JPH0471425B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention relates to a polyester container with improved flavor retention, and more specifically, by reducing the acetaldehyde concentration in the container wall,
This invention relates to a polyester container with improved flavor retention in the inner container. (Prior art) Containers made of polyethylene terephthalate produced by biaxial stretch blow molding have excellent pressure resistance, rigidity, transparency, and impact resistance, and also have relatively low gas permeability to oxygen, carbon dioxide, etc., so they can be used for various purposes. They are widely used as containers for liquid foods, seasonings, cosmetics, etc., and plastic cans with a polyethylene terephthalate container body whose opening is sealed with a metal lid are about to be put into practical use. . However, polyethylene terephthalate generates acetaldehyde due to thermal decomposition during thermoforming, and the acetaldehyde in the container wall transfers to the contents, resulting in the flavor of the contents.
The problem is that it damages the Conventional methods for reducing the acetaldehyde concentration due to thermal decomposition in polyethylene terephthalate include solid phase polymerization of polyethylene terephthalate after normal polymerization to reduce low molecular weight components or slightly increase the molecular weight, and molding during thermoforming. A method of lowering the temperature as much as possible and a method of reducing the shear (shear stress) during thermoforming as much as possible are being considered. (Problems to be Solved by the Invention) However, in manufacturing containers made of polyester such as polyethylene terephthalate, a substantially amorphous preform is formed by melting a general polyester and then injecting it into an injection mold. Since the preform is stretch-blown at a stretch molding temperature, increasing the molecular weight of polyester tends to reduce the injection moldability of polyester, and lowering the molding temperature reduces the load on the injection machine. This is not preferable because it makes the shear excessive, and lowering the shear tends to lower the molding speed and cause bubble entrainment, which is not preferable. Therefore, the present invention aims to provide a polyester container with improved flavor retention by reducing the acetaldehyde concentration contained in the polyester container wall without any particular adverse effect on the molding performance or physical properties of the polyester. Take it as a challenge. (Means for Solving the Problems) The present inventors added a thermoplastic polyamide having a terminal amino group concentration in the range of 0.05 to 50 mmol/100 g of resin to a thermoplastic polyester mainly composed of ethylene terephthalate units. 100
5×10 ^-7 to 10 parts by weight, preferably 5×
It has been found that when containers are formed from compositions containing as an acetaldehyde concentration reducing agent in amounts of 10 ^-4 to 10 parts by weight, the acetaldehyde concentration in the container wall can be significantly reduced. (Function) By thermal decomposition of polyethylene terephthalate,
The mechanism by which acetaldehyde is produced is as follows: Decomposition of polymer hydroxy end groups as shown in This is said to be due to the decomposition of the polymer main chain as shown in . The present invention is based on the finding that the incorporation of a certain amount of polyamide with a certain terminal amino group concentration into polyethylene terephthalate can significantly reduce the acetaldehyde concentration in the thermoformed container wall. That is, the terminal amino group-containing polyamide used in the present invention acts as a concentration lowering agent for acetaldehyde in polyethylene terephthalate, and although its mechanism of action has not yet been fully elucidated, the following formula It is thought that one of the reasons is that acetaldehyde is trapped at the amino group terminal of the polyamide by the reaction shown in . The polyamide used in the present invention is a polymeric substance and is dispersed in polyester, so unlike low molecular weight amino compounds, it does not migrate into the contents of the container through extraction or volatilization. It also has the advantage that it does not adversely affect the flavor of the contents. The terminal amino group-containing polyamide used in the present invention has a terminal amino group of 0.05 to 50 mmol/100 g.
The concentration of the polyamide resin, particularly preferably from 0.1 to 40
It is important to contain it at a concentration of mmol/100g polyamide resin. When the terminal amino group concentration is lower than the above range, the acetaldehyde scavenging ability is insufficient, while when the terminal amino group concentration is higher than the above range, the blending of polyamide tends to cause a problem of deterioration of the flavor of the container. be. In the present invention, the polyamide is contained in a range of 5 x 10 ^-7 to 10 parts by weight per 100 parts by weight of polyester.
