JPH09188786A - Ethylene copolymer composition and readily openable sealing material using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a readily openable sealing material useful as a sealing material for a plastic container, suitable in sealing strength and sealing stability especially to an impact-resistant polystyrene. SOLUTION: This composition comprises 30-95 pts.wt. of an ethylene/ unsaturated ester copolymer, 20-3 pts.wt. of a hydrogenated styrene/butadiene copolymer, 0-40 pts.wt. of a low-crystalline ethylene/α-olefin copolymer and 0-30 pts.wt. of a tackifier resin. The hydrogenated styrene/butadiene copolymer comprises a polybutadiene block segment (A) (<=25wt.% of 1,2-vinyl bond) and a butadiene/styrene random copolymer block segment (B) (>=70wt.% butadiene and 25-95wt.% vinyl bond content of the butadiene part). The block structure is obtained by hydrogenating >=90wt.% of a butadiene part of a straight-chain or branched chain block copolymer of the formula A-(B-A)n or (A-B)m ((n) is an integer of >=1 and (m) is an integer of >=2).

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a novel ethylene copolymer composition. More specifically, it relates to an ethylene copolymer composition suitable as an easily openable seal material.

[0002]

2. Description of the Related Art Plastic containers provided with easy-open lids are widely used as containers for various foods and drinks such as cup noodles, jelly, yogurt, and tofu, and pharmaceuticals. Various types of hot-melt adhesives have been proposed and put to practical use as the sealant layer of such an easily-openable lid material. For example, a composition of ethylene / vinyl acetate copolymer or ethylene / ethyl acrylate copolymer and a tackifier, a composition in which polyethylene or a low crystalline ethylene / α-olefin copolymer is mixed, and the like are hermetically sealed. It is known that it becomes an excellent sealing material having excellent properties and easy opening property. However, the types of plastic materials used for containers have increased,
As for new materials, there are some materials that cannot be adequately dealt with by conventional sealing materials, and the advent of new sealing materials is desired. Further, even in the case of a container using an existing plastic material, the desired value of the heat seal strength differs depending on the application, and therefore, a sheet material that can be easily adjusted to various heat seal strengths is also desired.

For example, in recent years, impact-resistant polystyrene has come to be used in various containers. When the above-mentioned conventionally used sealing materials are used, some of them have low sealing strength. However, some of them showed a sufficient value as the initial seal strength, but showed a defect that the seal strength decreased with time, and there was a problem in actual use.

[0004]

SUMMARY OF THE INVENTION Accordingly, the present inventors
An investigation was conducted to find a sealing material that exhibits sufficient sealing property and easy-opening property with respect to impact-resistant polystyrene, and has a small tendency for the sealing strength to decrease with time. As a result, ethylene
A composition consisting of an unsaturated ester copolymer and a hydrogenated product of a styrene / butadiene block copolymer having a specific structure shows suitable seal strength and is used as a seal material with little change in seal strength over time. I came to find what I could do. It has also been found that this seal material can widely adjust the seal strength by changing the composition.

Therefore, an object of the present invention is to provide a novel ethylene copolymer composition suitable as an easily openable seal material. Another object of the present invention is to provide an easily openable seal material, especially an easily openable seal material suitable for impact-resistant polystyrene. Still another object of the present invention is to provide a lid material obtained by laminating such an easily-openable sealing material on a base material.

[0006]

Means for Solving the Problems The present invention comprises 30 to 95 parts by weight of an ethylene / unsaturated ester copolymer, 20 to 3 parts by weight of a hydrogenated styrene / butadiene copolymer, and a low crystalline ethylene / α-olefin copolymer. The hydrogenated styrene-butadiene copolymer is composed of 0 to 40 parts by weight of a polymer and 0 to 30 parts by weight of a tackifying resin, and the 1,2-vinyl bond is 2
From a polybutadiene block segment (A) having a content of 5% or less and a butadiene / styrene random copolymer having a content of butadiene of 70% by weight or more, wherein the vinyl bond content of the butadiene portion is 25 to 95%. And the block structure is A- (B-
A) _n or (AB) _m (where n is an integer of 1 or more and m is an integer of 2 or more), the butadiene portion of the linear or branched block copolymer is hydrogenated at 90% or more. The present invention relates to an ethylene copolymer composition characterized in that The present invention also relates to an easily-openable sealing material comprising the above ethylene copolymer composition. The present invention also relates to a packaging material such as a lid material formed by laminating such an easily-openable sealing material on a base material.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail. The ethylene copolymer composition of the present invention comprises ethylene
It is composed of an unsaturated ester copolymer and a hydrogenated styrene-butadiene copolymer as essential components.

