JPH04353429A - Production of uniaxially stretched polyester sheet - Google Patents

Abstract

PURPOSE:To produce the uniaxially stretched polyester sheet free from uneven stretching and improved in rigidity. CONSTITUTION:A method for producing uniaxially stretched polyester sheet which is characterized by using nip rollers in pairs 11, 11' and 12, 12' as feed and receiving stretching rollers, respectively; providing stretching lines between such roller pairs across the almost entire width of a noncrystal polyester sheet; and subjecting the polyester sheet to uniaxial stretching in a low multiplying factor.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing thermoformable polyester sheets 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.
The present invention relates to a method for producing a polyester sheet for thermoforming that is highly economical.

0002

BACKGROUND OF THE INVENTION Conventionally, in the production of biaxially oriented polyester films without secondary forming, the film is stretched at a considerably high magnification, so there is no stretching team and the manufacturing method is well established. For example, as a method for improving the rigidity of polyester, biaxial stretching has been carried out in view of the balance of physical properties and moldability. Stretching is necessary, and an increase in costs due to the process and equipment is unavoidable. Further, biaxially stretched sheets are difficult to perform secondary molding due to their orientation, and are not suitable for thermoforming that involves secondary molding.

[0003] Stretched sheets for thermoforming that involve secondary forming need to have a low stretching ratio in order to maintain formability, and are therefore produced by low-magnification uniaxial stretching. However, low-magnification uniaxial stretching has a problem to be solved in that stretching spots are likely to occur.

0004

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for producing a uniaxially stretched polyester sheet that is stretched at a low stretching ratio. Another object of the present invention is to provide a method for producing a uniaxially oriented polyester sheet without stretching sections.

Still another object of the present invention is to provide a method for producing a low-magnification uniaxially stretched polyester sheet with improved rigidity. Further objects and advantages of the present invention will become apparent from the description below.

[0006]

[Means for Solving the Problems] According to the present invention, the above objects and advantages of the present invention can be achieved by
Uniaxial stretching characterized by using a nip roller as a stretching feed roller and a stretching take-off roller, and providing a stretching line between these rollers over almost the entire width of the amorphous polyester sheet to perform uniaxial stretching at a low magnification. This is achieved by a method for manufacturing polyester sheets.

[0007] The second aspect of the present invention is a method for producing a polyester sheet according to the first aspect, characterized in that a nip roller is used as the roller immediately after the stretching take-off roller.

The third aspect of the present invention is to use a polyester sheet with a crystallinity of 2 to 10% formed by keeping the cast roll temperature as high as possible, below the glass transition temperature, immediately after sheet extrusion, to a stretching feed roller and a stretching take-off roller. The method for producing the polyester sheet described above is characterized in that uniaxial stretching is performed using nip rollers.

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

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, decamethylene 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 it 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 easily occur. The value of IV is usually 0.5~
1.0, preferably 0.6 to 0.9. If it is less than 0.5, the mechanical properties will be extremely deteriorated, while if it is more than 1.0, it will be difficult to form. On the other hand, the degree of vacuum in the vent is 30T.
orr or less (preferably 10 Torr or less),
The raw material resin has a saturated moisture content of 3,000 to 7,000 in normal environments.
000 ppm, there is no particular problem. Further, the shape of the resin may be pellets (chips), fluff, or powder without any particular problem, and recycled molded products may 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, but the in-line method is preferable in terms of thermal energy. The polyester sheet that has been uniaxially stretched after film formation has a heat shrinkage rate of 20% or more in the stretching direction and less than 5% in the direction perpendicular to the stretching, and the thickness unevenness of the effective part of the sheet 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 stretching feed roller and a stretching take-up roller,
A stretching line is provided between the stretching rollers over the entire width of the polyester sheet, and the polyester sheet is stretched at a low ratio. Preferably, a nip roller is further used immediately after the drawing roller. In order to stretch more stably and uniformly, the distance between the stretch feed roller and the stretch take-up roller should be set to 300 mm or less (
A method of making the length as short as possible (preferably 100 mm or less), a method of employing two or more uniaxial multi-stage stretching using nip rollers as a stretching feed roller and a stretching take-off roller, a method of auxiliary heating of the stretching part with an infrared heater, etc. Adopted. It is more preferable to appropriately combine these methods.

