JP4485659B2 - Method for producing heat-shrinkable biaxially stretched laminated film - Google Patents

Description

[0001]
[Industrial application fields]
The present invention relates to a method for producing a polyamide-based heat-shrinkable laminated film that has excellent gas barrier properties and pinhole resistance and is suitably used for applications such as container lid materials.
[0002]
[Prior art]
Conventionally, as a packaging film having excellent gas barrier properties, a multilayer film in which a saponified ethylene-vinyl acetate copolymer (hereinafter referred to as EVOH) is sandwiched with a polyamide resin having excellent pinhole resistance and strength properties has been used. Yes.
[0003]
When the film is used for shrink wrapping, methods such as setting the heat treatment temperature after biaxial stretching low or lowering the relaxation treatment rate are used to impart heat shrinkability. Biaxial stretching treatment at ~ 200 ° C provides good stretchability and excellent dimensional stability in the width direction, but it is difficult to obtain a film with a high shrinkage rate suitable for tray shrink packaging applications. There was also a drawback that the stress at the time of shrinkage was too high and the tray was likely to be deformed.
[0004]
On the other hand, although a highly shrinkable film can be obtained by stretching in a low temperature region of 100 ° C. or lower, there is a problem that film cutting and apparatus troubles frequently occur due to an increase in stretching stress.
[0005]
[Problems to be solved by the present invention]
The present invention has been made to solve the above problems, and aims to gas barrier property superior, suitable tray shrink packaging, and manufactured to provide a method for producing easily polyamide highly shrinkable laminated fill beam To do.
[0006]
[Means for Solving the Problems]
The gist of the present invention is as follows.
It consists nylon 6 layer / EVOH layer / nylon 6 layer, extruding a laminated unstretched film is configured so that the thickness of the EVOH layer is 15 to 30% of the laminate film total thickness from a T-die, then the following conditions A method for producing a shrinkable biaxially stretched laminated film that is biaxially stretched simultaneously. EVOH represents a saponified product of ethylene-vinyl acetate copolymer.
Preheating temperature Tp (° C.) 60 ≦ Tp ≦ 75
Stretching temperature Ts (° C.) 75 ≦ Ts ≦ 90
Stretch zone passage time Rs (sec) 2.5 ≦ Rs ≦ 4.5
Heat treatment temperature Ta (° C.) 120 ≦ Ta ≦ 140
[0007]
DETAILED DESCRIPTION OF THE INVENTION
[0008]
The laminated film in the present invention has a two-layer / three-layer configuration consisting of nylon 6 layer / EVOH layer / nylon 6 layer. EVOH preferably has an ethylene component content of 25 to 35 mol%. A saponification degree of vinyl acetate of 96 mol% or more, preferably 99 mol% or more is excellent in gas barrier properties and strength, and is suitable.
If the ethylene content is less than 25 mol%, gels are likely to be formed, and if it exceeds 35 mol%, properties such as strength and gas barrier properties of the resulting film are undesirably lowered.
[0009]
The ratio of the EVOH layer to the total thickness of the laminated film needs to be in the range of 15 to 30%. If it is less than 15%, the gas barrier properties are insufficient, and the nylon 6 layer becomes thick, leading to an increase in shrinkage stress. On the other hand, if it exceeds 30%, the heat shrinkability is impaired.
[0010]
Moreover, it is preferable to set it as the range of 12-25 micrometers as thickness of the biaxially stretched laminated film in this invention. When the thickness is less than 12 μm, the shrinkage rate decreases, and when it exceeds 25 μm, the heat shrinkage stress increases, which is not preferable.
[0011]
Nylon 6 layer has lubricants and pigments such as talc, silica, alumina, magnesia, calcium carbonate, ethylenebisstearylamide, calcium stearate, heat stabilizer, antioxidant, plasticizer, mold release as long as the properties of the film are not impaired. An agent or the like can also be blended.
