JPS60232928A - Heat-contracting foamed film and manufacture thereof - Google Patents

Abstract

PURPOSE:To provide a shrinking label with its own properties and a buffer effect by blending organic decomposition-type foaming agent into three component copolymer of crystalline ethylene-propyrene-butane-1, extruding a stock foamed sheet obtained through the extrusion of a molten mixture and giving the sheet a specific thickness, a apparent specific gravity and a coefficient of contraction. CONSTITUTION:Organic decomposition-type foaming agent is blended into a three component copolymer of crystalline ethylene-propyrene-butane-1 at a crystal melting point of 115-145 deg.C. This mixture is molten and extruded into stock foamed sheet and is further elongated into a sheet of 0.05-0.4mm. thickness with an apparent specific gravity of 0.2-0.6 and a coefficient of contraction of more than 10% in one direction and four times that in another direction at 120 deg.C. Thus foamed film which is best suitable as a shrinking label and highly shock- proof is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a heat-absorbing foamed film and a method for producing the same. More specifically, the present invention relates to the foamed crystalline ethylene-propylene-butene-1 ternary co-conducting unparallel film having different heat shrinkage rates in the longitudinal and lateral directions, and a method for producing the same.

゛ Wrapping a heat-shrinkable film with a pattern or trademark printed on the periphery of the container as a label and protective film for glass bottles, metal or plastic rings, and other containers is being widely considered. The film used for this is a “shrink label”
A hexagonal film is used for unbalanced heat absorption, which has different heat shrinkage rates in the vertical and horizontal directions. When this shrink label is used for items that are easily damaged by a slight impact, such as glass bottles for carbonated drinks, etc., a heat-shrinkable foam film is used to provide a cushioning effect as a way to protect the glass bottles from damage. has been proposed, and heat-shrinkable expanded polystyrene film is widely used. However, glass bottles using this heat-shrinkable expanded polystyrene film as a shrink layer have poor impact resistance, so bottles filled with internal pressure such as charcoal + 11 beverages cannot be transported on roads. If this happens, the broken bottles will be scattered widely, which is dangerous. Also, the polystyrene of the label will emit black smoke when the glass bottle with the bell wrapped around it is remelted for collection and reuse. There is a problem in that it is undesirable from a sanitary standpoint. Therefore, it is necessary to peel off the labels one by one before melting the glass bottle, which has disadvantages such as increased costs.

By the way, attempts have been made to apply polypropylene filaments such as ethylene-propylene copolymerized films containing polypropylene and globylene with a large tg content to these shrinkable labels, and Japanese Patent Application Laid-Open No. 103951/1983 describes ethylene/propylene filaments.
An unbalanced chassis heat-shrinkable film using Propino 7 co-page combination, JP-A-57-49554 proposes a heat-shrinkable film with heat-sealing properties consisting of 2 to 3 layers, but it has a buffering effect. Not much is known about polypropylene foam shrinkable films.

Polypropylene has high crystallinity and the bath melt viscosity during extrusion is difficult to vI4t, so it is difficult to obtain uniform and fine foaming compared to polystyrene. Especially in the case of thin foam sheets, foaming is uneven, so when this sheet is stretched, Furthermore, problems such as non-uniform foaming or stretching breakage occur, making it impossible to obtain a good product. This is thought to be the reason why polypropylene foam shrink film has not yet been put into practical use.

In view of the above circumstances, the present inventor has developed a polypropylene-based heat-shrinkable film that takes advantage of its superior impact resistance compared to polystyrene and does not generate black smoke or soot when burned, and has an excellent cushioning effect and shrinkage. Various tests were conducted to obtain a heat-shrinkable foamed film that could be used as a label. As a result, a raw rebound foam sheet obtained by blending a crystalline ethylene-propylene-butene-1 terpolymer with a specific melting point with a specific weight ratio of an organic decomposable blowing agent and melt-extruding it under specific conditions was developed. The inventors have discovered that a foamed film having specific properties obtained by stretching in at least one direction within range d has extremely excellent suitability as a shrink label, and has thus arrived at the present invention.

