JPH0220344A - Heat-sealable lid material of container for hermetical seal packing - Google Patents

Abstract

PURPOSE:To increase the water resistance of a heat seal bonded part and to keep good adhesiveness for a long period of time by providing a heat seal material layer composed of a specific component to the single surface of a metal foil and providing a coating layer of a silane coupling agent to said layer. CONSTITUTION:A heat seal material layer containing a carboxyl modified material of a saponified ethylene/vinyl acetate copolymer is provided to the single surface of a metal foil and a coating layer of a silane coupling agent is provided to the surface of the heat seal material layer. As the metal foil, an aluminum foil is used in general. It is pref. to fill the heat seal material layer with an inorg. compound in order to secure low temp. sealability. An intermediate layer composed of a resin film of polyethylene or polypropylene may be interposed between the heat seal material layer and the metal foil. By this method, cushion properties at the time of heat-sealing are enhanced and the corrosion of the metal foil due to content such as dressing or mustard is prevented. Printing necessary in usual is applied to the other surface and a corrosionproof coat layer is further provided to the surface thereof. A container is made of glass, metal, ceramic or pottery.

Description

[Detailed description of the invention] Industrial applications The present invention relates to a heat-sealable lid material for a sealed packaging container.

Conventional technology Conventionally, in order to hermetically package powdered, liquid, or viscous foods in glass containers such as bottles, a metal cap is caulked to the mouth of the container after the food is filled, or a metal or synthetic resin cap is used. It was sealed by screwing on a screw cap or by putting a crown on it. Conventionally, a lid material has been coated with a thermoadhesive resin, and this lid material has been bonded to the mouth of a glass container by heat sealing.

Problems to be Solved by the Invention However, the above-mentioned caps and crowns have problems in that they are relatively difficult to open and are expensive. In addition, when heat-sealing the heat-adhesive resin coated on the lid to the mouth of a glass container, if the contents of the container are powder such as powdered milk or instant coffee, there is a gap between the mouth of the container and the lid. Although there is no decrease in the adhesive strength of the adhesive part, if the contents are liquid or viscous substances such as alcohol, juice, or jam, the heat-sealed adhesive part between the container mouth and the lid material may be damaged during storage. Water gets in and the adhesion strength decreases significantly.
In severe cases, there was a problem in that the lid material would peel off.

In particular, when directly thermally bonding a lid to the mouth of a glass container, the surface of the mouth of the glass container is porous;
Due to its relatively weak polarity and poor adhesion, it has recently been developed to use a carboxyl-modified saponified ethylene-vinyl acetate copolymer with improved adhesion as a heat-adhesive resin for lid materials. (For example, JP-A-60-17804
(See Publication No. 2). It is true that such thermoadhesive resins have excellent thermal adhesion properties in a very short time and at relatively low temperatures, but if water enters the bonded area after heat sealing, the adhesiveness may deteriorate. There was a problem in that there was a significant decrease in the adhesive strength and the lid material was easily peeled off from the adhesive interface.

By the way, it is already known to directly coat the mouth of a glass container with a silane coupling agent as a sealant (for example, see Japanese Patent Publication No. 5B-8273). The work of coating the sealant is extremely troublesome, and the surface of the opening of the glass container is porous and uneven, making it difficult to apply the sealant uniformly. Therefore, if the amount of sealing material applied is not sufficient, it will be difficult to achieve a uniform seal due to the unevenness of the opening, variations in parallelism, etc., and if the amount applied is too large,
There was a problem of high cost.

Furthermore, a method is already known in which a metal salt, a silane coupling agent, etc. are used as an anchor coat layer on the opening of a glass container, and this layer is further coated with a thermoadhesive resin (for example, Japanese Patent Publication No. Sho fil-9181 However, according to such conventional methods, some of the resin from the lid remains at the mouth of the container when the container is opened, which may impair the appearance. This increases the number of steps, resulting in poor container productivity and high costs.

