WO2007097525A1

WO2007097525A1 - Heat shrinkable film with high shrinkage and process for preparing same

Info

Publication number: WO2007097525A1
Application number: PCT/KR2007/000357
Authority: WO
Inventors: Won Seok Oh; Yeong Taek Oh
Original assignee: Dong Il Chemical Inc., Ltd.
Priority date: 2006-02-27
Filing date: 2007-01-22
Publication date: 2007-08-30
Also published as: KR100741935B1

Abstract

A process for preparing a heat shrinkable film with a high shrinkage for shrink-wrapping bottles is disclosed, which comprises a first step of drawing comprising heating undrawn film at heating section 1 to an appropriate temperature for drawing, first-drawing the heated film at drawing section 2 in the TD direction, fixing the polymer structure of the first-drawn film at annealing section 3, and cooling the film at cooling section 4, and a second step of drawing comprising heating the first-drawn film at heating section 1 ' to an appropriate temperature for drawing, second-drawing the heated film at drawing section 2' in the TD direction, fixing the polymer structure of the second-drawn film at annealing section 3', and cooling the film at cooling section 4'. The heat shrinkable film of the present invention has a shrinkage over 60 %, preferably about 60 to 70 %, and a shrinking strength below 2 kg/cm2 at 100 °C.

Description

HEAT SHRINKABLE FILM WITH HIGH SHRINKAGE AND PROCESS FOR PREPARING SAME

Technical Field

[1] The present invention relates to a heat shrinkable film for shrink-wrapping plastic bottles, glass bottles, and other containers, which functions a packaging film as well as a label. More particularly, the present invention relates to a heat shrinkable film with a high shrinkage, and a process for preparing the film.

[2]

Background Art

[3] A heat shrinkable film has been used for shrink-wrapping plastic bottles, glass bottles, and other containers (hereinafter "bottles", which functions a packaging film as well as a label. A heat shrinkable film is printed with contents as a label, the printed film is prepared in a tube form by tubing, the tube film is wrapped on a bottle, and, when hest is applied to the tube film, the tube film is shrink-wrapped on the bottle. The heat shrinkable film functions a packaging sheet for wrapping the bottles as well as a label in which necessary contents are printed.

[4] The heat shrinkable film for shrink-wrapping the bottles requires for good shrink- wrapping as follows: 1) a high shrinkage over 60 %, 2) a shrinking strength below 2 kg/D 3) a shrinkage below 5 % in the machine direction (longitudinal direction), 4) a deviation within +6% of the thickness of the film for quality printing, 5) a tensile strength of the film over 500 g/D in the machine direction for speed printing, 6) a static electricity below 14 Ω of the film for speed labeling, and 7) no rolling, wrinkling, spotting, drooping and the like after being shrunk. As all the requirements above should be met, it is not easy to prepare a right heat shrinkable film.

[5] In general, conventional heat shrinkable films are prepared by drawing undrawn films in the TD direction (transverse direction), prepared with synthetic resin. Fig. 1 is a schematic drawing which illustrates a process for producing a conventional heat shrinkable film.

[6] As illustrated in Fig. 1, an undrawn film is fed in the drawing machine and heated at the heating section 1 to an appropriate temperature for drawing. The undrawn film heated at heating section 1 is passing through drawing section 2 and drawn in the TD direction. The drawn film is passing through annealing section 3 and the polymer structure of the film is fixed. And, the film is passing through cooling section 4 and cooled slowly to become the polymer structure stabilized.

[7] As the speed of the film is kept constantly in the MD (machine direction) direction, a drawing of the film is carried out in the Td direction, but not in the MD direction. The heat shrinkable film for shrink-wrapping the bottles should be drawn in the TD direction instead of in the MD direction because the film should be horizontally shrunk around the bottle but not longitudinally or vertically. If the film is shrunk longitudinally or vertically, the printed contents on the film are squeezed.

[8] The technic for preparing a conventional heat shrinkable film as shown in Fig. 1 is publicly known to an ordinarily skilled person in the art to which the present invention pertains.

[9] The conventional heat shrinkable film has been used for shrink-wrapping of bottles as a packaging sheet as well as a label. The shrinkage of the film is not important in case that the diameter of the bottle is uniform or has no big difference. However, in case that the diameter of the bottle to shrink-wrap with the film has a big difference, like a big diameter of the body and a small diameter of the neck, the film should have a high shrinkage so as to shrink-wrap the small diameter part such as the neck. In other words, if the film is not sufficiently shrinkable to heat, the film cannot shrink-wrap the small diameter part. Accordingly, a lot of research to obtain a shrinkable film with a high shrinkage has been widely proceeded in the art.

