JPH08267686A - Heat forming polyester sheet and formed item thereof - Google Patents

Abstract

PURPOSE: To provide a polyester sheet with reduced likelihood of the occurrence of drawdown, a deflection of thickness and a cloudiness of a vessel, and having various heat forming conditions. CONSTITUTION: The main repeating unit is constituted of a polyester sheet layer (A) obtained by adding 0.02-0.5wt.% pyrometic acid anhydride to 99.98wt.%-99.5wt.% polyester of ethylene terephthalate to then be subjected to melt extrusion, and a polyester layer (B) having terephthalic acid as a main dicarboxylic acid and ethylene glycol as a diole component, and a crystal melting heat of 8.5cal/g or lower and inherent viscosity of 0.5-1.1. The laminate is that the difference of glass transit temperature of polyester resin forming both the layers is 10 deg. or lower, and the B layer is laminated on both the surfaces, and further the polyester sheet is that the B layer is in the substantially amolphous orientation and lies in the range of 1-90% in the overall thickness of the sheet, thereby obtaining a formed item by heat-forming this sheet.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to drawdown, uneven thickness,
The present invention relates to a polyester sheet having a container with a low fog and a wide range of thermoforming conditions.

[0002]

2. Description of the Related Art Saturated polyesters, particularly crystalline polyester resins typified by polyethylene terephthalate (hereinafter abbreviated as PET) are widely used as polymers for sheets and films including fibers. Taking advantage of low gas permeability, it has come to be applied to carbonated drinks, juices, bottles for beverages such as beer, cosmetic containers, and food trays. Above all, A-PE
The amorphous polyester sheet called T has attracted attention for its excellent recyclability, low pollution, and food safety, and its use amount has rapidly increased in recent years as a packaging material replacing vinyl chloride and polystyrene.

This polyester sheet is used as a blister pack for food and medicine containers and miscellaneous goods by thermoforming. Generally, a method of heating a sheet with a heater and shaping with a vacuum pressure or a pneumatic pressure is used.

However, since such a saturated polyester sheet has a low molecular weight as compared with a commonly used thermoforming sheet such as vinyl chloride or high impact polystyrene, the sheet is preheated by a heater or the like during thermoforming. In doing so, the phenomenon of sagging due to the weight of the sheet (hereinafter this phenomenon is abbreviated as drawdown) is likely to occur, and wrinkles and bridges are easily formed on the thermoformed product.

In particular, when thermoforming a cup-shaped deep-drawing container or a container having complicated ribs, it is necessary to sufficiently heat the sheet to be soft during thermoforming, and drawdown becomes remarkable. Further, when thermoforming is performed using a wide sheet having high productivity, this phenomenon becomes more remarkable. As a result, in the conventional A-PET, the strength of the container is reduced due to uneven thickness and the appearance defect rate due to the occurrence of bridges is high, and improvement is desired.

There have been many proposals for improving the drawdown of polyester. For example, a method of blending a polyfunctional carboxylic acid having a functionality of 3 or more as described in JP-A-5-295241, a method of weakly stretching a sheet as described in JP-A-5-293885, or increasing the degree of polymerization of a raw material A method of improving the drawdown of a sheet by using the resin is disclosed.

Improvements have also been made with thermoforming machines.
For example, a method of increasing the clamp width of the sheet in the heating zone or a method of holding the sheet by a chain is also used.

Although the drawdown is reduced by the method described in JP-A-5-295241, the unreacted polycarboxylic acid serves as a nucleating agent, so that the crystallization rate of the sheet is remarkably accelerated and the molded article becomes cloudy and transparent. It was difficult to obtain a good thermoformed product. Furthermore, in the method using this weak crosslinking, when a polycarboxylic acid necessary for reducing drawdown is blended, melt fracture occurs during film formation, or surface roughening of the container occurs during thermoforming, resulting in excellent appearance. Sheet and thermoformed product cannot be obtained.

[0009] Further, the improvement by weak stretching to the extent that does not impair the thermoformability of the sheet is slightly improved by temporary return of the sheet due to relaxation of internal stress, but to realize a drawdown as small as vinyl chloride. Not only is it insufficient, but it is not effective in improving the uneven thickness of deep drawing.

Further, the method of using a resin having a high degree of polymerization is not only economically disadvantageous but also causes a problem of deterioration of extrusion moldability due to an increase in melt viscosity, which makes mass production difficult.

[0011]

DISCLOSURE OF THE INVENTION As a result of intensive studies made by the present inventors in order to solve such conventional problems, as a result, P
When a cross-linking agent for preventing drawdown is blended by laminating polyester having a specific heat of crystal fusion and a specific glass transition point on both surfaces of a polyester sheet layer in which a specific amount of pyromellitic dianhydride is mixed with ET However, it is possible to form a sheet with a good appearance without melt fracture, and the sheet has improved drawdown at the time of thermoforming, surface roughness and fogging of the container, and good transparency without using a special thermoforming machine. It was found that a thermoformed container having no uneven thickness can be obtained under a wide range of thermoforming conditions, and the present invention has been completed.

