JPS6248698B2 - - Google Patents

Description

[Detailed description of the invention]

In the present invention, when sealing and heat-sealing a single-layer or laminated container made of a material mainly composed of propylene polymer,
The present invention relates to a heat-sealing material that is present in the sealing portion for heat-sealing and can be easily peeled off without destroying the container base material when the container is later opened. Polyolefins such as vinyl chloride (vinylidene) resin, polystyrene, polyethylene (hereinafter referred to as PE), and polypropylene (hereinafter referred to as PP) have excellent appearance, mechanical strength, moldability, packaging workability, economic efficiency, etc. It is widely used in various packaging containers. In containers made of these resins, dairy products,
BACKGROUND ART So-called seal pack packaging containers, which are filled with foods such as confectionery, tofu, and soft drinks and then heat-sealed, are attracting attention in the food packaging industry. This is because the packaging is simple, clean, easy to handle, and can be frozen. However, when PP, PE, or PS are sealed together, it is completely dependent 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, in the case of sealing using a combination of different materials such as PP and PE or PP and PS, the sealing strength necessary for a container cannot be obtained due to poor compatibility with each other, and this is insufficient for practical use. There are also aluminum foils coated with hot-melt adhesives or solution-based adhesives.
This was a food hygiene issue. The inventors of the present invention have improved the above-mentioned drawbacks by creating a seal that has sufficient sealing strength to completely protect the contents during the product manufacturing and distribution process, and that the container base In Japanese Patent Application No. 166393/1989, we proposed a sealed container whose sealed portion could be easily peeled off without destroying the container. Subsequently, as a result of intensive research into sealing materials to be used in the easily peelable heat-sealed parts of packaging containers that have a heat-sealed part made of a material whose main component is a propylene polymer, we found (1) A material with excellent balance between adhesive strength and peel strength, (2) ability to be peeled off smoothly (without giving a jerky feeling) with a constant force when peeled off by hand, and (3) excellent film processability. This discovery led to the present invention. That is, a sealing material used for an easily peelable heat-sealed part of a packaging container having a heat-sealed part made of a material mainly composed of a propylene polymer, the sealing material comprising a propylene polymer (A) 10-10. 80 parts by weight and 40-95% by weight of ethylene polymer and aromatic vinyl monomer
60 to 5% by weight of a modified ethylene polymer (B) obtained by grafting conditions. be. Examples of packaging containers used in the present invention include:
One example is a bag made of a laminated film in which the film mainly composed of PP is in contact with the surface of the sealing part (Figure 1). Another example is a molded container obtained by injection molding, blow molding, or injection blow molding, in which the filling opening for the contents is covered and sealed with a film such as aluminum foil or polyethylene terephthalate. Alternatively, it can be sealed with a laminated film in which a film containing PP as the main component is in contact with the surface of the sealed part (Figure 2). 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. In the present invention, the propylene polymer that is the main component material constituting the heat-sealed portion of the sealed packaging container refers to propylene homopolymer, propylene and other α-olefins, ethylene, or polar ethylenically unsaturated monomers. Copolymers (all copolymers containing 50% by weight or more of propylene, including block, random, and graft types). Specifically, for example, isotactic polypropylene, crystalline propylene-ethylene random copolymer, crystalline propylene-ethylene block copolymer, crystalline propylene-butene 1 random copolymer, crystalline propylene-C ₅ ~ C ₁₂ linear α
Representative examples include olefin copolymers, crystalline propylene-ethylene or butene 1- _C5 to _C12 linear α-olefin copolymers, acrylic acid grafted polypropylene, maleic anhydride-modified polypropylene, and the like. Furthermore, these polymers do not exclude those containing other miscible resins or elastomers in an amount of less than 50% by weight. Next, the heat sealing material used in the present invention, a material mainly composed of a propylene polymer (A) and a modified ethylene polymer (B), will be explained. As the propylene polymer constituting component (A), all of the propylene polymers listed above can be used. The aromatic vinyl monomer that can be used in producing the modified ethylene polymer of component (B) has the general formula (wherein R ₁ is a hydrogen atom or an alkyl atom having 1 to 4 carbon atoms). styrenic monomers represented by styrene, nuclear substituted styrenes such _as methylstyrene _, isopropylstyrene, chlorostyrene, Examples of α-substituted styrene include α-methylstyrene and α-ethylstyrene. A mixed system of styrene and a non-aromatic vinyl monomer such as acrylic acid is also applied (in this case, the aromatic vinyl monomer is
weight% or more). In addition, the ethylene polymers to be modified include ethylene homopolymers and copolymers of ethylene with other α-olefins or polar ethylenically unsaturated monomers (both copolymers containing 50% by weight or more of ethylene). (including block, random, and graft types). Specifically, for example, high-pressure, medium- or low-pressure polyethylene, ethylene-propylene copolymer, ethylene-propylene-butene 1 random copolymer, ethylene-vinyl acetate copolymer, ethylene-(meth)acrylic acid copolymer, ethylene-
