JP2884738B2 - Resin composition and container cap liner - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a resin composition having good sealing properties, food hygiene properties, flavor retention properties and practical performance. More specifically, excellent adhesiveness is obtained at the interface between the cap base material and the liner material, and the flexibility and heat resistance of the liner material heat sterilize or pressurize beverages, soft drinks, beer, etc., which are the contents of the container. The present invention relates to a resin composition suitable for a cap liner material, which has good sealing properties and preservability when the internal pressure rises during filling, and provides good sealing properties even in practical use when opening and retightening.

[Prior Art] At present, cork, soft PVC, ethylene resin, styrene resin and the like are used as liner materials for containers such as glass bottles and PET bottles. Cork liner materials are unstable in quality and have problems such as cork dust. Therefore, the use of cork liner materials is on a decreasing trend, and in recent years, they have been changed to soft PVC and ethylene-based resins. However, as the soft PVC liner material, there are also hygiene problems such as precipitation of a plasticizer, and at present, ethylene-based resin and styrene-based resin liner materials are widely used. Even with the current ethylene-based resin liner materials, good sealing properties cannot be obtained due to problems such as flexibility and heat resistance, which may cause a decrease in internal pressure or leakage of the contents, and the like. For this purpose, JP-A-58-183458 and JP-A-2-57569 propose to use a hydrogenated styrene resin as a liner material.

However, the conventional liner material has poor interfacial adhesiveness with the cap base material, and without the use of an adhesive, the liner material may peel off or slip off when the cap is opened, and the gap between the liner material and the cap base material during retightening. This has the disadvantage that the liner is liable to be distorted or deformed due to poor adhesion, and the sealing performance is reduced.

[Problems to be Solved by the Invention] An object of the present invention is to solve the above-mentioned problems in the prior art, and to have good food hygiene and excellent interfacial adhesion, and good sealing even when refastened. It is an object of the present invention to provide a resin composition suitable for a container cap liner from which is obtained.

Means for Solving the Problems The inventors of the present invention have conducted intensive studies on a method of maintaining good food hygiene and sealing properties and increasing the interfacial adhesion to a container cap base material. -The interfacial adhesion with the base material of the container cap is remarkably improved by blending the butadiene block copolymer with the polypropylene resin and the polypropylene resin in which liquid paraffin, unsaturated carboxylic acid or its anhydride is grafted. I found something.

That is, the present invention relates to (A) melt flow rate (230 ° C., 2.
16 kgf) hydrogenated styrene-butadiene block copolymer of 20 g / 10 min or less 5 to 90 wt%, (B) melt flow rate (230 ° C., 2.16 kgf) 0.1 to 50 g / 10 min of polypropylene resin 2 to 50 wt% % (C) Viscosity (37.8 ° C.) 50-350 centistokes liquid paraffin 10-70% by weight, (D)
The present invention relates to a resin composition containing 0.01 to 50% by weight of a polypropylene resin to which an unsaturated carboxylic acid or a derivative thereof is grafted.

[Action] The resin composition of the present invention comprises the following components.

(A) Hydrogenated styrene-butadiene block copolymer The hydrogenated styrene-butadiene block copolymer having a melt flow rate (JIS K7210, temperature 230 ° C., load 2.16 kgf) of 20 g / 10 minutes or less used in the present invention is styrene. Those having a content of 10 to 50% by weight and a hydrogenation rate of 80% or more can be used. Among them, those having a styrene content of 25 to 50% by weight, a hydrogenation ratio of 90% or more, and a melt flow rate of 10 g / 10 minutes or less are preferable.

The method for producing the hydrogenated styrene-butadiene block copolymer is not particularly limited.
According to the description in JP-A-6636, a block copolymer of styrene and butadiene which is hydrogenated with a hydrogenation catalyst such as a nickel-supported diatomaceous earth catalyst and has a hydrogenation rate of 80% or more can be used.

(B) Polypropylene Resin The polypropylene resin used in the present invention (JIS K7210, temperature 230 ° C., load 2.16 kgf) 0.1 to 50 g / 10 minutes is a crystalline polypropylene resin, and is a propylene homopolymer, ethylene -Propylene random copolymer, ethylene-propylene block copolymer, or a mixture of these polypropylene resins can be used. Further, the propylene content in the ethylene-propylene copolymer is preferably 70% by weight or more.

The melt flow rate of polypropylene resin is 0.1
5050 g / 10 min, but preferably 1-30 g / 10 min. Further, the polymerization method and the catalyst of the polypropylene resin are not particularly limited, and a slurry method, a gas phase method, or the like can be used. A type catalyst or the like can be suitably used. In this case, the transition metal compound may be supported on a halogen-containing magnesium compound such as magnesium chloride.

(C) Liquid paraffin The liquid paraffin used in the present invention has a viscosity (37.8 ° C) of 50.
~ 350 centistokes can be used, and those with 100-350 centistokes are preferred.

(D) Unsaturated carboxylic acid-grafted polypropylene resin As the unsaturated carboxylic acid used in the production of the unsaturated carboxylic acid-grafted polypropylene resin used in the present invention, maleic acid, acrylic acid, fumaric acid, succinic acid, itaconic acid, etc. Is raised. Further, examples of the derivatives include anhydrides, amides, imides, esters and the like. As the unsaturated carboxylic acid or a derivative thereof, maleic acid and an acid anhydride thereof are preferable.