In particular, it is also important to blend in an amount of 5 x 10 ^-4 to 10 parts by weight. Generally, when a thermoplastic polyamide is added to polyester, the acetaldehyde residual rate in the polyester (the ratio of the residual amount of acetaldehyde to the acetaldehyde concentration when no polyamide is added) decreases as the amount of polyamide added increases, but the acetaldehyde residual rate shows a tendency to gradually become saturated. Therefore, even if the amount of polyamide added is too large, the degree of decrease in the acetaldehyde concentration will not be significantly improved, and the transparency or mechanical properties of the polyester container will deteriorate. In the present invention, when the terminal amino group concentration in the polyamide is C mmol/100 g of resin and the number of blended parts of polyamide per 100 g of polyester is S, the polyester is expressed by the product C x S x 100.
The amount of polyamide per 100 g is most preferably in the range of 2 x 10 ^-3 to 20 mmol, particularly 6 x 10 ^-3 to 1 mmol. The terminal amino group concentration can be adjusted by controlling the molecular weight,
This can be carried out by adjusting the reaction molar ratio of the diamine component and dicarboxylic acid component, by terminal treatment at the time of termination of polymerization, etc. (Description of preferred embodiments of the invention) Polyester In the present invention, a polyester mainly containing ethylene terephthalate units is used as the polyester. This is because this polyester has excellent stretch moldability and also has excellent properties such as mechanical properties and transparency. As a polyester mainly composed of ethylene terephthalate units, 80 mol% or more of the acid component, especially 90 mol% or more, is a terephthalic acid component, and 80 mol% or more, especially 90 mol% or more of the diol component is an ethylene glycol component. Polyester is preferred. Polyethylene terephthalate is most preferred, but modified copolyesters can be used without losing the essence of polyethylene terephthalate, such as isophthalic acid, P-β-oxyethoxybenzoic acid, naphthalene 2,6-dicarboxylic acid. , diphenoxyethane-4,4'-dicarboxylic acid, 5-sodium sulfoisophthalic acid, adipic acid, sebacic acid or alkyl ester derivatives thereof, propylene glycol,
Copolyesters containing glycol components such as 1,4-butanediol, neopentyl glycol, 1,6-hexylene glycol, cyclohexanedimethanol, and ethylene oxide adducts of bisphenol A may also be used. The polyester used should have a molecular weight sufficient to form a film, and for this purpose it should have an intrinsic viscosity (IV) of 0.55 to 1.9 dl/g, particularly
A value in the range of 0.65 to 1.4 dl/g is desirable.
Among these, those with a relatively low molecular weight are used for injection molding, and those with a relatively high molecular weight are used for extrusion molding. Polyamide Polyamide As the polyamide, a polymerized fatty acid polyamide obtained by polycondensation of a polymerized fatty acid and a diamine that satisfies the above-mentioned conditions can be used. This polymerized fatty acid polyamide is obtained by condensing diamines with polymerized fatty acids obtained by polymerizing unsaturated fatty acids (for example, linoleic acid, linoleic acid, etc.) under heating and melting. An example of this is linoleic acid 2, which has a high group concentration and can significantly reduce acetaldehyde with the addition of a small amount.
Examples include condensation polymers of mercury and hesamethylene diamine. The molecular weight of these polyamides can be used without any particular restrictions as long as they are within the range of general film-forming ability, but as described below, 100ml of 96% sulfuric
It is generally desirable that the relative viscosity (ηREL) is in the range of 0.4 to 4.5 when measured at 25° C. by dissolving 1 gram of the polymer in water. Blend product The blend product of the present invention contains the above-mentioned polyester and terminal amino group-containing polyamide,
This blend may be prepared by mixing one or more of colorants, fillers, surfactants, lubricants, ultraviolet absorbers, antioxidants, nucleating agents, etc. in known proportions. It can be blended with. The blend used in the present invention may contain one or more thermoplastic resins other than those mentioned above for the purpose of modification, such as polyethylene, polypropylene, ethylene-propylene copolymer, ethylene-butene- 1 copolymers, ionomers (olefin resins such as ionically crosslinked olefin copolymers; polycarbonates; polyarylates, etc.). It is recommended that the blend be used in an amount of 100% or less.The blend may be prepared by dry blending pellets or powders of multiple types of resins to be blended, then melt-kneading and pelletizing. Since it is desirable to mix both of them evenly, it is advantageous to use a method in which multiple types of pellets or powders are mixed homogeneously using a Henschel mixer, etc., and then melt-kneaded. Advantageously, a method can be used in which a masterbatch is prepared by blending the polyamide with the polyester, melt-kneading the masterbatch, blending the masterbatch with the remaining polyester, and melt-kneading the same.Container and Molding Method The container according to the present invention is a method of preparing a masterbatch by blending the masterbatch with the remaining polyester and melt-kneading the same. This is carried out in a manner known per se, except that a blend is used.
