JP3762507B2 - Vacuum leakage inspection method for vacuum packaged products - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for inspecting all products for vacuum leakage in a manufacturing process of a vacuum packaged product having a relatively large vacuum volume, for example, a heat insulating panel using vacuum.
[0002]
[Prior art]
Vacuum packaged products are used in various fields, and in particular, vacuum packaged products using plastic laminated film bags as vacuum containers are not limited to the conventional food field and the like, and their application fields are becoming increasingly widespread in recent years. For example, there is a heat insulating panel in which a hard foam plastic plate is wrapped with a laminate film made of plastic or the like and the inside is evacuated. Application of such heat insulation panels to refrigerators and further to heat insulation structures of buildings is being studied.
[0003]
In such a vacuum packaged product, it is necessary to inspect the vacuum leakage for the total number of products in order to ensure reliability. The conventional inspection method has been identified by placing a vacuum packaged product in a vacuum chamber and expanding defective products. However, the vacuum chamber is expensive, and a large-sized panel can be a large facility because of its pressure-resistant structure. Moreover, it is necessary to always operate a large-capacity vacuum pump, resulting in a large power cost.
[0004]
[Problems to be solved by the invention]
It is an object of the present invention to provide a method for inspecting a product for vacuum leakage with simple equipment in a manufacturing process of a vacuum packaged product such as a heat insulating panel as described above.
[0005]
[Means for Solving the Problems]
The present invention solves the above-mentioned problems, and the weight of a vacuum packaged product having a bulk density of 0.5 g / cm ³ or less is measured immediately after the vacuum packaging, and is further placed in the atmosphere after a lapse of time. The vacuum leakage inspection of the vacuum packaging product characterized by measuring the weight of the same vacuum packaging product again, comparing the measured values of the weight before and after the above, and judging the leakage of the vacuum by the increase in the weight in the subsequent measurement. Is the method. Here, the vacuum packaged product is also characterized in that it is a heat insulating panel in which an open-cell foam plate is wrapped with a laminate film.
[0006]
DETAILED DESCRIPTION OF THE INVENTION
In the present invention, when a vacuum packaged product leaks, it is detected that the amount of air corresponding to the vacuum volume is increased. Since the average molecular weight of air distributed by the ratio of nitrogen and oxygen is 28.8, the weight of 22.4 liters of air at 0 ° C. and 1 atm is 28.8 g. Therefore, for example, in the case of a vacuum packaged product having a vacuum volume of 10 liters, if it completely leaks, the weight increases by 12.9 g. Furthermore, there is actually an influence of moisture in the air. Regarding this, since the molecular weight of water is 18 and smaller than the molecular weight of oxygen or nitrogen, it is expected to act in the direction of reducing the weight increase due to vacuum leakage. However, in the experiment on the above-mentioned heat insulation panel by the present inventors, the increase in weight is larger in the case of humid air than in the case of dry air. This is because the foam inside is in a dry state when the heat insulation panel is evacuated, and because it has a large surface area, it acts as a desiccant to absorb moisture in the air that has entered due to vacuum leakage. It is done. For this reason, the pressure of the air which invaded by an amount corresponding to the water vapor partial pressure is reduced, and further air enters.
[0007]
In the above example of a vacuum packaged product having a vacuum volume of 10 liters, if the outer volume and the vacuum volume are substantially equal and the bulk density is 0.1 g / cm ³ , the total weight is 1 kg. When neglected, the weight increase rate is about 1.3%. Such a change in weight can be sufficiently measured by a balance-type weighing device. Further in the example of the vacuum volume 10 l vacuum packaging, the total weight of 5kg if the weight increase is 0.26% in bulk density and the larger 0.5 g / cm ³ from the above, a volume density of 1 g / cm ³ If the total weight is 10 kg, the rate of weight increase will be 0.13%, but if it is about 0.1-0.2%, it can be said that it is close to the limit in industrial weight measuring equipment. Therefore, the vacuum leakage inspection method of the present invention is not universally used for any vacuum packaged product, and it is effective to apply it to a material having a sufficient vacuum volume and a relatively small bulk density. This is a problem with the vacuum volume described above. For example, when the vacuum space itself is small, as seen in vacuum packs for processed meat products, the amount of air that enters is small even if there is a vacuum leak. The method of the invention is inappropriate. Therefore, the range of the bulk density of the vacuum packaged product to be inspected is set to 0.5 g / cm ³ or less shown above .
[0008]
On the other hand, the vacuum leak inspection method of the present invention is particularly suitable for the heat insulating panels as described above. This thermal insulation panel is an open cell type, that is, a foam plate that can evacuate all the bubbles because adjacent bubbles can be ventilated and wrapped with a laminate film consisting of a layer of plastic and metal foil, etc., and the inside is evacuated It is. A hard plastic is generally used as the foam, but a pumice-like ceramic foam can also be used. In such a case, the vacuum volume is large and the method of the present invention can be effectively applied. On the other hand, since it is difficult to inspect a large panel like the above-described conventional method using a vacuum vessel, the method of the present invention is different from the conventional vacuum leak inspection method depending on the object. It can be said that they complement each other.
[0009]