Typical examples include (meth)acrylic acid ester copolymers, unsaturated carboxylic acid-modified polyethylene, and the like. Among these, polyethylene and ethylene-vinyl acetate copolymer are preferred. Furthermore, these polymers do not exclude those containing other miscible resins or elastomers in an amount of less than 50% by weight. The amount of the aromatic vinyl monomer used for modification is 40 to 95% by weight of the ethylene polymer and 60 to 5% by weight of the aromatic vinyl monomer unit, based on the total weight of the ethylene polymer. If the amount of 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 compatibility of the modified ethylene polymer with the propylene polymer (A) will deteriorate and the material This is not preferable because the properties (flexibility) and film molding processability deteriorate. Modified ethylene polymer in the present invention (component (B))
General modification methods such as melt grafting using an extruder, grafting by radiation irradiation, and grafting in a solution are used to obtain
For example, the following methods can be cited. That is, ethylene polymer particles (generally 1 to 7
mm, preferably 2-5 mm diameter) 40-95% by weight
impregnating at least 80% by weight of the vinyl monomer into the polymer particles in an aqueous suspension comprising 5 to 60% by weight of the vinyl aromatic monomer and a polymerization initiator; A modified ethylene polymer can be obtained by polymerizing. The method of impregnating the polymerization initiator and monomer used here,
Details of the polymerization method are as follows. Radical polymerization initiator: An aromatic vinyl monomer is impregnated into ethylene polymer particles in an aqueous medium without substantially polymerizing the monomer, and then the aqueous dispersion is heated to polymerize the monomer. However, the polymerization is usually promoted by a radical polymerization initiator. The polymerization initiator must be able to be impregnated into the ethylene polymer particles together with the monomer. Therefore, the radical polymerization initiator used is oil-soluble. Preferably, the decomposition 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 ethylene polymer particles with an aromatic vinyl monomer in an aqueous medium A typical method of impregnating ethylene polymer particles with a vinyl monomer in an aqueous medium is preferred for an aqueous dispersion of ethylene polymer particles. The process consists of adding and stirring monomers in which a polymerization initiator (and other additives as necessary) are dissolved. Another method is to add ethylene polymer particles to an aqueous dispersion of a monomer 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 step, the monomer is impregnated so that the amount of free monomer is 80% by weight or less of the amount of monomer used. Since ethylene polymers are relatively compatible with vinyl monomers, these monomers will impregnate the ethylene polymer particles during polymerization even if more than 80% by weight of the monomers are free before polymerization begins. Therefore, the polymer particles obtained by polymerizing these monomers do not precipitate independently from the modified ethylene polymer particles. The impregnation time is usually about 2 to 8 hours. The content of ethylene polymer 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. When impregnating ethylene polymer particles with vinyl monomer (and polymerization initiator), auxiliary materials such as plasticizers, lubricants, and antioxidants can be impregnated at the same time. In some cases, it may already be added to the polymer, or it can 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 monomer will polymerize and be modified. Ethylene polymer particles are produced.
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 the same post-treatment as for aqueous suspension polymerization of ordinary vinyl monomers (e.g. styrene) is carried out, the shape of the ethylene polymer particles used will be maintained almost unchanged and can be used immediately as a molding material. Modified ethylene polymer particles which can be obtained are obtained. The modified ethylene polymer of the present invention is presumed to be an ethylene polymer containing a homogeneously dispersed vinyl monomer, a vinyl monomer grafted onto an ethylene polymer backbone, or a mixture thereof. , the vinyl monomer-specific polymer particles do not exist separately from the ethylene polymer particles. When using an aromatic vinyl monomer-modified ethylene polymer, if the monomer unit is in the range of 60 to 5% by weight, an unmodified ethylene polymer may be mixed with the modified ethylene polymer. It may also be used as Propylene polymer (A) and this modified ethylene polymer
The blending ratio with (B) depends on the required value of sealing strength.
Generally 10 to 80 parts by weight of propylene polymer (A), preferably 20 to 60 parts by weight of modified ethylene polymer (B)
The amount is 90 to 20 parts by weight, preferably 80 to 40 parts by weight. If component (A) is less than 10 parts by weight, the sealing strength will be too low and the product will easily peel off during packaging or transportation. Moreover, if it exceeds 80 parts by weight, heat fusion will occur on the sealing surface, and the sealing strength will be too high, making it difficult to peel off. In addition, an impact-resistant substance may be added to the sealing material of the present invention, which has a large amount of monomer units, in an amount that does not account for the majority of the amount. Impact-resistant materials include those commonly known as thermoplastic elastomers;
Examples include ethylene-propylene copolymer rubber, styrene-butadiene copolymer rubber, styrene-conjugated diolefin block copolymer rubber, polyisobutylene rubber, and 1,2-polybutadiene rubber, but they do not give odor to the mixed resin. Ethylene-propylene copolymer rubber and styrene-conjugated diolefin block copolymer rubber are preferred because they have no heat deterioration resistance. In addition, in order to improve the extrusion processability and spreadability of the sealing materials of the present invention,
