JPS6236855B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a multilayer container having a multilayer structure and a method for manufacturing the same, and more specifically to a blow molded container having a multilayer structure with improved design, physical properties, etc., and having a multilayer structure in which different types of resin are laminated. Regarding the manufacturing method. In recent years, hollow containers made of thermoplastic resin have become lighter and lighter.
Cosmetics, food, etc. due to its safety against bursting etc.
Widely used as containers for foodstuffs, medicines, etc. With the improvement of blow molding technology, especially biaxial stretch blow molding technology, the development of hollow containers made of polyethylene terephthalate having crystallinity and excellent mechanical properties is progressing rapidly. However, biaxially oriented containers made of thermoplastic polyester mainly composed of polyethylene terephthalate do not have perfect performance, especially as food containers whose contents require a high level of gas barrier properties. , is still unsatisfactory due to its lack of gas nolier performance against oxygen.
Further, depending on the contents to be filled, it is necessary to color the container, and it is also necessary to block ultraviolet rays. Normally, dyes and pigments, ultraviolet absorbers, etc. can be added to the thermoplastic resin before molding in order to impart these properties, but they may be extracted by the contents to be filled, causing hygiene problems, or It has disadvantages such as spoiling the flavor. In order to solve these drawbacks, attempts have already been made to create a multilayer structure using resins with different properties. However, when molding a multilayer parison of crystalline thermoplastic resin using the sequential lamination molding method (method of sequentially molding an inner layer, intermediate layer, and outer layer), which is a well-known manufacturing method for a multilayer parison, there may be fluctuations in cooling efficiency during molding, and Depending on the form of the multilayer parison, cloudiness may occur around the gate at the bottom of the multilayer parison, or haze may occur over the entire parison, making it difficult to obtain a transparent multilayer parison. As a result of investigating the cause of this, we found that in the case of crystalline thermoplastic resins, such as polyethylene terephthalate and polyamide, when they are rapidly cooled from a molten state, they freeze as a transparent amorphous state.
When molding the intermediate and outermost layers in the sequential injection molding method, the next injected molten resin flows over the amorphized surfaces of the innermost resin layer and the intermediate resin layer, and is cooled through the resin layers. Because of this, it was difficult to rapidly cool the resin layer, and in particular, both resin layers at the contact surface part were found to thermally crystallize and become cloudy. A multilayer parison which has undergone crystallization in this manner not only has poor blow moldability, but also has drawbacks such as a decrease in the interfacial adhesive force between both resins and a loss of physical properties of the resulting hollow container. The present inventors have solved the above-mentioned drawbacks, and created a multilayer container that has desired performance such as hygiene, design, chemical resistance, gas permeability, transparency, etc. by combining two or more types of thermoplastic resins. As a result of intensive research into manufacturing methods, the present invention has been achieved. That is, a molding method in which at least two types of molten thermoplastic resins are continuously and alternately injected into a single mold in a single mold clamping operation at staggered timing using a molding machine having multiple injection cylinders. At least the mouth opening end is formed by forming the first injected thermoplastic polyester resin mainly composed of ethylene terephthalate repeating units on the inner and outer surface layers, and the later injected thermoplastic metaxylylene group-containing polyamide resin forming the intermediate layer. A multilayer parison having a single layer structure in some parts and a multilayer structure of 3 or more layers in other parts is blow molded using pressurized fluid at a temperature of the polyester resin of (Tg + 15) °C or higher and (2Tg + 15) °C or lower. A method for manufacturing a blow-molded container having a multilayer structure, characterized by: The multilayer container of the present invention has many features such as excellent physical properties, design, and