JPH0212825B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention is a method of sealing and heat-sealing a container made of a single layer or laminated with other materials of a material whose main component is a chlorine-containing vinyl compound polymer (it may be a single composition or may be a blend of multiple types of resins). The present invention relates to an easy-to-open container having a heat-sealed part that is present in the sealed part during sealing and can be easily peeled off without destroying the container base material when the container is later opened. Resins such as chlorine-containing vinyl (vinylidene-containing) compound polymers, polyolefins such as polystyrene, polyethylene, and polypropylene have excellent appearance, mechanical strength, moldability, ease of packaging design, and economic efficiency, and have been widely used in various packaging containers. It is used. Among these containers, so-called seal pack packaging containers, which are filled with contents and heat-sealed, are attracting attention in the packaging industry. This is because packaging is simple, clean, easy to handle, and can be frozen. However, when vinyl chloride polymers are heat sealed together, depending on the sealing conditions, Either a completely sealed state in which both interfaces are fused (difficult to peel), or a state in which the sealing is insufficient and has only extremely weak peel strength to the extent of no practical use can be achieved.
Furthermore, when sealing a combination of different materials such as vinyl chloride polymer and polystyrene or vinyl chloride polymer and polyolefin, the sealing strength necessary for a container cannot be obtained due to their poor compatibility with each other, making it impractical. I am not satisfied with this. There are also aluminum foils coated with hot-melt adhesives or solution-based adhesives.
This was a food hygiene issue. The present invention improves the above-mentioned drawbacks, has sufficient sealing strength to completely protect the contents during product manufacturing and distribution, and destroys the container base material when removing the contents. The purpose of the present invention is to provide a sealed container whose sealed portion can be easily peeled off without causing any damage. mass 60
10 to 100 parts by weight of a modified resin obtained by subjecting ~5% by weight to grafting conditions, and (2) an ethylene copolymer containing an unsaturated carboxylic acid or its derivative 90
An easily openable container having at least one container constituent material made of a material containing a chlorine-containing vinyl compound polymer as a main component, characterized by having a removable sealed heat-sealed part containing 0 parts by weight as a main component. It is. Examples of containers to which the present invention can be applied include molded containers obtained by injection molding, blow molding, vacuum or pressure molding, etc., with the filling opening made of a film such as aluminum foil or polyethylene terephthalate. One example is one that is covered and sealed (Fig. 1). By using the heat sealing material of the present invention in the sealing part of such a container, a sealed container that has sufficient sealing strength while being filled with contents and has easy peelability when taking out the contents is obtained. can be provided. The chlorine-containing vinyl compound polymer that is at least one constituent material of the sealed packaging container having a heat-sealed portion in the present invention includes, for example, vinyl chloride resin, vinylidene chloride resin, vinylidene chloride-vinyl chloride copolymer, and vinylidene chloride. -vinyl acetate copolymer,
There are vinyl chloride-vinyl acetate copolymers, graft copolymers in which vinyl chloride is grafted onto ethylene-vinyl acetate copolymers, and the like. In addition, various auxiliary agents such as plasticizers and stabilizers may be added to these polymers. Furthermore, by blending these polymers with other miscible resins or rubbers in an amount of less than 50% by weight, a wide range of qualities can be imparted. Next, the aromatic vinyl monomers that can be used in producing the aromatic vinyl monomer-modified EVA, which is the component (1), which constitutes the heat sealing material of the present invention are as follows: General formula (in the formula, R ₁ is a hydrogen atom or has 1 to 1 carbon atoms)
4 alkyl group, R ₂ to R ₆ are each a hydrogen atom,
(representing a halogen atom or an alkyl group having 1 to 4 carbon atoms) such as styrene, nuclear-substituted styrene such as methylstyrene, isopropylstyrene, chlorostyrene,
