JPH0347710A - Manufacture of thermoplastic resin composition and molded material - Google Patents

Abstract

PURPOSE:To improve drastically a quality, a cost and productivity, by a method wherein at the time of melting and kneading of thermoplastic resin and a particulate, a liquid containing the particulate whose diameter is specific or smaller is introduced into a moving layer of a granular matter in an unmolten state, the liquid is discharged by turning it into gas while sticking or accumulating the particulate to the moving layer of the granular matter and a mixture is melted and kneaded. CONSTITUTION:A loading hopper where a resin granular matter is closed up tightly is fitted to a resin feed port A through a chute. A suction blower is connected with a gas discharge port B through a filter. A particulate such as a titanium oxide or silica having a mean particle diameter of not exceeding 10mum, which has passed through, for example, a loading device, a classification device and a crushing device for an aggregate particle is mixed into a liquid and then the liquid containing the particulate is pressed into an introduction port C with a slurry pump. A nitrogen flowing device and vacuum pump are connected respectively with vent ports D1, D2. A cylinder outlet 3 is connected with a mouthpiece 6 having a slit hole through a gear pump 5. A resin composition is extruded on a rotary cooling drum, quenched and a sheet is obtained. Then the sheet is made into a film through biaxial orientation, cooled after thermal fixation and wound up.

Description

[Detailed Description of the Invention] (Industrial Application Field) The present invention relates to plastic products mixed with fine particles and additives,
For example, the present invention provides a method for manufacturing functional plastic materials that can be molded into fibers, molded products, biaxially stretched films, and the like.

(Prior art) Plastic materials processed into molded products have traditionally been made by melting and kneading fillers such as glass fibers, carbon fibers, whiskers, etc. with a size of about 1 micron or more into a thermoplastic resin. In mainstream methods (for example, see Japanese Patent Laid-Open No. 61-277421), there are problems in improving the appearance of molded products and the impact resistance of molded products. On the other hand, titanium oxide, carbon black,
When dispersing fine particles with a size of about 1 micron or less, such as magnetic materials, the mainstream method is to mix the fine particles during polymerization of thermoplastic resin and disperse them uniformly, but this method is not practical due to the high temperature of the reaction system. The materials used are limited to fine particles with good heat resistance, such as titanium oxide and carbon black, and they contaminate the polymerization equipment, requiring special equipment and a great deal of effort and expense for cleaning. There is a problem. In addition, a masterbatch method in which fine particles and additives are kneaded at high concentrations is well known, but it requires drying of the resin before kneading and drying of the masterbatch after kneading, which consumes a lot of energy and labor. Deterioration of the physical properties of the molded product due to the thermal history during the kneading process also poses a problem.

(Problems to be Solved by the Invention) Regarding the problems of molded products made from conventional plastic materials, we have developed a plastic material filled with submicron to micron-sized fine particles instead of the conventional filler of 10 to several tens of microns. There is a demand for technology to manufacture more advanced products, such as various molded products made by wafers, as well as two-wheeled stretched films, sheets, and fibers that have never existed before. In other words, it is necessary to develop a new technology that integrates a powder process that handles submicron to micron-sized particles and a polymer process. Originally, powder processes and polymer processes are different technologies, and the creation of a technology that harmonizes them can be achieved by harmonizing pneumatic transport technology for submicron-sized particles and polymer processes. This requires a technology for processing submicron particles that is compatible with polymer processes.

Generally, in the powder process, typical industrially implemented techniques include, for example, atomization using a sand mill and dust collection using a bag filter. However, it is not only difficult to achieve complete continuity as a powder process, but there are also problems such as moisture absorption and reaggregation of collected fine particles. Therefore, the problem to be solved by the present invention is to establish a new production technology that industrially and continuously micronizes and collects submicron-sized particles and incorporates them into the polymer process. It is.

