JPS6234618B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention relates to a container stopper, and more specifically, it has compressive stress-strain characteristics similar to cork, and has elasticity that is superior in sealing and gas barrier properties compared to cork. The present invention relates to a container sealing stopper consisting of a body. (Prior Art) Cork has conventionally been most widely used as a sealing stopper for containers containing beverages and the like. In other words, cork not only has excellent hygiene and flavor retention, but also has a large amount of strain per compressive stress in a relatively low stress range (high compression compliance), and can be sealed and sealed with relatively low stress. It has the characteristics of being able to be opened and also ensuring a secure sealing engagement with the container mouth. However, if cork is not kept moist with water, its sealability or gas barrier properties with the mouth of a container such as a bottle will be unsatisfactory, and since cork is a natural product, the surface of the cork If there is a medullary line in the container, there is a problem in that the gas barrier property between the container and the opening of the container is deteriorated. Ethylene-vinyl acetate copolymer (EVA) foam is known as a synthetic material for container closures that can replace amber closures. (Problem to be Solved by the Invention) However, the above-mentioned plug made of EVA foam has a smaller amount of strain per compressive stress than cork, especially in the low stress region, and has poor sealability and easy opening. It is inferior to cork in terms of plugging properties. In addition, ethylene-vinyl acetate copolymers have a unique odor, and thus are still not fully satisfactory in terms of flavor retention of the contents. Therefore, the technical problem of the present invention is to have compressive stress-strain characteristics similar to those of cork when wet, to have excellent sealing and gas barrier properties compared to natural cork, and to have hygienic properties and flavor retention. To provide a container sealing stopper made of a synthetic elastic material with excellent properties. (Means for solving the problems) In the present invention, in order to achieve the above-mentioned problems, as an elastic body for a container stopper, (A) a polymerized block of alkenyl aromatic hydrocarbon is used in an amount of 2 to 33% by weight of the whole. and (B) the hydrogenated alkenyl aromatic hydrocarbon-conjugated diene block copolymer, which contains hydrogenated alkenyl aromatic hydrocarbon-conjugated diene block copolymer and the hydrogenation degree of the conjugated diene block is 70% or more; A closed-cell foam with an expansion ratio of 1.1 to 4 times is used, consisting of a blend of agglomerates and polyolefins. (Function) Figure 4 of the attached drawing is a diagram showing the relationship between compressive stress and strain for various elastic bodies, where curve A is for cork in a wet state, curve B is for cork in a dry state,
C is a known low-foamed ethylene-vinyl acetate copolymer (expansion ratio 2.1 times); D is also a foamed ethylene-vinyl acetate copolymer (expansion ratio 2.2 times); E
is a foam (expansion ratio: 2 times) of a hydrogenated block copolymer of an alkenyl aromatic hydrocarbon and a conjugated diene (hereinafter sometimes simply referred to as a hydrogenated block copolymer) according to the present invention, and F is a foam of the present invention. Stress of foamed product of blend of hydrogenated block copolymer and polyolefin according to the invention (expansion ratio: 2x)
The distortion curves are shown respectively. Referring to the results shown in FIG. 4, the following facts become clear. Even though natural cork has a large compression compliance when wet, which is desirable as an elastic material for stoppers, the stress-strain curve when dry is quite different from that when wet, and the compression compliance is small, making it difficult to use as a stopper. Still unsatisfied with functionality. On the other hand, the compression compliance of known ethylene-vinyl acetate copolymer foams is greater than that of dry cork, and its performance is far behind that of wet cork. In contrast, when a foam of a hydrogenated block copolymer is used according to the present invention, particularly a foam of a blend of a hydrogenated block copolymer and a polyolefin, the stress-strain curve upon compression is It is located below the cork, and exhibits behavior similar to cork when wet. Considering the practical sealing function, the ideal sealing material should be one that deforms greatly in low stress regions and also exhibits strong resistance in high stress regions. In other words, the most ideal compression compliance is large in the low stress region and small in the high stress region. Looking at the product of the present invention in more detail in FIG. 4, the compressive compliance is large in the low stress region and small in the high stress region, and has an ideal sealing function. Known ethylene-vinyl acetate copolymer foams have low compressive compliance in high stress regions, but also low compressive compliance in low stress regions, which is far from ideal sealing performance. In addition, even when cork is wet, the compression compliance in the low stress region is large, and it is also large in the high stress region, and it is easy to see that the product of the present invention is superior as a container stopper. Thus, according to the present invention, by using the aforementioned hydrogenated block copolymer or a blend thereof with polyolefin in the form of a closed foam as a stopper, compressive stress and strain similar to cork when wet can be achieved. and, unlike natural cork, these properties are obtained regardless of whether or not the stopper is wetted with the liquid content, and have excellent sealability, uncorkability, and sealability or gas-sealability. A significant advantage is achieved in that the barrier properties are consistently obtained. Furthermore, although the hydrogenated block copolymer used in the present invention exhibits desirable elastic properties as described above, it cannot be thermoformed by extrusion molding, injection molding, etc. It is also a significant advantage that these molding methods allow the parts that come into contact with the container mouth to be manufactured to be intact and to have the desired surface. As already mentioned above, in a natural cork stopper, if the medullary wire enters the surface that contacts the container opening, the gas barrier properties will decrease, so in order to prevent this,
A good quality natural cork must be selected, and the cost of cutting the natural cork into the desired size and shape of the stopper can be avoided, resulting in unnecessary waste of other parts and extremely high costs. However, according to the present invention, by performing injection molding using the resin, there is an advantage that a plug having a desired shape and size can be provided at low cost without waste. The hydrogenated block copolymer used in the present invention is
In addition to the thermoplastic properties mentioned above, the double bonds in the conjugated diene units incorporated into the polymer chain are hydrogenated, making it different from conventional rubbers such as styrene-butadiene-rubber (SBR). , thermoplastic styrene-butadiene-styrene block copolymer (S
-B-S) and styrene-isoprene-styrene.
