JPS5915062A - Resin cap and its manufacture - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] The present invention relates to a resin cap and a method for manufacturing the same.
More specifically, it consists of a hard resin lid and a soft liner material applied to the inner surface of the top plate, and the liner is formed by pressure molding inside the lid and is firmly thermally bonded to the lid. This article relates to a resin cap and its manufacturing method.

Resin caps are suitable for various containers. However, the problem is that the part that engages with the container mouth lacks cushioning properties, making it difficult to achieve a high degree of sealing. For this reason, various proposals have been made to apply a soft elastomer as a liner material to the inner surface of the top plate of the hard resin lid. However, there are two problems with liner materials for resin caps that still need to be resolved. One of these is that it is generally difficult to adhesively fix the liner material to the lid, and the other is that the liner material peels off from the lid and falls off due to the torque when tightening or opening the lid. This is the problem.

Generally, as lid liners, polyvinyl chloride resin plastisol applied to the lid body and heated to gel is widely used, but this plastisol and its gelled products have no adhesive property to polyethylene or polypropylene. This is unsatisfactory from the standpoint of preventing the liner from falling off.

The present invention is an elastomer for liner formation, in which a blend of an ethylene resin and a natural or synthetic rubber or a thermoplastic elastomer, which will be described in detail below, is placed on a lid made of a hard olefin resin, and the blend is melted. It has been found that when an object is press-molded into a liner under specific conditions, the liner and the lid are firmly thermally bonded without passing through an adhesive layer.

That is, an object of the present invention is to provide a resin cap in which a soft liner material is firmly thermally bonded to a hard resin, and a method for manufacturing the same.

Another object of the present invention is to provide a resin cap in which the liner material is stably held without coming off from the lid despite the large torque applied when the resin cap is fastened to a container or when the container is opened, and a method for manufacturing the same. is to provide.

Still another object of the present invention is to provide a method for manufacturing a resin cap provided with a liner material at a high production rate, with a small number of steps, and without wasting resin.

According to the present invention, in the resin cap made of a lid made of a hard thermoplastic resin and a soft liner material applied to at least a portion of the top plate of the lid that engages with the container mouth, The hard resin is made of a hard olefin resin, and the liner phase is a mixture of an ethylene thermoplastic resin and a natural or synthetic rubber or a thermoplastic elastomer in a ratio of 95:5 to 5:5.
The liner is formed by pressing the molten blend in the lid in situ, and the liner is thermally bonded to the lid without passing through an adhesive layer. Provided is a resin cap characterized by:

According to the present invention, the lid made of a hard olefin resin is heated to a temperature of 50° C. or higher, and an ethylene thermoplastic resin is applied to at least the portion of the top plate of the lid that is to be engaged with the container mouth. and natural or synthetic rubber or thermoplastic elastomer in a weight ratio of 95:5 to 5:95 is applied in a molten state, and this melt is pressed with a plunger to form a predetermined liner shape. A method for manufacturing a resin cap is provided, which is characterized in that the resin cap is thermally bonded to the lid body.

The invention will be explained in detail below based on specific examples shown in the accompanying drawings.

In FIG. 1 showing the resin cap of the present invention, this cap consists of a lid (cap shell) 1 made of a hard thermoplastic resin and a liner 2 made of a soft elastomer.

The lid body 1 consists of a top plate part 6 and a skirt part 4 surrounding the top plate part 6, and the inner surface of this skirt part 6 is provided with a screw 5 for fastening to a container neck part (not shown). The liner material 2 is applied to the inner surface of the top plate part B of the lid body, and consists of a central thin part 6 formed by compression molding and a thick sealing ring 7 formed at the peripheral part to be engaged with the container opening. It has become. In this liner material 2, the central thin part 6 may be omitted and it may consist only of the sealing ring 7,
Further, the liner material 2 may have a uniform thickness throughout.

