WO1989001402A1 - Process for producing heat-shrinkable polyethylene film - Google Patents

Abstract

A process for producing heat-shrinkable polyethylene film having less thickness variation in a mottled pattern, excellent low-temperature heat-shrinking properties and excellent transparency, which comprises conducting tubular stretching under specific stretching temperature conditions of a resin composition mainly comprising a copolymer composed of ethylene and 1 to 10 % of at least one C4-C12 alpha-olefin and having a melting point of 0.3 to 2.0 g/10 min and a density of 0.86 to 0.92 g/cm3 at 25°C, more preferably a composition having an endothermic area below the melting point of 55 % or more based on the whole endothermic area in the melting curve obtained by using a differential scanning calorimeter. No excellent properties could be obtained by conventional linear low-density polyethylene having a geta (=[n]/[n]L; wherein [n] is a limiting viscosity of a polymer and [n]L is a limiting viscosity of a straight chain polymer of the same average molecular weight as that of the said polymer) of 0.3 to 0.7 which showed good transparency but which, in tubular bi-axial stretching, showed unstable stretchability, providing stretched film with large thickness variation in a mottled pattern.

Description

 Ten

Manufacturing method of polyethylene-based heat-shrinkable film

 The present invention relates to a shrink wrapping material, and more specifically, a thickness unevenness mainly composed of an ethylene-α-olefin copolymer having a parameter g * of 0.3 to 0.7, which indicates direct molecular chain resilience. The present invention relates to a method for producing a heat-shrinkable film, which has low transparency and excellent transparency and low shrinkage.

 Background art

 Conventionally, as heat-shrinkable films, polyvinyl chloride, polypropylene-based biaxially stretched films, polyamide-based biaxially stretched films, and the like have been known.

 Of these, polyethylene-based biaxially stretched films have been practically used because they have heat sealing properties and are inexpensive. In particular, in recent years, linear low-density copolymers of ethylene and α-olefin (hereinafter simply referred to as linear low- Polyethylene-based heat-shrinkable films using polyethylene (polyethylene) have attracted attention because of their excellent impact resistance and heat seal strength.

 However, among the linear low-density polyethylenes, those with g '= ννΐ / il L values of 0.3 to 0.7 have good transparency, but the conventional Tupla single-shaft using this resin is good. When a heat-shrinkable film is produced by a stretching method, for example, by applying the method of Patent Application Publication No. 361, 1982, No. 6142 as it is, a heat-shrinkable film is obtained, resulting in insufficient stretching stability. As the stretched film, only a film having a large thickness unevenness was obtained, and a film which was practically satisfactory could not be produced.

 Censor of the invention

The present inventors have studied a method for producing a polyethylene-based heat-shrinkable film having a small thickness unevenness and excellent low-temperature shrinkage using the above-mentioned resin having excellent transparency. As a result, the present invention has been achieved. That is, in the present invention, the value of § = [??] / C ^ '] L is 0.3 to 0.7 (where [] is the intrinsic viscosity of the polymer and [] is the same weight average molecular weight as the polymer. Intrinsic viscosity of direct polymer Bolimer), Melt index of 0.3 to 2.0 g / 1 Oniin, density of 0.86 to 0.92 gZcm ³ at 25 ° C and at least one kind of C4 to 12 When a heat-shrinkable film is produced by a tubular stretching method from a tubular unstretched film of a resin composition containing a copolymer containing 1 to 10% as a main component,

 (B) The temperature at the point of expansion is defined as the melting point of the resin composition (the endothermic main peak in the melting curve obtained by measuring with a differential scanning calorimeter (hereinafter abbreviated as DSC)).

 (□) The highest temperature is set at 1/4 to 1/3 of the distance of the stretching zone from the start point of expansion to the end point of expansion, and the maximum temperature and the surface temperature of the film at the start point of expansion are checked. The difference shall be 5 or less,

 (C) Lower the temperature at the expansion end point so that it is 15 to 2 (TC lower) than the maximum temperature.

 (2) Cool down to 60 ° C or less while traveling a distance of 0.8 times the distance of the stretching zone from the expansion end point

A method for producing a bolylene-based heat-shrinkable film having a small thickness unevenness and excellent low-temperature heat-shrinkability and transparency. In this case, the heat absorption area of the resin composition, which is obtained by measuring with a differential scanning calorimeter (hereinafter abbreviated as DSC), is preferably 10% lower than the melting point (endothermic main peak). The present invention relates to a method for producing a bolylene-based heat-shrinkable film characterized by being at least 5%.

