JP2001150508A - Method for molding thermoplastic resin sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To mold a thermoplastic resin sheet having no stripe on its surface and excellent in thickness uniformity over a long time by extrusion molding. SOLUTION: In a method for molding a thermoplastic resin sheet by cooling and solidifying a molten thermoplastic resin sheet, which is extruded from at least two extruers in such a state that two or more layers are laminated, on a rotary cooling drum, the moisture content (Xa) of the thermoplastic resin supplied to an extruder A and the moisture content (Xb) of the thermoplastic resin B supplied to an extruder B are set to a range satisfying formulae (1) Xa-Xb>=5 (ppm), (2) 20>=Xa>=50 (ppm) and (3) 5>=Xb>=30 (ppm) and the layer comprising the thermoplastic resin A is set on a sheet taking-over side and the layer comprising the thermoplastic resin B is set on a sheet taking-over side.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for forming a thermoplastic resin sheet. More specifically, when extruding and molding a thermoplastic resin sheet, it is possible to mold a sheet having no streaks on the surface and excellent in thickness uniformity and having few surface defects over a long period of time. About the method.

[0002]

2. Description of the Related Art A thermoplastic resin sheet represented by a polyester resin sheet is obtained by melting a thermoplastic resin with an extruder, extruding the sheet from a die, and cooling and solidifying the sheet with a rotary cooling drum. The sheet is often stretched uniaxially or biaxially in a stretching step to form a stretched film. However, streaky defects called die streaks occur on the surface of the sheet or film thus formed. Die streaks are generated due to foreign matter attached to the tip of the die lip, degraded polymer or the like. That is, when the molten resin extruded from the die comes into contact with the attached matter at the tip of the die, a convex or concave streak is formed on the surface of the extruded sheet, and this becomes a die streak. In particular, when the thermoplastic resin is a polyester resin, the generation of degraded products due to thermal decomposition is remarkable. When extruded for a long period of time, the degraded products (hereinafter referred to as "eyes") adhere to the tip of the die lip. , Which grows and causes die muscle.

[0003] Polyester films are used for magnetic tapes, photographic applications, plate making applications, and the like, but films with die streaks do not become products, resulting in a large loss in production. Also, the number of eyes that occur once increases over time,
The size also tends to increase. For this reason, when the die streaks exceed the control limit, it is necessary to suspend production and remove the streaks attached to the die lip with a metal spatula such as copper. Will be higher. As described above, since the die streaks not only lower the product quality but also significantly lower the productivity, a solution has been demanded.

As a method for suppressing the occurrence of die streaks, for example, Japanese Patent Application Laid-Open No. 7-40417 discloses a method for controlling the moisture content of a thermoplastic resin chip within a range of 40 to 60 ppm. However, in this method, the inherent viscosity of the obtained film is too low, and adverse effects such as cutting of a sheet in a stretching step and deterioration of mechanical properties such as breaking strength of a commercialized film occur.

[0005]

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems and to suppress the occurrence of blemishes when extruding a thermoplastic resin into a sheet, thereby achieving excellent thickness uniformity. Another object of the present invention is to provide a sheet forming method capable of greatly improving the productivity of a thermoplastic resin sheet having few surface defects. At the same time, it is an object of the present invention to provide a method for controlling the intrinsic viscosity of a commercialized film within a predetermined range to stabilize the film forming process and improve the quality.

[0006]

According to the present invention, there is provided, according to the present invention, at least two extruders, wherein a molten thermoplastic resin sheet laminated and extruded into two or more layers is cooled and solidified by a rotary cooling drum. In the method of forming a thermoplastic resin sheet to be formed, the moisture content (Xa) of the thermoplastic resin (A) supplied to the extruder (A) and the moisture content of the thermoplastic resin (B) supplied to the extruder (B) The rate (Xb) is expressed by the following formulas (1) to (3).
Wherein the layer composed of the thermoplastic resin (A) is a layer on the sheet take-up side, and the layer composed of the thermoplastic resin (B) is a layer on the side opposite to the sheet take-up side. This can be achieved by a method of forming a plastic resin sheet.

[0007]

Xa−Xb ≧ 5 (ppm) (1) 20 ≧ Xa ≧ 50 (ppm) (2) 5 ≧ Xb ≧ 30 (ppm) (3) (Equation (1) In the formulas (3) to (3), Xa represents the moisture content (ppm) of the thermoplastic resin (A) supplied to the extruder (A), and Xb represents the moisture content of the thermoplastic resin (B) supplied to the extruder (B). Indicates the moisture content (ppm).)