[10] One research for developing a shrinkable film with a high shrinkage is try to add additives or to substitute the material components. And, another research is try to change the conditions of the drawing process such as drawing temperature, drawing ratio, etc. However, these researches could not obtain a satisfactory result.

[11] In regard to the high shrinkage, as polyester (PET) film has a good draw ratio up to about 5-6, a high shrinkage can be obtained. However, the PET film has a strong shrinking force or shrinking strength which cannot be used on weak bottles. Further, the PET film shows a rapid shrinkage, a rolling, a wrinkling, etc.

[12] The shrinking force of the heat shrinkable film is an important factor as well as high shrinkage. Generally, PVC or PS film does not show a strong shrinking force.

[13] The inventors of the present invention have developed a new process that can prepare a heat shrinkable film with a high shrinkage and not so strong shrinking force.

[14]

Disclosure of Invention Technical Problem

[15] An object of the present invention is to provide a new process that can prepare a heat shrinkable film with a high shrinkage for shrink-wrapping bottles.

[16] Another object of the present invention is to provide a new heat shrinkable film with a high shrinkage for shrink-wrapping bottles.

[17] A further object of the present invention is to provide a new heat shrinkable film with a high shrinkage and with not so strong shrinking force for shrink-wrapping bottles.

[18] A further object of the present invention is to provide a new heat shrinkable film with a high shrinkage and no rolling, wrinkling, spotting, drooping for shrink- wrapping bottles.

[19] A further object of the present invention is to provide a new drawing system for preparing a heat shrinkable film with a high shrinkage for shrink-wrapping bottles.

[20] These and other objects of the present invention will become apparent from the following description and appended claims, taken in conjunction with the accompanying drawings.

[21]

Technical Solution

[22] The process for preparing a heat shrinkable film with a high shrinkage for shrink- wrapping bottles according to the present invention comprises a first step of drawing comprising heating undrawn film at heating section 1 to an appropriate temperature for drawing, first-drawing the heated film at drawing section 2 in the TD direction, fixing the polymer structure of the first-drawn film at annealing section 3, and cooling the film at cooling section 4 so as to become the polymer structure stabilized, and a second step of drawing comprising heating the first-drawn film at heating section 1 ' to an appropriate temperature for drawing, second-drawing the heated film at drawing section 2' in the TD direction, fixing the polymer structure of the second-drawn film at annealing section 3', and cooling the film at cooling section 4' so as to become the polymer structure stabilized.

[23] The first and second drawing steps may be carried out continuously or non- continuously.

[24] The heat shrinkable film is preferably prepared with PVC or PS resin.

[25] The heat shrinkable film of the present invention has a shrinkage over 60 %, preferably about 60 to 70 %, and a shrinking strength below 2 kg/D at 100 °C.

[26]

Brief Description of the Drawings

[27] Fig. 1 is a schematic diagram of a conventional process for preparing a heat shrinkable film.

[28] Fig. 2 is a schematic diagram of a process for preparing a heat shrinkable film with a high shrinkage according to the present invention, which comprises two step drawing system.

[29]

Best Mode for Carrying Out the Invention [30] Fig. 1 is a schematic diagram of a conventional process for preparing a heat shrinkable film. As illustrated in Fig. 1, an undrawn film is fed into the film drawing machine first to preheat the film to an appropriate temperature for drawing at heating section 1. The temperature at the heating section is not uniform. The temperature is low at the introducing part and increases along the end part. The temperature at heating section 1 will be different according to the material resin, and may be easily set by an ordinarily skilled person in the art.

[31] The undrawn film heated at heating section 1 is passing through drawing section 2 and drawn in the TD direction. The temperatures at heating and drawing sections 2 and 3 are important because, if they are not set properly, the drawing process cannot be smoothly proceeded and a good shrinkage cannot be achieved. Of course, the temperatures depend on the type of resin, physical properties of the film to be required, other process conditions, etc. Although the temperatures may be set by an ordinarily skilled person, it is preferable to set the temperatures to a minimum of the drawing temperature of the resin if possible.

[32] The drawn film is passing through annealing section 3 and the polymer structure of the film is fixed. And, the film is passing through cooling section 4 and cooled slowly to become the polymer structure stabilized.