The unsaturated ester in the ethylene / unsaturated ester copolymer includes vinyl acetate, vinyl ester such as vinyl propionate, methyl acrylate, ethyl acrylate, isobutyl acrylate, and acrylic acid n.
Examples thereof include unsaturated carboxylic acid esters such as butyl, isooctyl acrylate, methyl methacrylate and isobutyl methacrylate, and particularly (meth) acrylic acid ester. Among these, vinyl acetate and (meth) acrylic acid ester are preferably used.

The unsaturated ester content in the above copolymer is 3 to 25% by weight, particularly 5 to 20% by weight. It is possible to adjust the seal strength for impact-resistant polystyrene also by the content of this unsaturated ester. Generally, the higher the content, the higher the seal strength and the stability of the seal strength, but the amount is too large. If it becomes too much, stickiness will occur, and adverse effects such as an increase in the amount of heptane extractive components will occur, especially in food applications, so it should not be used favorably. Further, if the content is too small, or if polyethylene is used instead of this copolymer, the sealing strength against impact-resistant polystyrene is low and the stability of the seal is also reduced, which is not preferable.

The ethylene / unsaturated ester copolymer has a workability of 190 and a seal strength of 190.
C. and a melt flow rate at a load of 2160 g of 0.
1 to 500 g / 10 minutes, especially 1 to 150 g / 10 minutes is preferably used.

Such ethylene copolymers can be obtained by radical copolymerization under high temperature and high pressure, the production method thereof is widely known, and many kinds of copolymers are commercially available. .

In the present invention, a hydrogenated styrene / butadiene copolymer is used together with the above copolymer.
The styrene / butadiene copolymer, which is the base polymer of the hydrogenated styrene / butadiene copolymer, is a block copolymer composed of the polybutadiene block segment (A) and the block segment (B) of the butadiene / styrene random copolymer.

One block segment (A) constituting the block copolymer has 25% of 1,2-vinyl bonds.
Or less, preferably 20% or less, more preferably 15%
The following block segment consisting of polybutadiene, the other block segment (B) contains butadiene in an amount of 70% by weight or more, preferably 75 to 95% by weight, and the butadiene portion has a 1,2-vinyl bond content of 2 or less.
The butadiene / styrene random copolymer block segment is 5 to 95%, preferably 25 to 75%, more preferably 25 to 55%.

The block structure of the block copolymer consisting of the block segments (A) and (B) is A- (B
-A) _n or (AB) _m (where n is 1 or more, m
Is a linear or branched block copolymer represented by an integer of 2 or more). The proportion of block A in the block copolymer is usually 10 to 60% by weight, preferably 1
2 to 50% by weight, more preferably 15 to 40% by weight, and the proportion of block B is usually 90 to 40% by weight, preferably 88 to 50% by weight, more preferably 85 to 60% by weight.

When the 1,2-vinyl bond in the block A is more than the above range, the hydrogenated product has a low crystal melting point, which causes stickiness and an increased heptane extraction amount, so that the addition amount is limited. Therefore, there is a drawback that the allowable range of quality design is narrowed. When the butadiene component in the block B is less than the above range or when the 1,2-vinyl bond of the butadiene portion is out of the above range, the sealing property of the composition of the present invention, It is not preferable because it will reduce the sealing strength.

The ratio of the block A to the block B is preferably adjusted within the above range in order to improve the sealing property without substantially affecting the stickiness or the heptane extraction content.

