JPH04308728A - Thermoforming polyester sheet, thermoformed article and preparation thereof - Google Patents

Abstract

PURPOSE:To provide a thermoforming polyester sheet excellent in economical efficiency such that rigidity is higher than that of a conventional polyester molded article and the thickness of a sheet to be used can be reduced. CONSTITUTION:A polyester sheet is characterized by that the heat shrinkage factor in the stretching direction thereof is 20% or more and the heat shrinkage factor thereof in the direction right-angled to the stretching direction is -10% to below 5% and the thickness irregularity thereof is + or -15% or less and formed by uniaxially stretching a substantially non-crystalline polyester sheet with a degree of crystallization of 2-10% molded in such a state that the temp. of a cast roll 3 immediately after the extrusion of the sheet is set to as high a temp. region as possible equal to or lower than the glass transition temp. of the sheet by 1.5-2.6 times using nip rollers as feed-out rollers 11,11' and taking-up rollers 12,12' and further using nip rolles as the rollers immediately after the taking-up rollers 12, 12'.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thermoformable polyester sheet with improved rigidity. More specifically, the rigidity is improved by applying uniaxial stretching at a low magnification within a range that does not impede thermoformability, and the rigidity is greater than that of conventional polyester sheet moldings, making it possible to reduce the thickness of the sheet used. This invention relates to a polyester sheet for molding, a thermoformed product thereof, and a method for manufacturing the same.

0002

2. Description of the Related Art The market for thermoformed products made from amorphous polyethylene terephthalate (hereinafter referred to as A-PET) sheets has recently been expanding. A-PET sheet has the specific gravity, softening state, and texture of unplasticized vinyl chloride (hard PV).
C) It is similar to a sheet and has excellent transparency, cold resistance, impact resistance, chemical resistance, thermoformability, etc., so it is different from conventional P.
The company is moving into the VC field. Furthermore, it is thought that the use of A-PET will rapidly progress worldwide due to the decrease in the price of PET resin, the improvement of film forming processing technology, and the problem of waste incineration of PVC (chlorine gas generation).

0003

[Problems to be Solved by the Invention] However, even though the price of PET has decreased, the resin price is higher than that of PVC, and stretched polystyrene (which is expected to be the second most in-demand field after PVC)
OPS) has a difference in specific gravity and is expensive. Furthermore, since the rigidity is inferior to both, it is necessary to increase the thickness of the sheet used, which poses a problem.

[0004] Biaxial stretching is naturally considered to improve this rigidity from the viewpoint of physical property balance, moldability, etc., but biaxial stretching is performed by biaxial stretching in the machine direction (MD) and the direction perpendicular thereto (TD). It is necessary to perform a simple process and
A method for improving rigidity that does not increase the process cost of equipment is desired.

Further, biaxially stretched sheets are difficult to perform secondary molding due to their orientation, and a method for improving rigidity that allows secondary molding is desired.

[0006]

[Means for Solving the Problems] The present inventors have completed the present invention as a result of research and experiments with the above-mentioned problems in mind. That is, the present invention is characterized in that the heat shrinkage rate in the stretching direction is 20% or more, the heat shrinkage rate in the direction perpendicular to the stretching direction is -10% or more and less than 5%, and the thickness unevenness is ±15% or less. This is a uniaxially stretched polyester sheet.

[0007] The first manufacturing method of the present invention is to use a nip roller as a delivery roller and a take-up roller for stretching a substantially amorphous polyester sheet, and further to use a nip roller for the roller immediately after the take-up roller. ~2.5
This is a method for producing the above-mentioned polyester sheet, which is characterized by uniaxially stretching the polyester sheet.

[0008] The second manufacturing method of the present invention is to take a polyester sheet with a crystallinity of 2 to 10%, which has been molded at a cast roll temperature immediately after sheet extrusion in the high temperature range below the glass transition temperature, to a drawing delivery roller. The method for producing the polyester sheet described above is characterized in that a nip roller is used as the roller, and a nip roller is also used immediately after the take-up roller to uniaxially stretch the sheet by a factor of 1.5 to 2.5.