For example, sheets, pipes, or bottomed preforms for forming hollow containers are easily manufactured by extrusion molding, injection molding, compression molding, blow molding, or a combination thereof. When producing these sheets, pipes, or bottomed preforms, it is preferable that at least the portion of the polyester to be stretch-molded is substantially amorphous. Of course, the parts that are not stretch-molded, such as the neck and bottom of the bottle, may be thermally crystallized. The method for forming the container is not particularly limited. For example, by stretch-molding a sheet, a bottomed plastic can body can be obtained which is used by sealing a cup-shaped container with a uniaxially oriented side wall or a metal lid. Also, by bottoming out the pipe,
A bottomed preform for stretch blow molding is obtained,
Furthermore, by stretching the pipe in a uniaxial direction or by stretch blow molding it in a biaxial direction, a plastic can body is obtained which can be wrapped with a metal cap at both ends. Furthermore, a biaxially oriented plastic bottle can be obtained by stretching the bottomed preform in the axial direction and expanding and stretching it in the circumferential direction. In order to improve the heat resistance of these stretch-molded containers, the orientation can be thermally fixed by heat treatment in a mold or the like under conditions of shape restriction. The blend of the present invention can also be applied to film containers. In this case, the blend is formed into a film by a T-die method or the like, and this film is stretched in the longitudinal direction at a stretching temperature, and then direction using a tenter or other means to obtain a biaxially stretched film, and this biaxially stretched film is used for manufacturing containers. In addition, this blend can also be used as a tray-shaped container for cooking food in a microwave oven and/or toaster oven, etc. For example, the blend can be formed into a tray shape and then thermally crystallized. Improves heat resistance. The blend of the present invention can be used alone for manufacturing the above-mentioned containers, and can also be used with other materials, such as metal foils such as aluminum foil, copper foil, iron foil, tin foil, and TFS foil, and with gallibaric resins, such as It can also be used in the manufacture of containers in the form of a laminate with an ethylene-vinyl alcohol copolymer having an ethylene content of 20 to 70 mol%, a xylylene group-containing polyamide resin, or the like. In particular, when the former ethylene/vinyl alcohol copolymer and the blend of the present invention are used in coextrusion molding or co-injection molding, acetaldehyde generated by thermal decomposition of the ethylene/vinyl alcohol copolymer is also contained in the blend. The terminal amino groups of the thermoplastic polyamide have the advantage of trapping. (Application) By containing a small amount of thermoplastic polyamide as an acetaldehyde concentration reducing agent, the polyester container of the present invention can be used as a container for storing contents whose flavor is substantially impaired due to the presence of acetaldehyde. Useful for preserving flavor. Therefore, for example, oil and fat foods such as tempura oil and kirada oil; seasonings such as mayonnaise, dressing, and ketchup; various syrups such as ice syrup;
Confectionery such as water yokan and jelly; Alcoholic beverages such as shochu; Various carbonated drinks including cola, cider, plain soda, etc.; Straight juice such as lemon juice, orange juice, plum juice, grape juice, and strawberry juice. or fruit juice drinks such as fruit juice drinks containing nectar or agar; retractable drinks such as coffee and black tea; health-oriented drinks such as vitamin-fortified drinks, aloe drinks, herbal drinks, healthy vinegar drinks, and isotonic drinks; green tea, kombucha, Oolong tea, Amachi Yazuru tea, Hatomagi tea,
It is useful as a container for storing sugar-free drinks such as tea, persimmon leaf tea, ginseng tea, corn potage, consommé soup, shellfish extract drinks, mineral water, lactic acid bacteria drinks, fermented milk drinks, and others. (Example) The present invention will be explained by the following example. In addition, each measurement in each Example was performed according to the following method. () Intrinsic viscosity (IV) of thermoplastic polyester (PET) An Ubbelohde viscometer was used. Measurement was performed at 30°C using a mixed solvent of phenol/tetrachloroethane = 6/4 (weight ratio). () Relative viscosity (ηREL) of thermoplastic polyamide (PA) 1 g of thermoplastic polyamide resin was dissolved in 100 ml of 96% by weight sulfuric acid and measured at 25°C. () Terminal amino group concentration of PA ([-NH ₂ ]) The terminal amino group was determined by potentiometric titration. Namely, the thermoplastic polyamide (PA) used
About 1 g of each sample was strained and m-cresol (10 mmHg, 95-96
50 ml of the mixture was added and dissolved in a vacuum desiccator for 24 hours. Next, a special grade perchloric acid reagent (60% ethyl alcohol solution) was added to a mixed solution of purified isopropyl alcohol and propylene glycol in a volume ratio of 2:1 as a potential adjusting agent to adjust the concentration to 0.005N. , which was used as a titration reagent. Quantification of the terminal amino group was determined from the inflection point obtained from a plot of the apparent potential and perchloric acid consumption. Potentiometric titration was performed using a HM-5 PH meter manufactured by Toa Denpa Kogyo Co., Ltd. () Terminal carboxyl group concentration of PA ([−
COOH〕) To quantify the terminal carboxyl group, strain approximately 1 g of each sample and add 50 ml of benzyl alcohol (10 mmHg, 90-93°C fraction) distilled from special grade reagent.