hygiene, as well as excellent interlayer adhesion. Furthermore, by using a thermoplastic resin with excellent gas permeability resistance for the intermediate layer, a multilayer container with excellent gas barrier properties can be obtained. Furthermore, by containing an ultraviolet absorber and/or dye and pigment in the intermediate layer, a multilayer container with excellent hygiene and design can be obtained. In particular, the multilayer structure container according to the present invention has a structure in which the opening end portion of the mouth part is made of a single layer of thermoplastic resin forming the innermost layer and the outermost layer, and the middle layer is wrapped so that it is not exposed to the surface. It has the characteristic that the blended additives do not elute or migrate into the filling contents, and the intermediate layer does not devitrify or change in quality due to the filling contents, and maintains excellent initial performance. Thermoplastic resins that can be used for the innermost and outermost layers of the multilayer container of the present invention include:
A thermoplastic polyester resin mainly containing ethylene terephthalate repeating units, which includes, for example, isophthalic acid, diphenyl ether 4,4'-dicarboxylic acid, naphthalene 1,4- as part of the terephthalic acid component. or 2,6-dicarboxylic acid, adipic acid, sebacic acid, decane 1,10-dicarboxylic acid, hexahydroterephthalic acid and/or as part of the ethylene glycol component, e.g. propylene glycol,
1,4-butanediol, neopentyl glycol, diethyleglycol, 1,6-hexylene glycol, cyclohexanedimethanol, 2,2
-bis(4-hydroxyphenyl)propane,
40% of one or more other glycols such as 2,2-bis(4-hydroxyethoxyphenyl)propane
Examples include resins copolymerized in a range of mol % or less, preferably 20 mol % or less. Alternatively, it may be a polyester resin copolymerized with an oxyacid such as oxyethoxybenzoic acid. In addition, polyester elastomers copolymerized with dimer acid as the acid component and polyether glycol as the glycol component, polyester elastomers copolymerized with caprolactone, and ionic polyesters copolymerized with a small amount of 5-sodium sulfoisophthalic acid as the acid component. It may be hot. Furthermore, blends of these homopolymers, copolymers, etc. may also be mentioned. The thermoplastic resin constituting the intermediate layer of the multilayer container of the present invention is a metaxylylene group-containing polyamide resin that has excellent gas permeability. In addition, by adding colorants and ultraviolet absorbers to the resin layer that constitutes the intermediate layer of the container, there is no fear that the additives will elute or migrate into the contents, improving the storage performance of the contents. Can be done. Examples of colorants that can be used in the present invention include perylene dyes and pigments, perinone dyes and pigments, anthrapyridone dyes and pigments, anthraquinone dyes and pigments, quinoline dyes and pigments, quinacridone dyes and pigments, condensed azo dyes and pigments, and phthalocyanine. pigments, carbon black, transparent titanium oxide, Bengara, triiron tetroxide, titanium yellow, cobalt violet, ultramarine blue, etc., and the amount of these added is usually 100% of the thermoplastic resin.
It is preferably 0.5 parts by weight or less. Furthermore, examples of the ultraviolet absorber that can be used in the present invention include benzophenone derivatives and benzotriazole derivatives. A group having ultraviolet absorbing ability can also be introduced into the molecular chain of the thermoplastic resin. Examples include thermoplastic resins in which an ethylenically unsaturated monomer having ultraviolet absorbing ability is copolymerized in the production of polyacrylic resins and polyolefin resins. When the purpose is a colored container, the thermoplastic resins constituting the intermediate layer and the inner and outer surface layers do not necessarily have to be different resins, but the intermediate layer is colored with the same type of thermoplastic resin and the inner and outer surface layers are made colorless. Multi-layer containers, or multi-layer containers in which the middle layer, inner and outer surface layers are different colors, or multi-layer containers in which the middle layer is colorless and the inner and outer surface layers are colored, when the coloring agent is not a sanitary problem or depending on the contents to be filled. etc., and in addition to improving the preservation performance of the contents, it also improves the design and
A highly hygienic hollow container can be obtained. In addition, as a thermoplastic resin constituting the intermediate layer,
