JPH0930547A - Heat-insulation cover for packaging container - Google Patents

Abstract

PROBLEM TO BE SOLVED: To mold a heat-insulation cover having a high heat-insulating property, an excellent dimensional stability at a high temperature, a preventive property against thermal deflection, and a highly airtight fitting property, by use or a roam sheet chiefly made of a thermoplastic resin specified in the density, thickness, changing rate in the MD and TD directions, and changing rate in the thickness direction. SOLUTION: A heat-insulation cover 1 is constituted of a fitting groove 2 at the periphery, cut and rise parts for air or hot water discharge, and a thin protruded line 4 projected in the inside of the peripheral fitting groove 2 and it is molded from a thermoplastic foam resin sheet extruded, polystyrene foam resin sheet for instance. This foam sheet has 0.05-0.80g/cc in density, 0.3-3.0mm in thickness, 0.8-1.1 in changing rate in the MD and TD directions, and 0.9-1.3 in changing rate in the thickness direction as the features. It is preferable that the continuous bubble ratio of the foam sheet is 20-80%. The cover containing rubber components is effective to improve the brittleness. And a non-foam film of thermoplastic resin may be laminated at least on one side face.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heat insulating lid for a packaging container, for example, a lid that can be used as a heat insulating lid for an instant noodle container.

[0002]

2. Description of the Related Art As a conventional heat insulating lid for a packaging container, for example, in the case of a lid used for an instant noodle container, a molded product made of a non-foamed resin sheet is used with emphasis on airtightness. Although it is used, even though the fitting airtightness between the container body and the lid can be maintained, the heat insulation of the lid itself is inferior, so that the contents in the container cannot be sufficiently kept warm as a lid.

On the other hand, the lid formed of the foamed resin sheet has excellent heat insulating properties peculiar to the foamed resin as to the heat insulating property of the entire lid, but has a problem of poor dimensional stability at high temperatures. Specifically, for example, actual fairness 6-605
In the case of the conventional heat insulation lid formed from the extrusion-foam-molded polystyrene-based resin foam sheet described in Japanese Patent Publication No. 0, even if the open cell ratio is high, it is about 15%, usually 10% or less. When butane is used as the main ingredient of the foaming agent, when the hot water is poured onto the food in the container body, for example, instant noodles and the lid is closed, the butane remaining in the bubbles of the expanded polystyrene is at a high temperature of the hot water. Expansion cannot be suppressed and secondary foaming occurs, and as a result, the entire lid expands and deforms, resulting in poor dimensional stability at high temperatures.
There is a problem in that there is a gap in the fitting portion between the container body and the heat insulating lid, and the heating effect of hot water and the heat retaining effect of the lid are impaired.

Therefore, in the present invention, a heat insulating lid for a packaging container, which was invented for the purpose of solving the above-mentioned problems of the prior art, more specifically, high heat insulating property and high dimensional stability at high temperature. It was invented in an attempt to provide an insulating lid.

[0005]

As a heat insulating lid for a packaging container according to the present invention which can achieve the above objects,
Molded from a foamed sheet mainly made of thermoplastic resin, the density is 0.05 to 0.80 g / cc, the thickness is 0.3 to
3.0 mm, the rate of change in MD and TD is 0.8-
1.1, and the rate of change in the thickness direction is 0.9 to 1.3.

If the density is less than 0.05 g / cc, the amount of resin in the lid itself as a molded product will be small, it will be easily deformed by heat, and the strength during hot water cutting will be weak. Further, the molding accuracy is deteriorated, and the dimensional accuracy of the lid is deteriorated. Density 0.80
If it exceeds g / cc, the heat insulation will be poor even if the thickness is increased, and the cost will be high. If the thickness is less than 0.3 mm, the strength as a lid becomes weak and the heat insulation becomes poor. Thickness is 3.
If it exceeds 0 mm, the precision with the mold at the time of molding deteriorates, and the lid has a low fitting airtightness. When the rate of change in the MD direction and the TD direction is less than 0.8, heat causes contraction and deformation, and the lid is likely to be twisted or come off. Further, when the rate of change exceeds 1.1, expansion deformation occurs due to heat, and the fitting airtightness of the lid deteriorates. Furthermore, if the rate of change in the thickness direction is less than 0.9, shrinkage deformation occurs, and 1.
If it exceeds 3, expansion deformation occurs, which causes shape deformation and deterioration of fitting airtightness from any point.

Further, as the heat insulating lid of the present invention, in particular, the foamed sheet has an open cell rate of 20 to 80%.
When the open cell ratio is less than 20%, the foaming agent remaining in the cells easily causes foaming in practical use and the lid is easily deformed, and exceeds 80%. In practice, water vapor easily penetrates into the lid, and the hands become hot when draining water, making it difficult to hold the container.

