JP2000280314A - Method for melt extrusion of aliphatic polyester resin - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a melt-extrusion method capable of obtaining an extruded product which is continuously stable and has good physical properties and appearance. SOLUTION: The present invention relates to an aliphatic polyester polymer having a main repeating unit represented by a general formula -O-CHR-CO- (1) wherein R represents H or an alkyl group having 1 to 3 carbon atoms. When the aliphatic polyester resin as the main component is melt-extruded, the thermal decomposition index obtained from the relationship between the molten resin temperature and the residence time of the resin at the temperature is expressed by the following equation (2): Σ (ti × ΔTi) ≦ 2400 ( 2) is satisfied, and the shear rate at the extrusion die is 40.
This is a method for melt-extruding an aliphatic polyester resin, which is performed at a rate of 0 / sec or less.

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 an extruded product, and more particularly to a method for molding various molded products such as stretched films, yarns, yarns, nonwoven fabrics, sheets, tubes, bottles, and rods. Related to a novel melt extrusion method.

[0002]

2. Description of the Related Art Aliphatic polyester films such as polylactic acid films are decomposed in the natural environment when they are discarded. For example, polylactic acid films are naturally hydrolyzed in soil and then harmless decomposition products. It has been developed as a feature. Investigations into molded products utilizing such characteristics have been made for various various uses such as stretched films, yarns, nonwoven fabrics, sheets, tubes, and rods, and many patent applications have been filed for these uses. In the case of producing these molded articles, continuous molding by a general melt extrusion method in which a polymer is melted, transferred, and then discharged from various bases is desired.

However, compared to aromatic polyester polymers such as PET, aliphatic polyester polymers have a higher rate of thermal decomposition at the time of melt retention at temperatures lower than the thermal decomposition onset temperature, and are stable with less decomposition. The range of temperature and residence time is very narrow. If melt extrusion is performed under conditions outside this range, resin degradation due to thermal decomposition becomes severe. For this reason, a low molecular weight component is generated in the molten resin, and the generation and adhesion of the oligomer gas near the base, and the contamination due to the outflow of bubbles and degraded substances occur, which hinders the subsequent molding process, and There is a problem that physical properties and appearance of the product are deteriorated.

[0004]

SUMMARY OF THE INVENTION An object of the present invention is to provide a melt-extrusion method capable of solving the above-mentioned problems and obtaining an extruded product which is continuously stable and has good physical properties and appearance. To provide.

[0005]

Means for Solving the Problems The inventors of the present invention have made intensive studies to solve the above-mentioned problems, and found that when melt-extruding an aliphatic polyester resin containing a predetermined aliphatic polyester polymer as a main component, By making the thermal decomposition index and the shear rate at the extrusion die portion equal to or less than a predetermined value, it has been found that a continuously extruded product having good physical properties and appearance can be obtained continuously and stably. . That is, the present invention is as follows. An aliphatic having a main component of an aliphatic polyester polymer whose main repeating unit is a general formula -O-CHR-CO- (1), wherein R is H or an alkyl group having 1 to 3 carbon atoms. In the melt extrusion of the polyester resin, the thermal decomposition index obtained from the relationship between the molten resin temperature and the residence time of the resin at the temperature is expressed by the following equation (2): Σ (ti × ΔTi) ≦ 2400 (2) ti × ΔTi); thermal decomposition index t: residence time (minute) of molten resin ΔT; (molten resin temperature) − (melting point temperature of resin) (° C.) i: Section number in each melting point section is satisfied and extruded The shear rate at the base is 40
A method for melt-extrusion of an aliphatic polyester resin, which is performed at 0 / sec or less. The method for melt-extrusion of an aliphatic polyester resin according to the above, wherein the aliphatic polyester polymer is polylactic acid.

