone cannot prevent the generation of sulfur steel and hydrogen sulfide by chemical conversion treatment of the tin, and coating the base metal surface with paint etc. Even if efforts are made to prevent the formation of hydrogen sulfide, if food or beverage cans are subjected to a high-temperature sterilization process in low oxygen conditions or if food or beverage cans are stored for a long period of time even at room temperature, proteins will decompose and produce hydrogen sulfide or volatile low-molecular organic sulfides. is generated, sulfur oxides such as sulfite are reduced, and hydrogen sulfide is generated.
May produce a strange odor.

[0007] Furthermore, even when metals such as aluminum and zinc are added to the paint, depending on the pH of the contents, these metals may be eluted and contaminate the contents.

[0008] At present, there are very few practically effective additives for foods because they cause browning of the contents and produce a characteristic odor.

[0009]

[Means for Solving the Problems] As a result of various studies to solve this problem, the present inventors have found that volatile sulfide and sulfide ions are present between the coating layer and the metal material, which are permeable to sulfide and water. A laminate is made in which metal salts or monosaccharides that produce stable sulfides, fumarate, furfural, D-glucuronolactone, and potassium bromate are mixed, and hydrogen sulfide, etc., migrate from the contents into the laminate. The present inventors have discovered that it is possible to prevent bad odors and black discoloration by fixing this between a coating layer and a metal material that are permeable to sulfides and water, and have accomplished the present invention.

That is, the gist of the present invention is to provide a metal-resin laminate in which a coating layer permeable to sulfide and water is laminated on the surface of the metal material via an adhesive layer or the like. Metal salts that form volatile sulfides and sulfide ions and stable sulfides, or volatile sulfides and sulfide ions that form stable sulfides in the coating layer between the coating layer that is permeable to water. This metal-resin laminate has excellent desulfurization properties and is characterized by containing monosaccharides, fumarate, furfural, D-glucuronolactone, and potassium bromate.

[0011]

[Operation] The following experiment was conducted to confirm the effect of the desulfurization functional body of the present invention on suppressing the generation of volatile sulfides such as hydrogen sulfide.

First, the permeability of the resin used for the coating layer to hydrogen sulfide and sulfite gas was investigated.

Saturated hydrogen sulfide water or saturated sulfurous acid water is put into chamber A 1 in FIG. Distilled water was added and samples were taken at regular intervals to determine each concentration. Figure 2 shows the values calculated as the amount of permeation through a 0.1 mm film for 24 hours. This is because sulfurous acid or hydrogen sulfide in the can passes through the resin coating layer to form volatile sulfides and sulfide ions and stable sulfides.Metal salts, monosaccharides, fumarates, furfural, D-glucuronolactone , indicating that it can reach and react with potassium bromate or metal materials.

The metal material of the present invention may be a steel plate or one plated with one or more metals such as Zn, Ni, Cr, Mn, Fe, etc., or plastic,
Selected from materials such as paper, glass, and composites of these metals.

Further, in the present invention, a coating layer permeable to sulfides and water is laminated via an adhesive layer, and the coating layer is made of polymethylpentene or polybutadiene with a thickness of 10 μm to 100 μm. . Film thickness is 1
If it is thinner than 0 μm, pinholes are likely to occur in the membrane formation, and if they occur, heavy metal ions will dissolve into the contents. If it is too thick than 100 μm, the permeability to sulfides and water will be poor, and the contents will The desulfurization effect from

[0016] As the adhesive, polyester type, polyurethane type, polyacrylate type, modified vinyl type, elastomer type, olefin type, modified olefin type, etc. can be used alone or in the form of a mixture. A water-soluble polymer can also be dispersed or mixed into the adhesive.

The thinner the adhesive layer is, the better, but if it is too thin, the adhesive strength will be poor, so it is limited to 0.5 to 5 μm. As for the adhesive, it is also possible to apply it partially.

A feature of the present invention is that volatile sulfides and sulfide ions and metal salts that form stable sulfides are added to the layer between the metal material and the coating layer that is permeable to sulfides and water. However, as metal salts that produce stable sulfides, metals such as Ag, As, Hg, Cu, Sb, Bi, and Sn (IV
), Cd, Pb, Sn (II), Zn, Co, N
i, Fe, Mn salts, i.e. oxides, hydroxides, carbonates, basic carbonates, sulfates, chlorides, nitrates, acetates,
Among organic acid salts, less toxic ones are effective, especially Sn (IV), Pb, and Sn (II), which are less harmful to the human body.
, Zn, Ni, and Fe(III) salts.

