JPS587450B2 - Unidirectionally shrinkable expanded polystyrene resin sheet - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a novel unidirectionally shrinkable expanded polystyrene resin sheet for packaging articles. It expands in the other direction, i.e. shows contraction in only one direction.
The present invention also relates to a unidirectionally shrinkable expanded polystyrene resin sheet for packaging articles, which has a large number of closed cells inside and has excellent heat insulation and cushioning properties.

Items that show shrinkage when heated are:
Stretched polyvinyl chloride resin film, polyethylene resin film, crosslinked polyethylene resin film,
Polystyrene resin films, polypropylene resin films, polyvinylidene chloride resin films, and the like are well known.

As the thickness of these materials increases, their bendability decreases, making it difficult to shrink-cover small-diameter cylindrical objects.
In addition, it takes a long time to shrink due to heating, and furthermore, it is difficult to control uniform temperature during stretching, so the thickness is generally 0.1 mm or less, and even the thickest ones are limited to about 0.2 mm. It had been.

In addition, since none of these known shrinkable films have cushioning properties, they cannot be used for shrink-coating articles that are easily damaged by a slight impact, such as ceramics and glass products.

Furthermore, it has poor insulation properties, so it is necessary to keep it warm and cold.
For example, it was never used for pipe covers to prevent freezing.

In addition, the above-mentioned known shrink films, etc., not only biaxially stretched films but also uniaxially stretched films, show heat shrinkability in both axial directions, even if there is a difference in the ratio. It could not be used for constricted, gourd-shaped articles, such as brandy glasses, bottles, etc., in which protective coatings adhere tightly to the packaged object, or where one direction must expand rather than contract during packaging.

Therefore, the above-mentioned known shrink films have only been used for shrink wrapping foods, etc., for the purpose of preventing deterioration of quality, odour, and retaining water.

Relatively small-diameter pipes that require insulation and bendability to keep things warm and cold, such as water pipes to prevent freezing, or items that are easily damaged by a slight impact and require cushioning properties to prevent damage. ceramics such as vases, glassware such as cups,
Furthermore, various attempts were made to develop a shrinkable sheet suitable for protecting or packaging partially constricted gourd-shaped brandy glasses, bottles, etc., but none of them had properties that had heat insulating properties and curved cushioning properties. Needless to say, a unidirectionally shrinkable sheet is required that has the property of shrinking only in one direction when heated and shrinking, and then expanding slightly in the other direction perpendicular to that direction. They discovered this.

In other words, a shrinkable sheet that contracts simultaneously in both directions, one direction and the other direction perpendicular to this direction, can be formed into a cylindrical shape in advance, and a pipe, a glass product, or a bottle having a partial constriction can be placed inside the cylinder. If you heat and shrink the product after inserting it, it will become shorter than the size of the pipe, glass product, etc. To prevent this, cover it in advance and shrink it to the size of the pipe or other product you are trying to package. It would be better to make the sheet larger so that it does not become shorter, but doing so would increase the cost of shrink wrapping packaging, and since the sheet would shrink from both directions at the same time, a misalignment would occur between the sheet and the object to be wrapped.
Wrinkles occur because the misalignment is not uniform, making it impossible to obtain a shrink coating or shrink-wrapped product that is completely adhered, and furthermore, it only shrinks from both directions at the same time without showing any shrinkage along the waist. However, it has drawbacks such as not being able to be used in gourd-shaped products with a constriction.

On the other hand, if the material contracts only in one direction and expands in a direction perpendicular to the aforementioned direction upon shrinkage, the above-mentioned drawbacks will not occur at all when the material is heated and shrink-wrapped.

In particular, even if the item expands in the other direction, the expansion rate is smaller than the contraction rate in the one direction, and the contraction tension is stronger than the expansion force, so constricted gourd-shaped brandy glasses, vases, etc. are covered and packaged. After shrinking and adhering to the large diameter part of the packaged product, it expands in the length direction, and as a result, it stretches uniformly along the constriction, so there is no wrinkles at all, and the shrinkable sheet does not tear during shrinkage. This is because it has the advantage of being able to obtain a shrink-wrapped body without any damage.

