JPH0236625B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention is directed to the phenomenon that moisture permeates into the internal structure of the container body from the end surface of a container body mainly made of paper used for composite cans, etc., or that moisture in the container body structure evaporates from the end surface and dries. The present invention relates to a method for coating the end face of a paper container body to prevent this, and an end face coating composition used therefor. (Prior Art) Paper container bodies used for composite cans, etc., are made of, for example, polyethylene, aluminum, polyethylene, inner paper of a paper laminate film, etc.
Next, there is an intermediate layer made of polymerized craft boat, and on the outside of that, a surface paper made of paper, polyethylene, and aluminum laminate film printed on is polymerized using adhesive, and the main material is paper. For example, if the container body is placed in a humid condition, the paper may swell or peel due to moisture absorption from the edge of the cut container body, and if the container body is placed in a dry condition, the paper may swell or peel. If the paper loses moisture and shrinks, or the edge of the container body loses its flexibility, quality problems may occur, such as cracking at the edge when tightening the container lid. There is. However, conventionally, these container bodies have been stored and handled with their end faces cut off, despite the possibility of the above-mentioned problems occurring. Recently, there has been an increasing demand for high quality container bodies, such as hot-filled youth cans and composite cans used for nitrogen gas filling.In order to prevent the above-mentioned quality deterioration of the container body, moisture-proof and water-resistant materials are added to the end surface. A need has arisen for coated container bodies. Therefore, the method of covering the end face of the container body is as follows:
There is a method of heat-melting and bonding heat-melting synthetic resin materials (thermal welding type), or a method of applying a penetrating waterproofing agent made by dissolving synthetic resin in an organic solvent, but in the former case, the melting point of the synthetic resin material and the paper It is difficult to select a suitable synthetic resin material in terms of adhesive properties, etc.
In addition, it is difficult to handle because it tends to cause stringing during adhesion. In addition, in the latter case, it is difficult to form a coating on the end surface of the container body because it is easily absorbed by the paper material that forms the container body, and a large amount of penetrating waterproofing agent is required to form a coating on the end surface. In addition, there are safety issues, such as toxicity due to the organic solvent and high volatility and flammability. (Problems to be Solved) The present invention solves these conventional problems and provides a coating that is easy to handle, highly safe, and has excellent water resistance and adhesiveness and is continuous on the end face of the container body from the end face to the inside thereof. The purpose of the present invention is to provide a method for forming an end face coating composition and an edge coating composition suitable for the method. (Means for Solving the Problems) The present invention has been made to solve the above-mentioned problems, and the first invention provides a method for covering the end face of a paper container body. An aqueous dispersion containing either an ethylene/acrylic acid copolymer or an ethylene/methacrylic acid copolymer is applied to the end face, and the end face is heated and dried to form a continuous coating from the end face to the inside thereof. It is characterized by forming. The second invention is characterized in that the composition for coating the end surface of the paper container body is composed of an aqueous dispersion using either an ethylene/acrylic acid copolymer or an ethylene/methacrylic acid copolymer. . (Example) The present invention will be described in detail below. The paper container body 1 is made of various materials such as paper 2, polyethylene 3, aluminum 4, and adhesive, as shown in FIGS. Therefore, the coating 6 coated on the end surface 5 has good adhesion to those materials, has excellent waterproof properties, and has a strong and continuous coating integrated with the end surface 5 from the end surface to the inside thereof. In addition, the particles 7 in the composition penetrate between the fibers of the paper 2 and strengthen the bond with the film 6 due to the anchoring effect, and the composition is easy to handle and has high safety. As a result of investigation, it was found that an aqueous dispersion using either an ethylene/acrylic acid copolymer or an ethylene/methacrylic acid copolymer was optimal, and the present invention was completed. First, the aqueous dispersion of ethylene/acrylic acid copolymer will be explained. Ethylene/acrylic acid copolymer has a highly polar carboxyl group (-COOH) in its molecular chain, so it has excellent adhesion to various materials such as paper, synthetic resins such as polyethylene, tinplate, and metals such as aluminum. Furthermore, the coating formed because the carboxyl groups in the molecular chain form hydrogen bonds with other adjacent carboxyl groups to create a network structure has excellent durability and water resistance. Furthermore, an aqueous dispersion of the ethylene/acrylic acid copolymer can be produced without an emulsifier by the following reaction using an aqueous alkaline solution such as ammonium hydroxide. In other words, the ethylene/acrylic acid copolymer is given self-dispersibility by alkali neutralization, so it can be dispersed in water without using an emulsifier, and it is possible to achieve a particle size that is difficult to achieve with emulsifiers.
