JP4013225B2 - Packing process with excellent chemical resistance, especially solvent resistance - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for producing a packing used for a can lid and a lid of a jar (bottom) that are required to have chemical resistance, in particular, solvent resistance, and sealability.
[0002]
[Prior art]
Since the lining compound used for the lid (bottom) of the metal can is NBR or PVC plastisol, complete solvent resistance cannot be expected. Polyethylene can be expected to have chemical resistance, particularly solvent resistance. Conventionally, for example, a polyethylene sheet expanded 5 to 10 times for a 20-liter pail can lid is sliced into a thickness of 60 mm, a width of 75 mm, and a length of 913 mm, rounded into a ring shape, and welded at both ends as shown in FIG. However, since it is necessary to twist 90 degrees by hand in order to fit it into the can lid winding portion as shown in FIG. 7, it is not easy. Further, in the conventional method of fitting a foamed polyethylene sheet punched into the lid, there is a risk of causing gas leakage in the case of contents containing gas, such as carbonated beverages.
[0003]
[Problems to be solved by the invention]
Since the conventional method slices foamed polyethylene, there is no skin on the surface, and the cut surface comes out, so it must be inserted so as to be pressed into the winding part, particularly the undercurl part, with considerable pressure as shown in FIG. . Moreover, it takes time because it is done manually by one person.
In the case of a lid for a carbonated beverage containing gas, the one obtained by slicing foamed polyethylene has no skin on the surface, which may cause gas leakage.
[0004]
[Means for Solving the Problems]
Place the strand of unfoamed kneaded material kneaded with at least a foaming agent on the spacement of the can lid winding part at the lowest possible temperature using an extrusion molding machine. When a film punched in a circular shape is placed on the inner side of the lid, heated, foamed, and embossed, it is easy to obtain a chemical-resistant, particularly solvent-resistant packing with a skin on the surface. Settled.
[0005]
Embodiment
An example of the production method of the present invention will be described.
1) Kneading a low-density polyethylene with a foaming agent such as azodicarbonamide, a foaming accelerator such as zinc white, a cross-linking agent such as park mill peroxide, and a lubricant such as stearic acid at the lowest possible temperature using an extruder. It extrudes from a nozzle to a water tank and winds a strand around a brazed paper tube with a winder. Since kneading involves a cross-linking agent, if it is not performed at as low a temperature as possible, there is a risk of solidifying in the extruder. The operating temperature of the extruder is generally as high as 150 ° C. In the present invention, for example, low-density polyethylene having a melting point of 106 ° C. was kneaded at 110 ° C. or lower. A sheet having the same effect was obtained by kneading at 105 ° C. for a short time using a rubber kneading roll in addition to an extrusion molding machine, thinning out and tearing vertically to a predetermined width. You can also use a calendar.
[0006]
2) A predetermined length of the unfoamed kneaded material strand 9 is placed on the spacement 7. FIGS. 8 (a), (b), (c), (d), and (e) show an example in which a strand is placed as a loop 10 for a round can.
(A) The tip of the strand pulled out by the feed rolls 12 and 12 ′ from the brazed paper tube 11 is pressed by the presser (1) 14. (B) Rotate the round can model 13 to make one round of the strand along the model, and press the rear end with the presser (2) 15. The front end and the rear end of the strand are combined at the cutting portion 16 and are cut with a red hot nichrome wire. (Fusing). (C) The connector 17 is pressed against the joint and welded to form the loop 10.
(D) The loop 10 is adsorbed by the ring-shaped octopus foot 18 that has come down. (E) Move sideways and place it on the lid spacement.
[0007]
For rectangular cans and oval cans other than round cans, rectangular ribbon loops and oval ribbons obtained by molding at a temperature of 110 ° C or less from unfoamed kneaded strands using square or oval molds. Place a loop etc. on the lid spacement using octopus feet.
There is also a method in which the strand coming out from the die of the extruder is directly placed on the rotating lid spacement. In this case, a device for intermittently supplying the strands for each lid and a device for removing excess strands of the loop seam are required. In the case of a lid, an unfoamed kneaded sheet punched out in a circle is placed on the inner side of the crown.
[0008]
3) Thereafter, the lid is foamed through a hot air circulating furnace at 180 to 240 ° C. for 2 to 3 minutes. Foaming conditions vary depending on the type of foaming agent. The expansion ratio is preferably 6 to 10 times, and the gaps such as the under curl portion are sufficiently filled with the foam.
For heating, foaming can also be performed by emissive heat such as far infrared rays.
[0009]
4) Packing with excellent chemical resistance, especially solvent resistance, having a uniform smooth skin by embossing while hot. At this time, the expansion ratio is reduced to 3 to 5 times. 0 to 2 times is too hard. In the lid packing, the ring-shaped irregularities can be embossed on the skin as shown in FIG. 4, and the shape can be fitted well into the mouth of the glass bottle as shown in FIG.
[0010]
Since the foamed polyethylene packing thus obtained has a skin on the surface, no solvent or the like enters. The results of immersion tests on various contents such as solvents such as toluene, n-hexane, ethyl acetate and thinner, soy sauce, surfactant, silicone oil, acid and alkali were satisfactory.