Examples of α-substituted styrene include α-methylstyrene and α-ethylstyrene. In addition to styrene, a mixture system with a vinyl monomer other than styrene such as acrylic ester is also applicable. In addition, the EVA to be modified is not particularly limited, and can be produced by any conventional method such as high-pressure polymerization under 1000 to 3000 atmospheres or solution or emulsion polymerization under 1000 to 400 atmospheres. It can be anything. The vinyl acetate content of this EVA is 2
If the content is 50% by weight, a modified resin that achieves the object of the present invention can be obtained satisfactorily, but a content in the range of 5 to 35% by weight is particularly preferred. 0.5 to 150 expressed in melt index (MI)
g/10 minutes is preferable. The amount of modified aromatic vinyl monomer is 40 to 95% by weight of EVA and 60 to 5% by weight of aromatic vinyl monomer unit, based on the total weight of this and EVA. If the amount of the aromatic vinyl monomer is less than 5% by weight, the effect of the present invention will not be achieved, while if it exceeds 60% by weight, the material strength (flexibility) and film molding processability of the modified resin will deteriorate, which is undesirable. . EVA with aromatic vinyl monomer in the present invention
General modification techniques such as melt grafting using an extruder, grafting by radiation irradiation, and grafting in a solution are used for the modification, and examples thereof include the following techniques. That is, in an aqueous suspension containing 40-95% by weight of EVA particles (generally 1-7 mm, preferably 2-5 mm in diameter), 5-60% by weight of aromatic vinyl monomer and a polymerization initiator. , by impregnating at least 80% by weight of the vinyl monomer into the polymer particles and then polymerizing the monomer.
EVA is obtained. The method of impregnating the polymerization initiator and monomer used here,
Details of the polymerization method are as follows. Radical polymerization initiator EVA particles are impregnated with an aromatic vinyl monomer in an aqueous medium without substantially polymerizing the monomer, and then this aqueous dispersion is heated to polymerize the monomer. , polymerization is usually promoted by a radical polymerization initiator. This polymerization initiator must be able to be impregnated into the EVA particles together with the monomer. Therefore, the radical polymerization initiator used is oil-soluble. Preferably, the separation temperature is 50 to 150°C to obtain a half-life of 10 hours. Here, "decomposition temperature to obtain a half-life of 10 hours" means that when 0.1 mole of a polymerization initiator is added to 1 liter of benzene and left at a certain temperature for 10 hours, the decomposition rate of the polymerization initiator is It means that temperature which is 50%. It goes without saying that if the impregnation step is carried out at a sufficiently low temperature, a polymerization initiator that is more decomposable at lower temperatures can be used. Specific examples of radical polymerization initiators that can be used include lauroyl peroxide (62°C), benzoyl peroxide (74°C), t-butyl peroxybenzoate (104°C), dicumyl peroxide (117°C), etc. There are organic peroxides such as, azo compounds such as azobisisobutyronitrile (65°C), and others (the temperature in the above-mentioned cup is the above-mentioned half-life temperature). There is no limit to the amount of polymerization initiator, but it is generally about 0.01 to 10% by weight of the monomer weight used, usually 0.1 to 10% by weight.
It is about 2.0% by weight. The polymerization initiator is usually used dissolved in the vinyl monomer. Impregnation of EVA particles with aromatic vinyl monomers in an aqueous medium A typical method for impregnating EVA particles with vinyl monomers in an aqueous medium involves adding an aqueous dispersion of EVA particles, preferably a polymerization initiator (and The process consists of adding the monomer in which other additives (if necessary) are dissolved and stirring. Another method is to add EVA particles to an aqueous dispersion of monomers dissolved in a polymerization initiator and stir the mixture. During the impregnation process, virtually no polymerization occurs.
It should be operated at a sufficiently low temperature in relation to the decomposition temperature of the polymerization initiator used, generally between room temperature and 100°C. In this process, the amount of free monomer is equal to the amount of monomer used.
Impregnate the monomer to less than 20% by weight.