Aqueous dispersions with a size of 0.1μ or less can be produced. In addition, by applying the obtained aqueous dispersion to the end face of the container body and drying it by heating, ammonia as a neutralizing agent required for water dispersion of the ethylene-acrylic acid copolymer is released together with water as shown in the following reaction. As a result of evaporation and volatilization into the original acid form and loss of hydrophilicity,
A coating with extremely excellent water resistance can be formed on the end face. In particular, as mentioned above, the aqueous dispersion that has self-emulsifying properties by neutralizing carboxyl groups using ammonium hydroxide, which evaporates and volatilizes by heating and drying without using an emulsifying agent, is an ethylene/acrylic acid copolymer. Because there are no foreign substances such as surfactants on the particle surface, it has superior film forming properties, adhesive properties, and water resistance compared to ordinary aqueous polymer dispersions. Furthermore, ethylene/acrylic acid copolymer can be dispersed in water as an alkaline aqueous solution using an alkali metal hydroxide such as sodium hydroxide or potassium hydroxide instead of ammonium hydroxide; Since the oxide is non-volatile, it does not volatilize even if it is heated and dried after coating, and the coating becomes an ionomer type resin in which carboxyl groups are crosslinked with metal ions such as alkali metals. This ionomer type resin has excellent oil and fat resistance and toughness due to the crosslinking effect of metal ions, but the hydrophilic group (salt)
The presence of ammonium hydroxide tends to reduce the water resistance of the coating compared to when ammonium hydroxide is used, and the carboxyl groups are neutralized by metal ions, making it impossible to form hydrogen bonds. There is a tendency for the adhesion of the film to be lower than when it is used. Therefore, when the coating requires water resistance, an aqueous dispersion using ammonium hydroxide is more suitable, and when the coating requires oil and fat resistance, an aqueous dispersion using an alkali metal hydroxide is more suitable. Dispersions are more suitable. Next, the aqueous dispersion of ethylene/methacrylic acid copolymer will be explained. The ethylene/methacrylic acid copolymer has the following molecular structure. Ethylene/methacrylic acid copolymer is ethylene/methacrylic acid copolymer.
Like acrylic acid copolymers, it has carboxyl groups, so it has good adhesion to metals such as tinplate and aluminum, and adjacent carboxyl groups form hydrogen bonds with each other to form a network structure.
Although the resulting coating has excellent strength, it tends to have low adhesion to synthetic resins such as polyethylene and polypropylene. To produce an aqueous dispersion of ethylene/methacrylic acid copolymer, ethylene monomer and methacrylic acid comonomer are emulsion polymerized, a certain amount of alkaline aqueous solution is added to the resulting latex, and the resulting latex is heated and neutralized to remove carboxyl groups. By dissociating a part of it, it is possible to disperse it in water in the form of fine particles without using an emulsifier. Ammonium hydroxide or alkali metal hydroxide can be used as the alkali neutralizing agent, but if volatile ammonium hydroxide is used, an aqueous dispersion can be used as in the case of the ethylene/acrylic acid copolymer described above. By heating and drying after coating, ammonia evaporates and volatilizes together with water, returning to its original acid form, forming a coating with excellent water resistance. In addition, when a nonvolatile alkali metal hydroxide is used, the neutralizing agent does not volatilize even when heated and dried, resulting in an ionomer resin in which carboxyl groups are partially crosslinked with metal ions, as shown below. . Therefore, although the obtained film has excellent oil and fat resistance, the water resistance tends to decrease due to the presence of the hydrophilic group (salt). Furthermore, although ethylene/methacrylic acid copolymer has low adhesion to synthetic resins such as polyethylene, it has excellent adhesion to paper and metal and film strength, so it is not practical as a moisture-proof coating for the end surface of paper container bodies. No problem. Furthermore, while the minimum film forming temperature of an aqueous dispersion of ethylene/methacrylic acid copolymer is around 90°C,
The temperature of an aqueous dispersion of ethylene/acrylic acid copolymer is around 48°C, so when coating the end face of a container body made of a base material with weak heat resistance, ethylene/acrylic acid copolymer, which has a low film-forming temperature, is used. It is better to use an aqueous dispersion of As shown in the table below, aqueous dispersions using ethylene/acrylic acid copolymer and ethylene/methacrylic acid copolymer as dispersoid polymers, and as reference examples, water dispersions of vinyl acetate/ethylene copolymer using an emulsifier. Figure 4 shows the results of examining the effects of particle size and concentration on adsorption and penetration of particles into paper and penetration of water by capillary analysis using filter paper for each liquid. 1 Test piece: Filter paper cut to a width of 10 mm (the hole size is
1μ and 3μ) strips 2 Dispersion:

【table】

[Table] As shown in Figure 4, there are differences depending on the pore size of the filter paper, but as the particle size increases, water penetration into the filter paper tends to increase. , the penetration of water is extremely small,
At 0.1μ, almost no water penetration is observed. At a certain concentration, as the particle size decreases, the distance between particles becomes shorter, so when an aqueous dispersion is applied to a substrate, it tends to become concentrated by drying, and this concentrated layer transfers moisture to the paper. An aqueous dispersion with a small particle size is effective in forming a film without adding excess moisture to the paper to prevent penetration. In addition, for a given particle size, as the concentration increases, the distance between the particles decreases, so when applying an aqueous dispersion, it is necessary to reduce the penetration of water into paper to form a film. An aqueous dispersion with a small diameter and high concentration is suitable. Further, when an aqueous dispersion having a fine particle size is applied to paper, the particles enter the gaps between the paper fibers due to capillary action, and the anchoring effect strengthens the adhesion of the formed film. In addition, the paper structure used for container bodies usually has a porosity of approximately 40 to 60%, and the pores have a radius of
Since it has a capillary structure of 1μ to 10μ, the particle diameter of the polymer in the aqueous dispersion can be set to 0.03μ to 0.03μ, based on the relationship between the particle size shown in Figure 4 and the penetration of water separated from the particles into the paper. By setting it to 0.5μ, the anchoring effect can be exhibited. In addition, even if the particle size is small, in the case of a dispersion with a low concentration, water will penetrate into the paper more during the process of forming a film after application, so if such a water dispersion with a low concentration is used, If the end face of the container body is coated, there is a risk that the end face of the container body may swell due to penetration of moisture, resulting in unfavorable quality results. For this reason, even if the aqueous dispersion has a fine particle size, the concentration should be as high as possible. Therefore, the concentration of the aqueous dispersion used for coating the end surface of the container body should be 25
~40% is desirable. Furthermore, fibers such as paper have the property of being negatively charged in water, whereas in an aqueous dispersion of ethylene/acrylic acid copolymer or ethylene/methacrylic acid copolymer dispersed in an alkaline aqueous solution, dissociated carboxyl When the group is neutralized by a counter ion and is usually electrically neutral or slightly negatively charged, the particles are not adsorbed to the paper fibers but penetrate into the paper along with water and become anchored. This effect can strengthen the bond with the film formed on the surface of the paper. As mentioned above, an aqueous dispersion containing one of ethylene/acrylic acid copolymer and ethylene/methacrylic acid copolymer as a dispersoid is safe and easy to handle because it is aqueous, and is suitable for hot-melt coating. Does not cause the stringy phenomenon that is common with agents. Furthermore, when an aqueous dispersion with a fine particle size and relatively high concentration is applied to paper, it is applied continuously to the end surface of the container body from the end surface to the inside of the container without adding excess moisture to the paper. It is possible to form a film with excellent water resistance and adhesion. (Effects of the Invention) According to the present invention, the method for coating the end face of a paper container body according to the first invention includes coating an ethylene/acrylic acid copolymer or an ethylene/methacrylic acid copolymer on the end face of a paper container body. An aqueous dispersion using any one of these was applied and dried by heating to form a continuous coating on the end face from the end face to the inside thereof. Therefore, since it is an aqueous dispersion, it is easy to obtain a liquid with high concentration and low viscosity, so it is extremely easy to apply to end surfaces compared to solvent solutions or hot melt types, and it has excellent waterproofing properties by heating and drying. This has the advantage that a coating having adhesive properties can be continuously formed on the end face of the container body from the end face to the inside thereof. Further, the end surface coating composition for paper container bodies of the second invention includes ethylene/acrylic acid copolymer, ethylene/acrylic acid copolymer, ethylene/
It consists of an aqueous dispersion using any one of methacrylic acid copolymers. Therefore, since it is an aqueous dispersion, it is easy to obtain a liquid with high concentration and low viscosity, so it is easier to apply it to the end surface of a paper container body than a solvent solution or a heat-melting type. It is easy to handle because it does not cause stringing during application, and it is highly safe because it does not use organic solvents, and it forms a film with excellent waterproof and adhesive properties by heating and drying after application. There are effects such as being able to provide a composition that can.

[Brief explanation of drawings]

Figure 1 is a perspective view of the container body, Figure 2 is Figure 1.
Figure 3 is a cross-sectional view showing an example of a state in which a coating is formed on the end face of the line, Figure 3 is a cross-sectional view showing an example of a state in which a film is formed on the end face of the line shown in Figure 1, and Figure 4 is a diagram showing the particle diameter. FIG. 3 is a diagram showing the relationship between particles and the permeability of separated water into paper. 1... Container body, 5... End face, 6... Coating.

Claims (1)

[Claims] 1. An aqueous dispersion containing either an ethylene/acrylic acid copolymer or an ethylene/methacrylic acid copolymer is applied to the end face of a paper container body, and the end face is heated and dried. 1. A method for coating an end surface of a paper container body, the method comprising forming a continuous coating from the end surface to the inside thereof. 2 Ethylene/acrylic acid copolymer, ethylene/
1. An end surface coating composition for a paper container body, characterized by comprising an aqueous dispersion using any one of methacrylic acid copolymers. 3. Claim 2, which is an aqueous dispersion of an ethylene/acrylic acid copolymer or an aqueous dispersion of an ethylene/methacrylic acid copolymer whose carboxyl groups have been neutralized using an alkaline aqueous solution The edge coating composition for a paper container body as described above. 4. The end face coating composition for a paper container body according to claim 3, wherein the alkaline aqueous solution is ammonium hydroxide. 5 The particle size of the ethylene/acrylic acid copolymer is
The edge coating composition for a paper container body according to claim 3, wherein the composition has a particle diameter of 0.03 to 0.5μ. 6 The concentration of ethylene/acrylic acid copolymer is 25~
Claim 5 characterized in that it is 40%.
The edge coating composition for a paper container body according to item 1.