Method for manufacturing polyamide laminated resin tubes, polyamide laminated resin tubes and packaging bags

Abstract

To provide a method for manufacturing a polyamide-based laminated resin tube that can effectively prevent occurrence of a waviness in a heat-sealing portion, and a polyamide-based laminated resin tube and packaging bag that hardly cause a waviness in a heat-sealing portion.SOLUTION: There is provided a method for manufacturing a polyamide-based laminated resin tube. The method for manufacturing a polyamide-based laminated resin tube comprises: a base tube extrusion molding step of melt-extruding a resin composition into a tubular shape through an annular die to obtain a base tube; a cooling step for cooling the base tube; a stretching step for biaxially stretching the cooled base tube; and an annealing step of annealing the stretched based tube. In the annealing step, a relaxation rate of the stretched base tube is controlled to be 75% or more and less than 90%.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for producing a polyamide-based laminated resin tube, a polyamide-based laminated resin tube, and a packaging bag. [Background Art]

[0002] Conventionally, tube films containing a polyamide-based resin such as nylon resin have been widely used in various fields because of their gas barrier properties, and when stretched, they provide a film with toughness. For example, a tube film consisting of three layers: an outermost layer, an intermediate layer, and an innermost layer, is widely used for packaging. The polyamide-based laminated resin tube film as described above is used, for example, as a packaging bag for foods distributed in the market. In such use, the polyamide-based laminated resin tube film is cut into a predetermined length, and heat sealing is performed on both sides and the cut portion to form a packaging bag having a side seal portion and a bottom seal portion, i.e., a three-side sealed packaging bag. However, this process causes large undulations and wrinkles in the sealed portion. When several hundreds of such packaging bags are stacked to form a bundle, there has been a problem that the overlapping portions of the sealed portions bulge significantly larger than other portions, for example, the central portion of the packaging bags. As a result, the number of packaging bags that can be contained in one bundle decreases, and when a large number of packaging bags are forcibly stacked, there is a risk that the bundle may collapse, leading to a problem of poor transportation and conveyance efficiency. [Prior Art Literature] [Patent Literature]

[0003] [Patent Literature 1] Japanese Unexamined Patent Application Publication No. 2017-2114 [Patent Literature 2] Japanese Unexamined Patent Application Publication No. 2021-154661 [Summary of the Invention] [Problem to be Solved by the Invention]

[0004] The present invention was made to solve these problems and aims to provide a method for manufacturing polyamide laminated resin tubes that can effectively suppress the occurrence of warping in the heat-sealed portion. It also aims to provide polyamide laminated resin tubes and packaging bags that are less prone to warping in the heat-sealed portion. [Means for solving the problem]

[0005] The object of the present invention is a method for manufacturing a polyamide laminated resin tube, comprising: an extrusion tube forming step of melt-extruding a resin composition into a tubular shape from an annular die to obtain a base tube; a cooling step of cooling the base tube; a stretching step of biaxially stretching the cooled base tube; and an annealing step of annealing the stretched base tube, wherein the annealing step is controlled so that the relaxation rate of the stretched base tube is 75% or more and less than 90%.

[0006] In the above-described method for manufacturing a polyamide-based laminated resin tube, the cooling step is preferably a step of rapidly cooling the surface temperature of the raw tube to 30°C or below.

[0007] Furthermore, the aforementioned object of the present invention is achieved by a laminated resin tube comprising an outermost layer mainly composed of a polyamide resin and a polyester elastomer, an intermediate layer mainly composed of a modified polyethylene resin, and an innermost layer mainly composed of a polyethylene resin, characterized in that the thermal shrinkage rate after heat treatment for 5 minutes at a temperature range of 145°C to 165°C is 4.5% to 14%.