[33] As the speed of the film is kept constantly in the MD (machine direction) direction, a drawing of the film is carried out in the TD direction, but not in the MD direction. The heat shrinkable film for shrink-wrapping the bottles should be drawn in the TD direction instead of in the MD direction because the film should be horizontally shrunk around the bottle but not longitudinally or vertically. If the film is shrunk longitudinally or vertically, the printed contents on the film are squeezed.

[34] In fact, although the film is not drawn in the MD direction, a little shrinkage about 1 to 5 % occurs in the MD direction when the film is applied to shrink-wrap the bottles. However, the little shrinkage is acceptable not to cause the printed contents squeezed.

[35] As shown in Fig. 1, the conventional process for preparing a heat shrinkable film consists of one step drawing process, which is publicly known to an ordinarily skilled person in the art.

[36] The new process for preparing a heat shrinkable film with a high shrinkage according to the present invention consists of two steps drawing process. In other words, after an undrawn film is first-drawn in the drawing machine, and the first- drawn film is continuously second-drawn. Fig. 2 is a schematic diagram of a process for preparing a heat shrinkable film with a high shrinkage according to the present invention, which comprises two step drawing systems. As shown in Fig. 2, two sets of drawing machine are lined in series.

[37] The first-drawn film is followed to feed into the second drawing machine to preheat again the film to an appropriate temperature for drawing at heating section 1 '. The temperature at the heating section is not uniform. The temperature is low at the introducing part and increases along the end part. The temperature at heating section 1 will be different according to the material resin, and may be easily set by an ordinarily skilled person in the art.

[38] The film heated at heating section 1 ' is passing through drawing section 2' and second-drawn in the TD direction. The second-drawn film is passing through annealing section 3' and the polymer structure of the film is fixed. And, the film is passing through cooling section 4' and cooled slowly to become the polymer structure stabilized.

[39] The temperatures at the second drawing step are the same as at the first drawing steps, but they may be different one another. Usually the temperatures at the second step are determined depending on the residual heat of the first-drawn film, which will be easily carried out by an ordinarily skilled person in the art. Also, the temperatures at the second step depend on the type of resin, physical properties of the film to be required, other process conditions, etc. Although the temperatures may be set by an ordinarily skilled person, it is preferable to set the temperatures to a minimum of the drawing temperature of the resin if possible, thereby resulting in a high shrinkage over 60 %.

[40] For example, in a conventional process for preparing a PVC film, the temperature at the end of the heating section is about 103 °C, and the temperature at the drawing section is about 100 °C. On the other hand, in the process for preparing a PVC film according to the present invention, the temperature at the end of heating section 1 of the first step is about 93 °C which is lower than in the conventional process, and the temperature at drawing section 2 is about 90 °C. The temperatures at the second drawing machine are similar to those at the first drawing machine or a little bit lower than those, preferably about 1 to 5 °C lower. The temperatures at the second step depend on the type of resin, physical properties of the film to be required, other process conditions, etc.

[41] The draw ratio in the present invention comprising 2 steps drawing process is different from that of the conventional process comprising 1 step drawing process. In the conventional process, the draw ratio is in about 2.0 to 3.5. However, in the process of the present invention, the first drawing is carried out at the draw ratio of about 1.5 to 2.0, and the second drawing at the draw ratio of about 2.0 to 3.5.

[42] In the present invention, the first and second drawing steps may be carried out continuously or non-continuously. For the continuous process, as shown in Fig. 2, two sets of drawing machine are lined in series. The drawing machines have the same length in the MD direction. However, the second machine has a wider width in the TD direction than the first machine because a further drawing is carried out at the second machine. The installment of two sets of drawing machine can be easily done by an ordinarily skilled person in the art.

[43] On the other hand, the two step drawing according to the present invention may be carried out non-continuously. Thus, the second drawing is non-continuously carried out after the first drawing had been carried out. In the non-continuous process, the second machine has a wider width in the TD direction than the first machine because a further drawing is carried out at the second machine. The non-continuous process does not need a long place to install two sets of drawing machine in series. In the non- continuous process, two sets of drawing machine can be installed in parallel, or in separate places.

