JPH0573572B2 - - Google Patents

Description

[Detailed description of the invention]

A. Industrial Application Field The present invention relates to a method for producing a coextruded laminate made of polyester and an ethylene-vinyl alcohol copolymer. B. Prior Art Polyester films have excellent physical properties such as Young's modulus, tensile strength, heat resistance, and transparency, and are used for various packaging applications by taking advantage of these characteristics. On the other hand, ethylene-vinyl alcohol copolymer (hereinafter referred to as EVOH) has excellent gas barrier properties against enzymes, nitrogen, carbon dioxide, helium, etc., and aroma retention properties against various odors, and is widely used as a food packaging material. A laminate made of polyester, fusible resin, and EVOH that takes advantage of these characteristics has the potential to be used as a food packaging material with excellent mechanical strength, gas barrier properties, transparency, and heat resistance. In general, in the case of sheets and films, methods for obtaining laminates include dry lamination, in which each layer is laminated using an adhesive after each layer is formed, and sandwich lamination, and one method is used as a base material and the other is extruded. In addition to laminating or coating methods, there is also a coextrusion method as a recent technological trend. Among these lamination techniques, in lamination methods such as dry lamination, extrusion lamination, and solution coating, EVOH crystallization due to heating progresses, resulting in deterioration of the stretchability of the laminate.
There are problems such as increased costs due to the complexity of the lamination process. Even in the coextrusion molding method, in order to obtain a molded product that has a beautiful appearance, the thickness of each layer is uniform, and can be commercialized by post-processing (e.g. biaxial stretching processing, deep drawing processing), First, it is necessary to optimize the thickness structure of each layer and raw material combination, as well as molding conditions such as extrusion temperature, die temperature, resin flow path shape, cooling temperature, and cooling rate. The failure to obtain molded products of good quality after processing after stretching or deep drawing is often due to defects in the coextruded sheet or film subjected to secondary processing. The details of these defects are as follows. That is, an interfacial instability phenomenon occurs during coextrusion, resulting in a wavy appearance defect on the whole. In severe cases, the entire surface becomes extremely uneven, and the layers bite into each other, resulting in holes and tears. The extent of the appearance defect is
Even with a small amount, a fine satin-like pattern may appear on the entire surface, or a striped pattern may appear. If such a coextruded product with poor appearance is post-processed, the poor appearance will be further exacerbated and a net-like pattern will appear on the entire surface. Such wavy surface roughness and satin texture in coextrusion are related to the stability of multilayer flow. If the flow is unstable, it will appear as a wavy rough surface if it is severe, or as a matte finish or streaks if it is less severe. C Problems to be Solved by the Invention The present inventors have developed a composition of polyester/adhesive resin/EVOH/adhesive resin/polyester produced by coextrusion processing, and commercialized it by biaxial stretching processing or deep drawing processing. The present invention was developed after intensive research into a method for producing a good quality raw fabric that does not cause the above-mentioned problems. D Means for solving the problem The key point of the technology according to the present invention is to find the optimal range of combinations of viscosity and thickness structure of the resin forming each layer in order to obtain a stable five-layer flow in coextrusion. As a result of extensive research, it has become clear that by controlling the combination of the viscosity ratio and the thickness structure of each layer in the low shear rate region, it is possible to obtain molded products of good quality even after post-processing. The gist of this is that a multilayer molded product having a composition of polyester/adhesive resin/EVOH/adhesive resin/polyester is coextruded under conditions that satisfy the following formula. This is the manufacturing method. η _A /η _E ≦2 1/10≦L _A /L _E ≦1 η _P /η _E ≦2 1/10≦L _P /L _E ≦20 where η _A ...Temperature during multilayer molding, shear rate 50sec ^-1
Viscosity (poise) of adhesive resin at η _E ...Temperature during multilayer molding, shear rate 50sec ^-1
Viscosity (poise) of EVOH at η _P ...Temperature during multilayer molding, shear rate 50sec ^-1
