RU2398791C1 - Method of preparing polystyrene granulate capable of foaming - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: invention describes a method of producing a polystyrene granulate capable of foaming, involving a step for feeding a foaming agent into a mixing zone, mixing the foaming agent with molten polystyrene, homogenisation of the obtained mixture, cooling it to extrusion temperature, extrusion and granulation under conditions which prevent foaming. The method is characterised by that molar ratio of the foaming agent being fed to the specific carrying capacity of the apparatus in the mixing zone (Ks), which is the ratio of the amount of the passing stream of molten material, including polystyrene in kg/h to stirring rate in rpm, is kept in the range between 0.08 and 0.23, while maintaining temperature difference between the input and output at the homogenisation and cooling step in the range between 30 and 70°C.

EFFECT: obtaining polystyrene granulate through a continuous method with a narrow grain-size composition, which enables to obtain foamed articles with range of apparent density values 10-40 kg/m³ which have satisfactory application properties.

3 cl, 1 tbl, 9 ex

Description

The claimed invention relates to the chemistry of polymers, in particular to the production of expandable (expandable) polystyrene, and in particular to the production of polystyrene granulate containing a blowing agent (VA).

Foaming polystyrene (PSV) is widely used in civil and industrial engineering for the manufacture of polystyrene foam boards intended for thermal insulation, for the manufacture of shock-absorbing packaging for appliances, machine tools and large-sized household appliances, pipe insulation, etc. In all applications, PSV is required to ensure the optimal combination of physical and mechanical properties in foam products: the apparent density of the product, its strength characteristics and thermal conductivity. When using polystyrene foam boards as one of the layers of building envelopes, fire resistance is required.

Polystyrene foam products from PSV are obtained by a well-developed technology, which usually includes three stages: preliminary foaming of the PSV beads (granules) with water vapor at a temperature of 100-140 ° C, maturing of pre-foamed particles for 6-24 hours at room temperature and atmospheric pressure and final molding steam in a mold filled with pre-foamed and matured polymer particles.

The most common industrial method for producing PSV granules is the suspension method, according to which styrene is polymerized in an aqueous suspension with saturation of the formed VA beads during or after polymerization [see, for example, RU No. 2087486, M.cl. ⁶ C08F 112/08, 1997; US No. 5616413, M.C. ⁶ B22B 5/16, 1997; RU No. 2151153, M.cl. ⁶ C08J 9/224, 1998; RU No. 2243244, M.cl. ⁷ C08L 25/04, 2004, etc.]. The suspension method allows to obtain a polymer with a relatively low molecular weight (MM) - not higher than 200,000; foam suspension of any form with an apparent density of 35 kg / m ³ and lower, including very lightweight, with an apparent density of 10-15 kg / m ³ , which are used for thermal insulation, can be made from suspension PSV.

The disadvantages of the suspension method include high costs for the creation and operation of production, in addition, this method gives a large amount of wastewater to be treated. PSV beads obtained by the suspension method have a particle size distribution with a wide distribution of bead size, while PSV particles of a certain size (diameter) with a narrow particle size distribution are required to obtain high-quality foam products. The latter circumstance requires an additional operation of sieving and disposal of fractions unsuitable for foaming. The disposal of PSV beads is difficult due to the presence of VA in it.

In order to exclude the screening operation and the need to dispose of unsuitable fractions, polystyrene (PS) granules were obtained, for example, by extrusion, and then suspended in water in the presence of a stabilizer suspension and impregnated with a VA mixture of n-pentane with isopentane under pressure at a temperature of 90 ° C for 10 hours [EP No. 0834529, M.cl. ⁶ C08J 9/20, 1998]. Thus, wastewater again appears in the process and needs to be disposed of.

Subsequently, a technology was developed for the production of PSV granules, according to which VA is mixed with polystyrene in a melt, strands of polymer containing VA are extruded under conditions that prevent premature foaming, and granulated.