[0011]
[Example 1]
Melt flow 20-50, density 0.91-0.925, melting point 95-105 ° C. low density polyethylene 100 parts azodicarbonamide 3-5 parts, zinc white 3-5 parts, park mill peroxide 0.5- 1 part, 0.5-1 part of stearic acid is added, kneaded quickly at a low temperature of 100 ° C. to 110 ° C. and a die temperature of 110 ° C. using an extrusion molding machine, extruded from a 2-3 mm diameter die into a water bath, Wind it on a paper tube. A loop of a predetermined length of the unfoamed strand is obtained using a model for a round can and placed on a 330 mmφ pail can lid winding partial space space using an octopus foot. The method is shown in FIG. Next, if it passes through the heating furnace of 220 to 240 degreeC for every lid | cover for 2 to 3 minutes, it will foam 8 to 10 times. If the ring-shaped die is embossed while the temperature is not lowered, the foaming ratio is reduced to 4-5 times, and the skin surface becomes smooth. The 20-liter pail can lid thus obtained was optimal for cans of paints and adhesives containing solvents.
[0012]
[Example 2]
As in Example 1, a predetermined length of unfoamed kneaded strands extruded from a 2 mmφ die was made into a loop using a square can model, and this was placed on the top plate of the 5 gallon square can and on the coiled partial spacement of the main plate A five-gallon can obtained by placing a base plate on a plate and heating and foaming and embossing the packing, and a five-gallon can obtained by winding a base plate around the trunk was suitable as a paint can or thinner can. In particular, there is no sticking out of the packing material that is disliked during winding.
[0013]
[Example 3]
As a packing for food jar lids, a formulation in which a crosslinking agent is not added and a foaming agent is less than that in Example 1, that is, 100 parts of low density polyethylene, 0.5 to 1.5 parts of azodicarbonamide, 3 parts of zinc white, lubricant 0.5 to 1 part of a non-foamed kneaded sheet of 0.5 mm thickness obtained by thinning after kneading using a rubber kneading roll at 100 to 105 ° C. is punched into a circle, and this is placed inside the crown. The packing obtained by heating and foaming through a far-infrared tunnel dryer for 1.5 to 2.5 minutes and embossing into a shape as shown in FIG. The upper edge can be press-contacted, and there is no concern that the gas gradually escapes the contents containing gas such as carbonated drinks. The expansion ratio in this case was about 3 times.
[0014]
【The invention's effect】
According to the production method of the present invention, chemical resistance, particularly solvent resistance, is much superior to conventional products using NBR latex and polyvinyl plastisol as raw materials because ethylene is used as a raw material. The conventional method in which a sliced foamed polyethylene sheet is forcibly fitted manually into the lid wrapping part has a risk of leakage of the contents because the cut surface is exposed on the entire surface of the foamed polyethylene. The foamed kneaded strand or sheet is placed on the inside of the can-clamping partial spacement or crown, and is foamed. The skin is present on the surface where the content strikes, so there is no risk that the content will enter the packing. In this case, the surface of the skin can be molded into any shape such as irregularities because it is embossed after foaming and can be pressed against the upper edge of the mouth.
[Brief description of the drawings]
FIG. 1 is a plan view of a round can lid packing according to the present invention. FIG. 2 is a plan view of a square can lid packing according to the present invention. FIG. 3 is a cross-sectional view of a can lid according to the present invention.
FIG. 4 is an explanatory view of packing of the lid according to the present invention. FIG. 5 is a cross-sectional view (AA ′) of the can lid according to the present invention.
FIG. 6 is an explanatory diagram of a conventional foamed polyethylene packing. FIG. 7 is an explanatory diagram when a conventional foamed polyethylene packing is fitted. FIG. 8 is an application of an unfoamed kneaded material strand according to the present invention to a round can lid. Explanation drawing [Explanation of symbols]
1 Foamed polyethylene packing 2 Can lid 3 Crown 4 Glass shed 5 Foamed polyethylene packing skin 6 Conventional foamed polyethylene packing 6 'Same welded part 7 Can lid winding part spacement 8 Can lid winding part under curl 9 Unfoamed kneaded material Strand 10 Loop 11 Paper tube 12 and 12 'with sheet feeding roll 13 Model 14 for round can Presser foot (1)
15 Presser foot (2)
16 Cutting part 17 Connector 18 Octopus foot (adsorption device)
AA 'Lid cross section B Lid center

Claims (2)

A space of the coiled portion of the can lid (bottom) of a predetermined length of the unfoamed kneaded strand extruded by kneading at least a foaming agent into low-density polyethylene using an extrusion molding machine at a temperature of the melting point to 110 ° C. A process for producing a packing excellent in chemical resistance, particularly in solvent resistance, characterized in that it is placed on top, heated and foamed at a foaming temperature, and embossed to crush foam to form a skin while hot. Using a rubber kneading roll , at least a foaming agent is kneaded into low-density polyethylene at a temperature not lower than the melting point and not higher than 110 ° C , and the thinned unfoamed kneaded sheet is punched into a circle. A method for producing a packing excellent in chemical resistance, particularly solvent resistance, characterized in that foam is formed by crushing foam to form a skin .

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