Furthermore, conventionally, heat-sealable lidding materials (for example, JP-A-80-58
No. 549), as well as heat-sealing lid materials comprising a heat-sealing material layer made of an ionomer composition containing a silane coupling agent applied to one side of a metal foil through an ionomer layer (for example, JP-A No. (Refer to Publication No. 104971)
is already known, but when a silane coupling agent is mixed into the heat sealing resin of the lid material in this way, the silane coupling agent bleeds onto the surface of the heat sealing material layer, is diffused to the surface side, and becomes concentrated. Therefore, the amount of silane coupling agent present on the surface of the heat sealing material layer increases; however, the amount of silane coupling agent present varies depending on conditions such as the processing temperature during heat sealing, or depending on the time the lid material is left. ,
There was a problem in that it was very difficult to adjust the amount of silane coupling agent present on the surface to be heat sealed.

The purpose of the present invention is to solve the problems of the prior art described above, and to provide a material that has extremely excellent adhesion even to a porous and relatively weakly polar adhered surface such as the mouth of a glass container. Not only can the lidding material be heat-sealed to the mouth of the sealed packaging container in a short time, but also the amount of silane coupling agent that should be present on the surface of the heat-sealing material layer can be easily adjusted. Therefore, the adhesive force between the heat sealing material layer and the opening of the glass container is greatly strengthened, and the content of the container is a liquid or viscous substance such as alcohol, juice, or jam. Even in such cases, it is possible to reliably prevent water from entering the heat-sealed bonded area, greatly increasing the water resistance of the heat-sealed bonded area, and reducing the loss of adhesion in a water environment. An object of the present invention is to provide a heat-sealing lid material for a sealed packaging container that can maintain good adhesion for a long period of time and has excellent sealing properties.

Means for Solving the Problems In order to achieve the above object, the heat-sealing lid material for a sealed packaging container according to the present invention includes a carboxyl modified product of a saponified ethylene-vinyl acetate copolymer on one side of a metal foil. The heat sealing material layer is provided with a heat sealing material layer containing the heat sealing material, and a coating layer made of a silane coupling agent is provided on the surface of the heat sealing material layer.

As the metal foil, aluminum foil is usually used, but other metal foils may be used. For aluminum foil,
Its thickness is 5-200/ffi, preferably 20-6
It is 0m. When metal foil is used as the base material of the heat sealing material, it has excellent barrier properties and can effectively preserve the contents of desserts, cooked foods, etc. for a long period of time.

Further, as the carboxyl modified product of the saponified ethylene-vinyl acetate copolymer which is the main component of the heat sealing material layer, the following is used.

That is, melt index 1-300g/10
An ethylene-vinyl acetate copolymer having a hydroxyl equivalent weight of 1238-[i5T] and an ethylene content of 50 to 97% by weight, preferably 60 to 82% by weight is saponified to obtain a hydroxyl equivalent of 100%. A saponified product having an amount of ~3000 g/1 equivalent, preferably 200 to 1000 g/1 equivalent is prepared, and then a product obtained by graft polymerizing a carboxylic acid group-containing unsaturated compound to this saponified product is used.

Here, examples of the carboxylic acid group-containing unsaturated compound include acrylic acid, methacrylic acid, crotonic acid, itaconic acid, maleic acid, maleic anhydride, and citraconic acid. The obtained graft polymer, that is, the carboxyl modified product of the saponified ethylene-vinyl acetate copolymer, has an acid equivalent of 50,000 g/1 equivalent or less, preferably 1,000 to 30,000 g/1 equivalent as a whole.

In addition, in order to prevent so-called blocking, synthetic resins other than the above-mentioned resins may be blended into the heat sealing material depending on the case.

Moreover, as the above-mentioned silane coupling agent, one represented by the general chemical structural formula, Y RS i Xa is used.

In the formula, R is an alkyl group; For example, mercapto, amino, epoxy, vinyl, methacrylic, etc.

As the silane coupling agent, at least one silane compound selected from the group consisting of mercaptosilane, aminosilane, epoxysilane, vinylsilane, and methacrylsilane having the above general formula is used.