Blends of at least two or more thermoplastic resins (for example, blends of polycarbonate resin and methyl methacrylate resin disclosed in Japanese Patent Publication No. 43-13384 and polycarbonate resins disclosed in Japanese Patent Publication No. 46-31467) By using a blend of acrylic resin, saturated aliphatic polyolefin resin, polystyrene resin, or aromatic polyester resin, etc.), or a blend of the above thermoplastic resin and natural or synthetic pearl foil, conventional molded products can be made. A hollow container with better chemical resistance, mechanical properties, and pearlescent luster can be obtained. Hereinafter, the method for manufacturing a multilayer container according to the present invention will be explained in more detail with reference to the drawings. Basically, a molding machine with multiple injection cylinders is used to continuously and alternately inject at least two types of thermoplastic resin into a single mold with staggered timing in one mold clamping operation. It is necessary to first form the multilayer parison using a machine or mold. In other words, while injecting one thermoplastic resin, the other thermoplastic resin is injected with a slight delay, and the injection of the thermoplastic resin to be injected later is stopped before the injection of the destination thermoplastic resin is stopped. , or inject one thermoplastic resin, and once the injection of the resin is stopped, inject the other thermoplastic resin almost simultaneously,
At the same time as the injection is completed, the same thermoplastic resin as the one previously injected is injected. Specifically, as shown in Fig. 1, a manufacturing method in which a plurality of injection molding machines (two in the figure) are connected to one nozzle and a laminated parison is produced by performing the above molding operation; As shown in Figure 2, instead of connecting the nozzles, we used a mold with a structure in which the gates at the tips of each runner in the mold were connected, and the operation of the gates and the operation of the injection molding machine were controlled. First, a multilayer parison is manufactured by a manufacturing method in which a laminated parison is manufactured by the above-described forming operations in conjunction with each other. To explain in more detail a typical manufacturing method using the apparatus shown in Figure 1, 1 is a mold, 2 is a nozzle, 3 and 3' are cylinders of an injection molding machine that injects different types of thermoplastic resins. The thermoplastic resin 4 starts to be injected from the cylinder 3 of one injection molding machine, and the timing is slightly delayed and the injection starts from the cylinder 3' of the other injection molding machine.
When another thermoplastic resin 5 is injected from the thermoplastic resin 5, the thermoplastic resin 5 flows without mixing with the unsolidified portion (that is, the intermediate layer portion) of the preceding thermoplastic resin 4. Alternatively, if thermoplastic resin 4 is injected from cylinder 3 of one injection molding machine, and at the same time when this is stopped, another thermoplastic resin 5 is injected from cylinder 3' of another injection molding machine, thermoplastic resin 5
flows without mixing the unsolidified portion of the preceding thermoplastic resin 4. As a result, a multilayer molded product is obtained in which the thermoplastic resin 4 injected first forms the inner and outer surface layers, and the thermoplastic resin 5 injected later forms the intermediate layer. In this case, it is important to inject the thermoplastic resin 5 before the preceding molten resin of the thermoplastic resin 4 is completely cooled and solidified within the mold. The cross section of this molded article shows a multilayer structure in which thermoplastic resin 4/thermoplastic resin 5/thermoplastic resin 4 are laminated in concentric circles. However, the cross section of the gate part has thermoplastic resin 5 in the center and thermoplastic resin 4 around it.
Since the finished product has a two-layer structure in which the thermoplastic resin 5 is coated concentrically, during injection molding, after the injection of the thermoplastic resin 5 is completed, an additional thermoplastic resin 4 is applied afterward to completely replace the gate part with the thermoplastic resin 4, and this cross section is It can also have a three-layer structure. When this molding method is adopted, each resin is layered in an extremely short time, injected into the mold, and rapidly cooled, so even if the resin used is a crystalline resin such as polyethylene terephthalate, each interface without giving enough time to induce crystallization.