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail.

[Die streaks] The die streaks referred to in the present invention, when observed in a cross section in the sheet extrusion forming direction, show a convex shape or a concave shape. For example, the die streaks protrude on the surface of a polyester sheet in the same direction as the extrusion direction. Defects that form streaks or dents, 0.2% for 100 μm thick sheets
It often has a height or depth of about 2 μm.
Large ones can be observed with the naked eye, while small ones can be observed when sandwiched between two deflection plates.

In photographic and plate making applications, a polyester film is coated with a halogenated emulsion to produce a product. However, if there is a die streak defect, the emulsion will be spotted, so even a die streak not observed with the naked eye is not acceptable. . Therefore, production must be interrupted as soon as die streaks occur, and the streaks attached to the die lip must be removed with a metal spatula such as copper. The effect of suppressing die streaks can be evaluated by the number of continuous production days until the die streaks generated by the streaks attached to the die lip exceed the control limit and must be removed.

[Thermoplastic resin] The thermoplastic resin in the present invention includes polyesters such as polyethylene terephthalate, polybutylene terephthalate and polyethylene-2,6-naphthalate; polyolefins such as polyethylene and polypropylene; nylon 6 and nylon 66. It is a resin used for melt extrusion molding of polyamides, polyimides, polystyrenes, polycarbonates, polyvinyls and the like. The present invention is particularly suitable for polyesters, which are important quality defects when die streaks are formed during biaxial stretching.

The polyester in the present invention is a polyester comprising a dicarboxylic acid component and a glycol component. The dicarboxylic acid component is preferably an aromatic dicarboxylic acid such as terephthalic acid, isophthalic acid, or naphthalene-2,6-dicarboxylic acid. The glycol component is preferably ethylene glycol, diethylene glycol, tetramethylene glycol, neopentyl glycol, or the like. Such glycols are preferred.

The polyester in the present invention can be obtained, for example, by directly polycondensing an aromatic dicarboxylic acid and glycol. The polyester is obtained by subjecting a dialkyl ester of an aromatic dicarboxylic acid to a transesterification reaction with a glycol followed by polycondensation. Can also be obtained by Representative examples of such polymers include polyethylene terephthalate,
Polybutylene terephthalate, polyethylene-2,6-
Naphthalate can be mentioned. Polyester is
These copolymers may be used, or a third component other than these may be copolymerized.

The thermoplastic resin may contain a stabilizer, a lubricant, a pinning agent, a viscosity modifier, an antioxidant, a pigment, a coloring dye, a fluorescent brightener, an ultraviolet absorber, an antistatic agent and the like. .

[Thermoplastic Resins (A) and (B)] In the present invention, at least two extruders are used, and the extruder (A) is connected to the layer on the sheet take-up side (the side not in contact with the rotary cooling drum). Layer: also referred to as a layer on the air surface side) is supplied with a thermoplastic resin (A), and the extruder (B) is provided with a sheet on the side opposite to the sheet (the layer on the side in contact with the rotary cooling drum: cooling surface). The thermoplastic resin (B), which is the material of the side layer, is also supplied.

The thermoplastic resin (A) and the thermoplastic resin (B) can be selected from the above-mentioned thermoplastic resins, but are preferably selected from polyesters because the adhesive strength of the two layers becomes strong. It is particularly preferable that the polyester is composed of the same repeating unit since a single polyester sheet or polyester film having less die streaks can be obtained.

[Moisture content] In the present invention, the extruder (A)
Moisture content (Xa) of the thermoplastic resin (A) supplied to
The moisture content (Xb) of the thermoplastic resin (B) supplied to the extruder (B) needs to be in the range of the following formulas (1) to (3).

[0018]

Xa−Xb ≧ 5 (ppm) (1) 20 ≧ Xa ≧ 50 (ppm) (2) 5 ≧ Xb ≧ 30 (ppm) (3) (Equation (1) In the formulas (3) to (3), Xa represents the moisture content (ppm) of the thermoplastic resin (A) supplied to the extruder (A), and Xb represents the moisture content of the thermoplastic resin (B) supplied to the extruder (B). Indicates the moisture content (ppm).)

Thermoplastic resin (A) and thermoplastic resin (B)
By setting the water content of the above to the above range, a sheet or film having less die streaks and less decrease in intrinsic viscosity can be produced for a long period of time.