[0012]

Means for Solving the Problems That is, the present invention relates to (A) a polyester whose main repeating unit is ethylene terephthalate is 99.98% by weight to 99.5% by weight, and 0.02 to 0. A polyester sheet layer obtained by adding 5% by weight and melt-extruding, (B) terephthalic acid as a main dicarboxylic acid component, ethylene glycol as a main diol component, and a heat of crystal fusion of 8.5 cal /
a layer made of polyester having an intrinsic viscosity of 0.5 to 1.1 and a glass transition temperature difference between the polyester resins constituting the (A) layer and the (B) layer. A polyester laminate having a temperature of 10 ° C or lower, wherein the (B) layer is laminated on both sides, and
A substantially amorphous non-oriented polyester sheet having a layer in the range of 1 to 90% of the total thickness of the sheet, and a polyester molded article obtained by thermoforming the sheet.

The polyester (A) used in the present invention is preferably PET obtained by polycondensation of terephthalic acid and ethylene glycol, from the viewpoints of economy and resistance to aging.
Part of the terephthalic acid component is isophthalic acid, adipic acid,
Diphenyl carboxylic acid, diphenyl ether dicarboxylic acid, diphenyl sulfone dicarboxylic acid, sebacic acid,
Substituting one or more other dicarboxylic acid components such as naphthalene dicarboxylic acid, and part of the ethylene glycol components such as diethylene glycol, hexamethylene glycol, trimethylene glycol, propylene glycol, cyclohexanedimethanol, neopentyl glycol, butylene glycol, etc. Copolymerized polyesters substituted with one or more other glycol components such as

The total proportion of the copolymerization components in the PET (A) is preferably 20 mol% or less based on the total acid components. Further, in the polyester, inactive particles, lubricants, heat stabilizers, fluidity improvers, ultraviolet absorbers, antistatic agents, antifog agents and the like can be added within the range not deteriorating 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 amount of pyromellitic acid used in the present invention is 0.02.
~ 0.5 wt% is required, preferably 0.04 ~
It is 0.30% by weight. If the blending amount is less than 0.02% by weight, the effect of improving drawdown is small. on the other hand,
If the amount is more than 0.5% by weight, gelation becomes severe and a uniform sheet cannot be obtained.

Further, the copolyester to be laminated on the surface of the present invention has a heat of crystal fusion of 8.5 cal / g or less, more preferably 7.5 cal / g or less, and a glass of polyester resin constituting the main layer. Difference in transition temperature is 10
It is necessary that the temperature is not higher than 0 ° C, more 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.

If the difference in glass transition temperature is larger than 10 ° C., the difference in elastic modulus between the multilayers becomes extremely large during heating of the sheet for thermoforming, so that improper molding or uneven thickness may occur in the thermoformed product. It is not preferable because the range of thermoforming conditions becomes narrow. 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 entire sheet decreases due to the notch effect. on the other hand,
If the intrinsic viscosity exceeds 1.1, it becomes difficult to form a sheet and the economy is poor.

The polyester (B) 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 main layer. Any polyester can be used as long as the difference in 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, diphenyletherdicarboxylic acid, diphenylsulfonedicarboxylic acid, sebacic acid, naphthalenedicarboxylic acid, cyclohexanedicarboxylic 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 (B) have a heat of crystal fusion of 8.5 cal / g or less and a difference from the glass transition temperature of the polyester (A) of the main layer is 10 ° C. or less.

Copolymerization is the most preferable method of blending the third component into the polyester (B), 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. In these dicarboxylic acid diols and oxycarboxylic acids, the heat of crystal fusion of the polyester (B) is 8.5 cal / g or less, and the difference from the glass transition temperature of the polyester (A) constituting the main layer is 10 ° C. or less. If there is one, it may be used alone or in combination.

The proportion of the polyester (B) laminated on the surface of the sheet in the entire sheet is preferably 1 to 90%. When the ratio of the polyester 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, if it exceeds 90%, the effect of improving drawdown becomes small.

The thickness of the sheet of the present invention is not particularly limited, but is usually 50 to 2000 μm, preferably 150 to 10
It is 00 μm.

The sheet can be obtained by melt-extruding using 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 cooled as rapidly as possible in order to prevent a decrease in transparency due to crystallization, and the degree of crystallinity measured by the density method is preferably 10% by weight or less and the sheet haze is preferably 15% or less.

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 is preferable from the viewpoint of glossiness and thickness uniformity of the sheet. . As a method for blending pyromellitic acid to be blended with polyester, a known method can be applied and there is no particular limitation. For example, the components are preliminarily uniformly blended with a tumbler or a blender, and the mixture is fed to an extruder, or the components to be added to the polyester are preliminarily pelletized as a masterbatch and fed at the time of extrusion, polymerization. There is a method to add it sometimes.