Since EVA is relatively compatible with vinyl monomers,
Even if less than 20% by weight of monomers are free before the start of polymerization, these monomers will impregnate the EVA particles during polymerization, so the polymer particles obtained by polymerizing these monomers will not be modified. It does not precipitate independently from the EVA particles. The impregnation time is usually about 2 to 8 hours. The content of EVA particles and vinyl monomer in the aqueous dispersion is usually about 5 to 100 parts by weight per 100 parts by weight of water. Such aqueous dispersions can be maintained in a stable dispersed state simply by sufficient stirring, but dispersions can be prepared more easily and stably by using an appropriate suspension stabilizer. can. In this case, suspension stabilizers that can be used generally include those that can be used as suspension stabilizers during aqueous suspension polymerization of vinyl monomers, and specific examples include polyvinyl alcohol, methyl cellulose,
Water-soluble polymer substances such as hydroxycellulose, anionic surfactants such as alkylbenzene sulfonates, nonionic surfactants such as polyoxyethylene alkyl ethers, or water-insoluble inorganic salts such as magnesium oxide and calcium phosphate, etc. 0.01 for water alone or in combination
It is used in amounts of ~10% by weight. Vinyl monomer (and polymerization initiator) in EVA particles
When impregnating, plasticity, lubricant, antioxidant,
(These auxiliary materials may already be added to the EVA, or may be added after polymerization). Polymerization If the aqueous dispersion thus prepared is heated to a temperature above which the polymerization initiator used decomposes at an appropriate rate, the impregnated vinyl monomers will polymerize and be modified. EVA particles are generated. Since radical polymerization is to be carried out, heating should be carried out in an atmosphere substantially free of oxygen, and it is preferable to appropriately stir the aqueous dispersion during polymerization. The polymerization temperature is determined in relation to the decomposition temperature of the polymerization initiator used, but is generally about 50 to 150°C.
The polymerization temperature need not be constant throughout the polymerization period. The polymerization time is usually about 2 to 10 hours. The polymerization pressure is usually about normal pressure to 10 kg/cm ² . In addition, n-butyl mercaptan,
It is preferable to add a chain transfer agent such as n-dodecylmercaptan or t-dodecylmercaptan. After polymerization, if a treatment similar to the post-treatment of normal aqueous suspension polymerization of vinyl monomers (e.g. styrene) is performed, the shape of the EVA particles used will be maintained almost unchanged and can be used immediately as a molding material. Modified EVA particles that can be obtained are obtained. The modified EVA (i.e., component (1)) in the present invention is EVA containing a polymer made of uniformly dispersed vinyl monomers, or an EVA in which vinyl monomers are grafted onto the polymer backbone of EVA, or It is estimated that the composition is a mixture of
It does not exist separately from EVA particles. When using aromatic vinyl monomer-modified EVA, unmodified EVA may be mixed with the modified EVA as long as the monomer unit content is within the range of 5 to 60% by weight. The effects of the present invention can be achieved. Therefore, component (1) of the present invention is directly modified.
In addition to EVA, it also includes those diluted with unmodified EVA and having an aromatic vinyl monomer content in the range of 5 to 60% by weight. In addition, the ethylene copolymer containing an unsaturated carboxylic acid or its derivative, which is another component (2) constituting the heat sealing material used in the present invention, refers to ethylene (in some cases, ethylene and other α-olefin) and a copolymerizable unsaturated carboxylic acid or a derivative thereof (hereinafter referred to as unsaturated organic acids). In this case, the content of ethylene is 50
% by weight or more. As used herein, the term copolymers refers to random, block and graft copolymers. These alone are
Alternatively, two or more types can be used in combination. Unsaturated organic acids mean unsaturated organic salts such as acrylic acid, methacrylic acid, fumaric acid, maleic acid, and itaconic acid, or derivatives thereof such as esters, metal salts, amides, imides, and anhydrides. Specific examples of ethylene copolymers containing unsaturated organic acids include ethylene-acrylic acid copolymers, ethylene-methacrylic acid copolymers and metal ion crosslinked resins thereof, ethylene-ethyl acrylate copolymers, maleic anhydride, etc. Examples include acid-grafted polyethylene, maleic anhydride-grafted ethylene-vinyl acetate copolymer, and the like. When using the heat sealing material used in the present invention, other polymers, such as MI0 .5 to 100 g/10 min of low density polyethylene can be added. Furthermore, thermoplastic elastomers such as ethylene-propylene copolymer rubber, styrene-butadiene copolymer rubber, and styrene-conjugated diolefin block copolymer rubber can be added for the purpose of imparting impact resistance. The blending ratio of the modified EVA, which is component (1), and the unsaturated organic acid-containing ethylene copolymer, which is component (2), is 10 to 100 parts by weight of component (1) to 90 parts by weight of component (2). ~
0 parts by weight, preferably 50 to 100 parts by weight of component (1) and 50 to 0 parts by weight of component (2). If component (1) is less than 10 parts by weight, it is not preferable because the peel strength is highly dependent on the sealing temperature. Next, the mixed composition of each of these components is prepared using a batch kneading machine such as a Banbury mixer or a roll.