As the heat insulating lid of the present invention, it is particularly preferable that the thermoplastic resin is polystyrene resin or polyolefin resin.

As the heat insulating lid of the present invention, particularly when the foamed sheet contains a rubber component as described in claim 4, it is effective in improving brittleness. It is also preferable in terms of direct printing. When it is desired to further improve the printability or to increase the strength of the lid, a non-foamed film of a thermoplastic resin is laminated on one side or both sides of a foamed sheet by coextrusion as described in claim 5, or afterwards. You may laminate | stack by means, such as a heating roll and an adhesive agent.

Further, when the foamed sheet contains a filler as in claim 6, fine bubbles are formed to improve the surface hand-sliding property, and it is possible to prevent water vapor from seeping into the lid in practical use. it can.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION Next, preferred embodiments of the present invention will be exemplified below with reference to the drawings. 1 and 2 show a plan view and a bottom view of a heat insulating cover according to the present invention. The heat insulating cover 1 is formed from a foamed sheet of thermoplastic resin extruded and foamed, for example, a polystyrene resin foamed sheet. The density is 0.05 to 0.
80g / cc, thickness 0.3-3.0mm, MD direction and T
The change rate in the D direction is 0.8 to 1.1, the change rate in the thickness direction is 0.9 to 1.3, and the open cell rate is preferably set to 20 to 80%.

Regarding the above-mentioned rate of change, a section cut from a flat portion of the molded heat-insulating lid 1 by 50 mm × 50 mm square was heated for 150 seconds in a gear oven at 100 ° C. and then the dimensional change rate of the central section of the section was measured. Among them, the MD and TD directions are 0.8 to 1.1 and the thickness direction is 0.9 to 1.3. However, each rate of change is
It was calculated by the following formula.

MD, TD direction (rate of change) = (dimension after heating) / (dimension before heating = 50 mm) Thickness direction (rate of change) = (thickness after heating) / (thickness before heating) -thickness less than 0.3 mm ... The strength of the lid becomes weaker and the heat insulation becomes lower. More than 3.0 mm ... Mold accuracy is poor during molding, resulting in a lid with low fitting airtightness. -Density less than 0.05 g / cc ... The amount of resin in the lid itself is small, it is easily deformed by heat, and the strength during hot water removal becomes weak.

More than 0.80 g / cc ... Even if the thickness is increased, the heat insulation is poor and the cost is high. -Change rate (MD.TD) less than 0.80 ... Shrinkage deformation occurs due to heat, and the lid is twisted or comes off. Exceeding 1.10 ... Heat causes expansion change, resulting in poor fitting airtightness. (Thickness direction) Less than 0.90 ... Shrinkage deformation occurs due to heat, and deformation easily occurs.

Exceeding 1.30 ... The expansion changes due to heat, the shape of the fitting portion returns and the lid comes off. Next, the open cell rate is measured by the following measuring method.・ Measuring method: 25 mm x 25 from the flat part of the center of the lid
The continuous bubble ratio is defined as the ratio of the total volume of air bubbles communicating with the outside air to the volume calculated from the dimensions of mm square, and the measuring equipment is AIR COMPARIS manufactured by TOKYO SCIENCE Co., Ltd.
ON PYCNOMETERDEL 1000 (conforming to ASTM D-2856) was used.

[0016]

[Equation 1]

Open cell rate of less than 20%: The foaming agent remaining in the cells easily causes foaming in practical use and the lid is easily deformed. More than 80% ... In practical use, water vapor easily penetrates into the lid,
The hands become hot when boiling water, and the container cannot be supported by gripping.

Furthermore, it is preferable that the foam sheet, which is the main material of the heat insulating lid, contains a rubber component (claim 3), and the rubber content is 0.5 wt% to 30 wt%. The following problems occur, which is not preferable.・ Rubber content less than 0.5 wt% ... Molds are easily cracked.

More than 30 wt% ... Strength does not become strong even if the thickness is increased. Further, in practice, a non-foamed film of a thermoplastic resin, for example, when the foamed sheet is a polystyrene-based foamed sheet or a polystyrene-based non-foamed film is laminated on at least one surface of the foamed sheet (claim 4), the heat insulating lid 1 In addition to strengthening the above, the printing characteristics of the non-foamed film can be exhibited.