(Means for solving the problem) As for microparticle formation and its dust collection technology that can be incorporated into the polymer process, it is possible to integrate the powder process and the polymer process by wet grinding of particles using a sand mill and dust collection using a granular moving bed. This problem is now solvable. That is, the first aspect of the present invention, when melt-kneading a thermoplastic resin and fine particles, introduces a liquid containing fine particles with a particle size of 10 μm or less into a particle transfer layer of an unmolten thermoplastic resin to transfer the particles. This method of producing a thermoplastic resin composition is characterized in that the liquid is discharged as a gas while fine particles are attached or deposited on a layer, and the mixture of the granules and fine particles is melted and kneaded. The second invention also provides a method for melting and kneading a thermoplastic resin and an additive by introducing a solution or emulsion of the additive into a particulate matter transfer layer of an unmolten thermoplastic resin. A method for producing a thermoplastic resin composition, which comprises: adhering or depositing an additive to the mixture, discharging the solvent or dispersion medium as a gas, and then melting and kneading the mixture of the granules and the additive. . A third invention is a method for producing a molded article, characterized in that the thermoplastic resin composition is molded following the melting and kneading of the first and second inventions.

Thermoplastic resins used in the present invention include polyesters such as polyethylene terephthalate and polyethylene terephthalate, polyamides such as nylon 6, nylon 66, and nylon 12, polyolefins such as polyethylene and polypropylene, vinyl chloride, polycarbonate, polyurethane, ^BS resin, Also refers to known thermoplastic resins such as copolymers and mixtures thereof.

The fine particles in the present invention are at room temperature, preferably at 100°C.
The average particle size is 10 μm to inn, preferably luI
ll-1 nm, more preferably 0.5 am to 10n
m solid particles. In addition, fine particles and additives include titanium oxide, calcium carbonate, silica, talc, lithopone,
Zinc oxide, mica, barium sulfate, alumina, kaolin, carbon black, tin oxide, glass beads, gold, silver,
Metal powder such as copper, iron, lead, aluminum, calcium silicate, zirconium oxide, zirconium carbide, 7 Fez
Ferrites such as O3 and chromium dioxide, antimony trioxide, antimony pentoxide, bromine compounds, dyes and pigments (including fluorescent whitening agents), antistatic agents, antibacterial agents, crosslinking agents, stabilizers, etc. Examples include known additives and fine particles described in "Practical Handbook of Additives for Rubber", edited by Kunio Goto, published by Kagaku Kogyosha in 1972.

The amount of fine particles and additives blended into the thermoplastic resin is usually 50% by volume or less based on the resin granules, but in the present invention, the amount of fine particles and additives added to the thermoplastic resin is in the range of 1 to 50% by volume, particularly 5 to 40% by volume. It is effective when combined.

The liquid, solvent or dispersion medium used in the present invention includes water,
Examples include acetone, chloroform, ethane tetrachloride, cyclohexane, benzene, toluene, xylene, alcohols, ethers, etc., and liquids and solvents having a boiling point lower than the softening point of the thermoplastic resin are preferred. Further, it is preferable to heat the thermoplastic resin to a temperature that does not melt it or cool it, since the heating energy for the resin can be reduced.

The concentration of the fine particles in the liquid or the additive in the solution or dispersion is usually 1 to 80% by weight, often 10 to 60% by weight. Note that the transport speed (flow speed) of liquid containing fine particles is usually 0.
01 to 10 m/sec. If the flow rate is low, it is unfavorable in terms of reagglomeration of particles and clogging of piping, while if it is high, it is unfavorable in terms of wear of the equipment and piping.

In addition, when creating a stable or dense emulsion,
If necessary, various surface active agents, gelatin, gum arabic, etc.
Known emulsifiers such as alginic acids, fatty acid esters, and metal salts are used.