[0008] Furthermore, the aforementioned object of the present invention is achieved by a packaging bag manufactured using the above-mentioned polyamide laminated tube. [Effects of the Invention]

[0009] According to the present invention, it is possible to provide a method for manufacturing a polyamide-based laminated resin tube that can effectively suppress the occurrence of warping in the heat-sealed portion. Furthermore, it is possible to provide a polyamide-based laminated resin tube and packaging bag that are less prone to warping in the heat-sealed portion. [Brief explanation of the drawing]

[0010] [Figure 1] This is a block diagram illustrating a method for manufacturing a polyamide-based laminated resin tube according to one embodiment of the present invention. [Figure 2] This is a schematic diagram illustrating the curl state of the cut surface in a polyamide laminated resin tube. [Figure 3] (a) is an image of the side seal portion of the heat-sealed polyamide laminated resin tube according to Example 1, and (b) is an image of the bottom seal portion. [Figure 4] This image shows the raised state of the seal portion when 400 polyamide laminated resin tubes according to Example 1 are stacked. [Figure 5] This is an image of the sealed portion of a heat-sealed polyamide laminated resin tube according to Comparative Example 1. [Modes for carrying out the invention]

[0011] Hereinafter, a method for manufacturing a polyamide-based laminated resin tube according to one embodiment of the present invention will be described with reference to the attached drawings. As shown in the block diagram of Figure 1, the method for manufacturing a polyamide-based laminated resin tube according to the present invention comprises an extrusion raw material molding step S1, a cooling step S2, a stretching step S3, and an annealing step S4.

[0012] Here, the polyamide-based laminated resin tube suitably manufactured by the method for manufacturing polyamide-based laminated resin tubes is a laminated resin tube with a three-layer structure having an outermost layer, an intermediate layer, and an innermost layer. The outermost layer is a layer mainly formed of polyamide-based resin and polyester-based elastomer, the intermediate layer is a layer mainly formed of modified polyethylene-based resin, and the innermost layer is a layer mainly formed of polyethylene-based resin. Note that "mainly formed" means that it is permissible to include other components besides the target component and does not limit the content of the component, but usually it means that the content of the target component to the total layer components accounts for 50% by weight or more. Preferably, it means that the content accounts for 70% by weight or more, and more preferably 80% by weight or more to 90% by weight or more. The content may also be 100% by weight.

[0013] Furthermore, the outermost layer is, for example, the layer formed on the outside that does not come into contact with food when a packaging bag for packaging food is manufactured using the polyamide-based laminated resin tube according to the present invention. Examples of polyamide resins that can be used for the outermost layer include polyamides produced by polycondensation of ω-amino acids or copolymerization of diamines and dicarboxylic acids. Examples of polyester elastomers that can be used for the outermost layer include modified polyester elastomers. These modified polyester elastomers are obtained by modifying a saturated polyester thermoplastic elastomer containing a polyalkylene ether glycol segment with an unsaturated carboxylic acid or a derivative thereof.

[0014] The appropriate blending ratio of polyester elastomer in the polyamide-based laminated resin tube according to the present invention is within the range of 4 to 10% by weight, when the resin component constituting the outermost layer is considered to be 100% by weight. When the blending ratio of polyester elastomer is within this range, a polyamide-based laminated resin tube with excellent pinhole resistance in a frozen environment can be obtained. Furthermore, while the blending of polyester elastomer tends to reduce the strong puncture resistance inherent in polyamide resins, the reduction in puncture strength can be minimized when the blending ratio is within the above range of 4 to 10% by weight. Among these, a range of 5 to 7% by weight is preferable. In addition, inorganic or organic additives may be blended into the outermost layer as needed. Examples of such additives include antiblocking agents, nucleating agents, water repellents, antioxidants, heat stabilizers, and metal soaps.

[0015] The intermediate layer is a layer provided between the outermost layer and the innermost layer. Modified polyethylene resins that can be used in the intermediate layer include, for example, modified versions of low-density polyethylene (LDPE) and linear low-density polyethylene (LLDPE). Acid-modified materials are examples of modified materials, and maleic anhydride-modified polyolefins are preferred. The intermediate layer may consist only of modified polyethylene resin, but inorganic or organic additives, such as pigments, dyes, antioxidants, and heat stabilizers, can be appropriately blended as needed.

