JPH0523298B2 - - Google Patents

Description

[Detailed description of the invention]

INDUSTRIAL APPLICATION FIELD The present invention relates to a cap liner with excellent heat resistance. More specifically, the cap liner made of ethylene copolymer has significantly improved heat resistance without sacrificing its inherent flexibility and sealing properties against the contents, and can withstand thermal filling and heat sterilization of the contents, and has excellent sealing properties. The present invention relates to a cap liner that can be retained. Conventional Technology Currently, cork, soft PVC, olefin resin, etc. are used as cap liners for bottles. Because cork liners have high rebound elasticity, they were used as cap liners for bottles containing beer, carbonated drinks, etc., which are subject to internal pressure. Deterioration of sealing performance has become a problem due to loss of repulsion when used for a long period of time. In recent years, liners made of cork have been replaced by liners made of olefin resin, etc., due to problems such as poor sealing performance, generation of cork dust, and relatively high cost. In addition, soft PVC liners are flexible, have excellent sealing properties, and have relatively good heat resistance, but due to recent hygienic issues such as plasticizers and PVC monomers, they are being replaced by polyolefin resins, which have excellent hygienic properties. be. Polyethylene resins, ethylene-vinyl acetate copolymers, ethylene-propylene copolymers, ethylene-butene copolymers, and blends thereof are generally used for polyolefin resin liners. Among these, polyethylene resin has excellent hygienic properties, but since it is hard as a cap liner, its sealing performance is poor for bottles with poor bottle opening shapes. On the other hand, liners made of ethylene-based copolymers such as ethylene-vinyl acetate copolymers and liners made from the above-mentioned blends have excellent food hygiene properties, are flexible and have rubber elasticity, have excellent sealing properties, and have poor bottle mouth shape. It is possible to maintain sealing properties even for bottles of However, when these ethylene copolymer liners and the blended liners are heat-filled or heat sterilized, the resin softens and melts, resulting in deformation and loss of rubber elasticity. Therefore, the sealing performance is impaired. Therefore, there has been a need for a cap liner that is highly hygienic and maintains its sealing properties not only under storage conditions but also after the above-mentioned process of heat filling or heat sterilization. Problems to be Solved by the Invention The present inventors have solved the problem of the contents, which are the drawbacks of these ethylene copolymer liners, without substantially impairing the flexible and excellent sealing properties of the ethylene copolymer liners. Heat-resistant sealability during heating filling,
Heat-resistant sealability during the heat sterilization process after filling the contents,
As a result of various studies aimed at improving the sealing performance after cooling after the heat sterilization process, it was discovered that such problems could be solved by using a cap liner made of a specific polymer composition. The invention has been completed. Means for Solving the Problems That is, the present invention provides: A (a) 100 to 30 parts by weight of an ethylene-vinyl ester copolymer and/or an ethylene-unsaturated carboxylic acid ester copolymer (b) a linear polyethylene and/or or polybutene and/or polyester elastomer 0 to 70 parts by weight (c) crosslinking agent
30-90% by weight composition with a gel fraction of 5-89% obtained by melt-kneading and crosslinking 0.01-2 parts by weight B Linear polyethylene and/or polybutene and/or polyester elastomer 70
This is a cap liner with excellent heat resistance made of a polymer composition uniformly mixed with ~10% by weight. The ethylene-vinyl ester copolymer used as component A(a) of the present invention includes ethylene and vinyl acetate,
A copolymer with a carboxylic acid vinyl ester such as vinyl propionate, and an ethylene and vinyl acetate copolymer is most preferred. The vinyl ester concentration in the copolymer is preferably 3 to 25 mol%, particularly 7 to 22 mol%. Ethylene-unsaturated carboxylic acid ester copolymers include ethylene and carboxylic acids such as methyl acrylate, ethyl acrylate, n-butyl acrylate, isobutyl acrylate, methyl methacrylate, ethyl methacrylate, n-butyl methacrylate, and isobutyl methacrylate. It is a copolymer with ester. Further, the concentration of carboxylic acid ester in the copolymer is preferably 3 to 25 mol%, particularly 7 to 22 mol%. These copolymers are produced by high-pressure radical polymerization, and their melt flow rate (hereinafter abbreviated as MFR) is preferably in the range of 0.1 to 50 dg/min. In the present invention, component (b) selected from linear polyethylene, polybutene, and polyester elastomer can be used in combination with component (a). Linear polyethylene is a homopolymer of ethylene and ethylene and butene, 4-methylpentene-1
MFR0.1~50dg/min, density with copolymer with etc.