[0012]
The biaxially stretched laminated film obtained by the present invention has a shrinkage ratio in the longitudinal and transverse directions of 18 to 30%, preferably 20 to 25%, and no shrinkage stress when immersed in hot water at 90 ° C. for 5 minutes. 0.7 to 1.2 N / cm, preferably 0.74 to 1.15 N / cm. When the shrinkage rate is less than 18% or the shrinkage stress is less than 0.7 N / cm, tarmi or the like is generated and the practical performance as a shrink film for packaging is insufficient, the shrinkage rate exceeds 30%, or the shrinkage stress is 1 When it exceeds 2 N / cm, there is a problem that the tray is deformed when used as a substrate such as a tray.
[0013]
Next, the manufacturing method of the laminated film of this invention is described.
As a method for forming an unstretched sheet, several types of resin constituting each layer are melted with separate extruders, stacked in a multilayer structure in a feed block, and then extruded from a die (mono-manifold type). A multi-manifold method or the like in which several kinds of resins are extruded in a die on a multilayer structure can be used, but the multi-manifold method is preferable because of the high thickness accuracy of each layer. After co-extrusion from a T-die, a laminated unstretched sheet is obtained by quenching in the form of a cooling roll.
[0014]
It is necessary to preheat the obtained unstretched sheet at a temperature of 60 to 75 ° C. After that, by simultaneous biaxial stretching method, longitudinal, both laterally stretched in the range of 2.5 to 4.0 times. When the preheating temperature is less than 60 ° C., the film is easily broken during stretching, and the load on the stretching machine is large, so that troubles on equipment are likely to occur. On the other hand, when the preheating temperature exceeds 75 ° C., breakage during stretching tends to occur. When the draw ratio is less than 2.5 times, the mechanical strength and gas barrier properties of the obtained stretched film are lowered, and when it exceeds 4.0 times, the film is easily stretched and broken.
[0015]
The temperature of the simultaneous biaxial stretching zone must be in the range of 75 to 90 ° C., and the transit time must be in the range of 2.5 to 4.5 seconds . When the stretching temperature is less than 75 ° C., stretch breakage tends to occur. Moreover, when it exceeds 90 degreeC, a thermal contraction rate and gas-barrier property will fall. On the other hand, when the passing time of the stretching zone is less than 2.5 seconds or exceeds 4.5 seconds, stretching and cutting are likely to occur even in the temperature range.
[0016]
The stretched film needs to be heat-treated at a temperature of 120 to 140 ° C. If it exceeds 140 ° C., a sufficiently high shrinkage rate cannot be obtained, and if it is less than 120 ° C., troubles such as film breakage in the relaxation treatment zone and slipping out from the clip holding the end portion are likely to occur.
[0017]
The degree of relaxation treatment in the film width direction can be adjusted according to the application. In the present invention, the treatment can be performed at a relaxation rate of 1 to 6%.
[0018]
【Example】
Next, the present invention will be described more specifically with reference to examples.
In addition, the measuring method used for evaluation of an Example and a comparative example is as follows.
[0019]
(1) Film breaking frequency The operation for one day was performed, and the number of breaks of the film generated during that time was examined. It should be noted that breakage due to film formation failure of unstretched film and gripping failure of a stretching machine clip was excluded.
[0020]
(2) Hot water shrinkage rate / shrinkage stress A measurement sample obtained by cutting the film into a dimension of width 10 mm × length 100 mm in the vertical and horizontal directions was boiled in 90 ° C. hot water for 5 minutes, and then 20 ° C. and 65%. The dimensions after being allowed to stand for 2 hours under RH were measured, and the shrinkage ratio relative to the dimensions before the treatment was determined.
Also, loads were applied by hanging various weights on the measurement sample, the same boil treatment was performed, and the load conditions under which no dimensional change occurred before the treatment were examined, and the value was taken as the contraction stress.
[0021]
(3) Oxygen permeability Using OX-TRAN 2/20 manufactured by Modern Control, measured at 20 ° C. and 85% RH, and expressed in units of ml / m ² · day · MPa.
[0022]
(4) Evaluation of packaging state on tray LLDPE (19 μm) was laminated as an adhesive resin layer on the obtained laminated film and packaged on the top surface of a foamed tray made of PS (150 mm × 200 mm). Next, the packaged tray was passed through an oven heated to 120 ° C. for 10 seconds, and then the packaging state was observed. An article having excellent adhesion to the tray and having no deformation in the tray was judged good, and an article in which the remainder of the film in the square of the tarmi and the tray was produced, or an article in which the tray was deformed was rejected.
