Crystalline propylene polymer composition

Abstract: A crystalline propylene polymer composition comprising 100 parts by weight of a crystalline propylene polymer, 0.01 to 1 part weight of an aromatic peroxide and 0.001 to 1 part by weight of a hydrotalcite compound of formula (1), (Mg y Zn z ) 1-x Al x (OH) 2 (A) n-x/2 ·mH 2 O (1) wherein (A) n- is an anion having a valence of n and x, y and z are numbers satisfying y+z=1, 0≤y≤0.9, 0.1≤z≤1 and 0.2≤x≤0.8, and m is 0 or a positive number; showing improved resistance to the development of colour (pinking) and resistance to rusting.

Description: The present invention relates to a crystalline propylene polymer composition having improved resin flowability and processability. More specifically, it relates to a crystalline propylene polymer composition which is improved in melt flow property and is greatly improved in the prevention of color development (pinking), anti-rust property and heat stability. In recent years, there have been remarkable advances in the technology of activating to a high degree a highly active Ziegler catalyst formed of a solid catalyst containing magnesium and titanium and an organic aluminum compound. As a result, when a propylene polymer is prepared in the presence of the above catalyst, the step of removing the catalyst from the produced propylene polymer can be omitted. For this reason, a propylene polymer contains several ppm to hundreds ppm of a residual halogen. When the propylene polymer is molded under heat, an acidic component such as hydrogen halide is generated, which causes a problem that it greatly corrodes a molding machine and a mold, or deteriorates the resin. For overcoming the above problem, there is utilized a hydrotalcite disclosed in JP-A-55-80447. On the other hand, a propylene polymer is inexpensive and excellent in mechanical properties, and it can therefore be used for producing a variety of products such as a film, a sheet, a fiber, an injection-molded article, a molded article having a hollow portion inside, and the like. The above hydrotalcite has the following formula (2). Mg 1-x Al x (OH) 2 CO 3 2- x/2 ·mH 2 O However, the above hydrotalcite has the following problem. That is, when it is incorporated into a resin composition containing an aromatic peroxide as a molecular weight adjuster or a melt flow improver and when the resin composition is spun into a fiber (yarn) or injection-molded to produce an article having a complicated form, the spun fiber (yarn) or the molded article develops the color of pink or reddish brown. A resin composition containing a crystalline propylene polymer obtained by the method using a Ziegler catalyst but excluding the step of removing the catalyst and an aromatic peroxide for improving the crystalline propylene polymer in processability is poor in the heat stability and anti-rust property due the presence of a halogen derived from the catalyst. Even if the hydrotalcite of the above formula (2) is incorporated, the resin composition causes pinking at a molding/processing time. It is effective for preventing the pinking to incorporate a phenol-containing, sulfur-containing or phosphorus-containing antioxidant and a metal fatty acid salt. However, these components degrade the anti-rust property and heat stability of the resin composition, and the resin composition may sometimes cause a problem of "bleed-out". It is an object of the present invention to provide a crystalline propylene polymer composition improved in resin flowability and processability (moldability). It is another object of the present invention to provide a crystalline propylene polymer composition which has increased melt flow properties and is remarkably improved in the prevention of color development (pinking), anti-rust property and heat stability. It is further another object of the present invention to provide a resin composition which contains a crystalline propylene polymer and an aromatic peroxide and is improved in the pinking resistance, heat stability and anti-rust property of the crystalline propylene polymer. According to the present invention, there is provided a crystalline propylene polymer composition comprising 100 parts by weight of a crystalline propylene polymer, 0.01 to 1 part by weight of an aromatic peroxide and 0.001 to 1 part by weight of a hydrotalcite compound of formula (1), (Mg y Zn z ) 1-x Al x (OH) 2 (A) n- x/2 ·mH 2 O wherein (A) n- is an anion having a valence of n and x, y and z are numbers satisfying y+z=1 , 0≤y≤0.9, 0.1≤z≤1 and 0.2≤x≤0.8, and m is 0 or a positive number. Also provided is a molded article which comprises a crystalline polypropylene polymer composition of the invention. The present inventors have diligently studied to overcome the above problems and have found the following. When a specific hydrotalcite is incorporated into a propylene polymer composition, the propylene polymer composition is satisfactory in all of anti-rust property, heat stability and pinking resistance. Typically, the polymer