JPH0245965B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method and apparatus for forming a sealing gasket in a container closure. The container stopper may be, for example, a bottle cap, preferably a crown, although the invention is equally applicable to other types of closures, such as so-called threadable-in-place bottle caps or "RO" caps. . It is known to provide sealing gaskets in bottle closures by charging a plastic composition into the closure and then shaping it to form the gasket. Another possible method is to spin-line the closure by injecting a quantity of the liquid plastisol composition into the closure and then rotating the closure at high speed to disperse the plastisol onto the end panel of the closure; The plastisol is then melted by applying heat. British patent specification no.
No. 1054383 discloses that when the plastisol is centrifugally dispersed across the end panel of the cap and then heated with infrared radiation, the blowing agent is released, creating bubbles and melting the plastic composition into a closed porous structure. A method is described in which the liquid plastisol charged into the sealed stopper contains a blowing agent so as to obtain the following. It was then necessary to carry out the final shaping of the foam molded gasket thus formed using a cooling die or a punch which removed heat from the gasket by means of heat transfer contact. This ensures that the final gasket has a precisely controlled profile, although it has a porous structure due to the foaming action. In the applicant's UK Patent No. 1211780,
Before applying the molding operation with the aid of a contoured punch, a composition having a sealing action is charged into the closure, for example in the form of a fluidized powder preheated by infrared radiation. Case 1 of our UK Patent No. 1211780 is:
It has been shown that after contouring at 150°C, the plug can be passed through a hot air oven at 240°C to foam the gasket. Therefore, the disclosure of our British Patent No. 1211780 involves preheating the powder for sintering, contouring for forming the plastic gasket, and post-heating for forming and foaming the gasket (foaming). (if any agent is included). British Patent No. 1109849 discloses charging a sealant composition in the form of a plastisol into a closure, contouring the sealant composition using a punch, and then disintegrating the foam to melt the plastisol. Discloses a method for heating a molded gasket. The sealant composition is heated before, during or after the profiling step to a temperature insufficient to chemically decompose the blowing agent, and the closure and punch are preheated to a similar temperature. The wide temperature range used for this preheating is 135-171°C (275-171°C
340〓), and then in the post-heating process it becomes 149〓
Use a temperature of 218°C (300-425〓). Such a temperature range is such that before the profiling operation the plastisol is in a non-liquid gel state and then remains in that state until after the profiling operation where it undergoes a post-heating step, perhaps using infrared heating. It is. In order for the traditional thin center panel of the gasket to become transparent in the finished gasket, the chemical blowing agent selected has a decomposition temperature that is higher than the gelling temperature of the vinyl resin and lower than its melting temperature, resulting in melting. A thin, rigid outer shell of foamed resin forms over the expanded (foamed) outer annulus of the gasket, while the thin central body of the gasket is equally thin and thus strong enough to remain transparent. The melting shell must be continuous. The object of the invention is to utilize as much as possible the elasticity provided by the foamed plastic gasket. Another object of the invention is the provision of an apparatus for the production of low density foam gaskets in container closures which do not need to be more bulky than those described above. Accordingly, the present invention provides a method for forming a foamed gasket for sealing in a container closure, which consists of placing an amount of plastisol containing a blowing agent over the container closure, and removing the foam gasket from the blowing agent. The method consists of molding the plastisol at a temperature sufficient to initiate foaming of the plastisol upon release of gas, so that after molding the gasket has a porous structure, and then applying radiant heat to the plastisol for further foaming. Another object of the invention is to provide an apparatus for carrying out the above method, the apparatus comprising a plurality of individual molding sets including a closure and an anvil for supporting a punch and forming a gasket within the closure. a molded turret, a device for supplying a series of closures to the turret to reach a series of molded sets of the turret, and charging a predetermined amount of plastisol composition into each such closure provided; a device for transporting the closure from the turret after forming the gasket; a device for applying radiant heat to the closure coming out of the turret; a device for applying heat to the molded set of the turret; The temperature of the molding set was kept at 140-260°C to ensure the initiation of foaming of the plastisol charged by the charging device.