Based on these reasons, the present inventors have conducted intensive research to develop a shrinkable sheet that has heat insulation properties, bendability, cushioning properties, and the properties of shrinking in one direction and expanding in the other direction perpendicular to the said direction. As a result, the foamed polystyrene resin sheets currently on the market have properties such as heat insulation, bendability, and cushioning properties, and in particular, when the foamed polystyrene resin sheets are heated, the air in the closed cells constituting the sheets expands. By doing so, we focused on the fact that the sheet itself has the characteristic of volumetric expansion, so-called secondary foaming, and determined the shrinkage ratio under certain conditions in one direction of the sheet and in the other direction perpendicular to the said direction. The present inventors have found that by providing a shrinkable sheet, all of the drawbacks of conventionally known shrinkable sheets can be overcome, and the sheet can be suitably provided for shrink-wrapping products that require heat insulation, bendability, and cushioning properties. .

That is, in the present invention, there are many closed cells inside, the thickness is 0.1 to 2.0 mm, and the density is 0.4 to 0.06 g.
/cc, and when heated at a temperature of 130°C for a time that does not cause the bubbles to collapse, it contracts by at least 30% in one direction and in the other direction perpendicular to the above direction. a unidirectionally shrinkable expanded polystyrene resin sheet for article packaging, characterized by expanding by 7 to 25%;
The main points are as follows.

The expanded polystyrene resin sheet in the present invention includes:
Styrene homopolymer resins and copolymer resins, such as polystyrene resins, styrene-acrylonitrile copolymer resins, styrene-methyl methacrylate copolymer resins, styrene-acrylonitrile-butadiene copolymer resins, and blends of these resins. , foamed and made into a sheet shape are used.

Such a foamed polystyrene resin sheet is produced by, for example, inserting foamable polystyrene resin particles whose insides have been impregnated in advance with a known blowing agent such as propane, butane, pentane, dichlorodifluoroethane, etc., into a mold having an annular slit at the tip. The material is supplied to an attached extruder, melted and kneaded in the extruder, extruded from the mold into a cylindrical shape under atmospheric pressure while foaming, and then cut open.

Expanded polystyrene resin sheets obtained by the above-mentioned methods are known and commercially available.

Such a foamed polystyrene resin sheet is heated at a temperature of 130° C. to a time that does not cause the sheet to lose its original appearance and other properties, i.e., without destroying the large number of closed cells present inside the sheet. As shown in the table below, one direction and the other direction perpendicular to this direction when compressed show the contraction value of the joint ratio in both directions, or even if the contraction value is large or small, it is the direction of the larger contraction. The value does not exceed 30%, and there is currently no expanded polystyrene resin sheet that expands in the other direction perpendicular to the direction of contraction.

Measurement method: A foamed polystyrene resin sheet is cut 100 mm parallel to the longitudinal direction and 100 mm perpendicular to the longitudinal direction to create a number of square test pieces.

The center of each square test piece is held in a hollow state by a rod-shaped body with a small diameter such as a wire, and this is placed in a constant temperature bath maintained at a temperature of 130°C for each unit time, e.g.
, 2, 3,...Heat for seconds at a time.

And by heating, the sheet does not lose its original appearance and other properties, i.e.
The longitudinal direction and length of the test piece heated for the longest time until the air bubbles on the sheet surface are melted and destroyed by heat or the molecular orientation due to stretching is destroyed by heat and the flexibility, cushioning properties, etc. are not lost. Measure the dimension in the direction perpendicular to the direction, subtract each value from the dimension before heat shrinkage, divide the value by the dimension before heat shrinkage, and multiply the value by 100 to determine the shrinkage rate.