10,000 polyethylene wax or low density polyethylene having a melt index of 0.5 to 100 may be added within a range (usually 40% by weight or less) that does not impede the appropriate level of sealing strength, which is the object of the present invention. A mixed composition containing these propylene polymers (A) and modified ethylene polymers (B), and in some cases unmodified ethylene polymers and impact-resistant substances, etc., is prepared using a batch kneader such as a Banbury mixer or a roll. In addition, it can be easily obtained using a continuous extruder such as a single-screw extruder or a twin-screw extruder. Next, a packaging container having a sealed heat-sealed part made of a material containing propylene polymer as a main component is briefly explained with reference to FIGS. It is sufficient that this material is used in the construction, and other parts are made of paper (including synthetic paper), oriented polypropylene, metal foil, or other resins (polyamide, cellophane, polyethylene terephthalate, polycarbonate, etc.). However, due to the complexity of the manufacturing process, a laminated material in which paper, metal foil, various resins, etc. and propylene polymer are laminated is generally used. It is molded to fit inside the container (of course, it also includes containers whose main bodies are made solely of propylene polymer). Further, the method of using the sealing material made of the propylene polymer (A) and the modified ethylene polymer (B) of the present invention is applicable to the intended purpose if it is used for at least one of the sealing part of the container or the sealing part of the lid. is achieved. 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. The method for forming the sealing material of the present invention on either the packaging container or the sealing part of the lid includes:
A method in which a film of the sealing material is formed by a known film forming method such as an inflation method or a T-die method, and the film is interposed on the sealing surface of the container and sealed, or a content storage part or a lid. The sealing material is extrusion coated, dry laminated, wet laminated, or hot melt coated on the surface of the base material constituting the base material by a known method, or
Examples of methods include coextrusion lamination or coextrusion coating of both. The sealing portion of the container can be sealed using known techniques such as pressurized heat sealing using a heat sealer, impact heat sealing, induction sealing, and ultrasonic sealing. It can be done. By using the easily peelable heat sealing material of the present invention as a sealing material in the heat sealing part of a packaging container made of a material containing a propylene polymer as a main component, (1) The sealed portion does not peel off during the subsequent transportation of the product, and has moderate peelability when peeled off by hand, resulting in a well-balanced product in terms of strength. (2) When peeling off by hand, it can be peeled off smoothly with a constant and uniform force, and does not cause any unpleasant sensation of jerkiness. (3) When processing this sealing material into a film, it not only has good formability but also good roll windability, especially when the film is thick (50 μm or more). etc., you can get very good results. Hereinafter, the effects of the present invention will be explained using Examples. Example 1 20 kg of pure water, 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 create an aqueous medium, and ethylene-vinyl acetate copolymer (melt) was added to this. 5 kg of particles (index (M1) 12, specific gravity 0.943, vinyl acetate content 20% by weight) were suspended by stirring. Separately, 10 g of benzoyl peroxide and 5 g of t-butyl peroxide benzoate as polymerization initiators were dissolved in 5 kg of styrene, and this was added to the suspension system, and the temperature inside the autoclave was raised to 65°C and kept at this temperature for 3 hours. Styrene containing a polymerization initiator was then impregnated into the ethylene-vinyl acetate copolymer particles. This aqueous suspension was heated to 80°C and maintained at this temperature for 5 hours and then at 125°C for 5 hours to complete polymerization. It was confirmed that polystyrene was almost quantitatively present at 50% by weight in the obtained modified particles. This modified resin, a mixture of the above ethylene-vinyl acetate copolymer and propylene-ethylene random copolymer (MI, 7, ethylene content 3% by weight), was blended into a 30 m/m diameter T-die film molding machine. A film of approximately 50 μm was formed at a molding temperature of 180 to 200°C. These films and 12μ thick aluminum foil were bonded together using an adhesive to form a laminated film. The mixed resin layer (side A) of this laminated film was used as the sealing surface, and the 100μ propylene-ethylene random copolymer film (side B) was heat-sealed with a heat sealer, and the peel strength of the sealed portion was determined. It was measured. The results are shown in Table 1. Sealing conditions were as follows: using a hot plate heat sealer, sealing width 5mm, sealing pressure 2Kg/cm ² , sealing time 2
seconds, sealing temperature is 160-240℃. Peel strength was measured using a Schottsper type tensile tester.
The 180° peel strength was measured at 23°C with a sample width of 15 mm and a tensile speed of 300 mm/min. Furthermore, when these sealed items were peeled off by hand, they were all able to be peeled off smoothly with uniform force without any wobbling. Comparative Example 1 Table 1 shows the results of using the ethylene-vinyl acetate copolymer of Example 1 as the A side in Example 1.