It consists of a device that controls the value of . The invention also provides a closure that is lined by the method described above or by use of the device described above. In order that the invention may be more easily understood, the following description is made by way of example only with reference to the drawings. Referring now to FIG. 1, there is shown a seal lining device 1 which comprises a turret 3 having a plurality of gaskets supported at equiangularly spaced positions around its periphery and heated by gas burners 7. It includes a forming tool or punch 5. A similar gas burner (not shown) heats each anvil (not shown) which supports the metal closure from below as the associated punch 5 descends into the cap to form the gasket. The sealed stopper lined in this way is taken out onto a conveyor 11 in the form of a continuous conveyor belt that supplies the closed stopper to a downstream conveyor (19 in FIG. 2) and is transferred to a turret by a star wheel 9. taken from. Sealed plugs that are not lined but have been coated with lacquer are Hopper 15.
A charging star wheel (27' in FIG. 4, not shown in FIG. 1) feeds the turret from the plug sorting mechanism 13, which is fed by a plug sorting mechanism 13, which is fed by a charging star wheel (27' in FIG. 4, not shown in FIG. 1). When the plugs are taken out from the turret 3 to the conveyor 11 and pass around the star wheel 9, they are placed under a heating device 17 which emits infrared radiation which imparts radiant heat to the molded material of the gasket composition in the plugs. pass through. Next, in FIG. 2, a simple plan view of the seal lining device 1 is shown, and in this case, the position of the heating device 17 that emits infrared heat is indicated by 17a as being directly above the conveyor 11. , this conveyor is shown in this example as supplying a seal to one side of the conveyor 19. FIG. 3 shows a sectional view of the radiant heat radiating device 17a of the same figure, showing the infrared rays emitting quartz tube 2 in the gold-plated parabolic reflector 23 on the lower surface of the body 25 of the heating device.
1 is shown. If necessary, several such heaters 25 can be installed, for example in a single radiant tube 2
In order to obtain a wider range of action than would be possible in case 1, they are mounted end-to-end to provide a set of radiant heating elements. FIG. 4 shows a pair of hermetic lining devices 1 and 1' arranged in parallel, and their conveyor 1.
1 and 11' are respectively fed to the same conveyor 19, which in this example is arranged in parallel positions and extends across the width of the conveyor 19 from the bodies 25 of a plurality of heaters in FIG. It passes under the radiant heat radiation heater 17C. The seal lining device 1' on the right side shown in FIG.
The outline of the hopper is shown in dotted lines extending out of the plane of the charging star wheel 27', the forming turret 3' and the removal star wheel 9' seen from above. FIG. 4 further shows that the path of the closure around the charging star wheel 27' passes directly beneath the plastisol dosing devices 29', each of which is connected to the dosing device 29'.
9' is activated to release rapid successive pulses of liquid plastisol timed to reach the closure passing below. In the embodiment of FIGS. 3 and 4, the rows of plugs passing at close intervals along the conveyor belt 11 or 11' are arranged in a 90° direction on a downwardly sloping ramp 31 or 31', respectively. This inclined part conveys the sealed stopper to the conveyor 19.
The closures are then left irregularly distributed but very closely spaced along each side of the conveyor 19. In the embodiment of FIG. 4, conveyor 19 is a chain conveyor, so that it can withstand long-term radiant heat effects from radiant heater 17C. Similarly, in the embodiment of FIG. 2, the belts of conveyor 11 are formed from a material capable of withstanding the long-term heating effects of radiant heat, and may also be a chain conveyor. In use of the apparatus shown in FIG. 4, the hopper of each of the closure lining devices 1 and 1' is made of unlined closure material pre-applied with lacquer;
per minute to the charging star wheel (e.g. 27') of the closure lining device 1', which in this example is filled with a crown and the closure sorting mechanism is already rotating.