Specific examples of the silane coupling agent include γ-mercaptopropyltrimethoxysilane, γaminopropyltriethoxysilane, N-β(aminoethyl)γ-aminopropyltrimethoxysilane, γ-glycidoxypropyltrimethoxysilane, Examples include γ-glycidoxypropyltriethoxysilane, vinyltriethoxysilane, vinyltris(β-methoxyethoxy)silane, and γ-methacryloxypropyltrimethoxysilane.

The thickness of the above-mentioned heat sealing material layer is usually 5~aoo p.

Preferably it is 20 to 100 μm, and the thickness of the coating layer made of the silane coupling agent is usually 0.01 to 100 μm.
20 ro, preferably 0.1 to 10 ro.

Here, if the thickness of the coating layer made of the silane coupling agent is less than o or oi, it will be too thin and will not provide sufficient water resistance to the heat-sealed joint, resulting in poor adhesion in a water environment. Therefore, it is not desirable.

On the other hand, when the thickness of the coating layer made of the silane coupling agent exceeds 201 II/I, it is not preferable because not only the adhesiveness does not change much in an aqueous environment but also the cost increases.

To provide a coating layer made of a silane coupling agent on the surface of the heat sealing material layer, for example, a spray method, a dipping method,
Alternatively, a roll coating method or the like may be used.

Further, the heat sealing material layer is preferably filled with an inorganic compound in order to ensure low-temperature sealability and to prevent blocking during punching by press.

Here, examples of inorganic compounds include oxides, hydroxides, carbonates, and sulfates of magnesium, calcium, aluminum, titanium, and silicon, talc, clay, feldspar powder, mica, pallite, etc., and particularly preferred. Calcium carbonate, talc is used.

The average particle size of these inorganic compounds is 0.1 to 5071177,
It is preferably 0.5 to 30 m, and the inorganic compound is preferably 30 parts by weight or less, usually 0.1 to 20 parts by weight, per 100 parts by weight of a resin made of a carboxyl modified product of saponified ethylene-vinyl acetate copolymer. , preferably 1 to 10 parts by weight.

The carboxyl modified product and the inorganic compound are mixed using, for example, a single-screw extruder, a twin-screw extruder, a Banbury mixer, a kneader, etc., usually at a temperature of 15 to 200°C.

In addition, in order to provide a heat sealing material layer on one side of the metal foil, the above-mentioned heat sealing material is processed into a film in advance, and this film is coated with a polyester-isocyanate two-component reaction type, for example, on one side of the metal foil. They may be bonded using an adhesive such as an adhesive, or they may be bonded directly by extruding a molten heat sealing material onto one side of the metal foil using an extruder.

Further, if necessary, an intermediate layer made of a resin film such as polyethylene or polypropylene may be interposed between the heat sealing material layer and the metal foil. This improves cushioning properties during heat sealing and prevents corrosion of the metal foil due to contents such as dressing and mustard.

Note that the other side of the metal foil is usually subjected to necessary printing, and furthermore, an anticorrosive coating layer is provided on this surface.

The above-mentioned lid material having a coating layer made of a silane coupling agent is continuously stamped into a shape and size that covers the mouth of a glass container.

The hermetically sealed packaging container sealed by the heat-sealable lid according to the present invention is made of, for example, glass, metal, ceramic, or earthenware.

FIGS. 1 and 2 show specific examples of the heat-sealing lid material according to the present invention. First, the lid material shown in Fig. 1 has a heat sealing material layer (2) on one side of an aluminum foil (1) and an adhesive layer (
3), and a coating layer (5) of a silane coupling agent is provided on the surface of this heat sealing material layer (2). An anticorrosive coating layer (4) is applied to the other side of the aluminum foil (1).

The lid shown in Figure 2 has almost the same structure as the lid shown in Figure 1, but in order to prevent corrosion of the aluminum foil (1) by the contents, a polyethylene film is placed on one side of the aluminum foil (1). A heat sealing material layer (2) is provided on this middle layer (7) via an adhesive layer (3), and a silane cup is provided on the surface of this heat sealing material layer (2). A coating layer (5) of a ring agent is provided, a printing layer (6) is provided on the other side of the aluminum foil (1), and an anticorrosion coating layer (4) is provided on the surface.

