JPH10315312A - Thermoformed product made of polyester sheet and its manufacture - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve heat resistance and external appearance of a thermoformed product of a polyester sheet by specifying the degree of orientation and mean refractive index of the product of the sheet. SOLUTION: The polyester sheet is thermoformed to a thermoformed product having a thickness of, for example, 1/3 to 1/15 of that of the sheet. Then, the product is heat treated at, for example, 150 to 270 deg.C in a tensile state or in the state that it is brought into close contact with a male mold by thermal shrinkage. The thermoforming is preferably at, for example, 70 to 100 deg.C by a plug assist forming process. This product is set to the degree of orientation ΔP to a range of 0.05<=ΔP<=0.20 and mean refractive index nA of a range of 1.57<=nA<=1.62. To increase the degree of orientation, orientation magnification of the thermoforming is increased or the thermoforming is conducted at a low temperature. To increase the mean refractive index, heat treating temperature of the product is raised, or heat treating time is lengthened.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thermoformed product obtained by thermoforming a polyester sheet, and more particularly to a thermoformed product excellent in heat resistance.

[0002]

2. Description of the Related Art It is well known to manufacture thermoformed articles from polyester sheets by thermoforming such as vacuum forming, air pressure forming, and plug assist forming. Thermoforming is easy in molding operation, and the resulting thermoformed product is generally excellent in gas barrier properties and mechanical strength, and is therefore widely used in the manufacture of containers such as cups and various food trays.

However, thermoformed articles obtained from polyester sheets have poor shape stability at high temperatures, for example, 6%.
There is a drawback that when it is exposed to a temperature of about 0 to 100 ° C., it is easily deformed.

Various proposals have been made in the past to improve this disadvantage, but none of them has been satisfactory. For example, Japanese Patent Publication No. 44-5108 discloses that after heat-molding a polyethylene terephthalate film, the heat-molded product is heat-treated at 140 to 220 ° C. in a molding die to be crystallized, thereby improving heat resistance. Have been. However, this method has a problem that the thermoformed product is deformed at the time of heat treatment, and the impact resistance of the thermoformed product is reduced by the heat treatment. The decrease in impact resistance is considered to be due to the fact that spherulites are easily generated by this method, and the thermoformed product becomes brittle. As a modification of this method, heat treatment may be performed at a relatively low temperature of 60 to 140 ° C. to remove distortion of the thermoformed product without crystallization, but this has a small effect of improving heat resistance.

JP-A-54-43971, 43972
And JP-A-55-17516 disclose a method in which a polyester sheet is biaxially stretched and oriented, then thermoformed, and then the obtained thermoformed product is heat-treated. However, these methods have a small effect when a polyester sheet with a low degree of orientation is used, and conversely, when a polyester sheet with a high degree of orientation is used, the deep drawability is inferior, so that the appearance of the thermoformed product is poor. There is a problem that becomes.

JP-A-50-21051 discloses that an unstretched polyester sheet is uniaxially stretched 1.5 to 3.0 times at 70 to 100 ° C. and then heated with hot water at 90 to 95 ° C. A method is disclosed in which a contracted product is thermoformed as a molding material, and the thermoformed product is heat-set at 130 to 150 ° C. in a mold. JP-A-61-254326 discloses that
The unstretched polyester sheet is stretched 1.5 to 3.0 times in the biaxial direction by a simultaneous biaxial stretching machine at 70 to 100 ° C., and then heat shrunk at 70 to 120 ° C. as a molding material. There is disclosed a method in which air-pressure molding is performed at 100 ° C., and a thermoformed product is heat-set at 180 to 250 ° C. in a mold.
However, these methods have problems such as poor appearance of the thermoformed product due to poor deep drawability of the polyester sheet, a small improvement effect of heat resistance, and a decrease in impact resistance of the thermoformed product. There is.

[0007]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned prior art, and has as its object to provide a thermoformed product of a polyester sheet which is excellent in both heat resistance and appearance.

[0008]

According to the present invention, among the thermoformed polyester sheet products, those satisfying the following formulas (1) and (2) are excellent in both heat resistance and appearance. Was found. 0.05 ≦ ΔP ≦ 0.20 (1) 1.57 ≦ n _A ≦ 1.62 (2) (where, ΔP indicates the degree of plane orientation, and n _A indicates the average refractive index)

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION The polyester referred to in the present invention is
It is mainly composed of an aromatic dicarboxylic acid component and a glycol component. Examples of the aromatic dicarboxylic acid include terephthalic acid, 2,6-naphthalenedicarboxylic acid, other naphthalenedicarboxylic acids, phthalic acid, and isophthalic acid. As glycols, ethylene glycol, diethylene glycol, propylene glycol,
1,4-butanediol, neopentyl glycol,
Examples include 1,3- or 1,4-cyclohexanedimethanol. Further, bisphenol A, bisphenol S, or the like can also be used.