[0009] Furthermore, the polyester thermoformed product of the present invention is a polyester thermoformed product with excellent rigidity, which is obtained by thermoforming the above-mentioned polyester sheet of the present invention.

To explain the present invention in more detail, in the present invention, the polyester includes not only homopolymers such as polyethylene terephthalate and polyethylene naphthalate, but also 80 mol% or more of the dicarboxylic acid component,
Advantageously, a crystalline thermoplastic polyester resin in which 90 mol% or more is terephthalic acid or naphthalene-2,6-dicarboxylic acid and 80 mol% or more, preferably 90 mol% or more of the glycol component is ethylene glycol is used. used.

As a copolymerization component, when terephthalic acid is used as the main acid component, naphthalene-2,6-dicarboxylic acid is also included; on the other hand, when naphthalene-2,6-dicarboxylic acid is used as the main acid component, terephthalic acid is also included. , isophthalic acid, diphenyl dicarboxylic acid, diphenoxyethane dicarboxylic acid, diphenyl ether dicarboxylic acid, diphenylsulfone dicarboxylic acid, hexahydrodicarboxylic acid, hexahydroterephthalic acid, hexahydroisophthalic acid,
Examples include aromatic, alicyclic, and aliphatic bifunctional carboxylic acids such as adipic acid, sebacic acid, p-β-hydroxyethoxybenzoic acid, and ε-oxycaproic acid.

Further, as the glycol component, for example, diethylene glycol, triethylene glycol, polyethylene glycol, propylene glycol, 1,4-butanediol, neopentyl glycol, hexamethylene glycol, decane methylene glycol, 1,4-cyclohexanedimethanol, 2,2-bis(4'-β-
hydroxyethoxyphenyl)propane, bis(4'-
Examples include β-hydroxyethoxyphenyl)sulfonic acid.

[0013] The polyester in the present invention includes:
A small amount of a trifunctional or higher functional compound can be used as a copolymerization component within a substantially linear range.

The viscosity of the polyester of the present invention is preferably 1,1,2,2-tetrachloroethane/phenol=
Intrinsic viscosity (IV
) is in the range of 0.5 to 1.0 or less, more preferably 0.6 or more and 0.9 or less.

The polyester of the present invention may also contain known dyes and pigments, heat stabilizers, ultraviolet absorbers, lubricants, antistatic agents, etc., if necessary.

[0016] The sheet before stretching is substantially amorphous, and the degree of crystallinity is usually 2% or less. Although the thickness of the sheet is not particularly limited,
50 to 1000 μm, preferably 100 to 500 μm. The sheet width after stretching is not particularly limited. After stretching, it is preferable to use the portions obtained by removing 50 to 100 mm from both end edges for practical use.

The sheet film forming method used in the present invention may be a known method such as a touch roll method, an electrostatic application method, or an air knife method. The extruder may be a known type such as a single-screw extruder, twin-screw extruder, or tandem extruder, with or without a vent. If there is no vent or the vacuum level of the vent is 30 torr
If the material is worse than
00 ppm or less, preferably 50 ppm or less. If the moisture content is high, the IV drop of the sheet will be severe and fish eyes will occur. The value of IV is usually 0.5 or more, preferably 0.6 or more, and if it decreases too much, the mechanical properties will deteriorate extremely. On the other hand, the vacuum level of the vent is 30 Torr.
r or less (preferably 10 Torr or less), the raw resin has a saturated moisture content of 3,000 to 7,00 in a normal environment.
There is no particular problem if it is 0 ppm. In addition, the shape of the resin may be pellets (chips), fluff, or powder without any particular problem.
Recycling of molded articles may also be used.

[0018] In the uniaxial stretching method, the film-formed sheet roll may be once applied to a uniaxial stretching device, or the film may be uniaxially stretched (in-line) immediately after film formation. The in-line method is preferable in terms of thermal energy, but the heat shrinkage rate of the film-formed, uniaxially stretched polyester sheet is 20% or more in the stretching direction and less than 5% in the direction perpendicular to the stretching, and the effective part of the sheet is It is sufficient if the thickness unevenness is ±15% or less (preferably 10% or less).

