JPH02290483A - Heat insulating material - Google Patents

Abstract

PURPOSE:To enable prevention of mutual joining by covering a specific water-absorbing body with a sheathing material having water-passing holes and a hydrophobic surface and by setting the maximum swelling volume of the water-absorbing body and the maximum internal capacity of a vessel formed of the sheathing material in a prescribed relationship. CONSTITUTION:A heat insulating material 1 is constructed of a water-retaining water- absorbing body 2 and a sheet-like sheathing material 3 provided above and below the water-retaining water-absorbing body and covering the same. As for a suitable example of the water-absorbing body 2, a so-called water-absorbing polymer made by cross-linking an acrylic or hydrophilic polymer partially can be cited. As to the sheet-like sheathing material 3, a film and a sheet of general-purpose plastic, such as polyethylene or polypropylene, of which the surface is hydrophobic and which have water-passing holes 4 can be cited. In addition, the maximum swelling volume of the water-absorbing body 2 in a saturated state of water absorption is set to be the maximum internal capacity of the sheathing material 3. According to this constitution, the quantity of water extricated in a process from water absorption to freezing turns very small and thus the mutual joining of heat insulating materials is prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to cold insulators, and more particularly to ice-fusing materials.
<This invention relates to a simple cold insulating material that can be used particularly for small-lot transportation of fresh foods.

BACKGROUND OF THE INVENTION In recent years, methods have become popular for delivering fresh foods such as raw ham, meat, and fresh fish to consumers while keeping them at low temperatures using cold insulation materials.

Various cold insulation materials are used in this method, but
There may be problems in terms of safety and disposal. For example, dry ice, which is widely used, is relatively expensive and requires care in handling due to the generation of carbon dioxide gas and its low temperature properties, so it cannot be said that it is completely safe. In this respect, if water (ice) is used, it is inexpensive, non-toxic (safety), and easy to dispose of. However, on the other hand, there is a problem in that when the ice melts during transportation, the food gets wet.

Therefore, as a means to solve this problem, a method has been proposed in which water is absorbed into a water-retaining material and then frozen.

The general procedure flow when using the water-retentive material is as follows: water absorption, draining, freezing, packaging into small packs, transportation, and opening/disposal, and each procedure has various requirements. That is, first, in water absorption, from the viewpoint of work efficiency, a large number of cold insulators are put into water at once and allowed to absorb water. Here, the water absorption time is required to be as short as possible, for example 5 to 10 minutes. After absorbing the water, drain it by scooping it up with a wire mesh container and draining away the excess water. Here, it is required to be able to drain the water without any manual effort. Next, for freezing, place the entire container in the freezer to completely freeze. Here, it is required that no water remains between the cold insulation materials. If residual water exists, the cold insulating materials tend to stick together.

In the next step of making small Robacs, one to several cold packs are placed together with the food in an insulated transport container and sealed. Here, it is required that the cold insulating material, which is frozen in large numbers at once, can be easily separated one by one. This is achieved without the binding described above. Next, it is delivered door-to-door by courier. Finally, it is either put into the refrigerator in a household kitchen or discarded after cooking food.

As is clear from the above, binding is the biggest problem, and by solving this, it is possible to satisfy the demands for manpower and small-sized bags. .

Problems to be Solved by the Invention However, in the conventional method using water-retaining materials, a water-absorbing (water-retaining) material is wrapped in a hydrophilic or water-permeable sheet material. However, water often adheres to the outer periphery, resulting in the above-mentioned binding problem. As such countermeasures, the amount of water absorbed is regulated, the water is allowed to stand for a certain period of time before freezing, and the surface water is removed by mechanical means. In addition, attempts have been made to prevent mutual binding by devising the arrangement during freezing. However, such measures are complicated to handle and do not fundamentally solve the problem of binding.

Therefore, there is a desire for a cold insulating material that basically solves this problem of binding, thereby eliminating the complexity of handling, and meeting the requirement that it is difficult to bind to each other even when used in large quantities.

Means for Solving the Problems As a result of intensive research, the inventors of the present invention have found that a specific water absorbent body is wrapped in an exterior material having water passage holes and a hydrophobic surface, and the maximum swelling volume of the water absorbent body and the exterior material are determined. We have surprisingly found that the above-mentioned binding can be basically eliminated by creating a certain relationship between the maximum internal volume of the container formed by
, we have completed the present invention.

That is, the present invention comprises a water-retaining water absorbent body and a sheet-like exterior material that is provided above and below the water-absorbent body and whose periphery is joined to enclose the water-absorbent body, and the sheet-like exterior material has water holes and hydrophobic The present invention provides a cold insulating material, which has an elastic surface, and the maximum swelling volume of the water absorbent body in a saturated water absorption state is greater than or equal to the maximum internal volume of the sheet-like exterior material that encloses the water absorbent body. .

The present invention will be described below with reference to the drawings.