[0010] In addition to the above-mentioned aromatic dicarboxylic acid component and glycol component, the polyester may contain a small amount of other copolymer components. Such copolymerization components include:
Aliphatic dicarboxylic acids such as sebacic acid and adipic acid,
Oxycarboxylic acids such as p-oxyethoxybenzoic acid are mentioned. Further, a trifunctional carboxylic acid or alcohol may be contained to cause branching in the molecular chain.

In the present invention, a polyester composed of various components can be used as described above. Usually, a polyester mainly composed of polyethylene terephthalate is used. Among them, it is preferable to use polyethylene terephthalate in which ethylene terephthalate units account for 80 mol% or more, particularly 90 mol% or more, from the viewpoints of economy, moldability, and physical properties of the finally obtained molded article. When such a polyethylene terephthalate is used, the effect of improving heat resistance, which is the greatest feature of the present invention, is best exhibited. As the copolymerization component of polyethylene terephthalate, isophthalic acid, 2,6-
Naphthalenedicarboxylic acid, diethylene glycol, 1,
4-Cyclohexanedimethanol and the like are preferred.

The limiting viscosity of the polyester sheet to be subjected to thermoforming is 0.50 to 1.3 dl / g, particularly 0.60 to 1.3 dl / g.
It is preferably in the range of 1.1 dl / g. In general, when the intrinsic viscosity is less than 0.50 dl / g, the deep drawability at the time of producing a thermoformed product is poor, and the mechanical properties of the obtained thermoformed product, particularly, the impact resistance, tend to be poor. Conversely, a sheet having an intrinsic viscosity of more than 1.3 dl / g is difficult to manufacture, and the deep drawability when manufacturing a thermoformed product from the sheet tends to be poor.

Although the intrinsic viscosity of polyester decreases when melt-extruded into a sheet, the intrinsic viscosity does not substantially decrease during thermoforming of the sheet. Is almost equal to the intrinsic viscosity of

In the present invention, a polyester produced by melt polymerization or melt polymerization and solid phase polymerization by a conventional method can be used. In the production of polyester, various commonly used auxiliaries such as an esterification or transesterification catalyst, a polymerization catalyst, a stabilizer, a lubricant, and an antistatic agent can be appropriately added. In order to produce the thermoformed article according to the present invention from polyester, first, the polyester is formed into a sheet. If desired, various conventional additives such as an antioxidant, an ultraviolet absorber, a flame retardant, and a lubricant can be incorporated into the polyester to be molded. For example, the polyester can be colored to obtain a final colored thermoformed article. For coloring, it is preferable to use a master batch containing a coloring agent at a high concentration. If desired, a small amount of a polymer other than polyester, such as polycarbonate or polyolefin, can be blended. The compounding amount is usually 10% by weight or less of the whole, and 5% by weight.
It is preferable to stop below. In general, the incorporation of a polymer other than the polyester reduces the properties of the polyester, making it difficult to exhibit its excellent physical properties. However, as described above, the effect on the physical properties is small and often acceptable as described above.

The production of the polyester sheet may be carried out according to a conventional method. For example, a polyester sheet can be produced by drying a polyester, loading it into an extruder, extruding it into a molten sheet at 200 to 320 ° C., contacting it with a casting drum, and cooling and solidifying it. When using an extruder with a vent,
The drying time can be reduced or the drying can be omitted altogether. Further, a touch roll may be added to the casting drum, and the sheet-like polyester extruded from the extruder may be pressed against the casting drum by the touch roll.

The thickness of the polyester sheet is usually 0.1
〜１０10 mm. If the sheet is too thin, the impact resistance and rigidity of the finally obtained thermoformed product are poor, and the effect of improving the heat resistance is small. Conversely, if the sheet is too thick, deep drawability will be poor. The preferred thickness of the polyester sheet is 0.20 to 10 mm, particularly 0.50 to 10 mm
It is.

The polyester sheet may be a laminate of two or more layers, or may have been subjected to various surface treatments.