The density is in the range of 0.910 to 0.965 g/cm ³ , and preferably the density is in the range of 0.930 or more. Polybutene-1 is a polymer of butene-1,
Preferably, the MFR is in the range of 0.1 to 50 dg/min and the density is in the range of 0.890 to 0.940. Similarly, polyester elastomers that can be used as component A(b) include Hytrel manufactured by Dupont;
These include Pelprene manufactured by Toyobo Co., Ltd. and Alunite manufactured by Akzo Plastics. Polyester elastomers have superior load resistance and bending fatigue resistance over a wide temperature range compared to other thermoplastic elastomers, and this property is one of the features of the cap liner of the present invention. It will probably be used effectively when used as an ingredient. Examples of the crosslinking agent for component A(c) include peroxides and azo compounds, and among these, organic peroxides are particularly preferred. Examples of the organic peroxide include t-butyl peroxy acetate, t-butyl peroxy isobutyrate, t-butyl peroxy 2-ethylhexanate, and t-butyl peroxy pivalate. In the present invention, the blending ratio of each component (a), (b), and (c) must be within the following range. (a) Component 100 to 30 parts by weight (b) Component 0 to 70 parts by weight (c) Component 0.01 to 2 parts by weight The amount of component (a) is 30 parts by weight or less, that is, the amount of component (b) is 70 parts by weight. If it exceeds 100%, the properties of the cap liner will become stiff and the sealing performance at room temperature will deteriorate, which is undesirable. If the amount of component (c) is less than 0.01 part by weight, the heat resistance of the cap liner will be poor, the permanent deformation rate during heating will be high, and the sealing performance after cooling will be poor, which is not preferable. On the other hand, if it exceeds 2 parts by weight, the degree of crosslinking will increase too much,
The loss of plasticity results in a poor finish on the surface of the cap liner, which is undesirable because the sealing performance eventually deteriorates. In order to obtain composition A in which components (a), (b), and (c) are melt-kneaded and crosslinked, each component is mixed simultaneously or sequentially using a single screw extruder, twin screw extruder, Banbury mixer, etc. Kneading and crosslinking are carried out at a temperature of 150 to 280°C, preferably 160 to 250°C. The degree of crosslinking of the resulting composition A varies depending on the type and amount of component (c), kneading temperature, time, etc., but it can be adjusted so that the gel fraction is in the range of 5 to 89%. is necessary. If the gel fraction is less than 5%, heat resistance will be lacking, and the permanent deformation rate at high temperatures will increase;
If it exceeds 89%, the surface finish of the cap liner will be poor, and in any case, the sealing performance will deteriorate, which is not preferable. The polymer selected from linear polyethylene, polybutene and polyester elastomer used as component B of the present invention is the same as that already explained as component A(b). In the present invention, the blending ratio of component A and component B must be in the range of 30 to 90% by weight of component A and 70 to 10% by weight of component B. If the proportion of component A is less than 30% by weight, that is, the proportion of component B is greater than 70% by weight, the cap liner will lack flexibility and its sealing performance will be impaired. On the other hand, if the blending ratio of component A is 90% by weight or more, that is, the blending ratio of component B is 10% by weight or less, the moldability will be poor. If the moldability is poor, for example, when extruding a cap liner sheet using an extruder, it may not be possible to obtain a sheet with a good appearance and less uneven thickness, or it may not be possible to obtain a sheet with a good appearance and less uneven thickness, or it may not be rolled into a uniform sheet during in-shell molding. resulting in undesirable consequences. To uniformly mix component A and component B of the present invention,
They may be melt-mixed simultaneously or sequentially in a single-screw extruder, twin-screw extruder, Banbury mixer, or the like at a temperature of 150 to 280°C, preferably 160 to 250°C. The cap liner of the present invention is produced by applying the above-mentioned thermoplastic resin composition at about 150 to 250°C using an extruder.