In the case of polyester whose main component is ethylene terephthalate units, 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 sheet will undergo heat shrinkage in the direction perpendicular to the stretching direction. The ratio also increases, making it impossible to form the mold sufficiently during thermoforming. Further, the stretching temperature may be at least the glass transition temperature (Tg). The appropriate stretching temperature varies depending on the thickness and the running speed of the sheet, so it is difficult to set an upper limit, but if it is too high, the effect of improving the stiffness by stretching will be small. If the temperature is even higher, there is a risk of sticking and whitening.

A stretching line is provided between the stretching feed roller and the stretching take-off roller over almost the entire width of the amorphous polyester sheet. Preferably, the drawn line is fixed by a guide bar, edge or roller provided substantially perpendicular to the running direction of the polyester sheet. One or more such guide bars, edges or rollers can be provided between the stretching feed roller and the stretching take-off roller. Furthermore, another stretching take-off roller can be provided after the stretching take-off roller, and a guide bar or an edge can also be provided between the two stretching take-off rollers. In this case, the first stage of stretching can be performed first using a guide bar or edge between the stretching feed roller and the stretching take-off roller, and then the second stage of stretching can be performed using the guide bar or edge between both the stretching take-off rollers. .

The guide bar and the edge have a structure that allows temperature adjustment as appropriate. The stretching ratio is 1.5 regardless of whether the stretching is performed in one stage or in multiple stages of two or more stages.
It is preferable to set it to 2.5 times. The uniaxial stretching method of the present invention can be carried out more specifically, for example, as follows.

[0024] In the uniaxial stretching method, for example, an unstretched, non-oriented sheet is once extruded to form a film using an extruder, and then rolled. The thickness unevenness of the extruded sheet is usually ±10% or less, preferably ±5% or less. In the case of the amorphous polyester sheet used in the present invention, in order to prevent necking at both ends of the sheet before stretching, the cross-sectional shape of the sheet before stretching is 2 to 10% thicker at the center than at both ends, or when both ends are at least at least 10% thicker than at the center. In some cases, one having a ratio of 1.5 times or more is used.

[0025] After that, a method of providing a stretching device: a feeding device and a temperature control roll, heating the sheet to the stretching temperature, applying uniaxial stretching between a stretching feed roller and a stretching take-up roller, and heat setting if necessary (off-line); Alternatively, a method (in-line) in which uniaxial stretching is applied immediately after film formation of an unstretched, non-oriented sheet and heat setting is performed if necessary may be used. The stretching of polyester is influenced by the time after film formation, and an in-line method is preferable in terms of thermal energy.

[0026] As a uniform stretching method, for example, a guide bar and/or an edge which is appropriately temperature-controlled over the entire width of the polyester sheet is installed either singly or in combination between a stretching feed roller and a stretching take-up roller. A method of fixing the drawn line (point) is used. Furthermore, this method
A method in which a nip roller is used as the stretch feed roller and the stretch take-off roller, and the nip roller is used as the roller immediately after the stretch take-off roller, and the distance between the stretch feed roller and the stretch take-off roller is 300 mm or less, preferably 10 mm.
Examples include a method of making the length as short as possible (mm or less), a method of auxiliary heating of the stretched portion with an infrared heater, etc., and a method of combining two or more of them. Using these methods allows for more uniform stretching.

In order to maintain the orientation of the uniaxially stretched sheet, several heat-setting rolls are provided after stretching, and the roll temperature is set to 100°C or higher and 200°C or lower, and the sheet is heated such that the heat-setting time is within 3 minutes. Heat setting may also be performed. In addition to the heat setting of the sheet between rolls, after thermoforming the sheet is heated to 110°C or higher, preferably 1
Heat setting can also be performed at 30° C. or higher while controlling the degree of crystallinity and maintaining transparency.

The heat shrinkage of the uniaxially stretched polyester sheet in the stretching direction does not exceed 60% even when the stretching ratio is increased, and on the contrary shows a decreasing tendency. The heat shrinkage ratio in the stretching direction is expressed by the following formula 1.

[0029]

[Formula 1]

If this value is less than 0.9, it cannot be shaped during thermoforming. The uniaxially stretched polyester sheet obtained by the method of the present invention preferably has a heat shrinkage ratio expressed by Formula 1 between 0.93 and 0.98.

