JP3300738B2 - Polyester sheet and container with excellent impact resistance - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thermoforming polyester sheet and a thermoformed container having improved impact strength, particularly low-temperature impact strength, without impairing transparency and thermoformability.

[0002]

2. Description of the Related Art Saturated polyesters, especially crystalline polyester resins represented by polyethylene terephthalate (hereinafter referred to as PET), are widely used as polymers for sheet films including fibers, but have excellent chemical resistance and low chemical resistance. Making use of gas permeability, carbonated beverages, juices,
It has also been applied to beverage bottles such as beer, cosmetic containers, food trays and the like.

Among these, amorphous polyester sheets called A-PET have attracted attention for their excellent recyclability, low pollution, and food safety, and in recent years, their use has rapidly increased as a packaging material replacing vinyl chloride and polystyrene. I have. This polyester sheet is used as a blister pack for food and medicine containers and miscellaneous goods by thermoforming,
Utilizing its excellent transparency, it is used as a clear case for cosmetics, electrical equipment, and the like.

Conventionally, such a saturated polyester sheet has excellent impact strength at room temperature immediately after film formation and immediately after thermoforming. However, the impact strength has a large temperature dependency, and the impact strength is remarkably reduced at low temperatures. When used as a food container that is distributed at a low temperature such as frozen food, breakage is a problem.

Further, when a sheet or a molded article is stored in a high-temperature and high-humidity environment or left for a long time in a low-temperature and low-humidity environment, it changes with time (enthalpy relaxation) due to the aging of the polyester or the resin. Impact resistance has been lost, and there has been a problem that, when a container obtained by thermoforming is distributed on the market, breakage occurs, and thus improvement has been desired.

There have been many proposals for improving the impact resistance of polyester at low temperatures. For example, JP-A-58-171436, JP-A-1-16304
As described in JP-A No. 2 (KOKAI), there are a method of imparting orientation to a molded article, and a method of adding and dispersing impact-resistant rubber particles.

[0007] Alternatively, as described in JP-A-58-36408, a method of forming a multilayer with a polymer film having excellent impact resistance, or a method using a PET resin whose molecular weight is increased by solid-phase polymerization as a raw material. Using a polyester sheet having an intrinsic viscosity of more than 0.8.

However, the method of imparting orientation requires a special device for orienting the sheet and a manufacturing process, and is not economical. In addition, the thermoformability deteriorates, and a special thermoforming machine such as pressure forming is required. . In addition, depending on the shape of the container, there is a problem that the shaping is not completely performed and the fitting property is poor, and the width of molding conditions is narrow.

The method of adding and dispersing impact-resistant rubber particles can effectively improve low-temperature impact resistance, but significantly reduces the excellent transparency of A-PET.

In addition, when a high molecular weight PET resin is used, the polymerization must be advanced to a high degree, and it is necessary to further carry out solid-phase polymerization after melt condensation polymerization. It is difficult to use an extruder, which is not only economically disadvantageous, but also causes a problem of a decrease in extrudability due to an increase in melt viscosity, which makes mass production difficult.

[0011]

The inventors of the present invention have conducted intensive studies in order to solve such a conventional problem, and as a result, it has been found that polyester having an intrinsic viscosity of 0.50 to 0.80 has at least one An intrinsic viscosity obtained by copolymerizing 4-cyclohexanedimethanol in a specific range is 0.50 to 0.90.
A-PE by laminating a layer in which a polyester and a polyester elastomer are blended in a specific ratio
The present inventors have found that excellent impact properties, particularly low-temperature impact properties and impact properties after aging, are excellent while maintaining the transparency, thermoformability and mating properties of T.

[0012]

That is, the present invention relates to (A) a dicarboxylic acid component mainly composed of terephthalic acid and glycol having a proportion of 90 to 10 mol% of ethylene glycol and 10 to 90 mol% of 1,4-cyclohexanedimethanol. 95-65% by weight of a polyester having an intrinsic viscosity of 0.50-0.90 and a molecular weight of 500-200
Soft segment consisting of polytetramethylene glycol 0
A skin layer obtained by uniformly blending 5 to 35% by weight of a polyester elastomer having a
And (B) a polyester layer formed by condensation polymerization of terephthalic acid and ethylene glycol and having an intrinsic viscosity of 0.50 to 0.80. The layer (A) is laminated on at least one side, and the layer (A) has a thickness of 5 to 50
%, A sheet obtained by thermoforming the sheet, and a packaging container obtained by processing the sheet.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION The polyester used for the core layer (B) of the present invention includes not only PET but also a part of terephthalic acid component such as isophthalic acid, adipic acid, diphenylcarboxylic acid, diphenylether dicarboxylic acid, and diphenyl sulfone dicarboxylic acid. Substitution with one or more other dicarboxylic acid components such as acid, sebacic acid, naphthalenedicarboxylic acid, etc., and part of the ethylene glycol component is diethylene glycol, hexamethylene glycol, trimethylene glycol, propylene glycol, cyclohexanedimethanol, neopentyl Copolyesters substituted with one or more other glycol components such as glycols, butylene glycol, and the like.