[0016] The innermost layer is a layer formed on the inner side that comes into contact with food when, for example, a packaging bag for packaging food is produced using the polyamide-based laminated resin tube according to the present invention. The polyethylene-based resin that can be used for the innermost layer is an ethylene homopolymer or a copolymer containing ethylene as a main component. Specific examples thereof include branched low-density polyethylene, linear low-density polyethylene, and high-density polyethylene. Other polyethylene-based resins may also include copolymers or multi-component polymers of ethylene with (meth)acrylic acid, itaconic acid, maleic anhydride, vinyl acetate, vinyl propionate, etc., and may be random copolymers or block copolymers. The innermost layer may be composed of only the above polyethylene-based resin, but may be formed by blending inorganic or organic additives as necessary. Examples of the additives include lubricants such as erucic acid amide and stearic acid amide, anti-blocking agents (silica, talc, kaolin, etc.), slip agents, polyethylene wax, antioxidants and heat stabilizers, and dyes and pigments for coloring.

[0017] The total film thickness of the polyamide-based laminated resin tube is not particularly limited since it can be appropriately set according to the application and other factors, but is usually about 20 to 100 µm, preferably about 25 to 80 µm, and more preferably about 30 to 60 µm. The film thickness of each layer is generally as follows: the outermost layer is about 5 to 50 µm, preferably about 10 to 40 µm, more preferably about 12 to 30 µm; the intermediate layer is about 2 to 15 µm, preferably about 3 to 10 µm, more preferably about 4 to 8 µm; and the innermost layer is about 5 to 50 µm, preferably about 10 to 40 µm, more preferably about 12 to 30 µm.

[0018] In the method for producing a polyamide-based laminated resin tube according to the present invention, the extrusion raw tube forming step S1 is a step of obtaining a raw tube by continuously melt-extruding a resin composition into a tubular (cylindrical) shape from an annular die. This extrusion raw tube forming step S1 is implemented, for example, by an extrusion apparatus including a plurality of extruders and an annular die. More specifically, for example, the resin composition for forming the outermost layer, the resin composition for forming the intermediate layer, and the resin composition for forming the innermost layer are fed into each of three extruders set to an appropriate temperature, after melting and kneading the resin in each extruder, the resin compositions are co-extruded into a tubular shape with an annular die having a multilayer structure to form the raw tube. As the extruder and the annular die, various conventionally known extruders and annular dies can be used.

[0019] The tubular raw tube formed by the extrusion raw tube forming step S1 is guided to a cooling device, and the cooling step S2 is performed. This cooling step S2 is a step of rapidly cooling the surface temperature of the raw tube to 30°C or lower, and it is preferable that the surface temperature of the raw tube is set to 30°C or lower after the completion of the extrusion raw tube forming step S1. Also, as the cooling device for cooling the tubular raw tube formed by the extrusion raw tube forming step S1, various conventionally used cooling devices can be used.

[0020] The raw tube after cooling that has undergone the cooling step S2 in the cooling device is guided to, for example, a stretching machine, and the stretching step S3 is performed. The stretching step S3 is a step of biaxially stretching the raw tube. In the stretching machine, the raw tube is heated under appropriate temperature conditions, air is sealed in to stretch the raw tube and impart orientation. At this time, it is preferable to stretch the raw tube so that the area draw ratio in the machine direction (MD direction) × transverse direction (TD direction) is 4 times or more. More specifically, it is preferable to perform stretching such that the draw ratio in the machine direction × transverse direction is 2 times × 2 times or more. As the stretching machine used in the stretching step S3, any conventionally known stretching machine can be used.

