JPS6360733A - Heat-shrinkable foamed polyethylene sheet and preparation thereof - Google Patents

Abstract

PURPOSE:To enable the tight shrink-pack of an article to be packed just after heat-shrinking and the generation of no sag on the sheet after shrink-packaging, by keeping the ratio of the shrinking stress at the beginning of heat-shrinking to that after heat-shrinking at a specified value, when a heat-shrinkable foamed polyethylene sheet is heat-shrunk. CONSTITUTION:A heat-shrinkable foamed polyethylene sheet whose foaming magnification and gel fraction are 10-80 times and 20-55% respectively satisfies the equation 3<A/B<50, where A is the max. shrinking stress (g/cm<2>) at the beginning of heating when the heat-shrinkable foamed polyethylene sheet is heated at 135 deg.C and B is the shrinking stress (g/cm<2>) at 5min after the heating starts when heated at 135 deg.C. It is possible to shrink-pack smoothly an article to be packed in a heat-shrinking process because the articles to be packed can be tightly shrink-packed, the tightly packed state can be kept without any occurrence of sag after shrink-packaging, the sheet has high heat-resistance and mechanical strength and the allowance of the heat-shrinkage condition is large.

Description

Detailed Description of the Invention <Industrial Application Field> The present invention relates to a heat-shrinkable foamed polyethylene sheet and a method for producing the same, and more specifically to a heat-shrinkable foamed polyethylene sheet and a method for producing the same. The present invention relates to a shrinkable foamed polyethylene sheet and a method for producing the same.

<Prior art> Conventionally, heat-shrinkable foam sheets for shrink-wrapping and protecting various packaged items have been irradiated with ionizing radiation and stretched, with a gel fraction of 5 to 50, a foaming ratio of 5 to 50, and a heat-shrinkable foam sheet. Heat-shrinkable foam sheets and heat-shrinkable composite foam sheets having a ratio of lO to 90% are known (Japanese Patent Laid-Open No. 58-79
032 and JP-A-58-90944).

However, in the above-mentioned heat-shrinkable foam sheet, when the expansion ratio is increased in order to enhance the protection effect of the packaged object, the following problems occur.

■If a heat-shrinkable foam sheet is shrink-wrapped and then returned to room temperature, the cohesive strength of the foam sheet decreases, making it impossible to maintain a tightly packaged state. Especially 1. In the case of group packaging, the binding force is insufficient and it is difficult to maintain a tightly packed state. (2) When the bubble diameter is large due to a large expansion ratio, the heat-shrinkable foamed sheet will have creases or residual shadows caused by the creases, which is unfavorable in terms of appearance and reduces commercial value. ■Also, because the heat-shrinkable foam sheet with a high expansion ratio has high elasticity, it is difficult to slip on the convex parts and corners of the packaged object, etc., where it comes into contact with the heat-shrinkable foam sheet.
Moreover, since the tensile strength is small, the heat-shrinkable foam sheet partially loosens when packaged. In addition, even when heat-shrinking in a shrink tunnel, there is poor slippage at the contact part with conveyance rollers, etc., and there is no tensile strength. Various problems arise, such as the difficulty of shrink-wrapping the product. ■The allowable range of processing conditions during heat shrinkage is narrow, and in combination with the above (■), smooth shrink wrapping cannot be performed. In particular, in the case of a heat-shrinkable foam sheet with a low degree of cross-linking, the bubbles become immersed, which deteriorates the functions of the foam sheet, such as cushioning properties, heat insulation and heat retention, and the appearance of the sheet.

On the other hand, in order to solve the above-mentioned problems ① to ②, if the heat-shrinkable foam sheet is made with a low expansion ratio, the amount of material used per unit volume increases, thereby providing an inexpensive heat-shrinkable foam sheet. The problem arises that it cannot be done.

In addition, as a method for manufacturing a heat-shrinkable foam sheet as described above, the melt-extruded film and foam sheet are immediately first stretched, and a pair of rollers having different rotational speeds and temperatures and arranged closely is used. There is a method in which a heat-shrinkable foam sheet is continuously produced by further stretching the sheet in the longitudinal direction between 1 and 2 (Japanese Patent Publication No. 56-411i974);
A method of uniaxial or biaxial stretching at 20 to 200°C with an area ratio of 2 to 20 times is known (Japanese Patent Publication No. 43-203
Publication No. 87).

However, although the former production method is suitable for stretching an uncrosslinked foam sheet with a very small thickness and a low expansion ratio, it is not suitable for producing a heat-shrinkable foam sheet with a high expansion ratio and a crosslinked structure with high mechanical strength. is difficult to apply. That is, in the above method, it is difficult to firstly stretch a crosslinked foam sheet and then to secondly stretch it.

In addition, in the latter manufacturing method, a sheet kneaded with a decomposable blowing agent is crosslinked, then heated and foamed, and then,
Since biaxial stretching is used, the obtained sheet has fine bubbles, but it has the same problems as the above-mentioned conventional heat-shrinkable foam sheets.

Purpose This invention has been made in view of the above-mentioned problems, and is capable of shrink-wrapping a packaged item smoothly and without causing folds or wrinkles in a heat shrinking process, even as a foam sheet with a high expansion ratio. An object of the present invention is to provide an inexpensive heat-shrinkable foamed polyethine sheet that can maintain a tightly packaged state without loosening even after heat-shrinking, and a method for producing the same.

Means and operation for solving the above problems In order to achieve the above object, the first invention related to a heat-shrinkable foam sheet is a heat-shrinkable foam sheet having a foaming ratio of 10 to 80 times and a gel fraction of 20 to 55%. This heat-shrinkable foamed polyethylene sheet satisfies the following relational expression (1).
The heat-shrinkable foamed polyethylene sheet satisfies the
This solves the above-mentioned conventional problems.

3<A/B<50 0...(I) (wherein, A indicates the maximum shrinkage stress (g/cj) that appears at the beginning of heating when a heat-shrinkable foamed polyethylene sheet is heated at 135°C, and B is It shows the shrinkage stress (g/cj) 5 minutes after the start of heating when heated at 135°C. The same applies hereinafter.) The first invention having the above configuration uses a heat-shrinkable foamed polyethylene sheet. When heat-shrinked, the ratio of the shrinkage stress at the beginning of heat-shrinking to the shrinkage stress after heat-shrinking shows a specific value, so the binding force is large, and immediately after heat-shrinking,
Items to be packaged can be tightly shrink-wrapped, and the heat-shrinkable foamed polyethylene sheet will not loosen even after shrink-wrapping. In addition, heat-shrinkable foamed polyethylene sheets are crosslinked and have high heat resistance, mechanical strength, etc., and also maintain tensile strength, so they have good sliding properties with packaged items, conveyance rollers, etc. even when heated. and
Wide tolerance for heat shrinkage conditions.