Injected to supply crowns at early intervals at a rate of 1000 pieces. As this rapidly spaced crown passes under the plastisol foaming device 29' with the serrated skirt portion up, each crown is injected with approximately 180 to 200 mg of film weight of plastisol composition, and the plastisol is deposited at the ends of the crown. Adheres to the top of the panel. The gasket is formed from plastisol containing a blowing agent. Basically, these plastisols consist of a resin dispersed in a plasticizer that is insoluble at room temperature but capable of dissolving the resin at elevated temperatures. Plastisols may further contain other well-known ingredients such as lubricants, fillers, stabilizers and pigments. Although plastisols of other thermoplastics such as polymethyl methacrylate may also be used, plastisols of vinyl resins are particularly suitable as components for forming the gasket. Suitable vinyl resins include the preferred polyvinyl chloride, and other vinyl chloride polymers, such as copolymers of vinyl chloride and vinyl acetate, or polyvinyl acetate, polyvinyl butyrate, polyvinyl alcohol, polyvinylidene chloride, and vinylidene chloride. and copolymers of vinyl aromatic compounds such as styrene. The plasticizer used can be any of the known monomeric plasticizers that solvate the resin at elevated temperatures. In the case of vinyl resin, these plasticizers include:
Dioctyl phthalate, diisooctyl phthalate, di-2-ethyl-hexyl phthalate, didecyl phthalate, diisononyl phthalate, n-
Hexyl azealate, di-diisooctyl azealate diisodecyl phthalate, di(n-octyl, n-decyl) phthalate, acetyltributyl citrate, di-octyl sebacate, diisooctyl sebacate, dihexyl adipate,
Included are primary plasticizers such as dioctyl adipate, diisooctyl adipate, 2-ethylhexyldiphenyl phosphate, and tricresyl phosphate. Polymeric plasticizers such as polyesters derived from dibasic acids and glycols and/or epoxy modified oils can also be used. Secondary plasticizers, such as petroleum residue products widely used as rubber softeners and plasticizers, can also be used to supplement or replace a portion of the primary plasticizer. The selection of the particular plasticizer will depend on the ultimate purpose for which the gasket is used. In addition to resins and plasticizers, various other additives may also be included to modify the plastisol composition. These additives include anhydrous calcium sulfate,
Fillers such as talc, wood flour, diatomaceous earth, calcium carbonate, barium sulfate, kaolin and silica in various forms, tetrasodium pyrophosphate, salts of calcium, magnesium and zinc of saturated and unsaturated fatty acids, organotin complexes, epoxies resins, and stabilizers such as epoxidized esters of fatty acids, pigments such as iron oxide, carbon black, titanium dioxide and aluminum powder, and zinc resinates, lecithin, glycol stearate, propylene glycol laurate, and glycol monooleate. These include dispersants such as. Lubricants, flow agents and/or
Mold release agents such as hydrocarbon oils such as petrolatum (RTM), microcrystalline waxes and silicone oils can also be added. One or more blowing agents can be used that decompose when the plastisol is exposed to infrared radiation, cellularizing the plastisol to produce enhanced elastic properties and enhancing the properties of the plastisol used to form the sealing element. Reduce film weight. Suitable chemical blowing agents include azodicarbonamide, 3,3
-disulfohydrazide diphenyl sulfone, dinitrosopentamethylenetetramine, diazoaminobenzene and p,p'-oxybis(benzenesulfonyl hydrazide). The amount of blowing agent varies from about 0.2 to 5.0% based on the weight of the resin. Good cell formation with a strong melt skin is obtained when using 0.4 to 2.0% blowing agent in the formation of plastisols. The blowing agent may also contain one or more so-called accelerator components that lower the decomposition temperature and/or increase the decomposition rate of the blowing agent. Such ingredients include zinc oxide, which also acts as a stabilizer, as described above, and more preferably zinc salts of fatty acids (e.g.
zinc stearate or zinc octoate). The synchronized rotational movement of the charging star wheel 27', turret 3' and unloading star wheel 9' of the apparatus 1' advances rapidly successive crowns around the forming turret 3' and onto this crown. are subjected to the shaping action provided by the descending movement of each punch (5 in FIG. 1). (a) against its end panel as the metal crown is placed on a heated anvil (not shown); and (b) by contact with the contouring surface of the heated punch 5 during the machining movement. The heat applied to the plastisol component being molded raises the temperature of the plastisol at least to a value at which melting of the plastisol composition begins and the blowing agent decomposes and releases gas so that it begins to form the closed chamber foam structure of the gasket. Start. Thereafter, the forming punch is raised and the crown with the formed gasket is transferred against the removal star wheel 9' and then onto the transport conveyor 1.