[0021] The raw material (stretched raw tube) after the stretching step S3 is completed is led to an annealing apparatus and subjected to annealing (annealing step S4). In this annealing step S4, the annealing process is carried out by reheating under appropriate temperature conditions. During the annealing process, the draw ratio of the raw tube (stretched raw tube) passing through the annealing tower is controlled to relax the stretched raw tube in the longitudinal direction (MD direction) to a desired degree of relaxation. In addition, the amount of air supplied into the stretched raw tube is controlled to relax the stretched raw tube in the transverse direction (TD direction) to a desired degree of relaxation. By pre-setting the draw ratio of the raw tube (stretched raw tube) passing through the annealing tower and the amount of air supplied into the stretched raw tube in the control device of the annealing apparatus, the relaxation rates in the longitudinal direction (MD direction) and transverse direction (TD direction) of the stretched raw tube can be controlled to the desired values.

[0022] Here, during the annealing process, it is preferable to set the surface temperature of the tube immediately after exiting the annealing tower to be within the temperature range of 90°C to 120°C, and more preferably within the temperature range of 95°C to 115°C. The surface temperature of the tube immediately after exiting the annealing tower can be set to the above temperature range by adjusting the movement speed (time) within the annealing tower and the ambient temperature. Furthermore, it is preferable that the drive of the annealing apparatus is controlled so that the relaxation rate during the annealing process for the stretched original tube is within the range of 75% to less than 90%, more preferably 78% to 88%, in both the longitudinal (MD direction) and transverse (TD direction).

[0023] The annealed raw material (polyamide laminated resin tube) is, for example, wound onto a winding machine to form a tube film roll with a predetermined folding width, which is then used for subsequent inspection processes.

[0024] Furthermore, the polyamide laminated resin tube according to the present invention can be formed into a packaging bag by an automatic packaging machine or the like using a conventional method. Specifically, a packaging bag having an opening on one side can be obtained by cutting the polyamide laminated resin tube to a predetermined length and heat-sealing one of the cut portions with both sides of the tube film which are configured to a predetermined fold width. The contents to be packaged in the packaging bag are not particularly limited as long as they can be packaged, but it is preferable that the contents be distributed in a frozen environment after packaging. Examples include meat such as pork and chicken and processed foods thereof, fish fillets and processed foods thereof, etc.

[0025] The present invention will be described in more detail below with reference to examples, but the present invention is not limited in any way by these examples. [Examples]

[0026] A laminated resin film with a three-layer structure, having an outermost layer thickness of 15 μm, an intermediate layer thickness of 5 μm, and an innermost layer thickness of 15 μm, was formed by the above manufacturing method. A mixed composition consisting of a polyamide resin and a polyester elastomer was used as the resin composition for forming the outermost layer. The mixing ratio was 94 parts by weight of the polyamide resin and 6 parts by weight of the polyester elastomer. The polyamide resin used was nylon-6 (density 1140 kg / m³). 3 (relative viscosity 4.08, melting point 220℃) is used, and as a polyester elastomer, polyester elastomer (density 1060 kg / m³) is used. 3 (MFR=34, melting point 145℃) was used as the resin composition for forming the intermediate layer. 3 A resin with an MFR of 2.9 and a melting point of 90°C was used. Furthermore, the resin composition forming the innermost layer was C8 metallocene polyethylene (density 916 kg / m³). 3 A mixture of C8 metallocene polyethylene (MFR=1.0, melting point 122°C) with erucic acid amide (lubricant) was used. For the resin composition forming the innermost layer, 99 parts by weight of C8 metallocene polyethylene and 1 part by weight of erucic acid amide (lubricant) were used.