After being formed into a sheet with a thickness of 0.3 to 2.0 mm, preferably 0.5 to 1.0 mm, it is punched out using a punching machine with a diameter that matches the shape of the bottle and cap, and inserted into the cap. At this time, it is also possible to use an adhesive to bond the cap and liner. The cap liner of the present invention can also be produced by dropping the molten resin extruded from an extruder at around 150 to 250°C into the inside of the cap and then pressing it into a certain shape (in-shell molding method). .
The term cap here refers to all types of caps, including crowns, screw-on caps, and tear-off caps, and materials include aluminum, tin, and resin. Effect: A resin composition having a composition similar to that of the cap liner with excellent heat resistance according to the present invention was disclosed in the Japanese Patent Publication No. 55.
-Described in Publication No. 21050. That is, the publication describes a blend of a thermoplastic crystalline polyolefin resin and a cross-linked ethylene-vinyl acetate copolymer having a vinyl acetate content of 40 to 70% by weight.
Disclosed are elastoplastic compositions in which the blend has a gel content of 90% or more, which elastoplastics are useful in the manufacture of tires, hoses, belts, gaskets, molds, and molded parts by extrusion, injection molding, or compression molding techniques. It is stated that However, when the present inventor evaluated the technology described in the same publication as a heat-resistant capliner, it was found that the surface of the extruded sheet for capliner was extremely uneven, the sealing performance was insufficient, and the productivity during the production of the extruded sheet was significantly poor. It was found that practical application was difficult due to the following drawbacks. Thereafter, the present inventor made extensive efforts to improve the technology, and as a result, the present invention was achieved. That is, the present invention first utilizes the technique disclosed in the publication and (1) the ethylene-vinyl acetate copolymer used.
The technology in this publication is based on the vinyl acetate content produced by the solution method.
The present invention is a copolymer with a vinyl acetate content of 8-51% by weight, prepared by high-pressure bulk radical polymerization, as opposed to a 40-70% by weight copolymer such as pinatene. (2) While the gel fraction was 90% or more in the technique of the same publication, the gel fraction of the present invention is in a specific range of 5 to 89%. (3) As the A(b) or B component, a specific linear polyethylene Due to the use of polybutene and/or polyester elastomer, etc., the structure of the present invention makes it possible to obtain a cap liner with excellent heat resistance. The present invention will be explained using Examples and Comparative Examples. [1] Performance evaluation method The melt flow rate, deformation rate under load, permanent deformation rate, gel fraction, and actual heat-resistant sealability shown in the following Examples and Comparative Examples were measured by the following method. (1-1) Melt flow rate (MFR) According to JIS-K-7210, temperature 190℃, load 2160
The measurement was carried out under the conditions of g. (1-2) Load deformation rate, permanent deformation rate See Table 1 The flexibility of the liner is shown as the load deformation rate at 30℃. It is desirable that it be 10% or more. The heat resistance as a liner is shown by the permanent deformation rate at 100℃. It is desirable that it be 60% or less. Table 1 Heating load deformation test method Measuring machine: Toyo Seiki Load deformation tester Specimen: 10 x 10 x 3 mm Load: 40Kg Measuring method: Preheating time 30 minutes Loading time 10 minutes Recovery time 30 minutes A: Initial specimen Thickness B: Thickness after 10 minutes of loading C: Thickness after 30 minutes of load removal, and the load deformation rate and permanent deformation rate were calculated using the following formula. Load deformation rate = A-B/A x 100 Permanent deformation rate = A-C/A x 100 (1-3) Appearance of extruded sheet The material was made into a T-die sheet with a thickness of 0.7 mm at 180℃ using a 30 mmφ extruder. Fabrication. The unevenness on the surface of the sheet was observed and evaluated. (1-4) Heat-resistant sealability Equipment used Cap sealing machine 301A type (manufactured by Toyo Shokuhin Kikai) Aluminum cap (28mmφ) 120ml glass bottle (diameter 28mmφ) Thickness 0.7mm liner (27.5mmφ T-die sheet) Procedure Heat the bottle to 80℃ Fill with warm water leaving 10ml of space. Next, the cap with the liner inserted is attached to the bottle mouth using a cap sealing machine and sealed. Immediately place in an air oven at 130℃ and heat for 1 hour. Remove from the oven and measure the durability of reduced pressure after 24 hours. The durability of reduced pressure is determined using a vacuum tester manufactured by Yokoyama Keiki. If the reduced pressure value is low, it is determined that there is a leak. Usually in the range of 30±5cmHg. (1-5) Gel fraction A press sheet with a thickness of 0.5 mm (temperature 180°C) was prepared, and 0.5 g was sampled from it.