was added and dissolved at approximately 150°C. Next, add 0.01N of phenolphthalein to each solution as an indicator.
The amount of terminal carboxyl groups was determined by subtracting the amount consumed by benzyl alcohol using a potassium hydroxide titration solution. () Amount of acetaldehyde in the material (AA) The amount of acetaldehyde in the material was determined using the Celanese method. That is, about 1 g each of the body and mouth of the sample described in each example was ground at the same time in liquid nitrogen, and 30 to 40 mg of the sample was ground at the same time in liquid nitrogen.
After filling a pre-prepared glass insert, it was introduced directly into the injection section of a glass chromatograph (Shimadzu GC-6A model) and heated at 145°C for 20 minutes to volatilize the acetaldehyde in the material. After heating, the temperature of the column (Polapack Q, 3φ x 2m) was changed from room temperature to
The temperature was raised to 140°C and acetaldehyde analysis was performed. After the measurement, the weight of (sample + glass insert) was carefully determined, and the weight of the test sample was calculated from the difference from the weight of the glass insert. Results are average values of three repeated measurements. () Container transparency (haze, Hz) Transparency (haze) was measured using a direct reading haze meter manufactured by Toyo Seiki Seisakusho.
The haze value (Hz) of 0.24 mm thick) was measured. The results show the average of five measurements for each sample. Example 1 Polyethylene terephthalate (PET-A) with an intrinsic viscosity (IV) of 0.75 dl/g and an intrinsic viscosity (I.
Two types of polyethylene terephthalate (PET-B) have a relative viscosity of 0.52 and a terminal amino group concentration of 0.65 dl/g.
31.8mmol/100g, terminal carboxyl group concentration
31.22 mmol/100 g of polymerized fatty acid polyamide (polymerized fatty acid PA) strips were prepared in a ratio of PET-A: polymerized fatty acid PA = 100:10 (weight ratio), PET-B: polymerized fatty acid PA = 100:10 (weight ratio) Then, it was dry blended and pelletized using a pelletizer (temperature set for each part of the cylinder: 265°C, screw rotation speed: 30 rpm) to obtain two types of masterbatches (pellets): and. Further, two types of dry blends were prepared using a tumbler-type dry blender, consisting of PET-A: masterbatch = 10:1 = 1.0 parts by weight PET-B: masterbatch = 10:1 = 1.0 parts by weight. The obtained dry blend was transferred to Nissei Resin Kogyo Co., Ltd.
FS-170N injection molding machine, the weight is 37
g. A preform with a wall thickness of 4 mm was molded. The injection conditions at this time are: Barrel set temperature: (rear) 250℃, (middle)
265°C, (front part) 271°C, (nozzle part) 272°C Screw rotation speed: 70 rpm Injection pressure: 44 Kg/cm ² Cooling water temperature: 11°C Molding cycle: 36 seconds. The preform thus obtained was molded using an OBM-IG type biaxial stretch blow molding machine manufactured by Toyo Shokuhin Kikai Co., Ltd., with a full injection volume of approximately 1035 ml (weight 37 g).