The viscosity (poise) of the polyester at L _A ...Thickness of the thinner adhesive layer in the multilayer molded product L _E ...Thickness of the EVOH layer in the multilayer molded product L _P ...Thickness of the thinner adhesive layer in the multilayer molded product Adhesive Layer Thickness E More Detailed Description of the Invention The melt viscosity of a polymer varies greatly depending on temperature and shear rate, and the viscosity is determined only when these incidental conditions are determined. In coextrusion, in order to obtain a stable stratified flow, it is necessary to determine the viscosity under which conditions to consider.
Although it is understood that it is necessary to use raw materials with similar viscosities, it is not clear under what conditions the viscosity should be compared in reality. Since the distances are different, it is difficult to define the viscosity.The focus of this technology is how the viscosity and thickness should be in order to obtain a stable five-layer flow.As a result of intensive study, It was found that by controlling the viscosity ratio in the shear region and the thickness structure of each layer as factors, molded products with good quality could be obtained even after post-processing. The shear rate during molding was determined by temperature, channel shape, resin flow rate Temperature is defined as the temperature during molding. 50 sec ^-1 is set as a representative low shear value. Comparing the viscosity at high shear (more than 100 sec ^-1 ) does not match the experimental results. The unstable phenomenon of multilayer flow is caused by the shear at the layer interface, which is more distant from the wall than at the high shear (close to the flow channel wall) (low shear compared to the wall). It is necessary to compare the viscosity at the midpoint between the wall and the wall (approximately 0 shear).As a result of further investigation, it was found that
It was found that when the viscosity of EVOH is higher in this low shear region than that of the adhesive layer or polyester layer, a molded product of good quality (free of matte finish, streaks, and unevenness) can be obtained more stably. η _A /η _E needs to be 2 or less, and η _P /η _E needs to be 2 or less. When this value exceeds 2, the satin pattern becomes noticeable, and when it is even larger, a multilayer molded product is produced in which the layers bite into each other.
If the ratio of η _A /η _E and η _P /η _E is small, the pressure in each resin flow path may become unbalanced and stable laminar flow may not be obtained. Preferably, 1/10≦η _A / η _E ≦2, 1/10≦η _P /η _E ≦2. Furthermore, the values of η _A , η _E , and η _P are not particularly stipulated;
It may be within a range of about 10 ² to 5×10 ⁴ poise (at a resin temperature and a shear rate of 50 sec ⁻¹ ). The ethylene-vinyl alcohol copolymer mainly refers to a copolymer obtained by saponifying a copolymer of ethylene and vinyl acetate. From the viewpoint of gas barrier properties, thermal stability, co-stretchability, etc., the ethylene content is 20 to 60 mol%, preferably 25 to 45 mol%.
It is mole%. In addition, from the viewpoint of gas barrier properties, the degree of saponification of the vinyl acetate component is preferably 95% or more.
More than 98%. Furthermore, in order to particularly improve stretchability, tertiary units other than ethylene and vinyl alcohol units are added.
Components can be included within ranges that do not significantly affect barrier properties and moldability. The polyester resin used in the present invention may be any biaxially stretchable polyester, and includes polyesters such as ordinary homopolymers, copolymers, and polymer mixtures for film molding. The most suitable is polyethylene terephthalate (PET). Here, PET is mainly composed of ethylene glycol and terephthalic acid, and terephthalic acid accounts for 80 mol% or more of the acid component, preferably 90 mol% or more, and 80 mol% or more of the glycol component, preferably 90 mol%. The above is a polyester resin containing ethylene glycol, and other acid components include phthalic acid, naphthalene 1,4- or 2,6-dicarboxylic acid, diphenyl ether 4,4'-dicarboxylic acid, diphenyldicarboxylic acid, and diphenyl dicarboxylic acid. Examples include aromatic dicarboxylic acids such as enoxyethane dicarboxylic acid, fatty acid dicarboxylic acids such as adipic acid, sebacic acid, azelaic acid and decane-1,10-dicarboxylic acid, and alicyclic dicarboxylic acids such as cyclohexane dicarboxylic acid. These can be used alone or in combination of two or more in terephthalic acid in an amount of less than 20 mol% of the acid component. Other glycol components include aliphatic glycols such as propylene glycol, trimethylene glycol, tetramethylene glycol, diethylene glycol, polyethylene glycol, polypropylene glycol, polytetramethylene glycol, hexamethylene glycol, dodecamethylene glycol, and neopentyl glycol. , alicyclic glycols such as cyclohexanedimethanol, 2,2-bis(4'-β-hydroxyethoxyphenyl)propane, and other aromatic diols. These glycols can be included in amounts of less than 20 mole percent within the glycol component. The polyester resin used in the present invention may be copolymerized with polyfunctional components such as trimethylolpropane, pentaerythritol, trimellitic acid, and trimesic acid in an amount of 5 mol %, preferably less than 3 mol %. Additionally, additives such as colorants, antioxidants, ultraviolet inhibitors, antistatic agents, antibacterial agents, lubricants, and the like can be contained in appropriate amounts as required. The intrinsic viscosity of the polyester used in the present invention is determined by the weight ratio of phenol/tetrachloroethane being 50/50 from the viewpoint of mechanical properties of the obtained molded product.