The production of a thermoformed product from a polyester sheet can be carried out by any method commonly used for thermoforming of a polyester sheet, such as pressure forming, vacuum forming, plug-assisted pressure / vacuum forming, and blow molding. In one preferred method, the polyester sheet is thermoformed into a thermoformed article having a thickness of 1/3 to 1/15 of the thickness of the sheet, and then the thermoformed article is subjected to tension, ie, a male mold. Then, heat treatment is performed at a high temperature of 150 to 270 ° C. in a state of being closely contacted by heat shrinkage. The thermoforming is preferably performed by a plug assist method at a sheet temperature of 70 to 100 ° C.

The thermoformed product according to the present invention has a degree of plane orientation (Δ
P) and the average refractive index (n _A ) must be within the ranges of the following equations (1) and (2). 0.05 ≦ ΔP ≦ 0.20 (1) 1.57 ≦ n _A ≦ 1.62 (2) The degree of plane orientation (ΔP) is defined by the following equation (3).

ΔP = 0.5 × (nγ + nβ) −nα (3) (where, nα is the refractive index in the direction perpendicular to the surface direction of the polyester sheet, and nγ is the maximum value of the refractive index in the surface direction) , Nβ
Is the refractive index orthogonal to this).

According to the study of the present inventors, the degree of plane orientation of a thermoformed product is closely related to heat resistance, and the degree of plane orientation (ΔP)
It was found that those having a value of less than 0.05 or more than 0.20 had inferior heat resistance. The preferred range of the degree of plane orientation is 0.0
It is 5 to 0.18, especially 0.07 to 0.18. Most preferably, the degree of plane orientation is in the range of 0.10 to 0.18.

The average refractive index (n _A ) is defined by the following equation (4). n _A = (nα + nβ + nγ) / 3 (4) Those having an average refractive index (n _A ) of less than 1.57 or more than 1.62 undergo large thermal deformation when exposed to a high temperature. A preferred range of the average refractive index (n _A) is from 1.58 to 1.6
2, especially 1.59 to 1.61.

In order to set the degree of plane orientation (ΔP) and the average refractive index of the thermoformed product in the above ranges, various conditions known to affect these physical properties may be appropriately controlled. For example, in order to increase the degree of plane orientation, the stretching ratio in thermoforming may be increased, or thermoforming may be performed at a low temperature. In order to increase the average refractive index, the heat treatment temperature of the thermoformed product may be increased,
The heat treatment time may be extended.

The thermoformed article according to the present invention has a surface orientation degree and an average refractive index in the above-mentioned range, and furthermore, has a heated crystallization temperature measured at a heating rate of 20 ° C./min after melting and quenching. (T
cc) is preferably between 115 and 230 ° C. If the heating crystallization temperature is too low or too high, thermoforming is generally difficult and the resulting thermoformed product tends to have poor appearance. The preferred range of the elevated crystallization temperature is 125 to 200 ° C, particularly 140 to 200 ° C.

The thermoformed product according to the present invention has excellent appearance and heat resistance, and is therefore suitable for various uses requiring heat resistance. One example is a food container to be heat sterilized. In other words, for heat-sterilized hot foods to be filled as they are, or for heat sterilization after filling, conventional thermoformed products are difficult to use due to thermal deformation, but the thermoforming according to the present invention The product has excellent heat resistance and can be used without any problem.

Also, molded articles for use such as luggage which are exposed to high temperatures under the sun, etc., are suitable because they do not cause appearance defects or deterioration in physical properties due to deformation. Further, it is also suitable as an interior material for a bathtub, since hot water does not cause poor appearance or deterioration in physical properties.

[0027]

EXAMPLES The present invention will be described more specifically with reference to the following examples, but the present invention is not limited to the following examples. In addition, the measurement in an Example was performed as follows. (1) Intrinsic viscosity: 1.00 g of sample was mixed with phenol / tetrachloroethane = 50/50 (weight ratio) 100
The solution dissolved in ml was measured at 30 ° C.

(2) Amount of diethylene glycol and cyclohexanedimethanol: The sample was hydrolyzed and quantified by gas chromatography. (3) Heating Crystallization Temperature (Tcc): A 10 mg sample collected from a thermoformed product was melted while being held at 300 ° C. for 3 minutes in a nitrogen atmosphere, and then rapidly cooled to 10 ° C. or lower. Using a differential scanning calorimeter DSC20 manufactured by Seiko Denshi Co., the quenched material prepared above was heated from 20 ° C. at a heating rate of 20 ° C./min, and the exothermic peak temperature was raised to the crystallization temperature (Tcc).
And

(4) Plane orientation (ΔP) and average refractive index (n _A ): For a sample collected from a thermoformed product, the refractive index in the direction perpendicular to the plane direction at 23 ° C. using an Abbe refractometer ( nα) and the maximum value (nγ) of the refractive index in the plane direction and the refractive index (nβ) orthogonal thereto were measured, and were calculated from the measured values by the following equation. ΔP = 0.5 × (nβ + nγ) −nα n _A = (nα + nβ + nγ) / 3

(5) Average thickness: The thickness was measured at intervals of 5 mm, and the arithmetic average was calculated. Note that only the stretched portion was used for measuring the thickness of the thermoformed product, and the ear portion, which was the unstretched portion, was excluded. (6) Deep drawing formability: The appearance of 20 thermoformed products was visually observed and judged according to the following criteria.