As is clear from the above description, the present invention provides a polypropylene heat-shrinkable foam film that has properties suitable as a shrink label and has a buffering effect, and a method for producing the same.
- The purpose is to provide.

The present invention (second invention) has the following configurations (1) to 4).

(1) Crystalline ethylene with a crystal melting point of 115-145°C
Obtained by blending an organic decomposable blowing agent into a propylene-pute/-1 terpolymer and stretching in at least one direction a raw rebound foam sheet obtained by melt-extruding the blend,
Its thickness is 0.05~0.41111. The apparent specific gravity is 0.2
~0.6° Heat-shrinkable foam film 0 characterized by a shrinkage rate in one direction at 120°C of 10% or more and 4 times or more of the shrinkage rate in the other direction (2) Crystal melting point 115~ The ethylene-propylene-butene-1 terpolymer at 145°C was converted into propylene tt7ox
t% or more of ethylene-propylene-butene-1 ternary co-1
The heat-shrinkable foamed film described in (1) above, characterized in that it is formed using coalescence.

(3) Crystalline ethylene with a crystal melting point of 115-145°C
Propylene-butene-1 terpolymer K.

An organic decomposition plate @ foaming agent is blended with 0.1 to 1O weight tS, melt-extruded near the decomposition temperature of the foaming agent, and both sides of the melt-foamed sheet obtained by the extrusion are simultaneously rapidly cooled to 60°C or less to reduce the appearance. A foamed sheet with a ratio No. of 3 to 0.7 and a thickness of 0.2 or higher is prepared, and the sheet is unidirectionally heated at a temperature 10 to 60°C lower than the crystal melting point of the ethylene-tetrapyrene-butene-1 ternary co-combination. A method for producing a heat-shrinkable foamed film, which comprises pressing in at least one direction 4 to 30 times so that the stretching ratio in the other direction is 4 to 30 times the stretching ratio in the other direction.

(4) An ethylene-propylene-butene-1 terpolymer with a crystalline melting point of 115 to 145°C has a tetrapyrene content of 70
The method for producing a heat-shrinkable foam film as described in (3) above, characterized in that an ethylene-propylene-butene-1 terpolymer having a weight of - or more is used.

The configuration and effects of the present invention will be explained in detail below.

The raw material resin used in the present invention has a crystal melting point of 115~
A crystalline ethylene-globylene-butene-1 terpolymer at 145° C. is used. A suitable crystalline ethylene-propylene-butene-1 terpolymer is an ethylene-propylene-butene-1 terpolymer having a propylene component of 70% by weight or more and a crystalline melting point of 115 to 145. ℃
belongs to. An ethylene-propylene-butene-1 ternary copolymer with a crystal melting point of 120-i40°C is 41Km! Delicious.

In the present invention, the crystal melting point (hereinafter abbreviated as Tm) means:
Samples were heated at 10°C in a nitrogen atmosphere using a scanning differential calorimeter.
It refers to the peak temperature of the endothermic curve associated with the melting of the crystal obtained by increasing the temperature at a rate of /min. If the Tm of the copolymer used in the present invention exceeds 145°C, it will be difficult to obtain fine and uniform foaming.
In addition, the shrinkage property is poor (1+), and if Tm is less than 115°C, the film becomes extremely flexible and the workability in winding the film, 9-bag processing, etc. is significantly reduced, which is not preferable.

Comprehensively considering the cost of the raw material resin, the productivity of the film according to the present invention, and the label shrinkability as the film's use, if the copolymerization ratio of ethylene is 01 to 6, and the copolymerization ratio of butene-1 is is 1 to 15% and Tm is 120
Especially the ethylene-tetrapyrene-butene-1 terpolymer at ~140°C! It's 1t. In addition, melt 7 of the copolymer
a-v-)(MIFR)ri is desirably selected in the range of 0.1 to 15 depending on the decomposition temperature of the blowing agent.