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION The aliphatic polyester polymer which can be used in the present invention has a main repeating unit represented by a general formula -O-CHR-CO- (1) (wherein R is H or a group having 1 to 3 carbon atoms). (Indicating an alkyl group). In the above formula, examples of the alkyl having 1 to 3 carbon atoms include methyl,
Ethyl, n-propyl, isopropyl and the like can be mentioned. Specific examples include polylactic acid, polyglycolic acid, and poly (2-oxybutyric acid), but are not limited thereto as long as they have the above-mentioned repeating unit. Further, even if the aliphatic polyester polymer alone,
It may be a mixture or copolymer of two or more aliphatic polyester polymers. When an asymmetric carbon is contained in the repeating unit of the aliphatic polyester polymer, L-
There are optical isomers such as a isomer, a DL-isomer, and a D-isomer, and any of them and a mixture of these isomers may be used. A preferred aliphatic polyester polymer is polylactic acid for reasons such as moldability, heat resistance and cost.

[0007] The aliphatic polyester polymer preferably contains at least 90 mol%, more preferably at least 95 mol% of the above repeating unit. Examples of the unit that can be included in addition to the above repeating unit include an aliphatic ester unit derived from an oxycarboxylic acid and a unit derived from an aliphatic ester obtained from a diol and a dicarboxylic acid.

The above-mentioned aliphatic polyester polymer can be produced by a known method such as ring-opening polymerization of a corresponding dehydrated cyclic ester compound of α-oxyacid.

The molecular weight of the aliphatic polyester polymer which can be used in the present invention is 1 × 10 ⁴ to 50 in terms of weight average molecular weight.
× 10 ⁴ , preferably 4 × 10 ⁴ to 30 × 10 ⁴ . If the weight-average molecular weight is less than 1 × 10 ⁴ , the physical properties of the obtained molded article are remarkably inferior, which is not preferable for achieving the object of the present invention. On the other hand, the weight average molecular weight is preferably 1 × 10 ⁴ or more in order to sufficiently ensure the extrudability at the time of molding and the stretch moldability with, for example, a uniaxial or biaxial stretching machine. On the other hand, if the weight average molecular weight is larger than 50 × 10 ⁴ , it becomes a high-viscosity polymer, so that there is a problem that melt extrusion becomes difficult.

As long as the aliphatic polyester resin is the one containing the above aliphatic polyester polymer as a main component, the aliphatic polyester resin usable in the present invention further includes generally used thermoplastic resins, rubbers, inorganic fillers, antioxidants, Nucleating agent, plasticizer,
A composition to which a compatibilizer, a coloring agent, an antistatic agent, and the like are added may be used. In the present specification, the expression "mainly composed of an aliphatic polyester polymer" means that the aliphatic polyester polymer is contained in an amount of 90% by weight or more, preferably 95% by weight or more.

In general, in order to produce a molded article using an aliphatic polyester resin by extrusion molding, a polyester polymer is melted at a temperature not lower than the melting point and lower than the thermal decomposition starting temperature,
A continuous molding method of transferring and discharging from a die is used. According to this method, molded products such as stretched films, yarns, yarns, nonwoven fabrics, sheets, tubes, bottles, and rods can be obtained. The extruder used here is not particularly limited, and includes various devices such as a single-screw extruder, a twin-screw extruder, an extruder with a vent, and an extruder without a vent. As the base, a general base having a shape and a structure corresponding to various molded products can be used.

Further, a quantification pump, a filtration device, and the like may be incorporated in the extrusion step. These molding methods and molding apparatuses are known per se and are widely used.

According to the present invention, when the above-mentioned aliphatic polyester resin is molded by the above-mentioned general molding method and molding apparatus, it is continuously and stably formed by molding under predetermined conditions described below. This makes it possible to obtain a good extruded product in both appearance and appearance.

The aliphatic polyester polymer has a higher thermal decomposition rate at the time of melting retention at a temperature lower than the thermal decomposition start temperature and a stable temperature with less decomposition than the aromatic polyester polymer represented by PET or the like. The range of residence time is extremely narrow. If melt extrusion is performed under conditions outside this range, resin degradation due to thermal decomposition becomes severe.
For this reason, a low molecular weight component is generated in the molten resin, and the generation and adhesion of the oligomer gas near the base, and the contamination due to the outflow of bubbles and degraded substances occur, which hinders the subsequent molding process, and There is a problem that physical properties and appearance of the product are deteriorated.