It can be easily obtained using a continuous extruder such as a single screw extruder or a twin screw extruder. There is no particular limitation on the order of blending; for example, for a composition consisting of modified EVA, unmodified EVA, and an ethylene copolymer containing unsaturated organic acids, these three components may be blended simultaneously in a kneader. Alternatively, a kneaded product of modified EVA and unmodified EVA (corresponding to component (1)) may be prepared and the unsaturated organic acid-containing ethylene copolymer may be mixed therein. Alternatively, modified EVA may be mixed in a kneader for mixing the unsaturated organic acid-containing ethylene copolymer and unmodified EVA. Next, as briefly explained above with reference to FIG. It is sufficient that these materials are used in the sealing part, and other parts may be made of paper, metal foil, or other resins (polyamide, cellophane, polyethylene terephthalate, polycarbonate, etc.). However, due to the production process residue, generally a laminated material is used in which paper, metal foil, other resin, etc. and a chlorine-containing vinyl compound polymer are laminated, and this chlorine-containing vinyl compound polymer is used. The layer is formed so that it lies inside the container. Of course, a container made only of a chlorine-containing vinyl compound polymer may also be used. Furthermore, the method of using the sealing material of the present invention achieves the object if it is used for at least one of the sealing part of the container and the sealing part of the lid. Moreover, although it is sufficient to use it only for the sealing part, it is generally used in the form of a laminate with other materials. As a method for forming the sealing material of the present invention on either the container or the sealing portion of the lid, a film is formed by a known film forming method such as an inflation method or a T-die method, and this film is then applied to the container. or by extrusion coating, dry lamination, wet lamination, hot melt coating, or both. Examples of methods include coextrusion lamination or coextrusion coating. The sealing portion of the container can be sealed using known techniques such as pressurized heat sealing using a heat sealer, impact heat sealing, dielectric sealing, and ultrasonic sealing. It will be done. Hereinafter, the effects of the present invention will be explained with reference to Examples. Since the evaluation of easy peelability was carried out using sheets or films, such examples will be shown. Example 1 20 kg of pure water and 600 g of tribasic calcium phosphate and 0.6 g of sodium dodecylbenzenesulfonate as suspending agents were added to an autoclave with a capacity of 50 mm to form an aqueous medium, and to this was added ethylene-vinyl acetate copolymer (MI15 g). /10 minutes, specific gravity 0.950, vinyl acetate content 28% by weight) 7 kg of particles were suspended by stirring. Separately, as a polymerization initiator, 3 g of benzoyl peroxide and 3 g of t-butyl peroxyvivalate were dissolved in 3 kg of styrene, and this was added to the suspension system, and the temperature inside the autoclave was raised to 50°C. The mixture was held for 3 hours to impregnate styrene containing a polymerization initiator into the ethylene-vinyl acetate copolymer particles. This aqueous suspension was heated to 60°C and maintained at this temperature for 3 hours and then at 90°C for 7 hours to complete polymerization. The styrene content in the obtained modified particles is approximately
It was confirmed that 30% by weight was present (reaction rate omitted).
100%). The modified resin alone and the modified resin and ethylene-ethyl acrylate copolymer (manufactured by Nippon Unicar Co., Ltd.)
A predetermined amount of DPDJ8026 (hereinafter referred to as EEA) was blended using a 30 mm diameter T-die film forming machine.
Each film was formed into a film with a thickness of about 50μ at a molding temperature of 160 to 180°C. These films and 7μ thick aluminum foil were pasted together with an adhesive to form a laminated film.