A known method of producing granules capable of foaming PS, according to which the polymer melt and VA are fed into the mixing zone, mix VA with polymer with intensive shear mixing in the first static mixer, maintain the mixture with intensive shear mixing in the second static mixer, cool the mixture with stirring in the third static mixer to an intermediate temperature, then the mixture is cooled to a granulation temperature, the polymer melt is extruded through a die with rapid cooling and granules comfort pressurized [RU №2295439, M.kl. ⁷ B29B 9/06, 2007]. In each static mixer, the temperature is maintained in a certain range, depending on the ratio of the values of the VA stream and the maximum possible VA stream, and the weighted polymer melt and VA melt flows are maintained in a certain ratio throughout the cascade. Thereby, it is possible to process a wide range of polystyrene in PSV and to obtain PSV, which provides PPP with an apparent density of 12 to 55 kg / m ³ .

The disadvantage of the method according to RU No. 2295439 is that the resulting finished product - PSV has a wide particle size distribution: particle size of 0.9-1.4 mm (examples 4, 5, 7); 1.4-2.0 mm (examples 3, 6); in addition, the patent does not provide indicators of the physico-mechanical properties of expanded polystyrene, the raw material for the production of which is expandable polystyrene according to the specified patent.

Experience shows that the size of the obtained PSV granules is influenced by many factors, namely the design of the granulator, the rheology of the initial polystyrene and the granulation conditions.

Such parameters of processing into foam products as pre-foaming, filling with pre-expanded beads of the mold and its sintering during molding, depend on the size and size distribution of the PSV granules, that is, parameters on which the physicomechanical parameters of expanded polystyrene depend.

The closest set of essential features to the claimed method is a method of producing a foamable PS, including the polymerization of styrene to obtain a PS with a weight average molecular weight (Mw)

more than 170,000, degassing the obtained polymer melt, introducing (feeding) VA into the polystyrene melt in the mixing zone in a static or dynamic mixer, mixing VA with the melt at a temperature of at least 150 ° C, cooling the mixture to a temperature of at least 120 ° C, unloading through a nozzle grill with holes whose diameter at the exit does not exceed 1.5 mm and granulation of the outgoing strands [US application No. 2005/0156344, M.cl. ⁷ B29C 44/00, 2005]. It is indicated (examples and claims 6-8, 10-15, 19-20 of the claims) that the size of the PSV granules can be controlled by the addition of plasticizers, changing the melt temperature, the geometric parameters of the granulating device, as well as the addition of 0.05-1.5% mass, water, performing the function of a nucleator, moreover, water is introduced and homogenized into the melt PS before the introduction of VA.

In the method according to US No. 2005/0156344 using a granulating head with holes with a diameter of not more than 1.5 mm (claim 1 and claim 16 of the formula), preferably 0.2-1.2 mm (claim 9 of the formula) and get granules with a diameter 0.4-1.8 mm (p. 22 of the formula). Granulation is performed at a melt temperature of polystyrene mixed with VA, 160-200 ° C (examples 1 and 2) and a temperature of the granulation head 180-240 ° C (example 2). With increasing temperature of the melt and the head, with the addition of water or plasticizers, with a change in the geometry of the holes in the granulating head, it is possible to reduce the diameter of the beads with the same diameter of the holes. It is indicated that the PSV granules obtained according to US No. 2005/0156344 give, when foaming, “foamed particles with a fine-mesh foam structure that was detected under the microscope” (examples 7 and 8, adding water) or “foamed particles with a homogeneous foam structure” (examples 9 and 10). However, neither the physicomechanical parameters of polystyrene foam, which was obtained from the PSV granules, nor its apparent density are given.

The disadvantage of the method according to US No. 2005/0156344 can be considered insufficiently narrow particle size distribution of the obtained finished product, for example, in example 11 it is indicated that only 80% of PSV particles have a size of from 0.62 to 0.8 mm.

The technical result achieved in the claimed invention is to obtain a continuous granular method of polystyrene with a narrow particle size distribution, as close as possible to a spherical shape and containing a foaming agent, which provides foam products with a wide range of apparent densities from 10 to 40 kg / m ³ having satisfactory consumer properties.

The specified technical result is achieved in that in a method for producing a foamable polystyrene granulate, which includes the steps of mixing polystyrene with a nucleator and other processing aids, mixing a blowing agent with a polystyrene melt, homogenizing the resulting mixture, cooling it to an extrusion temperature, granulation under conditions that prevent foaming, support ratio of the amount of blowing agent supplied (in moles) to the specific throughput of the equipment in the mixing zone (Кс) in the range of 0.08-0.23 while maintaining the temperature difference at the inlet and outlet of the stage of homogenization and cooling of the mixture within 30-70 ° C. In this case, to obtain PSV, polystyrene is used with a ratio of medium viscosity molecular weight (Mv) to polydispersity coefficient (i.e., ratio of medium viscosity molecular weight (Mw) to number average molecular weight (Mn)) in the range of (70-115) × 10 ³ .

