JP3326758B2 - Method for producing polypropylene molded article - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to
The present invention relates to a method for producing a polypropylene molded article having no wrinkles, excellent surface properties, and small warpage.

[0002]

2. Description of the Related Art Conventionally, amorphous resins such as vinyl chloride and styrene resins are plasticized in an extruder and formed into a predetermined shape by a die attached to the extruder tip. A method of obtaining a compact by cooling and solidifying in a cooling zone such as a sizing plate, a sizing die, and a water tank is used.

On the other hand, crystalline resins such as polypropylene
Since the molding shrinkage is larger than that of the amorphous resin, the surface of the irregular-shaped extruded molded body is likely to be rough and wrinkled, and it is difficult to obtain a molded body having excellent surface properties. In addition, polypropylene has a large specific heat and is difficult to be cooled quickly. Therefore, when a molded article having a complicated shape is extruded in a different shape, there is a problem that the molded article is likely to be warped in the longitudinal direction.

[0004]

In order to improve the moldability of polypropylene in the form extrusion, for example, a method of adding an inorganic filler to reduce molding shrinkage, or directly connecting to a die provided at the tip of the extruder. A method of performing pre-solidification with a forming die has been proposed. However, even these methods have not solved all of the above problems.

Accordingly, an object of the present invention is to propose a method for producing a molded polypropylene article which has no surface roughness and wrinkles, has excellent surface properties, and has a small warpage.

[0006]

Means for Solving the Problems The present inventors have conducted intensive studies on the above-mentioned problems, and as a result, it has been found that there is no surface roughness and wrinkles on the surface of the molded body, the surface is excellent, and the polypropylene molding is small in warpage. The present inventors have found a method for producing a body and have completed the present invention.

That is, the present invention relates to (a) polypropylene
50 to 95% by weight (b) A polypropylene composition containing 50 to 5% by weight of talc having a particle size of 3 to 30 μm is extruded by an extruder, and then the surface is cooled and solidified in a cooling zone.
This is a method for producing a polypropylene molded article, which comprises stretching at a stretching ratio of 1.005 to 1.200 times.

The polypropylene used in the present invention is not particularly limited. However, in order to obtain a molded article of polypropylene having excellent surface properties and small warpage, the polypropylene has a melt flow rate of 0.1 to 10 g / 10 min. It is preferably from 0.2 to 7 g / 10 min. Further, the polypropylene of the present invention is a homopolymer of propylene, or propylene and ethylene, 1-butene, 1-
It may be a random or block copolymer with an α-olefin such as hexene, 1-octene, and 4-methyl-1pentene. When the copolymer is a random copolymer, the amount of the α-olefin to be copolymerized is 5 mol.
% Or less, and in the case of a block copolymer, preferably 20 mol% or less.

In the present invention, talc having a particle size of 3 to 30 μm is blended with the polypropylene. Talc is a mineral generally represented by the structural formula Mg ₃ Si ₁₀ (OH) ₂ . The particle size of talc must be 3 to 30 μm, preferably 5 to 20 μm,
It must be 50% by weight, preferably 10 to 40% by weight. Here, the particle size of talc is represented by the major axis of talc flakes. Talc particle size less than 3μm or 30μm
If it exceeds, the surface of the molded body becomes rough, which is not preferable. When the amount of talc to be mixed is less than 5% by weight, molding shrinkage is large, so that wrinkles and sink marks are generated on the surface of the molded article. When the amount exceeds 50% by weight, poor mixing of polypropylene and talc occurs, and Rough skin occurs on the body surface.

In the method for producing a polypropylene molded article according to the present invention, the above-mentioned polypropylene composition is plasticized in an extruder, and is extruded into a predetermined shape by a die provided at the extruder tip. Is cooled and solidified, and then stretch ratio is 1.005 to 1.20.
Stretch at 0x.

In the present invention, as the extruder and the die provided at the tip of the extruder, those generally used can be used without any limitation, and the extrusion temperature of the polypropylene composition is 170 to 270 ° C., and furthermore, , 180 to 250 ° C.

In the present invention, any method may be used for cooling and solidifying the surface of the profile-extruded polypropylene composition in the cooling zone. For example, a method of contacting the profile-extruded polypropylene composition with air, cooling water or air. Examples include a method of forcibly spraying, a method of passing through a sizing die provided with a jacket through which a coolant such as cold water circulates, and a method of passing through a water tank. However, in the cooling zone, since the stretching is performed subsequently, the surface of the molded body is cooled and solidified, and the inside of the molded body is not completely solidified, and it is necessary to maintain a state in which stretching can be performed. Such a state is achieved by appropriately selecting the extrusion temperature of the polypropylene composition, the type and temperature of the refrigerant, the length of the cooling zone, the take-up speed of the molded product, and the like.

The most important point in the method for producing a molded polypropylene article of the present invention is that the molded article which has been cooled and solidified on the surface and which has not been completely cooled and solidified on the inside and which is still stretchable is stretched. Magnification 1.005 to 1.20
The stretching is performed at 0 times, more preferably at 1.010 to 1.100 times. By stretching at a stretching ratio in the above range, it is possible to obtain a molded article having extremely small warpage in the longitudinal direction. When the stretch ratio is less than 1.005 times, the effect of improving the warpage of the molded body is not remarkable, and when the stretch ratio exceeds 1.200 times, the molded body is cut or cracks are generated on the surface of the molded body. I will. As a method of stretching, for example, two sets of take-off devices are provided after the cooling zone, and each take-up device grasps both sides of the molded body that has come out of the cooling zone, and the take-out device on the extruder side and the subsequent take-up device. This can be performed by changing the take-up speed of the apparatus.