In addition, the second invention related to the manufacturing method includes a foam sheet forming step of melt-extruding an ethylene polymer to form a foam sheet, a crosslinking step of crosslinking the foam sheet obtained in this foam sheet forming step, and this crosslinking step. After that, the sheet is heated and stretched at a heating medium temperature that is equal to or higher than the melting point of the ethylene polymer and does not exceed 100°C above the melting point, and the stretched foam sheet is heated to a temperature lower than the melting point of the ethylene polymer. Through the drawing process of rapidly cooling to a temperature of
A heat-shrinkable foamed polyethylene sheet satisfying the following relational formula (III) is manufactured.

3<A/B<50 0...(I Since the highly elastic foam sheet is stretched at a temperature higher than the melting point of the ethylene polymer and cooled to a temperature lower than the melting point of the ethylene polymer, the ratio of the shrinkage stress at the beginning of heat shrinkage to the shrinkage stress after heat shrinkage is reduced. , indicates a specific value 7
, a heat-shrinkable foamed polyethylene sheet that has a large binding force, allows tightly shrink-wrapping of the packaged item immediately after heat shrinkage, and does not cause any slack in the heat-shrinkable foamed polyethylene sheet even after shrink-wrapping. It is possible to manufacture it.

The present invention will be explained in detail below.

Ethylene-based polymers constituting heat-shrinkable polyethylene foam sheets include various polyethylenes such as ultra-low density polyethylene, low-density polyethylene, medium-density polyethylene, high-density polyethylene, linear low-density polyethylene, and ultra-high molecular weight polyethylene; chlorine; polyethylene; ethylene-propylene copolymer, ethylene-vinyl acetate copolymer, ethylene-α-olefin copolymer, ionomer, ethylene-acrylic acid copolymer, ethylene-methacrylic acid copolymer, ethylene-acrylic acid alkyl ester Copolymers, copolymers with ethylene monomers such as ethylene-methacrylic acid alkyl ester copolymers; ethylene and crosslinkable vinylsilanes, such as trichlorovinylsilane,
Examples include copolymers with dichloromethylvinylsilane, dichlorodivinylsilane, and γ-methacryloyloxypropyltrimethoxysilane. Among these ethylene-based polymers, the above-mentioned polyethylenes with good crosslinking efficiency, particularly low-density polyethylene, and copolymers of ethylene and the above-mentioned crosslinkable vinyl silane are preferred.

The copolymer of ethylene and crosslinkable vinylsilane is preferably a copolymer of 0.01 to 5% by weight, preferably 0.05 to 1.5% by weight, of crosslinkable vinylsilane. It may be any copolymer such as a polymer or a graft copolymer.

The above ethylene polymers may be used alone or in combination of two or more.

In addition, the above-mentioned ethylene-based polymer can have various molecular weights, but in order to increase the stress during heat shrinkage and increase the stretching ratio, it is important to have a melt index of 0.05.
Those having ~4.0 are preferable. If the melt index is less than 0.05, the foaming efficiency during extrusion foaming will decrease, and if it exceeds 4.0, the shrinkage stress during heat shrinkage will not only decrease. , During the stretching process and heat shrinkage, not only uniform stretching and shrink packaging are not possible, but also volume thinning, etc. is likely to occur.

In addition, the above ethylene polymer has a density of 0.90
Those having a value of 0 to 0.969 are preferred.

Further, the above ethylene polymer may be used in combination with other organic polymers. Other organic polymers include olefin polymers such as polypropylene and polybutadiene; acrylic polymers such as polymethyl methacrylate, polyethyl methacrylate, and polyethyl acrylate; polystyrene,
Examples include styrene-based polymers such as styrene-butadiene copolymer; polyester, epoxy resin, polyurethane, polyamide, polyvinyl acetate; various rubbers such as natural rubber, butadiene rubber, butyl rubber, and polyisoprene rubber. These organic polymers can be used alone or in combination of two or more in a proportion of 50% by weight or less.

The heat-shrinkable foamed polyethylene sheet made of the above-mentioned ethylene polymer, etc. may have an appropriate expansion ratio depending on the type of the item to be packaged, the use of the foam sheet, etc., but the expansion ratio may be 10 to 80 times. Preferably. Foaming ratio is 10
If it is less than double, the buffering properties, heat insulation, etc. will not be sufficient.
If it exceeds 80 times, creases or wrinkles remain during shrink packaging, which is not only unfavorable in terms of appearance, but also makes it impossible to obtain a product with sufficiently high mechanical strength.

Further, the heat-shrinkable foamed polyethylene sheet described above has a crosslinked structure that is crosslinked by radiation irradiation or the like, and has high mechanical strength, heat resistance, and the like. The above-mentioned crosslinked structure may be formed by any crosslinking means, but it is preferably crosslinked by electron beam irradiation, which is safe, has good operability, and can efficiently adjust the degree of crosslinking. Further, a copolymer of ethylene and a crosslinkable vinylsilane crosslinked by a condensation reaction in the presence of water is also preferable because the crosslinking density can be easily adjusted by adjusting the amount of the crosslinkable vinylsilane used.

The foamed sheet having the above-mentioned crosslinked structure may have various degrees of crosslinking, but the gel fraction indicating the degree of crosslinking is
20 to 55% is preferred. The above gel fraction is 20%
If it is less than that, not only will the degree of neck-in in which the foamed sheet tightens during the stretching process increase, but also the shrinkage stress during heat shrinkage will be small, and the heat resistance and mechanical strength will not be sufficient, making it difficult to stretch and shrink. The heat shrinking process for packaging tends to cause volumetric shrinkage or thickening, bursting of bubbles, and tearing of foam sheets. In addition, the gel fraction is 5
If it exceeds 5%, the possible stretching ratio decreases and only a small heat shrinkage ratio can be obtained.

Note that the gel fraction referred to herein was determined by the following calculation formula.

(W/Wo) X100-Gel fraction (%) where W
o indicates the weight of the crosslinked foamed sheet, and Wl indicates the dry weight of the undissolved components after the crosslinked foamed sheet is refluxed in boiling toluene for 10 hours to remove dissolved components.