The main feature of the present invention is that while the lid body 1 is made of a hard olefin resin, the liner 2 is composed of an ethylene thermoplastic resin and a natural or synthetic rubber or a thermoplastic elastomer in a ratio of 95:5 to 5:95. The liner 2 of this blend is directly thermally bonded to the lid 1.

Conventionally, low-density polyethylene has been known as a thermoplastic resin with liner properties, and this low-density polyethylene is applied in a molten state to a metal container lid shell coated with adhesive paint, and then embossed with a plunger. It is known to provide a container lid with a liner. However, when low-density polyethylene is applied directly into the polypropylene lid using this method, the adhesive strength of the liner is on the order of 0.1 kg/φ28 groove, and the liner detaches from the resin cap. From the standpoint of defense against 1 hit, this is unsatisfactory.

However, in the present invention, a blend of an ethylene thermoplastic resin and a natural or synthetic rubber or a thermoplastic elastomer is selected as the liner material, and this is formed into a liner inside the lid body by a melt-pressing method. Preferably, when the lid 1 is preheated to a temperature of 50° C. or higher during this press molding, the liner 2 and the lid 1 can be firmly thermally bonded to each other without using a special adhesive.
Its adhesive strength is 1klliI/φ28 or more, especially 4k
It improves to a level of g/φ28 or higher.

According to the present invention, since the liner 2 is firmly adhered to the lid 1, the liner is not only prevented from coming off during transportation and handling of the cap, but also the tightening torque and opening torque for the container are reduced. 2, the liner 2 is prevented from peeling off from the lid 1, and significant advantages are achieved in terms of preventing the liner from coming off and maintaining sealing performance.

In addition, by an extremely simple operation of supplying molten resin into the molded lid and stamping it with a cooled plunger, molding into the desired liner shape and thermal bonding to the lid can be performed all at once. It has the advantage that the number of steps is small, the operation is simple, and the resin cap with liner can be manufactured at a high production rate, for example, as high as 1200 caps/min.

Further, according to the present invention, as described above, there is no need for special adhesive or adhesive application operation, and resin is wasted less than when the liner is punched out into a disc or the like and then inserted into the cap. There are no significant economic advantages.

Furthermore, since the liner constituent material does not contain any plasticizers unlike the case of vinyl chloride resin liners, it is also significantly superior in hygienic properties and flavor retention.

The present invention utilizes the new finding that an elastomer component such as synthetic rubber mixed into an ethylene thermoplastic resin significantly improves the thermal adhesion to a hard olefin resin lid in a short time. be.

In other words, as already pointed out, resins made of ethylene alone, such as low-density polyethylene, exhibit almost no thermal adhesion to the lid resin. It is recognized that it significantly imparts activity to thermal adhesion. Regarding the activation effect on this thermal bonding, there is a chemical factor such as the presence of a chemically affinity or active component for the lid to be bonded, as well as a chemical factor in which thermal bonding occurs at the same time as the melt is formed. We also need to take into account the physical issues that must be addressed.

That is, under the molding and thermal bonding conditions used in the present invention, the polymer in a molten state must be molded while being cooled, and the thermal bonding must be completed during this short period of time in the molten state.

For crystalline polymers such as ethylene homopolymer, the transition from melt to solid is rapid and does not allow enough time for thermal bonding, and this change can cause large strains to remain at the adhesive interface (・5 This is thought to be a major cause of poor thermal adhesion.On the other hand, in the present invention, in the case of a blend of ethylene-based thermoplastic resin and an elastomer such as synthetic rubber, the contribution of rubber elasticity is As a result, the rapid and sudden change to a molten body-solid body is alleviated, and the liner material remains molten or softened for a longer period of time at the interface between the lid and the liner material, and as a result, the thermal bond becomes stronger. It is recognized that the strain remaining at the bonding interface is effectively eliminated or alleviated because this molten or softened state lasts for a longer period of time and there is also a contribution from rubber-like elasticity.

Particularly, this blend has a combination of moderate cushioning properties and easy deformability due to the inclusion of the elastomer component, and provides excellent sealing properties.