As the polypropylene resin, a polypropylene homopolymer, an ethylene-propylene random copolymer, an ethylene-propylene block copolymer, or a mixture of these polypropylene resins can be used.

As the graft amount, those treated with 0.01 to 10% by weight can be used.

As a method for producing a graft polypropylene-based resin using an unsaturated carboxylic acid or a derivative thereof, various conventionally known methods can be used. For example, there is a method in which a polypropylene-based resin is melted and copolymerized by adding a graft monomer as described above in the presence of a radical initiator.

The grafting reaction can be usually performed at 60 to 350 ° C,
Organic peroxides such as 2,5 dimethyl 2,5 di (t-butyl) hexane and 1,4 bis (t-butylperoxyisopropyl) benzene can be used as the radical initiator. 0.001 to 1 part by weight with respect to parts by weight.

In the composition of the present invention, the mixing ratio of each component is
(A) The hydrogenated styrene-butadiene block copolymer is 5 to 90% by weight, preferably 10 to 80% by weight. If the blending ratio of the hydrogenated styrene-butadiene block copolymer is less than 5% by weight, the flexibility is remarkably reduced, and the sealing property when the cap liner is used and the opening property in practical use may be impaired. If it exceeds 90% by weight, the heat resistance is impaired, and the liner may be easily deformed during hot filling and heat sterilization.

(B) the polypropylene resin is 2 to 50% by weight,
5-40% by weight is preferred. If the amount exceeds 50% by weight, the flexibility may be remarkably reduced.

(C) the amount of liquid paraffin is 5 to 70% by weight,
10-60% by weight is preferred. If the amount is less than 5% by weight, workability and flexibility may be significantly reduced.

(D) The polypropylene resin to which the unsaturated carboxylic acid or anhydride is grafted is 0.01 to 50% by weight,
40% by weight is preferred. If the amount is less than 0.01% by weight,
The interfacial adhesion with the cap base material may decrease.

In the resin composition of the present invention, the components shown above and various additives used as desired, such as antioxidants, antistatic agents, neutralizing agents, lubricants, antiblocking agents,
An ultraviolet absorber, a pigment used for coloring, and the like can be blended. Further, it can be prepared by melt-kneading inorganic fillers such as calcium carbonate, talc, barium sulfate and the like used for fine adjustment of physical properties according to a conventional method, and compounding them.

The melt kneading can be performed by a method using a single screw extruder, a twin screw extruder, a Banbury mixer, or other conventional melt kneading methods, and can be performed at a melt kneading temperature of 180 to 300 ° C.

The method for molding the resin composition of the present invention into a container cap liner is not particularly limited, but is extruded, or molded into a plate having a thickness of 0.5 to 2 mm by a sheet molding device such as a roll mill, and cut in accordance with the cap shape. Alternatively, the liner can be formed by punching. In addition, a fixed amount of molten resin is extruded into a preheated cap shell by the in-shell mold method, and pressed into the cap shell using a pressing die to form a liner.

As an applicable cap of the liner material of the present invention, a screw-type container cap that performs tightening by relative rotation of the container and the cap can be used.

[Examples] Next, the present invention will be described in detail with reference to examples and comparative examples, but the present invention is not limited to these examples.

(Examples 1 and 2) Hydrogenated styrene-butadiene block copolymer (MF
R = 1.0 g / 10 minutes, styrene content 35% by weight, hydrogenation rate 99
%), Polypropylene resin (manufactured by Tosoh Corporation, trade name "J5200A" MFR = 20g / 10min), liquid paraffin (viscosity 76
Centistokes) and maleic anhydride-grafted polypropylene (modified amount = 1.5%) at the mixing ratio shown in Table 1 and then melt-kneaded at 230 ° C using a single screw extruder to prepare pellets. did. The obtained pellet was mounted as a liner on an aluminum cap (φ28) by an in-shell mold, and a liner peeling test was performed. Also,
A PET bottle (1.5 liter) was filled with carbonated water (gas pressure: 4 VOL), and a drop impact leak test (height: 20 cm, angle: 10 °) and an opening test were performed.

(Comparative Examples 1, 2) Pellets were prepared by mixing at the mixing ratios shown in Table 1 and melt-kneading in the same manner as in Examples 1 and 2. Each test was performed in the same manner as in Examples 1 and 2, using the obtained pellets.

As is clear from the test results in Table 1, the resin composition comprising the composition of the present invention exhibited excellent interfacial adhesion, sealing properties, and opening properties.

[Effects of the Invention] The resin composition of the present invention maintains food hygiene, flavor retention, and interfacial adhesion with a cap base material, flexibility,
It has good sealing properties, heat resistance and openability in practical use, and also has good sealing properties when re-tightened, and is significantly improved as compared with conventional compositions.

Claims (2)

(57) [Claims] 1. A melt flow rate (230 ° C., 2.16 kg)
f) 5 to 90% by weight of a hydrogenated styrene-butadiene block copolymer of 20 g / 10 minutes or less, (B) 2 to 50% by weight of a polypropylene resin having a melt flow rate (230 ° C., 2.16 kgf) of 0.1 to 50 g / 10 minutes %, (C) 5-70% by weight of liquid paraffin having a viscosity (37.8 ° C.) of 50-350 centistokes, and (D) 0.01-50% by weight of a polypropylene resin grafted with an unsaturated carboxylic acid or a derivative thereof. A resin composition for a cap liner. 2. A container cap liner formed by molding the resin composition according to claim 1.