JPH0587523B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing a polypropylene molded article that prevents uneven gloss from occurring. Polypropylene is generally widely used as molded products such as fibers, films, sheets, and structures, but it has the problem that uneven gloss occurs on the surface of injection molded products depending on molding conditions, which significantly reduces its commercial value. . A technique that has been attracting particular attention recently is a method in which polypropylene with a desired molecular weight is obtained by producing a polymer with a large molecular weight and decomposing it, for example, by the action of radicals to reduce the molecular weight. When injection molded products are manufactured using polypropylene obtained by this method (hereinafter also referred to as decomposed PP), uneven gloss is noticeable. The present inventors have conducted intensive research on preventing uneven gloss when producing injection molded polypropylene products. As a result, it was found that the molecular weight distribution of polypropylene has a significant effect on the uneven gloss on the surface of injection molded products of the polypropylene. That is, as polypropylene decomposes, its molecular weight decreases and its molecular weight distribution narrows, and as the molecular weight distribution narrows, the above-mentioned problems become more pronounced. The present invention is based on this knowledge, and by injection molding using decomposed PP with a ratio ( _w / _o ratio) of weight average molecular weight ( _w ) to number average molecular weight ( _o ) representing molecular weight distribution of 6.5 or more. To provide a method for producing a polypropylene molded article, which almost completely prevents the occurrence of uneven gloss on the surface of the resulting injection molded polypropylene article. That is, the present invention is a method for producing a polypropylene molded article, which is characterized by injection molding using polypropylene whose molecular weight has been reduced by decomposition treatment and whose _w / _o ratio is 6.5 or more. In the present invention, polypropylene is a general term for propylene homopolymers and copolymers of propylene and other α-olefins, such as ethylene. Furthermore, the term "molded product" is a general term that includes structures generally obtained by injection molding, as well as plate-like bodies, sheet-like bodies, and the like. In the present invention, it is extremely important to use decomposed PP with a _w / _o ratio of 6.5 or more, preferably 7 or more in order to obtain a molded article with no uneven gloss on the surface. That is, the present invention prevents the generation of uneven gloss on the surface of the injection molded product to be significantly caused by the molecular weight distribution expressed by the _w / _o ratio becoming narrower than the above-mentioned certain range due to manufacturing conditions or decomposition treatment. This is based on new findings that when decomposed PP with a wide molecular weight distribution is used, uneven gloss is significantly improved. Therefore,
Molded products obtained using polypropylene with a _w / _o ratio smaller than the above range, or molded products obtained using polypropylene that has a wide molecular weight distribution but has not been subjected to decomposition treatment, may have insufficient improvement in surface gloss unevenness. is insufficient and cannot achieve the purpose of the invention. In addition, in terms of strength, such as the bending modulus of elasticity of the molded product, the polypropylene mentioned above preferably has _{a w} / _o ratio of less than 10, preferably 8 or less, or a melt flow index (hereinafter also referred to as MI) of 6 or less. used for. When obtaining the decomposed PP having the specific molecular weight distribution used in the present invention, the M _w / _o ratio tends to decrease significantly due to decomposition.
So that _{the w} / _o ratio after decomposition is within the above range.
Decomposition can be carried out using polypropylene having a relatively high _w / _o ratio as a raw material. Generally _w / _o
The ratio is 10 or more, preferably 10 to 50, more preferably
It is preferable to use polypropylene of 15 to 30% as a raw material and decompose it to produce decomposed PP having the above-mentioned _w / _o ratio. Of course, the decomposed PP has a _w / _o ratio of 10
However, when increasing the decomposition rate in order to increase the MI of the decomposed PP to improve processability, _{the w} / _o ratio may be as low as 100% before it is decomposed to the desired molecular weight. If the lower limit is too high, it may be difficult to reduce the molecular weight sufficiently. The raw polypropylene having the above-mentioned high _w / _o ratio can be obtained by the above-mentioned known methods. Moreover, the decomposition of the raw material polypropylene can be carried out by any known method without any particular restriction. Generally, a method of heat treating polypropylene in the presence of a radical generator is suitable. As the radical generator, an organic peroxide is preferably used. Examples of typical organic peroxides include ketone peroxides such as methyl ethyl ketone peroxide and methyl isobutyl ketone peroxide; diacyl peroxides such as isobutyl peroxide and acetyl peroxide; diisopropylbenzene hydroperoxide and other hydroperoxides. Oxide; 2,5-dimethyl 2,5-di-(t-butylperoxy)hexane,
Dialkyl peroxides such as 1,3-bis-(t-butylperoxyisopropyl)benzene;
1,1-di-t-butylperoxy-cyclohexane and other peroxyketals; alkyl peresters such as t-butylperoxyacetate and t-butylperoxybenzoate; t-butylperoxyisopropyl carbonate and other peroxyketals; Examples include carbonate. The amount of the organic peroxide to be used varies depending on the set value of the molecular weight of polypropylene at the degree of decomposition, etc., and cannot be determined unconditionally, but it is 0.001 to 1.0 with respect to polypropylene.
Weight %, preferably 0.01 to 0.5 weight %, is common. In addition, in the above method, the mixing of polypropylene and the radical generator can be carried out if the radical generator is present when the polypropylene is heat-treated.
The mixing method is not particularly limited. For example, there is a method of mechanical mixing using a mixer such as a blender, a method of dissolving the radical generator in a suitable solvent, adhering it to polypropylene, and mixing by drying the solvent. Further, the heat treatment temperature is a temperature higher than the melting temperature of polypropylene and higher than the decomposition temperature of the radical generator. However, if the heat treatment temperature is too high, thermal deterioration of polypropylene will occur. Generally, the heat treatment temperature is preferably set within the range of 170 to 300°C, particularly 180 to 250°C. As can be understood from the above explanation, the injection molded products obtained by the method of the present invention have almost no uneven surface gloss, and are particularly suitable for decomposed PP, where uneven surface gloss is a major problem in injection molding. In the production of molded articles using the decomposed PP, excellent effects are exhibited when the molecular weight distribution of the decomposed PP is adjusted to the above range. Although the method of the present invention is particularly effective when producing molded articles by injection molding, it can also be employed without particular problem in producing molded articles such as sheets and films by other molding methods, such as extrusion molding. EXAMPLES Hereinafter, examples will be shown to specifically explain the present invention, but the present invention is not limited to these examples. The following methods were used to measure various properties shown in the Examples and Comparative Examples below. (1) Melt index (also written as MI)
Measured according to ASTM D-1238 (2) Ethylene content Ethylene content in the block copolymer was determined by infrared absorption spectroscopy. (3) Molecular weight distribution _w / _o measuring device is Waters GPC
Using 150C, the solvent was 0-dichlorobenzene,
The measurement temperature was 135°C. (4) Gloss unevenness Visually observe the injection molded test piece for measuring flexural modulus. If no gloss unevenness is observed, mark ◎, if very slight unevenness is observed, mark ○, if slightly observed, △
The evaluation was made by marking the items with a mark and marking the other items with an x. Generally speaking, uneven gloss tends to appear more concentrically than with Kate.
The period changes depending on injection molding conditions. (5) Flexural modulus The test piece is Nikko Ankelberg V22A−
Made using a 120-type injection molding machine, ASTM D
-790. (6) Izot impact strength test specimens were prepared in the same way as the bending test specimens.
Measured according to ASTM D-256. Example 1 20 times the mole of diethylaluminum monochloride (also known as AlEt ₂ Cl) and 0.02 times the mole of diethylene glycol relative to titanium trichloride (also known as TiCl ₃ ) were added to a 300 mm stirred polymerization tank purged with propylene gas. Dimethyl ether (also known as Diglyme) is added, followed by liquid propylene.
200 and hydrogen gas as a molecular regulator were introduced, the temperature was raised to 65°C, and then 3.4 g of TiCl ₃ (manufactured by Marubeni Solvay) was added to initiate polymerization. During the polymerization, hydrogen gas was supplied and the gas phase concentration was controlled using gas chromatography to maintain a constant concentration. First, the gas phase hydrogen concentration was set at 13.6 mol% so that the MI of the polymerized polymer was 500, and polymerization was continued for 1 hour and 20 minutes. Then, only unreacted propylene and hydrogen were purged from the top of the polymerization tank. Subsequently, 150% propylene and 15 times the mole of AlEt ₂ Cl were added again to the polymerization tank in which the polymerization polymer remained, and hydrogen gas was introduced. Then, the temperature was raised to 65°C to start polymerization again. Hydrogen gas is supplied during polymerization, and the MI of the polymer produced during the polymerization step is 0.01.
The gas phase hydrogen concentration was set at 0.35 mol% so that the polymerization was continued for 3 hours. After the polymerization is completed, the polymer slurry is discharged from the bottom discharge valve of the polymerization tank into the flash tank, unreacted propylene is purged to stop the polymerization, and then heptane is added at 200 °C and methanol is added.
The slurry was made into a slurry and stirred at 60°C for 1 hour to decompose the catalyst. Subsequently, 100 ml of water was injected, the catalyst decomposition product was extracted into the aqueous phase, and the aqueous phase was separated and removed.
The heptane slurry of the polymer was separated into solid and liquid using a centrifuge, and the solid was sent to a dryer and dried for 6 hours to obtain a white granular crystalline polymer. On the other hand, a portion of the filtrate was collected, and after heptane was removed, APP was recovered. The MI of the polymer is 1.8, and the APP by-product rate is 3.4%.
It was hot. The organic peroxide 1,3-bis(t-butylperoxyisopropyl)benzene (also referred to as BPB) was added to the thus obtained white granular polypropylene in the proportions shown in Table 1, and an antioxidant and a heat stabilizer were added. Agents and lubricants were added and mixed using a Henschel mixer. Next, the resin temperature at the die exit was set to 230 using a Nakatani Machinery VSK40 40mmφ extruder with Bennato.
The mixture was decomposed while controlling the temperature at °C and extruded to obtain a pellet-like polymer. The MI, molecular weight distribution, _w / _o , gloss unevenness, and flexural modulus of the polymer were measured. The results are shown in Table-1.

[Table] * No. 1 is untreated Example 2 Using the same equipment as Example 1, 20 times the molar
AlEt ₂ Cl and 0.02 times the mole of Diglime were added, then 200 ml of liquid propylene and hydrogen gas were introduced, and the temperature was raised to 65° C., followed by the addition of 3.5 g of TiCl ₃ to initiate polymerization. Hydrogen gas was supplied during polymerization, and the hydrogen gas phase concentration was controlled using gas chromatography so that the MI of the resulting polymer was 1.7. After polymerization was carried out for 3 hours, the polymer slurry was discharged into a flash tank from the bottom drain valve of the polymerization tank, and unreacted propylene was purged to stop the polymerization. The subsequent processing was carried out in the same manner as in Example 1,
A white granular crystalline polymer was obtained. of the polymer
The MI was 1.7 and the APP side production rate was 0.8%. Subsequently, the same organic peroxide as in Example 1 was mixed with the polymer as shown in Table 2, and an antioxidant, a heat stabilizer, and a lubricant were further added thereto and mixed in a Henschel mixer. Thereafter, the same procedure as in Example 1 was carried out to obtain pellets. The physical properties of the polymer were measured in the same manner as in Example 1, and the results are shown in Table 2.

[Table] *Nos. 2 and 3 are comparative examples.
Example 3 Using the white granular polypropylene polymerized in Example 1, 2,5-dimethyl-2,5-di-(t-butylperoxy)hexane shown in Table 3 was used instead of the organic peroxide BPB. (also written as MBH),
1,1-di-t-butylperoxy-3,3,5
Pellets were obtained in the same manner as in Example 1, except that -trimethylcyclohexane (also referred to as BMC) and t-butylperoxyisopropyl carbonate (also referred to as BPC) were used, respectively. The physical properties of the polymer were measured in the same manner as in Example 1, and the results are shown in Table 3.

[Table] Comparative Example 1 Pellets were obtained by decomposition treatment in the same manner as in Example 3, except that the white granular polypropylene polymerized in Example 2 was used. The physical properties of the polymer were measured in the same manner as in Example 1, and the results are shown in Table 4.

[Table] Example 4 (A) Synthesis of aluminum ethoxy 20wt of AlEt ₃ was placed in a flask 2 purged with nitrogen.
604ml of heptane solution containing % and 20wt of _AlEt2Cl
610 ml of heptane solution containing %. Next, 302 ml of a heptane solution containing 1.0 wt% ethanol was gradually added dropwise and mixed at room temperature. After dripping, 70
The temperature was raised to 0.degree. C., and the reaction was carried out for 1 hour to synthesize aluminum ethoxy. (B) Polymerization of polypropylene Using the same equipment as in Example 1, 750 ml of the aluminum ethoxy synthesized in (A) was added to the aluminum.
0.15 times the mole of p-ethyl anisate and liquid propylene 200 and hydrogen as a molecular weight regulator were charged, the temperature was raised to 65° C., and 7.0 g of TiCl ₃ was added to initiate polymerization. During polymerization, hydrogen gas was supplied and the hydrogen gas phase concentration was controlled using gas chromatography so that the MI of the produced polymer was 1.7. After polymerization for 3 hours, the polymer slurry was discharged from the bottom drain valve of the polymerization tank into a flash tank.
Polymerization was stopped by purging unreacted propylene.
The subsequent treatments were carried out in the same manner as in Example 1. The obtained polymer had an MI of 1.9 and an APP by-product rate of 1.4%. The thus obtained white granular polypropylene
BPB was added in the proportions shown in Table 5, and then the same procedure as in Example 1 was carried out to obtain pellets. The physical properties of the polymer were measured in the same manner as in Example 1, and the results are shown in Table 5.

[Table] No. 4 shows a comparative example.
Example 5 Polymerization of block copolymer Polymerization was carried out in the same manner as in Example 1, except that the same catalyst system as in Example 1 was used, and the MI of the resulting polymer was set at 2.5 and the polymerization time was set at 2 hours. After the slurry of the produced propylene homopolymer was discharged to a flash tank and unreacted propylene was purged, the polymer was transferred to a slurry tank, and 150 ml of heptane was added to form a slurry. Subsequently, the polymer slurry was transferred to a polymerization tank set at 50°C, and ethylene gas, propylene gas, and hydrogen gas as a molecular weight regulator were supplied. The supply of ethylene gas and propylene gas was controlled by gas chromatography so that the molar ratio of ethylene/propylene in the gas phase region was 1/4, and the supply of hydrogen gas was controlled to be 20 mol% in the gas phase region. I went. After carrying out the polymerization reaction for 2 hours under these conditions, the produced block copolymer was discharged into a flash tank to purge unreacted propylene, and then methanol 40% was injected and stirred at 60°C for 1 hour to remove the catalyst. Disassembled. The mixture was then treated in the same manner as in Example 1 to obtain a white granular crystalline polymer. The MI of the polymer was 1.6 and the ethylene content was 4.2% by weight. The organic peroxide BPB was added to the thus obtained block copolymer in the proportions shown in Table 6, an antioxidant, a heat stabilizer, and a lubricant were added and mixed in a Henschel mixer. Next, the resin temperature at the die exit was measured using a Nakatani Machinery VSK40 vented 40mmφ extruder.
The mixture was decomposed while controlling the temperature to 230°C and extruded to obtain a pellet-like polymer. The physical properties of the polymer were measured and shown in Table 6.

[Table] Comparative Example 2 By one-stage polymerization using the following polymerization method
Polypropylene was produced with an MI of 6.3 and _{a w} / _o ratio of 14.6. A 20 times molar amount of aluminum siloxide _{(Et 2.0 AL}
[OSiH ₂ (CH ₃ )] _0.3 Cl _0.7 ) and 2.5 times Morno P-ethyl anisate (also written as Diglyme) were added, then liquid propylene 2001 and hydrogen gas as a molecular regulator were introduced and the mixture was heated to 65 °C. Polymerization was initiated by raising the temperature and subsequently adding 3.4 g of TiCl ₃ (manufactured by Marubeni Solver). During the polymerization, hydrogen gas was supplied and the polymerization was continued for 3 hours while being controlled by gas chromatography to keep the gas phase concentration constant. After the polymerization is completed, the polymer slurry is discharged from the bottom discharge valve of the polymerization tank into a flash tank, and unreacted propylene is purged to stop the polymerization. Next, heptane 2001 and methanol 401 are injected to form a slurry and heated at 60℃. The catalyst was decomposed by stirring for 1 hour.
Subsequently, 100 liters of water was injected, the detailed medium decomposition product was extracted into the aqueous phase, and the aqueous phase was separated and removed. The heptane slurry of the polymer was separated into solid and liquid using a centrifuge, and the solid was sent to a dryer and dried for 6 hours to obtain a white granular crystalline polymer. On the other hand, a portion of the concentration was collected and APP was recovered after removing heptane. An antioxidant, a heat stabilizer, and a lubricant were added to the thus obtained white granular polypropylene and mixed in a Henschel mixer. Next, Nakatani Machinery VSK40 with vent
A pellet-like polymer was obtained by extrusion using a 40 mmφ extruder while controlling the resin temperature at the exit of the die to 230°C. The MI of the polymer is 6.3, molecular weight distribution
M _w / _o is 14.6, gloss unevenness is O, flexural modulus is,
It was 16000Kg/ ^cm2 .

Claims (1)

[Claims] 1 Polypropylene molding characterized by injection molding using polypropylene whose molecular weight has been reduced by decomposition treatment and whose ratio ( _w / _o ) between weight average molecular weight ( _w ) and number average molecular weight ( _o ) is 6.5 or more. method of manufacturing the product.