JPH0571032B2 - - Google Patents

Description

[Detailed description of the invention]

<Industrial Application Field> The present invention relates to a heat-shrinkable sheet, and more particularly, to a heat-shrinkable sheet that is shrink-wrapped in various packaging items. <Prior Art and its Problems> Conventionally, polystyrene-based films, polyethylene-based films, and the like have been known as films used for non-foamed layers of heat-shrinkable sheets. These non-foamed films are used as packaging materials for fragile containers, such as glass bottles, because they play a role in preventing fragments from scattering when the containers are shrink-wrapped, such as glass bottles, if they break. ing. By the way, as shown in Table 1, the above-mentioned polystyrene-based non-foamed film has excellent heat shrinkability, printability, and rigidity, but is relatively weak against impact and brittle. It is not possible to effectively prevent glass fragments from scattering when the glass is broken. Moreover, because of its relatively low melting point, it has poor heat resistance, making it unsuitable for retort sterilization at high temperatures, for example. In addition, in polyethylene non-foamed film,
Although it is excellent in terms of heat shrinkability and prevention of scattering of fragments when the container is broken, its rigidity and heat resistance are not very good, and its printability is also not good. For this reason, it has been proposed to use a non-foamed polypropylene film which has good heat resistance and prevents fragments from scattering when the container is broken. However, polypropylene-based non-foamed films are inferior to the above-mentioned polystyrene-based and polyethylene-based non-foamed films in terms of heat shrinkability.
Furthermore, it cannot be said to be better in terms of printability and rigidity than the polystyrene-based non-foamed film. Therefore, although it has excellent heat resistance and prevents fragments from scattering when containers are broken, it is difficult to develop heat-shrinkable sheets using polypropylene non-foamed films that have heat-shrinkability, printability, and rigidity. It is difficult to obtain. Table 1 shows the characteristics of such polystyrene-based non-foamed films, polyethylene-based non-foamed films, and polypropylene-based non-foamed films. In Table 1, PS stands for polystyrene, PE
indicates polyethylene, and PP indicates polypropylene.

[Table] In Table 1, the symbol ◎ is excellent, ○ is good, △ is fair.
× indicates not allowed.
<Purpose> This invention was made in view of the above problems, and improves heat shrinkability, printability, and rigidity, and improves production in packaging of items to be packaged at high temperatures, such as shrink packaging. It is an object of the present invention to provide a heat-shrinkable sheet that not only improves safety but also serves to prevent fragments from scattering when a container is damaged, thereby enhancing safety. <Means and effects for solving the problems> The heat-shrinkable sheet of the present invention for achieving the above object is made by laminating a non-foamed film layer and a foamed layer of polyolefin, both of which have heat-shrinkable properties. A heat-shrinkable sheet, wherein the polyolefin non-foamed film layer contains 60 to 95% by weight of an olefin polymer and 5 to 40% by weight of an inorganic filler, and the olefin polymer has a melting point of 120 to 145°C.
It is a propylene-based polymer in the range of . According to the heat-shrinkable sheet having the above structure, [] In general, an inorganic filler having a lower specific heat and higher thermal conductivity than the olefin polymer is added to the heat-shrinkable sheet.