Further, the heat-shrinkable foamed polyethylene sheet is formed by being stretched in order to impart heat-shrinkability. The heat shrinkage rate of this heat-shrinkable foamed polyethylene sheet can be set as appropriate depending on the form of the item to be packaged, etc.
30-8 in the direction of flow of the foam sheet at 5°C
0%, -15% to +15% in the width direction of the foam sheet,
In particular, those of -7 to +796 are preferred. If the shrinkage rate in the machine direction is less than 30%, it is difficult to shrink-wrap the packaged item, and 80% is the limit at which a heat-shrinkable foam sheet can normally be produced. Furthermore, if the shrinkage rate in the width direction is outside the above range, it is difficult to thermally shrink the material in an attractive manner. The above heat shrinkage rate in the width direction can be obtained without stretching in the width direction, and is within a practically acceptable range for shrink packaging. The above heat shrinkage rate is determined by immersing a heat-shrinkable foamed polyethylene sheet in a glycerin bath heated to 135°C for 5 minutes, then cooling it with water, and determining the dimensions of the heat-shrinkable foamed polyethylene sheet before and after shrinkage. This is what I found from.

Further, the heat-shrinkable foamed polyethylene sheet may be biaxially stretched, and in this case, for the same reason as the stretching ratio in the width direction, the stretching ratio is 30 to 80% in the machine direction and in the width direction, respectively. It is sufficient as long as it has a heat shrinkage rate.

Further, the heat-shrinkable foamed polyethylene sheet may have an appropriate thickness depending on the application, but the thickness is 0.3 to
15 mm is preferred. If the thickness is less than 0.3 mm, the cushioning properties, heat insulation, etc. will not be sufficient, and the
If it exceeds mm, the thermal conductivity decreases, so that it becomes impossible to quickly heat and cool the film during stretching or heat shrinking, resulting in problems such as the inability to quickly shrink-wrap the packaged items.

The heat-shrinkable foamed polyethylene sheet needs to satisfy the following relational expression (I), 3<A/B<5
0 (1) Preferably, 3<A/B<30.

When the above A/B is outside the above range, it becomes difficult to perform quick and tight shrink packaging. In other words, depending on the shape and unevenness of the item to be packaged, the foam sheet may get caught, the foam sheet may become loose, or even creases may remain, making it difficult to tightly package the item. .

The above-mentioned shrinkage stresses A and B are as shown in FIG.
A fixed chuck (1) with a load cell (3) at one end (
a, and the other end is similarly attached to another fixed chuck (2°), and the l! It is determined by quickly storing the material in an oven at 50°C and measuring the shrinkage stress. In addition, each of the above fixed chucks [2] (2
°) are respectively fixed to fixed beds (4) (4°). When the shrinkage stress of a heat-shrinkable polyethylene sheet is measured as described above, the shrinkage stress generally shows a peak value at the beginning of the measurement, and then gradually decreases, as shown in FIG. The above A value and B value respectively indicate the maximum shrinkage stress at the beginning of heat contraction (corresponding to the shrinkage stress at the above peak value) and the shrinkage stress at the time point when 5 minutes have passed from the start of the measurement. In addition, in the heat-shrinkable foamed polyethylene sheet of the present invention, the peak of the above A value clearly appears.

The above A seems to correspond to the tightening force based on the contraction force at the time of heat contraction of the heat-shrinkable foamed polyethylene sheet, and B is the degree of loosening of the foamed sheet after heat-shrinking, i.e. , which seems to correspond to the cohesive force in steady state. Therefore, by using a heat-shrinkable foamed polyethylene sheet that has large values for both A and B,
It is possible to maintain the tightly packaged state of the packaged item for a long period of time.

In addition, when the above B value is small, the friction coefficient of the sheet surface increases due to heating during shrink packaging, and some tackiness also appears, so the contact resistance with the packaged item and the conveyance roller in the shrink tunnel increases. However, uniform shrink wrapping is not possible, and the heat-shrinkable foam sheet becomes loose, partially thin, and sometimes the sheet is torn. Moreover, if the heating conditions are excessive, the shape of the bubbles will collapse, the appearance of the package will deteriorate, and the volume will also increase. On the other hand, if heating is insufficient, shrinkage will not be sufficient, making it impossible to obtain a product that is in close contact with the packaged item, and making it difficult to adjust the heating conditions.

More specifically, heat-shrinkable foamed polyethylene sheets with a high expansion ratio have low strength, and the foam itself has a small weight and is soft, so it is used for light packaging applications that require cushioning and heat insulation properties. , the heat shrinkage stress may have a relatively small value.

On the other hand, a heat-shrinkable foamed polyethylene sheet having a low expansion ratio has a high rigidity and a large weight, so it is used for heavy-duty packaging and needs to have a large heat-shrinkage stress. In order to satisfy the above conditions and maintain the tightly packaged state of the packaged item for a long period of time, it is preferable that the heat-shrinkable foamed polyethylene sheet satisfies the following relational expression (II).

A × Expansion ratio > 4000 BXQ @ Magnification > 400″ ------- (II) In the above formula (II), if the value of A × Expansion ratio is less than 4000, the tightening force at the beginning of heat contraction is small, and Rapid shrinkage is not performed, making it difficult to shrink-wrap the packaged items.Furthermore, if the value of B x foaming ratio is less than 400, various troubles will occur in the shrink tunnel.Also,
After heating and shrink-wrapping, it may be difficult to tightly wrap the product.

Note that the heat-shrinkable foamed polyethylene sheet described above may be laminated with other films or sheets. The materials for the above films and sheets include olefin polymers such as polyethylene and polypropylene, polyesters such as polyethylene terephthalate, polystyrene, and styrene.
Examples include various synthetic resin films and sheets such as styrene polymers such as butadiene, nylon, polyvinyl chloride, and polyvinylidene chloride. Further, the above-mentioned films and sheets may be non-foamed or foamed, and preferably, they are stretched and have heat shrinkability.

Below, a method for manufacturing a heat-shrinkable foamed polyethylene sheet according to the second invention will be explained.

In the second invention, the heat-shrinkable foamed polyethylene sheet includes a foamed sheet forming step of foaming the ethylene polymer, a crosslinking step of crosslinking the ethylene polymer constituting the foamed foamed sheet, and a crosslinked foamed sheet. Manufactured by a stretching process.

The above-mentioned foam sheet forming step is carried out by combining the ethylene polymer with a blowing agent and using a known method such as a circinilla die or the like, and an appropriate method such as a plug method, an inflation method, a T-die method, or the like. Examples of the above-mentioned blowing agents include carbon dioxide gas, methane, ethane, propane,
Hydrocarbons such as butane, pentane, hexane, Freon 1
1. Volatile blowing agents such as fluorinated hydrocarbons such as Freon 12, ethers such as methyl ether and ethyl ether, and ketones such as acetone; ammonium carbonate, sodium bicarbonate, azodicarbonamide, N-, N-di Examples include decomposable foaming agents such as nitrosopentamethylenetetramine. Among the above foaming agents, volatile foaming agents that do not leave residue on the foam sheet and are odorless are preferred. Note that the above foaming agent is used in an appropriate amount, for example, 0.5 to 5% by weight. In addition, when forming a foam sheet, talc, kaolin, calcium carbonate, etc. may be used as a foam nucleating agent in an appropriate amount, for example, 1
~10% by weight may be used.