The total proportion of the copolymer components in the PET (B) is preferably at most 10 mol% based on the total acid components. Further, it may contain a trifunctional or more functional compound or a monofunctional compound within a range considered to be substantially linear. Furthermore,
A heat stabilizer, a fluidity improver, an ultraviolet absorber, an antistatic agent, an antifogging agent and the like can be added to the polyester within a range that does not lower the transparency. When matting is required, a coloring agent such as titanium dioxide, calcium carbonate, iron oxide, or carbon black can be contained.

The intrinsic viscosity of this PET is measured in a phenol / tetrachloroethane mixed solvent having a weight ratio of 60/40 at 20 ° C., and the intrinsic viscosity is required to be 0.50 to 0.80. Preferably it is 0.60 to 0.80. If it is less than 0.50, the mechanical strength of the final product is not sufficient, and particularly the impact strength at low temperature is not sufficient. On the other hand, when the intrinsic viscosity exceeds 0.80, the raw material PET resin must be subjected to a high degree of solid phase polymerization, which is economically inferior.

The copolymerized polyester used as the polyester (A) to be laminated on the surface of the sheet of the present invention is composed of a dicarboxylic acid component containing terephthalic acid as a main component, ethylene glycol 90 to 10 mol%, 1,4-cyclohexanedimethanol 10 The amount of 1,4-cyclohexanedimethanol obtained by polycondensing a glycol component in a proportion of .about.90 mol% and copolymerized is preferably from 20 to 8%.
0 mol%.

When the proportion of 1,4-cyclohexanedimethanol is less than 10 mol%, or when the copolymerization exceeds 90 mol, the compatibility with the polyester elastomer to be blended is lowered and the transparency is lowered. Alternatively, the crystallization of the molded article tends to proceed during thermoforming, and the thermoformability deteriorates. The ratio of cis and trans of 1,4-cyclohexanedimethanol used is not particularly limited, but is 4: 6.
0 to 10 is good in terms of impact strength.

The intrinsic viscosity of the copolymerized polyester is 0.50
~ 0.90, particularly preferably 0.60 ~
0.90. When the intrinsic viscosity is lower than 0.50, the mechanical strength of the final product is not sufficient, and particularly the impact strength at low temperature is not sufficient.

The polyester elastomer blended with the polyester (A) laminated on the surface of the present invention is a polyester / polyether block copolymer in which the hard segment is a polyester and the soft segment is a polytetramethylene glycol .

The hard segment is preferably polybutylene terephthalate or polyethylene terephthalate having good compatibility with the polyester (A) serving as a matrix, but a part of the terephthalic acid component may be replaced with isophthalic acid, adipic acid, or the like as long as the compatibility is not inhibited. Diphenyl dicarboxylic acid, diphenyl ether dicarboxylic acid, diphenyl sulfone dicarboxylic acid, sebacic acid, substituted with one or more other dicarboxylic acid components such as naphthalenedicarboxylic acid, etc., ethylene glycol and part of 1,4 butanediol component diethylene glycol, Hexamethylene glycol, trimethylene glycol, propylene glycol,
It may be replaced with one or more other glycol components such as cyclohexanedimethanol, neopentyl glycol and the like.

The soft segment needs to have flexibility at the operating temperature. That is, it must have a glass transition temperature lower than the atmosphere temperature actually used, and have sufficient heat resistance that can be blended with polyester. A preferred soft segment is polytetramethylene glycol having a molecular weight of 500 to 2,000. When the molecular weight is less than 500, sufficient flexibility cannot be imparted. On the other hand, when the molecular weight exceeds 2,000, the compatibility when blended with the polyester becomes insufficient and the transparency is lowered, which is not preferable.

The content of polytetramethylene glycol, which is a soft segment component of the polyester elastomer, is 10 to 45% by weight . If the amount is less than 10% by weight, the flexibility when blended is insufficiently imparted.
If it exceeds 5% by weight, the transparency at the time of blending is undesirably reduced.