It is clearly distinguished from block copolymers (S-I-S). That is, in this hydrogenated block copolymer, the unsaturated bonds derived from the diene are saturated by hydrogenation, so it has almost no off-taste or off-odor.
Therefore, no foreign taste or odor is transferred to the contents, and flavor retention is extremely excellent. Moreover, as will be described in detail later, this polymer has an extremely high molecular weight, prevents the resin component from being extracted and transferred into the contents, and has excellent hygienic properties. Furthermore, the hydrogenated block copolymer used in the present invention exhibits significantly less stress relaxation even when subjected to long-term aging or high-temperature thermal history, and as a result, sealability is reliably maintained over a long period of time. . Furthermore, polyolefins and olefin copolymers tend to develop environmental stress cracks due to attack by content vapor, etc., but when this hydrogenated block copolymer is blended with polyolefins, such environmental stress cracks can be effectively prevented. It has the advantage of being eliminated. If the proportion of alkenyl aromatic hydrocarbon polymer blocks in the copolymer is less than 2% by weight, the necessary thermoformability cannot be obtained;
If the amount is more than 1, the compression compliance in the low stress region becomes small, which is not preferable for the purpose of the present invention. In addition, the degree of hydrogenation of the conjugated diene block is 70
%, the flavor retention properties when used as a stopper will be inferior to those within the scope of the present invention. (Description of Structure) In FIG. 1 showing an example of a container stopper of the present invention, this container stopper includes an annular member 1 made of an elastic body.
and a core 2 made of glass or hard plastic. The core 2 has a handle 3 formed integrally therewith at one end thereof. The inner circumferential surface 4 of the annular elastic body 1 has a diameter slightly smaller than the outer diameter of the core 2, and tightly engages the outer circumferential surface of the core 2 inserted into the hole of the elastic body 1. Elastic body 1
The outer circumferential surface 5 of is a tapered surface,
It is adapted to resiliently engage the inner surface of a container mouth (not shown). Grooves 6 and 7 are provided at the upper and lower ends of the elastic body holding portion of the core 2, and washers 8 and 9 made of an elastic resin such as polyethylene are fitted into these grooves 6 and 7. An annular member 1 made of an elastic body is fixed onto a core 2 so as not to shift. In FIG. 2 showing an example of another type of container stopper,
The elastic body 1a has a cylindrical shape with one end rounded, and is made of hard plastic or the like.
The other end portion is inserted into the central recess 11 of 0 and fixed with adhesive (not shown) or the like. The stopper shown in FIG. 3 is made of a cylindrical elastic body 1b, and is fitted into the mouth of a wine pin to seal the stopper. In the present invention, in any form of the stopper, the elastic body portion 1, which contacts the inner surface of the container opening,
1a and 1b are formed from a hydrogenated product of a block copolymer of an alkenyl aromatic hydrocarbon and a conjugated diene, or a blend of this hydrogenated block copolymer and a polyolefin. The alkenyl aromatic hydrocarbon unit of the block copolymer used in the present invention has the following formula: In the formula, R ₁ is a hydrogen atom or a lower alkyl group, and R ₂ is a hydrogen atom or a lower alkyl group. Examples include monomers represented by the following, particularly those consisting of styrene, vinyltoluene, α-methylstyrene, etc. can be, while as a conjugated diene unit, the formula In the formula, R ₃ is a hydrogen atom or a lower alkyl group, and examples thereof include monomers represented by the following, particularly those consisting of butadiene and isoprene. Polymerization block of alkenyl aromatic hydrocarbons (A)
is preferably in the range of 2 to 33% by weight based on the total block copolymer from the viewpoint of rubber-like elastic properties and thermoformability.