The moisture content (Xa) of the thermoplastic resin (A) in the present invention is in the range of 20 to 50 ppm, the upper limit of which is 40 ppm and the lower limit of which is 30 ppm. It is preferable because the suppression of the decrease in the intrinsic viscosity is further improved. If the moisture content of the thermoplastic resin (A) is less than 20 ppm, the effect of suppressing die streaks is insufficient, and if the moisture content exceeds 50 ppm, the intrinsic viscosity of the film during melt extrusion decreases greatly, and the intrinsic viscosity of the film decreases. Therefore, it is not preferable because the film quality cannot be maintained and bubbles are generated in the sheet to cause cutting.

Further, the moisture content of the thermoplastic resin (B) (X
The range of b) is 5 to 30 ppm, but the upper limit is 20 ppm.
It is preferable that the lower limit is 10 ppm, and the lower limit is 10 ppm, because the effects of the present invention, ie, suppression of die streaks and suppression of decrease in intrinsic viscosity, are further excellent. The moisture content of the thermoplastic resin (B) is 5p
If it is less than pm, it is necessary to increase the drying temperature or lengthen the drying time, and the deterioration of the thermoplastic resin at the time of drying becomes large, and the productivity is undesirably reduced. On the other hand, if the water content exceeds 30 ppm, the intrinsic viscosity at the time of melt extrusion greatly decreases, and the intrinsic viscosity of the film decreases, so that it is not possible to maintain the film quality.

Furthermore, in the present invention, the moisture content (Xa: ppm) of the thermoplastic resin (A) and the thermoplastic resin (B)
It is necessary that the difference from the water content (Xb: ppm) is 5 ppm or more. When the difference in the moisture content is within this range, the effect of suppressing the die muscle can be exhibited.

[Thickness Configuration] In the present invention, the thickness (Ta) of the thermoplastic resin (A) layer constituting the sheet and the thickness (Tb) of the thermoplastic resin (B) layer are within the range of the following formula (4). Preferably, there is.

[0024]

1 ≧ Tb / Ta ≧ 99 (4) (In the formula (4), Ta is the thickness (mm) of the thermoplastic resin (A) layer constituting the sheet, and Tb is the thermoplastic resin (B ) Represents the thickness (mm) of the layer.)

The thickness (Ta) of the thermoplastic resin (A) layer,
When the thickness (Tb) of the thermoplastic resin (B) layer is within the above range, the properties of the obtained sheet can be improved, and the sheet or film can be stably manufactured for a long period of time. it can.

In the present invention, it is sufficient that the thermoplastic resin (A) layer is the outermost layer on the sheet take-up side, and the thermoplastic resin (B) layer is the outermost layer on the sheet-reverse side. Alternatively, three or more layers in which another layer is laminated between both layers may be used.

[Intrinsic Viscosity] In the present invention, the intrinsic viscosity (Ia) of the chip of the thermoplastic resin (A) supplied to the extruder (A) and the thermoplastic resin (B) supplied to the extruder (B) are used. It is preferable that the intrinsic viscosity (Ib) of the chip and the intrinsic viscosity (Is) of the thermoplastic resin sheet are in the range of the following formula (5).

[0028]

Is × (Wa + Wb) / (Ia × Wa + Ib × Wb) ≧ 0.9 (5) (In the formula (5), Ia is the thermoplastic resin (A) supplied to the extruder (A). ) Is the intrinsic viscosity of the chip, Ib is the extruder (B)
Intrinsic viscosity of the thermoplastic resin (B) chip supplied to
Is is the intrinsic viscosity of the thermoplastic resin sheet, Wa is the supply speed of the thermoplastic resin (A) chip supplied to the extruder (A), and Wb is the thermoplastic resin (B) supplied to the extruder (B). Represents the feed rate of the chip. )

By controlling the molding conditions so that the intrinsic viscosity is within the above range, in addition to setting the thickness composition ratio of the sheet within the above range, the intrinsic viscosity of the film can be controlled within a predetermined range, and the quality can be improved. It is possible to stabilize the film forming process while improving the quality.

The intrinsic viscosity of the dried thermoplastic resin chip supplied to the extruder is calculated as a weighted average from the intrinsic viscosities of the chip on the sheet take-up side and the chip on the sheet opposite take-up side and the supply amount as described above.

[Film Forming Method] In the present invention, at least two extruders are used to extrude a thermoplastic resin, and a molten sheet of the thermoplastic resin laminated in two or more layers is extruded.
At this time, a die capable of laminating two or more thermoplastic resins is used. Examples of such a die include a die for multilayer extrusion in which two or more layers of molten resin can join in a layer in the die. 2 by feed block
It may be a die in which more than one layer of molten resin can join in layers.