The above foam sheet can be foamed to an appropriate expansion ratio depending on the type of packaged item, the use of the foam sheet, etc. by adjusting the extrusion temperature of the ethylene polymer, the type and amount of blowing agent used, etc. However, as mentioned above, one with a foaming ratio of 10 to 80 times is preferable.

Next, the above foam sheet is crosslinked to improve its mechanical strength and
Increase heat resistance, etc. This crosslinking process involves ionizing radiation,
For example, radiation crosslinking by irradiation with ultraviolet rays, electron beams, α rays, β rays, γ rays, X rays, etc., benzoyl peroxide, dicumyl peroxide, 1,3-bis(tert-butylperoxyisopropyl)benzene, etc. Further, when the ethylene polymer is a copolymer of ethylene and crosslinkable vinylsilane, the crosslinking is carried out by condensing a protective copolymer in the presence of water. In the crosslinking step, the foamed sheet is adjusted to have a gel fraction of 20 to 55%.

In addition, when crosslinking is performed by irradiation with ultraviolet rays among the above ionizing radiations, the foamed sheet is pre-contained with a photopolymerization initiator such as benzophenone or benzoyl methyl ether, and then irradiated with ultraviolet rays from a high-pressure mercury lamp, xenon arc, metal halide lamp, etc. Using a light source that generates, the irradiation intensity is 80
It is sufficient to irradiate at ~100 W/cm. Further, among the above-mentioned radiations, in order to crosslink the foam sheet by electron beam irradiation, an appropriate irradiation dose can be selected, but an irradiation dose of 1 to 60 Mrad, particularly 3 to 50 Mrad is preferable.

Among the above-mentioned radiation crosslinking, crosslinking by electron beam irradiation is preferable because it is safe, easy to operate, and can be crosslinked efficiently. Further, crosslinking by condensation reaction of a copolymer of ethylene and crosslinkable vinyl silane is also preferred since the crosslinking density can be easily adjusted by adjusting the content of the crosslinkable vinyl silane. Note that the peroxide crosslinking may be performed in combination with the radiation crosslinking.

Note that if stretching is performed before the above-mentioned crosslinking step, not only will the stretching efficiency be reduced, but it will also be difficult to obtain a material with large heat shrinkage stress. Therefore, in order to obtain a material with a large heat shrinkage stress, the foamed sheet that has undergone the above-mentioned crosslinking process usually has a heat shrinkage rate of -10 to +30% in the flow direction of the foam sheet and a heat shrinkage rate of -15 to +15% in the width direction. It is preferable to have one.

In order to impart heat shrinkability to the foamed sheet that has undergone the above-mentioned crosslinking step, the foamed sheet is stretched. This stretching process is carried out simultaneously with the extrusion in the foaming process, or after the extrusion.
This is carried out by heating if desired, uniaxially or biaxially stretching, preferably uniaxially stretching, to a predetermined stretching ratio, and then rapidly cooling.

In addition, in order to obtain a heat-shrinkable foamed polyethylene sheet that satisfies the above formulas (1) and (II) through the above-mentioned stretching process, the temperature must be at least the melting point of the ethylene polymer constituting the heat-shrinkable foamed polyethylene sheet. It is necessary to stretch the foam sheet at the lowest possible temperature in an instant and in a short period of time, and to quickly cool it immediately after stretching. Preferably, the foam sheet is stretched so that shear force is applied between the front and back surfaces during stretching. It is better to do so.

As is clear from Figure 3, which shows the relationship between the temperature and the elongation at break of a crosslinked foam sheet made of polyethylene, the elongation at break is determined by the melting point (K) of the ethylene polymer constituting the foam sheet. It shows the lowest value near the melting point, and increases rapidly at temperatures above the melting point. Furthermore, the change in elongation at break at temperatures above the melting point varies greatly depending on the gel fraction, which indicates the degree of crosslinking of the foam sheet. In addition, in the case of a non-crosslinked material, fusing occurs at a temperature higher than the K point, making measurement virtually impossible. Therefore, in order to increase the stretching efficiency, it is preferable to stretch at a temperature that is higher than the melting point of the ethylene-based polymer, maintains the molecular orientation state until cooling, and allows rapid cooling. The stretching temperature of the foamed sheet, which has high mechanical strength, heat resistance, etc., is a heating medium temperature that is equal to or higher than the melting point of the ethylene polymer and does not exceed 100°C above the melting point, and the stretched material itself It is preferable to carry out the process at a temperature not exceeding 50° C. above the melting point in order to improve workability and stretching effect. Note that as the heating medium, an appropriate one such as a roll described below can be used.

In addition, the stretching of the foamed sheet is preferably carried out in as short a time as possible in order to improve the molecular orientation.
It is preferred that the stretching be carried out within a time period of 1 second or less, particularly 1 second or less.

Further, the foamed sheet after stretching is rapidly cooled to a temperature lower than the melting point of the ethylene polymer and as low as possible, especially to a temperature of 100°C or lower, in order to maintain the state of molecular orientation due to stretching. is preferable.

The foamed sheet can be stretched at various ratios, but it is preferably stretched at a stretching ratio of 1.5 to 5 times. In particular, in order to increase productivity, the foamed sheet is stretched at the same time as the extrusion of the foamed sheet. It is preferable to carry out crosslinking immediately and then uniaxially stretch the foamed sheet in the machine direction.

If the stretching ratio is less than 1.5 times, the heat shrinkability will not be sufficient, and it is practically difficult to stretch more than 5 times. Shrinkage stress becomes small, making shrink packaging difficult.

When stretched at the above magnification, the heat shrinkage rate of the heat-shrinkable foamed polyethylene sheet is 3% in the flow direction of the foamed sheet.
0 to 80%, -15 to 15% in the width direction of the foam sheet
%.

As for the stretching method, it is preferable to use a roll stretching method equipped with rolls made of a heat conductor that can be brought into direct contact with the foamed sheet and rapidly heated and cooled.

According to this roll stretching method, the above various conditions can be satisfied.

As shown in FIG. 3, the foamed sheet is stretched by the roll stretching method using at least a pair of rolls (11
) (12) is carried out between. That is, this pair of rolls (11) and (12) have a radius r1, the first roll (11) that heats the foam sheet (13), and the first roll (11) that has a radius r2.
a foam sheet (
13) and a second roll (12) that stretches and cools the
By making the rotational speed of the second roll (12) higher than that of the first roll (11),
The foam sheet (13) having a thickness of t is fed to the first roll (11) and has a thickness of t. Foam sheet (1
3) Stretch in the machine direction. In addition, foam sheet (13)
The stretching ratio can be arbitrarily set by adjusting the rotational speed ratio of the first roll (11) and the second roll (12).