The vacuum leakage inspection method of the present invention measures the weight within a short time after vacuum packaging, and then measures the weight of the same vacuum packaged product again after a lapse of time. That is, the weight of the same article is tracked and measured, and is referred to as the previously measured weight. Weight comparisons should be made on the same item, even on the same product mass production line. That is, since the method of the present invention makes a difference in weight of the order of 1% a problem, there is a possibility that accurate judgment cannot be made even with the same type of product due to variation in the weight of individual products.
[0010]
The previous weight measurement is preferably performed immediately after vacuum packaging, that is, as soon as possible, for example, within 2 minutes. If the time after vacuum packaging is long, if the vacuum leak is relatively severe, the weight has already increased at the time of the previous measurement, and the difference from the weight in the subsequent measurement becomes small, making accurate judgment difficult. is there. The time interval until the subsequent weight measurement is usually, for example, about 30 minutes after the previous weight measurement. This is because it is normal for air to enter very quickly when there is a vacuum leak. Of course, it is possible to measure after a long period of time such as a full day from the previous weight measurement immediately after vacuum packaging.
[0011]
As described above, when the time interval between the front and rear weight measurements is long, the buoyancy due to air changes with changes in temperature and pressure, resulting in measurement errors. The rate is 10/273, that is, 3.7% if the air temperature fluctuates by 10 ° C., or 1% if the air pressure fluctuates by 10 mbar. If the external volume of the vacuum package is almost equal to the vacuum volume, and there is a temperature rise of 10 ° C, even if there is no vacuum leak, it will be a rate of 3.7% of the weight change that should occur when the vacuum is completely leaked. The weight will increase. If the external volume of the vacuum packaged product is twice the vacuum volume, the change is twice the above. However, especially when a plurality of the same articles are manufactured at the same time, since there is a similar weight change in most articles without vacuum leakage, there is no misunderstanding even if no correction is calculated.
[0012]
【Example】
The vacuum leakage inspection method of the present invention was applied to a heat insulating panel whose inside was evacuated. This heat insulation panel is formed by packaging an open cell foam of an unsaturated polyester resin with an aluminum sheet coated with a polyester resin, and sealing it while sucking up to 0.05 mbar with a vacuum pump. The external dimensions are 18 mm thick × 650 mm wide × 1500 mm long, and the weight when vacuumed is about 1480 g.
[0013]
The above panel without vacuum leakage has virtually no change in weight, but the example with vacuum leakage has an increase in weight of 19.2 g (1.30%) after 30 minutes. In the measurement after 24 hours of the same, the increase in weight compensated for the change in buoyancy due to the change in temperature and pressure was 21.7 g (1.47%) compared to immediately after vacuum packaging. In other words, it can be seen that the vacuum leakage proceeds in a relatively short time when there is a vacuum leakage, and most of the weight increase appears in the initial stage. Therefore, in the normal case, the vacuum leakage can be detected even if the second measurement is performed at a relatively short interval such as 30 minutes or 1 hour after the measurement immediately after vacuum packaging.
[0014]
FIG. 1 shows an example of an apparatus for inspecting the heat insulation panel for a vacuum leakage in a factory production line. The heat insulation panel 1 whose inside is evacuated by a vacuum packaging device (not shown) is sent to a product warehouse (not shown) by a belt conveyor 3 that runs at a relatively low speed. The first weighing device 2 is located immediately from the vacuum packaging device on the entrance side of the belt conveyor, and is installed on the side of the belt conveyor to take the heat insulation panel from the belt conveyor, measure the weight, and then return to the belt conveyor. It has become. The second weighing device 4 is located near the exit side of the belt conveyor, and is installed on the side of the belt conveyor to measure the weight of the heat insulation panel by the same method as the first weighing device. The weight measurement result is sent to the arithmetic unit 5, and the measurement results of the first and second weighing devices of the same heat insulation panel are compared, and the elapsed time between the weight measurement by the first and second weighing devices is also compared. To be recorded.
[0015]
【The invention's effect】
According to the vacuum leakage inspection method for a vacuum packaged product of the present invention, inspection of a large-sized object such as a heat insulation panel in which the inside is evacuated, which has been difficult to apply the conventional inspection method, can be performed with simple equipment at low cost. Can do.
[Brief description of the drawings]
FIG. 1 is a diagram showing an example of an apparatus for carrying out the method of the present invention.
DESCRIPTION OF SYMBOLS 1 Thermal insulation panel 2 1st weighing apparatus 3 Belt conveyor 4 2nd weighing apparatus 5 Arithmetic unit

Claims (2)

For a vacuum packaged product having a bulk density of 0.5 g / cm ³ or less , the weight thereof is measured immediately after the vacuum packaging, and the weight of the same vacuum packaged product is measured again after a lapse of time in the state of being placed in the atmosphere. A vacuum leakage inspection method for a vacuum packaged product, comprising comparing the measured values of the weight before and after and determining the leakage of the vacuum based on the increase in weight in the subsequent measurement.   2. The vacuum leakage inspection method for a vacuum packaged product according to claim 1, wherein the vacuum packaged product is a heat insulating panel obtained by packaging an open-cell foam board with a laminate film.

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