Each resin layer is amorphized and a molded product with good transparency can be obtained. An ideal injection pattern during molding is shown in FIG. 3, and a schematic diagram of the resulting multilayer parison is shown in FIG. Figure 3 shows a graph in which the horizontal axis represents time and the vertical axis represents injection pressure.While polyethylene terephthalate (PET) is continuously injected as thermoplastic resin 4 at an injection pressure of _P1 , A program is shown in which meta-xylylene group-containing polyamide (SM) as the plastic resin 5 is injected for an arbitrary time with a delay of an arbitrary timing. Although the injection pressure of SM at this time is shown in the figure as being the same as P ₁ , it may be higher or lower than P ₁ . FIG. 4 is a cross-sectional view of a multilayer parison, showing that it has a structure in which an SM layer is sandwiched between PET layers. In the figure, the SM is stacked up to the vicinity of the threaded part 13 of the multilayer parison, but this flow position can be changed arbitrarily depending on the timing of injection of the SM. In short, at least the mouth opening end portion 14
is a single layer of PET, and the body portion 15 to be stretched is formed into multiple layers. The shape of the multilayer parison can be any expandable geometry. The thickness of the thermoplastic resin layer constituting the intermediate layer depends on molding conditions (plasticization capacity of thermoplastic resin 5, timing of injection of the resin, etc.), melt viscosity and crystallization rate of thermoplastic resins 4 and 5, etc. variable;
Usually, the ratio of the intermediate thermoplastic resin layer 5 to the total thickness of the innermost and outermost thermoplastic resin layers (resin 5 thickness/resin 4 thickness ratio) can be controlled to about 0.05 to 20. In the multilayer parison of the present invention, this ratio is preferably between 0.1 and 1. Depending on the injection timing of two types of thermoplastic resin during injection molding, the body part 1 away from the gate
5 may have three layers, and the gate area 16 may be slightly disordered to form a multilayer parison of three or more layers, and such a multilayer parison may also be used. Although the above description has mainly been about manufacturing a multilayer parison having a three-layer structure, it is also possible to use three or more molding machines to mold a multilayer parison having a more complicated structure. Furthermore, the thermoplastic resin forming the inner and outer surface layers and/or the intermediate layer may further contain an antistatic agent, a thermal oxidative deterioration inhibitor, an antibacterial agent, a lubricant, an ingredient that improves the adhesion between the two resins, and impact resistance. Additives such as incompatible and finely dispersible polymers that improve strength can be blended in appropriate proportions. In addition, viscosity increasing agents and viscosity reducing agents are added to change the thickness of each layer of the multilayer parison by combining with injection conditions, and a crystallization accelerator is added to form a multilayer parison with reduced transparency. You can also do that. The multilayer parison thus obtained is heated to a temperature range that allows stretching using a conventional biaxial stretching blow molding machine, and then expanded and stretched in a blow mold to produce a biaxially oriented container. As a result of a peel test using a sample cut out from the obtained container, when the multilayer parison of the present invention was used, the interfacial layer of both resins obtained by sequential molding had a higher density than when using a multilayer parison. , it is recognized that it has a high adhesive strength. When blow molded, the excellent effects of each of the plurality of thermoplastic resins can be effectively exhibited, and a hollow container having excellent physical properties, design properties, etc. can be provided. If desired, before blow molding, only the surface layer of the multilayer parison may be partially or entirely crystallized (made cloudy) by solvent treatment, heat treatment, etc., and then blow molded to obtain a hollow container having a ground glass surface. You can also do that. Normally, when using a polyester resin mainly composed of ethylene terephthalate repeating units, the temperature of the polyester resin is (Tg + 15) °C or higher and (2Tg +
15) Stretching is preferably carried out at a parison temperature below 0.degree. C., especially between 85 and 150.degree. Therefore, it is preferable to modify thermoplastic resins of different types by copolymerization, blending, etc. so that they can be stretched in this temperature range. The stretching ratio is usually about 1.1 to 4 times in the vertical direction and about 2 to 7 times in the horizontal direction (circumferential direction) (based on the circumferential length)
is preferable, and the area stretch ratio (vertical direction stretch ratio ×