○ There is no problem as a product △ There is a slight problem in appearance and there is a possibility that it may not be a product in some cases × Insufficient drawing, wrinkles, tears, etc., poor appearance and no product

(7) Heat resistance: Twenty thermoformed products were added to 100
After being kept in a hot air oven set at 30 ° C. for 30 minutes, it was taken out and left for 1 hour in an atmosphere at 23 ° C. and a relative humidity of 65%. The appearance of this product was visually observed and judged according to the following criteria.な し No significant difference from before heat treatment △ Slight change in appearance × Notable difference from before heat treatment

Example 1 A polyethylene terephthalate having a composition shown in Table 1 containing isophthalic acid and diethylene glycol was added under vacuum for 160
After drying at 12 ° C. for 12 hours, the mixture was melt-extruded into a sheet at 290 ° C. using an extruder, contacted with a casting drum at 40 ° C., and cooled and solidified to produce an unstretched sheet having a thickness of 1.0 mm. Its intrinsic viscosity is 0.70dl
/ G.

This sheet was cut into 200 × 200 mm, heated to 90 ° C., and the diameter of the bottom was 50 mm, the diameter of the mouth was 60 mm and the depth was 90 mm using a male mold.
It was shaped into a cup with rounded corners. The male mold is a wooden mold covered with flannel cloth, and temperature control is not performed.
Next, while keeping the molded product fixed in the male mold, it was placed in a hot air oven set at 240 ° C., kept for 3 minutes, taken out and allowed to cool at room temperature. The average thickness of the obtained molded product was 0.14 mm. The results are shown in Table 1.

Example 2 An unstretched polyester sheet having a thickness of 1.0 mm was prepared in the same manner as in Example 1 except that polyethylene terephthalate having the composition shown in Table 1 containing 1,4-cyclohexanedimethanol and diethylene glycol was used. Was manufactured.
Its intrinsic viscosity was 0.75 dl / g.

A thermoformed product having an average thickness of 0.14 mm was produced in the same manner as in Example 1 except that the polyester sheet was used and the heating temperature of the sheet was 92 ° C. The results are shown in Table 1.

Comparative Example 1 The polyester sheet produced in Example 1 was heated to 100 ° C., and vacuum molded by a plug assist method using a female mold corresponding to the male mold of Example 1. No heat treatment was performed. The average thickness of the obtained molded product was 0.25 mm. The results are shown in Table 1.

Comparative Example 2 An unstretched polyester sheet having a thickness of 1.0 mm was prepared in the same manner as in Example 1 except that polyethylene terephthalate having the composition shown in Table 1 containing 1,4-cyclohexanedimethanol and diethylene glycol was used. Was manufactured.
Its intrinsic viscosity was 0.75 dl / g.

A molded product was obtained in exactly the same manner as in Comparative Example 1 except that this polyester sheet was used and the heating temperature of the sheet was 115 ° C. The average thickness of the molded product is 0.25m
m. The results are shown in Table 1.

[0040]

[Table 1]

Claims (4)

[Claims] 1. A thermoformed product obtained by thermoforming a polyester sheet, characterized by satisfying the following formulas (1) and (2): 0.05 ≦ ΔP ≦ 0.2 (1) 57 ≦ n _A ≦ 1.62 (2) (where, ΔP indicates the degree of plane orientation, and n _A indicates the average refractive index) 2. The thermoformed product according to claim 1, wherein the temperature-rise crystallization temperature is 115 to 230 ° C. 3. The thermoformed product according to claim 1, wherein the thermoformed product is a food container to be sterilized by heating. 4. A process of thermoforming a polyester sheet into a thermoformed product having a thickness of 1/3 to 1/15 of the thickness of the sheet, and subjecting the thermoformed product to a heat treatment at 150 to 270 ° C. under tension. The method for producing a thermoformed product according to any one of claims 1 to 3, wherein: