JPS602346A - Manufacture of inside box for heat-insulating box - Google Patents

Abstract

PURPOSE:To prevent the occurrence of whitening and cracking of a synthetic resin sheet when being cooled by a method in which a synthetic resin sheet of a given thickness is subjected to monoaxial stretching process at 120-150 deg.C, and the stress-concentrating portion of the sheet is subjected to a stretching process in the direction orthogonal to the stretching direction of the sheet. CONSTITUTION:A synthetic resin, e.g., ABS resin, etc., is melted at about 220 deg.C in an extruder 7, passed through a die 8 to regulate its thickness to a fixed one, passed through a polishing roll 9 to give it a gloss, and hen passed through stretching process rolls 11 at 120-150 deg.C to obtain a sheet 10'. The sheet 10' is heated and covered on a vacuum mold 12 with a vacuum hole, pressed into the mold 12 by means of a plug 13 from above, and then molded by evacuation to vacuum. In this case, a rib 5 for rack receiver as a stress-concentrating portion 6 is formed and stretched even to the direction (y) orthogonal to the stretching direction (x) of the sheet 10', and therefore, the portion 6 of the inside box 2 is stretched to two directions.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a method of manufacturing an inner box for a heat insulating box used for refrigerators, freezers, etc.

Conventional Structure and Problems Therebelow, a conventional method of manufacturing an inner box and its structure will be explained with reference to FIGS. 1 to 3.

In FIG. 1, 1 is a heat insulating box such as a refrigerator. 2 is an inner box made of synthetic resin such as ABS, 3 is an outer box, and 4 is a foamed heat insulating material such as polyurethane foam, which is integrally foamed between the inner box 2 and the outer box 3. Reference numeral 6 denotes a shelf support lip that is provided when the inner box 2 is created, and for example, near the flange at the tip thereof is a stress concentration portion 6 where stress is concentrated. FIG. 2 is a sectional view taken along the line nn' of the cross-sectional box shown in FIG. 1, and the appended numbers represent the same items as in FIG. 1.

Next, a method of manufacturing the above-described inner box 2 and its operation will be explained. In FIG. 3, 7 is an extruder, 8 is a die, and 9 is a polishing roll. It has a first step in which a synthetic resin such as ABS is melted at a temperature of about 220°C in an extruder 7, adjusted to a constant thickness with a die 8, and polished with a polishing roll 9 to create a sheet 10. This sheet 1° is then vacuum formed to form the inner box 2 having the stress concentration portion 6 described above, which is the second step.

The inner box 2 is formed in this way, and when the inner box 2 is cooled when used as the heat insulating box 1 as shown in FIGS. , when the stress caused by the difference in thermal expansion coefficient and elastic modulus between the foam insulation material 4 such as polyurethane and the inner box 2 is concentrated, whitening or whitening may occur in the X direction in Figure 1 due to the stretching effect of vacuum forming. Although cracking does not occur, the stretching has no effect on stress in the y direction, so it has the drawback of causing whitening and cracking. One method to overcome this drawback is generally to make the radius of the shape of the stress concentration part 6 sloppy. However, with this method, the shape of the inner box 2 becomes unsharp and it looks bad. Uke had the disadvantage that its functionality was also impaired.

Other methods include applying a protective material such as a water-soluble acrylic adhesive to the stress concentration area 6 from the foamed heat insulating material 4 side such as polyurethane, or applying an adhesive tape. However, since these materials have high adhesion to the inner box 22 and the foam insulation material 4, when thermal stress occurs, the thermal stress acts directly on the inner box 2 through the adhesive layer, making it impossible to prevent cracking. Ta. In some cases, a polyethylene film is attached to the stress concentration area 6, but it has poor adhesion to the foamed heat insulating material 4 and is released from the inner box 2 with a slight force, or is constantly released from the mold. Therefore, the inner box 2 had a disadvantage in that it had an unfavorable appearance.

OBJECTS OF THE INVENTION The present invention eliminates the drawbacks of the above-mentioned conventional examples, and
When an inner box with a stress concentration area is made of synthetic resin such as BS resin and used as a heat insulating box, the purpose is to prevent the stress concentration area from whitening or cracking when cooled. be.

Structure of the Invention In order to achieve the above-mentioned object, the present invention applies stretching processing in a uniaxial direction at about 120 to 160°C during sheet production such as extraction molding to the stress concentration portion, and also applies the stretching process in the uniaxial direction during thermoforming such as vacuum forming. The stress concentration area is stretched in the direction perpendicular to the sheet stretching direction, and by stretching in two directions, the stress concentration in the stress concentration area causes whitening.

This prevents cracking.

DESCRIPTION OF EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS. 1 to 6. First, in the first step, a synthetic resin such as HeBS is melted at about 220°C in an extruder 7, adjusted to a constant thickness with a die 8, and polished with a polishing roll 9. Unlike the conventional method, it is not immediately vacuum formed, but is heated from about 120°C to 1
The sheet 10' is stretched at 50° C. (in the X direction in FIG. 4). Next, as a second step, as shown in FIG. 6, the stretched sheet 10' is heated and covered with the vacuum forming mold 12 having a vacuum hole, and the plug 1-3 is inserted from above. Then, it is pressed so as to fit into the mold 12, and then further vacuum degassed and molded. At the same time in this vacuum forming, the ribs 5 for the shelf supports as the stress concentration portions 6 described above are formed.