The uniaxially stretched sheet according to the present invention preferably has a thickness unevenness of ±15% or less, more preferably ±10%.
% or less. In the case of polyester, the stress in the stretched portion is higher than that in the unstretched portion, so that the unstretched portion is stretched and uniformly stretched. In addition, in practice, the thickness unevenness of the sheet is ±15
% or less, but by providing stretching lines (dots), the uniformity of uniaxial stretching can be easily improved and the thickness spots can be reduced.

The thermoforming method for the uniaxially stretched polyester sheet may be any conventionally known method, including hot plate forming, vacuum forming, pressure forming, vacuum pressure forming, and the like. Rigidity was evaluated using tensile modulus for sheets, and bending strength and stiffness for thermoformed products.

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.

[0035]

[Formula 2]

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

[0037]

[Formula 3]

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.

[0042]

[Example] Hereinafter, it will be explained in more detail with examples.
The present invention is not limited to these examples.

Comparative Example 1 Pellets of polyethylene terephthalate (hereinafter referred to as PET) having an intrinsic viscosity (IV) of 0.85 were polymerized using antimony trioxide as a polymerization catalyst, and were placed in an undried state with a vent 2.
A substantially unstretched, non-oriented sheet having a width of 960 mm and a thickness of 800 μm was obtained using a touch roll method using an axial extruder (cast roll temperature: 55° C.). This sheet was molded into a length of 160 mm, a width of 130 mm, using a Kiefel thermoforming machine.
As a result of thermoforming to a depth of 35 mm, the molding was good. The results obtained are shown in Table 1.

Example 1 The unstretched non-oriented sheet of Comparative Example 1 was preheated using four 400φ 80°C preheating rollers, and a 400°C infrared heater was applied from the top of the sheet between the feed roller and take-up roller. A guide bar is provided on the lower side of the sheet, the stretching point is fixed (stretching device A method), and the sheet is stretched in the longitudinal direction with a peripheral speed ratio of 1:1.5.
It was stretched 5 times and cooled. The infrared heater was fixed about 3 cm above the sheet surface so that its long axis was parallel to the direction perpendicular to the running direction of the sheet. Further, the guide bar was installed on the sheet surface (projection surface) at the rearmost position (on the sheet traveling direction side) of the measurement position of the infrared heater.

[0045] Regarding the stretching point, the roll spacing was 100 m.
m, and the unstretched sheet was placed on a guide bar at 80°C to a length of 2
mm, and was fixed by contacting with a contact angle of 90 degrees. As a result, no stretching unevenness due to the polarizing plate was observed. Next, the stretched sheet was thermoformed to a length of 160 mm, width of 130 mm, and depth of 35 mm using a thermoforming machine manufactured by Kiefel. The shapeability during thermoforming was good, and the moldability was no different from that of the unstretched, non-oriented sheet (Comparative Example 1), and a rigid container was obtained. The results obtained are shown in Table 1.

Example 2 A sheet was produced in the same manner as in Example 1, except that the stretching ratio was doubled. As a result, no stretching unevenness due to the polarizing plate was observed, and a container with good thermoformability and rigidity was obtained. The results obtained are shown in Table 1.

Example 3 A sheet was produced in the same manner as in Example 1, except that the stretching ratio was increased to 2.5 times. As a result, no stretching unevenness due to the polarizing plate was observed, and a container with good thermoformability and rigidity was obtained. The results obtained are shown in Table 1.

Comparative Example 2 A sheet was produced in the same manner as in Example 1, except that the stretching ratio was increased to 3 times. As a result, no stretching unevenness due to the polarizing plate was observed. However, the heat shrinkage ratio was 0.32 and the thermoformability was poor, and the shape could not be sufficiently formed during thermoforming, making it impossible to obtain a container. The results obtained are shown in Table 1.

Comparative Example 3 The unstretched non-oriented sheet of Comparative Example 1 was preheated using four 400φ preheating rollers at 80°C, the distance between the feed roller and the take-up roller was set to 100 mm, and the sheet was heated at 400°C.
An infrared heater was irradiated from above the sheet, and the sheet was stretched twice in the longitudinal direction at a circumferential speed ratio of the feed roller and the take-up roller of 1:2 without providing a guide bar, and then cooled. As a result, stretching unevenness due to the polarizing plate was observed. The stretched sheet was thermoformed to a length of 160 mm, width of 130 mm, and depth of 35 mm using a thermoforming machine manufactured by Kiefel. Thermoformability varied depending on the position of the sheet, with some parts being good at forming and others not being able to be formed. The results obtained are shown in Table 1.