 BRIEF DESCRIPTION OF THE FIGURES

 FIG. 1 is a conceptual diagram of a tuber stretching apparatus used in the present invention.

FIG. 2 is an enlarged view of an extended portion of FIG. BEST MODE FOR CARRYING OUT THE INVENTION

The resin composition used in the present invention is a resin composition containing as a main component one or more linear low-density polyethylene which is a copolymer of ethylene and α-olefin having at least 4 to 12 carbon atoms. , and the and, g * = [^] / il Shino value is the 0.3 to 0.7 and a density of 0.86 to 0.92 the value of the is eg 'ones GZcm ³ is 0.7 If the ratio is more than 0.3, the stretched film obtained by using this is not yet sufficiently transparent, and if it is less than 0.3, the degree of linearization is insufficient, and the mechanical properties that are characteristic of linear low-density polyethylene are insufficient. All of them are unsuitable for the purpose of the present invention because of their poor strength. If the density exceeds 0.92 gZcm ³ , the low heat shrinkage is not sufficient. Conversely, if the density is less than 0.86 g cm ³ , the anti-locking of inorganic fine particles etc. due to too soft or blocking Even with the combined use of the agents, it cannot be improved sufficiently.

 The resin cord composition used in the present invention is mainly composed of linear low-density poly (ethylene) as described above. In particular, the melting point (endothermic main peak) in the melting curve measured using DSC is particularly high. The ratio of the heat-absorbing area of less than 10 degrees lower than the total heat-absorbing area to the total heat-absorbing area (hereinafter abbreviated as heat-absorbing area ratio) of 55% or more is particularly preferable because it has excellent stretching stability over a relatively wide temperature range.

 A method of obtaining a melting curve by the above differential scanning calorimeter (in the present invention, a differential thermal analyzer (DSC-200) manufactured by Seiko Denshi Kogyo KK) was used. First, 6 to 8 mg of a sample was placed in an aluminum pan. Enclose, raise to 190 ° C in a nitrogen stream, hold at this temperature for 1 hour, then cool to room 10 at a rate of about 10 ° C, and then return to room temperature from room 10 to 190 ° C. The melting point and the endothermic area ratio are determined from the DSC chart obtained by increasing the pressure per minute.

Examples of the α-olefins having 4 to 12 carbon atoms copolymerized with ethylene include butene-11, pentyne1-1, hexene1-1, hebutin-11, octene1-1,4-methylpentine-11, Decene-1, Dedecene-1, Dodecene-1 Are exemplified.

 The copolymerization ratio of α-olefin used in the copolymerization is preferably 0.5 to 10 mol%.

 In the present invention, in addition to the above-mentioned linear low-density polyethylene, if desired, a high-pressure polyethylene, an ethylene monoacetate copolymer, an ionomer, an ethylene propylene copolymer may be used as long as the object of the present invention is not hindered. Additives such as ethylene polymers such as polymers, lubricants, antiblocking agents and antistatic agents can be used in combination.

 Hereinafter, a method for producing a heat-shrinkable bolylene-based film according to the method of the present invention will be described with reference to FIGS. 1 and 2. Fig. 1 is a conceptual diagram of the tubular stretching device, and Fig. 2 is an enlarged view of the stretched part. The tubular unstretched film used in the present invention can be produced by melt-extruding the above resin composition (hereinafter, simply referred to as a resin composition) by a known method, and rapidly solidifying it.