The hydrogenation rate of the styrene / butadiene copolymer is 90% or more, preferably 95% to 100%, of the double bonds of the butadiene components of block A and block B. If the hydrogenation rate is less than the above range, the heat resistance and weather resistance of the ethylene copolymer composition of the present invention are adversely affected, which is not preferable. The weight average molecular weight of block A and block B is usually 5,000 or more, preferably about 10,000 to 100,000.

In the present invention, as described above, a system comprising only an ethylene / unsaturated ester copolymer and a hydrogenated styrene / butadiene copolymer can be used, but the heat seal strength has a slightly large temperature dependency, Also, since fine adjustment of the seal strength is not always easy, low crystalline ethylene
It is desirable to use an α-olefin copolymer and / or a tackifying resin together.

The ethylene / α-olefin copolymer which can be used for this purpose has a crystallinity based on X-rays of usually 1 to
It is a low crystallinity copolymer of 20%, preferably 3 to 15%. That is, it is not preferable to use a completely amorphous copolymer because the oil resistance is lowered. It is preferable to use a copolymer having a narrow composition distribution and a narrow molecular weight distribution as such a copolymer. For example, in the presence of a combination catalyst of a transition metal compound such as a vanadium compound or a zirconium compound and an organoaluminum compound, ethylene and α- It can be obtained by random copolymerization of olefins. α
-As the olefin, propylene, 1-butene, 1-
Pentene, 1-hexene, 1-octene, 4-methyl-
1-Pentene etc. can be illustrated. Among these, it is desirable to use an α-olefin having 4 or more carbon atoms, especially 1-butene. Depending on the catalyst system used and the type of α-olefin, the amount of α-olefin is usually 7 to 2 in order to obtain a copolymer having the above crystallinity.
Polymerization may be carried out at a rate of 0 mol%, particularly 8 to 16 mol%. As the copolymer, 190 ° C., 2
Melt flow rate at 160g load is 0.1-5
It is preferable to use the one of 00 g / 10 minutes, particularly 1 to 150 g / 10 minutes.

Examples of the tackifying resin that can be used in the present invention include aliphatic hydrocarbon resins, alicyclic hydrocarbon resins, aromatic hydrocarbon resins, polyterpene resins, rosins and styrene resins. It is used in the ordinary hot melt adhesive field. More specifically, examples of the aliphatic hydrocarbon resin include a polymer containing an olefin having 4 to 5 carbon atoms or a diene as a main component. As the alicyclic hydrocarbon resin, a resin obtained by polymerizing a diene component of spent C ₄ or C ₅ fraction after cyclization dimerization and polymerization, a resin obtained by polymerizing a cyclic monomer such as cyclopentadiene, or hydrogen thereof Examples thereof include additives and resins obtained by nuclear hydrogenation of aromatic hydrocarbon resins. As the aromatic hydrocarbon resin, vinyltoluene, α-methylstyrene, isopropenyltoluene,
The unsaturated aromatic hydrocarbon of C ₈ -C _10, such as indene can be exemplified a resin as a main component. Examples of the polyterpene resin include polymers such as α-pinene, β-pinene and dipentene, terpene / phenol resin, hydrogenated terpene resin and the like. Examples of rosins include rosin, polymerized rosin, hydrogenated rosin, rosin ester, and hydrogenated or polymerized products thereof. In addition, styrene resin is styrene, vinyltoluene,
Examples thereof include polymers such as α-methylstyrene and isopropenyltoluene, and low molecular weight polymers such as mutual copolymers thereof. When importance is attached to color tone, odor, food hygiene, etc., hydrogenated aromatic hydrocarbon resin or hydrogenated polyterpene resin is preferably used.

In the present invention, the ratio of each component is 30 to 95 parts by weight of ethylene / unsaturated ester copolymer, preferably 35 to 90 parts by weight, and 20 to 3 parts by weight of hydrogenated styrene / butadiene copolymer. , Preferably 15 to 5 parts by weight, and a low crystalline ethylene / α-olefin copolymer is 0
˜40 parts by weight, preferably 5 to 35 parts by weight, and tackifying resin in an amount of 0 to 30 parts by weight, preferably 5 to 20 parts by weight (total 100 parts by weight). It is necessary to adjust the total amount of the hydrogenated styrene / butadiene copolymer and the tackifying resin to be in the range of 5 to 35 parts by weight, particularly 10 to 35 parts by weight, the heat seal strength and its stability, and oil resistance. It is preferable in consideration of sex.

