JPH08156211A - Thermoforming polyester sheet - Google Patents

Abstract

PURPOSE: To easily mold a thermoformed container having uniform wall thickness and high in transparency by laminating a skin layer having specific crystal heat of fusion and intrinsic viscosity to at least the single surface of a polyester core layer having specific intrinsic viscosity. CONSTITUTION: A core layer is formed from polyester with intrinsic viscosity of 0.5-1.1 obtained by the polycondensation of terephthalic acid and ethylene glycol. A skin layer composed of polyester consisting of terephthalic acid being a main dicarboxylic acid component and ethylene glycol being a main diol component and characterized by that crystal heat of fusion is 8.5cal/g or less and intrinsic viscosity is 0.5-1.1 is laminated to at least the single surface of the core layer to form a crystal non-oriented polyester sheet. In this case, it is necessary that the difference between the glass transition temps. of polyesters constituting the skin layer and the core layer is set to 10 deg.C or lower and the thickness of the skin layer is set to a range of 1-30% with respect to the total thickness of the sheet.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention provides a highly transparent thermoformed container free from uneven thickness under a wide range of thermoforming conditions without impairing the excellent mechanical properties of polyethylene terephthalate (hereinafter abbreviated as PET). A polyester sheet that can be obtained.

[0002]

2. Description of the Related Art Saturated polyesters, particularly crystalline polyester resins typified by PET, are widely used as polymers for sheet films including fibers, and carbon dioxide is utilized by taking advantage of their excellent chemical resistance and low gas permeability. Beverages,
It has come to be applied to bottles for beverages such as juice and beer, cosmetic containers, and trays for food.

Among them, the amorphous polyester sheet called A-PET has attracted attention for its excellent recyclability, low pollution and food safety, and in recent years, its amount has rapidly increased as a packaging material replacing vinyl chloride and polystyrene. There is. 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 in which cosmetics, electric devices, etc. are put.

Conventionally, since such a saturated polyester sheet has crystallinity, if it is overheated during thermoforming, a whitening phenomenon due to crystallization occurs and the excellent transparency of A-PET is impaired. In particular, when thermoforming a cup-shaped deep-drawing container or a container having a complicated rib, it is necessary to sufficiently heat the sheet to be soft during thermoforming, and unmodified polyester may cause clouding or uneven thickness of the container. However, the problem is that the appropriate range of thermoforming conditions is very narrow, and improvement has been desired.

Conventionally, there have been many proposals for a method for improving the thermoformability of a polyester sheet. For example, as described in JP-A-51-81857 and JP-A-51-38335, JP-A-4-293920, a method of copolymerizing a component which inhibits crystallinity to prevent crystallization during heating, or PETG There is a method using a so-called copolyester of alicyclic diol and ethylene glycol.

However, if the amount of the copolymerizable component that inhibits the crystallinity is small, the effect of improving the thermoformability is low, and it is difficult to improve the uneven thickness during deep drawing. Further, the thermoformability is improved by increasing the amount of the copolymerization component, but A-PET
The flexibility and impact resistance possessed by are impaired, which is not preferable. Although PETG is excellent in transparency, thermoformability, and mechanical properties, it is necessary to use a thicker sheet than a general sheet because the sheet is weak, and PETG is economically inferior and is generally used. The current situation is not.

[0007]

DISCLOSURE OF THE INVENTION The inventors of the present invention have made extensive studies in order to solve such conventional problems. As a result, the polyester having an intrinsic viscosity of 0.5 to 1.1 has an intrinsic viscosity of at least one side. A polyester sheet in which a low crystalline polyester having a viscosity of 0.5 to 1.1 and having a specific heat of crystal fusion and a glass transition temperature is extremely thinly laminated, has an uneven thickness without impairing the mechanical properties of PET. It was found that a thermoformed container having high transparency and a high transparency can be obtained under a wide range of thermoforming conditions, and that it is extremely economical, leading to the present invention.

[0008]

That is, the present invention uses (A) terephthalic acid as a main dicarboxylic acid component, ethylene glycol as a main diol component, and has a heat of crystal fusion of 8.5.
A skin layer made of polyester having cal / g or less and an intrinsic viscosity of 0.5 to 1.1, (B) terephthalic acid and ethylene glycol are polycondensed, and the intrinsic viscosity is 0.5.
A polyester laminate having a core layer made of a polyester of 1.1 to 1.1 and having a glass transition temperature difference of 10 ° C. or less between the polyester resins forming the (A) layer and the (B) layer. Thus, the (A) layer is laminated on at least one side, and the (A) layer is in the range of 1 to 30% of the total thickness of the sheet, which is a substantially amorphous non-oriented polyester sheet.