FIG. 1 is a cross-sectional view schematically showing the cold insulating material of the present invention. Figures 2 to 4 are for explaining the production and use of the cold insulating material of the present invention. Figure 2 is a perspective view showing the constituent materials of the cold retaining material, and Figure 3 is a perspective view showing the constituent materials. FIG. 4 is a perspective view showing the cold insulating material swollen by water absorption; FIG.

Referring to FIG. 1, the cold insulating material (1) of the present invention consists of a water-retaining water absorbent body (2) and a sheet-like exterior material (3) provided above and below the water-retaining water absorbent body and wrapping the water-retaining water absorbent body.

First, to explain the water absorbent body, it quickly absorbs a large amount of water, and after absorbing water, it does not easily release water as a liquid even if some external stimulus such as pressure is applied. Use something that also has water retention properties. Suitable examples of such water absorbers include so-called water absorbing polymers obtained by partially crosslinking acrylic acid-based or hydrophilic polymers. Usually, water-absorbing polymers are
If it is allowed to swell freely upon water absorption, it will be 10 to 10
0 0fl! The volume is t. Such water-absorbing polymers may be in the form of fibers or sheets, or may be in the form of sheets in combination with fibrous or film substrates such as woven or non-woven fabrics. The powder form is available through the water holes (4), which will be described later.
) and is difficult to retain inside, making it unsuitable.

Note that materials such as sponges, cotton, and nonwoven fabrics that easily release absorbed water by pressure or the like are not suitable as the water absorbent material in the present invention. However, there is no problem in using these together with a water-absorbing polymer.

Next, as the sheet-like exterior material (3) that wraps the water absorbent body,
A material having a hydrophobic surface and having water passage holes (4) as shown in FIG. 1 etc. is used.

Hydrophobicity is necessary in order to exclude water from the surface as much as possible (as long as the surface is hydrophobic, a multilayer material using a hydrophobic material in the surface layer can of course be used). Examples of such hydrophobic exterior materials include polyethylene,
Examples include films and sheets of general-purpose plastics such as polypropylene. Any material can be suitably used as long as it does not itself absorb water or dissolve in water. In this respect, materials that structurally retain water, such as porous materials and nonwoven fabrics, are inappropriate as exterior materials in the present invention, even if they are hydrophobic.

The thickness of the film or sheet used as the exterior material must have appropriate flexibility, do not interfere with the swelling of the internal water-absorbing material with water, and must not be easily torn during normal handling. It is fine as long as it satisfies
Although it depends on the material, a thickness of 10 to 200 μm is generally used. As described later, the exterior material must be joined by some means after the water absorbent is sandwiched inside (see Figures 2 and 3), so we recommend using a material that can be joined by the commonly used heat sealing method. is preferred. Note that even if the material itself is not sealable, it can be heat-sealed by providing an appropriate sealant layer.

Furthermore, the water holes (4) in the exterior material form a passage through which necessary and sufficient water is supplied to the internal water absorbent body when the entire body is immersed in water. Regarding the number, size, etc. of the water passage holes (4), it is desirable to provide as many large holes as possible from the viewpoint of rapid water absorption required in the water absorption process. On the other hand, from the viewpoint of binding during freezing and retaining the ice inside the water absorbent when it melts during transportation, it is desirable that the pores be as small as possible. Specifically, according to experiments conducted by the present inventors, the porosity of the sheet (area of pores in unit area) is 1 to 10%, and the size (diameter) of pores is 0.5. ~2mm
was found to be suitable. Also, the number of holes is l
Approximately 1 to 15 pores per cm" are suitable, and if there are 50 or more pores, even small pores tend to bind. However, since many factors such as the water absorption capacity of the water absorbing material are involved, The above data is just a guideline, and it is desirable to select the size, number, etc. of the pores as appropriate, mainly from the viewpoint of rapid water absorption and water retention.

Such selection can be easily made through appropriate experiments. However, it can be clearly said that a material with a large pore size such as a net is unsuitable, and a so-called micro bolus of 100 μm or less is not preferred.

Note that the shape of the hole is not particularly limited, but from the viewpoint of workability, it is usually desirable to have a circular or square shape.

Furthermore, in the present invention, a specific relationship is established between the maximum swelling volume of the water absorbent in a saturated water absorption state and the maximum internal volume of the exterior material. That is, the maximum swelling volume is greater than or equal to the maximum internal volume.