1' and travels on the conveyor 19 toward the radiant heater 17C. The temperature of the anvil/punch molding set is
The temperature of the forming punch is selected to be approximately 140 to 260℃, preferably 170 to 240℃, and more preferably 180 to 220℃, and the temperature of the forming punch is 10℃ higher than the temperature of the anvil.
A low level is fine. The configuration shown in FIG.
Although it is desirable to drive a single conveyor belt so that a total of 2000 closures pass under 17C per minute, the embodiments of Figs. Having its own heating device 17 or 17a makes this arrangement more compact and is considered desirable. As mentioned above, in the embodiment of FIG.
7 is placed on the take-out star wheel to provide a two-step heat dissipation effect before the lined crown reaches the conveyor 11, in the embodiment of FIG. 2 the crown reaches the conveyor 19. A heating device is arranged above the conveyor 11 to ensure that two stages of heat dissipation are provided. To illustrate the effectiveness of the method according to the invention, the following example is presented. Example Two LP360 type 1kw heat dissipation tubes (wavelength 1.2 to
An infrared parabolic heater producing a heat output of 5 watts/cm ² at 2 μm, with a total energy consumption of 1 kW per tube, can be used in a plug lining device of the type shown in Figure 3. It is movably mounted on the transport conveyor 11. To simulate different lengths of infrared heaters along the conveyor, each heater
It was moved synchronously and parallel to the lined crown, which was transported over a distance ranging from 500 mm to 500 mm. During this test, the anvil of the molded turret was heated to 210°C.
The forming punch 5 is heated to 200°C, and the height of the heating element above the conveyor 19 is
It was 12.5mm. The specific gravity value (SG value) of plastisol at the time of injection into the crown is 1.2, and the SG value of the completed crown gasket is shown in Table 1. In this table, the value for length "0" is the value when the heater is shut off. Show that.

[Table] The specific gravity values shown for heater lengths of 300, 400, and 500 mm are based on the amount of blowing agent in the plastisol composition, even if the entire amount of blowing agent is decomposed, considering the deterioration of a portion of the gasket. and the SG value is
The fact that 0.60 is sufficient makes it highly desirable. EXAMPLE The test of the example was repeated with the heating element set 25 mm above the cooling conveyor 19. All other parameters were the same as in the case, and the results are shown in Table 2.

[Table] A radiant heat panel known by the trade name WATLOW producing an output of 3 watts/cm ² at wavelengths between 3 and 4 μm is transported along a conveyor, again with a pair of lined closures below it. It was installed on the conveyor 19 shown in FIG. Gasket SG without infrared heater
The value was determined to be approximately 1.0, and two separate tests were performed, one with a travel distance of 0.5 m and the other with a travel distance of 1 m. For 0.5m, the final
The SG value decreased to 0.87, but for a moving distance of 1 m, the SG value decreased to 0.70. Example Two 360s that emit infrared light with a wavelength of 1.2 to 2 μm
A single infrared parabolic heater using a mm long tube (LP360 type, 1 kw/h) was installed 35 mm above the conveyor 11 as shown at 17a in FIG. This tube was parallel to the direction of movement of the crown. The gasket's SG value was 0.95, compared to the gasket's SG value of 1.0 to 1.06 observed when no infrared radiant heat was applied for the second time. EXAMPLE The test of the example was repeated using a single 360 mm long 2 kW heater tube (LP360, 2 kW/h) in place of the two 1 kW heaters used in the example. The tube was again placed parallel to the path of the crown along the transport conveyor 11. During the first run, the temperature of the anvil is 210°C, the temperature of the forming punch is 200°C, and the SG value of the gasket is between 1.02 and 1.07 without a second infrared heat radiation; static heater
When I turned it on, it was 0.93. In the second test, where the anvil temperature was 220°C and the forming punch temperature was 210°C, the SG value of the gasket obtained without the heater was
The gasket SG value dropped to 0.81 when the heater was activated. EXAMPLE The experiment of the example was repeated selecting the temperature of the second test of the example in the same heating regime. However, the forward speed of the belt of the conveyor 11 is 25
% decreased. The SG value of the gasket without the second infrared heat radiation was 0.99, but when the heater was activated, the SG value of the gasket was 0.99.