Since it is contained at a proportion of 40% by weight, the specific heat of the heat-shrinkable sheet decreases and the thermal conductivity increases. Therefore, the heat shrinkage time of the non-foamed film layer can be shortened, and the heat shrinkage characteristics of the non-foamed film layer can be improved. [] Furthermore, since it is filled with an inorganic substance having high heat resistance, it is possible to further raise the heat distortion temperature to a desired temperature, thereby improving heat resistance. [] Furthermore, the rigidity of the non-foamed film layer can be increased due to the filling effect of the inorganic filler. This increases the compressive strength of the ring crush, and by forming it into a cylindrical shape, for example, it becomes easy to fit it into a bottle or the like, and productivity in shrink packaging can be increased. Moreover, the same filling effect can improve printability. [] Cushioning properties can be increased by laminating foam layers. The heat-shrinkable sheet according to the present invention will be explained in detail below. The heat-shrinkable sheet of the present invention is made by laminating a polyolefin-based non-foamed film layer and a foamed layer, both of which have heat-shrinkable property. , propylene-based polymers are suitable. Propylene-based polymers include isotactic polypropylene, syndiotactic polypropylene, atactic polypropylene; propylene-ethylene copolymer, propylene-α-olefin copolymer, propylene-diolefin copolymer, propylene-vinyl monomer copolymer, Propylene-ethylene-butene copolymer; Examples include copolymers such as polypropylene-acrylic acid copolymer, polypropylene-methacrylic acid, propylene-acrylic acid alkyl ester copolymer, propylene-methacrylic acid alkyl ester copolymer, etc. . Incidentally, the above copolymer may be a random, block or graft copolymer. Further, each of the above-mentioned polymers may be used alone or in a mixture of two or more. Among these, in order to provide heat resistance, the first
As can be seen from the table, propylene-based polymers are suitable, and propylene-ethylene copolymers or propylene-ethylene-butene copolymers are preferred as they exhibit greater flexibility (preventing bottle fragments from scattering). Olefin polymers with various molecular weights can be used, but in order to increase the stress during heat shrinkage and increase the stretching ratio, for example, those with a melt flow index (MFI) of 0.05 to 6.00 are recommended. is preferred. If MFI is less than 0.05, molding processability during extrusion molding will decrease, and if MFI exceeds 6.00, not only will shrinkage stress during heat shrinkage become small, but also uniform stretching and
Shrink packaging is not possible. Furthermore, problems such as volume thinning are more likely to occur. The above olefin-based polymer is heated at a temperature of, for example, 130°C.
Polymers with a melting point of 120 to 145°C are suitable so that they can be sterilized in a high-temperature retort for 20 minutes, and propylene-based polymers are suitable. If the melting point is less than 120°C, it will not be able to cope with the high temperatures during retort sterilization as described above, resulting in poor heat resistance, and if the melting point is 145°C or higher, it will be poor in heat shrinkability. The melting point herein refers to the crystal melting point peak temperature measured by differential thermal scanning (DSC). If a material with a melting point in this range is selected, the heat-shrinkable sheet will be less susceptible to thermal deformation since the inorganic filler will be contained in an amount of 5 to 40% by weight to 60 to 95% by weight of the olefinic polymer. Temperature, heat resistance, thermal conductivity, etc. can be further improved. Examples of inorganic fillers contained in olefinic polymers include powdered materials such as silica, mica, talc, diatomaceous earth, clay, calcium carbonate, titanium oxide, alumina, and barium sulfate. , talc or calcium carbonate are preferred. The above inorganic fillers may be used alone or in combination of two or more. Further, as the inorganic filler, one having an appropriate particle size is selected, and one having an average particle size of 30 μm or less is preferable. If the average particle size exceeds 30 μm, the smoothness of the film surface will be lost, the printing properties will be poor, and the appearance will be poor, which is disadvantageous. An average particle size of 20 μm or less is preferred. The filling amount of these inorganic fillers is 5 to 40% by weight, preferably 10 to 30% by weight, based on 60 to 95% by weight of the olefinic polymer. If the filling amount of the inorganic filler is less than 5%, there will be no filling effect as described above, and if it exceeds 40%, stretching will be hindered. The inclusion of such an inorganic filler can improve the shrinkability even when a polypropylene polymer with poor heat shrinkability is used, and also improves the printability, rigidity, etc. of the heat shrinkable sheet. In addition, since the rigidity can be improved, the cylindrical non-foamed film can be easily fitted into a bottle etc. during shrink packaging, and workability can be improved. A non-foamed polypropylene film containing such an inorganic filler is stretched to provide heat shrinkability. The heat shrinkage rate of the non-foamed film can be set as appropriate depending on the form of the packaged item, but for example, as mentioned above, it contains 5 to 40% by weight of an inorganic filler. In this case, with respect to the uniaxial direction of the unwrapped film,
