DE4420989B4 - Process for increasing the proportion of β-modification in polypropylene - Google Patents

Abstract

method to increase the proportion of β-modification in polypropylenes, characterized in that the polypropylenes together with dicarboxylic acid salts of metals of the 2nd main group of the periodic table as β-nucleating agents melts and cools, the oxalates of metals of the 2nd main group in quantities of 0.5-60 Parts by weight based on 100 parts by weight of polypropylene in the dicarboxylic acid salts not included.

Description

The The invention relates to a method for increasing the proportion of β-crystal modification in polypropylenes.

• a) einer zweibasischen organischen Säure und
• b) einem Oxid, Hydroxid oder Salz eines Metalles der Gruppe IIA des Periodensystems zum Polypropylen erhalten werden.

Polypropylene usually crystallizes on cooling from the melt in the monoclinic α-modification. The hexagonal β-modification, which is characterized above all by better mechanical properties, in particular by improved impact strength and increased stress cracking resistance, is preferably obtained by adding special β-nucleating agents or β-nucleating agents. The β-modification may, for example, according to EP-B-177 961 by addition of quinacridone pigments, according to DE-OS 36 10 644 by addition of a 2-component mixture

• a) a dibasic organic acid and
• b) an oxide, hydroxide or salt of a metal of group IIA of the periodic table to the polypropylene are obtained.

Next the most important thing is the improved mechanical properties Characteristic of β-nucleated Polypropylenes that the β-modification already melts in the temperature range of 148 ° C to 152 ° C, while the α-modification first over 160 ° C melts.

However, the addition of the known β-nucleating agents has the particular disadvantage that, for example, in the case of quinacridone pigments, even at very low amounts of less than 10 ppm, a pink discoloration of the polypropylene occurs, which is unsuitable for many applications. The β-nucleating mixture according to DE-OS 36 10 644 especially has the disadvantage that a considerable part of the polypropylene can be present in the α-modification. Further disadvantages of the nucleating mixture according to DE-OS 36 10 64.4 result from the fact that the acids used in the existing modern extrusion plants conditions, with temperatures of up to 270 ° C and above are present, and in addition to the removal of low molecular weight impurities under vacuum, already evaporate. Furthermore, these nucleating agents also show a certain discoloration of the polypropylene, which is rendered noticeable in particular by an excessively high yellowness index.

The The object of the invention was therefore primarily β-nucleating agents for polypropylenes too find where the above mentioned Disadvantages do not occur and with the help of polypropylene with high β-crystal content to be obtained. These problems could be solved by adding certain Dicarboxylic acid salts too dissolved the polypropylenes become.

object Accordingly, the invention is a method for increasing the proportion of β-modification in polypropylenes, characterized in that the Polypropylene together with dicarboxylic acid salts of metals 2nd main group of the periodic table as a β-nucleating agent and optionally with other usual ones additives melts and then cools.

One Another object of the invention is the use of dicarboxylic acid salts of metals of the 2nd main group of the periodic table as R nucleating agent in polypropylenes, as well as polypropylenes, the dicarboxylic acid salts of metals of the 2nd main group of the periodic table as β-nucleating agents contain.

There are several possibilities for determining the proportion of β-modification. On the one hand, the proportion of β-modification from the DSC analysis can be calculated from the ratio of the melting peaks from the second heating according to the formula: (β-area) :( α-area + β-area) be determined. A further possibility is the determination of the β content by the k value from the X-ray wide-angle diagram using the Turner-Jones equation (A. Turner-Jones et al., Makromol. Chem 75 (1964) 134): k = Hβ 1 / [Hβ 1 + (Hα 1 + Hα 2 + Hα 3 )]

Hα ₁ , Hα ₂ and Hα ₃ mean the height of the three strong α-peaks and Hβ ₁ the height of the strong β-peak. The k value is zero in the absence of the β form and has the value 1 if only the β modification is present. However, the values obtained by the two methods of determination are not necessarily the same. Since the β-modification is thermodynamically unstable and from about 150 ° C in the energetically favorable α-Mo changed in the DSC analysis at a heating rate of, for example, 10 ° C / min from 150 ° C, a certain proportion of the β-modification in the α-modification (time to heat from 150 ° C to the melting point of α -PP), which in effect indicates that the DSC analysis always shows a lower β-content in the PP than actually exists.