A cylindrical bottle was molded. The bottle molding conditions are a preform temperature of 100
After heating at ℃ for 30 seconds, blow molding was performed in a mold for 4 seconds. For comparison, bottles consisting of PET-A and PET-B alone were also created in the same manner. The amount of acetaldehyde in each bottle material and the transparency of the obtained biaxially stretched blow bottles were measured according to (V) and (Vi) described above. The results are shown in Table 1. Comparative Example 1 For 100 parts by weight of PET-A used in Example 1,
Relative viscosity is 3.42, terminal amino group concentration is 1.637m
mol/100g, terminal carboxyl group concentration 1.669m
mol/100g of polycapramide (nylon 6)
1.0 part by weight was added and dry-blended for 10 minutes at room temperature using a tumbler-type dry blender. Using the same injection and blow molding conditions as in Example 1, a cylindrical bottle with a full fill volume of approximately 1035 ml (weight 37 g) was molded. The amount of acetaldehyde was measured in the same manner as in Example 1 for these biaxially stretched blow bottles. The results are shown in Table 1. Comparison row 2 For PET-B 10 kg used in Example 1, polyhexamethylene adipamide (nylon 6,6, relative viscosity 1.27, amino group concentration less than 4.429 mmol/100 g, terminal carboxyl group concentration 4.486 mmol/100 g) was added and mixed thoroughly using a Henschel mixer, and then pelletized using the pelletizer used in Example 1 to form PET-B/nylon 6,6 matter batches (pellets). I got it. The master batch obtained in this way,
PET-B chips (pellets) were used in the tumbler type dry blender described in Example 1 to obtain three types of dry blends shown below. Master batch: PET-B=1:200=
0.0005 parts by weight Masterbatch: PET-B=1:100=0.001
Part by weight Masterbatch: PET-B = 1:10 = 0.01 part by weight The dry blend thus obtained,
Using the injection molding machine and biaxial stretch blow molding machine described in Example 1, a cylindrical bottle with a full fill volume of approximately 1035 ml (weight 37 g) was produced under the same injection and blow molding conditions as in Example 1. Molded. Regarding these biaxially stretched blow bottles, the amount of acetaldehyde and the transparency of the containers were measured in the same manner as in Example 1. The results are shown in Table 1. Comparative Example 3 The relative viscosity of PET-A used in Example 1 is
2.24, terminal amino group concentration is 0.471 mmol/100g,
Polymethacrylene adipamide (nylon MXD6) with a terminal carboxyl group concentration of 0.483 mmol/100 g
were dry blended using the tumbler type dry blender described in Example 1 at the following blending ratio (weight ratio). PET-A:MXD6=100:0.5=0.5 parts by weight PET-A:MXD6=100:2.0=2.0 parts by weight PET-A:MXD6=100:4.0=4.0 parts by weight PET-A:MXD6=100:8.0=8.0 Weight part PET-A:MXD6=100:15.0=15.0 weight part These five types of dry blends were prepared in Example 1.
Using the injection molding machine and biaxial stretch blow molding machine described in Example 1, the full injection volume was approximately 1035 ml (weight 37 g) under the same injection and blow molding conditions as in Example 1.
A cylindrical bottle was molded. Regarding these biaxially stretched blow bottles, the amount of acetaldehyde and the transparency of the containers were measured in the same manner as in Example 1. The results are shown in Table 1.

[Table] As is clear from Table 1, in Example 1 using a polymerized fatty acid polyamide with a high concentration of terminal amino groups, the effect of reducing acetaldehyde is significantly greater than that of other comparative examples even with the addition of a small amount. I understand that. Furthermore, there is no substantial difference in the transparency of the container compared to that of polyethylene terephthalate alone, indicating that the addition of polymerized fatty acid polyamide does not impair transparency.

Claims (1)

[Claims] 1 Thermoplastic polyester mainly composed of ethylene terephthalate units with a terminal amino group concentration of 0.05
A polyamide obtained by polycondensation of a polymerized fatty acid and a diamine in the range of 50 mmol/100 g resin is added at a concentration of 5 x 10 ^-7 per 100 parts by weight of polyester.
1. A polyester container with improved flavor retention, characterized by comprising a composition containing an acetaldehyde concentration lowering agent in an amount of 10 to 10 parts by weight.