According to the heat sealing lid material of the present invention, a coating layer (5) of a silane coupling agent is provided on the surface of the heat sealing material layer (2) containing a carboxyl modified product of a saponified ethylene-vinyl acetate copolymer. Because of this, there is little decrease in adhesive strength in a water environment, and good adhesion can be maintained for a long period of time, resulting in excellent sealing properties.This is thought to be due to the following reasons. .

That is, for example, heat sealing materials applied to lids of glass containers contain -〇H groups and -CO because the upper surface of the mouth of the glass container is porous, has relatively weak polarity, and has poor adhesive properties.
Resins containing many functional groups such as OH groups, such as carboxyl-modified saponified ethylene-vinyl acetate copolymers in which 10H groups or -COOH groups are introduced into polyvinyl acetate, are used to improve adhesion. However, even if such resin is used, the processing time for heat sealing is very short, so the functional groups in the heat sealing resin interact with the glass component on the top surface of the mouth of the glass container and form hydrogen bonds. It is thought that the resin adheres to the glass surface mainly due to van der Waals force, even though it is not formed. In particular, immediately after heat sealing, the molecular segments of the heat sealing resin undergo thermal movement and their orientation is disordered, so that hydrogen bonds occur and they are adhered primarily by van der Waals forces. After heat sealing, the functional groups are gradually arranged on the glass surface over time, form hydrogen bonds with the silanol groups on the glass surface, and the adhesive strength gradually increases.

However, when the contents of a glass container are liquid or viscous, the glass surface at the container mouth is hydrophilic, so water molecules tend to get wet, forming a multi-molecular layer of water molecules, which makes heat sealing difficult. The van der Waals forces at the bond are weakened and the hydrogen bonds are also broken, resulting in a significant decrease in adhesive strength.

On the other hand, according to the heat-sealing lid material of the present invention, since the silane coupling agent is present on the surface to be thermally bonded to the mouth of the glass container, the heat-sealing resin of the lid material and the surface of the glass container are bonded together. The adhesive force with the mouth surface becomes very strong, and therefore water can be effectively prevented from entering the adhesive interface, greatly increasing the water resistance of the heat-sealed adhesive part.

Example Next, examples of the present invention will be described together with comparative examples.

Example 1 As shown in FIG. 1, on the other side of an aluminum foil (1) having a thickness of 50/Iff and having an anticorrosion coating layer (4) on one side,
A heat sealing material film which is a modified product obtained by graft polymerizing acrylic acid to a saponified product of ethylene-vinyl acetate copolymer, and which is uniformly dispersed and mixed with 5% by weight of calcium carbonate having an average particle size of about 1IyI. Made by Dumilan (registered trademark, manufactured by Takeda Pharmaceutical Co., Ltd.), thickness 50/I
After providing the heat sealing material layer (2) of ff by dry lamination via the adhesive layer (3), an amino-based silane coupling agent (trade name: Al10) is applied to the surface of the heat sealing material layer (2).
0, manufactured by Nippon Unicar Co., Ltd.) by a roll coating method and dried at 100°C for 5 minutes.
Silane coupling agent coating layers (5) having various thicknesses were formed to produce lid materials (samples Nos. 011 to 5).

The various lid materials thus obtained were punched out using a punching press into a predetermined shape and size corresponding to the opening (lO) of a glass container.

Next, the glass container was filled with water at 40°C, and the lid material was placed at the mouth of the container at a temperature of 200°C and a pressure of 160 kgf.
The lids were heated and pressurized for 2 seconds under the conditions of 1000 ml/piece, and these lids were directly bonded to the mouth (10) of the glass container by heat sealing to seal the container. Then, the peel strength of the lid material immediately after heat sealing and the peel strength of the lid material after the sealed glass container was left in an inverted state at 40° C. for 30 days were measured, and are shown in the table below.