[0027] In the cooling step S2 of this Example 1, after the completion of the extruded tube molding step S1, the tube is cooled to a surface temperature of 30°C. In the stretching step S3, the tube is formed with a stretch ratio of 3.0x3.3x in the longitudinal and transverse directions. In the annealing step S4, the laminated resin film surface temperature is set to 104°C, and the annealing relaxation ratio is set to 80%x85% in the longitudinal and transverse directions. [Examples]

[0028] The laminated resin film was formed in the same manner as in Example 1, except that the outermost layer had a thickness of 19 μm, the middle layer had a thickness of 5 μm, and the innermost layer had a thickness of 15 μm. [Examples]

[0029] The laminated resin film was formed in the same manner as in Example 1, except that the outermost layer had a thickness of 15 μm, the middle layer had a thickness of 5 μm, and the innermost layer had a thickness of 21 μm. Comparative Example 1

[0030] The process was carried out in the same manner as in Example 1, except that in the stretching step S3, the stretching ratio was set to be 3.0 times × 3.3 times in the longitudinal direction × transverse direction, in the annealing step S4, the annealing treatment was performed under conditions that the surface temperature of the laminated resin film was 104°C, and the annealing relaxation ratio was set to be 90% × 98% in the longitudinal direction × transverse direction, and in the cooling step S2, the surface temperature of the original tube was cooled to 40°C after the completion of the extruded original tube molding step S1.

[0031] The polyamide-based laminated resin tubes produced in Examples 1-3 and Comparative Example 1 were obtained by winding them onto a winding machine as tube film rolls with a folded width of 200 mm.

[0032] The polyamide-based laminated resin tubes according to Examples 1-3 and Comparative Example 1 were evaluated for pinhole resistance, heat shrinkage, bag-making properties, and appearance.

[0033] Regarding the evaluation of pinhole resistance, puncture strength and scratch resistance were evaluated. For puncture strength evaluation, the puncture strength was measured according to the measurement method compliant with JIS Z-1707 (1997). Specifically, the test specimen was fixed, and a semicircular needle with a diameter of 1.0 mm and a tip radius of 0.5 mm was punctured at a speed of 50 mm per minute, and the maximum stress until the needle penetrated was measured. Five test specimens were used, and the average value was calculated as the measurement result.

[0034] For the scratch resistance evaluation, a test specimen was attached to a jig consisting of a weight-shaped aluminum fixture with a semicircular needle (1.0 mm in diameter, 0.5 mm in radius) at its tip. The needle tip was then brought into contact with an aluminum plate (surface roughness Ra=0.02) via the test specimen. A 200 g load was then applied to the jig. The jig was moved back and forth parallel to the aluminum plate at a speed of 4000 mm / min over a travel distance of 10 mm. A tester was placed on both the jig and the aluminum plate. Measurement was stopped when a pinhole appeared in the test specimen, indicating electrical conductivity, and the number of reciprocations was measured. This evaluation was conducted using a Shinto Scientific Surface Quality Measurement Device TYPE:14DR.

[0035] For heat shrinkage, the obtained polyamide laminated resin tube was cut to a length of 150 mm, and cross lines 100 mm in the MD direction and 100 mm in the TD direction were drawn on the center of the tube with an oil-based marker. The obtained sample was placed in a dry heat gear oven (manufactured by Toyo Seiki Seisakusho Co., Ltd.) heated to a predetermined temperature for 5 minutes, and the length of the cross lines after heat treatment was measured in both the MD and TD directions. The dry heat shrinkage rates in the MD and TD directions were calculated using the following formulas. The dry heat temperature was varied in 10°C increments within the temperature range of 100°C to 190°C. <Formula 1> Dry heat shrinkage rate (%)=(100―L / 100)×100 L: Length of the crosshairs after heat treatment

[0036] The bag-making properties were evaluated by cutting the obtained polyamide laminated resin tube in the width direction and leaving it in an environment with a temperature of 35°C and a humidity of 80% for 24 hours, then checking the curl state at the cut surface. If a large curl occurs at this cut surface, it becomes difficult to stack many laminated resin tubes. In addition, when sealing contents into a bag with a three-sided seal (a seal form in which the cut portion and both sides of the tube film, which are configured to a predetermined fold width, are heat-sealed) or one-sided seal (a seal form in which the cut portion is heat-sealed), if curl occurs at the cut surface of the laminated resin tube, the workability will be poor. Furthermore, when checking the curl state at the cut surface, as shown in the schematic cross-sectional view of Figure 4, the evaluation is performed by measuring the angle θ between the tangent line S at the tip of the curled cut surface and the imaginary line T along the longitudinal direction of the laminated resin tube.