[0014]

According to the method for producing a molded polypropylene article of the present invention, it is possible to obtain a molded article of polypropylene which has no surface roughness and wrinkles, has excellent surface properties, and has a small warpage.

[0015]

EXAMPLES The present invention will be described below with reference to examples and comparative examples, but the present invention is not limited to these examples. Prior to the examples, the extruder, the sizing die, the stretching method, the cross-sectional shape of the molded article, and the method for evaluating the surface properties and warpage of the molded article used in the examples will be described.

(1) Extruder An extruder having a diameter of 50 mm and L / D = 25 was used to extrude the polypropylene composition in an irregular shape. The cylinder set temperature was 200 ° C. and the die set temperature was 180 ° C.

(2) Sizing Die A hole for evacuation is provided in the inner wall of the sizing die, and a vacuum sizing die is used to bring the molded body into close contact with the inner wall of the sizing die by this suction force. By circulating water at 20 ° C,
The compact was cooled. In addition, the length of the sizing die is 50 mm, and the distance between the die and the sizing die is 150 mm.
Kept.

(3) Stretching method The pair of rubber rolls (first roll) is gripped on both sides of the molded body that has exited the sizing die and is taken out. Thereafter, the take-up speed is reduced by the same rubber roll (second roll). Changed and stretched. The distance between the first roll and the second roll was 500 mm. The stretch ratio of the molded product was determined by the following equation.

Stretching ratio = Taking-up speed of second roll / Taking-up speed of first roll (4) Cross-sectional shape of molded product The cross-sectional shape of the molded product is shown in FIG. The numerical values in FIG. 1 are dimensions (unit: mm).

(5) Method for Evaluating Surface Properties of Molded Body The surface of the obtained molded body was visually observed, and the following three grades were evaluated.

；: The surface of the molded body is good without surface roughness and wrinkles.

(2) The surface of the molded product is slightly rough and wrinkles are observed.

×: Surface roughness, wrinkles, etc. were observed on the surface of the molded product, and the surface properties were poor.

(6) Evaluation method of warpage of molded article The difference in height between the center and the end when the molded article cut to a length of 500 mm was allowed to stand horizontally was measured as the amount of warpage.
The following three-stage evaluation was performed.

；: The amount of warpage is less than 5 mm Δ: The amount of warpage is 5 mm or more and less than 10 mm ×: The amount of warpage is 10 mm or more Was mixed with a supermixer and melt-kneaded with a 50 mm extruder to obtain pellets. The pellet was extruded from a predetermined die using an extrusion molding machine, and was passed through a sizing die to cool and solidify the surface. Next, drawing was performed at a take-up speed of the first roll of 1000 mm / min and a take-up speed of the second roll of 1030 mm / min, that is, at a draw ratio of 1.030, to produce a polypropylene molded article. Table 1 shows the evaluation results of the surface properties and warpage of the obtained molded body.

Examples 2 and 3 A polypropylene molded article was produced in the same manner as in Example 1 except that the particle size of talc was changed to 5 and 20 μm. The results are shown in Table 1.

Comparative Examples 1 and 2 A polypropylene molded article was produced in the same manner as in Example 1, except that the particle size of talc was changed to 1 and 38 μm. The results are shown in Table 1.

Examples 4 and 5 In Example 1, the amount of talc was changed to 10 and 40% by weight.
A polypropylene molded article was produced in the same manner as in Example 1 except that the composition was changed to. The results are shown in Table 1.

Comparative Examples 3 and 4 A polypropylene molded article was produced in the same manner as in Example 1, except that the amount of talc was changed to 3 and 55% by weight. The results are shown in Table 1.

Examples 6 and 7 In Example 1, the take-up speed of the second roll was changed.
A polypropylene molded article was produced in the same manner as in Example 1, except that the stretching ratio was changed to 1.010 and 1.120. The results are shown in Table 1.

Comparative Examples 5 and 6 In Example 1, the take-up speed of the second roll was changed.
A polypropylene molded article was produced in the same manner as in Example 1 except that the stretching ratio was changed to 1.002 and 1.250. The results are shown in Table 1.

[0032]

[Table 1]

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a polypropylene molded body manufactured in Examples and Comparative Examples, taken along a plane perpendicular to the longitudinal direction.

Continuation of the front page (51) Int.Cl. ⁷ Identification symbol FI // B29K 23:00 B29K 23:00 (56) References JP-A-56-120742 (JP, A) JP-A-57-73033 (JP, A) JP-A-61-72038 (JP, A) JP-A-2-175739 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) B29C 47/00-47/96 B29C 55 / 00 C08J 5/00-5/24 C08K 3/34 C08L 23/10

Claims (1)

(57) [Claims] (1) Polypropylene composition containing (a) 50 to 95% by weight of polypropylene (b) 50 to 5% by weight of talc having a particle size of 3 to 30 μm is extruded by an extruder, and then the surface is cooled in a cooling zone. Cool and solidify, then
A method for producing a molded polypropylene article, comprising stretching at a stretching ratio of 1.005 to 1.200 times.