The foamed sheet (13) is preferably stretched by the roll stretching method described above so as to satisfy the following relational expression (IV).

0≦L<30 t o (I'/) (in the formula, L is the thickness t of the foam sheet after stretching to the radius r2 of the first roll (11) surface and the second roll (12) In the above equation (IV), if L is out of the above range, not only will rapid stretching not take place within a short time, but it will also reach the cooling zone within a short time. It cannot be moved, and stretching due to shear deviation between the front and back surfaces of the sheet is unlikely to occur. Therefore, it becomes difficult to obtain a heat-shrinkable foamed polyethylene sheet with large heat-shrinkage stress.

In addition, for the same reason as above, it is preferable that the stretching step is performed under conditions that the distance between the rolls (11) and (12) satisfies the following relational expression.

0.5 mm < D < 70 mm According to the roll stretching method described above, the foam sheet (13) having heat insulating and heat retaining properties can be quickly heated and cooled, and moreover, the shear force can be reduced between the front and back surfaces of the foam sheet (13). In the foamed sheet (13), not only the molecular orientation but also the shape of the cells and the arrangement of the cells are oriented, so it is possible to obtain a heat-shrinkable foamed polyethylene sheet with a large heat-shrinkage stress. The resulting heat-shrinkable foamed polyethylene sheet also does not crease during heat-shrinking.

In addition, in the above-mentioned roll stretching method, in order to increase the stretching efficiency, the temperature of the first roll (11) is set to a temperature equal to or higher than the melting point of the polyethylene-based poly that constitutes the foamed sheet (13), preferably a polyethylene polyethylene. The temperature of the second roll (12) is lower than the melting point of the ethylene polymer constituting the foamed sheet (13), particularly at a temperature of 100°C or lower. It is preferable to

In addition, in the above roll stretching method, the foam sheet (13)
Heating and cooling may be performed using a plurality of heating rolls and cooling rolls, or the foamed sheet (13) may be preheated and sent to the first roll (11). Note that the first roll (1
Prior to step 3), the foam sheet (13) is passed through a high-temperature atmosphere and rapidly heated, and the first roll (11) is set at a temperature of 1 m degrees below the melting point of the ethylene polymer. The foamed sheet (13) may be stretched while slightly cooling only the surface;
), and as described above,
It is preferable to set the temperature of the roll (11) at a temperature higher than the melting point of the ethylene polymer and relatively low at 1 FiL degree.

The heat-shrinkable foamed polyethylene sheet obtained as described in L can be formed to have an appropriate thickness depending on the application, but as described above, a thickness of 0.3 to 15 mm is preferable.

Note that the heat-shrinkable foamed polyethylene sheet described above may be laminated with the various films and sheets described above. These films and sheets may be laminated by co-extrusion with the resin that is the material of the film or sheet in the foam sheeting process and laminated by heat fusion, such as ethylene-vinyl acetate copolymer, polyurethane, etc. , or may be laminated using a suitable adhesive. Furthermore, if the ethylene polymer, which is crosslinked by radiation irradiation, or a resin having an unsaturated double bond is used as the adhesive, these adhesives can be crosslinked along with the ethylene polymer. Greater sheet integrity. Examples of the resin having unsaturated double bonds include polybutadiene, epoxy acrylate, urethane acrylate, polyester acrylate, and methacrylates thereof.

The thus obtained heat-shrinkable foamed polyethylene sheet is wrapped around the packaged item on one to four sides by heat sealing, etc., and then wrapped in a shrink tunnel for 100 to 250 minutes.
By heat-shrinking at a temperature of about 0.degree. C., various items to be packaged can be shrink-wrapped. Incidentally, in order to perform the shrink-wrapping operation smoothly, an appropriate number of air vent holes, cuts, etc. may be formed in the heat-shrinkable foamed polyethylene sheet.

The heat-shrinkable foamed polyethylene sheet of the present invention has high heat-insulating properties, shock-absorbing properties, heat resistance, mechanical strength, etc., and has high heat-shrinkage stress as described above, so it can be used for various packaging items, such as glass bottles. For cushioning and protection of glass products, ceramics and other fragile items, mirror finished products, electronic parts, electrical products, precision mechanical parts, etc., as well as temperature control equipment, automobile coolers, duct covers for these, and water pipes. It is suitable for use in tank covers, etc. to prevent dew condensation, and for insulation and heat retention of various tanks.

<Example> The present invention will be described in detail below based on examples.

Example 1 As polyethylene, melt index (hereinafter, Ml
0.27, density 0.919, and melting point 106°C, and using butane as a foaming agent, a foamed sheet with a foaming ratio of 47 times and a thickness of 3.5mm was produced by extrusion foaming, and this foamed sheet An applied voltage of 1 in a nitrogen stream to
The foamed sheet was crosslinked by irradiation with an electron beam of 13 Mrad at 70 KV.

Next, the crosslinked foam sheet was preheated in an oven at 115° C. and stretched by the roll stretching method shown in FIG. 3 above. That is, as the first roll, the radius r1-
50 mm x roll temperature 112 °C, second roll with radius r 2-50 mm % roll temperature 40 °C, L = 24.1 mm, foam sheet feeding speed 2.0 m/min, stretching ratio in the machine direction The foamed sheet was stretched under the conditions of 1.7 times the stretching time and 0.54 seconds.

The obtained heat-shrinkable foamed polyethylene sheet has a foaming ratio of 46 times, a thickness of 2.2 mm, and a gel fraction of 36%, and has heat shrinkage characteristics of 40% in the machine direction and 2 in the width direction. %, A/B-8,4, A x foaming ratio-15000.
It had a value of B x expansion ratio -1750.

Then, various articles were shrink-wrapped using the above-mentioned heat-shrinkable foamed polyethylene sheet. In other words, the articles were placed between the folded sheets, heat-sealed on three sides, and multiple air vent holes with a diameter of 5 m+s were made. established, 13
When the package was passed through a shrink tunnel at 5°C for 12 seconds to perform shrink packaging, the package was able to be shrink-wrapped smoothly without getting caught on the transport rolls in the shrink tunnel, and the package was tightly adhered to the entire package. I was able to do this. In addition, the resulting package has a good appearance with almost no traces of creases, no broken air bubbles, and no surface roughening, and maintains a tight and tightly packaged state for a long period of time. Ta.

The foam sheet before stretching has a heat shrinkage rate of 8 in the machine direction.
%, and the heat shrinkage rate in the width direction was 5%.

