DE1940132A1 - Thermoplastic molding compounds made from polyoxymethylenes - Google Patents

Description

FARBWERKE HOECHST AG. formerly Master Lucius & Brüning File number: P - Fw 6175

Date: August 4, 1969
Dr.Eg/br

Thermoplastic molding compounds made from polyoxymethylene ^

It is known that polyoxymethylenes (POM) have a very pronounced tendency to crystallize. Already at If their melt is less supercooled, a rapid growth of spherulites can be observed, which are usually far larger than are the wavelength of light and which give the material considerable opacity. They also arise as a result of the crackling process Numerous microscopic cracks and internal stresses inside and on the surface of the material. " Due to these cracks and internal stresses, the mechanical properties of moldings, e.g. injection molded parts, are made of polyoxymethylene adversely affected. The aforementioned flaws are all the more pronounced, the larger the individual spherulites are. ■

It is also known that adding 0.0001 to 0.5 percent by weight of talc can give high molecular weight polyoxymethylenes and uniformly distributing the inorganic nucleating agent in the organic material having the crystal structure of standardize injection molded parts and so from one coarse spherulite structure * with medium spherulite diameters from 100 microns to homogeneous structures with spherulite diameters of 4 to 8 microns (cf., Deutsche Interpretation document 1,247,645). Since these are injection-molded samples, the sizes given above relate to them on preparations that had been crystallized under pressure at temperatures between 50 and 100 ° C.

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The invention relates to thermoplastic molding compositions made from polyoxymethylenes with reduced specific viscosities of 0.07 to 2.5 dl «g and Kristallitschmelzpunkten between 4Θ * · and 180 ⁰ C, the VXM an inorganic nucleating agent in an amount from 0.0005 to 1.0 weight percent , based on the total mixture, characterized in that the polyoxymethylene spheres formed during isothermal crystallization of the molding compound under a pressure of 1 atm at 150 ^° C. have diameters between 30 and 250 microns, preferably between 50 and 150 microns.

The molding compositions according to the invention are expediently prepared by first mixing polyoxymethylene powder with the commonly used oxidation, heat and light stabilizers and the inorganic nucleating agent on a high-speed mixer (approx. 1000 to 2000 rpm) and then at temperatures between 140 and 240 ⁰ C, preferably from 170 to 220 ⁰ C, are processed into granules in an extruder.

Äiis dem'sö "erhartenen granulate is to determine the spherulite d ß polyoxymethylene: a film produced (see FIG.

__ ^ Q ^ iD ^ crh ^ microscopic examination of this film determine the .mij |,% lere spherulite size of the polyoxymethylene. Is the size of the phärolite, not in the one according to the invention

The range is set to the desired range by varying the quantity and / or the grain size of the nucleating chip and / or by using a different mixing unit. For example, you can enlarge the spherulites the concentration of the inorganic nucleating agent can be reduced or its particle size can be increased, while the concentration of the nucleating agent can be increased accordingly or its particle size can be reduced in order to reduce the size of the spherulites, y X-

The spherulite size of a given polyoxymethylene is largely dependent on the pressure and temperature conditions at Crystallization dependent, as the following table 1 shows:

Table 1 /

Spherulite size of a copolymer of 98 percent by weight trioxane and 2 percent by weight ethylene oxide (RSV value Ό.

Nucleating agent Art

Amount (wt .-%)

Spherulite size (microns) after crystallization at 150 ° C, 1 kt

80 ^W C, 50 at

Talc tai-kum

0.005 0.01

419

125

124 39 27

yT-

Under polyoxymejyiylenes in the sense of d ^ r

Copolymers of formaldehyde, or a cyclic oligo

mers of formaldehyde, preferably

Under__Horaopolymer, isaten are_such polymers of formaldehyde or a cyi & rtseiieji ö ^ ajffe ^ eren of ^ formaldehyde, the OH end groups ^ dj ^^ hschegic change, ~ for example, by esterification or etherification, i / are stabilized against degradation. -i ■ '... / "^

As polyoxymethylenes> in ^ b ^ s_ond; ere copolymers from Trioxane and cyclic ethers act 3 to 5 ring members, preferably Epoxides, and / or cyolischeii AcetalM: with 5 to 11 Ring members, preferably 5 to 8 ring members, and / or linear polyformals, "z, Bc polydioxolane, are used.

10 98087 2

As comonomers for trioxane are mainly compounds of formula

CH ₉ - (CHR) - / 0- (CH ₉ ) 7-0

_{9 9}

used, in which R is a hydrogen atom, an aliphatic Alkyl radical with 1 to 6, preferably 1 to 3 carbon atoms, or a phenyl radical, χ is an integer from 1 to 3, where y is zero jst, y is an integer from 1 to 3, where χ is zero and ζ is 2, and ζ is an integer from 3 to 6, preferably 3 or 4, where χ is zero and y is 1.