The amount of the polyester elastomer to be uniformly blended with the polyester (A) to be laminated on the surface of the present invention must be 5 to 35% by weight. When the amount is less than 5% by weight, the low-temperature impact resistance is insufficiently imparted. On the other hand, when the amount exceeds 35% by weight, the crystallinity of the sheet is increased due to the influence of the hard segment of the polyester elastomer, and the thermoformability of the sheet is reduced. Not preferred. As a blending method, a film may be formed after melt-kneading in advance with a kneading machine, or a chip may be blended and supplied at the time of forming a sheet.

Further, the relative viscosity ηrel of the polyester elastomer used in the present invention is a value measured at a concentration of 1.0 g / dl at 20 ° C. using a phenol / tetrachloroethane mixed solvent having a weight ratio of 60/40. It is preferably 0 or more. If it is lower than 3.0, the effect of improving the impact when blended is insufficient.

The thickness of the sheet for carrying out the present invention is not particularly limited, but is usually 50 to 1500 μm, preferably 150 to 800 μm.

The sheet can be obtained by melt-extrusion using an ordinary polyester extruder such as a single-screw extruder or a twin-screw vent-type extruder, and cooling the molten resin by a cooling drum. The sheet is preferably quenched as much as possible to prevent a decrease in transparency due to crystallization. The crystallinity of the main layer (core) is 10% by weight or less (density 1.348 g / cm ³ or less), and the sheet haze is 5% or less. Is desirable.

In order to obtain the sheet of the present invention, a known co-extrusion apparatus having a feed block die, a multi-manifold die and the like can be used. Further, it can be produced by a known technique such as melt lamination or dry lamination, but co-extrusion is preferred from the viewpoint of sheet quality.

As a film forming method, there are a method of sandwiching and cooling between metal rolls (touch roll method), an electrostatic application method, an air knife method and the like. Is preferred.

A-PE is an in-line recycle that pulverizes ears that appear when a sheet is cut into a predetermined width during film formation and skeleton parts that have been punched out of a container after thermoforming and returns as raw materials.
T is generally used, but in the present invention, it can be blended with the main layer (core) within a range that does not extremely lower the intrinsic viscosity of the sheet.

The proportion of the polyester (A) to be laminated on the surface of the sheet is preferably from 5 to 50%, but particularly preferably from 10 to 30% from the viewpoints of economy and quality stability. When the proportion of the polyester (A) to be laminated on the surface in the whole sheet is smaller than 5%, it is difficult to form the skin layer uniformly, and the effect of improving the impact property is small. On the other hand, if it exceeds 50%, not only is the effect of further improving the low-temperature impact resistance small, but also the use of a large amount of expensive polyester (A) is not economically disadvantageous, but also the transparency of the sheet and thermoformed article. Tends to decrease, which is not preferable.

The layer on the surface of the container in which the copolymerized polyester and the polyester elastomer are blended must be laminated on at least one side, and preferably on both sides. When used by laminating on only one side, the container is obtained by thermoforming so that the copolymerized polyester layer is on the outside of the container.

The product of the present invention may be manufactured by any method such as vacuum forming, compressed air forming, hot plate forming, plug assist forming, reverse draw forming, air slip forming, or a combination of these methods. .

[0033]

Industrial Applicability The present invention is excellent in impact strength, especially at low temperature and after aging, without impairing processing characteristics such as transparency, thermoformability, and recyclability, and is used for food packaging containers and frozen desserts. Ideal for containers and decoration lids.

[0034]

EXAMPLES The present invention will be described in more detail with reference to the following Examples, but it should not be construed that the present invention is limited thereto.
In addition, each characteristic value measurement was performed according to the following method.

(1) Intrinsic viscosity A phenol / tetrachloroethane mixed solvent having a weight ratio of 60/40 was used and measured at a concentration of 1.0 g / dl at 20 ° C.

(2) Measurement of molecular weight The sample was dissolved by using a mixed solution of hexafluoroisopropanol and chloroform, and chloroform was used as an eluent at 35 ° C. and a flow rate of 1.0 ml / min. It was determined in terms of standard polystyrene using UVD-2.

(3) Measurement of Glass Transition Temperature The glass transition temperature of the polyester elastomer was 983 Dynamic Mechanical A manufactured by DuPont.
1 ° C./min by resonance vibration measurement using an analyzer
The measurement was performed under the following conditions, and the elastic modulus was determined from the inflection point temperature.