Incidentally, crystalline glupylene homopolymer and ethylene/propylene block copolymer can only be obtained as non-uniform foamed products using a blowing agent. The film also becomes non-uniform and its heat shrinkability is extremely poor, making it unusable.

The organic decomposition blowing agent used in the present invention is solid at room temperature, has a decomposition temperature higher than the Tm of the skeleton ethylene-globylene-butene-1 terpolymer, and cannot be heated above the decomposition temperature. Compounds that decompose while producing gases such as nitrogen, carbon dioxide, and agas, such as azodicarbonamide, metal salts of azodicarbonate, hydrazodicarbonamide, M, M'- Examples include dinitrosopentamethylenetetramine and p-toluenesulfonyl hydrazide.

The amount of the blowing agent added to the ethylene-globylene-butene-1 terpolymer is in the range of 0.1 to 1.0 weight - 〇,
0.2 to 0.7% Km by weight is preferable.

Furthermore, the ethylene-globylene-butene-1 terpolymer and organic decomposition W! Antioxidants, lubricants, antistatic agents, small amounts of other polymers, etc. can also be mixed into the foaming agent. Especially 0.05~1. It is desirable to use a combination of a B-combining antioxidant and a lubricant such as a metal soap or fatty acid amide.

The ethylene-propylene-butene-1 terpolymer of the present invention and the organic decomposer blowing agent may be blended, that is, mixed, by a known method such as mixing with a conventional high-speed mixer, mixing with an extruder, or Banbury mixing. Mix at a temperature below the decomposition temperature.

In addition, a master patch made by mixing 5 to 50% of the VH foaming agent in the armpit ethylene-propylene-butene-1 ternary copolymer is mixed into a predetermined amount of the ethylene-propylene-butene-1 ternary co-constitution copolymer. However, it may be set to a predetermined ratio. In addition, the foaming agent 100mK can be used as a market auxiliary agent or a dispersant.
On the other hand, a mixture of 10 to 200 parts of metal soap, fatty acid, fatty acid amide, etc. may be mixed with the ethylene-propylene-butene-1 ternary compound.

Next, a mixture consisting of the KM ethylene-propylene-butene-1 ternary copolymer and the foaming agent is supplied to an extruder, and melt-extruded near the decomposition temperature of the cough foaming agent, and both sides of the extruded melt-foamed sheet are Rapid cooling to below 60℃, apparent specific gravity 0.3~
0.7, thickness CJ, create a foam sheet of 2 m or more.

The melt extrusion temperature in this case is adjusted so that the resulting foamed sheet with a thickness of 0.2 square centimeters or more has an apparent specific gravity of 0.3 to 0.7. Specifically, the temperature is preferably within ±15°C of the decomposition temperature of the blowing agent. For example, in the case of azodicarbonamide (decomposition temperature of 205°C), the resin temperature at the die exit is 190°C.
~220°C is desirable. The molten foam sheet that comes out of the die is placed on a cooling roll or immersed in water, and both sides of the sheet are heated to 60°C.
Cool rapidly below. If only one side is rapidly cooled, the surface of the other side to be slowly cooled will become larger and the surface will become extremely rough, making it impossible to obtain a smooth sheet and resulting in extremely uneven foaming of the product film.

Furthermore, if the sheet is cooled at a temperature exceeding 60° C., the sheet tends to stick, and the stretchability decreases, making it difficult to obtain a uniform product.

The most desirable method is to rapidly cool the sheet by sandwiching it between two cooling rolls having a surface temperature of 20 to 50°C.10 The resulting foamed sheet has a thickness of 0.2u or more and an apparent ratio of ff10.2 to 0. .7 is desirable.

If the thickness is less than 0.2 m, pinholes are likely to occur during stretching and foaming will be uneven. Also, the apparent specific gravity is 0.
If it does not reach 2, stretch breakage is likely to occur, and if it exceeds 0.7, a foamed film with poor stretching effect will be obtained.