The modified resin layer of this laminated film is used as a sealing surface,
A 0.2 mm thick polyvinyl chloride sheet was heat sealed. The sealing conditions were as follows: a hot plate heat sealer was used, the sealing width was 5 mm, the sealing pressure was 2 Kg/cm ² , the sealing time was 2 seconds, and the sealing temperature was 130 to 190°C. Peel strength was measured using a Schottsper type tensile tester at a sample width of 15 mm and a tensile speed.
The 180 degree peel strength was measured at 23°C at 300 mm/min. The results are shown in Table 1.

[Table] Example 2 The styrene content was approximately reduced by the method in accordance with Example 1.
A modified resin containing 50% by weight (reaction rate approximately 100%) was obtained. The modified resin and ethylene-vinyl acetate copolymer (MI 15 g/10 min, specific gravity 0.943, vinyl acetate content
After blending a predetermined amount of (20% by weight) and EEA,
Each film was about 50μ. This film and a 7 μm thick aluminum foil were pasted together with an adhesive, the modified resin layer was used as the sealing surface, a 0.20 mm thick polyvinyl chloride sheet was heat sealed, and the peel strength was measured. The test method is the same as in Example 1. The results are shown in Table 2.

[Table] Comparative example 1 Low density polyethylene (MI8g/10min, specific gravity
Modified low-density polyethylene containing approximately 30% by weight of styrene (reaction rate approximately 100%) was obtained in accordance with Example 1 using particles (0.918) and styrene. Samples of the modified resin alone, a blend of 50 parts by weight of the modified resin and 50 parts by weight of EEA, ethylene-vinyl acetate copolymer (MI 15 g/10 min, specific gravity 0.943, vinyl acetate content 20% by weight) alone, and Samples obtained by blending 50 parts by weight of the ethylene-vinyl acetate copolymer and 50 parts by weight of EEA were made into films each having a thickness of approximately 50 μm, a laminated film was made with this film and aluminum foil having a thickness of 7 μm, and the modified resin layer was sealed. Heat-seal a 0.2 mm thick polyvinyl chloride sheet as the surface.
Its peel strength was measured. The test method is the same as in Example 1. The results are shown in Table 3. The modified low density polyethylene alone and together with it
Blends with EEA and ethylene-vinyl acetate copolymers alone have too weak a sealing strength with the adherend (polyvinyl chloride) and are unsuitable for the purpose of the present invention. Also, ethylene-vinyl acetate copolymer and
EEA blend systems have a practical problem because the peel strength has a very large temperature dependence.

[Table] Example 3 Using a method based on Example 1, ethylene-vinyl acetate copolymer (MI 30 g/10 min, specific gravity 0.953, vinyl acetate content 33% by weight) was used to produce a styrene content of 10%.
% modified resin by weight was obtained. The modified resin alone, a blend of 20 parts by weight of the modified resin and 80 parts by weight of ethylene-vinyl acetate copolymer (MI2g/10 min, specific gravity 0.938, vinyl acetate content 16% by weight), and the modified resin 20
Approximately 50μ of a blend of 80 parts by weight and 80 parts by weight of EEA
A laminated film was made from this film and a 7μ thick aluminum foil, and a 0.2mm thick polyvinyl chloride sheet was heat sealed using the modified resin layer as the sealing surface, and its peel strength was measured. The test method is the same as in Example 1. The results are shown in Table 4.

【table】 [Brief explanation of drawings]

FIG. 1 represents a molded container. 1a and 1b are sealing layers (at least one is the sealing material of the present invention), 2
a and 2b are container base materials (one of them may be a single layer), and 3 is a sealed portion.

Claims (1)

[Claims] 1 (1) 10 to 100 parts by weight of a modified resin obtained by subjecting 40 to 95% by weight of an ethylene-vinyl acetate copolymer and 60 to 5% by weight of an aromatic vinyl monomer under grafting conditions;
and (2) a chlorine-containing vinyl compound polymer characterized by having a removable hermetically sealed portion consisting mainly of 90 to 0 parts by weight of an ethylene copolymer containing an unsaturated carboxylic acid or a derivative thereof. An easy-to-open container whose main component is at least one container constituent material.