[0019] As a method for obtaining stretch orientation by stretching at a relatively high temperature, the cooling roll (cast roll) temperature is set as high as possible below the glass transition temperature during extrusion film formation to obtain a film that is substantially transparent and has a crystallinity of 2 to 2. 10%, preferably 3-6
A method of forming a film on a sheet of 10% is mentioned.

In the stretching method of the present invention, a nip roller is used as a sending roller and a take-up roller for stretching, and a nip roller is used as a roller immediately after the take-up roller. In order to achieve more stable and uniform stretching, the distance between the stretching delivery roller and take-up roller should be as short as possible to 300 mm or less (preferably 100 mm or less), or two or more stages using nip rollers for the drawing delivery roller and take-up roller. A method employing uniaxial multi-stage stretching, a method of auxiliary heating of the stretching section with an infrared heater, etc. are employed. It is more preferable to appropriately combine these methods.

[0021] If the stretching ratio is less than 1.5 times, the improvement in strength and rigidity will be small, while if it exceeds 2.5 times, the heat shrinkage rate in the direction orthogonal to the stretching direction of the sheet will also increase, making it impossible to form the sheet sufficiently during thermoforming. . Further, the stretching temperature may be at least the glass transition temperature (Tg). Since the appropriate stretching temperature varies depending on the thickness, it is difficult to set an upper limit in particular, but if it is too high, the effect of improving the rigidity by stretching will be small. If the temperature is even higher, there is a risk of sticking and whitening. If the heat shrinkage rate in the stretching direction is less than 20%, such as a sheet uniaxially stretched at a stretching ratio of less than 1.5 times, the effect of improving rigidity will be small. This heat shrinkage rate does not exceed 55% even if the stretching ratio is increased, and on the contrary shows a decreasing tendency. Also,
If the heat shrinkage rate in the direction perpendicular to the stretching exceeds 5%, shaping becomes difficult during thermoforming.

Generally, the thickness unevenness of the extruded sheet is ±1
0% or less, and usually requires ±5% or less. However, in the case of the polyester sheet of the present invention, the cross-sectional shape of the sheet before stretching is 2 to 10% thicker at the center than at both ends;
Alternatively, both ends may need to be at least 1.3 times larger than the center. In the uniaxially stretched sheet of the present invention, the thickness unevenness is ±15% or less, preferably ±10%.
It is as follows. In the case of polyester, the stress in the stretched part is higher than that in the unstretched part, so that the unstretched part is stretched and uniformly stretched. Furthermore, if the stretching direction during uniaxial stretching does not meet the conditions, it will become extremely uneven, but in practice it can be used as long as the thickness unevenness is ±15% or less.

In order to maintain the orientation of the uniaxially stretched sheet and improve its heat resistance, several heat setting rollers are provided after stretching, and the rollers heat set the sheet through the sheet at a temperature of 100 to 200° C. for 3 minutes or less. Good too. Heat-setting methods include passing through a heat-setting box after stretching, running on the surface of a plate heater, using several heat-setting rollers and running on the roller surface, using an infrared heater, etc., and using a combination of these. There is a way.

The thermoforming method for the polyester sheet of the present invention may be any conventionally known method, such as hot plate forming, vacuum forming, pressure forming, vacuum pressure forming, and the like.

As described above, the present invention provides a polyester sheet for thermoforming that has improved rigidity by uniformly uniaxially stretching it at a low stretching ratio of 1.5 to 2.5 times without impairing thermoformability, and the same. A thermoformed article and a manufacturing method are provided.

The stiffness was evaluated using tensile modulus in the case of sheets, and by bending strength and stiffness in thermoformed products.

[0027]

[Effects of the Invention] Substantially amorphous polyester sheets have heretofore been used for thermoforming purposes, but they are more expensive than PVC or OPS. In contrast, the present invention provides a polyester sheet for thermoforming that can be relatively easily uniaxially stretched to improve rigidity and have a uniform thickness, and a method for producing the same, and is extremely useful industrially.