To obtain a uniform sheet, pyromellitic dianhydride sufficiently dried so that ring-opening reaction does not occur is mastered by using a low melting point polyester having an extrusion temperature of 50 ° C. or more lower than the melting point of pyromellitic dianhydride. A method in which chips are prepared in advance and supplied at the time of sheet extrusion is preferable.

The thermoforming method for the sheet may be vacuum forming, pressure forming, hot plate forming, plug assist forming, reverse draw forming, air slip forming, etc., or a combination of these methods, but the present invention is not limited thereto. Then, either method may be used. In addition, the clear case may be manufactured by any method used for vinyl chloride, polyolefin sheet and the like.

[0028]

EFFECTS OF THE INVENTION The present invention has mechanical properties, recyclability, etc.
-It is a polyester sheet that has a wide range of thermoforming conditions with little drawdown, uneven thickness, and fogging of the container while maintaining the characteristics that PET originally has, and for deep-drawing beverage cups, trays with complicated ribs, blister packs, etc. Optimal.

[0029]

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) Appearance of sheet: A sheet having a mirror-like surface was evaluated as ◯, a sheet having a slightly curved surface was evaluated as Δ, and a sheet having melt fracture and poor transparency was evaluated as x.

(3) Drawdown During thermoforming, the amount of sagging of the sheet under an appropriate temperature condition capable of forming the container is less than 5 cm, the one with 5 to 10 cm is the medium, and the one with more than 10 cm is the most. did.

(4) 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.

(5) Thermoforming condition width The sheet surface temperature at which thermoforming can be completed was measured with a non-contact type infrared radiation thermometer. A sheet having a range of thermoformable sheet surface temperatures of 15 ° C or more 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.

(6) Heat of fusion of crystals, glass transition temperature Differential running calorimeter (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 heating rate of 10 ° C./min to determine the heat of crystal fusion (ΔH) and the glass transition temperature (Tg) (FIG. 1).
reference).

Examples 1-10, Comparative Examples 1-8 Measured in a phenol / tetrachloroethane mixed solvent having a weight ratio of 60/40 at 20 ° C., an intrinsic viscosity of 0.65.
Copolymerized PET (isophthalic acid 30 mol%) has a water content of 2
Premixed with pyromellitic dianhydride that has been dried to 100 ppm or less and sufficiently dried so that ring-opening reaction does not occur, and kneaded with a biaxial kneader at 200 ° C. to give a pyromellitic dianhydride concentration of 10% by weight. % Master chip was prepared in advance.

When melt extrusion was performed using a multi-layer extruder with a biaxial vent under conditions of 285 ° C. and the degree of vacuum of the vent portion was 5 mmHg, when the film was formed by the touch roll method, the master of pyromellitic dianhydride was homopolyester. Resin (intrinsic viscosity 0.
70, glass transition temperature 69 ° C, heat of crystal fusion 12.5 ca
1 / g). The polyester described in the example was laminated on the upper and lower layers (skin layer) to produce a three-layer structure sheet having the composition shown in the example having a thickness of 800 μm and a sheet width of 1050 mm, and evaluated.

Then, the sheet was preheated to a temperature not lower than the glass transition temperature and not higher than the melting point, and a vacuum molding machine with a plug assist (clamping interval 1
(000 mm), a cup-shaped container was prepared and evaluated.

The above results are shown in Table 1.

[0040]

[Table 1]

[Brief description of drawings]

FIG. 1 shows a heat of crystal fusion (Δ
FIG. 3 is a schematic explanatory diagram of a method for obtaining H) and a glass transition temperature (Tg).

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical display location C08K 5/09 KJV C08K 5/09 KJV C08L 67/02 C08L 67/02 // B29K 67:00

Claims (2)

[Claims] 1. A polyester having 99.98% by weight of (A) a main repeating unit is ethylene terephthalate.
Pyromellitic dianhydride 0.02-based on 9.5% by weight
A polyester sheet layer obtained by adding 0.5 wt% and melt-extruding, (B) terephthalic acid as a main dicarboxylic acid component, and ethylene glycol as a main diol component,
A polyester comprising a polyester layer having a heat of crystal fusion of 8.5 cal / g or less and an intrinsic viscosity of 0.5 to 1.1 and constituting the layer (A) and the layer (B). A polyester laminate having a resin glass transition temperature difference of 10 ° C. or less, wherein the (B) layer is laminated on both sides, and the (B) layer has a thickness of 1 to 1 of the entire sheet.
A substantially amorphous non-oriented polyester sheet in the range of 90%. 2. A polyester molded product obtained by thermoforming the sheet according to claim 1.