The unstretched film obtained in this way is supplied to, for example, a stretching device as shown in Fig. 1, and when bubbles are generated by injecting air into the tube between nibroll 2 and nibroll 3, expansion and stretching are performed. Adjust the temperature so that the temperature of the expansion starting point 101 is within the temperature range of 20 to 30 C below the melting point of the resin (the main peak of the DSC chart). This adjustment can be made by adjusting the air pressure to be injected into the tube, the heating devices 4 and 5 and the cooling device 6. If the temperature at the expansion start point is higher than the above range, the film in the vicinity of the expansion start point is too soft, the stretching tension is reduced and abnormal expansion occurs, resulting in uneven stretching. On the other hand, when the temperature at the expansion start point is lower than the above-mentioned temperature range, so-called neck stretching tends to occur, and the thickness unevenness of the obtained film becomes large, and the transparency is poor. Therefore, the object of the present invention cannot be achieved. If the temperature is further lowered, the internal pressure of the bubble becomes excessive and so-called puncture frequently occurs, which is not preferable. Also, in order to make the stretching process uniform and to reduce the thickness unevenness, when the length of the stretching zone from the expansion starting point 101 to the expansion end point 103 is L, the expansion starting point 10 An upward angle gradient is set so that the position from 1 to LZ 4 to L / 3 advances to the maximum temperature, and the difference between the maximum temperature and the expansion starting temperature is within 5 digits. The angle of the expansion end point 103 should be lower by 15 to 20 C than the maximum angle, and during the travel from the expansion end point by a distance of 0.8 times the length L of the stretching zone. Cool down to 60 or less.

 If the maximum temperature exceeds 5 degrees higher than the expansion start point, the tensile strength of the film decreases, the heat shrinkage of the obtained film decreases, and bubble expansion becomes unstable, causing bubble oscillation. Conversely, if the gradient of the angle is set to a descending gradient while passing LZ 4 to L3 after passing the expansion start point 101, the stability of the stretched purple is improved, but the stretch does not progress in a vertical and horizontal balance. In either case, the thickness unevenness of the obtained stretched film becomes large, and the object of the present invention cannot be sufficiently achieved. On the other hand, if the temperature drop between the maximum temperature point 102 and the stretching end point 103 is smaller than 15 ° C., the bubbles become unstable and the thickness unevenness increases, which is not preferable. Conversely, if the temperature drop is set to exceed 20, the internal pressure of the bubble will increase abnormally and the stability of the expansion starting point 101 will be lost, and the upper part of the bubble will easily roll and the thickness unevenness will increase, which is preferable. Absent.

 Furthermore, in order to stabilize the bubble, it is preferable to cool rapidly even after reaching the expansion end point 103. That is, quenching is carried out at a temperature of 60 ° C or less while traveling a distance of 0.8 times the length L of the stretching zone from the expansion end point. If not rapidly cooled, the entire bubble is liable to sway, and the sway causes local unevenness in stretching, resulting in large unevenness in the thickness of the obtained film.

By specifying the temperature gradient in the stretching step as described above, the stability of bubbles during expansion and stretching can be improved, and as a result, a film with small thickness unevenness can be obtained. (Action and effect)

 Among the linear low-density polyethylenes, the resin with a relatively small value of 8Γ · of 0.3 to 0.7 has excellent transparency, but in the case of linear low-density polyethylene, which has been conventionally known, Although stable bubble-like stretching was difficult under the same conditions as described above, by applying the method of the present invention, it was possible to obtain a film with stable stretching, small thickness unevenness, and excellent practicability. Became.

 (Example)

 Hereinafter, the present invention will be described specifically with reference to Examples, but the present invention is not limited to these Examples.

 The measurements shown in this example were performed by the following methods.

 (1) Heat shrinkage

 After accurately measuring the length of each side of the film specimen cut to about 1 Ocm to the nearest length and width to the nearest 0.1 mm, immerse it in a glycerin bath adjusted to a predetermined temperature for 10 seconds, and remove it. After gently rinsing in water at room temperature, the length of each side was accurately measured again.

 (Α-Α ')

 X 100 (%)

 A

 However, A, A, is the average of the two side lengths of the measured values before and after contraction, respectively.

(2) Film temperature

 The temperature of the film during the stretching process is about 1 mm in diameter and about 15 mm in exposed length, and the tip of a chrome-melon constantan-type thermocouple (Anritsu Keiki C-505 thermo-cuttable 0 to 100 Ω) is applied to the running film surface. Contact was made, and the film strength was taken with the indicated value 30 seconds later.

 (3) Uneven thickness of film

Using a continuous thickness gauge (Anritsu continuous thickness measuring device), the difference between the height of the highest valley and the lowest valley of the chart measured on a sample film 25 cm at a speed of 30 OcmZ 1 / 2 was regarded as thickness unevenness.

 (4) Transparency (haze)

 The ratio of the scattered light transmittance to the parallel light transmittance was shown as a percentage using an integrating sphere light transmittance measuring device based on JIS-K6714.