In the case of the present invention, since the coating layer on the surface of the laminate functions as a blocking layer that does not completely transmit large molecules such as heavy metal ions, they may be eluted into the contents like zinc white in C enamel. Unlike additives for the contents, they do not change the quality or color of the contents, so it is possible to select from a wider range of substances that produce stable sulfides.

Furthermore, in order to stabilize these metal sulfides, etc., they are dispersed in an adhesive, the pH of which is set higher than that of the contents, for example from 8.0 to 11.0, and metal salts are added therein. One type or two or more types may be mixed.

These metal salts or their composites are dissolved or dispersed in water or a solvent, applied to a metal body by brushing, spraying, roller coating, etc., and then coated with sulfide and water resistant A transparent coating layer may also be adhered. Alternatively, it may be mixed in advance into the inner surface of the coating layer that is permeable to sulfides and water.

[0022] The effective coating amount of these metal salts differs depending on the metal, so it cannot be determined unconditionally, but generally speaking, the coating amount of the metal salt is 0.005 g/m2 to 0.5 g/m2. The period between was valid. 0.005g
/m2, no effect will be observed, and if it is less than 0.5g/m2, no effect will be observed.
m2 or more, the adhesion of the coating layer, which is permeable to sulfides and water, deteriorates. However, when these metal salts are mixed into the inner surface of a two-layer film,
Since the degree of deterioration of adhesion is small, even if it is mixed up to 2 g/m2, the adhesion will not be deteriorated.

In addition, a hydrophilic coating layer is applied on the metal in order to facilitate the reaction of converting volatile sulfide into non-volatile sulfide, or to promote the oxidation reaction of the underlying metal, and in some cases, to simultaneously provide an oxygen scavenging effect. It is also useful to provide a A hydrophilic coating layer is formed from a binder that easily dissolves or swells in water at room temperature, and has an affinity for water, including, but not limited to, a water-soluble polymer that dissolves in water. Solid content concentration approximately 0.1-20% by weight
An aqueous solution of is preferred. Examples of water-soluble polymers include starch, gelatin, cellulose derivatives, polyvinyl alcohol, acrylic acid, methacrylic acid, and esters thereof.

The metal salt or its composite may be mixed with the hydrophilic coating layer and coated, and a coating layer permeable to sulfide and water may be adhered thereon. It may be coated on the surface and a coating layer permeable to sulfides and water may be adhered thereon, or it may be mixed in an adhesive and coated.

[0025]

[Examples] The present invention will be specifically explained below based on Examples.

Example 1. First, a polyurethane adhesive containing 10 g/1 zinc acetate was applied onto a 0.24 mm thick cold rolled steel plate using a reverse roll coater to form a dry film with a thickness of 1 μm. Then, the steel plate temperature was raised to 20°C for 30 seconds in a gas oven.
After drying and heating to 0° C., a 50 μm thick polymethylpentene film was immediately laminated using a roll laminator while maintaining that temperature as much as possible, and immediately cooled to obtain a resin-coated steel sheet with desulfurization function. The following beer test was conducted using the obtained sample as a sample.

Beer test: Add 50pp of sodium sulfite as SO2 to beer that has been commercially produced for 3 months.
m, and put 200 ml into a 350 ml glass container in carbon dioxide gas. Seal the sample with a lid,
The amount of hydrogen sulfide in the container kept at 40°C for one week was measured using gas chromatography.

Example 2. First, a solution of 3% hydroxyethyl cellulose and 5% tin tartrate adjusted to pH 8 was coated on a metal substrate to a dry film thickness of 0.3 μm, and then a 1 μm dry film was applied on top.
A sample was prepared by applying a polyurethane adhesive and laminating 50 μm of polymethylpentene using a roller laminator. The above beer test was conducted on this board.

Example 3 A 3% aqueous solution of hydroxyethyl cellulose was coated on a metal substrate to a dry film thickness of 0.3 μm, and a 10%
A 5% zinc white dispersed in a polyurethane adhesive containing an ion exchange resin was applied to give a dry film thickness of 1 μm, and then a 50 μm thick polymethylpentene was immediately laminated using a roller laminator. This sample was subjected to a beer test and an oxygen scavenging ability test.

Oxygen scavenging ability test: Using a resin-coated steel plate sample as the lid of a cylindrical glass container with a diameter of 65 mm and an internal volume of 350 ml, beer was poured in a 0.6 vol% O2 - CO2 gas atmosphere so as to have a head space of approximately 24 ml. (referred to as test specimen A).

[0031] The same container was coated with 60 mg/dm2 of commercially available epoxy phenol resin paint for cans, and a baked No. 50 tin plate (tin coverage: 5.6 g/m2) was used as a lid in the same manner as the resin-coated steel plate. Pour into beer and seal (referred to as test specimen B).