Dispersion or dissolution of fine particles and additives is usually carried out by mechanical stirring using stirring blades, baffles, etc., shaking using ultrasonic waves, mixing using a static mixer, injection through a narrow gap, or the like. For example, liquids containing fine particles are usually ball milled,
The mixture is suitably adjusted using a wet pulverizer such as a vibration mill or a sand mill, but wet classification operation or filtration using a filter can be combined as necessary. When using a media stirring mill, the filling amount of glass beads or alumina beads as the media, particle size, processing time, number of passes, etc. are appropriately selected. If fine particles in the liquid tend to condense,
It is preferable to use a suspending agent for uniform and stable dispersion. Suspending agents include gum arabic, gelatin,
carboxymethylcellulose, sodium alginate,
Examples include barium sulfate, talc, glue, etc., and are selected as appropriate.

The liquid containing fine particles adjusted in this way has the properties of the fine particles,
Depending on the mixing ratio (weight concentration) of fine particles and liquid, liquid flow rate, transport distance, etc., the liquid is delivered through an appropriate metering liquid pump, piston pump, Ulrich pump, etc., and piping.
The resin particles are introduced into the transfer layer.

In the present invention, the granular material has a length of 0.1 to 1 in three directions.
It refers to granules or powders with a size of 0 mm, preferably 1 to 5 mm. The thermoplastic resin particulate transfer layer is obtained by a mechanism having the function of supplying, filling, and discharging thermoplastic resin particulates. For example, it can be easily obtained using a single-screw or twin-screw kneading extruder heated to a temperature below the melting point or softening point of the thermoplastic resin and above the boiling point of the liquid. It can also be obtained with a static tubular mixing device.

When forming such a thermoplastic resin particle transfer layer using a twin-screw kneading extruder, the screw diameter should be set to D.
In this case, it is preferable to form the resin particles so that the residence time is about 1 to 3 minutes between 3 and 15D from the supply port. If it is less than 2D, collection of fine particles or adhesion of additives will not be sufficient, while if it exceeds 20D, the dust collection effect will be saturated and the device will become long, which is not preferable. Further, the liquid, solvent, or dispersion medium containing fine particles and additives introduced into the particulate matter transfer layer is heated here and becomes a gas.

For example, the adhesion or accumulation of fine particles by the thermoplastic resin particle movement layer is due to the so-called inertial dust collection effect, that is, as the fine particles gradually adhere to the surface of the resin granules, the fine particles adhere to each other, and furthermore. A bridge is formed, and a deposited layer of fine particles is formed in the resin granule layer. The filtration effect of this deposited fine particle layer is the key point of the present invention. This filtration effect depends on the flow rate of the gas or liquid, the moving speed of the resin particles, the particle size, properties, and specific gravity. In addition, along with the accumulation of fine particles,
Although the pressure loss increases, in the present invention, the mixture of resin granules and fine particles is constantly moved in the direction of the subsequent process and renewed, so the pressure loss can be kept almost constant, resulting in an efficient and stable process. It becomes possible to collect fine particles. Generally, 50% by weight or more, and in many cases 80% by weight or more, of the fine particles are collected in resin granules.

The gas from which fine particles and additives have been removed may be discharged from either the part that supplies the thermoplastic resin granules or the part that melts and kneads it, but it is preferably done on the supply side, and then the resin It can also be shared with the granular material supply port (
(See Figure 3). It is also possible to suction and discharge by applying negative pressure with a blower or the like.

Melting and kneading of the mixture of thermoplastic resin granules, fine particles, and additives in the present invention is carried out, for example, using a kneading extruder having a cylinder fitted with a screw or rotor (Revised Lithographic Chemical Engineering Handbook, p. 916-919). , edited by the Chemical Engineering Society, Maruzen ■, published in 1986, reference). If the thermoplastic resin contains moisture, or if you want to remove some liquid, solvent, dispersion medium, or gas mixed in with melting, install a vent and apply negative pressure or nitrogen flow. It is preferable to deaerate, and further, along with melting and kneading,
For polyester resins, nylon resins, polyethylene resins, etc. where the thermoplastic resin deteriorates or volatile matter is generated, use a twin-screw kneading extruder equipped with two or more vents and screws rotating in the same or different directions. If used, it is preferable because it has a devolatilizing effect that can be operated in high vacuum.