In the present invention, any polymer exhibiting rubber-like elasticity at around room temperature can be used as the elastomer to be blended with the ethylene thermoplastic resin. Typical examples of such elastomers include ethylene propylene rubber (EPE).
), ethylene propylene diene rubber (EPDM)
, polyinobutylene rubber (PIB), butyl rubber (I
IR), styrene butadiene rubber <SBl? ,),
-Butadiene rubber (BR), natural rubber, isoprene
Rubber, silicone rubber, butadiene/isoprene.

Rubber, acrylic rubber, fluororubber, acrylonitrile butadiene rubber (#JBR), chloroprene rubber (
CR), synthetic or natural rubber such as urethane rubber, halogenated polyethylene, ethylene-vinyl acetate elastomeric polymer, polyester ether (PEE), butene-1
(PBl), styrene-butadiene-styrene block copolymer (SBS), styrene-isoprene-styrene block copolymer (SIS), hydrogenated styrene-butadiene-styrene block copolymer (SEBS), hydrogenated styrene-isoprene Mention may be made of other elastomeric polymers such as -styrene block copolymer (5EIS), styrene-bugen block copolymer C3B). These elastomers may be used alone or in combination of two or more. In the present invention, among the above-mentioned elastomers, it is particularly preferable to use ethylene propylene rubber (1!; PR), ethylene propylene diene rubber (CEPDM), or polyisobutylene rubber (IIR). These elastomers, in combination with the above-mentioned polyolefin resin, provide a molded article with properties particularly suitable for liners.

For example, many natural or synthetic rubbers derived from dienes have aliphatic double bonds in their molecular chains,
When used as a liner, it tends to impart an undesirable odor to the contents. The above-mentioned three types of elastomers have little such tendency, and even when the liner is stored or heated, these blended elastomer components have relatively little tendency to migrate to the contents (liquid contents).

%, suitable elastomers include ethylene-propylene copolymer rubber (EPR) with an ethylene content in the range of 50 to 80% by weight, and ethylene propylene with an ethylene content in the above range and a small amount (1 to 5 mol). %) of unsaturated components such as dicyclopentadiene, ethylythenenorbornene, 1°4-hexadiene, and methylenenorbornene. These ethylene/propylene rubbers generally have 3
It has a molecular weight of 0,000 to oo,ooo, but from the viewpoint of melt moldability, it is desirable to have a molecular weight smaller than ioO,ooo.

Furthermore, when a styrene-diene block copolymer such as EBB, 81&, 5EBS, or 5EIS is blended, the environmental stress resistance of the liner is also significantly improved. In addition to density polyethylene, crystalline ethylene-propylene copolymer, crystalline ethylene-butene-1 copolymer, crystalline ethylene-vinyl acetate copolymer, crystalline ethylene-acrylic acid ester copolymer, etc. Can be used.

The molecular weight of the ethylene-based resin to be used may generally be within a film-formable molecular weight range, for example, an average molecular weight of 5.
,000 to 400,000, or melt index (ASTM-1238) MI=0.05 to 30.0? / 10 m1n (D can be used suitably.

In the invention, the ethylene thermoplastic resin and the elastomer component are mixed in a ratio of 95:5 to 5:95, particularly 90:10.
from 10:90 to 10:90, most preferably from 85:15 to 10:9
It is also important to use a weight ratio of 0. That is, if the blending ratio of the ethylene resin is less than the above range, the melt moldability will be reduced, and if the blending ratio of the elastomer component is less than the above range, the thermal adhesiveness will be reduced.

When forming this friend, the solubility index (Solubilityparameter) between the ethylene resin and the elastomer
It is preferable to combine them so that the difference in the values (met sr ) is 1.0 or less, particularly 0.5 or less.

The state of dispersion mixing in a polymer blend is closely related to the miscibility of the blended polymers, and the less miscible the polymer, the thicker the particle unit.