The stretching ratio in the transverse direction is preferably about 5 to 8 times. A cross-sectional view of a typical example of the multilayer container of the present invention thus obtained is shown in FIG. Reference numeral 17 indicates a mouth opening end portion, and this portion has a single layer structure without an intermediate layer. Further, reference numeral 18 denotes a thin body portion, which has a multilayer structure of three or more layers, and is biaxially oriented by blow molding. The obtained multilayer container can be further heat-treated, if desired, to improve the dimensional stability under heat. Further, if desired, after forming into a parison stage and/or a container, it may be printed or subjected to a scratch-resistant treatment or the like. The present invention will be explained below with reference to Examples. Furthermore, methods for measuring the main characteristics measured in the present invention are shown below. (1) Inherent viscosity [η] of polyethylene terephthalate (PET); Measured at 30°C using a mixed solvent of phenol/tetrachloroethane = 6/4 (weight ratio). (2) Relative viscosity ηrel of metaxylylene group-containing polyamide (SM); 1 g of resin was dissolved in 100 ml of 96% sulfuric acid and measured at 25°C. (3) Density ρ; [Sample collection method] The multilayer parison was divided into an upper part, a middle part, a lower part, and a bottom part, and a cylindrical or dome-shaped sample with a width of 5 to 10 mm was obtained using a hacksaw. This was further divided into two semicircular shapes and mechanically separated into respective layers. Using this, a section up to 0.5 mm from the surface on the contact surface side was cut out using a cutter to obtain specimens for density measurement. [Density measurement method] For PET, a carbon tetrachloride-n-heptane density gradient tube is used;
For this, a carbon tetrachloride-toluene gradient tube was used, and the density value was calculated from the equilibrium resting position of the sample. (Measurement temperature in both cases was 30°C) (4) Transparency and haze: Calculated from the following formula according to JIS-K6714 using Hazemeter S manufactured by Toyo Seiki Co., Ltd. Transparency = T ₂ / T ₁ × 100 (%) Baize = T ₄ - T ₃ (T ₂ / T ₁ ) / T ₂ × 100 (%)
) T ₁ ; Incident light amount T ₂ ; Total light transmission amount T ₃ ; Scattered light amount by the device T ₄ ; Scattered light amount by the device and sample (5) Oxygen permeation amount; It was measured by pressure change at 30°C using a method according to ASTM-D-1434-58.
(cc/m ²・24hr・atm) (6) Water vapor permeation rate; 40℃ according to JIS-Z-0208,
It was measured from the weight increase by the Cupp method at 90% RH. (g/m ²・24 hours) Examples 1 to 10 Using an M-140-MJ injection molding machine manufactured by Meiki Manufacturing Co., Ltd., a multilayer structure having the structure shown in FIG. 4 consisting of various resin compositions shown in Table 1 was manufactured. Got parison. This parison has a bottomed test tube shape with an outer diameter of 35 mm, a length of 140 mm, and a wall thickness of 5 mm.The opening end of the mouth has a single-layer structure made of inner and outer resin layers, and the body has a three-layer structure. have The molding conditions and the thickness of each layer constituting the multilayer parison are summarized in Table 1. The details of the thermoplastic resin used are as follows. PET-1: Polyethylene terephthalate
[η] = 0.72 PET-2: Polyethylene terephthalate
[η] = 1.0 SM: Metaxylylene adipamide (methaxylylene/paraxylylene = 99/1 weight ratio) ηrel =
2.2

【table】

[Table] When the density value of the contact surface layer portion at the interface between each layer of the multilayer parison obtained in Example 1 was measured, the density value of the inner layer (PET) surface layer portion was 1.338 to 1.339 g/
cc The middle layer (SM) surface layer part is on both the inner layer side and the outer layer side.
1.206~1.208g/cc, outer layer (PET) surface part
1.338 to 1.339 g/cc, and it can be seen that both are in a highly transparent amorphous state. In addition, in place of PET, a copolymerized polyester mainly composed of ethylene terephthalate repeating units, Example 1
When similar molding was performed using SM with a different composition instead of the SM used in , the density of polyester was 1.33 to 1.345 g/cc, and the density of SM was 1.20 to 1.215.
g/cc and a multilayer parison with excellent transparency was obtained. On the other hand, in the parison molded by starting injection of PET and SM at the same time (Comparative Example 1), PET and SM were melted and mixed, resulting in a parison having a pearl-like appearance. The multilayer parison obtained in Example 1 and an outer diameter of 35 mm,
A transparent parison made of 100% PET with a wall thickness of 4 mm and a length of 140 mm (Comparative Example 2) (molding conditions: cylinder temperature 270 x 290 x 290 ℃ from the hopper side, injection pressure gauge pressure 40 Kg / cm ² , mold temperature 20 ℃, Injection holding time 15
25 seconds, injection cooling time 25 seconds) using a biaxial stretching blow molding machine, the moving speed of the stretching rod was 22 cm/sec, the compressed gas pressure was 20 Kg/cm ² , the stretching temperature was 130°C, and the stretching ratio was (2.04 in the axial direction x 2.04 in the circumferential direction). The container was blow molded under the condition of 2.74) = 5.59. The results are shown in Table 2.