In the present invention, the shrinkage rate when heated to a temperature of 130° C. until a time during which bubbles do not burst refers to the above-mentioned measurement method and measurement value.

As is clear from this table, all commercially available expanded polystyrene resin sheets are designed not to expand in the other direction perpendicular to the contraction direction.

This is because conventional foamed polystyrene resin sheets are all intended for producing molded products such as cups, plates, and lunch boxes.

If a foamed polystyrene resin sheet expands in even one direction when heated, it will become wavy during molding, resulting in overlapping undulating peaks or air leakage during vacuum molding.
This is because a suitable molded product cannot be obtained.

The expanded polystyrene resin sheet in the present invention has at least 30
% or more, and expands by 7 to 25% in the other direction perpendicular to the above direction.

Conventionally commercially available expanded polystyrene resin sheets either shrink at approximately the same rate in one direction and in the other direction perpendicular to that direction, or expand in one direction even if the shrinkage value is large or small. Because it does not show any trends,
When using this sheet to shrink-cover pipes, etc., it is necessary to fix both ends of the sheet so that it does not shrink, and then heat it to shrink it. Heating is not done as uniformly as others,
Furthermore, because the sheet was fixed, it was not possible to obtain a beautiful shrink-coated product because the sheet was torn, and furthermore, it could not be applied at all to shrink-wrapping constricted gourd-shaped brandy glasses, bottles, etc.

On the other hand, the shrinkable expanded polystyrene resin sheet of the present invention has a shrinkage rate of 30% or more in one direction and expands in the other direction perpendicular to the said direction.
When shrinking, items that contract in this direction contract before items that expand in other directions, so that by making the direction of contraction correspond to the direction of contraction, it is possible to shrink wrap a brandy glass, etc. The brandy glass is formed in advance into a cylindrical shape so that the direction of contraction on the side wall corresponds to the direction of expansion of the same size as the brandy glass in the length direction, and the brandy glass is placed in the cylinder. When the glass is heated after being inserted, the side wall moves toward the center and comes into close contact with the larger diameter part of the brandy glass before expanding in the length direction, and then the part corresponding to the constriction expands along the constriction. It is possible to suitably obtain a shrink-coated packaging product that contracts in the radial direction while expanding in the lateral direction, adheres closely along the waist, and does not generate any wrinkles.

For this reason, the shrinkable expanded polystyrene resin sheet of the present invention can be contracted in one direction and expanded in the other direction perpendicular to that direction, without causing wrinkles, and against products having any partially constricted parts. It is preferably used because it can be applied to any field.

The shrinkable foamed polysterene resin sheet of the present invention is the above-mentioned 13
It is necessary that when heat-shrinked at a temperature of 0° C., the shrinkage rate in one direction is 30% or more relative to the dimension before shrinkage.

With a shrinkage rate of 30% or less, it may be possible to use it for items that do not require a large shrinkage rate, such as pipes, but since the shrinkage rate is small for items that have a partial constriction, it can be used along this constriction. This method is undesirable because it has drawbacks such as not being able to obtain a product that adheres tightly to the product, and also requires a long time to shrink, and furthermore, the adhesion between the shrink sheet and the packaged object is poor.

If the shrinkage rate is too high, if the sheet is bent and the ends are joined with adhesive or heat fusion to form a cylindrical shape and then heat-shrinked, the joint may peel off or the sheet may Although there may be drawbacks such as tearing, foamed polystyrene resin sheets do not exhibit a heat shrinkage rate high enough to cause problems in heat-shrink packaging operations, no matter how high the shrinkage rate is made.

Furthermore, the shrinkable expanded polystyrene resin sheet of the present invention must undergo negative contraction, that is, expansion, in the other direction perpendicular to the contraction direction.

Items that show expansion elongate well with contraction in the direction of contraction, resulting in a shrink-wrapped product along the waist, while items that show contraction do not show a tendency to elongate along the waist, resulting in shrink-wrapped products that follow the waist. There is a drawback that the product cannot be obtained.