By the specific throughput of the equipment in the mixing zone, we mean the ratio of the amount of material flowing to the mixing speed (screw speed per minute).

At the melting stage, the polystyrene mixture is maintained at a temperature of 180-250 ° C; and at the stage of homogenization - cooling, the temperature of the mixture of polystyrene with a blowing agent is maintained at the inlet of 180-210 ° C and at the outlet of 140-180 ° C.

As polystyrene in the present method can be used homopolystyrene grades STIROVIT ^® (TU 2214-001-11175949-2003) or other grades of PS (for example, according to GOST 20282-86), the molecular weight of which is in a given range of values of the ratio Mv to Mw / Mn. To produce PSV, a polystyrene melt with similar molecular characteristics can also be used, obtained as a result of continuous polymerization in a mass of styrene and which has passed the stage of removal of unreacted monomer.

As a blowing agent, substances selected from the group consisting of saturated C ₄ -C ₈ hydrocarbons, such as butane, isobutane, pentane, isopentane, hexane, isohexane and octane, preferably pentane or isopentane, or mixtures thereof, were used.

The processed mixture contained a nucleator, which was used as fine powders of talc, calcium carbonate, kaolin, a mixture of citric acid and sodium bicarbonate, as well as azodicarbonamide, azodiisobutyronitrile, etc. The nucleator in an amount of 0.05-5.0% wt. mixed with polystyrene or already with the prepared melt of polystyrene.

The processed mixture may contain substances that prevent burning (flame retardants). Hexabromocyclododecane in an amount of 1-5% wt., Preferably 1.5-2.0% wt., Was usually used as a flame retardant. with a synergistic supplement. As a synergistic additive, magnesium-aluminum hydrotalcite, metal hydroxides, phosphorus compounds, inorganic and organic phosphates, phosphites or phosphonates, or mixtures thereof can be used.

As a technological additive, weakening the transmission of infrared radiation through a polystyrene foam plate, as a result of which improved heat-insulating properties are achieved, carbon black, graphite, titanium dioxide and metal particles, for example aluminum or a combination thereof, can be used. These additives are introduced in an amount of 0.6-6.0% of the total mass of the charge, preferably after plasticization of the polymer and before the introduction of the blowing agent. These additives color the beads in gray (black) color. However, other dyes can be used, for example phthalocyanine, and in particular, an orange dye.

Upon receipt of granules of expandable polystyrene, stabilizers of thermal and light destruction were also used. As a stabilizer of thermal and light degradation, for example, octadecyl-3- (3,5-ditretbutyl-4-hydroxyphenyl) propionate or a mixture of tris- (2,4-ditretbutylphenyl) phosphite with octadecyl-3-3 (3 , 5-ditretbutyl-4-hydroxyphenyl) propionate in an amount of 0.05-0.1% wt. by mass loading.

All of these processing aids can be directly mixed with polystyrene or a polystyrene melt obtained from a continuous styrene polymerization unit; they can also be administered as appropriate concentrates.

The invention is further illustrated by examples, but not limited to.

Example 1

100 parts by weight are fed into the mixing zone of the gravitometric dosage unit. STYROVIT 106B polystyrene with a viscosity average MM (Mv) equal to 216000 and a polydispersity coefficient (Mw / Mn) of 2.3 (ratio Mv), the polydispersity coefficient is 94 × 10 ³ ), 2.0 wt. . hexabromocyclododecane, 0.5 parts by weight the nucleator is talc.

The resulting mixture is fed into the loading zone of a twin-screw extruder with a screw length ratio L to diameter D equal to 31: 1, where at a temperature of 180-210 ° C all components are melted and mixed in the melt, after which a foaming agent is fed into the mixing zone through an injector - pentane in an amount of 6.5% wt. under pressure up to 120 bar. In the mixing zone, VA is homogenously mixed with the polystyrene melt. The specific throughput of the extruder in the mixing zone (Ks) is 1.75 kg / h / 1 / min. The ratio of the amount of pentane (in moles) to the specific throughput of the equipment in the mixing zone (Ks) is 0.18.