Here, the term "maximum swelling volume" in a saturated water-absorbing state as used herein refers to the term "maximum swelling volume" in which the water-absorbing material is given excess water without any restraint, allowing it to freely absorb water and swell to maximize its water-absorbing ability. It refers to the volume when the In addition, the term "maximum internal volume of the exterior material" assumes a container (without holes) obtained by joining the exterior materials described later without adding a water absorbent (for example, when water is placed in a water pillow) (e.g., the internal volume when filled) is the maximum amount of water when filled inside at normal pressure. By configuring a cold insulating material with a water absorbing body and an exterior material that have such a relationship between the maximum swelling volume and the maximum internal volume, all the water left in the container when absorbing water is absorbed by the water retaining material. It will be held inside. That is, even if water is absorbed, the water-absorbing body remains in the state before reaching its maximum water-absorbing capacity, and since there is residual water-absorbing capacity, the free surface water is completely absorbed. Therefore, the amount of water liberated during the process of water absorption and freezing becomes extremely small.
This prevents the cold insulation materials from binding together. Preferably, the ratio of (maximum internal volume of exterior material)/(maximum swelling volume) is in the range of 0.50 to 0.95, taking into consideration the elongation (flexibility) and strength of the exterior material when it absorbs water and swells. shall be.

In order to satisfy such a relationship, it is convenient to use a water absorbent material that can easily obtain the desired water absorption capacity. From this point of view, water-absorbing polymers obtained by radiation polymerization are advantageously used.

The cold insulating material (1) of the present invention is made by sandwiching the water absorbing body as described above between the exterior material (3) as described above (see Figure 2), and joining the periphery of the exterior material (3) as shown in Figure 3 to integrate it. (An example of a joint is indicated by reference numeral 5 in the drawings.) Examples of such bonding methods include heat seam welding, high frequency welding, ultrasonic welding, and sewing using a sewing machine.

The maximum swelling volume of the water absorbent body can be adjusted not only by the water absorption capacity of one (unit) water absorbent sheet, but also by increasing or decreasing the number of water absorbent sheets as shown in FIG.

The thus obtained cold insulating material of the present invention rapidly absorbs water and swells as shown in FIG. 4 just by being immersed in water. By freezing it in that state, it can be suitably used especially for small-lot transportation of fresh foods. In addition, we also offer cold insulation materials for cakes and fresh sweets, cold insulation materials for portable refrigerators, medical cold compress materials,
It can also be suitably used as a cold compress material for sports.

Function The cold insulating material of the present invention can be simply immersed in water, and since it uses a water-absorbing polymer with high water absorption,
Water can be absorbed quickly.

Furthermore, due to the water absorption ability that remains even after water is absorbed, there is no adhesion of water, making it difficult for mutual binding to occur.

The present invention will be explained in more detail with reference to Examples below.

Example I A polyamide nonwoven fabric with a basis weight of 35 g/m'' was impregnated with an aqueous solution of sodium acrylate monomer (monomer concentration 42% by weight) to give a coating weight of 80 g/m''.

Immediately after impregnation, using an area beam electron beam irradiation device manufactured by Nissin High Voltage Co., Ltd., in a nitrogen atmosphere, an acceleration voltage of 200 KV, a dose of 4 Mrad, and a dose rate of 1 4 Mrad were applied.
A sheet-like water absorbent was obtained by irradiating with an electron beam under the condition of /sea. This sheet had excellent water retention properties, and the maximum swelling volume at saturated water absorption was 6000 cm3 per 1 m'' sheet.

Next, this sheet was cut into 9×14 cm square pieces.
Five sheets were stacked together to form a water absorbent body with a maximum swelling volume of 454 cm3.

Furthermore, the water absorbent was sandwiched between two polyethylene films (thickness: 40 μm) each having 6 holes/cm" with a diameter of 0.8 mm, and the four sides were heat-sealed so that the internal dimensions were 5 cm square. The maximum internal volume of the packaging material at this time was 340 cm3, and the ratio of (maximum internal volume of packaging material)/(maximum swelling volume) was approximately 0.75.

The structure obtained in this manner was immersed in water for 10 minutes to allow the water absorbent to sufficiently absorb water, and after being pulled out of the water and briefly drained, it was immediately stored in a freezer at -1O°C. Frozen. When the cold insulating materials were taken out from the freezer after being completely frozen, they could be easily separated one by one, and there was no binding between the cold insulating materials. Furthermore, when this cold insulating material was placed in an insulated container made of expanded polystyrene and sealed, it exhibited a cold retention effect for a long time, and even after the ice melted, there was almost no leakage of water into the container, which was favorable.

Next, the difference in binding properties was experimentally investigated between the obtained cold insulating material of the present invention and a cold insulating material whose maximum swelling volume was smaller than the inner volume of the exterior material. In the experiment, cold insulators were created by using the same water absorbent body and exterior material as in Example 1, and by varying the heat-sealed bonding dimensions of the exterior material, and the immersion in water and freezing procedures were also the same as in Example 1.
I did the same thing.

The results are shown in Table 1 below.

1st table The symbols in the drawings have the following meanings.

Claims (1)

[Claims] (1) Consists of a water-retentive water absorbent body and a sheet-like exterior material that is provided above and below the water absorbent body and whose periphery is bonded to enclose the water absorbent body, and the exterior material has water passage holes and a hydrophobic surface. death,
A cold insulating material characterized in that the maximum swelling volume of the water absorbent body in a saturated water absorption state is greater than or equal to the maximum internal volume of the exterior material that encloses the water absorbent body.