 (5) s-s' = ίνΐ / i l L

 Here, [] is the intrinsic viscosity of the polyethylene copolymer to be measured and was determined by dissolving decalin as a solvent at 甩 ぃ 135 C. [7?] L is the limiting viscosity of linear poly (ethylene) having the same weight average molecular weight as the polyethylene copolymer of the above sample. This value is the weight average molecular weight <M> measured by the light scattering method. It can be obtained from w by an approximate calculation according to the following equation.

^{ίηΐ L = 5.29 X 10 - 4} X <M> w 0 - T13

Example 1 _¾

A linear polyethylene-based copolymer resin of ethylene and octene-11 (8Γ is 0.59, melting point 125 ° (Density at 25 ° C is 0.915 gZ cm ³ , melt index 1.0) It was extruded from a tubular die of a 66 marauder and quenched by internal and external water cooling to obtain a tubular unstretched film with a diameter of 65 cm and a thickness of 370 Z. The endothermic area ratio of the resin of this unstretched film measured by DSC was 58.9. The obtained unstretched film was supplied to a tubular one-stretcher running in the vertical direction as shown in Fig. 1, and a preheater and four annular infrared heaters were installed in four sections. Table 1 shows the stretched bubbles formed by adjusting the heater 5 and the cooling air ring capable of jetting cool air obliquely upward, and adjusting the air pressure into the tube between the nib α-rail 2 and the nip roll 3. Depending on the conditions, the biaxially stretched film is 16mZ It was able to produce long-term stability to.

The vertical distance L in the stretching zone was about 2 lcm, the outside diameter of the baples was 24 Omm, and the point of highest temperature of the film was about 6.0 cm below the starting point of expansion. The biaxially stretched film was guided to another tube-shaped annealing device whose temperature was controlled to 70 ° C, annealed for 10 seconds, cooled to room temperature, folded again, taken out and wound up.

 The thickness, uneven thickness, haze, and heat shrinkage of the obtained film were measured, and the results are shown in Table 1.

Example 2

A linear polyethylene copolymer resin of ethylene and putin-1 (g * with a melting point of 0.65 and a melting point of 18.7, at a temperature of 25 ° C and a density of 0.906'gZcm ³ , with a melt index of 0.8) was used as in Example 1. As a result, an unstretched tubular film having a diameter of 65 mm and a thickness of 359 i was obtained. The endothermic area ratio of the unstretched film resin measured by DSC was 53%.

 The obtained unstretched film was formed into a stretchable film in the same manner as in Example 1, and a biaxially stretched film could be stably manufactured at 13 m / min for a long time under the conditions shown in Table 1.

 The vertical distance L in the stretching zone was about 20.5 cra, the outer diameter of the bubble was 25 Oram, and the point of maximum temperature of the film was about 5.8 cm below the starting point of expansion.

The biaxially stretched film was guided to another tube-shaped annealing device whose temperature was adjusted to 70 ° C. After annealing for 10 seconds, the film was cooled in the room し て, folded again, taken out and wound up.

 The thickness, uneven thickness, haze, and heat shrinkage of the obtained film were measured, and the results are shown in Table 1.

Example 3-Linear polyethylene copolymer resin of ethylene and butene-11 (g * 0.45, melting point 116 ° C, 25. Density at C: 0.89 g cm ³ , melt index) 1.0) to 0.3% of solid fine particles (trade name: Syloid # 244, manufactured by Fuji Davison) with an average particle size of 2 z, and the same as in Example 1 with a diameter of 65 mm and thickness A 385 // tubular unstretched film was obtained. The endothermic area ratio of the unstretched film resin measured by DSC was 56%.

 A stretched bubble was formed from the obtained unstretched film in the same manner as in Example 1, and a biaxially stretched film could be stably produced at 15 m / min for a long time under the conditions shown in Table 1.

 The vertical distance L in the stretching zone was about 20.2 cm, the outside diameter of the bubble was about 250, and the point of maximum film temperature was about 5.4 cm below the starting point of the expansion.

 The biaxially stretched film was guided to another tube-shaped annealing apparatus whose temperature was adjusted to 70, and after annealing for 10 seconds, cooled in the room し て, folded again, taken out and wound up.

 The thickness, uneven thickness, haze, and heat shrinkage of the obtained film were measured, and the results are shown in Table 1.