[0037] Regarding the appearance, the obtained polyamide laminated resin tube was cut to a length of 2m, and the surface was visually inspected to see if any deformation had occurred by holding both ends of the tube. In addition, the total light transmittance and haze value were measured using a direct-reading haze meter manufactured by Toyo Seiki Seisakusho Co., Ltd. Furthermore, the obtained polyamide laminated resin tube was cut to a length of 300mm, and one cut portion and both sides of the tube film were heat-sealed (three-sided seal). The occurrence of warping at this heat-sealed portion was visually evaluated, and the degree of bulging at the seal portion when 400 heat-sealed laminated resin tubes (tube films) were stacked was checked.

[0038] The following describes the evaluation results for pinhole resistance, heat shrinkage resistance, bag-making properties, and appearance. First, Table 1 shows the evaluation results for pinhole resistance. From Table 1, it can be seen that all of Examples 1-3 and Comparative Example 1 have a puncture strength of 10N or more and scratch resistance that can withstand more than 200 back-and-forth cycles, indicating that there are no problems with pinhole resistance.

[0039] [Table 1]

[0040] Table 2 shows the dry heat shrinkage rates in the MD and TD directions when the dry heat temperature is varied in 10°C increments within the range of 100°C to 190°C. In Table 2, the heat shrinkage rate at 145°C is calculated as the arithmetic mean of the heat shrinkage rates at 140°C and 150°C, and the heat shrinkage rate at 165°C is calculated as the arithmetic mean of the heat shrinkage rates at 160°C and 170°C. From the results in Table 2, it can be seen that the laminated resin tubes of Examples 1 to 3 have significantly smaller heat shrinkage rates in both the MD and TD directions compared to Comparative Example 1. In particular, in the dry heat temperature range of 100°C to 150°C, the heat shrinkage rate in both the MD and TD directions is 10% or less, which is approximately 50% or less of the heat shrinkage rate in Comparative Example 1. Furthermore, while a temperature range of 145°C to 165°C is assumed for heat sealing, in this temperature range, Examples 1 to 3 exhibit a heat shrinkage rate of 4.5% to 14%. More specifically, the heat shrinkage rate in the MD direction is 8% to 13.5%, and the heat shrinkage rate in the TD direction is 4.5% to 10.5%, which is about 70% or less of the heat shrinkage rate in Comparative Example 1. From this, it can be seen that the laminated resin tubes of Examples 1 to 3 can effectively suppress the occurrence of warping and wrinkling in the heat-sealed portion compared to the laminated resin tube of Comparative Example 1.

[0041] [Table 2]

[0042] Table 3 shows the results of the evaluation of bag-making properties (cut surface curl), shape sagging evaluation, total light transmittance, haze value, occurrence of waviness in the heat-sealed portion, and the state of the raised seal portion when 400 heat-sealed laminated resin tubes (tube films) are stacked. Figure 5 shows an image of the heat-sealed portion of the heat-sealed laminated resin tube according to Example 1, and Figure 6 shows an image of the raised seal portion when 400 laminated resin tubes (tube films) according to Example 1 are stacked. Figure 5(a) is an image of the side seal portion, and (b) is an image of the bottom seal portion (seal portion at the cut portion).

[0043] [Table 3]

[0044] In Examples 1 and 2, slight curling of the cut surface occurred within 45 degrees, and in Example 3, curling of the cut surface occurred within an acceptable range of 45 to 90 degrees. On the other hand, in Comparative Example 1, curling of the cut surface occurred within 180 to 360 degrees. Thus, it was confirmed that the laminated resin tubes in Examples 1 to 3 did not exhibit significant curling at the cut surface and were easy to heat seal.