The measurement method will be explained below. (1) Intrinsic viscosity (IV) 1,1,2,2-tetrachloroethane/phenol = 4
A sample was dissolved in a 0/60 mixed solvent and measured at 20°C using an Ubbelod viscometer.

(2) Place the heat shrinkage sheet 20cm x 20cm in a dry heat oven,
Leave at 30°C for 30 minutes. Then, after cooling, the dimensions are measured at the center, 10 cm x 10 cm. When l0 is the dimension before heat shrinkage and l is the dimension after heat shrinkage, the heat shrinkage rate is given by the following formula.

[0030]

[Formula 1]

(3) Crystallinity Calculated from the density d measured using a density gradient tube using the following formula.

[0032]

[Formula 2]

However, da: density of amorphous state (for example, 1.335 g/ml for polyethylene terephthalate), d
c: Density in crystalline state (for example, 1.455 g/ml for polyethylene terephthalate).

(4) Tensile Modulus Tensile modulus is used to evaluate the rigidity of the sheet. Made by Orientech: Using Tensilon RTA-100,
Measured in accordance with JIS tensile test. However, the tensile speed was 50 mm/min.

(5) Bending strength and waist strength of the container Bending strength (see FIG. 2) and waist strength (see FIG. 3) are used to evaluate the rigidity of the container. Autograph AGS-500S manufactured by Shimadzu Corporation is used. However, the head speed was 50 mm/min.

(6) Heat Resistance of Container Hot water was poured into a thermoformed container and evaluated at the temperature at which the container deformed.

[0037]

[Example] Examples 1 to 3, Comparative Examples 1 and 2 Melt polymerization using antimony trioxide as a polymerization catalyst IV = 0.65
polyethylene terephthalate resin (hereinafter referred to as PET resin)
The undried pellets were formed into a film using a vented twin-screw extruder to obtain a sheet with a width of 960 mm and an average thickness of 500 μm. (Comparative example 1, cast roll temperature 55°C)

0038
] Also, using the apparatus shown in Fig. 1, sheets were similarly formed and uniaxially stretched to 1.5 times, 2.0 times, 2.5 times (Examples 1 to 3), and 3.0 times (Comparative Example 2). (The infrared heater was irradiated from above the sheet with a preheating roller temperature of 80° C. and a stretching roller interval of 280 mm.) As a result, thickness unevenness was within 12% and no stretching unevenness was observed. Each sheet was molded using a Kiefel thermoforming machine to a length of 160 mm, a width of 130 mm, and a depth of 35 mm.
It was made into a thermoformed container of mm. The bending strength and waist strength of these containers were measured and the results are shown in Table 1. If the stretching ratio exceeded 2.5 times, sufficient shaping could not be achieved during thermoforming.

Examples 4 to 6, Comparative Examples 3 and 4 I was melt-polymerized using a germanium dioxide catalyst and then solid-phase polymerized.
PET resin with V=0.85 was vacuum dried at 130° C. for 18 hours to have a moisture content of 45 ppm. This was formed into a sheet using a 75φ single-screw extruder and stretched in the same manner. This raw sheet was molded into a molding machine (manufactured by Kansai Automatic Molding Machine Co., Ltd.) to a length of 190 mm.
A thermoformed container with a width of 100 mm and a depth of 20 mm was made. If the stretching ratio exceeded 2.5 times, sufficient shaping could not be achieved during thermoforming. Table 1 shows the results of measuring the bending strength and waist strength of these containers.

[0040]

[Table 1]

Examples 7 and 8 Between the stretch take-off roller and the immediately following nip roller
A stretched sheet was produced in the same manner as in Example 2, except that three heating rollers of φ were provided, uniaxial stretching was performed, and then heat setting was performed at 110° C. and 150° C., and then thermoformed to obtain a container. As can be seen from Table 2, the stretched sheet had improved heat resistance, and the container also had improved rigidity and heat resistance.