The expansion rate of the shrinkable foamed polystyrene resin sheet of the present invention in the direction of expansion has a preferable value depending on the shape of the object to be packaged.

For example, in the case of a large constriction shape such as a brandy glass, a value close to 20% is preferable.

If the expansion rate exceeds 25%, when shrink-wrapping, expansion and contraction occur at the same time or expansion starts first, resulting in wavy shapes and making it impossible to obtain a shrink-wrapped body that evenly adheres to the packaged object. Therefore, in the present invention, a material with an expansion rate of 7 to 25% is used.

The shrinkage rate of the present invention when heated is 3.
0% or more and has the property of expanding in the other direction perpendicular to the said direction, commercially available foamed polystyrene resin sheets, such as those shown in the previous table, can be obtained by Product type # made by Seishin Kogyo Co., Ltd. with a thickness of 1.38 mm and a density of 0.07 g/cc
2000 (shrinkage rate in one direction 20%, shrinkage rate in the other direction 7%) was heated to a temperature of 120°C to soften it, and then heated in the opposite direction in one direction showing a shrinkage rate of 20%. It is easy to stretch the sheet by 1.5 times or more than the previous size of the sheet, and let it shrink freely in the other direction due to the influence of the tension when stretching in one direction in addition to the contraction force of the sheet itself. will be achieved.

It can also be obtained by appropriately changing the blow-up ratio or pulling speed during extrusion production of a foamed polystyrene resin sheet.

The shrinkable expanded polystyrene resin sheet of the present invention obtained by such a method has a thickness of 0.1 to 2.0 mm,
It is necessary that the density is 0.4 to 0.06 g/cc.

If the thickness is less than 0.1 mm, the insulation and cushioning properties will be poor, and the properties of the expanded polystyrene resin sheet will decrease.
．． If it exceeds 0 mm, the shrinkable sheet itself has heat insulating properties, and due to this heat insulating effect, the outer layer and inner layer are not heated evenly during heating, resulting in non-uniform shrinkage.

Moreover, the bendability deteriorates, making it impossible to use it for small-diameter cylindrical objects, which is not preferable.

In addition, shrinkable sheets with a density of 0.4 g/cc or more have the disadvantage that they are too rigid and have poor cushioning properties, and their bendability is poor, making them unusable for small-diameter cylindrical objects. On the other hand, if it is less than /cc, it is not preferable because it becomes too flexible and cannot absorb impact, making it unsuitable for packaging articles that are easily damaged by a slight impact.

Since the shrinkable polystyrene foam sheet of the present invention has the properties described above, it can be used to insulate small-diameter pipes that require insulation for heat and cold insulation, such as water pipes to prevent freezing. It is advantageously used as an impact protection material for pottery and glass products that are easily damaged by a slight impact, particularly for gourd-shaped glass products that are partially constricted.

Examples will be further explained below.

Example A product made by Sekisui Plastics Co., Ltd., with a thickness of 1.0 mm and a density of 1.36 g/cc (product type 1 x 630S), measured according to the measurement method of the present invention, the shrinkage rate of shrinkage in one direction was While heating a foamed polystyrene resin sheet with a shrinkage rate of 25% and a shrinkage rate of 9% in the other direction perpendicular to the direction in a heating chamber at a temperature of 120°C, The sheet is fixed, and only the other end is pulled to 1.5 times its original size by a tensioning device, and stretched in one direction only.In the other direction, where the shrinkage rate is small, the sheet is stretched in one direction in addition to the shrinkage force of the sheet itself. A unidirectionally shrinkable foamed polystyrene resin sheet was made by allowing the sheet to shrink freely under the influence of tension.

This shrinkable foamed polystyrene resin sheet was heated again for 8 seconds using the measurement method of the present invention to measure the shrinkage rate, and the heat shrinkage rate in the stretching direction was 53%, and that in the other direction perpendicular to this direction was 53%. The shrinkage rate at time was -7% (7% expansion).