It is preferably at least 40% or more, and -10 to 10% with respect to the direction orthogonal to the axial direction of the non-wrapping film. Heat shrinkage rate in stretching direction (uniaxial direction) is 40%
If the shrinkage rate is less than the above range, it will be difficult to tightly shrink-wrap the packaged item, and if the shrinkage rate in the direction orthogonal to the stretching direction is outside the above range, it will be difficult to thermally shrink the product in a healthy manner. Note that, in the heat-shrinkable sheet, a foamed sheet is laminated as a foamed layer inside the non-wrapping film in order to ensure cushioning properties and protect, for example, a glass bottle or the like as an object to be packaged from impact. in this case,
When this foamed layer contains 10 to 30% by weight of the above-mentioned inorganic filler, the rigidity, thermal conductivity, etc. of the foamed layer can be improved. The materials for this foam sheet include not only olefin polymers such as polyethylene and polypropylene, but also polyesters such as polyethylene terephthalate, styrene polymers such as polystyrene, high impact polystyrene, styrene-butadiene copolymer, and many others. I can give an example. Among these, the foamed sheet is stretched in the same way as the non-foamed film and has an appropriate heat shrinkage rate. In addition, foaming agents for the foam sheet include carbon dioxide gas, nitrogen gas, etc., azo compounds such as azodicarbonamide, azide compounds such as terephthalazide, mixtures of bicarbonates such as sodium bicarbonate and citric acid, methane, Examples include hydrocarbons such as propane and butane, fluorinated hydrocarbons such as Freon 11 and Freon 12, and low boiling point liquids or gases such as esters and ketones. These blowing agents are
One type or a mixture of two or more types may be used in an appropriate amount depending on the expansion ratio, for example, 0.1 to 5.0% by weight. Also,
The foamed sheet is preferably made of the same polymer as the non-foamed film, particularly propylene-ethylene copolymer or propylene-ethylene-butene copolymer. The method for manufacturing a heat-shrinkable sheet of the present invention will be briefly explained below. The heat-shrinkable sheet can be manufactured by any suitable method, such as a program method using a circular die, an inflation method, or a method using a T-die. That is, a composition made of the above-mentioned material for a heat-shrinkable sheet is extruded into a film by a conventional method. At this time, in order to impart heat shrinkability to the extruded film, stretching is performed in at least one of the uniaxial flow directions. In addition, the stretching ratio may be adjusted so that the shrinkage rate of the heat-shrinkable sheet becomes the above-mentioned heat shrinkage rate, and conventional methods such as pin tenter method,
This can be carried out by any suitable method such as a clip tenter method or a roll stretching method, and it is usually preferable to stretch in a uniaxial direction. In order to obtain the heat-shrinkable sheet consisting of multiple layers, the non-foamed film is bonded to the non-foamed film using a solution type, hot melt type or other adhesive such as ethylene-vinyl acetate copolymer or propylene-vinyl acetate copolymer. The non-foamed film and the foamed sheet may be laminated together, or the non-foamed film and the foamed sheet may be melted and coextruded, and both may be laminated in a molten state. Further, in forming the laminated sheet, the foamed sheet may be stretched in advance to impart heat shrinkability, and then laminated with a stretched non-foamed film. After laminating the foamed sheet, both of the above may be stretched at the same time. <Examples> The present invention will be described in more detail below based on Examples. Note that the measurement conditions for the average particle system of the inorganic filler were based on JISZ8901. Further, the following examples are heat-shrinkable sheets with improved cushioning properties, which are formed by laminating foam layers. Example (A) 90% by weight propylene-ethylene-random copolymer with MFI 1.2, melting point 137°C and average particle size
A mixture of sodium bicarbonate and citric acid was added and injected as a blowing agent. (B) Also, 45% by weight of a propylene-ethylene-random copolymer with an MFI of 1.2 and a melting point of 137°C;
Propylene-ethylene- MFI5.5, melting point 132℃
45% by weight of random copolymer and 10% by weight of calcium carbonate with an average particle size of 0.07μm.
was added and injected. (C) Mix each mixture of (A) and (B) above with a diameter of 65 mm for (A) and (B).
The mixture of (A) was extruded at an extrusion rate of 19 kg/Hr, and the mixture of (B) was extruded at an extrusion rate of 6 kg/Hr with a diameter of 85 mm.