Ethylene oxide is particularly suitable as a cyclic ether; Likewise Styrene oxide, propylene oxide and epichlorohydrin are well suited.

Glycol formal (= 1,3-diosiane), butanediol formal (= 1,3-dioxepane) and diglycol formal are particularly suitable as cyclic acetals (= 1,3,6-trioxocane). 4-Chloromethyl-1,3-dioxolane and hexanediolformai (= 1,3-dioxonane) are also very suitable.

The trioxane copolymers are stabilized against thermal degradation through hydrolytic degradation up to primary alcohol end groups.

The molding compositions according to the invention can be used when mixing the Components stabilizers against the influence of heat, oxygen and light are added. As heat stabilizers e.g. polymaids, amides of polybasic carboxylic acids, Amidines, hydrazines, ureas and poly (N-vinyl lactams), as Oxidation stabilizers are phenols, especially bisphenols, and aromatic amines and used as light stabilizers OirHydroxybenzophenon- and BenzotEiazoleivate used, the stabilizers in amounts from 0.1 to in total

109808/2028

10, preferably 0.5 to 5 percent by weight, based on the Total mixture, are used.

The values for the reduced specific viscosity (RSV values) of the polyoxymethylenes used according to the invention (measured on a solution of polyoxyraethylene in butyrolactone with additive of 2 percent by weight diphenylamine at 140 ° C in a concentration of 0.5 g / 100 ml) are between 0.07 and 2.50

-1 1

dl'g, preferably between 0.14 and 1.20 dl-g. ; their crystallite melting points are in the range from 140 to 180.degree. C., preferably from 150 to 170.degree. The density of the polyoxymethylene used according to the invention
(measured according to DIN 53 479).

polyoxymethylene used is 1.40 to 1.45 g * ml ".

Inorganic nucleating agents are compounds understood that do not melt at processing temperatures of the polyoxymethylenes, are not soluble in them and at When the melt cools, crystallization nuclei form. The nucleating agents must neither have a strong acidic nor a strong alkaline effect, otherwise they either lead to a breakdown of the polymer and / or give rise to severe discoloration.

Silicates of magnesium and aluminum are mainly used as nucleating agents, e.g. talc, antigorite, llontmorillo- \ nite and keolinite, furthermore the double carbonate of magnesium and calcium (dolomite) as well as magnesium oxide and sulphide, zinc oxide and sulphide and titanium dioxide. The aforementioned magnesium salts have proven to be particularly good nucleating agents, talc and calcium magnesium carbonate showing the best effect.

Of essential importance for setting an optimal spherulite size of the polyoxymethylene is not only the type of nucleating agent, but also the amount and grain size of the nucleating agent and the type of mixing device used.

109808/2028

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The nucleating agents are used in amounts from 0.0005 to 1.0 Percentage by weight, based on the total mixture, in the polyoxymethylene mixed in. Amounts between 0.005 and 0.5 percent by weight of nucleating agents are preferably used.

The result is with increasing concentration of the nucleating agent an increasing reduction in the spherulite size of the polyoxymethylene (see Table 4). In order to achieve the same spherulite sizes, when using a nucleating agent with smaller grain size a lower concentration of nucleating agent necessary than when using a nucleating agent with larger particles (see Table 5).

The increase in the cost of the nucleating agent in the polyoxymethylene melt and thus its effectiveness depends to a large extent on the type of mixing device used. When using a single-screw extruder with a low kneading effect, under otherwise identical processing conditions, larger spherulites are obtained with the same amount and grain size of a nucleating agent than when using a twin-screw extruder with a very strong mixing effect (see Table 3). ^: = '\' - '' .- ■■

Moldings made from polyoxymethylenes nucleated according to the invention are distinguished from moldings made from non-nucleated polyoxymethylenes through improved ball indentation hardness and torsional rigidity and especially through significantly increased, through one Drop test determined impact strength (see Table 2). When using polyoxymethylenes with spherulite sizes below The impact strength is 30 microns or above 250 microns of the test specimen compared to the non-nucleated test specimen Polyoxymethylene only slightly-improved while in the field From 30 to 250 microns a sudden increase in impact strength can be observed (see Table 4).