The case where such a shrinkable foamed polystyrene resin sheet is used to cushion a ceramic vase, which is easily damaged by a slight impact, will be explained with reference to the drawings.

The shrinkable expanded polystyrene resin sheet has a dimension in the shrinking direction of 355 mm and a dimension in the expanding direction of 270 m.
The sheet is cut into lengths of m, curved into a circular shape in the shrinking direction, and both ends are joined 11 by heat fusion to create a shrinkable cylindrical sheet 1 shown in FIG. 1 that shrinks toward the center of the diameter. did.

Inside this cylindrical sheet 1, as shown in FIG. A vase 2 was inserted between the neck portion 24, body portion 22, and base portion 23 in which the outer diameter of the constricted leg portion 25 was 55 mm and the height was 220 mm.

After insertion, the sheet 1 was heated for 8 seconds in a heating chamber maintained at a temperature of 130° C. to shrink the sheet 1, resulting in a vase protected and covered with a shrinkable polystyrene foam resin sheet having cushioning properties, as shown in FIG. I got 2.

When the state after the heat shrinkage was observed, the shrinkable cylindrical sheet 1 had no wrinkles at all, adhered well to the vase 2, and even along the constriction, the vase 2 was closely attached with a large constriction. The portions of the sheet that had previously protruded from the top and bottom shrunk significantly, and 12 sheets were obtained that were bent until they were parallel to the top and bottom surfaces of the vase.

The dimension in the height direction of the shrinkable cylindrical sheet 1 after heat shrinkage has expanded to about 295 mm, and the property of the cylindrical sheet 1 to expand in the height direction causes it to curve into the upper and lower surfaces of the vase 2. It is clear that this method is very effective in obtaining a complete package along the waist.

Comparative Example 1 In Example, a foam that co-shrinks in two directions has a shrinkage rate of 55% in one direction and a shrinkage rate of 23% in the other direction perpendicular to the direction when measured according to the measuring method of the present invention. A shrink-wrapped vase similar to the example was obtained except that a polystyrene resin sheet was used.

When this shrink-wrapped body was observed, it was found that the constriction was overflowing, but the upper and lower surfaces of the vase were not curved, and the upper and lower sides were not bent.
1 and 23 were obtained, and the constrictions 24 and 25 were wrinkled.

Comparative Example 2 In Example, when measured according to the measuring method of the present invention, the shrinkage rate in one direction is 45% and the shrinkage rate in the other direction perpendicular to the said direction is 40%, which is approximately the same rate in two directions. The same shrink-wrapped body was obtained in the same manner as in the example except that a foamed polystyrene resin sheet showing shrinkage of .

When this shrink-wrapped product was observed, it was found that there was no curvature in the upper and lower surfaces of the vase, and that it did not follow the constriction in any way, and many wrinkles were generated.

[Brief explanation of the drawing]

The drawings show an example of shrink-wrapping a vase using the unidirectionally shrinkable expanded polystyrene resin sheet of the present invention, and FIG. 1 is a perspective view of the sheet in a cylindrical shape, and FIG. FIG. 3 is a cross-sectional view of a vase inserted into a cylindrical sheet, and FIG. 3 is a cross-sectional view of a vase shrink-wrapped, in which 1 is the unidirectionally shrinkable polystyrene foam resin sheet of the present invention, and 2 is the vase. 2' is a vase shrink-wrapped by the sheet 1.

Claims (1)

[Claims] 1 There are many closed cells inside, the thickness is 0.1 to 2.0 mm, the density is 0.4 to 0.06 g/cc, and the bubbles are not destroyed at a temperature of 130 ° C. A unidirectional shrinkable product for packaging articles, characterized in that, when heated for an extended period of time, the product shrinks by at least 30% in one direction and expands by 7 to 25% in the other direction perpendicular to said direction. Expanded polystyrene resin sheet.