(4) Sheet Haze Using a haze meter NDH-20D manufactured by Nippon Denshoku Co., Ltd., the haze (haze value) of the sheet was measured by a method according to JIS-K-7105.

(5) Impact Strength of Container A test piece having a diameter of 90 mm was prepared from the bottom of the thermoformed container, and a punching speed of 5 m / sec. The maximum load at -20 ° C and the crack generation energy were measured under the conditions of a punch diameter of 13 mm and a die diameter of 3 inches. The strength after the change over time was measured after aging at 40 ° C. × 60% humidity × 10 days.

(6) Drop strength of container 330 in a cup-shaped container having a diameter of 130 mm and a depth of 70 mm.
g of water, the lid (engagement lid) was closed, the container was allowed to stand in a -20 ° C constant temperature bath for 24 hours, and then dropped from a height of 1.0 m onto a concrete surface for evaluation. Strength after change over time is 40 ° C
After aging of × humidity 60% × 10 days, water was added and the same drop test was performed to evaluate. Those that did not crack at all were rated as 、, those with a probability of breaking of 10% or less were rated as Δ, and those with a probability of breaking greater than 10% were rated as ×.

Examples 1 to 4 and Comparative Examples 1 to 9 Melt extrusion was performed from a T-die using a multilayer extruder equipped with a twin screw vent at 285 ° C. and a degree of vacuum at a vent of 5 mmHg.
Film formation was performed by a touch roll method to obtain sheets of various configurations with a thickness of 500 μm. The copolyester and the polyester elastomer were used by chip blending during film formation.

Next, the above-mentioned sheet is preheated to a temperature higher than the glass transition temperature and lower than the melting point, and a cup-shaped container having a diameter of 130 mm × a depth of 70 mm is set in a vacuum forming machine equipped with a female mold adjusted to a temperature of 45 ° C. A lid was made. The test conditions and evaluation results described above are summarized in Tables 1 and 2.

[0043]

[Table 1]

[0044]

[Table 2]

The sheets and molded products of Examples 1 to 4 obtained satisfactory results in all evaluation and measurement items. On the other hand, when the thickness of the skin layer (A) is thin as in Comparative Example 2, almost no improvement in low-temperature impact resistance is recognized as compared with Comparative Example 1 in which no skin layer is provided. Further, even when the amount of the polyester elastomer to be disposed in the skin layer (A) is small as in Comparative Example 3, the improvement in low-temperature impact resistance is insufficient. Conversely, if the blending amount is too large, as in Comparative Example 4, the sheet will have high crystallinity, and the thermoforming of the sheet will not be successful, making it impossible to obtain a container worthy of later evaluation. When the copolymerized polyester used for the skin layer (A) or the polyester used for the core layer (B) has too low intrinsic viscosity as in Comparative Examples 5 and 6, the mechanical strength of the container as the final product is selected. However, the impact strength at low temperatures was not sufficient. When the copolymerization ratio of the glycol component (1,4-cyclohexanedimethanol) of the copolymerized polyester used for the skin layer (A) is set outside the range as in Comparative Example 7, Comparative Example 8, or Comparative Example 9, a sheet or a molded product is formed. The transparency (haze) of the product was reduced, the thermoformability of the sheet was significantly deteriorated, and the strength of the obtained product was also low.

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int. Cl. ⁷ , DB name) B32B 1/00-35/00 C08L 67/00-67/08

Claims (3)

(57) [Claims] (A) a dicarboxylic acid component mainly containing terephthalic acid and 90 to 10 mol% of ethylene glycol;
95-65% by weight of a polyester having a specific viscosity of 0.50-0.90 and a polytetramethylene glycol having a molecular weight of 500-2000 by condensation polymerization of a glycol component having a ratio of 10-90 mol% of 4-cyclohexanedimethanol .
10 to 45 layers of soft segment components consisting of recall
% Of a polyester elastomer in an amount of 5 to 35% by weight, (B) terephthalic acid and ethylene glycol are polycondensed, and the intrinsic viscosity is 0.1%.
A polyester layer comprising a polyester layer having a thickness of 50 to 0.80, wherein (A)
A sheet wherein the layers are laminated on at least one side, and the layer (A) is in the range of 5 to 50% of the total thickness of the sheet. 2. A polyester container obtained by thermoforming the sheet according to claim 1. 3. A polyester packaging container obtained by punching, bending and assembling the sheet according to claim 1.