Table: The blow-molded container obtained from the multilayer parison according to the invention had excellent gas (oxygen) permeability and transparency. In addition, the interlayer adhesion between PET and SM was good, and the container had sufficient mechanical strength as a pressure-resistant container. Example 11 The multilayer parison manufactured in Example 1, the parison of Comparative Example 2, and the parison of Comparative Example 2 were molded by successive molding from the inner layer while changing the molds sequentially using the N-95 type injection molding machine manufactured by Japan Steel Works. Multilayer parison shown (inner layer: PET 2mm / middle layer: 1.5mm / outer layer: PET 1.5
mm) was stretch blow molded under the conditions shown in Table 4.

[Table] The density of each interface surface layer in the multilayer parison obtained in Comparative Example 3 is 1.348 g/cc on the surface layer of the inner layer PET, and 1.348 g/cc on the surface layer of the middle layer SM on the inner layer side.
The concentration was 1.221 g/cc, 1.224 g/cc on the outer layer side, and 1.349 g/cc on the surface layer of the outer PET layer, and the multilayer parison was cloudy.

[Table] Table 5 shows the physical properties of a typical example of the obtained biaxially oriented container.
It was shown to.

[Table] The multilayer biaxially oriented container according to the present invention not only has excellent gas barrier properties, transparency, and interfacial adhesion, but also has excellent hygiene because the middle layer is not exposed at the opening end of the mouth. Even with SM, which has somewhat poor water resistance due to its orientation, there were no problems and a container that was stable over a long period of time was obtained. Furthermore, the biaxially oriented container formed from the multilayer parison of Example 5 had excellent heat shrinkage resistance when filled with high-temperature liquid.

[Brief explanation of the drawing]

Figures 1 and 2 are explanatory diagrams illustrating the relationship between an apparatus for manufacturing a multilayer parison by the method of the present invention and a mold, and both are overviews of the case where a multilayer parison is manufactured using two injection molding machines. It shows. FIG. 3 is an explanatory diagram showing an ideal injection pattern when manufacturing a multilayer parison of the present invention made of PET and SM using the apparatus and mold shown in FIG. 1, and FIG. FIG. 3 is a cross-sectional view of the obtained multilayer parison. Moreover, FIG. 5 is a sectional view of the multilayer container of the present invention. 1: Mold, 2: Nozzle, 3, 3': Cylinder, 4, 5: Thermoplastic resin, 6: Molded part mold,
7: Runner mold, 8: Injection molding machine, 9: Nozzle, 10: Runner, 11: Valve gate, 1
2: Cylinder, 13: Threaded portion, 14: Mouth opening end portion, 15: Body portion, 16: Near gate portion, 1
7: Mouth opening end portion, 18: Thin body portion.

Claims (1)

[Claims] 1. Using a molding machine having a plurality of injection cylinders, at least two types of thermoplastic resins are melted into a single mold in one mold clamping operation and are continuously and at different timings. In the alternate injection molding method, the first injected thermoplastic polyester resin mainly consisting of ethylene terephthalate repeating units is formed as the inner and outer surface layers, and the later injected thermoplastic metaxylylene group-containing polyamide resin is formed as the intermediate layer. A parison having at least a single layer structure at the opening end portion and a multilayer structure of three or more layers at the other portions is heated with pressure fluid at a temperature of (Tg + 15) °C or higher and (2Tg + 15) °C or lower of the polyester resin. A method for producing a blow-molded container having a multilayer structure, the method comprising blow-molding the container by blow-molding the container. 2. The method for producing a blow-molded container having a multilayer structure according to claim 1, wherein the thermoplastic xylene group-containing polyamide resin injected later is a thermoplastic resin containing a facial cleanser and/or an ultraviolet absorber.