Weigh. Place this in a 50ml Erlenmeyer flask and add 50ml of toluene. Seal tightly and leave at room temperature for 72 hours. After the elapsed time, it was filtered through a 60 mesh wire mesh, and the weight of what remained after drying and undissolved was measured to calculate the gel fraction. Gel fraction % = weight of undissolved material/initial weight x 100 [2] Materials (2-1) Materials used Listed in Table-2 (2-2) Preparation of crosslinked composition A Table-3, Table The compound shown in -4 was kneaded and crosslinked at 180° C. using a 40 mmφ extruder (L/D=28 screw mixing type).
A non-crosslinked composition shown in Comparative Example was also extruded under the same conditions. (2-3) Preparation of final composition Crosslinked composition A obtained in (2-2) and B polyolefin resin and/or polyester elastomer are melt-kneaded in the ratios shown in Tables 3 and 4. The kneading conditions were 180℃ using a 40mmφ extruder (L/D=28, mixing type). However, when using polyester elastomer, the temperature
The temperature was 220℃. Example 1 Ethylene-vinyl acetate copolymer (a-1) 100
Part by weight and 0.4 part of organic peroxide (c-1) were kneaded and crosslinked. 50 parts by weight of the obtained crosslinked composition A and 50 parts by weight of linear polyethylene (b-1) were kneaded. The obtained composition was evaluated in terms of basic physical properties required as a cap liner, deformation rate under load, permanent deformation rate, and extruded sheet appearance, and the results are shown in Table 2. The gel fraction of crosslinked composition A was also measured. Examples 2 to 6 Predetermined amounts of ethylene-vinyl acetate copolymer (a-1) and linear polyethylene (b-
1) The composition of organic peroxide (c-1) is shown in the table below.
A composition for a cap liner was obtained by changing the composition as shown in 2. The obtained composition was evaluated in the same manner as in Example 1, and the results are shown in Table 3. Example 7 An experiment was conducted in the same manner as in Example 3 using ethylene-vinyl acetate copolymer (a-2) instead of ethylene-vinyl acetate copolymer (a-1). Example 8 An experiment was conducted in the same manner as in Example 3 using ethylene-ethyl acrylate copolymer (a-6) instead of ethylene-vinyl acetate copolymer (a-1). Example 9 In Example 3, when obtaining crosslinked composition A, polybutene was used instead of linear polyethylene (b-1).