The present invention can be applied to extrusion molding of a thermoplastic resin, and can be particularly preferably applied to an extrusion molding flat stretching film forming method. Extrusion molding Flat stretching film forming method is to extrude molten resin from a die with parallel slits, form it into a sheet, and then sequentially or simultaneously stretch it in a vertical or horizontal biaxial direction with a roll, stenter, etc. to form a film And a conventionally known method can be applied.

For example, polyester is melt-extruded, solidified on a rotary cooling drum and formed into an unstretched sheet.
A method of sequentially stretching or simultaneously stretching two to six times in the longitudinal direction by a roll peripheral speed difference and two to six times in the horizontal direction by a stenter method or the like and performing heat fixing at about 160 to 250 ° C. can be mentioned.

However, the present invention is effective in the case where the biaxial stretching of the flat method emphasizes the die streaks generated at the die lip and makes it more conspicuous. Is not applicable.

[Explanation of Drawing] FIG. 1 shows an example of an embodiment used in the present invention. The dried thermoplastic resin chip is supplied to two extruders (not shown) to be melted, extruded in two layers from a die 1 and formed into a sheet, and is pinned on a rotary cooling drum 2 by a pinning device (a book). In the example, a DC high voltage is applied to the electrostatic wire 3 attached on the sheet to the power supply 4.
It is shown by the electrostatic pinning method of applying the pin from the pin)
The sheet 5 is rapidly cooled and solidified.

Observing the state of die streaks, although die streaks are also formed on the sheet retraction side 6, the size is smaller than the die streaks on the sheet retraction side 7, and the growth of the die streaks. Is also slow. Therefore, by suppressing the die streaks on the sheet take-up side, it is possible to significantly prevent a decrease in product quality and a decrease in productivity due to the die streaks. Muscle generation and growth can be suppressed.

The method of measuring the moisture content of chips is generally a method of sampling dried chips and measuring them off-line. However, a method of constantly measuring on-line after drying or immediately before being supplied to an extruder is preferable. As an alternative to measuring the chip moisture content, a method of measuring the melt viscosity of the polymer is also a preferable method.

In the drying step, the moisture content of the chips is controlled by measuring the moisture content of the chips to adjust the drying temperature and the drying time, or by blowing steam. Alternatively, a method of adding water and steam immediately before the extruder may be used.

[0039]

The present invention will be described in more detail with reference to the following examples.

Example 1 A polyethylene terephthalate chip was dried at 160 ° C. for 4 hours and supplied to an extruder (A) on the sheet take-up side. Chip moisture content after drying is 30
ppm and the intrinsic viscosity were 0.62 dl / g. Also,
The polyethylene terephthalate chips were dried at 165 ° C. for 4 hours and supplied to the extruder (B) on the sheet reverse side. The chip moisture content after drying, 20 ppm, and the intrinsic viscosity were 0.62 dl / g.

The polyethylene terephthalate melted in the extruder (A) and the extruder (B) are joined in a die, and the sheet thickness ratio of the sheet take-up side layer to the sheet anti-take-up side layer becomes 1: 9. The number of screw rotations of the extruder is set as described above to extrude the molten laminated polyethylene terephthalate into a sheet, and then cooled and solidified by a rotating cooling drum rotating at a peripheral speed of 60 m / min. A layer sheet was obtained. The intrinsic viscosity of this polyethylene terephthalate sheet is 0.58 dl / g
And the inherent viscosity of the dried chips (calculated by weighted average)
The reduction rate of the intrinsic viscosity of the sheet with respect to was 6.5%. Further, the quality of the sheet was good and the film forming process was stable without cutting. In addition, the intrinsic viscosity was measured in o-chlorophenol at 35 ° C.

The effect of suppressing the formation of die streaks was evaluated by the continuous molding time until the die streaks exceeded the control limit. As the control limit value, an increase / decrease value of the film thickness due to the die streak was used. Specifically, the thickness of the die streak portion was set to ± 0.40% of the film thickness. As a result, it was possible to operate smoothly without interrupting production for six consecutive days.

Examples 2 to 4 As shown in Table 1, by changing the intrinsic viscosity of the polyethylene terephthalate used, the drying conditions of the chips, and the screw rotation speeds of the extruders (A) and (B), the water content of the chips was changed as shown in Table 1. A two-layer polyethylene terephthalate sheet was obtained in the same manner as in Example 1 except that the ratio and the composition ratio of the sheet thickness were changed. Table 1 shows the evaluation results. As is evident from Table 1, the intrinsic viscosity reduction rates were all within 10%, the die streak generation suppressing effect was excellent, and the vehicle could be operated smoothly.

