JPH0872106A - Injection compression molding method for polypropylene - Google Patents

Abstract

PURPOSE: To obtain a method for injection compression molding polypropylene without sinkmarks, warpage, and the like with a good appearance quality, superior rigidity and mechanical characteristics, such as a heat resistance, and esp. an improved face impact strength. CONSTITUTION: Polypropylene having an ultimate viscosity of 2.0-12.0dl/g measured in 135 deg.C tetralin is injected into a mold having a space of a thickness that is 1.2-2.0 times larger than a thickness of a final molded piece at a shear speed of 10000-50000sec<-1> at a nozzle part. When 60-90% of the total polypropylene injection amount is injected, mold closing is started. When the injected polypropylene is cooled to a temperature of 130-180 deg.C, mold closing is completed. In this manner, the polypropylene is injection compression molded.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention has good appearance quality such as sink marks and warpage, and excellent mechanical properties such as rigidity.
The present invention relates to a method for molding polypropylene having improved surface impact strength.

[0002]

2. Description of the Related Art A general injection molding machine is used to mold general polypropylene, and the injection pressure is up to 2000 kgf /
There are known a method of injection-filling into a predetermined metal mold at about cm ² and cooling and molding, and a method of pressurizing and cooling with a predetermined metal mold using a press molding machine. In addition, in the molding of ultra-high molecular weight polyethylene, it is known to perform injection compression molding in order to prevent delamination of the surface of the molded product and improve dimensional accuracy.

[0003]

Polypropylene having an intrinsic viscosity of 2.0 to 12.0 dl / g measured in 135 ° C. tetralin has rigidity, heat resistance, and impact resistance as compared with generally commercially available polypropylene. , And a polymer having remarkably excellent mechanical properties such as surface hardness. However, since these polypropylenes have extremely high viscosity when melted and have poor fluidity, it is difficult to mold them with an ordinary injection molding machine.

In the case of molding a product having a large projected area with a conventional injection molding machine, general polypropylene can be molded without any particular problem, but the intrinsic viscosity is 2.0 to 12.0 dl / g.
The polypropylene of the above type has problems that undulations and sink marks are generated on the surface of the molded product, the appearance quality is deteriorated due to warpage, and that one having high surface impact strength, which is one of the mechanical properties, cannot be obtained.

[0005]

As a result of intensive studies on the above-mentioned problems, the present inventors have found that the appearance quality is good, the mechanical properties such as rigidity are excellent, and the surface impact strength is particularly improved. They found that a product was obtained, and completed the present invention.

That is, in the present invention, polypropylene having an intrinsic viscosity of 2.0 to 12.0 dl / g measured in tetralin at 135 ° C. is used to form a gap having a thickness 1.2 to 2.0 times the thickness of the final molded product. The injection speed is 10,000 to 5
The injection is performed at 0000 sec ^-1 , and the mold closing is started when 60 to 90% of the total injection amount is injected, and the mold closing is completed when the temperature of the injected polypropylene is cooled to 130 to 180 ° C. It is a characteristic polypropylene injection compression molding method.

The polypropylene used in the present invention is 1
Intrinsic viscosity of 2.0 to 1 measured in tetralin at 35 ° C
2.0 dl / g, more preferable range is 2.2-8.0
dl / g. When the intrinsic viscosity is less than 2.0 dl / g, it is not preferable because the polypropylene does not exhibit remarkably excellent mechanical properties as compared with generally commercially available polypropylene. Further, if the intrinsic viscosity exceeds 12.0 dl / g, a molded product with good appearance quality cannot be obtained even by injection compression molding.

The polypropylene used in the present invention is 13
The intrinsic viscosity measured in 5 ° C. tetralin is 2.0-12.
If it is 0 dl / g, it may be produced by any method, and it can be produced by any known method using a Ziegler type polymerization catalyst and its improved catalyst without any limitation. For example, a titanium compound conventionally known as a catalyst and an organoaluminum compound can be used in combination, and if necessary, various electron donors such as ester and ether can be combined. The polymerization mode may be continuous or batch type, and may be solution polymerization performed in a solution of heptane or the like, slurry polymerization using propylene itself as a solvent, or gas phase polymerization. Polymerization is usually carried out by supplying propylene and hydrogen as required in the temperature range of 0 to 100 ° C., and after the predetermined polymerization is completed, the polymerization is stopped with a polymerization terminator such as isopropyl alcohol. In the polymerization of polypropylene, the polypropylene used in the present invention can be obtained by, for example, reducing the amount of hydrogen, which is a molecular weight modifier, to a very small amount, or performing the polymerization without using hydrogen.