Generally, the solubility index (5
olubility parameter, S P
), but this SP value can also be applied to miscibility in the case of polymer blends, and the smaller the difference 1ΔSP1 between the SP values of each polymer, the better the miscibility, and the better the dispersion state. Becomes good. Therefore, in order for the elastomer to be dispersed in the form of fine particles in the ethylene resin base, 1Δ
It is desirable that the value of SP1 is small.

Table 1 below shows solubility index C8P values for ethylene resins and elastomers that can be used in the present invention.

Table 1 J'E 3. [] EPR7,95 EPDM 8.0 11R7,7 PR-18,3 PEE 10.7 PI B 8.05 CR9,4 NR9,3 The above resin composition may optionally contain formulations known per se. Agents such as ultraviolet absorbers, stabilizers, lubricants, antioxidants, antiblocking agents, pigments, dyes, antistatic agents, etc. can be blended according to known formulations.

In the present invention, in order to blend the ethylene resin elastomer, any means known per se can be used. A molten mixture having an island structure is formed.

Examples of hard olefin-based resins constituting the lid include monoolefins, especially ethylene, in which each of 8-fold and R1 is a hydrogen atom, an alkyl group having 4 or less carbon atoms, or an aryl group; Homopolymers or copolymers of propylene, butene-1, pentene-1,6-methylbutene-1,2-methylpentene-R4-methylpentene-1, and styrene can be used. Generally, it is important that these olefin polymers or copolymers be crystalline in order to have sufficient mechanical strength when used as a lid.

Suitable examples of such polyolefins include medium-density or high-density polyethylene (PE), polypropylene (PP), crystalline ethylene-propylene copolymer, polybutene-L-IJ pentene-1.
, poly-4-methylpentene-1 (P4MP1).

In the method of the present invention, when press-forming the molten material in the lid, it is recommended to heat the book in advance to a temperature of 50'C or higher in order to increase the strength of thermal bonding between the liner and the lid, especially for heavy packaging. Become. For example, in the case of a combination of a polypropylene lid and a low-density polyethylene-ethylene-propylene copolymer rubber blend, the adhesive strength when the melt is press-molded on the lid at room temperature is 1. Oky/φ28mm or less, while the adhesive strength when press molding the bath melt on the lid heated to 70'G is 2.5 kli'/2
Improved by 8 mu width.

The reason why the thermal adhesion of the liner is improved by preheating the lid to which the liner is applied is not precisely known, but it is thought to be as follows. That is, the molding of the resin melt into a liner shape is generally carried out under cooling, as described above. Therefore, as already pointed out, under such conditions, the melting or softening state of the liner resin necessary for thermal bonding takes an extremely short time, and strain tends to remain at the bonding interface. .

On the other hand, if the lid is heated in advance, not only will the resin constituting the lid be activated for thermal bonding, but also the liner polymer that comes into contact with the lid will melt or melt during thermal bonding. It is recognized that the softening state is shifted to the longer time side, and the strain that tends to remain at the adhesive interface is more effectively eliminated or alleviated, and the adhesive strength is significantly improved.

In Figures 2-A to 2-C for explaining the method of the present invention, first, the lid body 1 is preheated to a temperature of 50°C or higher (
Figure 2-A). For this purpose, the lid 1 is placed on an anvil 11 equipped with a heater 10, and a plunger 12 equipped with a heater 10 is also pushed on the inner surface of the lid 1 (7).
to heat the lid body 1. Heating may be performed by any means other than heat transfer from a heater, such as infrared radiation heating, heating in a heating furnace, or blowing hot air. The heating temperature of the lid 1 may be 50'C or higher, particularly 60C or higher, and lower than the softening point of the resin constituting the lid. -Even within the above range, the higher the heating temperature, the better the adhesive strength, so the specific temperature to be used should be determined in accordance with the type of ethylene copolymer constituting the liner material so as to obtain the desired adhesive strength. good. Further, the heating temperature of the lid body 1 is allowed to exceed the softening point for a short period of time.