Comparative Example 1 A 100 μm polyethylene terephthalate two-layer sheet was obtained in the same manner as in Example 1 except that the moisture content of the dry chips supplied to the extruder (A) (sheet take-up side) was changed to 10 ppm. . As a result, since the die streaks exceeded the control limit on the second day, the production was interrupted and the eyes and dirt attached to the die lip were removed, resulting in a decrease in productivity.

Comparative Example 2 A two-layer polyethylene terephthalate sheet having a thickness of 100 μm was obtained in the same manner as in Example 3 except that the moisture content of the dried chips supplied to the sheet take-off side was changed to 60 ppm. As a result, although the number of continuous operation days was 9 days, the intrinsic viscosity of the sheet became 0.55 or less of the reference value, and the sheet was cut frequently, and the productivity was reduced.

[0046]

[Table 1]

[0047]

According to the present invention, when a thermoplastic resin chip is melted and extruded into a sheet shape from a die of an extruder to form a thermoplastic resin sheet having two layers, it is supplied to the extruder. The moisture content of the thermoplastic resin chip on the sheet take-up side after drying is 20 to 50 ppm, and the moisture content of the thermoplastic resin chip on the anti-dry sheet side after drying supplied to the extruder is 5 to 30 ppm. By controlling the moisture content of the thermoplastic resin chip on the sheet take-up side to be at least 5 ppm greater than the moisture content of the thermoplastic resin chip on the sheet take-off side, there is no streak on the surface and excellent uniformity in thickness. It is possible to form a sheet having less surface defects for a long time, and the industrial value of the present invention is remarkable.

[Brief description of the drawings]

FIG. 1 is a diagram showing an example of an embodiment used in the present invention.

[Explanation of symbols]

 1. Die 2. 2. Rotary cooling drum Electrostatic wire 4. DC high voltage device 5. Sheet

Claims (3)

[Claims] In a method for forming a thermoplastic resin sheet, wherein at least two extruders are used to cool and solidify a thermoplastic resin molten sheet laminated and extruded into two or more layers by a rotary cooling drum, an extruder (A) is used. )) And the moisture content (Xb) of the thermoplastic resin (B) supplied to the extruder (B) are represented by the following formulas (1) to (Xa).
The layer of the thermoplastic resin (A), which is in the range of the formula (3), is a layer on the sheet take-up side, and the thermoplastic resin (B)
Wherein the layer composed of is a layer on the side opposite to the sheet taking-up side. Xa−Xb ≧ 5 (ppm) (1) 20 ≧ Xa ≧ 50 (ppm) (2) 5 ≧ Xb ≧ 30 (ppm) (3) (Equation (1) In the formulas (3) to (3), Xa represents the moisture content (ppm) of the thermoplastic resin (A) supplied to the extruder (A), and Xb represents the moisture content of the thermoplastic resin (B) supplied to the extruder (B). Indicates the moisture content (ppm).) 2. The thickness (Ta) of the thermoplastic resin (A) layer constituting the sheet and the thickness (T) of the thermoplastic resin (B) layer.
The method for forming a thermoplastic resin sheet according to claim 1, wherein b) is within the range of the following formula (4). 1 ≧ Tb / Ta ≧ 99 (4) (In the formula (4), Ta is the thickness (mm) of the thermoplastic resin (A) layer constituting the sheet, and Tb is the thermoplastic resin (B ) Represents the thickness (mm) of the layer.) 3. The intrinsic viscosity (Ia) of the thermoplastic resin (A) chip supplied to the extruder (A) and the intrinsic viscosity (Ia) of the thermoplastic resin (B) chip supplied to the extruder (B). I
3) Molding such that b) and the intrinsic viscosity (Is) of the thermoplastic resin sheet fall within the range of the following formula (5).
3. The method for molding a thermoplastic resin sheet according to item 1. Is × (Wa + Wb) / (Ia × Wa + Ib × Wb) ≧ 0.9 (5) (In the formula (5), Ia is the thermoplastic resin (A) supplied to the extruder (A). ) Is the intrinsic viscosity of the chip, Ib is the extruder (B)
Intrinsic viscosity of the thermoplastic resin (B) chip supplied to
Is is the intrinsic viscosity of the thermoplastic resin sheet, Wa is the supply speed of the thermoplastic resin (A) chip supplied to the extruder (A), and Wb is the thermoplastic resin (B) supplied to the extruder (B). Represents the feed rate of the chip. )