It was supplied to a 0.75mm circular die. (D) Using the circular die described above, a flat film was extruded to obtain a heat-shrinkable sheet consisting of a foam layer and a non-foam layer with a width of 530 mm, a thickness of 1.0 mm, and a basis weight of 662 g/ ^m2 . . (E) Next, this heat-shrinkable sheet is passed through a heating furnace at 100 to 120°C and a pair of preheating rolls with a surface temperature of 115°C, and after being sufficiently preheated, it is passed through a stretching roll with a surface temperature of 50°C. For example, 7 in the flow direction (MD)
Stretched twice. (F) Then, after cooling with a cooling roll with a surface temperature of 30℃, the width is 501mm, the thickness is 0.19mm, and the basis weight is 110g/m ²
A heat-shrinkable sheet was obtained. Example (A) 90% by weight of propylene-ethylene-random copolymer with MFI 1.2, melting point 137°C and average particle size 10μ
m and 10% by weight of talc were mixed. The same blowing agent as in the example was added to these. (B) Also, 40% by weight of a propylene-ethylene-random copolymer with an MFI of 1.2 and a melting point of 137°C;
Propylene-ethylene- MFI5.5, melting point 132℃
40% by weight of random copolymer and 20% by weight of calcium carbonate with an average particle size of 0.07μm.
was added and injected. (C) Each mixture of (A) and (B) above was treated in the same manner as in Example (C) above. (D) Similarly to the above example, a flat film was extruded using a circular die to form a film with a width of 530 mm consisting of a foamed layer and a non-foamed layer.
A heat-shrinkable sheet having a thickness of 0.95 mm and a basis weight of 659 g/m ² was obtained. (E) Next, this heat-shrinkable sheet was
(E) Processed in the same way as (F), width 505mm, thickness 0.16mm,
A heat-shrinkable sheet with a basis weight of 115 g/m ² was obtained. Example (A) 50% by weight of a propylene-ethylene-random copolymer having an MFI of 1.2 and a melting point of 137°C was mixed with 50% by weight of a propylene-ethylene-random copolymer having an MFI of 5.5 and a melting point of 132°C. The same blowing agent as in the example was added to these. (B) Also, 45% by weight of a propylene-ethylene-random copolymer with an MFI of 1.2 and a melting point of 137°C;
Propylene-ethylene- MFI5.5, melting point 132℃
45% by weight of random copolymer and 10% by weight of calcium carbonate with an average particle size of 0.07μm.
was added and injected. (C) Each mixture of (A) and (B) above was treated in the same manner as in Example (C) above. (D) Similarly to the above example, a flat film was extruded using a circular die to form a film with a width of 530 mm consisting of a foamed layer and a non-foamed layer.
A heat-shrinkable sheet having a thickness of 1.02 mm and a basis weight of 661 g/m ² was obtained. (E) Next, this heat-shrinkable sheet was
(E) Processed in the same way as (F), width 495mm, thickness 0.20mm,
A heat-shrinkable sheet with a basis weight of 112 g/m ² was obtained. Comparative Example (A) 50% by weight of a propylene-ethylene-random copolymer having an MFI of 1.2 and a melting point of 137°C was mixed with 50% by weight of a propylene-ethylene-random copolymer having an MFI of 5.5 and a melting point of 132°C. The same blowing agent as in the example was added to these. (B) Also, 50% by weight of a propylene-ethylene-random copolymer with an MFI of 1.2 and a melting point of 137°C,
Propylene-ethylene- MFI5.5, melting point 132℃
50% by weight of random copolymer was mixed. (C) Each mixture of (A) and (B) above was treated in the same manner as in Example (C) above. (D) Similarly to the above example, a flat film was extruded using a circular die to form a film with a width of 530 mm consisting of a foamed layer and a non-foamed layer.
A heat-shrinkable sheet having a thickness of 1.04 mm and a basis weight of 660 g/m ² was obtained. (E) Next, this heat-shrinkable sheet was
(E) Processed in the same way as (F), width 494mm, thickness 0.21mm,
A heat-shrinkable sheet with a basis weight of 110 g/m ² was obtained. Comparative Example (A) A 100% by weight propylene-ethylene copolymer having an MFI of 3.0 and a melting point of 162°C was prepared. The same blowing agent as in the example was added to this. (B) Also, 90% by weight of a propylene-ethylene copolymer having an MFI of 3.0 and a melting point of 162°C and 10% by weight of calcium carbonate having an average particle size of 7 μm were mixed. (C) Each of the materials (A) and (B) above was treated in the same manner as in Example (C) above. (D) Similarly to the above example, a flat film was extruded using a circular die to form a film with a width of 530 mm consisting of a foamed layer and a non-foamed layer.