used in the present invention is produced in the presence of a Ziegler catalyst. The polymer used in the present invention is typically produced without removal of the catalyst and comprises trace amounts of halogen, for example from several ppm to hundreds ppm of a halogen. Examples of the propylene polymer include a propylene homopolymer, a copolymer produced from propylene and another α-olefin and a copolymer produced from propylene and vinyl acetate, or the like. The other α-olefin includes ethylene, 1-butene, 1-pentene and 4-methylpentene-1. More specifically, the propylene polymer is typically a propylene homopolymer or a propylene copolymer such as a propylene-ethylene block or random copolymer and a propylene-ethylene-1-butene copolymer. Examples of the aromatic peroxide include hydroperoxide, dialkyl peroxide, diacyl peroxide, peroxyester, peroxydicarbonate, ketone peroxide and peroxyketal. Typically, the aromatic peroxide used in the present invention contains a benzene ring. The aromatic peroxide used in the present invention can be cumene hydroperoxide, diisopropylbenzene hydroperoxide, tert-butylcumyl peroxide, dicumyl peroxide, α,α'-bis(tert-butylperoxy-m-isopropyl)benzene, benzoyl peroxide, 2,4-dichlorobenzoyl peroxide, m-toluoyl peroxide, cumyl peroxyneodecanoate, tert-butyl peroxybenzoate, di-tert-butyldiperoxyisophthalate, 2,5-dimethyl-2,5-di(benzoylperoxy)hexane, cumyloxyperoctoate or cumyl peroxyneohexanoate. In the present invention it is particularly preferred to use those aromatic peroxides which have a 1 minute's half value period temperature of at least 70°C, since the resin composition can be homogeneously kneaded and the molecular chain of the resin is properly cut. Typically, in the above formula (1), (A) n- is at least one of CO 3 2- , HPO 4 2- , OH - , ClO 4 - , NO 3 - , acetate ion and tartarate ion. The hydrotalcite compound of the formula (1) can be produced by the method disclosed in JP-B-46-2280, JP-B-47-32198 and JP-B-51-29129. The hydrotalcite compound of the formula (1) particularly preferably has a BET specific surface area of 30 m 2 /g or less and an average secondary particle diameter of 5 µm or less. When the crystalline propylene polymer has a high processing temperature, the hydrotalcite compound of the formula (1) may be calcined at 150 to 350°C before use, for preventing any foaming of the resin due to the generation of gas. The hydrotalcite compound of the formula (1) or the calcined product thereof may be surface-treated with at least one of a higher fatty acid such as stearic acid, a higher fatty acid metal salts such as an alkali metal salt of oleic acid, a coupling agent such as a silane-containing, aluminum-containing or titanate-containing coupling agent, a higher fatty acid amide, a higher fatty acid ester and wax. The composition of the present invention may contain, as required, any one of a phenol-containing antioxidant, an organic phosphoric acid antioxidant such as organic phosphite, a thioether-containing antioxidant, an ultraviolet light absorbent, hindered-amine-containing and nickel-containing light stabilizers, an antistatic agent, a lubricant such as calcium stearate, a nucleating agent and a colorant, which are all used with general polyolefins. The present invention will be explained more in detail with reference to Examples hereinafter. In Examples, "part" stands for "part by weight". Examples 1 - 6 The following components were mixed with a Henschel mixer at 1,200 rpm for 5 minutes, and then the mixture (composition) was melt-kneaded at 230°C at 50 rpm and extruded to obtain pellets. The pellets were used for conducting the following tests. Table 1 shows the results. Components: Polypropylene-ethylene copolymer (Cl content = 30 ppm) 100 parts Dicumyl peroxide (DCP) Amount changed Hydrotalcite compound (HT) Amount changed Irganox 1010 0.05 part Ultranox 626 0.05 part 〈Anti-rust property〉 A well-polished and deoiled soft steel plate having a size of 40 x 40 mm was buried in a sample of the above pellets and heated at 230°C for 1 hour. Then, the soft steel plate and the sample were allowed to cool, the steel plate was taken out of the sample, and a resin on the steel plate surface was removed. The steel plate was placed in a desciccator adjusted to a relative humidity of 93 %, and allowed to stand at 60°C for 1 week. Then, the soft steel plate was visually evaluated for a degree of the occurrence of rust as follows. 1: No rust occurred. 2. Thin rust occurred partly. 3. Thin rust occurred wholly. 4. Thick rust occurred partly. 5. Thick rust occurred wholly. 〈Heat stability〉 A sample of the above pellets was allowed to stand in an oven at 140°C for 1 week while being mixed once a day. The deterioration of the resin was evaluated on the basis of melt flow rates (MFR) as follows. The sample was measured for melt flow rates before and after the sample was allowed to stand for the deterioration as described above, and the heat stability was expressed in terms of (MFR after the deterioration)/(MFR before the deterioration). 