Example 4 Stretching was carried out using the stretching apparatus shown in FIG. That is, using antimony trioxide as a polymerization catalyst, the polymerized intrinsic viscosity (I
V) 0.85 PET resin pellets are left undried to form a substantially unstretched, non-oriented sheet with a width of 960 mm and a thickness of 600 μm using a vented twin-screw extruder, and preheated in-line at 80°C with a diameter of 400 mm. The sheet is preheated by four rollers, an edge is provided on the lower side of the sheet between the feed roller and the take-up roller, and the stretching point is fixed (stretching device B method, see Figure 1). It was stretched 1.5 times in the longitudinal direction at a speed ratio of 1:1.5 and cooled.

The infrared heater was similarly fixed at the same position as in Example 1. Further, the edge was installed in the same manner as in Example 1. For the stretching point, the roll spacing is 80
2mm length of unstretched sheet on the edge at 90℃
, were fixed by contacting at a contact angle of 90 degrees. As a result, no stretching unevenness due to the polarizing plate was observed. The stretched sheet was molded using the same thermoforming machine as in Example 1, and the shaping during thermoforming was good and a rigid container was obtained. The results obtained are shown in Table 1.

Example 5 Using germanium dioxide as a polymerization catalyst, PET resin pellets having an intrinsic viscosity (IV) of 0.85 were polymerized using a vented twin-screw extruder to a width of 960 mm and a thickness of 600 μm without drying.
A substantially unstretched, non-oriented sheet of m is formed into a film, and the sheet is preheated in-line with two preheating rollers of 400φ at 80°C, and the edge is first placed on the upper side of the sheet between a feed roller and a take-up roller, and then a 20 mm Edges are provided on the lower side of the sheet at intervals, and the stretching points are fixed (stretching device C
method), the peripheral speed ratio of the feed roller and take-up roller is 1:2
．． 5 was stretched 2.5 times in the longitudinal direction and cooled. Regarding the stretching point, the roller interval was set to 150 mm, and the unstretched sheet was fixed by contacting the 90° C. edge with a length of 1 mm and a contact angle of 90 degrees. As a result, no stretching unevenness was observed. The stretched sheet was molded using the same thermoforming machine as in Example 1, and the shaping during thermoforming was good and a rigid container was obtained. The results obtained are shown in Table 1.

[0053]

[Table 1]

Examples 6 and 7 Between the stretch take-off roller and the immediately following nip roller
After uniaxial stretching with three 0φ heating rollers, 110
A stretched sheet was produced in the same manner as in Example 4, except that heat setting was performed at 150°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.

[0055]

[Table 2]

Examples 8 and 9 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.

[0057]

[Table 3]

Examples 10 and 11 Uniaxial stretching was carried out directly in-line in the same manner as in Example 4, 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 10 and 11, 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.

[0059]

[Table 4]

[Brief explanation of the drawing]

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 Twin screw 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, 19 drawing wire (edge).

Claims (8)

[Claims] Claim 1: An amorphous polyester sheet is processed at a low magnification by using a nip roller as a stretching feed roller and a stretching take-off roller, and by providing a stretching line between these rollers over almost the entire width of the amorphous polyester sheet. A method for producing a uniaxially stretched polyester sheet, comprising uniaxially stretching. [Claim 2] The amorphous polyester sheet has a thickness of 1.5 to 2
．． The method according to claim 1, wherein the film is uniaxially stretched by a factor of 5. 3. The method for producing a polyester sheet according to claim 1, characterized in that a nip roller is used as the roller immediately after the stretching take-off roller. 4. The method for producing a polyester sheet according to claim 1, wherein the distance between the stretching feed roller and the stretching take-up roller is 300 mm or less. 5. The method for producing a polyester sheet according to claim 1, 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 1, 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 high temperature range below the glass transition temperature, using a nip roller as a stretching feed roller and a stretching take-off roller. 2. The method for producing a polyester sheet according to claim 1, wherein the polyester sheet is uniaxially stretched. 8. A polyester thermoformed article with excellent rigidity obtained by thermoforming the uniaxially low-strength stretched polyester sheet according to claim 1.