A similar experiment was conducted using 1(b-2). Example 10 In Example 3, linear polyethylene (b-
A similar experiment was conducted using polybutene-1 (b-2) instead of 1). Example 11 In Example 3, a similar experiment was conducted using polybutene-1 (b-2) instead of the chain polyethylene (b-1) to be kneaded with the crosslinked composition A. Example 12 A similar experiment was conducted in Example 3 using polyester elastomer (b-3) instead of linear polyethylene (b-1) to be kneaded with crosslinked composition A. All of Examples 1 to 12 exhibited good basic physical properties as a cap liner. These results are shown in Table 3. Comparative Example 1 20 parts by weight of ethylene-vinyl acetate copolymer (a-1), 80 parts by weight of linear polyethylene (b-1),
Examples of compositions obtained by kneading 70 parts by weight of crosslinked composition A obtained using 0.4 parts by weight of organic peroxide (c-1) and 30 parts by weight of linear polyethylene (b-1) Evaluation was performed in the same manner as in 1. The deformation rate under load at 30°C is small and lacks flexibility as a cap liner. Comparative Example 2 A composition obtained using 20 parts by weight of the crosslinked composition A of Example 2 and 80 parts by weight of linear polyethylene (b-1) was similarly evaluated. Similar to Comparative Example 1, the cap liner lacked flexibility. Comparative Example 3 The same evaluation was performed on the crosslinked composition A of Example 1. It is inferior to the composition of Example 1 in terms of heat resistance and sheet appearance. Comparative Example 4 Similarly, the crosslinked composition A of Example 2 was evaluated in the same manner. The results were similar to those of Comparative Example 3. Comparative Examples 5 to 8 Similar evaluations were performed on the blend compositions obtained without using the organic peroxide (c-1) in Examples 3, 7, 10, and 12. 100
In the heating load test at ℃, the sample cracked or the permanent deformation rate was large, and the heat resistance was insufficient. Comparative Examples 9, 10, 13 to 16 Similar evaluations were performed on the materials used in this experiment. Comparative Examples 11 and 12 Generally, an ethylene-vinyl acetate copolymer having a vinyl acetate content of 2 to 10 mol% is used as a capliner. Similar evaluations were performed on ethylene-vinyl acetate copolymers (a-3) and (a-4) as equivalent products to these cap liners. Comparative Examples 17 and 18 Similar experiments were conducted using the composition described in Japanese Patent Publication No. 55-21050. The sheet of the obtained composition had large surface irregularities and was unsuitable as a cap liner. Further, this composition was evaluated by kneading it with linear polyethylene in the same manner as in the method of the present invention, but the sheet appearance was not improved. Example 13 and Comparative Example 19 In order to confirm the performance as a cap liner, heat-resistant sealability was evaluated. The results are shown in Table-5.

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[Table] Comparative Example 20 90 parts by weight of ethylene-vinyl acetate copolymer (a-1), 10 parts by weight of propylene-ethylene copolymer (J340 manufactured by Mitsui Petrochemical Industries, Ltd.), and peroxide (c- 1) 0.4 parts by weight was kneaded and crosslinked. The MFR of the composition obtained by kneading 80 parts by weight of the obtained crosslinked composition and 20 parts by weight of the above J340 is 0.08 dg/min,
In the 30℃ load test, the load deformation rate was 34%, the permanent deformation rate was 13%, and in the 100℃ load test, the load deformation rate was 71%,
The permanent deformation rate was 66%. Although the composition has flexibility, the permanent deformation rate is too large, making it unsuitable as a cap liner.

Claims (1)

[Scope of Claims] 1 A (a) 100 to 30 parts by weight of ethylene-vinyl ester copolymer and/or ethylene-unsaturated carboxylic acid ester copolymer, (b) linear polyethylene and/or polybutene and/or 30-90% by weight of a composition with a gel fraction of 5-89% obtained by melt-kneading and crosslinking 0-70 parts by weight of a polyester elastomer and (c) 0.01-2 parts by weight of a crosslinking agent, and B linear polyethylene and/or or polybutene and/or polyester elastomer 70
A cap liner with excellent heat resistance made of a polymer composition uniformly mixed with ~10% by weight. 2 A (a) A patent in which the ethylene-vinyl ester copolymer and/or ethylene-unsaturated carboxylic ester copolymer has a vinyl ester and/or unsaturated carboxylic ester content of 3 to 25 mol%. A cap liner with excellent heat resistance according to claim 1.