The polyester (B) used in the core layer of the present invention is not limited to PET, but a part of the terephthalic acid component is isophthalic acid, adipic acid, diphenylcarboxylic acid,
Substituting one or more other dicarboxylic acid components such as diphenyl ether dicarboxylic acid, diphenyl sulfone dicarboxylic acid, sebacic acid, naphthalene dicarboxylic acid, etc., and part of the ethylene glycol component is diethylene glycol, hexamethylene glycol, trimethylene glycol, propylene glycol, It includes copolyesters substituted with one or more other glycol components such as cyclohexanedimethanol, neopentyl glycol, butylene glycol and the like.

The total proportion of the copolymerization components in the polyester (B) is preferably 10 mol% or less, more preferably 5 mol% or less, based on the total acid components. Further, a compound having three or more functional groups or a monofunctional compound may be contained within the range considered to be substantially linear. Further, 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 reduce the transparency.
Further, when matting is required, a coloring agent such as titanium dioxide, calcium carbonate, iron oxide or carbon black may be contained.

The intrinsic viscosity is 60/40 at a weight ratio of 60/40.
When measured in a mixed solvent of phenol / tetrachloroethane, the intrinsic viscosity is required to be 0.5 to 1.1, and particularly preferably 0.55 to 0.85. If it is less than 0.5, the mechanical strength of the container is insufficient, and especially the impact strength at low temperature is insufficient. In addition, the drawdown of the sheet during preheating during thermoforming is significantly increased, and uneven thickness and wrinkles are likely to occur in the molded product, which is not suitable. On the other hand, when the intrinsic viscosity exceeds 1.1, it becomes difficult to form a sheet and the economy is poor.

Further, the polyester (A) to be laminated on the surface of the present invention has a heat of crystal fusion of 8.5 cal / g or less, preferably 7.5 cal / g or less, and the polyester resin constituting the main layer. Difference from glass transition temperature is 10
It is necessary that the temperature is not higher than 0 ° C, preferably not higher than 7 ° C.
When the heat of crystal fusion is larger than 8.5 cal / g, the range of suitable thermoforming conditions is narrow and the container is liable to whiten during thermoforming, which is not preferable.

Further, when the difference in glass transition temperature is larger than 10 ° C., for example, when polycarbonate, polyarylate, etc. are laminated, the difference in elastic modulus between the multilayers becomes significantly large during heating of the sheet for thermoforming, so that thermoforming is performed. It is not preferable because the product may have improper shaping or uneven thickness, and the width of appropriate thermoforming conditions may be narrowed. The intrinsic viscosity is required to be 0.5 to 1.1, particularly preferably 0.55 to 0.85. If it is less than 0.5, the mechanical strength of the entire sheet is lowered due to the notch effect.
On the other hand, when the intrinsic viscosity exceeds 1.1, it becomes difficult to form a sheet and the economy is poor.

The polyester (A) to be laminated on the surface of the present invention contains terephthalic acid as a main dicarboxylic acid component and ethylene glycol as a main diol component and has a heat of crystal fusion of 8.5 cal / g or less and constitutes a core layer. Any polyester can be used as long as the difference from the glass transition temperature of the polyester resin is 10 ° C. or less.
Examples of the third component used include the following compounds.

That is, as the dicarboxylic acid component, isophthalic acid, adipic acid, diphenylcarboxylic acid, diphenyl ether dicarboxylic acid, diphenyl sulfone dicarboxylic acid, sebacic acid, naphthalene dicarboxylic acid, cyclohexane dicarboxylic acid and / or diethylene glycol, hexamethylene glycol as the diol component. Examples thereof include polyesters obtained by copolymerizing 10 mol% or more of trimethylene glycol, propylene glycol, cyclohexanedimethanol, neopentyl glycol and butylene glycol. These polyesters have a heat of crystal fusion of 8.5 cal / g or less and a difference from the glass transition temperature of the polyester (B) in the core layer of 10 ° C.
It is the following.

Copolymerization is the most preferable method of blending the third component, but in some cases a high molar copolymer resin can be blended with PET before use.

In some cases, an oxycarboxylic acid such as parahydroxybenzoic acid can also be used. These dicarboxylic acid diols and oxycarboxylic acids have a polyester crystal heat of fusion of 8.5 cal / g or less,
Further, as long as the difference from the glass transition temperature of the polyester resin constituting the core layer is 10 ° C. or less, one kind thereof may be used alone or a plurality thereof may be used in combination.

Drawing ratio (ratio of container depth to container diameter)
When thermoforming a deep-drawing thermoformed product with a value of more than 0.8 or a complicated tray with a rib shape, it is necessary to make the sheet sufficiently soft during heating. With unmodified A-PET, the surface of the molded product is It becomes cloudy.

It is considered that this is because the oriented skin layer on the surface of the sheet during film formation is crystallized at the time of heating during thermoforming. It was found that it is not necessary to use low copolyester, and deep drawability and fogging of the container are significantly improved by laminating a low crystalline polyester having a specific heat of crystal fusion only on the very surface layer of the sheet. did.