That is, by forming the stress concentration portion 6, the inner box 2 is stretched in the stretching direction of the sheet 10' or in the y direction perpendicular to the stretching direction of the sheet 10'. In the concentrated portion 6, stretching has been applied in two directions, x and y. FIGS. 6 and 7 are graphs showing the relationship between temperature and critical strain value at which cracks occur in the inner box 2 in uniaxial and biaxial stretching processes. Both Figures 6 and 7,
The horizontal axis indicates the stretching temperature, and the unit is °C.

The vertical axis indicates the critical strain value at which cracks occur in the inner box 2 stretched at the above temperature. From these figures, in -axial and biaxial stretching processing, when the processing temperature is increased, approximately 12
It can be seen that from 0°C to about 150'C'j, the critical strain value at which cracks occur in the inner box 2 is almost constant, but as the temperature rises above that, the critical strain value decreases. In addition, the critical strain value at which cracks occur in the inner box 2 is larger in biaxial stretching than in uniaxial stretching, so biaxial stretching is more effective in preventing cracks in the inner box 2. I understand.

When creating the sheet 10 by extrusion molding using the extrusion molding machine 7,
The thermal stress concentration part 6 of the conventional inner box 2 which has not been stretched by the stretching roll 11 is covered with a foamed heat insulating material 4 such as polyurethane during actual operation such as cooling operation as a refrigerator or during stocking in a warehouse or the like. Due to the difference in coefficient of thermal expansion and modulus of elasticity between the inner box 2 and the inner box 2, thermal stress is generated and
Cracks may occur due to chemical attack by the No. 1 blowing agent. The critical strain at which this crack occurs differs depending on the thermal stress concentration area 6 and the type of inner box 2, but in the case of the tip of the shelf support lip 6, it is measured under normal refrigerator usage conditions or when stocked in extremely cold regions. The result was 0.
We were able to obtain a value of 0.8%.

Therefore, by adopting the inner box that has been subjected to the biaxial stretching process described above, for example, during the sheet 10 production process such as extrusion molding using the extrusion molding machine 7, the sheet 10' can be stretched in the direction perpendicular to the sheet 10' stretching process. In the added inner box 2, the critical strain value at which cracking occurs is 0.88%, so the critical strain value at which cracking occurs is 0.3% to 0.5%, which would cause cracking under normal use conditions as a refrigerator or when stocked in a severely cold region. This provides the effect that no cracking occurs even when a strain of 8 inches is applied.

Effects of the Invention As is clear from the above explanation, the present invention is applicable to the production of an inner box made of thermoplastic resin such as ABS having a stress concentration part near the flange, and to the production of a sheet such as extrusion molding in the stress concentration part. Sometimes, stretching is applied in the uniaxial direction at about 120°C to 150°C, and stretching is also applied in the direction perpendicular to the stretching direction of the sheet during vacuum forming, so by using this method, the effect of biaxial stretching can be improved. By being able to manufacture an inner box with added stress, the critical strain value at which cracks occur in the inner box is improved, and it is said that cracks will not occur even if a strain of about 0.3% to 0.8 inches is applied to the stress concentration area. It is effective,
Furthermore, it is possible to eliminate protective materials such as water-soluble acrylic adhesives and adhesive tapes, which are currently used to prevent cracks from occurring in stress concentration areas of the inner box.

[Brief explanation of the drawing]

Figure 1 is a perspective view of the insulation box, Figure 2 is the 111i911
3 is an explanatory diagram of the conventional inner box manufacturing process, FIG. 4 is an explanatory diagram of the inner box manufacturing process of an embodiment of the present invention,
FIG. 6 is an external view of the vacuum forming machine, and FIGS. 6 and 7 are graphs showing the relationship between the stretching temperature and the critical strain value at which cracks occur in the inner box in uniaxial stretching and biaxial stretching. 2...Inner box, 5...Shelf support lip, 6...
... Stress concentration part, x, y ... Stretching direction. Name of agent: Patent attorney Toshio Nakao and 1 other person Kabuto 1
Figures 2, 9, 5, Figure 6-1, Ko≦I, Nakanopi, Δ, Figure 7, 2, # Surname Yi, P2, trjX, Flea, Zui.

Claims (1)

[Claims] A first step of creating a sheet of a predetermined thickness by extrusion molding or the like from a synthetic resin such as ABS, and heating the sheet to form a box shape with a convex or concave portion as a stress concentration area such as a shelf support. a second step of vacuum forming; in the first step, the sheet is stretched in a uniaxial direction under a temperature condition of 12C to 160C; and in the second step, the sheet is stretched in a uniaxial direction; A method for manufacturing an inner box for a heat insulating box, in which a portion of the inner box is stretched in a direction perpendicular to the stretching direction of the sheet.