Example 2 In this example, as shown in Figure 1, the same heat sealing material layer (2) as in Example 1 was applied on one side of the aluminum foil (1) via an adhesive layer (8). After dry lamination, an epoxy-based silane coupling agent (trade name A-187, manufactured by Nippon Unicar Co., Ltd.) was applied to the surface of the heat sealing material layer (2) by a roll coating method.
By drying at 0°C for 5 minutes, the thickness is 0.4717
A silane coupling agent coating layer (5) of No. 11 was formed to produce a lid material (sample No. 8).

The lid material thus obtained was subjected to a sealed packaging test in the same manner as in Example 1, and the results are shown in the table below.

Comparative Example For comparison, the same heat sealing material layer (
2) was provided by dry lamination, but the lid materials were not provided with the silane coupling agent coating layer (5), and a sealed packaging test was conducted on these lid materials in the same manner as in Example 1. The results obtained are also shown in the table below.

(Margins below) As is clear from the table above, according to the heat-sealing lid material of the present invention, a coating layer made of a silane coupling agent is provided on the surface of the heat-sealing material layer. It has very good adhesion to the surface, and even after a glass container filled with water is stored upside down for a long time, the adhesion of the lid material does not decrease, and it has good water resistance and excellent sealing performance.

On the other hand, according to a comparative example lid material using a heat sealing material that does not use a silane coupling agent, the lid material peels off when a glass container is stored upside down for a long time, resulting in poor water resistance. Met.

Effects of the Invention As described above, the heat-sealing lid material for a sealed packaging container according to the present invention has a heat-sealing material layer made of a carboxyl modified product of a saponified ethylene-vinyl acetate copolymer provided on one side of the metal foil. Since a coating layer made of a silane coupling agent is provided on the surface of the heat sealing material layer, it is suitable even for adhered surfaces that are porous and have relatively weak polarity, such as the mouth of a glass container. It has very good adhesive properties, and not only can the lid material be heat-sealed to the mouth of the sealed packaging container in a short time, but it also allows the silane coupling agent to be present on the surface of the heat-sealing material layer. The amount can be easily adjusted and the adhesive force can be increased reliably, which greatly strengthens the adhesive force between the heat sealant layer and the mouth of the glass container, and therefore the mouth of the glass container is generally The part is hydrophilic, and in addition, even if the contents of the container are liquid or viscous, such as alcohol, alcohol, or jam, it prevents water from entering the heat-sealed part. The water resistance of the heat-sealed area is greatly increased.
There is little decrease in adhesive strength in a water environment, a good adhesive state can be maintained for a long period of time, and it has excellent sealing properties.

Further, according to the heat-sealing lid material of the present invention, after filling food with food as in the past, a metal cap can be caulked to the mouth of the container, a metal or synthetic resin screw cap can be screwed, or a crown can be screwed onto the mouth of the container. Since the container is not covered or sealed, it is easy to open, and the sealing cost of the hermetically sealed packaging container is reduced because no cap or crown is used.

Furthermore, there is no resin left at the container mouth when the container is opened, so the appearance of the container mouth is clean after opening, and heat sealing can be performed at a relatively low temperature, making it easy to install filling and sealing equipment. This has the effect of reducing costs and operating costs, and improving the workability of filling and sealing.

[Brief explanation of the drawing]

FIG. 1 is a partially enlarged sectional view showing a specific example of the product of the present invention, and FIG. 2 is a partially enlarged sectional view showing another specific example. (1)... Aluminum foil, (2)... Heat sealing material layer, (8)... Adhesive layer, (4)... Anti-corrosion coating layer,
(5)...silane coupling agent coating layer. Applicants for the above patents: Takeda Pharmaceutical Company Limited Showa Aluminum Co., Ltd.

Claims (1)

[Claims] A heat sealing material layer containing a carboxyl modified product of saponified ethylene-vinyl acetate copolymer is provided on one side of the metal foil,
A heat-sealing lid material for a sealed packaging container, characterized in that a coating layer made of a silane coupling agent is provided on the surface of the heat-sealing material layer.