The present inventors conducted experiments in which aliphatic polyester polymers having different molecular weights were used and the resin temperature during melt extrusion and the residence time at the temperature were changed, and the thermal decomposition index was not more than a predetermined value. If so, it was found that there was little thermal decomposition, and there was no problem in the subsequent molding step and molded product, and the present invention was reached. That is, in the present invention,
The thermal decomposition index is 2400 or less, preferably 1800 or less, more preferably 1000 or less.

In the present invention, the thermal decomposition index is determined by the difference [ΔT (° C.)] between the molten resin temperature and the melting point of the resin in each section of the extrusion process, and the residence time (minute) at the molten resin temperature in each section. And the product [Σ
(Ti × ΔTi)]. That is, the thermal decomposition index is represented by the following equation (2): Σ (ti × ΔTi) ≦ 2400 (2) where Σ (ti × ΔTi); thermal decomposition index t: residence time (minute) of molten resin ΔT; ( (Molten resin temperature) − (melting point temperature of resin) (° C.) i;

Here, each of the melting sections is, for example, an extruder, a pipe, and a die defined as one section in an apparatus including an extruder, a sheet forming die, and a pipe connecting the extruder and the die. When a quantification pump, a filtration device, and the like are incorporated between the extruder and the die, a section number is assigned to each of these apparatuses, and calculation is performed assuming that a section has been added.

Here, the residence time of the molten resin is a value of an average transit time calculated from the discharge amount per hour from the die and the internal volume of each section.

Here, the molten resin temperature means an average value of the resin temperatures detected at several temperature detecting terminals provided in each section.

Even when the melt extrusion is performed with the thermal decomposition index being less than the above-mentioned value, a decrease in the melt viscosity is small, a melt fracture, a rough skin, and the like are caused, and a molded article having poor appearance may be obtained. In general, melt fracture means that breakage occurs on the surface of a melt due to unstable flow of a molten resin. There are various reasons for this occurrence depending on the flow conditions, conditions, and the like, and these causes are known. The melt fracture which is a problem in the present invention means what occurs when the shear stress and the shear rate at the extrusion die exceed a certain value.

The present inventors conducted an extrusion experiment in which the shear rate at the base was changed, and found that if the shear rate was below a predetermined value, no melt fracture or rough skin would occur, and the present invention was accomplished. Was. That is, in the present invention, the shear rate is 400 / sec or less, preferably 3 / sec.
00 / sec or less. When the shear rate exceeds 400 / sec, even if the thermal decomposition index is 2400 or less,
Melt fracture and rough skin may occur.

For example, when a die for film molding is used, the following equation (3) γ = 6Q / (Wh ² ) (3) where γ: shear rate (1 / sec) Q: molten resin flow rate (Cm ³ / sec) W: lip width of the base part (cm) h: A value obtained from lip opening (cm) of the base part.

The above-mentioned aliphatic polyester resin is melt-extruded with a thermal decomposition index and a shear rate at a die portion of a predetermined value or less to smoothly and continuously produce a molded article having excellent appearance and physical properties. Obtainable.

[0024]

EXAMPLES The present invention will be described in more detail with reference to the following examples, which are merely examples, and the present invention is not limited thereto. The generation of decomposed gas, the generation of degraded products, and the poor appearance in this example and comparative examples were performed by visual judgment.

Example 1 Sheet molding was performed using a polylactic acid pellet having a weight average molecular weight of 73000 and a melting point of 168 ° C. and comprising an extruder, a sheet molding die, and a pipe connecting the extruder and the die. Was done. As the screw of the extruder, a full flight type screw having a diameter of 65 mm and L / D (length / diameter) = 29 was used.
And a lip width of 300 at the tip of this pipe.
A device equipped with a T die having a lip opening of 0.31 mm and a lip opening of 0.31 mm was used. Using this device, the screw rotation speed 50 rpm
The resin was extruded at a discharge rate of 80 cm ³ / min. The resin temperature and residence time in each section under the extrusion conditions were 200 ° C. for 10 minutes with an extruder and 200 minutes with a pipe, respectively.
C., 5 minutes, 200 ° C., 9 minutes with a die. The thermal decomposition index calculated therefrom was 768. The shear rate at the die lip was 296 / sec. There is no generation of decomposition gas and outflow of degraded products during this sheet molding,
No appearance defect due to melt fracture was observed in the obtained sheet.