[Table] Example 2 Styrene-modified low-density polyethylene (styrene units 30
% by weight) was obtained. The modified resin, styrene-butadiene block rubber (Tuffrene manufactured by Asahi Kasei Corporation), and the propylene-ethylene random copolymer of Example 1 were blended in predetermined amounts to form a film of about 50 μm. A laminated film of this film and a 12μ aluminum foil was prepared, and the resin layer (side A) was used as the sealing surface, and the peel strength between it and a 100μ propylene-ethylene random copolymer film (side B) was measured. The sealing temperature is 160-240℃. Table 2 shows the results.
Shown below. Comparative Example 2 Table 2 shows the results of using the low density polyethylene of Example 2 as the A side in Example 2.

【table】 [Brief explanation of the drawing]

FIG. 1 shows a bag made of laminated film, and FIG. 2 shows a molded container. 1a and 1b are sealing layers (at least one is the sealing material of the present invention, and the other may be a material containing a propylene polymer as a main component) 2
The packaging base materials a and 2b (one of them may be a single layer), and 3 represent the sealed portion.

Claims (1)

[Claims] 1 A sealing material for use in an easily peelable heat-sealed part of a packaging container having a heat-sealed part made of a material containing a propylene polymer as a main component, the sealing material comprising a propylene polymer (A) 10 to 80%. Parts by weight: 40-95% by weight of ethylene polymer and 60-5% by weight of aromatic vinyl monomer
90 to 20 parts by weight of a modified ethylene polymer (B) obtained by subjecting the modified ethylene polymer (B) to grafting conditions.