[44] The material resin includes a PVC resin, a PS (polystyrene) resin, and the like, which will have advantages and disadvantages, respectively. PVC resin has been widely used for the heat shrinkable film because PVC film is cheap, and excellent in printing, tubing, shrinkage, anti-chemicals. However, the conventional PVC film has a shrinkage up to 55 %. The present invention has solved this low shrinkage problem and provided a PVC film with a high shrinkage about 60 to 70 % through the two steps drawing process. In this invention, PVC resin can be preferably used as a material.

[45] PS resin can be also used in this invention. In particular, PS film can be used on PS bottles as a label. In this case, recycling is easier because the bottle and label are made of the same material.

[46] However, PS film can be preferably used on PET bottles as a label. In this case, the

PET and PS can be easily separated by gravity separation because the gravities of PET and PS are different. In the gravity separation, PS is floating in the water, but PET is sunk. The PS film for shrink-wrapping prepared by the two steps drawing process according to the present invention may have a high shrinkage about 60 to 70 %.

[47] The shrinking force of the PET and PS films are acceptable for a heat shrinkable film.

[48] The present invention will be discussed in detail in the following examples, and the following examples are submitted to illustrate but not to limit the scope of the appended claims.

[49]

[50] Comparative Example

[51]

[52] A shrinkable film of a thickness of 50 D was prepared from a PVC film in accordance with one step drawing process in a conventional drawing machine. The temperatures were 103 °C at the end part of the heating section, 101 °C at the drawing section, 93 °C at the annealing section, and 65 °C at the cooling section. The speed of the PVC film in the drawing machine was 60 m/min. This is one of conventional films for shrink-wrapping.

[53] Shrinkage and shrinking strength of the PVC film were measured and the results were shown in Table 1. The shrinkage was measured both in TD and MD directions after the film was submerged in a water tank for 10 seconds at the temperature of 100, 90, 80, and 70 ⁰C. As shown in Table 1, all the shrinkages were less than 55%. The shrinkage was calculated by the following equation.

[54]

[55] Shrinkage (%) = (length before shrinking -length after shrinking)/(length before shrinking) xlOO

[56]

[57] A tensile strength, tear strength, thickness, and static electricity of the PVC film were measured and the results were shown in Tables 2 to 5. The tensile strength and tear strength at three different spots were measured in the TD and MD directions, and their mean values were also shown. The thickness and static electricity at 10 different spots were measured, and their mean values were also shown. The PVC shrinkable film of the comparative example as a conventional film has tensile strength, tear strength, thickness, static electricity and shrinking strength within a proper range for a shrinkable film for shrink-wrapping.

[58]

[59] Example 1

[60]

[61] A shrinkable film of a thickness of 50 D was prepared from a PVC film in accordance with two steps drawing process of the present invention. The temperatures were 93 °C at the end part of the heating section 1, V, 91 °C at the drawing section 2, 2' 83 °C at the annealing section 3, 3', and 65 °C at the cooling section 4, 4'. The speed of the PVC film in the drawing machine was 60 m/min. The width of the undrawn film was 80 cm, the width of first-drawn film was 130 cm, and the width of the second- drawn film was 400 cm.

[62] Shrinkage and shrinking strength of the PVC film were measured and the results were shown in Table 1. The shrinkage was measured both in TD and MD directions after the film was submerged in a water tank for 10 seconds at the temperature of 100, 90, 80, and 70 °C. As shown in Table 1, the shrinkage at 100 °C in TD was 63 %.

[63]

[64] Example 2

[65]

[66] A shrinkable film was prepared in the same manner as in Example 1 except that the temperatures were 93 °C at the end part of the heating section 1, 1 ', 91 °C at the drawing section 2, 2' 83 °C at the annealing section 3, 3', and 65 °C at the cooling section 4, 4'.

[67] Shrinkage and shrinking strength of the PVC film were measured and the results were shown in Table 1. The shrinkage was measured both in TD and MD directions after the film was submerged in a water tank for 10 seconds at the temperature of 100, 90, 80, and 70 ⁰C. As shown in Table 1, the shrinkage at 100 °C in TD was 66 %.

[68] [69] Table 1 [70]

[71] [72] As shown in Table 1, the shrinkage is greater than 60 % at 90 and 100 °C in Examples 1 and 2 according to the present invention. Despite, the shrinkage at 90 and 100 °C of a conventional film in Comparative Example is not greater than 55 %. The films prepared in Examples 1 and 2 have a shrinking strength of less than 2 kg/D which are satisfied for a heat shrinkable film.