The mass obtained in the mixing zone with a temperature of 200 ° C is fed to a homogenization and cooling apparatus, where the melt is cooled to a temperature of 160 ° C. The temperature difference at the inlet and outlet of the homogenization and cooling stage of the mixture is 40 ° C.

Then the mass passes through a short static mixer to equalize the concentration and temperature profile of the flow and enters the granulator with an underwater granulation system. In the cutting chamber of the underwater pelletizing system, a water temperature of 40-70 ° C and a pressure of 8.0-10.0 bar are maintained. The resulting mixture of water and expandable polystyrene granules is fed to a centrifugal dryer, where the granules are separated from the water and dried.

For the finished product, the following indicators were determined:

- particle size distribution: average particle diameter, mm, mass fraction of granules after sieving on a sieve with a mesh size of 1.6 mm and 0.5 mm,%, mass fraction of the main fraction,%, according to TU 2291-008-56925804-2008;

- mass fraction of blowing agent,%, according to OCT 301-05-202-92Е,

- mass fraction of residual monomer,% wt., according to GOST 15820-82.

From the obtained granules of expandable polystyrene (PSV), polystyrene plates were made by a non-pressurized method, which includes the stages of: pre-foaming PSV with steam at a temperature of 100-104 ° C, intermediate storage (maturation) of pre-foamed granules, sintering them with the molding of the block and its subsequent cutting into plates.

For the resulting foam products (plates), the following indicators were determined:

- density, kg / m ³ , according to GOST 17177-94;

- compressive strength at 10% linear strain, MPa, according to GOST 17177-94;

- ultimate strength in static bending, MPa, according to GOST 17177-94;

- coefficient of thermal conductivity at (25 ± 5) ° C, W / (m × K), according to GOST 7076-94;

- water absorption in 24 hours,% by volume, according to GOST 17177-94;

- cell size, microns, according to SP - 30/08;

- time of independent burning (self-extinguishing), sec.

The values of the properties of PSV granules and indicators of physical and mechanical properties and thermal conductivity of the obtained polystyrene foam plate are given in the table.

Examples 2-6; 7K-9K

The experiments were carried out as in example 1, but polystyrene was taken with different values of Mv and Mw / Mn, the amount and composition of the expanding agent and the ratio of Mv / Mw / Mn were changed.

The loading recipe, the conditions for the production of PSV granules, their properties and the values of the properties of the polystyrene foam plates obtained from them are given in the table.

As can be seen from the table, the inventive method allows to obtain granules of a spherical shape of an expandable polystyrene of uniform particle size distribution with a narrow distribution of granule size. In industrial conditions, polystyrene plates with high strength characteristics (compressive strength and tensile strength under static bending) were obtained from the produced granules by molding. In addition, the inventive method can significantly improve the heat-insulating properties of polystyrene foam boards: the thermal conductivity coefficient for boards containing graphite is 0.029-0.030 W / m × K versus 0.034-0.038 W / m × K for boards obtained in control examples, and 0.037- 0.043 W / m × K for polystyrene boards according to GOST 15588-86. The water absorption obtained by the present method of foam is approximately 2-3 times lower than the water absorption of consignments of extruded polystyrene boards made without observing the claimed techniques. The resulting foam products are characterized by a low content of residual monomer styrene, which provides improved sanitary and hygienic properties of these products.