[0045] Furthermore, regarding the evaluation of shape deformation, no shape deformation that would be problematic in use was observed in Examples 1 to 3 and Comparative Example 1, and it was confirmed that they had a good appearance.

[0046] Furthermore, the total light transmittance was approximately the same for Examples 1 to 3 and Comparative Example 1. In addition, regarding the haze value, the laminated resin tubes of Examples 1 to 3 showed a smaller value compared to Comparative Example 1, confirming improved transparency.

[0047] Furthermore, regarding the occurrence of warping in the heat-sealed portion, in all three examples (1 to 3), almost no warping was observed in the side seal portion. Although slight warping was observed in the bottom seal portion, it was deemed to be at a level that did not pose any problems during use. On the other hand, in the laminated resin tube according to Comparative Example 1, significant warping and wrinkles were observed, as shown in the image in Figure 5.

[0048] Furthermore, regarding the state of the raised seal portion when 400 heat-sealed laminated resin tubes (tube films) are stacked, it was confirmed that the laminated resin tubes according to Examples 1 to 3 had minimal raised seals and could be stacked neatly. On the other hand, in the case of the laminated resin tube according to Comparative Example 1, the raised seal portion was too large, resulting in the inability to stack 400 tubes.

[0049] Based on the above, the laminated resin tubes according to Examples 1 to 3, which are formed so that the relaxation rate in annealing step S4 is in the range of 75% to less than 90%, can reduce (minimize) the waviness generated at the seal portion, and even when many laminated resin tubes are stacked, the bulging at the seal portion can be suppressed and they can be stacked neatly, thereby improving the transportability of laminated resin tubes that are stacked in bundles of several hundred.

[0050] Furthermore, the inventors of the present invention, in addition to the above-mentioned Examples 1 to 3, manufactured laminated resin tubes by setting the cooling conditions in cooling step S2 to over 30°C, similar to Comparative Example 1. The pinhole resistance, heat shrinkage resistance, and bag-making properties of the obtained laminated resin tubes were substantially the same as those of Examples 1 to 3. On the other hand, regarding appearance, the haze value increased (to the 11% level) and transparency decreased (the evaluation results regarding appearance other than the haze value were the same as those of Examples 1 to 3). From this, it was confirmed that crystallization of the resin can be suppressed by cooling the surface temperature of the raw tube to 30°C or below after the completion of the extrusion raw tube molding step S1, and the transparency of the obtained laminated resin tube can be improved.

[0051] Furthermore, the inventors of the present invention have additionally manufactured laminated resin tubes in relation to Examples 1 to 3 above, by setting the relaxation rate during the annealing process in step S4 to 70% or more and less than 75% in both the longitudinal direction (MD direction) and the transverse direction (TD direction). The resulting laminated resin tubes showed reduced heat shrinkage and bag-making properties that were approximately the same as those of Examples 1 to 3, but were found to have inferior pinhole resistance. From this, it can be seen that setting the relaxation rate in annealing step S4 to 75% or more is preferable from the viewpoint of increasing the strength of the laminated resin tubes. [Explanation of Symbols]

[0052] S1 Extrusion raw material forming step S2 Cooling Step S3 Extension Step S4 Annealing Step

Claims

1. A polyamide-based laminated resin tube comprising an outermost layer mainly composed of a polyamide resin and a polyester elastomer, an intermediate layer mainly composed of a modified polyethylene resin, and an innermost layer mainly composed of a polyethylene resin, A polyamide-based laminated resin tube characterized by having a heat shrinkage rate of 4.5% to 14% after a 5-minute heat treatment at a temperature range of 145°C to 165°C.

2. A packaging bag manufactured using the polyamide-based laminated resin tube described in claim 1.

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