The value fell to 0.79. As previously mentioned in the examples, some deterioration of the gasket was observed when maintaining the second heat dissipation over a distance of 300 mm along the transport conveyor 19. This degradation can be avoided if the spacing of the heater above the crown is increased. Therefore, the application of foaming heat by infrared rays is not strong enough to cause the surface of the plastisol composition to begin to degrade and thereby harm the taste of the contents when the crown is later used (i.e., the heater is not applied too closely to the plastisol surface). care must be taken not to bring them close or to not increase the intensity of the radiant heat.) Similarly, to ensure optimal absorption efficiency, it is desirable to experiment with different wavelengths of infrared radiation to match the absorption properties of the particular plastisol used. In each of these examples, the gasket SG
Values were measured after peeling the gasket from the crown. It will, of course, be understood that the present invention is concerned with applying sufficient heat during the molding process to ensure that foaming begins as soon as the punch is retracted. Although it is possible to operate at low temperatures (e.g. in the range of 140 to 170°C, depending on the blowing agent used), the heated punch does not produce foaming but results in partial melting of the composition.
According to the invention, the foaming heat is applied in two stages, thus proposing that the temperature of the forming punch must be high enough to ensure that the first foaming process takes place in the thermoforming process. be. The second step occurs after molding by applying radiant heat directly to the plastic composition of the gasket. Keeping in mind that the initial SG value of the plastisol in each example was 1.2, Table 1 shows that the initial decrease in SG value due to foaming caused by tool temperature was 0.3 to 0.4, and that the gasket temperature The subsequent reduction in SG value (for heater travel of 225 mm) achieved without any trace of deterioration of
It shows that it was between 0.17 and 0.27. Thus, nearly half of the foaming effect (as measured by the decrease in SG value) is a result of the temperature in the forming punch and anvil. Further comparative tests were conducted using a fixed infrared post-heating system that was inactive for three of the six test runs and activated during the other three runs. PVC
A plastisol was prepared consisting of resin, plasticizer, blowing agent and small amounts of other additives. This particular composition had a specific gravity of 1.20 at 140°C and a specific gravity of 0.61 at 200°C, which is equal to maximum foaming. In this way, starting from the standard specific gravity of 1.20 before the molding process, a specific gravity reduction value of 0.59 was set as a condition with the latent foaming degree as 100%. The post-heating device is activated and the punch anvil is heated to three temperatures (Q ₁ corresponds to punch temperature 180 °C and anvil temperature 190 °C, Q ₂ corresponds to 210 °C, respectively)
and 220℃, Q ₃ is 230℃ and 240℃ respectively
The result of setting it to operate in (corresponding to) is as follows. That is, in the case of Q ₁ , the specific gravity after molding and post-heating is
1.20 corresponds to zero foaming state. In Q ₂ , the specific gravity without post-heating is
1.02 (corresponding to a latent foaming degree of 30.5%), and 0.94 (corresponding to a latent foaming degree of 44%) when post-heating was performed. For Q ₃ , the specific gravity without post-heating was 0.88 (corresponding to a latent foaming degree of 54.2%), and with post-heating it was 0.81 (corresponding to a latent foaming degree of 66.1%). From the operation in Q ₂ and Q ₃ it is clear that the degree of foaming occurring in the first stage is well over half of the total foaming action occurring in the process. As a result of Q ₃ , where an optimal foaming condition of 66.1% was obtained, the appearance of the completed gasket was whitish yellow in both the peripheral area and the center panel of the gasket, but due to the decomposition of the gasket. Without a trace, the central panel of the gasket was foamed to such an extent that it no longer had the transparent appearance targeted by the method of GB 1109849. The resulting gasket exhibited good elastic properties necessary for adequate sealing performance.