It is desirable to have a value of 0.55 dl/g or more in a mixed solvent (30°C). If you need to prevent drawdown during coextrusion of sheets, pipes, etc., or if low-temperature impact resistance of the final molded product is required, 0.8 dl/
In some cases, polyesters having a weight of at least 100 g are preferred. If there is no particular advantage of increasing the viscosity from the viewpoint of the molding method and physical properties, a polyester of 0.55 to 0.8 dl/g may be used. The adhesive resin adheres to both polyester and EVOH during coextrusion, and in order to cover the difficulty of stretching EVOH with polyester, it has adhesive strength sufficient to transmit stretching stress.
Furthermore, it is necessary that the laminated film after post-processing has sufficient adhesion strength to cause no problems when actually used. Examples of these include carboxyl group-modified polyolefin, carboxyl group-modified ethylene-ethyl acrylate copolymer, carboxyl group-modified ethylene-vinyl acetate copolymer, modified styrene-butadiene copolymer latex, polyacrylate, polyurethane, and is published in Japanese Patent Application Publication No. 1983
A polyester in which an aluminum element and a monocarboxylic acid are bonded as described in No. 115327 can be used. Note that carboxyl modification herein means modification with an unsaturated carboxylic acid or its anhydride (eg, maleic anhydride, acrylic acid). Such as polyester, adhesive resin, EVOH
The coextrusion method according to the present invention may be a multi-manifold merging T-die method, a feedblock merging T-die method, or an inflation method. In this case, the relative relationship of viscosity between the resins is also related to the relative thickness of each layer, and it is important to keep the interface as far away from the channel wall as possible. Therefore, in order to stabilize the laminar flow, the thickness ratio of each layer must also be incorporated into the elements. L _A /L _E ranges from 1/10 to 1. If the adhesive resin layer is smaller than 1/10, it may be difficult to obtain a raw fabric with a good appearance during coextrusion. Particularly when the viscosity of the adhesive resin layer is high, problems tend to occur when this thickness ratio is small. In addition, L _A /L _E may be 1 or less from the viewpoint of cost and physical properties, and preferably 1/2 or less. L _P /L _E ranges from 1/10 to 20. If it is smaller than 1/10, it is difficult to obtain a raw fabric with a good appearance during coextrusion. If it exceeds 20, it is difficult to obtain a molded product with sufficient barrier properties. i.e.
EVOH's barrier properties cannot be utilized. Preferably, the range is 1/3≦L _P /L _E ≦10, and optimally 1/3≦L _P /L _E ≦5. The coextruded product can be made into a stretched film that is uniaxially or biaxially stretched and heat-treated, a tray or cup by vacuum-pressure forming, or a bottle by stretch blow molding from a pipe or the like. These molded products after post-processing have excellent transparency, oxygen barrier properties, strength, etc., so they can be used for various foods such as pickles, puddings, miso, snacks, etc.
Mainly used for packaging biscuits, oil confections, katsuobushi, mochi, carbonated drinks, alcoholic beverages, etc. The present invention will be explained in detail in the following examples. F Example Example 1 The viscosity measured at 270℃ and 50sec ^-1 is EVOH (ethylene 32 mol%, saponification degree of vinyl acetate component 99.3 mol%)
...η _E = 5×10 ³ (poise) Ethylene-vinyl acetate copolymer modified with maleic anhydride ... η _A = 4×10 ³ (〃) PET (polyester consisting of ethylene glycol and terephthalic acid components) )......η _P = 2×10 ³ (〃) Using the raw materials, polyester/adhesive resin/
A film was formed using the following molding conditions using the composition of EVOH/adhesive resin/polyester. Extruder is EVOH
The size of the die is 60φ for adhesive resin, 40φ for adhesive resin, and 65φ for polyester.The feedblock method is used for the die merging method. die temperature 270
A five-layer sheet with a total thickness of about 1000 μm was produced under conditions of a cooling roll of 60° C. and a take-up speed of 1.5 m/min. The result of measuring the resin temperature at the die exit is 253~
It was 275℃. The results are shown in Table 1.