The melt-kneaded thermoplastic resin composition containing dispersed fine particles or additives is extruded from an outlet provided at the tip of the cylinder, and is directly passed through a die for obtaining fibers, sheets or films, or a mold for obtaining molded products. It can be molded by a known method such as being introduced into a mold, or it can be first made into a chip or powder and then subjected to molding.

Next, the present invention will be explained with reference to device diagrams.

In FIG. 1, 1 is a cylinder of a twin-screw kneading extruder. Two screws 2 rotating in the same direction are fitted into this cylinder l. The cylinder L has a resin supply hole A, a gas outlet B, an inlet C1 for a liquid containing fine particles, an additive solution or an emulsion, and two vent holes Dl spaced apart in the longitudinal direction of the cylinder L.

D2 are arranged in order. Resin supply port A is cylinder L
The lower, downstream end is the outlet 3. Further, in the present invention, the melting start portion of the resin granules is located between the introduction port C and the vent hole D1. The screw 2 has a diameter of 65 mm, and the upstream side of the inlet C is in the deep groove 2a of 15III11, the melting start part is the kneading desk and the deep groove becomes shallow and deep 2d, and the kneading part is in the shallow groove 2c of the 4 kneading desk. The ventro part provided in the section is a slightly deep groove 2d of 6m+a. A heater (not shown) is attached to the cylinder. Further, the length of the deep groove portion 2a is 780 m, the length of the melting start portion 2b is 195 m, and the shallow groove portion 2c including the vent portion.

2d is 585 towers, and the distance between B and C is 585 m.

A closed charging hopper for resin granules is attached to the resin supply port A via a chute. An intake proer is connected to the gas exhaust port B through a filter. For example, fine particles that have passed through a fine particle input device, a classification device, and an agglomerated particle crushing device (not shown) are mixed into a liquid, and then a liquid containing fine particles is forced into the inlet C by a slurry pump.

A nitrogen flow device (not shown) is connected to the pen and trolley D1, and a vacuum pump (not shown) is connected to the venturo D2.

Further, the cylinder outlet 3 is connected to a mouthpiece 6 having a slit hole through a gear pump 5, and the resin composition is extruded from the slit hole onto a rotating cooling drum and rapidly cooled to obtain a sheet. Next, this sheet is biaxially stretched to form a film, which is then heat-set, cooled, and rolled up.

In FIG. 2, 1 is a screw of a single screw extruder,
Separated in the longitudinal direction, from the upstream side, a resin supply port A, an inlet C1 for a liquid containing fine particles, an additive solution, or an emulsion.
A gas exhaust port B and a pentro D are arranged in this order. Further, in the present invention, the melting start portion of the resin granules is located between the exhaust port B and the vent hole D. The screw 2 has a diameter of 70 mm, and the diameter of the screw 2 is 16 mm on the upstream side of the exhaust port B.
The melting start part gradually becomes a shallow groove 2b, the kneading part becomes a 4III11 shallow groove 2c, and the vent hole part becomes a slightly deeper groove 2d. A heater (not shown) is attached to the cylinder.

For example, a closed charging hopper for resin particles is attached to the resin supply port A via a chute (not shown), and an intake blower is connected to the gas exhaust port B through a filter. A liquid containing fine particles is pressurized into the inlet C, and a vacuum pump is connected to the vent D.

Further, the outlet 3 of the cylinder is connected to a spinneret 6 via a distribution pipe 4 and a gear pump 5, and the resin composition is extruded from the pores and wound up to obtain fibers.

FIG. 3 shows an example in which, in FIG. 1, the gas is separated from resin particles through the resin supply port A using, for example, a wire mesh filter, and then exhausted from a cloth bag.

Figure 4 shows resin granules at A and powdery resin granules at A.
’ and continuously fed with a screw feeder, 3
An example will be shown in which ~12 stationary mixing elements 8 are arranged to form a particulate matter moving layer. Incidentally, the inlet C can also be arranged in the biaxial deep groove portion 2a.