As a method for laminating the non-foamed film, an in-line method or an outline method for directly laminating the non-foamed film of the thermoplastic resin extruded from the extruder on the foamed sheet before the non-foamed film is completely cooled, or an in-line method is used. Alternatively, in outline, the thermoplastic resin extruded from the extruder is used as a binder, and a non-foamed film of thermoplastic resin prepared in advance (whether pre-printed or plain) is laminated on the foam sheet. Method, further, while heating a non-foamed film of a thermoplastic resin (blank or printed product) prepared in advance with a heating roll, a method of laminating by pressure bonding to a foamed sheet,
After joining and stacking the foamed sheet and non-foamed film,
A method called co-extrusion in which a laminated foam sheet is obtained by extruding from a cylindrical die can be adopted.

Furthermore, in practice, it is preferable that the foamed sheet contains a filler (claim 5), and the content of the filler is 0.5 wt% to 10 wt%. Outside this range, the following problems occur. It is not preferable because it occurs. -Filler content less than 0.5 wt% ... The bubbles do not become fine and the surface smoothness of the molded product deteriorates.

More than 10% by weight: During practical use, water vapor easily penetrates into the lid and the hands become hot when the water is drained, and the container cannot be supported. For the production of the foamed sheet which is the main material of the heat insulating lid, the thermoplastic resin, the nucleating agent and the additive are uniformly mixed, and the mixture is supplied to the first extruder through the hopper. The mixture was sufficiently melted in an extruder to obtain a resin composition. Then, the foaming agent was pressed in and melt-mixed. The molten mixture is transferred to a second extruder and uniformly cooled. At this time, in order to make the open cell rate higher than that of a foamed sheet of a usual thermoplastic resin, the temperature of the resin is 5 ° C. higher than the temperature of the resin of a usual extrusion foaming.
Set and control -20 ° C higher.

After that, it is extruded and foamed from a cylindrical die,
The obtained cylindrical foamed body is cooled and formed, and at a point on the circumference, a necessary number of sheets are incised with a cutter, and this is wound up to obtain a foamed sheet. Examples of the thermoplastic resin include polystyrene resin, polyolefin resin such as polypropylene and polyethylene. Particularly preferred as the polystyrene resin is polystyrene or a copolymer of maleic anhydride, methyl methacrylate, butadiene, acrylonitrile and styrene with rubber.

As the foaming agent, volatile foaming agents such as propane, n-butane, i-butane, n-pentane and i-pentane are preferably used alone or as a mixture, and azodicarbonamide and dinitrosopentamethylene are suitable. An organic foaming agent such as tetramine, an organic acid such as sodium bicarbonate or citric acid, or a combination of a salt thereof with a bicarbonate is suitable, and carbon dioxide, nitrogen, water and the like can also be used as the foaming agent.

As the nucleating agent, talc, sodium hydrogen carbonate, ammonium hydrogen carbonate, calcium carbonate, clay,
Citric acid and the like. As an additive, an additive within a range that does not impair the performance as a heat-insulating lid, such as a coloring agent, a flame retardant, a lubricant (hydrocarbon, fatty acid) in obtaining a thermoplastic resin foam having desired properties. Type, fatty acid amide type, ester type, alcohol type, metal soap silicon oil, wax such as low molecular weight polyethylene), spreading agent (liquid paraffin, polyethylene glycol, polybutene, etc.), dispersant and the like may be added.

The method of molding the heat-insulating lid 1 of the present invention is called contact heating molding which is suitable for a thin molded product, and uses a hot plate and a female mold heated to a predetermined temperature. The sheet to be molded is sandwiched between the two, and the sheet is brought into close contact with the hot plate and heated, and then compressed air is fed from a plurality of small holes formed in the hot plate and pressed against the female mold on the opposite side. At this time, suction is performed through a small number of small holes formed in the female mold to form the sheet along the shape of the female mold.

Another molding method is a molding method which is mainly used for molding foamed sheets (suitable for a molded product having a large thickness), and the sheet is passed through a heating zone and heated from both sides to be softened. The method of molding in the molding zone is roughly classified into single-sided vacuum forming, double-sided vacuum forming, match mold forming, and the like. Further, according to the foamed sheet described above, it is possible to perform good molding along the molding die without causing excessive foaming even at a molding location or a corner location where the thickness is partially uneven.

In the structure of the heat insulating lid 1, 2 is a peripheral fitting groove, 3 and 3'are cut-and-raised parts for air or hot water, and 4 is a thin ridge protruding inside the peripheral fitting groove 2. Is shown. The peripheral fitting groove 2 and the narrow ridge 4 have good fitting properties with the container body 10 as shown in a partial cross-sectional view in FIG. In addition, 5 indicates a printed portion, and a fine bubble diameter of the heat insulating lid 1 is 0.3 mm or less, specifically 0.2 mm.
It is applied to the lid surface having a bubble diameter of.