Next, in FIG. 2-B, the molten pellets 16 of the blend described above are supplied to the inner surface of the heated lid 1 through an extrusion die (not shown).Finally, in FIG. 2-C In this step, the cooled plunger 16 is lowered into the lid 1 to form the melt into the desired shape of the liner 2 according to the shape of the top surface of the plunger, and the liner 2 is thermally bonded to the lid 1. let

The invention is illustrated by the following example.

Example 1゜Low density polyethylene CMI 6.5, density 0.9172
and ethylene vinyl acetate copolymer (hereinafter referred to as EVA) (
(VA amount: 28%) was blended at a constant rate at 170°C in an extruder. This was molded with high concentration polyethylene.
8. Molten state inside the cap (0.4 at 180℃)
f) and immediately stamped with a certain shape. At this time, the temperature of the cap was changed and the embossing was performed. The adhesion between the liner and the cap (adhesive strength at 28++ oa width) was examined under each condition. The sealing properties of the caps for each stripe were also investigated.

Similarly, test results for sealing performance (1) Adhesiveness: X Adhesive strength: 1/28 mπ or less ○: 1/28 mπ or more Q) Sealing performance Among the caps mentioned above, those with a cap temperature of 50°C J
A sustained pressure test was conducted based on IS, S'9017.

However, the bottle used was a 1101 bottle with certain scratches on the item. The tightening torque was 20ky-crIL.

Test Results Example 2 Similar to Example 1, adhesiveness and sealing performance were investigated using low density polyethylene and ethylene propylene rubber (hereinafter referred to as EPR) (75% ethylene, 25% propylene).

Test results Example 6゜Low density polyethylene and polyimbutylene rubber (hereinafter referred to as PI
It is written as B. Vistanex MML-100 was kneaded with Esso C Ltd. H)'t Banbury and tested in the same manner as in Example 1.

Test results Example 4゜ Styrene-in-prene-styrene copolymer (SIS) rubber on low density polyethylene and polypropylene Example 1
Blended in the same manner as above and conducted the same test. However, high-density polyethylene and polypropylene were used for the cap material.

Test results (1) Liner material (polyethylene, 5RS), cap (high-density polyethylene) (2) Liner material (polyethylene, 5IS) cap (polyethylene cross) Liner material (polypropylene, SIS cap material (high-density polyethylene) '4) Liner material (polypropylene, 5IS) Cap material (polypropylene) Example 5 Other: (1) 1,2 polybutadiene and low density polyethylene as liner material, polyethylene as cap material.Q) Butyl rubber and polyethylene as liner material, Nylon, 4-methylpentene-1, etc. were investigated as the cap material, but almost the same results as in Example 1 were obtained.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing the concept of the present invention. 2nd-A to 2-
Figure C is a process diagram showing the concept of the farming method of the present invention. 1...Resin cap, 2...Liner, 12...
Plunger, 16... Pellet Fig. 1 Fig. 2-A Fig. 2-B Fig. 3 Fig. 2-C

Claims (1)

[Claims] (1) In a resin cap consisting of a lid made of a hard thermoplastic resin and a soft liner applied to at least a portion of the top plate of the lid that engages with the container mouth, the hard resin is made of a hard thermoplastic resin. The liner material is made of olefin resin, and the liner material is a mixture of ethylene thermoplastic resin, natural or synthetic rubber, or thermoplastic elastomer, and gold 95:5 to 5:5.
The liner is formed by in-situ compression molding of the molten blend in the lid, and the liner is thermally bonded to the lid without passing through an adhesive layer. A resin cap characterized by: Q) Heat the entire lid made of hard olefin resin to a temperature of 50°C or higher, and apply ethylene thermoplastic resin and natural or synthetic rubber to at least the part of the top plate of the lid that should engage the container mouth. Alternatively, a blend containing a thermoplastic elastomer at a weight ratio of 95:5 to 5:95 is applied in a molten state, and this melt is pressed with a plunger to form a predetermined liner shape, and the lid is heated. A manufacturing method for a resin cap characterized by adhesive bonding.