Next, the obtained foam sheet is 10 to 60% lower than the Tm of the ethylene-propylene-butene-1 terpolymer as the raw material resin.
℃ At a low temperature, in the case of -axis stretching, 4 degrees in the vertical or horizontal direction.
~10 times, in the case of biaxial stretching, simultaneous or sequential stretching so that the stretching ratio in one direction is 4 times or more than the stretching ratio in the other direction, and the area stretching ratio is 6 to 30 times. The film is then heat-treated as necessary and one or both sides of the film are subjected to corona discharge treatment. The stretching conditions for these foam sheets were within the range of the above conditions at t4, and the resulting product film had a thickness of 0.05 to Q, 41'a. The shrinkage rate in one direction at 120° C. is 10% or more and is 4 times or more the shrinkage rate in the other direction. In the case of a -axially stretched film, the desirable stretching conditions are 20 to 50°C below the Tm of the kyoelectric composite.
Stretch 4-8 times at low temperature. In the case of two-wheel stretching, both 1
After stretching 1.1 to 2.5 times on or between two or more heated rolls kept at a temperature 20 to 60°C lower than the combined Tm, horizontal/vertical stretching is performed at a temperature higher than the longitudinal stretching temperature. This is a continuous stretching method in which the material is stretched in the transverse direction by 6 to 12 times in a tenter so that the ratio is 4 or more. The stretched film is subsequently cooled by a heat-treated air cooling method, a cooling roll, a cooling belt, or the like, if necessary.

Among the heat-shrinkable foamed films obtained in this way, those suitable for shrinkable labels are further limited, and have a thickness of 0.05 to 0.
41Em, apparent specific gravity 0.2 to 0.6°, shrinkage rate in one direction at 120°C must be 1O- or more, and at least 4 times the shrinkage rate in the other direction. Thickness is 0.05
If it is less than ta, the needle impactability as a label will be poor, and the foamed cells will be non-uniform and the appearance will be poor. If it exceeds 0.4N, the shrinkage temperature will be high, and when used for a bottle having a curved part, the shape of the curved part of the label after shrinkage will be uneven, resulting in a poor appearance.

The apparent specific gravity does not reach 0.2, but the butterfly foam cells are coarse.
It's uneven, and if you print on this item (labels always need to be printed), the print will be very unclear and it won't look good! damage. In addition, if it exceeds 0.6, the buffering effect is poor;
If bottles come into contact with each other, they are extremely likely to break.

On the other hand, if the shrinkage rate in 1 20 CIC in one direction does not reach 10, the shrinkage will be insufficient and the adhesion of the label to the bottle will be insufficient and non-uniform. It is also important for labels to have a shrinkage rate of 4 times or more in the other direction. For example, if the foamed film is sealed with the horizontal direction facing the axial direction and the vertical direction facing the circumferential direction to create a film cylinder, which is then covered with a bottle and heat-shrinked, the film cylinder will fit around the bottle. Heat shrinks along the outer circumferential surface,
It is preferable to shrink only in the circumferential direction (the vertical direction of the film); if the 10-axis direction (horizontal direction of the film) shrinks, the film will shrink in the upward and downward directions of the cylinder, so the upper and lower edges will be shelled and jagged. In particular, when printed, the printed pattern becomes distorted and the appearance becomes extremely poor.

As can be understood from this phenomenon, unbalanced heat shrinkability, which shrinks only in the circumferential direction of the cylindrical film and shows virtually no dimensional change in the axial direction, is essential for shrinkable labels. It is suitable that the shrinkage rate of the film used in the circumferential direction at 120 DEG C. is at least four times that in the axial direction. In addition, in the case of a known uniaxially stretched film, when its shrinkage rate is measured, it shrinks in the stretching direction, but
In many cases, the film stretches in the opposite direction in the other direction, but in practice, when a cylindrical film is placed in a bottle and heat-shrinked, the film of the present invention does not elongate in the axial direction and damage the outer wall. Since it cannot be used, it is fully practical.

In addition, the heat-shrinkable foamed film obtained by the present invention can be subjected to various surface treatments, laminated with other films,
It can also be used for applications such as metal vapor deposition. 1 more
It can be applied not only to coating labels on bottles, but also to coating rod-shaped bodies and spherical bodies such as various containers and the legs of table sashes.
It can also be printed to display product names, advertisements, precautions, etc.