[0042]

[Table 2]

Comparative Example 5 The distance between the stretching rollers in the uniaxial stretching apparatus shown in FIG. 1 was set to 350 m.
m, and no nip roller was used immediately after the stretching take-off roller. In this case, when the stretched sheet was observed with a polarizing plate, the thickness unevenness was less than ±30% and the striped stretching unevenness was so pronounced that it was difficult to put it into practical use.

Examples 9 and 10 The non-stretched, non-oriented sheet used in Example 2 had a flat cross-sectional shape with an average thickness of 500 μm. Example 9
In this case, the average thickness is 500 μm, the center part is 520 μm, and both ends are 4
A sheet having a cross-sectional shape of 90 μm (approximately 6% gently convex at the center) was used as the original sheet (Example 9). In Example 10, the average thickness of the central portion was 500 μm and the edge portions at both ends were 70 μm.
Using raw sheets having a cross-sectional shape of 0 μm (edges at both ends 1.40 times larger than the center), each sheet was uniaxially stretched to twice the size as in Example 2. The thickness unevenness of these uniaxially stretched sheets was further improved compared to Example 2. The results are shown in Table 3.

[0045]

[Table 3]

Examples 11 and 12 Uniaxial stretching was carried out directly in-line in the same manner as in Example 2, except that the temperature of the cast roll was changed to 68°C and 72°C. Next, these were thermoformed and evaluated. The results are shown in Table 4. In Examples 11 and 12, an improvement in rigidity was observed compared to Example 2. In addition, the glass transition temperature of the PET resin of Example 2 is 74 to 76°C.

[0047]

[Table 4]

[Brief explanation of drawings]

FIG. 1 is a schematic explanatory diagram of a stretching device used in manufacturing the sheet of the present invention.

FIG. 2 is a schematic diagram showing a method for measuring the bending strength of a container made from the sheet of the present invention.

FIG. 3 is a schematic diagram showing a method of measuring the stiffness of a container made from the sheet of the present invention.

[Explanation of symbols]

1 Melt extruder, 2 Sheet mold, 3 Cast roll, 4, 5 Guide roller, 6, 6', 17, 17' Nip roller, 7, 8, 9
, 10 preheating roller, 11, 11' stretching feed roller (nip roller)
, 12, 12' stretching take-off roller (nip roller), 13, 13' cooling roller (nip roller), 1
4 infrared heater, 15, 16 cooling roller, 18 winding.

Claims (8)

[Claims] Claim 1: The heat shrinkage rate in the stretching direction is 20% or more, and the heat shrinkage rate in the direction perpendicular to the stretching direction is -10% or more and 5%.
1. A uniaxially stretched polyester sheet having a thickness unevenness of ±15% or less. 2. The uniaxially stretched polyester sheet according to claim 1, which has been heat set. 3. A substantially amorphous polyester sheet is uniaxially stretched by a factor of 1.5 to 2.5 using nip rollers for the sending out roller and take-up roller for stretching, and a nip roller for the roller immediately after the take-up roller. The method for producing a polyester sheet according to claim 1, characterized in that: 4. The method for producing a polyester sheet according to claim 3, wherein the distance between the stretching feed roller and the take-up roller is 300 mm or less. 5. The method for producing a polyester sheet according to claim 3, wherein the sheet is a raw sheet having a cross-sectional shape in which the thickness at the center is 2 to 10% thicker than at both ends. 6. The method for producing a polyester sheet according to claim 3, wherein a raw sheet having a cross-sectional shape in which the thickness at both ends is at least 1.3 times or more thicker than the thickness at the center is used. [Claim 7] A polyester sheet with a crystallinity of 2 to 10% is formed by keeping the cast roll temperature immediately after sheet extrusion in the highest possible range below the glass transition temperature, using a nip roller as a sending roller and a take-up roller for stretching, and further 2. The method for producing a polyester sheet according to claim 1, wherein the uniaxial stretching is carried out by a factor of 1.5 to 2.5 using a nip roller also as a roller immediately after the take-up roller. 8. A polyester thermoformed product having excellent rigidity obtained by thermoforming the polyester sheet according to claim 1.