The degree of hydrogenation in (B) is desirably 70% or more, particularly 90% or more, in order to suppress the decrease in opening torque after heat treatment to a low level. The polymerization block (A) of alkenyl aromatic hydrocarbons is
It is desirable to have an average molecular weight of 4,000 to 115,000, while the conjugated diene polymerization block (B) has an average molecular weight of 20,000 to 450,000 in view of the elastic properties required for container stoppers and hygienic properties. The bonding type of both polymer blocks is most preferably ABA type, but B-A-B type or A
- Type B can also be used. Hydrogenated block copolymers are, for example,
As described in Japanese Patent No. 6636, etc., it is easily produced by hydrogenating a block copolymer of an alkenyl aromatic hydrocarbon and a conjugated diene in the presence of a hydrogenation catalyst such as Raney nickel. The elastomer resin for plugs used in the present invention can be blended with ingredients known per se according to known formulations.
For example, in order to adjust the opening force to an easy-to-open level, fatty acids, derivatives such as amides thereof, and lubricants such as various waxes are added, and titanium dioxide is added to color the liner or to impart opacity. White pigments such as carbon black, red iron,
Coloring pigments such as tartrazine lake can be added, and calcium carbonate, talc, etc. can be added to adjust the physical properties.
Fillers such as clay and barium sulfate can be added.
In addition, anti-blocking agents such as silica can be added to prevent blocking, and antioxidants such as externally harmful phenols can be added to prevent thermal deterioration during processing into plugs or sterilization. . In the most preferred embodiment of the present invention, the aforementioned hydrogenated block copolymer (2) and polyolefin (2) are used in the form of a mixture, ie, a blend, as the plug material. That is, in this embodiment of the present invention, by blending the hydrogenated block copolymer and the polyolefin, the stress-strain characteristics during compression are very similar to those of cork when wet, and the thermoformability is improved. is significantly improved compared to the block copolymer alone. Furthermore, while maintaining the excellent properties of polyolefin, it is possible to significantly suppress a decrease in opening force due to thermal history, and to significantly improve the tendency for cracking due to environmental stress and the decrease in sealing performance due to impact. The polyolefins used include low-, medium-, or high-density polyethylene, crystalline polypropylene, crystalline ethylene-propylene copolymer, ethylene-propylene-butene-1 copolymer, ionically crosslinked olefin copolymer (ionomer), Examples include one or a combination of two or more of ethylene-vinyl acetate copolymers and the like. For the purposes of the present invention, the hydrogenated block copolymer (2) and polyolefin (2) are preferably used in a weight ratio of 95:5 to 10:90, particularly 90:10 to 30:70. That is, if the blending ratio of the hydrogenated block copolymer is less than the above range, it is difficult to bring the compression compliance into a range suitable for container stoppers, and the blending ratio of the hydrogenated block copolymer is Increasing the amount of hydrogen block copolymer beyond the above range is disadvantageous from an economic point of view, and the thermoformability is poorer than when the amount of hydrogen block copolymer is within the above range, and it becomes similar to wet cork. It becomes difficult to obtain compressive stress-strain characteristics. In the stopper of the present invention, the resin has a foaming ratio of
It is also very important to form a closed cell foam of 1.1 to 7 times, especially 1.1 to 3.5 times. In this specification, the expansion ratio means a density-based ratio. If the expansion ratio is lower than the above range, it is difficult to make the compressive stress-strain characteristics similar to those of wet cork, while if the expansion ratio is higher than the above range, the gas barrier properties will decrease. death,
Moreover, the flavor retention of the stopper is reduced, which is not preferable. The closed foam of the resin can be easily produced by kneading the resin with a chemical blowing agent such as azodicarbonamide, and injecting the kneaded composition into a mold with a plug-shaped cavity. can get. Alternatively, the above-mentioned kneaded composition may be extruded into any shape such as a cylinder, and this molded product may be cut into predetermined dimensions to be used as a cork substitute stopper. The container stopper of the present invention has the remarkable advantage that even when the stopper has the shape shown in FIG. 3, it is easy to screw in a corkscrew and it is also easy to open the stopper. (Example) Next, an example of the present invention will be shown. Examples 1 to 5 100 parts of each of the materials shown in Table 1, 1 part of a blowing agent (azodicarbonamide), and 0.1 part of a lubricant (erucic acid amide) were dry-blended in a 40 mmφ extruder (screw L/D= 15, resin temperature 140℃),
The mixture was cooled in water and pelletized in a conventional manner to produce various pellets for synthetic plugs. Using these various sample pellets, synthetic plugs with an outer diameter of 22 mm and a height of 38 mm were made using an injection molding machine (Neomatsu 350/120, 10 oz, manufactured by Sumitomo Heavy Industries, molding temperature, zone 5 = 180°C, zone 4 = 200°C) , Zone 3 = 210℃, Zone 2 =
Each material was molded separately at 200°C (Zone 1 = 180°C). Comparative Example 1 Natural cork cut into an outer diameter of 22 mm and a height of 38 mm is used. Comparative Examples 2 to 3.5 Synthetic plugs were molded using each material in the same manner as in the examples, using the same compounding ratios. Comparative Example 4 Using a material that was pelletized in the same manner as in Example and further added with 1 part of sodium hydrogen carbonate and dry-blended, a synthetic stopper was molded using an injection molding machine (molding temperature, Zone 5 = 220°C, Zone 4 = 230°C). , zone 3=
Molding was performed at 230°C, zone 2 = 200°C, zone 1 = 180°C). To measure the amount of oxygen permeation of these various synthetic stoppers, place a bottle with a capacity of 500 ml and an inner diameter of 17.5 mm in water, turn it upside down, replace the inside of the bottle with nitrogen gas, and then close the bottle with a synthetic stopper. Place the sample bottle at a temperature of 37°C and relative humidity.