Comparative Example 1 A voltage of 170K was applied to the foam sheet of Example 1 in a nitrogen stream.
The foamed sheet was crosslinked by irradiation with an electron beam at V and 4 Mrad. Next, stretching was performed in the same manner as in Example 1.

The obtained heat-shrinkable foamed polyethylene sheet had an expansion ratio of 44 times, a thickness of 2.0 mm, and a gel fraction of 7%, and its heat-shrink characteristics were as follows: heat shrinkage in the flow direction was 51%, and heat shrinkage in the width direction was 51%. ratio 6%, A/B-75, A x foaming ratio -16500,
It had a value of B x expansion ratio -220.

When the above heat-shrinkable foamed polyethylene sheet was passed through a shrink tunnel and shrink-wrapped in the same manner as in Example 1, the heat-shrinkable foamed polyethylene sheet adhered to the transport roller and the packaged items in the shrink tunnel. , it was not possible to obtain a good package. In addition, the range of heat shrinkage conditions was very narrow, and good packaging could only be obtained under limited conditions. Furthermore, the obtained package also showed a deterioration in appearance due to roughening of the cells in the foam.

The heat shrinkage rate of the foamed sheet before stretching was 14% in the flow direction and 9% in the width direction.

Example 2 The polyethylene had an MI of 2.2, a density of 0.922, and a melting point of -107°C (Mitsubishi Yuka Industries Co., Ltd. splitting product name, AH-40), and a blowing agent of liquefied natural gas (LP) was used.
Using G), a foamed sheet having a foaming ratio of 23 times and a thickness of 2.7 mm was produced in the same manner as in Example 1 above. A voltage of 170 KV and 17 Mra was applied to this foam sheet in a nitrogen stream.
The foamed sheet was crosslinked by irradiation with electron beam d.

Next, stretching was performed in the same manner as in Example 1, except that the stretching ratio was 1.8 times.

The obtained heat-shrinkable foamed polyethylene sheet has an expansion ratio of 22 times, a thickness of 1.5 mm, and a gel fraction of 40%.The heat shrinkage characteristics are as follows: heat shrinkage rate in the machine direction is 44%, and heat shrinkage rate in the width direction is 44%. Shrinkage rate 2%, A/B-14.8, AX foaming ratio -86
It had a value of 00, B x expansion ratio -580.

When shrink-wrapping was carried out in the same manner as in Example 1, no problems occurred during heat shrinkage, and tight shrink-wrapping was achieved without any local loosening. Moreover, the obtained package had a good appearance, with no trace of creases or roughening of air bubbles.

The heat shrinkage properties of the foamed sheet before stretching were 9% in the machine direction and 4% in the width direction.
and B both showed values below the detection limit.

Comparative Example 2 A crosslinked foamed polyethylene sheet was produced in the same manner as in Example 2, and then stretched under the following conditions.

That is, L = 900 mm, the foam sheet is preheated before the first roll, and the first roll and the first
The area between the first roll and the second roll was stored in an oven at 120°C. Also, the temperature of the first roll is also 12
The temperature was adjusted to 0°C, and the second roll and subsequent rolls were placed outside the oven, and the second roll was cooled to 4°C by water cooling.
The temperature was adjusted to 0°C, and the feeding speed of the foam sheet was 1.64 m/min.
The foamed sheet was stretched at a stretching ratio of 1.8 times and a stretching time of 23.5 seconds.

The obtained heat-shrinkable foamed polyethylene sheet has a foaming ratio of 21 times, a thickness of 1.4 mm, and a gel fraction of 40%, and its heat-shrinkage properties are as follows: heat shrinkage in the machine direction is 41%, and heat shrinkage in the width direction is 396. , A/B-1,4, A x expansion ratio -1155,
It had a value of B x expansion ratio -825.

Then, using the heat-shrinkable foamed polyethylene sheet,
Various items to be packaged were shrink-wrapped in the same manner as in Example 1. However, the shrinkage stress at the initial stage of heat shrinkage was weak, and tight packaging could not be achieved.

In particular, when the packaged items are complex in shape or angular, tight shrink packaging is difficult.

Further, the heat-shrinkable foamed polyethylene sheet of the resulting package had strong creases, which was unfavorable in terms of appearance.

Example 3 High-density polyethylene with an MIo of 6, a density of 0.96, and a melting point of 130°C was used as the polyethylene, and a butane/fluorocarbon mixed foaming agent was used as the coloring agent.
Extrusion foaming was carried out in the same manner as above, the foaming ratio was 48 times, and the thickness was 2.0.
A foam sheet of No. 1 was produced. This foamed sheet was irradiated with an electron beam of 22 Mrad at an applied voltage of 170 KV in a nitrogen stream to crosslink the foamed sheet.

Next, stretching was carried out in the same manner as in Example 1 under the following conditions. That is, the temperature of the oven for preheating the foam sheet and the temperature of the first roll were 135°C, the temperature of the second roll was 40°C, the length was 43 mm, the feeding speed of the foam sheet was 2.0 m/min, Stretching ratio: 2.0 times,
The foamed sheet was stretched for a stretching time of 0.87 seconds.

The obtained heat-shrinkable foamed polyethylene sheet has a foaming ratio of 4.
7 times, thickness 0.9mm, gel fraction 34%, heat shrinkage properties: 46% heat shrinkage in machine direction, 3% heat shrinkage in width direction, A/B-10,9, A× Foaming ratio = 13060,
It had a value of B×expansion ratio −1200.

Example 1 using the above heat-shrinkable foamed polyethylene sheet
When shrink-wrapping was performed in the same manner as above, there were no creases or the like, and various items to be packaged could be shrink-wrapped extremely well and tightly. Furthermore, the packaged items remained tightly packaged for a long period of time.

The foamed sheet before stretching had a heat shrinkage rate of 6% in the machine direction and a heat shrinkage rate of 6% in the width direction.

Example 4 As the ethylene polymer, water-crosslinkable polyethylene (Mitsubishi Yuka Industries Co., Ltd. cleavage product name, Linklon A composition consisting of this ethylene polymer and dibutyltin dilaurate as a crosslinking catalyst,
A foamed sheet was produced by extrusion foaming using butane as a foaming agent.

This foamed sheet was placed in an environment of a temperature of 55° C. and a humidity of 60% RH for 3 days, and was crosslinked by moisture. This foaming sheet has a foaming ratio of 36 times, a thickness of 2.8 mm, and a gel fraction of 37%.
It had a

Next, the foamed sheet was stretched, but at that time, the temperature of the preheating oven and the first roll was set to 130°C.
The foamed sheet was stretched in the same manner as in Example 1, except that the stretching was carried out at 0.8 °C and for a stretching time of 0.8 seconds.