At the β-nucleating agent according to the invention it is a one-component system, which thermally up to about 400 ° C. is stable. With the present β-nucleating agent can without the addition of further additives, a proportion of β-modification from to about 80% (according to DSC method) or with a k-value according to Turner-Jones of at least 0.94 to 0.97 can be achieved. Similarly high levels of β-modification are also achieved if the polypropylene like other additives z. As antioxidants, UV stabilizers, light stabilizers, lubricants, Anti-blocking agents, antistatic agents, colorants, chem. Degradiermittel and / or fillers contains.

According to the invention as a β-nucleating agent or β-nucleating agent It is also possible to use mixtures of different dicarboxylic acid salts. The inventively used dicarboxylic contain preferably at least 7 C-atoms, particularly preferred are salts the pimelic acid or suberic acid, for example, Ca-pimelate or Ca-suberate.

The Concentration of the β-nucleating agent in polypropylene is above all the desired content of β-crystallites dependent and is preferably 0.001 to 2, more preferably 0.01 to 1 wt.% Related on the polypropylene.

Among polypropylenes are both homopolymers of propylene and copolymers with other olefinic comonomers, such as. As ethylene, butene, pentene, 1-methylpentene, hexene, octene to understand. The content of comonomers in the propylene copolymers is usually about 2 to 50 mol%. Both statistical and block copolymers can be used. Before given to polypropylenes with a predominantly stereoregular arrangement in the polymer chain, such. B. isotactic or elastomeric polypropylenes used, as they are available, for example, as Daplen ^® in Fa. PCD polymers, or in DE-A-43 21 498 are described. The proportion of stereoregular polypropylenes in the polypropylenes used is preferably more than 80% by weight.

The β-nucleated according to the invention Polypropylene can according to usual Manufacturing methods, such. B. by extrusion or injection molding, to finished parts be further processed with good mechanical properties.

Comparative Example C1

One Polypropylene homopolymer powder (PP-B) with a melt index (MFI at 230 ° C / 2.16 kg according to ISO 1133 / DIN 53735) of 0.3 g / 10 min (corresponding to Daplen BE 50 from Fa. PCD polymers) was with 0.2 wt.% Ca stearate (Faci) as a catalyst deactivator and inner lubricant, 0.1% by weight Irgafos PEPQ (Ciba-Geigy) and 0.2% by weight of Irganox 1010 (Ciba-Geigy) as stabilizer or antioxidant and 0.3% by weight of distearyl thiodipropionate (DSTDP, Ciba-Geigy) as heat stabilizer mixed in an intensive mixer and on a single-screw extruder at a melt temperature of 230 ° C kneaded and granulated. The granules became 2.5 at 220 ° C mm thick plates pressed. The Turner-Jones k-value measured on these plates was 0.01, corresponding to 1% of β-polypropylene crystallites.

Examples 2-5

Analogous for Comparative Example C1 plates were made of polypropylene, however, adding the β-nucleating agents and additives listed in Table 1 were. The K values measured on the plates are at least 0.94, corresponding to a content of at least 94% β-polypropylene crystallites. The K values and the values for the percentage of β crystals measured by the DSC method are also listed in Table 1.

The Ca salts of the dicarboxylic acids (pimelic and suberic acids) used as β-nucleating agents were prepared by reaction of one mole of dicarboxylic acid with one mole of CaCO ₃ in aqueous ethanolic solution at 60 to 80 ° C. The precipitated as a fine precipitate salt was filtered off and dried to constant weight.

Table 1

Examples 6 to 15

The listed in Table 2 Polypropylene powder (PP) were each added with 0.05 wt% magnesium aluminum hydroxycarbonate (MAHC, Kyowa) as a catalyst deactivator, 0.05% by weight of Ca stearate, 0.05% by weight Irgafos 168, 0.05% by weight Irganox 1010, as well as in the examples 7, 9, 11, 13 and 15 in addition with 0.1% by weight of Ca-pimelate as β-nucleating agent mixed in an intensive mixer and on a twin-screw extruder at a melt temperature of 230 ° C extruded and granulated. On the granules, the proportion of β-modification determined by the DSC method. The values are summarized in Table 2.