The hydrogenated styrene-butadiene copolymer is effective for improving the sealing property of impact-resistant polystyrene, especially for imparting the stability of the sealing strength, but if the blending ratio is too large, the sealing strength is increased. Becomes excessively large, or the amount of heptane extracted becomes too large to be used in oily foods.

The addition of the low crystalline ethylene / α-olefin copolymer generally contributes to the improvement of the sealing property to the high impact polystyrene without impairing the oil resistance, but in many cases,
When used in excess, it may impair the processability in extrusion coating the composition of the present invention onto a substrate, and therefore should not be incorporated in a large amount. The addition of a tackifying resin is also effective in improving the sealing property to impact-resistant polystyrene, but if it is excessively added, the oil resistance and processability are impaired, so it is desirable to adjust the content to a suitable level.

The above-mentioned composition of the present invention may be blended with other thermoplastic resins, such as polyethylene, in a small amount in order to adjust the sealing strength and the like. In addition, various known additives may be added in arbitrary amounts. Typical examples of such additives include, for example, improvement of extrusion processability, prevention of blocking,
Examples thereof include additives used for the purpose of improving the slipperiness of the film. More specifically, palmitic acid amide, stearic acid amide, behenic acid amide, oleic acid amide, erucic acid amide, oleyl palmidamide, stearyl palmidoamide, methylenebisstearylamide, various amides such as ethylenebiserucic acid amide, Polyalkylene glycol such as polyethylene glycol and polypropylene glycol, hydrogenated castor oil,
Inorganic additives such as silica and talc. Appropriately, the blending amount of these is in the range of about 0.1 to 3% by weight in the case of an inorganic additive, and in the range of about 0.01 to 1% by weight for the other additives. Examples of other additives that can be optionally blended include antioxidants, heat stabilizers, light stabilizers, antistatic agents, pigments and dyes.

The composition of the present invention is prepared by mixing the above-mentioned components simultaneously or sequentially. As a mixing method, a method of melt mixing using a single-screw extruder, a twin-screw extruder, a Banbury mixer, various kneaders and the like is preferable, and the mixing order is not particularly limited.

The ethylene copolymer composition thus obtained has a melt flow rate of 1 to 150 g / 10 at 190 ° C. under a load of 2160 g, in consideration of extrusion processability.
It is desirable that it is adjusted to about a minute.

The ethylene copolymer composition of the present invention is effective as an easily openable sealant. When used as an easily-openable seal material, it is often used in a form laminated on a base material. As the base material, paper, aluminum, polyester,
Various materials such as polyethylene, polypropylene, aluminum vapor-deposited polyester, aluminum vapor-deposited polypropylene, and silica vapor-deposited polyester can be used. The base material does not have to be a single layer, and may be a laminate of two or more kinds.

In order to laminate the ethylene copolymer composition of the present invention on a substrate, a film is formed from the composition by a casting method or an inflation method in advance, and the composition is laminated on the substrate by a dry lamination method. Is directly applied to the substrate by extrusion coating, polyethylene or the like is used as an adhesive layer, the substrate is laminated by sandwich lamination via the adhesive layer, and the substrate and the composition are coextruded. be able to.

The laminate having the ethylene copolymer composition thus obtained as a seal layer can be used as a packaging material. In particular, when used as a lid material for various containers, the lid material has excellent sealing property and easy opening property. Applicable containers are containers of various shapes such as polystyrene, polypropylene, polyester, polycarbonate, polyvinyl chloride and the like. In particular, it is a lid material that exhibits excellent performance for impact-resistant polystyrene containers. Such a container with a lid
For example, yogurt, pudding, bean beans, sour, tofu, jelly, lactic acid drink, Japanese confectionery, processed meat and other food and drink, medicine,
It can be used for various packaging such as medical containers and toner.