Comparative Example 1

A linear polyethylene copolymer resin of ethylene and butene-1 (8Γ · 0.89, melting point 122, 25, density 0.923 gZcm ³ , melt index 0.8) was prepared in the same manner as in Example 1. An unstretched tubular film with a diameter of 6 mm and a thickness of 366 mm was obtained. The endothermic area ratio of the unstretched film resin measured by DSC was 63.8%.

 A stretch bubble was formed from the obtained unstretched film in the same manner as in Example 1, and a biaxially stretched film could be stably manufactured for 16 m in a long time under the conditions shown in Table 1.

 The vertical distance L in the stretching zone was about 21. Ocm, the outside diameter of the tuple was 241 πππ, and the point of maximum temperature of the film was about 6.2 cm below the starting point of expansion.

This film was guided to another tube-shaped annealing apparatus whose temperature was controlled to 70 C, and after annealing for 10 seconds, it was cooled in the room 溫, again folded, taken out and wound up. The thickness, uneven thickness, haze, and heat shrinkage of the obtained film were measured, and the results are shown in Table 1.

 As can be seen from the results of this example, there was no particular problem with the stability of the pubble, but the thickness unevenness of the obtained film was large and the haze was 8%, which was unsatisfactory in transparency. Comparative Example 2

Ethylene and Okuten - 1 linear Boriechiren copolymer resin of (3 '0.9 2, melting point 126, 25 density in ° C is 0. 92 g cm ^3, a melt-in deck scan 1.0) Example 1 A tubular unstretched film with a diameter of 65 and a thickness of 366 Z was obtained in the same manner as described above. The endothermic area ratio of the unstretched film resin measured by DSC was 59.4%.

 A stretched bubble was formed from the obtained unstretched film in the same manner as in Example 1, and a biaxially stretched film was produced at a rate of 15 m / min under the conditions shown in Table 1. The obtained film had a large thickness unevenness. The vertical distance L in the stretching zone was about 21. Ocm, the outer diameter of the bubble was 234 mm, and the point of maximum temperature of the film was about 6.2 cm below the starting point of expansion.

The film was guided to another tube-shaped annealing apparatus whose temperature was adjusted to 70, annealed for 10 seconds, cooled to room temperature, folded again, taken out and wound up.

 The thickness, uneven thickness, haze, and heat shrinkage of the obtained film were measured, and the results are shown in Table 1.

Comparative Example 3

 In the same manner as in Example 1, a tubular unstretched film having a thickness of 370 / z was obtained using the same linear low-density polyethylene as the resin.

Except that the temperature of the expansion start point and the temperature of the highest temperature point of the unstretched film were higher than the temperature range specified in the method of the present invention as shown in Table 1, the conditions of the present invention were used. In the same manner as in the above, a biaxially stretched film was produced in the amount of 16 mZ. During production, the bubble was unusually expanded and unstable, making it impossible to manufacture continuously for a long time.

 Comparative Example 4

 A tubular unstretched film having a thickness of 370 was obtained in the same manner as in Example 1 except that the same linear low-density polyethylene as in Example 1 was used as the resin.

The temperature of the unstretched film and the temperature of the highest temperature point were set to a temperature lower than the temperature range specified in the method of the present invention, as shown in Table 1, except that the temperature was not lower than the temperature range specified in the method of the present invention. A biaxially stretched film was produced at 16 mZ in the same manner as in 1 _{ bubbles occurred during production and only a film having no practicality was obtained. Comparative Example 5

 A tubular unstretched film having a thickness of 360 / was obtained in the same manner as in Example 2 except that the same linear low-density polyethylene as in Example 2 was used as the resin.

 This unstretched film was subjected to tubular stretching in the same manner as in Example 2 except that the cooling after passing through the expansion end point was insufficient as shown in Table 1. However, the bubble rocked and could not maintain stable stretching.