[0023]
In addition, the film raw material used for evaluation of an Example and a comparative example is as showing below.
(1) Nylon 6; A1030BRF manufactured by Unitika
(2) EVOH: Eval EP-F101BZ (ethylene copolymerization rate 32 mol%) manufactured by Kuraray Co., Ltd.
[0024]
Example 1
Nylon 6 is extruded from the first extruder at 250 ° C (X layer) using the T-die for two types and three layers, and EVOH is melted and extruded from the second extruder at a temperature of 225 ° C (Y layer). The sheets laminated in the order of X / Y / X with a multi-manifold type die are brought into close contact with a cooling drum whose temperature is adjusted to a surface temperature of 18 ° C. and rapidly cooled, and the thickness of each layer is X / Y / X = 60 / An unstretched film having a total thickness of 150 μm was obtained at 30/60 μm.
Next, the obtained unstretched film was guided to a stretching machine and simultaneously biaxially stretched through each zone adjusted to the preheating / stretching and heat treatment temperatures shown in Table 1 to obtain a stretched film having a thickness of 15 μm.
Stretching was stretched 3 times in the longitudinal direction and 3.3 times in the transverse direction, and the speed was adjusted so that the passing speed of the stretching zone was 3 seconds. The relaxation rate in the film width direction in the heat treatment zone was 5%.
In addition, the transit time of each zone is as follows.
Preheating zone 4.6sec
Stretch zone 3.0sec
Heat treatment zone 1 set 0.9sec
2 sets 1.6sec
3 sets 1.6sec
4 sets 1.4sec
[0025]
Examples 2-3
Except that the thickness of each layer is as shown in Table 1, it was extruded and stretched in the same manner as in Example 1 to obtain a stretched film having a thickness of 15 μm.
[0026]
[Table 1]
[0027]
As shown in Table 2, a film suitable for shrink packaging of a tray container having a high shrinkage rate and a low shrinkage stress can be obtained by a stable operation. Moreover, the gas barrier property is also good.
[0028]
Comparative Examples 1-2
Except for the thickness of each layer shown in Table 1, it was extruded and stretched in the same manner as in Example 1 to obtain a stretched film having a thickness of 15 μm.
[0029]
Comparative Examples 3-4
Extruded and stretched in the same manner as in Example 1 except that the obtained unstretched sheet was subjected to water absorption treatment at 55 ° C. for 60 seconds, and stretched under the thickness configuration shown in Table 1 and preheating / stretching temperature conditions. A stretched film having a thickness of 15 μm was obtained.
[0030]
Comparative Example 5
Except for stretching under the preheating / stretching temperature conditions shown in Table 1, extrusion and stretching were performed in the same manner as in Example 1 to obtain a stretched film having a thickness of 15 μm.
[0031]
Comparative Example 6
Except for stretching under the heat treatment temperature conditions shown in Table 1, extrusion and stretching were performed in the same manner as in Example 1 to obtain a stretched film having a thickness of 15 μm.
[0032]
Table 2 shows the evaluation results of the physical properties, stretchability, and packaging state of the stretched film obtained in the comparative example.
[0033]
[Table 2]
[0034]
【The invention's effect】
According to the present invention, a biaxially stretched laminated film with improved gas barrier properties and shrink wrapping properties can be obtained stably.

Claims (1)

A laminated unstretched film composed of 6 layers of nylon / EVOH layer / 6 layers of nylon and configured so that the thickness of the EVOH layer is 15 to 30% of the total thickness of the laminated film is extruded from a T-die, then under the following conditions: A method for producing a shrinkable biaxially stretched laminated film that is simultaneously biaxially stretched. EVOH represents a saponified product of ethylene-vinyl acetate copolymer.
Preheating temperature Tp (° C.) 60 ≦ Tp ≦ 75
Stretching temperature Ts (° C.) 75 ≦ Ts ≦ 90
Stretch zone passage time Rs (sec) 2.5 ≦ Rs ≦ 4.5
Heat treatment temperature Ta (° C.) 120 ≦ Ta ≦ 140