[0032] Place the test specimens A and B in a constant temperature bath at 20°C.
After the time has elapsed, both test specimens are shaken for 5 minutes using a shaker, and then the residual oxygen in the container is measured using an oxygen concentration meter, and the oxygen removal ability is evaluated using the following formula.

[0033]

[Math 1]

Example 4. A 3% aqueous solution of hydroxyethyl cellulose is applied on a metal substrate to a dry film thickness of 0.3 μm, and a 10%
A polyurethane adhesive containing an ion exchange resin was applied to give a dry film thickness of 1 μm, and a 60 μm laminated polymethylpentene film was immediately laminated using a roller laminator. This laminated polymethylpentene is a film in which a 10 μm thick modified polymethyl pentene containing 5% zinc white and a 25 μm thick polymethyl pentene are laminated. A beer test and an oxygen scavenging ability test were conducted on this resin-coated steel sheet sample.

Comparative Example A 3% aqueous solution of hydroxyethyl cellulose was coated on a metal substrate to a dry film thickness of 0.3 μm, and 10%
A polyurethane adhesive containing an ion exchange resin was applied to give a dry film thickness of 1 μm, and then a 50 μm thick polymethylpentene was immediately laminated using a roller laminator. This sample was subjected to a beer test and an oxygen scavenging ability test.

Table 1 shows the evaluation results of each example and comparative example. Example 1. Example 2 is a desulfurization functional steel sheet manufactured by adding zinc acetate to the adhesive. Example 3 is a desulfurization functional steel sheet manufactured by adding tin tartrate to the hydrophilic film. In Example 4, zinc white and ion exchange resin were added to the adhesive. Apply an aqueous solution of hydroxyethyl cellulose for hydrophilic coatings adjusted to pH 8 with caustic potash, then apply an adhesive on top of it.
It is manufactured by laminating polymethylpentene film to which zinc white is added. It can be seen that the amount of hydrogen sulfide generated in the beer test was significantly smaller than the comparative example in which no metal salt was added.

[0037] By the way, hydrogen sulfide was found to be 13pp in the beer test.
b) When beer is stored for 8 weeks at 40℃, the amount of hydrogen sulfide generated is 2.3ppb, and when stored at 20℃ for 8 weeks, the amount is 1.5ppb. It never became. In the case of normal beer, it is said that an off-flavor is felt when hydrogen sulfide is 5 ppb or more. In all of the examples, the concentration was 13 ppb or less in the beer test, so there was no problem in practice.

The results of the oxygen scavenging ability test conducted at the same time are also shown in Example 4.
．． was almost the same as that of the comparative example, and the adhesion of the film, which was separately tested, was not particularly impaired.

[0039]

[Table 1]

[0040]

[Effects of the Invention] As can be seen in the examples, the desulfurization can made of the steel plate of the present invention does not contain hydrogen sulfide or volatilization even after being packed with food or beverages containing sulfur-containing proteins and stored at high temperatures for a long period of time. It can be stored without emitting odors that are thought to be caused by organic substances.

[Brief explanation of drawings]

FIG. 1 is a diagram showing a transmission coefficient measuring device.

FIG. 2 is a diagram showing changes in permeability coefficients of sulfite and hydrogen sulfide to a polymethylpentene film measured using the apparatus of FIG. 1 depending on temperature.

[Explanation of symbols]

1... Chamber A (83 ml of water saturated with sulfite or hydrogen sulfide) 2
…Chamber B (83ml of pure water)

Claims (2)

[Claims] Claim 1: A metal-resin laminate in which a coating layer permeable to volatile sulfides and water is laminated on the surface of a metal material via an adhesive layer, in which the metal material and volatile sulfide and water are permeable. The coating layer between the coating layer, which is permeable to A metal-resin laminate with excellent desulfurization performance, characterized in that it contains saccharides, fumarates, furfural, D-glucuronolactone, and potassium bromate. [Claim 2] A hydrophilic coating layer is applied to the surface of the metal material,
In a metal-resin laminate, a coating layer permeable to volatile sulfides, oxygen and water is laminated thereon via an adhesive, and the metal material is permeable to sulfides, oxygen and water. Metal salts that form volatile sulfides and sulfide ions and stable sulfides, or monosaccharides that form volatile sulfides and sulfide ions and stable sulfides, and fumaric acid are added to the coating layer between the two coating layers. A metal-resin laminate with excellent desulfurization and oxygen scavenging properties, characterized in that it contains salt, furfural, D-glucuronolactone, and potassium bromate.