[0030]

EFFECTS OF THE INVENTION According to the present invention, an ethylene copolymer composition suitable as an easily openable seal material can be provided. Particularly, it is possible to provide an ethylene copolymer composition which is an easily openable sealing material having appropriate sealing strength and sealing stability against impact-resistant polystyrene.

[0031]

EXAMPLES Examples and comparative examples are shown below to explain the effects of the present invention. The composition and physical properties of the raw material resins used in the examples and comparative examples and methods for evaluating the physical properties of the obtained laminated material are as follows.

1. Raw material resin (1) Ethylene / vinyl acetate copolymer Various ethylenes shown in Table 1 below with different vinyl acetate contents
A vinyl acetate copolymer was used.

[0033]

[Table 1]

(2) Hydrogenated styrene-butadiene copolymer "DYNARON E460" manufactured by Japan Synthetic Rubber Co., Ltd.
0P "Styrene / ethylene butylene / olefin crystal block copolymer MFR: 5.6 g / 10 min Density: 0.91 g / cm ³ Styrene content: 20 wt%

(3) High-pressure low-density polyethylene "Mirathon M10P" manufactured by Mitsui Petrochemical Co., Ltd. MFR: 9.5 g / 10 minutes Density: 0.917 g / cm ³

(4) Low crystalline ethylene / α-olefin copolymer "Toughmer A4085" MFR 3.6 g / 10 minutes manufactured by Mitsui Petrochemical Co., Ltd.

(5) Tackifier "Arcon AM-1" manufactured by Arakawa Chemical Co., Ltd. Ring-and-ball method alicyclic hydrocarbon resin having a softening point of 115 ° C (nuclear hydrogenated resin of aromatic hydrocarbon resin)

2. Lamination Method The composition pellets were melt-extruded from a T-die at a die exit temperature of 230 ° C. by an extruder having a diameter of 65 mm, and stretched PET (thickness 12 μm) / low-density polyethylene film (thickness 20 μm) that had been prepared in advance. A polyethylene film surface of a flexible material having a two-layer structure consisting of was subjected to extrusion coating under the conditions of a processing speed of 60 m / min and a coating thickness of 30 μm to obtain a laminated material.

3. Laminated Material Properties Measurement Method Next, the heat-sealing strength of the obtained laminated material and its change with time were measured by the following methods. (1) Heat seal strength The laminated base material was heat-sealed with a strip-shaped sample of impact-resistant polystyrene using a heat sealer, and the heat-sealing strength was measured (N / 15 mm). Heat-sealing conditions Temperature 120 ° C., 140 ° C., 160 ° C. Time 1 sec Pressure 0.2 MPa The measurement was performed after heat-sealing and after aging for 1 day under the condition of 23 ° C. × 50% RH.

(2) Time-dependent change in heat-sealing strength Samples sealed under the above-mentioned heat-sealing conditions were
After aging for 14 days at 3 ° C x 50% RH,
The heat seal strength was measured.

[Example 1] 70.0 parts by weight of EVA, 15.0 parts by weight of hydrogenated styrene-butadiene copolymer,
Tackifier 15.0 parts by weight, silica 2.0 parts by weight, erucic acid amide 0.2 parts by weight, polyethylene glycol 0.
1 part by weight of the mixture was mixed with a single screw extruder at a resin temperature of 150 ° C.
The composition was melt-mixed under the following conditions to obtain a composition. A laminated material was prepared from this composition by the method described above, and the physical properties (heat seal strength and change with time of heat seal strength) were measured. Table 2 shows the results.

[Example 2] 70.0 parts by weight of EVA, 15.0 parts by weight of hydrogenated styrene-butadiene copolymer,
Tackifier 15.0 parts by weight, silica 2.0 parts by weight, erucic acid amide 0.2 parts by weight, polyethylene glycol 0.
1 part by weight of the mixture was mixed with a single screw extruder at a resin temperature of 150 ° C.
The composition was melt-mixed under the following conditions to obtain a composition. A laminate was prepared from this composition by the method described above, and the physical properties were measured. Table 2 shows the results.