The present invention will be described in detail below, but the present invention is not limited to the following examples.

Examples 1-3. Comparative Examples 1 to 3 7Zodicarponamide 0 was added to the polypropylene and ethylene-propylene-butene-1 terpolymer shown in Table 1.
．． 4% by weight, butylated hydroxytoluene 0.1λf%
Add 0.2 ftll1 of calcium stearate and mix at 40°C with a high-speed mixer (trade name Henschel mixer).
Mixed for 6 minutes to obtain 6 formulations.

This blend was passed through an extruder with a T-die at 200°C.
The foamed sheet was melt-extruded and rapidly cooled while being sandwiched between two cooling rolls maintained at 40°C to obtain foam sheets with thicknesses of 0 and sm. Next, this foamed sheet was stretched 6.0 times in the vertical direction on a heating roll kept at 100°C, heat treated on a heating roll at 105°C, and rapidly cooled on a cooling roll at 20°C, so that the thickness was 0.15. A simple foamed-stretched film was obtained. The appearance of the foamed sheet of each formulation is in a foamed state with a specific gravity of 5, the appearance of the resulting foamed film is in a foamed state with a specific gravity of 1, and the 120°C yield in the vertical and horizontal directions are also listed in Table 1.

As is clear from Table 1, the ethylene-propylene-butene-1 terpolymer used in the present invention has a small apparent specific gravity, uniform foam cells, and a foamed stretched film. Moreover, it has excellent heat shrinkability, and is found to be extremely excellent as a heat shrinkable foamed film.

The foaming state of the shrink tower mechanism *40 in Note *3 of Table 1 was measured or observed as follows.

The shrinkage rate was determined by immersing a film cut into 102 square pieces in a glycerin bath at 120° C. for 10 seconds and taking it out, and expressing the shrinkage rate of the length of each side.

Those with a Δ in front of the number indicate that they did not shrink but instead grew.

The foaming state was determined by visually observing the presence or absence of uneven foaming in the width and length directions of the sheet and the uniformity of the foam cells.

Examples 4-10. Comparative Examples 4 to 6 Ethylene content 5.0% by weight, butene-1 content 4.5
A second ethylene-propylene-butene-1 terpolymer (containing 0.1% by weight of butylated hydroxytoluene and 0.3% by weight of calcium stearate) with a weight of 11%, Tm = 126°C, MFR-3.0 A predetermined amount of the blowing agent shown in the table was added, mixed for 3 minutes in a Henschel mixer, and then extruded and rapidly cooled in the same manner as in Example 1 at the extrusion temperature shown in Table 2. The foam sheet was uniaxially stretched at each stretching temperature and stretching ratio shown in Table 2, heat treated on a roll at the same temperature as the stretching temperature, and cooled on a cooling roll at 20°C to obtain 10 types of foaming and axial stretching. Got the film. At this time, the stretchability of each sample, the appearance of the obtained film, the specific gravity foaming state, the shrinkage rate at 120° C., and the sharpness of printing are also listed in Table 2.

In Table 2, the stretchability was evaluated as good if it could be stretched continuously for 60 minutes or more at a stretching speed of 50 m/min, and as poor if it could not be continuously operated due to stretch breakage. In addition, the sharpness of the printing was evaluated using a commercially available printing ink for polypropylene (Porepu P manufactured by Toyo Ink ■) on the obtained film.
Print the base with a gravure printing machine using color),
A case where the ink smeared and the base line was unclear was evaluated as poor, and a case where there was no ink bleed and the base line was clear was evaluated as good.

Example 11 The copolymerization ratio of ethylene is 4.0% by weight, the copolymerization ratio of butene-1 is 3.0% by weight, Tm=130°C.