The main agent of the foaming agent of the heat insulating lid 1 may be nitrogen, carbon dioxide or the like in addition to butane. Further, the shape structure of the heat insulating lid 1 can be variously implemented in addition to the above-mentioned prism, and FIGS. 4 and 5 show a plan view and a bottom view of a circular shape having different shapes. ′ And the thin ridge 4 are the same as in the previous embodiment.

[0030]

EXAMPLES Table 2 shows the heat-insulating lid thus obtained, which was obtained by passing the mixture having the compounding ratio shown in Table 1 through an extruder, laminating a film on the obtained foamed sheet, and molding the mixture.

[0031]

[Table 1]

[0032]

[Table 2]

(Evaluation Criteria for Lid) * Fitness ・ Matches with the container body and does not rattle ... ◎ ・ Matches with the container body but has rattling to the extent that there is no problem in use ... ○ ・ Does not match with the container body and comes off when inverted… × * Heat insulation Put hot water (95 ℃) in the container body, put the lid on it, and press the lid with your hand when draining the water ・ It is not hot… ◎・ It's hot but you can somehow hold it ... ○ ・ It's hot and you can't hold it ... × ＊ Hot water deformation Put the contents in the container body, put hot water (95 ° C), and
After a minute, remove the hot water, and-No deformation is seen ... ◎ -It is slightly deformed, but there is no problem in use ... ○ -It is deformed and the contents spill or the lid comes off ... × * Crack- No cracks occur in the molding process (during punching) or in the transportation test ... ◎ ・ Some of them occur in the molding process, but do not newly occur in the transportation test ... ○ ・ New cracks occur in the transportation test but there is no problem It is… △ ・ There are many cracks, which is a problem in practice… ×

[0034]

As described above, the heat insulating lid according to the present invention is
Density 0.05 to 0.80 g / cc, thickness 0.3 to 3.0
mm, MD and TD direction change rate is 0.8-1.1, thickness direction change rate is 0.9-1.3, shrinkage deformation and expansion deformation due to heat hardly occur, dimensional stability It is possible to provide the one excellent in the airtightness of fitting with the container body. Therefore, even when the lid is used at a high temperature, deformation of the entire heat insulating lid is suppressed, and the problem that a gap is formed in the fitting portion between the container body and the heat insulating lid is solved. Further, it has a high heat insulating property, and when it is used as a lid for a container body containing hot water, it can be used as a heat-insulating lid that is not hot even if the lid is pressed by hand when draining hot water and is easy to grasp.

In particular, when a foamed sheet containing a rubber component is used as the heat insulating lid according to the present invention, brittleness can be improved. Further, when the open cell rate is set to 20 to 80%, it becomes more difficult for thermal deformation to occur, and
It is difficult for water vapor to permeate during practical use, and the heat insulating effect can be enhanced. When the foamed sheet contains a filler, air bubbles become fine and the lid surface becomes smooth and beautiful, and it is possible to provide the lid surface directly printed without using a non-foamed film laminated.

Further, when a foamed sheet laminated with a non-foamed film is used, printability can be improved and strength can be enhanced.

[Brief description of drawings]

FIG. 1 is a plan view.

FIG. 2 is a bottom view.

FIG. 3 is a partial cross-sectional view showing a state in which the container body is closed.

FIG. 4 is a plan view showing a modified shape.

FIG. 5 is a bottom view of the same.

[Explanation of symbols]

 1 Heat-insulating lid 2 Peripheral fitting groove 3, 3 ′ Cut and raised part for air and hot water draining 4 Fine ridge 5 Printed part

Claims (6)

[Claims] 1. Molded from a foamed sheet mainly made of a thermoplastic resin, having a density of 0.05 to 0.80 g / cc, a thickness of 0.3 to 3.0 mm, and a change in MD and TD directions. The rate is 0.8 to 1.1, and the rate of change in the thickness direction is 0.9 to
A heat insulating lid for a packaging container, which is 1.3. 2. The heat insulating lid for a packaging container according to claim 1, wherein the foamed sheet has an open cell ratio of 20 to 80%. 3. The heat insulating lid for a packaging container according to claim 1, wherein the thermoplastic resin is a polystyrene resin or a polyolefin resin. 4. A heat insulating lid for a packaging container according to claim 3, which is a foamed sheet containing a rubber content in a polystyrene resin. 5. A heat insulating lid for a packaging container according to claim 1, wherein a non-foamed resin film made of a thermoplastic resin is laminated on at least one surface of the foamed sheet. 6. The heat insulating lid for a packaging container according to claim 1, wherein the foamed sheet contains a filler.