Table. Production conditions and properties of the finished product No.
p / p Indicators Units Examples one 2 3 four 5 6 one Mv 216000 235,000 235,000 253000 245000 200,000 2 Mw / mn 2,3 2.6 2,3 2.2 3.3 2.85 3 Ratio: Mv / (Mw / Mn) 94000 90400 102100 115,000 75,000 70,000 four Foaming Agent: 4.1 pentane % wt. 6.5 - 3,5 - 4.2 isopentane % wt. - 6.0 - 7.0 4.3 A mixture of pentane and isopentane (80:20) % wt. 6.5 4,5 5 Nucleator % wt. 0.5 0.55 0.55 0.4 0.2 0.5 6 Flame retardant % wt. 2.0 2.0 2.0 2.0 2.0 - 7 Graphite % wt. - - - 3.0 6.0 6.0 8 The ratio of the amount of blowing agent (in moles) to Ks 0.18 0.16 0.18 0.12 0.08 0.23 9 The temperature difference at the inlet and outlet stages of the homogenization and cooling of the mixture ° C 40 60 fifty 70 65 thirty 10 Size (diameter) of granules mm 1.0-1.1 0.8-0.9 1.2-1.4 0.6-0.8 0.6-0.8 1.2-1.4 eleven Mass fraction of the main fraction, not less % 98.0 98.0 98.0 98.0 98.0 98.0 12 Mass fraction of blowing agent % 6.4 5.9 6.4 4.3 3,5 6.9 13 Mass fraction of residual monomer, no more % 0.05 0.05 0.05 0.05 0.05 0.05 fourteen Foam density kg / m ³ 19.0 23.0 14.0 29.0 40,0 10.0 fifteen Compressive strength at 10% deformation MPa 0.11 0.14 0,07 0.18 0.28 0.05 16 Static Bending Strength MPa 0.20 0.25 0.13 0.26 0.38 0.11 17 Thermal conductivity at (25 ± 5) ° C W / m × K 0,033 0,033 0,038 0,033 0,030 0,029 eighteen Water absorption in 24 hours % by volume 0.7 0.6 1,5 1,0 1,1 1.8 19 Cell size μm 110 120 150 90 80 85

Table continuation No. p / p Indicators Units Examples 7K 8K 9K one Mv 260,000 235,000 210000 2 Mw / mn 2.2 3.3 2.5 3 Ratio: Mv / (Mw / Mn) 118,000 71000 84000 four Foaming Agent: 4.1 pentane % wt. - - 6.0 4.2 isopentane % wt. 7.0 - - 4.3 A mixture of pentane and isopentane (80:20) % wt. - 6.0 - 5 Nucleator % wt. 1,0 1,0 0.5 6 Flame retardant % wt. 2.0 2.0 2.0 7 Graphite % wt. - - - 8 The ratio of the amount of blowing agent (in moles) to Ks 0.25 0.18 0.06 9 The temperature difference at the inlet and outlet stages of the homogenization and cooling of the mixture ° C 90 60 40 10 Size (diameter) of granules mm 1.4-2.0 1.0-1.6 0.9-1.4 eleven Mass fraction of the main fraction, not less % 96.0 96.0 96.0 12 Mass fraction of blowing agent % 6.8 5.5 5.5 13 Mass fraction of residual monomer, no more % 0.1 0.1 0.1 Indicators of expanded polystyrene plates GOST 15588-86 fourteen Foam density kg / m ³ 15.0 27.0 32,0 up to 15.0 up to 25.0 up to 35.0 fifteen Compressive strength at 10% deformation MPa 0.06 0.12 0.02 0.05 0.10 0.20 16 Static Bending Strength MPa 0.08 0.2 0.2 0,07 0.18 0.35 17 Thermal conductivity at (25 ± 5) ° C W / m × K 0,038 0,035 0,034 0,042 0,039 0,040 eighteen Water absorption in 24 hours % by volume 2,8 2.0 1,6 3.0 2.0 1.8 19 Cell size μm 200 140 150 - - -

Claims (3)

1. A method of producing a foamable polystyrene granulate, comprising the steps of supplying a blowing agent to the mixing zone, mixing the blowing agent with a polystyrene melt, homogenizing the resulting mixture, cooling it to an extrusion temperature, extruding and granulating under conditions that prevent foaming, characterized in that they maintain the ratio the molar amount of blowing agent supplied to the specific throughput of the equipment in the mixing zone (Ks), which is the ratio of the amount of melt flowing material flow, including polystyrene in kg / h to the mixing speed in revolutions per minute, in the range of 0.08-0.23 while maintaining the temperature difference at the inlet and outlet of the stage of homogenization and cooling within 30-70 ° FROM. 2. The method according to claim 1, characterized in that polystyrene is used with a ratio of medium viscosity molecular weight (Mv) to polydispersity coefficient (Mw / Mn) in the range of (70-115) · 10 ³ . 3. The method according to claim 1, characterized in that as a technological additive, graphite is taken, taken in an amount of 0.6-6.0% by weight of the load.