The obtained heat-shrinkable foamed polyethylene sheet has an expansion ratio of 3.
5 times, thickness 1.6mm, gel efficiency 32%, heat shrinkage properties: 38% heat shrinkage in machine direction, 1 heat shrinkage in width direction.
%, A/B-7,3, A x foaming ratio -10600, B x
It had a foaming ratio of -1450.

Using this heat-shrinkable foamed polyethylene sheet, Example 1
Shrink packaging was carried out in the same manner as in Example 1, and as in Example 1, a very excellent package was obtained. Moreover, the packaged product maintained a tightly packed state for a long period of time.

Comparative Example 3 The foamed sheet of Example 4 was used as the crosslinked foamed sheet, and the foamed sheet was stretched in the same manner as in Comparative Example 2.

The obtained heat-shrinkable foamed polyethylene sheet has an expansion ratio of 3.
4 times thicker, 1.9 mm thick, and has a gel fraction of 37%, and its heat shrinkage properties are 35% in the machine direction and - in the width direction.
2%, A/B-1,3, A x foaming ratio -1770, B x
It had a foaming ratio of -1360.

When shrink-wrapping was performed in the same manner as in Example 1 using two pairs of heat-shrinkable foamed polyethylene sheets, as in Comparative Example 2, the shrink-wrapping could not be done tightly and the heat-shrinkable foamed polyethylene sheets were folded. Some wrinkles appeared.

<Effects of the Invention> As described in -1- below, according to the heat-shrinkable foamed polyethylene sheet of the first invention, the ratio of the shrinkage stress at the beginning of heat shrinkage to the shrinkage stress after heat shrinkage is a specific value. Since a is done,
To quickly and strongly heat-shrink a heat-shrinkable foamed polyethylene sheet without causing trouble during shrink packaging. In addition, as a heat-shrinkable foamed polyethylene sheet with a high expansion ratio, it is possible to tightly shrink-wrap the packaged item immediately after heat shrinkage, and even after shrink-wrapping, the heat-shrinkable foamed polyethylene sheet does not loosen. It is possible to maintain the tightly packed state without causing any problems. In addition, heat-shrinkable foamed polyethylene sheets are cross-linked and have high heat resistance and mechanical strength, and have a wide tolerance for heat-shrinking conditions, making it possible to smoothly shrink-wrap items during the heat-shrinking process. Can be done.

Further, according to the second invention, when producing a heat-shrinkable foamed polyethylene sheet, stretching is carried out at a temperature lower than the melting point of the ethylene-based polymer constituting the heat-shrinkable foamed sheet, so that it has a crosslinked structure, Even foamed sheets with high mechanical strength and heat resistance can be easily stretched. In addition, after stretching, it is cooled to a temperature below the melting point of the ethylene polymer, so that the stretched state can be maintained and
Due to the stretching process, the mechanical strength is even greater than that of the foamed sheet before stretching, and the packaged item can be tightly shrink-wrapped immediately after heat shrinkage, and even after shrink-wrapping, the heat-shrinkable foamed polyethylene sheet does not loosen. It is possible to inexpensively produce a heat-shrinkable foamed polyethylene sheet that can maintain a tightly packaged state without causing damage.

[Brief explanation of the drawing]

Figure 1 is a diagram showing the method for measuring heat shrinkage stress, Figure 2 is a diagram showing the measurement results of heat shrinkage stress, Figure 3 is a schematic diagram showing the main parts of the roll stretching method, and Figure 4 is a diagram showing the heat shrinkage stress. FIG. 2 is a diagram showing the relationship between temperature and elongation at break of a foamed polyethylene sheet. (11)...First roll, (Step 2)...Second roll, (13)...Foamed sheet. Patent Applicant Sekisui Plastics Co., Ltd. Figure 1 Figure 2 Time (minutes) Figure 3 Procedure Amendment (spontaneous) November 13, 1985 1, Case Indication 1988 Patent Application No. No. 205487 2, Title of the invention: Heat-shrinkable foamed polyethylene sheet and method for manufacturing the same 4, Agent Kita 1. 5. Date of amendment order (voluntary) Corrected as shown in the attached sheet. (Corrected as B x foaming magnification > 400 (ri/a1) """■" in Book 2, page 22, lines 16 and 17. 2. Scope of Claim 1, Foaming magnification 10 to 80 times , a crosslinked heat-shrinkable foamed polyethylene sheet having a gel fraction of 20 to 55% and a heat shrinkage rate of 30 to 80% in the flow direction satisfies the following relational expression (I). A heat-shrinkable foamed polyethylene sheet. 3<A/B<50 0...<I) (wherein A is the maximum shrinkage that appears at the beginning of heating when the heat-shrinkable foamed polyethylene sheet is not heated at 135°C. 2. Heat-shrinkable foamed polyethylene sheet The heat-shrinkable foamed polyethylene sheet according to claim 1, wherein: satisfies the following relational expression (II). A x foaming ratio > 4000-〇u〉 Lee Bx foaming ratio > 4003 """ (II) 3,
The heat-shrinkable foamed polyethylene sheet has a thickness of 0.3~
b. A heat-shrinkable foamed polyethylene sheet according to claim 1. 1. The heat-shrinkable foamed polyethylene sheet is heated to 135°C.
The heat-shrinkable foamed polyethylene sheet according to claim 1, which has a heat shrinkage rate of -15 to +15% in the width direction. 5. A foamed sheet forming step in which the ethylene polymer is melt-extruded to form a foamed sheet, a crosslinking step in which the foamed sheet obtained in this foamed sheet forming step is crosslinked, and after this crosslinking step, the heating temperature is set to the above ethylene polymer. The following relational formula (It ) A method for producing a heat-shrinkable foamed polyethylene sheet, the method comprising obtaining a heat-shrinkable foamed polyethylene sheet that satisfies the following. 3<A/B<50 -------<m) (where A is the maximum shrinkage stress (g/aj
), and B indicates the shrinkage stress (t/aJ) 5 minutes after the start of heating when heated at 135°C) 6. The ethylene polymer has a melt index of 0,
67, a method for producing a heat-shrinkable foamed polyethylene sheet according to claim 5, wherein the ethylene polymer has a density of 0.900 to 0.05.
, 969. The method for producing a heat-shrinkable foamed polyethylene sheet according to claim 5 above. 8. A method for producing a heat-shrinkable foamed polyethylene sheet according to claim 5, wherein the foamed sheet is crosslinked by electron beam irradiation. 9. The method for producing a heat-shrinkable foamed polyethylene sheet according to claim 5, wherein a copolymer of ethylene and crosslinkable vinyl silane is used as the ethylene polymer, and the copolymer is crosslinked in the presence of moisture. 10. The temperature of the foamed sheet is above the melting point of the ethylene polymer, and the temperature of the foamed sheet is 55% lower than the melting point.
A method for producing a heat-shrinkable foamed polyethylene sheet according to claim 5, which is carried out in a temperature range not exceeding 0°C. 11. The method for producing a heat-shrinkable foamed polyethylene sheet according to claim 5, wherein the foamed sheet is uniaxially stretched 1.5 to 5 times in the machine direction. 12. The method for producing a heat-shrinkable foamed polyethylene sheet according to claim 5, wherein the foamed sheet is stretched within a stretching time of 5 seconds or less and immediately cooled. 13. As a foamed sheet before the stretching process, the heat shrinkage rate in the machine direction is -10 to +30%, and the heat shrinkage rate in the width direction is -15 to +30%.
6. The method for producing a heat-shrinkable foamed polyethylene sheet according to claim 5, using a foamed sheet having a carbon content of +15%. 14. When the foam sheet is continuously stretched between a pair of rolls arranged in the flow direction of the foam sheet and having different rotational speeds, the pair of rolls is a first roll that heats the foam sheet, and a first roll that heats the foam sheet. It consists of a second roll that cools the foam sheet that has passed through the first roll, and the thickness t of the foam sheet after being stretched to the radius of the first roll surface and the second roll. The method for manufacturing a heat-shrinkable foamed polyethylene sheet according to claim 5, wherein the distance between tangents to the surface of an imaginary cylinder obtained by adding . 0≦L<30to, -...-(IV)15, 1st
15. The method for producing a heat-shrinkable foamed polyethylene sheet according to claim 14, wherein the roll has a temperature equal to or higher than the melting point of the ethylene polymer. 16. Claim 1 above, wherein the second roll has a temperature below the melting point of the ethylene polymer.
4. The method for producing a heat-shrinkable foamed polyethylene sheet according to item 4. 17. The method for producing a heat-shrinkable polyethylene sheet according to claim 14, wherein the second roll has a temperature of 100° C. or less.