The bottle was left standing upright under 50% conditions for 5 days, the gas inside the bottle was measured by gas chromatography, and the amount of oxygen gas permeated per 24 hours was determined using equation (1) shown below. Regarding the capping performance, using the same bottle as described above, the sample composition was capped, and the force required to close the cap was measured using a push-pull gauge. In addition, as for opening performance, the force required to pull out a closed sample stopper was measured using a push-pull gauge. The water leakage test was conducted in accordance with JIS Crown S-9017.
The results of each installation are shown in Table 1. (A-B)/100 x 500 x 24/C...(1) A: Oxygen gas content (%) after C time B: Oxygen gas content (%) immediately after nitrogen substitution C: Until oxygen gas measurement time (H). For the sensory test, the content is 500ml and the inner diameter of the mouth is 500ml.
100 ml of distilled water was put into a 17.5 mm bottle, the bottle was closed with a sample stopper, and the bottle was left lying on its side at 37°C for one week, and the odor and taste of the distilled water were examined. The symbols in Table 1 have the following meanings. ABA = Hydrogenated block polymer of 1.3-butadiene and styrene (specific gravity 0.92, styrene content 33%, solution viscosity of 20wt% toluene solution at 25℃ 2000 ops hydrogenation amount 90%) SBR = styrene butadiene rubber (density 0.95 , melt index 2.6) PP = polypropylene (density 0.90, melt index 10) LDPE = low density polyethylene (density 0.917, melt index 6.5) EVA = ethylene vinyl acetate copolymer (vinyl acetate content 14%, density 0.93, melt Index 15) Plugability: 10 kg or less is considered good and is indicated by a ○ mark, 10
Items exceeding Kg are considered defective and marked with an x. Openability: 5 kg or less is considered good and is indicated by a ○ mark, 5
Items exceeding Kg are considered defective and marked with an x. Sensory test = Tests with no change in odor or taste are considered good and are marked with an ○; those with transfer of odor or taste are considered poor and marked with an x.

[Table] (Effects of the Invention) According to the present invention, it has compressive stress-strain characteristics similar to those of cork when wet, has superior sealing properties and gas barrier properties compared to natural cork, and has hygienic properties. A sealing stopper with excellent flavor retention is provided. Furthermore, although the hydrogenated block copolymers and their blends used in the present invention exhibit desirable elastic properties as plugs as described above, they cannot be thermoformed by extrusion molding, injection molding, etc. By using these molding methods, it is possible to manufacture the part that comes into contact with the container mouth with no damage and to form a desired surface.

[Brief explanation of the drawing]

FIG. 1 is a plan view including a half cross section of one embodiment of the present invention, and FIGS. 2 and 3 are a plan view and a perspective view including a half cross section showing other embodiments of the present invention. FIG. 4 is a graph showing the relationship between stress and strain during compression of the synthetic stopper of the present invention, natural cork, and other synthetic stoppers. 1, 1a, 1b are elastic bodies, 2 is a core, 3 is a handle,
6 and 7 indicate grooves, and 8 and 9 indicate washers, respectively.

Claims (1)

[Scope of Claims] 1. A container stopper in which at least the portion that contacts the inner surface of the container opening is made of an elastic material, wherein the elastic material contains (A) a polymer block of alkenyl aromatic hydrocarbon of 2 to 33% of the total weight. %, and the degree of hydrogenation of the conjugated diene block is 70% or more, or (B) the hydrogenated alkenyl aromatic hydrocarbon-conjugated diene. A container closure characterized by being made of a closed-cell foam made of a blend of a block copolymer and a polyolefin and having an expansion ratio of 1.1 to 4 times. 2. The container stopper according to claim 1, wherein the blend contains a hydrogenated block copolymer and a polyolefin in a weight ratio of 95:5 to 10:90.