The ratio of the polyester (A) to be laminated on the surface of the sheet to the total thickness of the sheet is 1 to 30.
%, But from the viewpoints of economy and stability of quality, 5 to 20% is preferable. When the ratio of the polyester (A) laminated on the surface to the entire sheet is less than 1%, it becomes difficult to form the skin layer uniformly. On the other hand, when it exceeds 30%, not only the effect of further improving the thermoformability is small, but also a large amount of expensive polyester (A) is used, which is economically unfavorable.

The sheet thickness used for producing the present invention is not particularly limited, but is usually 50 to 2000 μm, preferably 100 to 1000 μm.

The sheet can be obtained by melt-extruding with a usual extruder for polyester such as a single-screw extruder or a twin-screw vent extruder, and cooling the molten resin with a cooling drum. The sheet is preferably quenched as much as possible in order to prevent a decrease in transparency due to crystallization, the crystallinity of the core layer is 10% by weight or less (density 1.348 g / cm3 or less), and the sheet haze is 5 or less.
% Or less is desirable.

In order to obtain the present invention, it is possible to use a known coextrusion device having a feed block die, a multi-manifold die and the like. Also, it can be manufactured by known techniques such as melt lamination and dry lamination,
Coextrusion is preferred because of the quality of the sheet.

Further, 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, but the touch roll method from the viewpoint of glossiness and thickness uniformity of the sheet. Is preferred.

In-line recycling is an A-PE in which ears that appear when the sheet is cut into a predetermined width during film formation and the skeleton portion that is punched out of the container after thermoforming are crushed and returned as raw materials.
Although it is generally used for T, in the present invention, it can be compounded into the main layer within a range that does not extremely reduce the intrinsic viscosity of the sheet.

The product of the present invention may be formed by any of vacuum forming, pressure forming, hot plate forming, plug assist forming, reverse draw forming, air slip forming, etc., or a combination of these.

[0027]

EFFECTS OF THE INVENTION The sheet of the present invention maintains the characteristics inherent to A-PET, such as transparency, mechanical properties, and recyclability, has no uneven thickness, and is extremely economical, and is suitable for deep-drawing beverage cups and Best suited for trays with complicated ribs, blister packs, etc.

[0028]

The present invention will be described in more detail with reference to the following examples, but the present invention is not limited thereto.
Each characteristic value was measured according to the following method.

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

(2) Thermoformability A cup-shaped container having a diameter of 80 mm and a depth of 120 mm was produced by a vacuum forming machine with plug assist. The case where a perfect container was formed was evaluated as ◯, the case where the patterning was complete but the transparency was poor was evaluated as Δ, and the case where the patterning was incomplete or uneven thickness was evaluated as x.

(3) Width of thermoforming conditions The sheet surface temperature at which thermoforming can be completed was measured with a non-contact type infrared radiation thermometer. A sheet having a thermoformable sheet surface temperature range of more than 15 ° C was evaluated as ◯, a sheet having a temperature of 10 to 15 ° C as Δ, and a sheet having a temperature of less than 10 ° C as x.

(4) Heat of fusion of crystal, glass transition temperature Differential running calorimeter (manufactured by Rigaku) (Model DSC-823
0) was used and the measurement was carried out by a method according to JIS-K-7105. The rapidly cooled sheet in a substantially amorphous state was measured in a nitrogen stream at a temperature rising rate of 10 ° C./minute to determine the heat of crystal fusion (ΔH) and the glass transition temperature (Tg). (See Fig. 1)

Examples 1 to 9 Comparative Examples 1 to 8 Melt extrusion was performed from a T die using a multi-layer extruder with a biaxial vent under conditions of 285 ° C. and a vacuum degree of a vent portion of 5 mmHg, and a film was formed by a touch roll method. By doing this, sheets having various structures described in Examples and having a thickness of 800 μm were obtained.

Then, the above sheet was preheated to a temperature not lower than the glass transition temperature and not higher than the melting point, and a cup-shaped container was prepared and evaluated by a vacuum molding machine with a plug assist equipped with a female mold whose temperature was controlled at 45 ° C. Table 1 shows the results.

[0035]

[Table 1]

[Brief description of drawings]

FIG. 1 is a schematic view showing a measurement chart of heat of crystal fusion and glass transition temperature of polyester resin.

Claims (2)

[Claims] 1. A polyester having (A) terephthalic acid as a main dicarboxylic acid component, ethylene glycol as a main diol component, and a heat of fusion of crystal of 8.5 cal / g or less and an intrinsic viscosity of 0.5 to 1.1. And a (B) core layer made of a polyester obtained by polycondensing terephthalic acid and ethylene glycol and having an intrinsic viscosity of 0.5 to 1.1. The (A) layer and the (B) ) A polyester laminate in which the difference in glass transition temperature of the polyester resin constituting the layer is 10 ° C. or less, the (A) layer is laminated on at least one side, and the (A) layer is the entire sheet. A substantially amorphous non-oriented polyester sheet in the range of 1 to 30% of the thickness. 2. A polyester molded product obtained by thermoforming the sheet according to claim 1.