〈Prevention of color development〉 A sample of the above pellets was press-molded at 230°C for 5 minutes to obtain a 2 mm thick plate, and the plate was measured for an "a value" with a color difference meter supplied by Tokyo Denshoku K.K. The a value shows a color change from green to red, and the greater the value is, the closer to red the color is. Example HT DCP Amount a value Anti-rust property MFR MFR ratio kind, Amount 1 1 0.1 0.2 0.0 1 27.3 1.06 2 2 0.1 0.1 0.2 1 25.0 1.05 3 3 0.1 0.1 0.1 1 26.5 1.04 4 2 0.01 0.1 0.1 2 6.8 1.05 5 2 1.0 0.2 0.3 1 22.5 1.05 6 2 0.1 0.3 0.3 1 46.0 1.08 7 2 0.005 0.2 0.4 2 30.4 1.08 Ca-St 0.1 Notes to Table 1: Amounts (part by weight) of HT and DCP: per 100 parts by weight of polypropylene/ethylene copolymer. Kinds of HT: 1 = Zn 0.67 Al 0.33 (OH) 2 (CO) 0.165 ·0.51H 2 O 2 = (Mg 0.75 Zn 0.25 ) 0.67 Al 0.33 (OH) 2 (CO 3 ) 0.165 ·0.51H 2 O 3 = (Mg 0.50 Zn 0.50 ) 0.75 Al 0.25 (OH) 2 (CO 3 ) 0.125 ·0.63H 2 O Ca-St: Calcium stearate (lubricant) Comparative Examples 1 - 4 Pellets were prepared in the same manner as in Example 1 except that no hydrotalcite compound was used, that neither hydrotalcite compound nor DCP was used or that the hydrotalcite compound was replaced with calcium stearate (Ca-St) or a hydrotalcite compound (Mg 4.5 Al 2 (OH) 13 CO 3 ·3.5H 2 O) which came under the hydrotalcite compound of the formula (2), and the so-obtained pellets were evaluated in the same manner as in Example 1. Table 2 shows the results. CEx. HT or Ca-St DCP Amount a value Anti-rust property MFR MFR ratio Kind, Amount 1 - 0 0 0.4 1 4.9 1.22 2 - 0 0.1 0.3 5 28.6 1.33 3 Ca-St 0.1 0.2 0.4 3 33.5 1.12 4 4 0.1 0.2 2.5 1 28.3 1.06 Notes to Table 2: CEx. = Comparative Example HT used in CEx. 4 = Mg 4.5 Al 2 (OH) 13 CO 3 ·3.5H 2 O Example 7 and Comparative Example 5 0.05 Part of a phenol-containing antioxidant [octadecyl-3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], 0.05 part of a phosphite-containing antioxidant [tris(2,4-di-tert-butylphenyl)phosphite], 0.15 part of tert-butyl peroxybenzoate (BPB) and either 0.1 part of the same hydrotalcite compound as that used in Example 2 or 0.1 part of the same hydrotalcite compound as that used in Comparative Example 4 were mixed with 100 parts of a polypropylene homopolymer with a Henschel mixer, and then the mixture (composition) was melt-kneaded at 260°C at 30 rpm and extruded to obtain pellets. The pellets were press-molded at 230°C for 5 minutes to obtain a 2 mm thick plate, and the plate was measured for an "a value" in the same manner as in Example 1. Table 3 shows the results. HT BPB Amount a value kind, Amount Example 7 2 0.1 0.15 0.5 Comparative Examaple 5 4 0.1 0.15 3.2 According to the present invention, there is provided a crystalline propylene polymer composition which hardly corrodes a metal of a mold, etc., is free from developing a pinkish color, and gives a molded article having excellent heat stability.

Claims: A crystalline propylene polymer composition comprising 100 parts by weight of a crystalline propylene polymer, 0.01 to 1 part by weight of an aromatic peroxide and 0.001 to 1 part by weight of a hydrotalcite compound of formula (1), (Mg y Zn z ) 1-x Al x (OH) 2 (A) n- x/2 ·mH 2 O wherein (A) n- is an anion having a valence of n and x, y and z are numbers satisfying y+z=1 , 0≤y≤0.9, 0.1≤z≤1 and 0.2≤x≤0.8, and m is 0 or a positive number. A composition according to claim 1, wherein the polymer is produced in the presence of a Ziegler catalyst. A composition according to claim 2, wherein the polymer is produced without removal of the catalyst and comprises trace amounts of halogen. A composition according to any one of the preceding claims, wherein the polymer is a propylene homopolymer or a propylene copolymer. A composition according to any one of the preceding claims, wherein the aromatic peroxide contains a benzene ring. A composition according to any one of the preceding claims, wherein (A) n- is at least one of CO 3 2- , HPO 4 2- , OH - , ClO 4 - , NO 3 - , acetate ion and tartrate ion. A composition according to any one of the preceding claims, wherein the compound of formula (1) has a BET specific surface area of 30m 2 /g or less and an average secondary particle diameter of 5 µm or less. A composition according to any one of the preceding claims, wherein the compound of formula (1) is surface-treated with at least one of a higher fatty acid, a higher fatty acid metal salt, a coupling agent, a higher fatty acid amide, a higher fatty acid ester or wax. A composition according to any one of the preceding claims, wherein the compound of formula (1) is calcined at 150 to 350°C. A molded article which comprises a crystalline propylene polymer composition according to any one of the preceding claims.

Inventors: NOSU TSUTOMU, SAWA YOSHIHARU, NOSU, TSUTOMU, SAWA, YOSHIHARU
Applicants: KYOWA CHEM IND CO LTD, KYOWA CHEMICAL INDUSTRY CO., LTD.
Application year: 1996
Main classification: C08K13
IPC codes: C08K5, C08L23, C08K3