In the present invention, it is preferable to use a mixture of a high molecular weight polypropylene and a low molecular weight polypropylene in order to improve the fluidity during molding and, in turn, the moldability.

The high-molecular-weight polypropylene constituting such a mixture has an intrinsic viscosity of 4.5 to 12.0 dl / g, and further 5.
It is preferably from 5 to 8.0 dl / g. On the other hand, as the low-molecular-weight polypropylene, the intrinsic viscosity measured in tetralin at 135 ° C. is 0.1 in order to prevent miscibility with the high-molecular-weight polypropylene, bleed-out, and the mechanical properties of the high-molecular-weight polypropylene.
03-3.5 dl / g, further 0.05-3.0 dl
It is preferably in the range of / g.

In the present invention, the mixture of high molecular weight polypropylene and low molecular weight polypropylene is in the range of 5 to 100 parts by weight, more preferably, the above low molecular weight polypropylene to 100 parts by weight of high molecular weight polypropylene.
Mixing in the range of 10 to 80 parts by weight is preferable for obtaining good moldability. The intrinsic viscosity of the mixture obtained by mixing is 2.2 to 4.5 in order to obtain good moldability.
It is preferably in the range of dl / g, more preferably 2.2 to 4.3 dl / g.

The mixing of the high molecular weight polypropylene and the low molecular weight polypropylene is carried out by individually polymerizing the high molecular weight polypropylene and the low molecular weight polypropylene by the above-mentioned method and dry blending using a Henschel mixer, or melt blending using an extruder or the like. There is a method of doing.

Further, the polypropylene in the present invention is obtained by continuously polymerizing a high molecular weight polypropylene and a low molecular weight polypropylene by multistage polymerization,
It is preferably used because flow marks and spots are reduced and the moldability is further improved. The multi-stage polymerization of polypropylene may be either continuous type or batch type as long as high molecular weight polypropylene and low molecular weight polypropylene are continuously produced, solution polymerization performed in a solution such as heptane, using propylene itself as a solvent. Slurry polymerization,
Alternatively, it may be gas phase polymerization.

The respective polymerization ratios and intrinsic viscosities of the high-molecular-weight polypropylene and the low-molecular-weight polypropylene, and the intrinsic viscosity of the multi-stage polymer are such that the ranges described above are satisfied. The polymerization temperature, the polymerization pressure, the polymerization time in the multi-stage polymerization, and the The concentration and addition method of the molecular weight modifier may be controlled appropriately. Further, the order of polymerization of the high molecular weight polypropylene and the low molecular weight polypropylene may be either.

In order to improve the mechanical properties, the polypropylene used in the present invention has an isotactic pentad fraction of 0.960 or more, more preferably 0.965 or more, as determined by ¹³ C-NMR. It is preferable. As a polymerization method for increasing the isotactic pentad fraction, a small amount of propylene is prepolymerized in the presence of a titanium compound, an organoaluminum compound, an organosilicon compound and an iodine compound as disclosed in JP-A-2-170802. It is preferable to use the prepolymerized catalyst obtained in this way.

The polypropylene used in the present invention is a homopolymer of propylene, or propylene and ethylene, 1
It may be a random or block copolymer with other α-olefins such as -butene, 1-hexene, 1-octene, and 4-methyl-1pentene. When the copolymer is a random copolymer, the amount of other α-olefin to be copolymerized is 5 mol% or less, and in the case of a block copolymer,
The amount of the other α-olefin is preferably 20 mol% or less.

Upon molding, the polypropylene used in the present invention may be added with additives such as heat stabilizers, weather resistance stabilizers, nucleating agents, fillers, pigments and lubricants which have been conventionally used.

In the injection compression method of the present invention, polypropylene is injected into a mold in which a gap having a thickness of 1.2 to 2.0 times, preferably 1.3 to 1.8 times the thickness of the final molded product is formed.
That is, before injection of polypropylene, the mold is already opened in the above-mentioned gap. Even if the mold gap is formed in the above range during the injection of polypropylene, the injection pressure at the time of injection cannot be lowered, and furthermore, warpage and sink marks cannot be reduced, which is not preferable. Further, if the gap between the molds is less than 1.2 times the thickness of the final molded product, the warpage and the sink mark become large, and if it exceeds 2.0 times, the sink mark at the end of the molded product becomes large, which is not preferable.

In the present invention, the injection speed is 10,000 to 50.
000 sec ^-1 , preferably 15,000 to 40,000 s
Inject polypropylene with ec ^-1 . The injection speed of the present invention means the average value of the shearing speed of polypropylene in the nozzle portion in the range where 0 to 80% of the total injection amount is injected, and the shearing speed (γ) is the radius of the nozzle hole r (C
m) and the injection rate is Q (cm ³ / sec), γ = 4
It is a value calculated by Q / πr ³ (sec ⁻¹ ). If the injection speed is less than 10000 sec ^-1 , the warp is large due to a large pressure difference between the gate and the end of the molded product, which is 500
When it exceeds 00 sec ^-1 , jetting occurs when polypropylene passes through the gate, and sink marks on the surface of the molded product increase, which is not preferable. Furthermore, if the injection amount of polypropylene exceeds 80% of the total injection amount, the injection speed is set to 1 so that burr or burn does not occur in the molded product.
It is preferably set to 0000 sec ^-1 or less.

In the present invention, the mold closing is started when 60 to 90%, preferably 65 to 85% of the total injection amount of polypropylene is injected. When the mold closing is started at less than 60% of the total injection amount, the molded product is apt to warp, and when the mold closing is started at more than 90%, it becomes difficult to obtain a molded product having a predetermined thickness and the molding is performed. It is not preferable because burrs are likely to occur in the product.

In the present invention, the mold closing is completed when the temperature of the injected polypropylene is cooled to 130 to 180 ° C, preferably 140 to 170 ° C. Here, the temperature of polypropylene is a value obtained by measuring the temperature of polypropylene at the midpoint of the distance between the contact point between the molded body in the mold and the gate and the end of the molded body farthest from the gate with an infrared temperature sensor. When the temperature of the injected polypropylene is less than 130 ° C and the mold closing is completed, the end of the molded product cannot be filled and the sink mark becomes large, and when the mold closing is completed when the temperature exceeds 180 ° C, the polypropylene after the mold closing is completed. This is not preferable because the shrinkage of the molded product will increase due to the shrinkage of.

As the injection molding machine and mold used for the injection compression molding of the present invention, known ones can be used without any limitation,
For example, an injection compression molding machine having a function of changing the mold clamping force during molding, hydraulic pressure, or a mold having a structure in which the cavity volume can be changed by a spring can be used.

[0023]

Industrial Applicability The polypropylene injection compression molding method of the present invention improves the appearance quality of polypropylene, has good mechanical properties, and particularly has improved surface impact strength. Therefore, the polypropylene injection compression molding method of the present invention is used for molding gears, mechanical parts such as packings, automobile parts such as inner panels, wheel caps, door trims, OA equipment housings, and various lining materials that require mechanical strength. It can be used as a method.

[0024]

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, a molding machine, a mold, an injection compression method, and a measuring method used in the examples will be described.

(1) Molding machine A toggle type injection compression molding machine having a mold clamping force of 100 tons was used.
The cylinder temperature of the molding machine was set to 220 ° C.

(2) Mold 160 mm long × 120 mm wide × 30 mm high × thickness 1.
A box was molded with a mold having an 8 mm cavity. The gate was a φ8 mm direct gate. The mold temperature was set to 80 ° C.

(3) Intrinsic viscosity Measured in tetralin at 135 ° C.

(4) Injection compression method (a) Polypropylene was injected into a mold opened by a predetermined amount, and compression was performed with a mold clamping force of 100 tons from the time when the predetermined amount was injected.

(B) Resin is injected into a mold clamped with a mold clamping force of 20 tons, and a mold clamping force of 1 is obtained from the time when a predetermined amount of the mold is opened.
Compression was performed at 00 tons.

(5) Mold opening amount A value obtained by dividing the cavity gap at the time when the mold was opened to the maximum by the thickness of the final molded product was defined as the mold opening amount.

(6) Injection speed The shearing speed of polypropylene when passing through a nozzle hole having a radius of 2 mm was obtained from the following equation and used as the injection speed.

Injection speed (sec ^-1 ) = 4 Q / πr ³ where Q: injection rate (cm ³ / sec) r; nozzle hole radius = 0.2 (cm) (7) injection rate The value obtained by dividing the screw movement amount by the screw movement amount from the start of injection to the end of injection was taken as the injection ratio.

(8) Resin temperature An infrared temperature sensor was installed on the mold cavity surface at a position 65 mm away from the gate on the diagonal line on the bottom surface of the box, and the temperature of polypropylene was measured to obtain the resin temperature.

(9) Sink mark The surface of the molded product was visually observed and the following three-stage evaluation was performed.

○: No sink mark is seen △: Sink mark is slightly seen ×: Sink mark is large (10) Warp amount Place the bottom of the box on a horizontal surface with the bottom of the box down, and measure the distances between the four corners of the bottom of the box and the horizontal. The largest distance among them is the amount of warpage.

(11) Flexural Modulus A test piece of 128 mm × 12.7 mm × 1.8 mm was cut out from the molded product to prepare a flexural elastic modulus according to ASTM: D790.

(12) Surface impact strength According to JIS: K7211, tip radius 7 mm, weight 10
The 50% breaking height with a 0 g weight was measured. The occurrence of cracks was judged to be destruction.

(13) Pencil Scratch Hardness Using a tester specified by JIS: K5401, a load of 1
It was measured at 00 g.

Example 1 According to the method described in Example 1 of Japanese Patent Application No. 6-136007, titanium-containing polypropylene, triethylaluminum, and cyclohexylmethyldimethoxysilane were used as catalysts, and 0.006 NL of hydrogen was initially supplied, Temperature 75
Polymerization of high molecular weight homopolypropylene (intrinsic viscosity 6.3 dl / g) at 110 ° C and pressure of 25 kgf / cm ² is carried out for 110 minutes, then 95 NL of hydrogen is supplied, and low molecular weight homopolypropylene (intrinsic viscosity 0.6 dl at a temperature of 60 ° C) / G) was polymerized for 70 minutes. 135 of the obtained homopolypropylene
The intrinsic viscosity was 3.8 dl / g and the isotactic pentad fraction was 0.962 as measured in tetralin at ℃.

The homopolypropylene was opened with a mold opening amount of 1.6.
Shear speed 28,000 sec at nozzle part
-Injection at ^-1 , the mold closing starts at the time of injection rate 72%,
The mold was closed at a constant speed and completed in 5 seconds. The resin temperature at the time when the mold closing was completed was 152 ° C. With respect to this homopolypropylene molded article, the sink mark, the amount of warpage, the flexural modulus, the surface impact strength, and the pencil scratch hardness were measured. The results are shown in Table 1.

Example 2 100 parts by weight of a high-molecular-weight homopolypropylene polymerized according to the method described in JP-A-3-7704 and having an intrinsic viscosity of 5.8 dl / g isotactic pentad fraction 0.961 and an intrinsic viscosity. Low molecular weight homopolypropylene 43 with 0.5 dl / g and isotactic pentad fraction 0.963
By mixing 1 part by weight with a Henschel mixer, the intrinsic viscosity is 2.
A homopolypropylene having 9 dl / g was obtained. This homopolypropylene was injected into a mold having a mold opening amount of 1.7 times at a shear rate of 19000 sec ^-1 at the nozzle portion, the mold closing was started at the injection rate of 83%, and the mold closing was completed in 3 seconds. . The resin temperature at the time when the mold closing was completed was 166 ° C. The results are shown in Table 1.

Example 3 A homopolypropylene polymerized according to the method disclosed in JP-A-3-7704 and having an intrinsic viscosity of 8.7 dl / g and an isotactic pentad fraction of 0.961 was used to open the mold 1.
Shear speed at the nozzle is 36000se in a 4 times mold.
Injection was performed at c ^-1 , and the mold closing was started at the injection rate of 67%, and the mold closing was completed in 7 seconds. The resin temperature was 143 ° C. when the mold closing was completed. The results are shown in Table 1.

Comparative Example 1 Injection compression molding was carried out in the same manner as in Example 1 except that homopolypropylene having an intrinsic viscosity of 1.5 dl / g and an isotactic pentad fraction of 0.963 was used. The results are shown in Table 1.

Comparative Example 2 The same homopolypropylene as in Example 1 was subjected to ordinary injection molding at a shear rate of 28,000 sec ^-1 at the nozzle. The results are shown in Table 1.

Comparative Example 3 The same homopolypropylene as in Example 1 was used with a mold clamping force of 20 to.
Shear speed of 2800 at nozzle
Injection was performed at ⁰ sec ^-1 , and the mold closing was started from the time when the mold was opened 1.5 times. The injection rate at this time was 76%, and the resin temperature at the time of completion of mold closing was 151 ° C. The results are shown in Table 1.

Examples 4 and 5 and Comparative Examples 4 and 5 Injection compression molding was performed in the same manner as in Example 1 except that the mold opening amount was changed as shown in Table 1. The results are shown in Table 1.

Examples 6 and 7, Comparative Examples 6 and 7 Injection compression molding was carried out in the same manner as in Example 1 except that the shear rate at the nozzle portion was changed as shown in Table 1. The results are shown in Table 1.

Examples 8 and 9 and Comparative Examples 8 and 9 Injection compression molding was performed in the same manner as in Example 1 except that the injection ratio at the start of mold closing was changed as shown in Table 1.
The results are shown in Table 2.

Examples 10 and 11, Comparative Examples 10 and 11 Injection compression was performed in the same manner as in Example 1 except that the mold closing speed was changed and the resin temperature at the time of completion of mold closing was changed as shown in Table 1. Molded. The results are shown in Table 2.

Example 12 In the prepolymerization of titanium-containing polypropylene, propylene was polymerized according to the method shown in Example 1 of Japanese Patent Application No. 6-136007, except that ethyl iodide was used. A homopolypropylene having a content of 3.6 dl / g and an isotactic pentad fraction of 0.972 was obtained. This polypropylene was subjected to injection compression molding in the same manner as in Example 1. The results are shown in Table 2.

[0052]

[Table 1]

[0053]

[Table 2]

─────────────────────────────────────────────────── ───

[Procedure amendment]

[Submission date] October 6, 1994

[Procedure Amendment 1]

[Document name to be amended] Statement

[Name of item to be amended] Claims

[Correction method] Change

[Correction content]

[Claims]

[Procedure Amendment 2]

[Document name to be amended] Statement

[Correction target item name] 0006

[Correction method] Change

[Correction content]

That is, in the present invention, polypropylene having an intrinsic viscosity of 2.0 to 12.0 dl / g measured in tetralin at 135 ° C. is used to form a gap having a thickness 1.2 to 2.0 times the thickness of the final molded product. Injecting into the mold where the shear rate at the nozzle part is 10,000 to 50,000 sec ^-1 , and 60 to 90% of the total injection amount is injected, mold closing is started, and the temperature of the injected polypropylene is 130. A method for injection compression molding of polypropylene, characterized in that the mold closing is completed when cooled to ˜180 ° C.

[Procedure 3]

[Document name to be amended] Statement

[Correction target item name] 0019

[Correction method] Change

[Correction content]

In the present invention , the shear rate at the nozzle is 1
0000 to 50,000 sec ^-1 , preferably 15,000
Inject polypropylene at -40,000 sec ^-1 . The shear rate at the nozzle portion of the present invention is 0 to 8 of the total injection amount.
The average shear rate of polypropylene at the nozzle in the range where 0% is injected. Shear rate (γ)
Is the radius of the nozzle hole is r (cm) and the injection rate is Q (cm ³
/ Sec), it is a value calculated by γ = 4Q / πr ³ (sec ⁻¹ ). Shear rate at the nozzle is 100
If it is less than 00 sec ^-1 , the warp is large because the pressure difference between the gate and the end of the molded product is large, and 50,000 sec.
^If it exceeds ^-1 , jetting will occur when polypropylene passes through the gate, and sink marks on the surface of the molded product will increase, which is not preferable. In addition, when the injection amount of polypropylene exceeds 80% of the total injection amount , the shearing speed at the nozzle part is set so that burr or burn does not occur in the molded product.
The degree is preferably 10,000 sec ^-1 or less.

[Procedure amendment 4]

[Document name to be amended] Statement

[Name of item to be corrected] 0032

[Correction method] Change

[Correction content]

(6) Shear rate at the nozzle section The shear rate at which polypropylene passes through a nozzle hole having a radius of 2 mm was obtained from the following equation and used as the shear rate at the nozzle section .

[Procedure Amendment 5]

[Document name to be amended] Statement

[Correction target item name] 0033

[Correction method] Change

[Correction content]

Shear rate at nozzle (sec ^-1 ) = 4 Q / πr ³ where Q: injection rate (cm ³ / sec) r; nozzle hole radius = 0.2 (cm) (7) injection rate The value obtained by dividing the screw movement amount from the injection start by the screw movement amount from the injection start to the injection end was defined as the injection ratio.

Claims (1)

[Claims] 1. Gold having polypropylene having an intrinsic viscosity of 2.0 to 12.0 dl / g measured in tetralin at 135 ° C. and having a gap 1.2 to 2.0 times the thickness of the final molded product. The mold has an injection speed of 10,000 to 50,000 sec ^-1
The mold is closed when 60 to 90% of the total injection amount is injected, and the temperature of the injected polypropylene is 130
A polypropylene injection compression molding method, characterized in that the mold closing is completed when cooled to ˜180 ° C.