[Brief explanation of the drawing]

FIG. 1 is a perspective view showing a closure lining device according to the invention, and FIG. 2 is a plan view showing an apparatus similar in general construction to the apparatus of FIG. 1 but having a modified second stage fusion heat radiating device. FIG. 3 is a detailed cross-sectional view along the line - of FIG. 2, and FIG. 4 is a detailed cross-sectional view of FIG. 1 and FIG. Figure 3 is a plan view of yet another configuration of two closure liners similar to that shown; 1... Seal lining device, 3, 3'... Turret, 5... Punch, 7... Gas burner, 9...
Take-out star wheel, 9'... Take-out star wheel, 11, 11'... Conveyor,
13... Sealed classification mechanism, 15... Hopper, 17
... Heating device, 17a ... Radiant heat radiation device, 19
...Conveyor conveyor, 21...Radiation tube, 23...
Parabolic reflector, 25...body, 27'...charging star wheel, 29'...plastisol injection device, 31...inclined part.

Claims (1)

[Scope of Claims] 1. A certain amount of plastisol containing a foaming agent is placed in a sealed container, and after the plastisol is molded into the shape required for the completed gasket, radiant heat is applied to the plastisol to form a porous gasket. A method of forming a foamed sealing gasket in a container closure comprising the step of imparting a structure to the completed gasket, wherein the step of molding the plastisol is sufficient to cause the plastisol to begin foaming by release of the blowing agent. heating to a temperature such that the gasket already has a porous structure after molding. 2. said forming step comprises compressing said plastisol using heated punches of an anvil/punch forming tool set, the temperature of said forming tool set being maintained in the range of 140 to 260°C; A method according to claim 1, characterized in that: 3. The temperature of the molding tools forming the above set is 170 to 240°C.
The method according to claim 2, characterized in that it is within the scope of. 4. A method according to any one of the preceding claims, characterized in that immediately after molding the gasket, radiant heat is applied by an infrared heater above the movement path of the seal plug provided with the gasket. 5. A method according to claim 4, characterized in that the applied infrared heat has a wavelength in the range of 1 to 4 μm. 6 More than half of the overall decrease in specific gravity in the two-stage foaming process is due to the first stage, which is simultaneous with the molding process.
A method according to any of the preceding claims, characterized in that the observation is performed after the step of applying heat but before the step of applying radiant heat in the second step. 7. A method according to any of the preceding claims, characterized in that the plastisol consists of a vinyl resin suspended in a plasticizer. 8 A molding turret 3 provided with a plurality of sets of individual molding tools consisting of an anvil that supports the seal and a punch 5 that molds a gasket within the seal, and a molding tool that forms successive sets of the turrets. A device 13 for supplying a series of closures to the turret, a device for charging a predetermined amount of plastisol composition into each supplied closure, and a device 9 for removing the closures from the turret after forming the gasket. A device 17 for applying radiant heat to the sealing plug coming out of the turret, and a device applying heat to the molding tools forming a set of the turret. In the device, when used, the temperature of the molding tools of the set is controlled to a value within the range of 140 to 260° C. so as to ensure the initiation of foaming of the plastisol charged by the plastisol charging device. A device characterized in that it is provided with a device. 9. Claim 8, characterized in that the sealed transport device includes a take-off star wheel 9, a main transport conveyor 19, and a transport conveyor 11 between the take-off star wheel 9 and the main transport conveyor. equipment. 10. Apparatus according to claim 9, characterized in that said device 17 for providing radiant heat is arranged on the periphery of said extraction star wheel. 11. The apparatus according to claim 9, characterized in that a device 17a for applying radiant heat is arranged above the conveyor 11. 12. The apparatus according to claim 9, characterized in that a device 17C for applying radiant heat is arranged above the main conveyor 19.