Ethylene-propylene-butene-1 terpolymer with MFR of 5.5 (butylated hydroxytoluene 0.2% by weight)
, 0.4 x amount of azodicarbonamide (containing 0.4 weight of calcium stearate) was added and mixed in a Henschel mixer, followed by an extruder, a T-die, a vertical stretching device (heated roll method), and a horizontal stretching device. (Tentor one type) etc. using an extruder and T
It was melt extruded at a die temperature of 195°C, and rapidly cooled on both sides while being nipped between two mirror-finished rolls having a surface temperature of 40°C to create a raw rebound foam sheet with a thickness of 1.2 cm and an apparent specific gravity of 0.69. . Next, this sheet was heated at 100°C for 1 time in the vertical direction.
．． After stretching 5 times, it was then stretched to 8.0 in the horizontal direction at 105°C.
Stretch it twice, hold this tension for 4 seconds, then relax for 4 seconds.
Heat fixation was performed at the same temperature for 2 seconds, and after further cooling to 20°C, it was removed from the clip, and one side was subjected to corona discharge treatment, and the thickness was 0.0951111. A foamed biaxially stretched film with an apparent specific gravity of 0.485 was obtained.

The shrinkage rate of this film at 120°C is 5% vertically.

The width was 41 inches, and as a result of printing in the same manner as in Example 4, the print clarity was also good. Also, the diameter of this film is 55mm so that the horizontal direction is the diameter direction and the vertical direction is the height direction.
n, formed into a cylindrical shape with a height of 100 cm and a diameter of 5 Q tm.
', covered with i1% and 1ootl paper tubular body, 20
Heated at 0°C for 5 seconds. As a result, the film was completely adhered to the tubular body in the diametrical direction, did not shrink at all in the height direction, and had a well-adhesive color and packaging in which the printing base grains were not distorted at all.

Examples 12-15. Comparative Examples 7 to 9 In Example 11 above, the stretching ratios in the vertical and horizontal directions were changed to produce foamed films with different horizontal/vertical shrinkage ratios at 120°C.
Form it into the same cylinder shape in the same way as above, cover it with the same paper cylinder, and
Heat shrinkage was performed by blowing hot air at 20° C. for 10 seconds. Table 3 shows the shrinkage state of the film at this time and the presence or absence of the printed substrate pattern. Note that when the stretching ratio in the vertical and horizontal directions exceeded 30 times, breakage occurred frequently during the horizontal stretching, and a product film could not be obtained.

Table 3

Claims (4)

[Claims] (1) A raw rebound foam sheet obtained by blending an organic decomposition type blowing agent into a crystalline ethylene pyrene-butene-1 terpolymer having a crystalline melting point of 115 to 145°C and melt extruding the blend. It is obtained by stretching in at least one direction of
1. A heat-shrinkable foamed film characterized by a φ of 10% or more and 4 times or more the axis absorption rate in the other direction. (2) An ethylene-pyrene-butene-1 ternary copolymer with a crystalline melting point of 115 to 145°C is a propylene-containing Jt70
Claims (1) characterized by using an ethylene-propylene-butene-1 terpolymer with a content of 1% or more
) The heat-shrinkable foam film described in ). (3) Crystalline ethylene with a crystal melting point of 115-145°C
The propylene-butene-1 terpolymer was added to the obtained melt-foamed sheet, and both sides of the sheet were simultaneously rapidly cooled to 60°C or less to give an apparent specific gravity of 0.3 to 0. A foamed sheet with a thickness of 0.2 mm or more is prepared, and the sheet is stretched at a temperature 10 to 60 degrees Celsius lower than the crystal melting point of the ethylene-tetrapyrene-butene-1 ternary complex, with the stretching ratio in one direction being equal to that in the other direction. A method for producing a heat-shrinkable foamed film, which comprises stretching the film in at least one direction by 4 to 30 times to a stretching ratio of 4 times or more. (4) The ethylene-propylene-butene-1 ternary copolymer with a crystal melting point of 115 to 145°C is characterized by using an ethylene-propylene-butene'-1 ternary copolymer with a propylene content of 70 weight tons* or more. A method for producing a heat-shrinkable foam film according to claim (3).