Claims (1)

[Claims] 1. A cross-linked heat-shrinkable foamed polyethylene sheet having an expansion ratio of 10 to 80 times, a gel fraction of 20 to 55%, and a heat shrinkage rate of 30 to 80% in the machine direction satisfies the following relational expression: (
A heat-shrinkable foamed polyethylene sheet that satisfies (I). 3<A/B<50...(I) (where A is a heat-shrinkable foamed polyethylene sheet, 1
The maximum shrinkage stress that appears at the beginning of heating when heated at 35℃ (
g/cm^2), and B indicates the shrinkage stress (g/cm^2) after 5 minutes have passed from the start of heating when heated at 135°C) 2. The heat-shrinkable foamed polyethylene sheet is Claim 1 above satisfies the following relational expression (II):
A heat-shrinkable foamed polyethylene sheet as described in . A x Expansion ratio > 4000 B x Expansion ratio > 400... (II) 3. The heat-shrinkable polyethylene foam sheet has a thickness of 0.3
Claim 1 above, which has a diameter of 15 mm
A heat-shrinkable foamed polyethylene sheet as described in . 4. The heat-shrinkable foamed polyethylene sheet according to claim 1, wherein the heat-shrinkable foamed polyethylene sheet has a heat shrinkage rate of -15 to +15% in the width direction at 135°C. 5. A foam sheet forming step in which the ethylene polymer is melt-extruded to form a foam sheet, a crosslinking step in which the foam sheet obtained in this foam sheet forming step is crosslinked, and after this crosslinking step, the heating temperature is set to the above-mentioned ethylene polymer. The following relational formula (III ) A method for producing a heat-shrinkable foamed polyethylene sheet, the method comprising obtaining a heat-shrinkable foamed polyethylene sheet that satisfies the following. 3<A/B<50...(III) (In the formula, A is a heat-shrinkable foamed polyethylene sheet.
Maximum shrinkage stress (g) that appears at the beginning of heating when heated at 5℃
/cm^2), and B indicates the shrinkage stress (g/cm^2) 5 minutes after the start of heating when heated at 135°C) 6. The ethylene polymer has a melt index of 0.0.
5 to 4.0.
A method for producing a heat-shrinkable foamed polyethylene sheet as described in 2. 7. Ethylene polymer has a density of 0.900 to 0.96
9. The method for producing a heat-shrinkable foamed polyethylene sheet according to claim 5, wherein the heat-shrinkable foamed polyethylene sheet has a 8. A method for producing a heat-shrinkable foamed polyethylene sheet according to claim 5, wherein the foamed sheet is crosslinked by electron beam irradiation. 9. The method for producing a heat-shrinkable foamed polyethylene sheet according to claim 5, wherein a copolymer of ethylene and crosslinkable vinyl silane is used as the ethylene polymer and crosslinked in the presence of moisture. 10. The foam sheet is stretched at a temperature of the foam sheet at a temperature higher than the melting point of the ethylene polymer and 50°C higher than the melting point.
The method for producing a heat-shrinkable foamed polyethylene sheet according to claim 5, which is carried out at a temperature not exceeding . 11. The method for producing a heat-shrinkable foamed polyethylene sheet according to claim 5, wherein the foamed sheet is uniaxially stretched 1.5 to 5 times in the machine direction. 12. Stretching the foam sheet within a stretching time of 5 seconds or less,
A method for producing a heat-shrinkable foamed polyethylene sheet according to claim 5, wherein the sheet is immediately cooled. 13. As a foamed sheet before the stretching process, the heat shrinkage rate in the machine direction is -10 to +30%, and the heat shrinkage rate in the width direction is -15 to +1
The method for producing a heat-shrinkable foamed polyethylene sheet according to claim 5, using a foamed sheet having a carbon content of 5%. 14. When the foam sheet is continuously stretched between a pair of rolls arranged in the flow direction of the foam sheet and having different rotational speeds, the pair of rolls is the first to heat the foam sheet.
and a second roll that cools the foam sheet that has passed through the first roll, and the thickness t_ of the foam sheet after being stretched to the radius of the first roll surface and the second roll.
The method for producing a heat-shrinkable polyethylene foam sheet according to claim 5, wherein the distance L between the tangents to the surface of the imaginary cylinder, which is an addition of 0, satisfies the following relational expression (IV). 0≦L<30t_0...(IV) 15. Production of a heat-shrinkable foamed polyethylene sheet according to claim 14, wherein the first roll has a temperature equal to or higher than the melting point of the ethylene polymer. Method. 16. The method for producing a heat-shrinkable foamed polyethylene sheet according to claim 14, wherein the second roll has a temperature lower than the melting point of the ethylene polymer. 17. The method for producing a heat-shrinkable polyethylene sheet according to claim 14, wherein the second roll has a temperature of 100° C. or less.