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The molding compositions according to the invention can be mechanically, e.g. by chopping or grinding, comminuting to granules, schnitzels, flakes or powder; they can be thermoplastic, e.g. by injection molding or extrusion, to moldings e.g. bars, rods, plates, films, "tapes and tubes, are processed.

example 1

a) A copolymer of 98 percent by weight trioxane and 2 percent by weight Ethylene oxide, which has a density of 1.41 g * ml ~ ", an RSV value of 0.73 dl * g ~ and a crystallite melting point of 166 ° C, 0.5 percent by weight of bis (2-hydroxy-3-tert-butyl-5-methyl-phenyl) methane and 0.1 Percentage by weight of dicyandiamide and mixed with varying amounts of calcium-magnesium-carbonate and in a single-screw extruder Homogenized at 200 C. The residence time in the cylinder is about 4 minutes. The particle size. distribution of the nucleating agent is as follows:

1 micron and smaller: 43 percent

2 Mkron: 38 percent

3 microns: 10 percent

4 microns: 2 percent

5 microns and larger: 7 percent

b) The spherulite size is measured on the products obtained, by melting the polyoxymethylene granulate between two glass plates at 180 ° C and then Crystallize at 150 C under atmospheric pressure a film of about 10 * micron thickness is produced, which is examined microscopically.

1Θ9808 / 2 028

In addition, plates having the dimensions 60 60 χ χ 2 mm at a melt temperature of 200 ⁰ C and a mold temperature of 80 ° C sprayed to be subjected to test the impact strength a · drop test. For this purpose, a plate stretched on a frame is exposed to impact stress by letting a drop hammer weighing 100 g fall from different heights. The level at which 50% of the panels are destroyed is given as a measure of the impact strength.

The ball indentation hardness is measured according to VDE 0302 with a loading time of 10 seconds on injection-molded test specimens.

The torsional stiffness was tested on 2 mm press plates DIN 53 447 measured at a temperature of 120 ° C and a Bellas processing time of 60 seconds.

The mechanical properties of non-nucleated and nucleated polyoxymethylene are from the table below 2 can be seen

Table 2

Nucleation
Kind ' resources ■■
• Lot
(Wt.%) Spherulite size
(Micron) Bullet
pressure
hardness"
(kp'cm) Torsχonsτ
stiffness case
height
(cm 1 - .. _ 493 1400 1290 23 2 0.2 69 1470 1670 130 3 like 2 0.3 49 1490 1650 115

TnCk

* i'tc

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The dependence of the spherulite size of the polyoxymethylene The following table 3 shows the type of mixing device:

Table 3. ,

Nucleating agents ^ acium
onaÜk lot
(Wt.%) Spherulite size when using a Art 2 _> Single screw ex
truders 1 - 0.1 500 microns 2 Magn
C ^? To 0.2 90 microns 3 how <wm / J) oL 69 microns Twin screw
extruders 500 microns 30 microns 25 microns r>, * L / ^ s / t- ^ f \
c $ cti (__ / _f / j .

a) According to Example I, a 98 percent by weight copolymer is obtained Trioxane and 2 percent by weight ethylene oxide, which has a density of 1.41 g * inl ~, an RSV value of 0.68 dl'g "and a crystallite melting point of 164 ° C has, mixed with stabilizers and nucleating agents, but instead of calcium magnesium carbonate now used talc.

Distribution The particle size / nucleating agent is as follows

10 microns and smaller: 53 percent

20 microns: 14 percent

3o microns ί 10 percent

40 microns: 7 percent

. 50 microns and larger: 16 percent,,

109808/2628

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b) The dependence of the spherulite size, measured according to Example Ib), and the impact strength of the polyoxymethylene the following table 4 shows the amount of nucleating agent:

Table 4

Nucleation funds lot Spherulite size Height of fall Art (Wt.%) (Micron) (cm) 1 _ 0.005 490 14th 2 talc 0.01 171 198 3 talc 0.05 129 235 4th talc 0.1 137 232 5 talc 0.3 61 177 6th talc 0.5 22nd 92 7th talc 1.0 19th 84 8th talc 20 " 35

Example 3

a) According to Example 1, a 98 percent by weight copolymer is obtained Trioxane and 2 percent by weight ethylene oxide,

,-1

an HSV value of

that has a density of 1.11 g «ml
0.75 dl * g and a crystallite melting point of 166 C, mixed with stabilizers and nucleating agents, talc of different grain sizes being used as nucleating agents.

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b) The influence of the amount or the grain size of the nucleating agent on the spherulite size of the polyoxymethylene, measured after crystallization at 150 ° C. and 1 atm shown in the following table 5:

Tabel

Nucleating agents Art lot Grain size Spherulite size (Wt.%) (Micron) (Micron) talc 0.05 like example 2a) 1 talc 0.05. below 1 142 2 talc 0.1 like example 2a) 89 3 talc 0.1 below 1 50 4th 30th
I.

109808/202 8

Claims (1)

Claim: Thermoplastic molding compounds made from polyoxymethyl ions with reduced specific viscosities between 0.07 and 2.5 dl'g "and crystallite melting points between i * ö ^ and 180 ° C, containing an inorganic nucleating agent in an "amount of 0.0005 to 1.0 percent by weight, based on the total mixture, characterized in that the. at the Isothermal crystallization of the molding compound under a pressure of 1 atm at 150 ° C formed polyoxymethylene spherulites Be between 30 and 250 microns in diameter. 109808 /? 028