[Table] Example 2 The viscosity measured under the conditions of 270℃ and 50sec ^-1 is EVOH (ethylene 28 mol%, saponification degree of vinyl acetate component 99.0 mol%)... η _E = 2 × 10 ³ (poise) , 5×10 ³ (poise) Maleic anhydride-modified ethylene-vinyl acetate copolymer...η _A =3×10 ³ (poise), 1×10 ³
(Poise) PET Polyester consisting of ethylene glycol component and terephthalic acid component... η _P = 0.5×10 ³
Sheet molding was carried out in the same manner as in Example 1 using raw materials of 3×10 ³ (poise) and 3×10 3 (poise). Thereafter, vacuum-pressure forming was performed using the sheet. At this time, the drawing ratio (depth/diameter) was 1, the deep drawing temperature was 100 to 110℃,
The compressed air pressure is 10Kg/ ^cm2 . The results are shown in Table 2.

[Table] *1 EVOH layer...η _E =2×10 ³ (poise) Adhesive layer...η _A =3×10 ³ (poise) PET layer...η _P =3×10 ³ (poise) *2 EVOH Layer...η _E =5×10 ³ (poise) Adhesive layer...η _A =1×10 ³ (poise) PET layer...η _P =0.5×10 ³ (poise) Comparative Example 1 Used in Example 1 A raw sheet having a thickness different from that of Example 1 was prepared depending on the raw material, and deep drawing was performed using the raw sheet. The results are shown in Table 3.

[Table] Comparative Example 2 The viscosity measured at 270℃ and 50sec ^-1 is EVOH (ethylene 38 mol%, saponification degree of vinyl acetate component 99.2 mol%)... η _E = 2 × 10 ³
(Poise) Ethylene-vinyl acetate copolymer modified with maleic anhydride...η _A =2×10 ³ (Poise), 5×10 ³
(Poise) PET (ethylene glycol component and terephthalate)
Polyester consisting of an acid component)...η _P = 2×10 ³
(poise) and 5×10 ³ (poise), a molding test similar to that in Example 1 was conducted. The results are shown in Table 4.

[Table] Example 3 and Comparative Example 3 Using the raw materials used in Example 1, coextrusion was performed with the balance of the thickness structure of each layer changed. Also, deep drawing and biaxial stretching tests were conducted using it. Deep drawing conditions are the same as in Example 2 (however, the drawing ratio is 0.5)
Biaxial stretching was carried out at a stretching temperature of 90° C. for 3 times in length and 3 times in width. The results are shown in Table 5.

[Table] G Effects of the Invention According to the present invention, multi-layer molding of polyester/EVOH/polyester has no surface roughness, each layer has a uniform thickness, and has excellent mechanical strength, gas barrier properties, transparency, and heat resistance. You can get things.

Claims (1)

[Claims] 1. A multilayer molded product having a composition of polyester/adhesive resin/ethylene-vinyl alcohol copolymer/adhesive resin/polyester is coextruded under conditions that satisfy the following formula. A method for producing a multilayer molded product. η _A /η _E ≦2 1/10≦L _A /L _E ≦1 η _P /η _E ≦2 1/10≦L _P /L _E ≦20 where η _A ...Temperature during molding, shear rate 50sec ^- Viscosity (poise) of adhesive resin at ¹ η _E ... Viscosity (poise) of ethylene-vinyl alcohol copolymer at molding temperature and shear rate of 50 sec ^-1 η _P ... At molding temperature and shear rate of 50 sec ^-1 Viscosity of polyester (poise) L _A ... Thickness of the thinner adhesive layer in the multilayer molded product L _E ... Thickness of the ethylene-vinyl alcohol copolymer layer in the multilayer molded product L _P ... Thickness of the ethylene-vinyl alcohol copolymer layer in the multilayer molded product , the thickness of the thinner polyester layer 2 1/10≦η _A /η _E ≦2 1/10≦η _P /η _E ≦2 The method for producing a multilayer molded product according to claim 1 . 3. The method for producing a multilayer molded article according to claim 1, which satisfies the following: 1/10≦LA/LE≦1/2 1/3≦LP/LE≦10. 4. The method for producing a multilayer molded article according to claim 1, wherein the thickness ratio of the thinner polyester layer to the thicker polyester layer is 1/3 or more. 5. The method for producing a multilayer molded article according to claim 1, wherein the mixed solvent of polyester with a weight ratio of phenol/tetrachloroethane of 50/50 has an intrinsic viscosity [η] of 0.55 dl/g or more at 30°C. . 6. The method for producing a multilayer molded article according to claim 1, wherein the ethylene-vinyl alcohol copolymer has an ethylene content of 20 to 60 mol%.