Table 2:

Used PP powder:

• PP-B:

  Propylene homopolymer with a melt index (230 / 2.16) of 0.3 g / 10 min

  PP-D:

  Propylene homopolymer with a melt index (230 / 2.16) of 2.0 g / 10 min

  PP-K:

  Propylene homopolymer with a melt index (230 / 2.16) of 7.0 g / 10 min

  PP CHC:

  propylene / ethylene (C ₃ / C ₂ ) random copolymer having a C ₂ content of 8 mol% and a melt index of 1.2 g / 10 min

  PP-DSC:

  heterophasic C ₃ / C ₂ copolymer with a C ₂ content of 20 mol% and a melt index of 3.2 g / 10 min

The used PP types correspond to commercially available PP types from the company PCD Polymers. The melt index was at 230 ° C / 2.16 kg according to ISO 1133 / DIN Measured 53735.

Comparative Example V16

A polypropylene powder having a melt index of 7 g / 10 min (PP-K) was mixed with 0.05% by weight Irgafos 168, 0.05% by weight Irganox 1010 and according to DE-OS 36 10 644 with 0.1 wt.% Ca. Stearate and 0.1 wt.% Pimelic acid as a β-nucleating agent mixed in an intensive mixer and extruded on a single-screw extruder at a melt temperature of 230 ° C and granulated. The granules were injection molded into plates of 3 mm thickness and the yellowness index (YI) was measured to be 4.9 according to ASTM D 1925. The yellowness index is a measure of the yellowness of the polymer.

Of the Proportion of β-PP crystals was included according to DSC 69%

Examples 17 and 18

Analogous for Comparative Example V16, PP plates were produced from PP-K, but instead of Ca-stearate and pimelic acid as β-nucleating agent 0.1% by weight according to the invention Ca-pimelate were added. In Example 17, an additional 0.1 % By weight of Ca stearate added. Yellowness Inex was β-nucleated according to the invention Polypropylenes at -2.6 (Example 17) and -2.2 (Example 18), ie significantly better than Comparative Example V16.

Of the Proportion of β-PP crystallites was included according to DSC 84.4% (Example 17) and 74.4% (Example 18).

Claims (11)

Process for increasing the proportion of β-modification in polypropylenes, characterized in that the polypropylenes are melted together with dicarboxylic acid salts of metals of the 2nd main group of the Periodic Table as β-nucleating agent and cooled, the oxalates of metals of the 2nd main group in quantities of 0.5-60 parts by weight, based on 100 parts by weight of polypropylene, of the dicarboxylic acid salts are not included. Method according to claim 1, characterized in that the polypropylenes in common with dicarboxylic acid salts of metals of the 2nd main group of the periodic table as β-nucleating agents and with other usual ones Zusäzen melts and cools, the oxalates of metals of the 2nd main group in quantities of 0.5-60 Parts by weight based on 100 parts by weight of polypropylene in the dicarboxylic acid salts not included. Method according to claim 1, characterized in that the dicarboxylic acid at least seven carbon atoms contains. Method according to claim 1, characterized in that the dicarboxylic acid pimelic acid or suberic is. Method according to one the claims 1-3, by in that the dicarboxylic acid salt is Ca-pimelate or Ca-suberate is. Method according to one the claims 1-4, by characterized in that the β-nucleating agent in a concentration from 0.001 to 2% by weight, based on the polypropylene. Method according to one the claims 1-5, by characterized in that the polypropylenes used a predominantly stereoregular Own construction. Use of dicarboxylic acid salts of metals of 2nd main group of the periodic table except the oxalates of metals the 2nd main group in an amount of 0.5-60 parts by weight based on 100 parts by weight of polypropylene as β-nucleating agent in polypropylenes Polypropylenes, the dicarboxylic acid salts of metals of the 2. Main group of the periodic table except the oxalates of metals the 2nd main group in an amount of 0.5-60 parts by weight based on 100 parts by weight of polypropylene as β-nucleating agent included. Polypropylene according to Claim 9, characterized that the k-value according to Turner-Jones at least 0.94. Use of the polypropylenes according to one of claims 9 or 10 for the production of finished articles by conventional processing methods.