Example 2 A sheet was formed in the same manner as in Example 1 except that a filtration device was incorporated between the pipe of the extrusion device and the die. The resin temperature and residence time at the filtration device were 200 ° C. and 10 minutes. The calculated thermal decomposition index was 1080. The shear rate at the die lip is 296 /
Seconds. There was no outflow of the deteriorated material during the sheet molding, but a small amount of decomposition gas was generated. The resulting sheet did not show any poor appearance due to melt fracture.

Comparative Example 1 A sheet was formed in the same manner as in Example 2 except that the resin temperature in each section was raised by 40 ° C. The calculated thermal decomposition index was 2448. The shear rate at the die lip was 296 / sec. During this sheet formation, a large amount of gas was generated around the die, and a large amount of bubbles and degraded substances flowed out. The resulting sheet did not show any poor appearance due to melt fracture.

Example 3 Example 1 except that the die lip opening was set to 0.27 mm.
A sheet was formed in the same manner as described above. The thermal decomposition index is 768
Met. The shear rate at the die lip is 3
65 / sec. There is no generation of decomposition gas and no outflow of degraded materials during this sheet molding, and the end of the obtained sheet is
Poor appearance such as rough skin was observed.

Comparative Example 2 Example 1 except that the die lip opening was set to 0.23 mm.
A sheet was formed in the same manner as described above. The thermal decomposition index is 768
Met. The shear rate at the die lip is 5
04 / sec. There was no generation of decomposition gas and no outflow of degraded materials during this sheet molding, but the resulting sheet
A lot of poor appearance due to melt fracture or rough skin was found on the entire surface of the sheet.

Example 4 The resin temperature in each section was set at 220 ° C., and the weight average molecular weight was 1
A sheet was formed in the same manner as in Example 2 except that 30,000 polylactic acid (melting point: 168 ° C.) was used. The thermal decomposition index was 1768. The shear rate at the die lip was 296 / sec. There was no outflow of the deteriorated material during the sheet molding, but a small amount of decomposition gas was generated. The resulting sheet did not show any poor appearance due to melt fracture.

Examples 1 to 4 and Comparative Examples 1 and 2 are summarized in Table 1.

[0032]

[Table 1]

As can be seen from Table 1, the thermal decomposition index is 2
When the shear rate was 400 or less and the shear rate was 400 / sec or less, no or little decomposed gas was generated in the production process, and there was no outflow of degraded substances. Moreover, in the molded product, a molded product having no or no appearance defect due to melt fracture or rough skin was obtained.

[0034]

According to the method for melt-extrusion of an aliphatic polyester resin of the present invention, an extruded product having good physical properties and appearance can be obtained continuously and stably.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) B29L 23:00 24:00 (72) Inventor Naonobu Oda 10-24 Toyocho, Tsuruga-shi, Fukui Toyobo (72) Inventor Tadashi Okudaira 2-1-1 Katata, Otsu-shi, Shiga F-term in Toyobo Co., Ltd. Research Institute 4F207 AA24 AE10 AG01 AG07 AG08 AG14 AR06 AR11 AR17 KA01 KA17 KF01 KK11 KK13 KK41 KM14 KM15 4J002 AA015 AC005 CF181 FD010 FD020 FD070 FD090 FD100 FD200

Claims (2)

[Claims] An aliphatic polyester polymer in which a main repeating unit is a general formula —O—CHR—CO— (1) wherein R is H or an alkyl group having 1 to 3 carbon atoms. When the aliphatic polyester resin as the component is melt-extruded, the thermal decomposition index obtained from the relationship between the molten resin temperature and the residence time of the resin at the temperature is expressed by the following equation (2): Σ (ti × ΔTi) ≦ 2400 (2 Here, 但 し (ti × ΔTi); thermal decomposition index t; residence time of molten resin (minute) ΔT; (molten resin temperature) − (melting point temperature of resin) (° C.) i; Satisfactory and the shear rate at the extrusion die is 40
A method for melt-extrusion of an aliphatic polyester resin, which is performed at 0 / sec or less. 2. The method according to claim 1, wherein the aliphatic polyester polymer is polylactic acid.