Example 3 70.0 parts by weight of EVA, 15.0 parts by weight of hydrogenated styrene / butadiene copolymer,
Tackifier 15.0 parts by weight, silica 2.0 parts by weight, erucic acid amide 0.2 parts by weight, polyethylene glycol 0.
1 part by weight of the mixture was mixed with a single screw extruder at a resin temperature of 150 ° C.
The composition was melt-mixed under the following conditions to obtain a composition. A laminate was prepared from this composition by the method described above, and the physical properties were measured. Table 2 shows the results.

[Example 4] 40.0 parts by weight of EVA, 10.0 parts by weight of hydrogenated styrene-butadiene copolymer,
Low crystalline ethylene / α-olefin copolymer 30.0 parts by weight, tackifier 20.0 parts by weight, erucic acid amide 0.
A mixture of 2 parts by weight and polyethylene glycol 0.1 part by weight was melt-mixed with a single screw extruder under the condition of a resin temperature of 150 ° C. to obtain a composition. A laminate was prepared from this composition by the method described above, and the physical properties were measured. Table 2 shows the results.

[Comparative Example 1] EVA in Example 1
A resin composition was prepared in the same manner as in Example 1 except that 70.0 parts by weight of high-pressure low-density polyethylene was used instead of, and a laminated material was prepared from this composition by the above-mentioned method, and the physical properties were measured. Table 2 shows the results.

Comparative Example 2 80.0 parts by weight of EVA, 20.0 parts by weight of tackifier, 2.0 parts by weight of silica, 0.2 parts by weight of erucic acid amide without adding hydrogenated styrene / butadiene copolymer. Parts, and 0.1 parts by weight of polyethylene glycol were prepared, and a laminate was prepared from this composition by the above method, and the physical properties were measured. Table 2 shows the results.

[Comparative Example 3] 40.0 parts by weight of EVA, 40.0 parts by weight of a low crystalline ethylene / α-olefin copolymer, 20.0 parts by weight of tackifier without adding hydrogenated styrene / butadiene copolymer. Parts by weight, erucic acid amide 0.2
A mixture of 1 part by weight of polyethylene glycol and 0.1 part by weight of polyethylene glycol was prepared, and a laminate was prepared from this composition by the above-mentioned method, and the physical properties were measured. Table 2 shows the results.

[0048]

[Table 2]

Claims (7)

[Claims] 1. An ethylene / unsaturated ester copolymer 30
˜95 parts by weight, 20 to 3 parts by weight of hydrogenated styrene / butadiene copolymer, 0 to 40 parts by weight of low crystalline ethylene / α-olefin copolymer and 0 to 30 parts by weight of tackifying resin. The added styrene / butadiene copolymer is a polybutadiene block segment (A) having a 1,2-vinyl bond content of 25% or less and a butadiene / styrene random copolymer having butadiene content of 70% by weight or more. Vinyl bond content is 25 ~
95% of the block segment (B), and the block structure is A- (BA) _n or (AB) _m
(Wherein n is an integer of 1 or more and m is an integer of 2 or more), which is obtained by hydrogenating 90% or more of the butadiene portion of the linear or branched block copolymer. Copolymer composition. 2. The ratio of block A to block B in the hydrogenated styrene-butadiene copolymer is block A
The ethylene copolymer composition according to claim 1, wherein the content is 10 to 60% by weight and the content of block B is 90 to 40% by weight. 3. The ethylene copolymer composition according to claim 1, wherein the unsaturated ester content of the ethylene / unsaturated ester copolymer is 5 to 25% by weight. 4. The ethylene copolymer composition according to claim 1, wherein the low crystallinity ethylene / α-olefin copolymer has a crystallinity of 1 to 20%. 5. The ethylene copolymer composition according to claim 1, wherein the tackifying resin is a hydrogenated petroleum resin. 6. An easily openable seal material comprising the ethylene copolymer composition according to claim 1. 7. A packaging material comprising a base material and an easily-openable sealing material according to claim 6 laminated on the base material.