A heat-shrinkable sheet having a thickness of 1.02 mm and a basis weight of 660 g/m ² was obtained. (E) Next, this heat-shrinkable sheet is passed through a heating furnace at 130°C and a pair of preheating rolls with a surface temperature of 130°C, and after being sufficiently preheated, it is passed through a stretching roll with a surface temperature of 50°C, for example, to It was stretched 7 times in the direction (MD). (F) After cooling with a cooling roll with a surface temperature of 30℃, width 496mm, thickness 0.20mm, basis weight 110g/
A heat-shrinkable sheet of m ² was obtained. The above examples, and comparative examples,
Table 2 shows the compressive strength, printability, wrinkles of the sheet at the bottom of the bottle, heat shrinkage rate, and heat resistance of each of the heat-shrinkable sheets obtained. In Table 2, the evaluation of printability was based on the degree of ink fixation in grabber printing. The wrinkles of the sheet at the bottom of the bottle were evaluated based on the quality of the fit at the bottom of the bottle when the heat-shrinkable sheet was shrink wrapped in a glass bottle with a capacity of 300 ml. The shrinkage rate is when the stretched heat-shrinkable sheet is exposed to hot air at 130°C for 15 seconds. Heat resistance was evaluated when the heat-shrinkable sheet attached to the bottle was exposed to steam at 130°C for 20 minutes. The compressive strength was determined by measuring ring crush, and the measurement conditions for ring crush (MD direction) were in accordance with JISP8126.

[Table] In Table 2, the symbol ◎ is excellent, ○ is good, △ is fair.
× indicates not allowed.
Thus, the heat-shrinkable sheet of the present invention not only increases the cushioning properties as a material property by laminating the foam layers, but also has excellent heat resistance, printability, bottle fragment scattering prevention properties, etc. due to the above-mentioned properties of the non-foamed film. This is clearly seen from Table 2 above. That is, each example contained 10 to 20% by weight of an inorganic filler in a non-packaged film and had a melting point of 132 to 137°C.
showed an extremely high heat shrinkage (MD) compared to, for example, a comparative example whose melting point was set at 145°C or higher, and was able to effectively exhibit the desired heat shrinkage. Furthermore, in terms of compressive strength, all comparative examples,
, and the rigidity was also good. <Effects of the Invention> As described above, according to the heat-shrinkable sheet of the present invention, a polyolefin non-foamed film layer and a foamed layer, both of which have heat-shrinkable properties, are laminated, and the foamed layer provides cushioning. In addition to improving properties, the non-foamed film layer contains 5 to 40% by weight of an inorganic filler.
The above polyolefin polymer has a melting point of 120-145℃
Since it is a propylene-based polymer in the range of
It not only maintains excellent printability and bottle fragment scattering properties, but also has excellent heat shrinkability, rigidity, and heat resistance. Therefore, for example, it facilitates shrink packaging, heat sterilization, etc., improves work efficiency and productivity, increases the protective effect of containers, and enhances safety when handling bottles. It has the unique effect of being able to

Claims (1)

[Scope of Claims] 1 A heat-shrinkable sheet comprising a laminated polyolefin-based non-foamed film layer and a foamed layer, both of which have heat-shrinkable property, wherein the polyolefin-based non-foamed film layer is made of an olefin-based polymer 60. 95% by weight and 5 to 40% by weight of an inorganic filler, wherein the olefin polymer is a propylene polymer having a melting point in the range of 120 to 145°C. 2. The heat-shrinkable sheet according to claim 1, wherein the propylene-based polymer is a propylene-ethylene copolymer or a propylene-ethylene-butene copolymer. 3. The heat-shrinkable sheet according to claim 1, wherein the inorganic filler has an average particle size of 30 μm or less. 4. The heat-shrinkable sheet according to claim 1 or 3, wherein the inorganic filler is talc or calcium carbonate. 5 The non-foamed film layer has a surface area of at least 40% in the uniaxial direction and -10% in the direction orthogonal to the axial direction.
The heat-shrinkable sheet according to claim 1, which has a heat-shrinkability of ~10%.