 Industrial applicability

The heat-shrinkable film produced as described above, which has a small thickness unevenness, has excellent uniformity as a film, so that the film can be handled smoothly in the laminating process and the packaging process with other films. Because of its excellent transparency and heat-sealing properties, it can be used as an extremely excellent packaging material. table 1

 Unit Practical 'Print 2' Practical 3 Comparative Example 1 Comparative Example 2 Comparative Example 3. Hiroshi 4 'Comparative Example 5

 % y n. 0

J ϋ · 1 18. 7 密度 0. 915 0. 906 0. ο 3 0. 923 0. 920 0 * S i 5 0. 91 0. 906 メルトインデックス g 0分 1. 0 0. 8 1 - ϋ 0. 8 J. 0 0. 8 吸站面棋比 % 58. 9 53 56 63. 8 59. 4 58. 9 58 - 9 53 状未征忡フィルムの 125. 0 1 J 8. 7 122 126

J ϋ1 18.7 Density 0.915 0.906 0.ο 3 0.93 0.920 0 * Si 5 0.91 0.906 Melt index g 0 min 1. 0 0.8 1-ϋ 0 8 J. 0 0.8 Ratio of stadium game to game% 58. 9 53 56 63. 8 59. 4 58. 9 58-9 53

 Diameter mm 65 65 65 '65 65 65 65 65 Thickness β 370 359 305 366 366 370 370 360 360

 Feeding speed of unenrolled Nakam film m / min 3.6 2.9 3. 2.3.6 3.3.6 3.3.6 3.6.2.7

 't o n Length of the middle zone (L) mm 202 J 210 220

 Bg ¾ 閗 Start point anglec 99 94 92 97 103 1 1 1 93 94

Degree of S 髙 pointc 102 98 96 100 107 1 15 97 98

Distance from; mm 60 58 54 62 62 62 58 65. iS degree of end point 86 80 78 84 89 97 80 87 Expansion! 0.8 L from end point * C 55 55 56 50 58 58 57 70 Just

 Outer diameter of Yanbu bubble mm 240 250 250 241 234 ** Pickup m / min 16 13 15 16 15 16 J 6 13 Result

 Stability of bubble O Ο-Δ Ο Ο Δ X X X

, Of the Ennobu film

 Thickness 22.5 20.8 21.3 22.2 24.4

 Thickness unevenness. ± 8 ± 90 ft

 % 3.1 "2.8 ο

 Haze 3. 2 8 5

 Heat recovery rate

 70 "C-MD% 5. 9 7. 2 8 4 Ω Ι 3.1 3.5

 TD% 6.4 7.5 8.5 5.6 6.5

 80 * C -MD% 8.8] 0 3] 1.5] 5.3 17.4

 TD% 12.2 13, 5 12.1 25. 1 27.0

 Ί 0 ΟMD% 27.6 34.8 35.0 45.2 49.6

 TD% 36. 9 42. 5 40. 4 44. 6 49. 5

 it: · ·) Shows that the outer diameter of the purple has changed to ¾.

 Bubble stability The O mark in jtffl indicates that the bubble during the ebb and flow is stable in the shape of a Si fc.

 It also shows that the Δ bubble was occasional,

 X "bubbles shake significantly, indicating that a stable film could not be obtained,

o

Claims

The scope of the claims 1. g '= [7?] The value of [] is 0.3 to 0.7 (where is the intrinsic viscosity of the polymer, [] _L is the intrinsic viscosity of the linear polymer), and the melt index is 0.3. ~ 2.0 g / 1 Omin, 25. Ethylene and at least one C ₄ ~ density in C is ^{0. 86~0 92 g / cm 3 (} :. ₁₂ of α- Orefin 1 resin composition mainly composed of a copolymer of 10% When producing a heat-shrinkable film from a tubular unstretched film by the Tupler stretching method,  (A) The temperature of the expansion start point is determined by the melting point of the resin composition (the endothermic main peak in the melting curve obtained by measurement with a differential scanning calorimeter (hereinafter abbreviated as DSC)). age,  (Ii) The maximum temperature shall be at a point 1 to 4 to 1/3 of the distance of the stretching zone from the expansion start point to the expansion end point, provided that the difference between the maximum temperature and the film surface temperature at the starting point of expansion. Is less than or equal to 5,  (C) Lower the temperature at the end point of the expansion so that it is 15 to 20 ° C lower than the maximum temperature.  (2) Cooling to 60 ° C or less while proceeding a distance of 0.8 times the distance of the stretching zone from the expansion end point A method for producing a bolylene-based heat-shrinkable film having a small thickness unevenness and excellent low-temperature heat-shrinkability and transparency.  2. A claim wherein the resin composition has a melting curve obtained by DSC measurement, wherein an endothermic area whose temperature is 10 degrees lower than the melting point (endothermic main peak) is 55% or more of the total endothermic area. 2. The method for producing a polyethylene heat-shrinkable film according to item 1 above.