[73] [74] Table 2 [75]

[76] [77] Table 3

[79] [80] Tensile strength was measured for the films of Comparative Example and Examples 1 and 2, and shown in Table 2. Tear strength was measured for the films of Comparative Example and Examples 1 and 2, and shown in Table 3. The tensile strength and tear strength were measured at three different spots in TD and MD directions, and their each mean value is also shown. The films of Examples 1 and 2 are acceptable for a heat shrinkable film.

[81] [82] Table 4 [83]

(;M)

[84] [85] Table 5 [86] (ohms)

Mean

1 2 3 4 h H H 9 10 value

Comparative

13. 6 12.8 13 6 13 2 14 1 14 2 13. 8 13 2 12 ¹J 13.9 13.6

Example

Example 1 12. 8 13.1 13 8 13 6 14 2 14 6 13. 8 13 1 14 0 14.2 13.7

Example 2 13. 1 12.8 13 8 14 2 13 6 13 8 14. 6 13 1 14 2 14.0 13.7

[87] [88] Thickness and static electricity of the films of Comparative Example and Examples 1 and 2 were measured and the results are shown in Tables 4 and 5 above. The thickness and the static electricity were measured at 10 different spots and their mean value is also shown. The films of Examples 1 and 2 were observed to have a proper thickness and a static electricity.

[89] [90] Simple changes and modifications of the present invention can be easily employed by those who are ordinarily skilled in the art, and these changes and modifications are deemed to be with the scope of the present invention.

Claims

[1] A process for preparing a heat shrinkable film with a high shrinkage for shrink- wrapping bottles, which comprises: a first step of drawing comprising heating undrawn film at heating section 1 to an appropriate temperature for drawing, first-drawing the heated film at drawing section 2 in the TD direction, fixing the polymer structure of the first-drawn film at annealing section 3, and cooling the film at cooling section 4 so as to become the polymer structure stabilized; and a second step of drawing comprising heating the first-drawn film at heating section 1 ' to an appropriate temperature for drawing, second-drawing the heated film at drawing section 2' in the TD direction, fixing the polymer structure of the second-drawn film at annealing section 3', and cooling the film at cooling section 4' so as to become the polymer structure stabilized.

[2] The process as defined in Claim 1 wherein said first and second drawing steps are carried out continuously.

[3] The process as defined in Claim 1 wherein said first and second drawing steps are carried out non-continuously.

[4] The process as defined in Claim 1 wherein said first and second drawing steps are carried out at the minimum temperature for drawing.

[5] The process as defined in Claim 1 wherein the drawing temperature of said first drawing step is about 1-5 °C higher than the temperature of said second drawing step.

[6] The process as defined in Claim 1 wherein the draw ratio of said first drawing step is about 1.5-2.0 and the draw ration of said second drawing ratio is about 2.0-3.5.

[7] A heat shrinkable film with a high shrinkage for shrink-wrapping bottles, which is prepared by two steps drawing process comprising a first step of drawing comprising heating undrawn film at heating section 1 to an appropriate temperature for drawing, first-drawing the heated film at drawing section 2 in the TD direction, fixing the polymer structure of the first-drawn film at annealing section 3, and cooling the film at cooling section 4 so as to become the polymer structure stabilized, and a second step of drawing comprising heating the first- drawn film at heating section 1 ' to an appropriate temperature for drawing, second-drawing the heated film at drawing section 2' in the TD direction, fixing the polymer structure of the second-drawn film at annealing section 3', and cooling the film at cooling section 4' so as to become the polymer structure stabilized, wherein the heat shrinkable film has a shrinkage over 60 % and a shrinking strength below 2 kg/cm² at 100 °C. [8] The heat shrinkable film as defined in Claim 7 wherein said shrinkage is about

60-70% at 100 °C. [9] The heat shrinkable film as defined in Claim 7 or 8 wherein said film is prepared with PVC or PS resin. [10] An apparatus for preparing a heat shrinkable film with a high shrinkage for shrink-wrapping bottles, which comprises two drawing machines that are installed in series. [11] The apparatus as defined in Claim 10, wherein said drawing machines draws the film in TD direction. [12] The apparatus as defined in Claim 10, wherein the width of said first drawing machine is larger that the width of said second drawing machine. [13] The apparatus as defined in Claim 12, wherein the ratio of the width of said first drawing machine to the width of the undrawn film is about 1.5-2.0 and the ratio of the width of said second drawing machine to the width of said firs drawing machine is about 2.0-3.5.