(Example) The present invention will be explained below using examples.

Example 1 IVO074 was installed in the resin supply port A of the twin-screw kneading extruder shown in Figure 1.
, size 3.0 mmφX3. 0 mmL of polyethylene terephthalate chips were supplied at a rate of 83 kg/hour, and hot water containing anatase-type titanium oxide with an average particle size of 0.3 μm was introduced into the inlet C (40% by weight at 1 degree, temperature 90'' C1 water slurry).
was introduced at a rate of 42.5 kg/hour, steam was discharged from the exhaust port B, and the cylinder temperature was set at the deep groove section 120→210"C1 melting start section 280"C, kneading section and vent section 290"C, and the ventro DI was Ventro D2 is 5 to 10 Torr
After kneading under reduced pressure to Torr, it is extruded from a 290"C slit-type nozzle onto a rotating cooling drum and rapidly cooled to a thickness of 1.
．． An amorphous sheet with a mark of 1 was obtained. Next, make this sheet 1
Stretched 3.0 times in the machine direction at 00°C and stretched 11 times in the transverse direction.
The film was stretched 3.0 times at 0°C, heat-set at 200°C, cooled, and wound. The resulting film has a thickness of 125
It was white and opaque in μm, and the TV was 0.60. Note that stretch forming could be performed continuously and stably.

The obtained film had a good white color with no discoloration or agglomerates due to polymer decomposition by-products, and was extremely useful as a support for reflective photography.

Example 2 A film was prepared in the same manner as in Example 1, except that fluorescent whitening shaved Eucopha BGM (manufactured by Sandoz) was suspended in a hot water slurry containing titanium oxide at a concentration of 0.11% by weight, and this was introduced into the inlet C. Molded. The obtained film exhibited an excellent whiteness similar to brilliance, and the whiteness was the same in all parts, indicating that the optical brightener was mixed uniformly.

Example 3 A film was prepared in the same manner as in Example 1, except that the fluorescent brightener Ducofer S (manufactured by Sandoz) was dissolved in a hot water slurry containing titanium oxide at a concentration of 0.11% by weight and introduced into the inlet C. Molded. As in Example 2, the obtained film exhibited brilliant and excellent whiteness, and the whiteness was the same in all parts, indicating that the fluorescent whitening agent was mixed uniformly.

Example 4 η to the resin supply port A of the uniaxial kneading extruder in FIG.

= 2.70 (measured in 95.7% sulfuric acid, 25°C) size 2.0 mm φX2. 19 OmmL nylon 6 tips
．． 8 kg/hour, water containing carbon black with an average particle size of 20 nm (10% by weight, room temperature, glue double star content) was introduced into the inlet C at a rate of 2 kg/hour, and water vapor was introduced from the exhaust port B. It was discharged. Cylinder temperature at deep groove part 120→
The temperature was set at 180°C1 melting start part 250°C1 kneading part and vent part 260°C, and after kneading under reduced pressure of Ventro D to 10 Torr, it was extruded from a spinneret at 265°C.
The undrawn yarn was oiled and wound at 1000 m/min.

Next, this undrawn yarn was drawn 3.6 times to produce a 208 denier/96 filament black spun-dyed nylon fiber.

Note that the operations from kneading to stretching could be performed stably.

The obtained black spun-dyed nylon fiber had a strength of 3.3 g/d, an elongation of 40%, and uniform coloring.

Example 5 An average molecular weight of 8 was added to the resin supply port A of the twin screw kneading extruder in Figure 1.
0000, polyethylene chips with a size of 3.0 mm x 3.0 mm are supplied at a rate of 80 kg/hour, and a titanium oxide particle having a tin oxide film of 15% by weight on the surface is introduced into the inlet C at a rate of 0.75 mm. Water Y (concentration 40% by weight, temperature room temperature) containing conductive fine particles (hereinafter referred to as conductive particles , water slurry) was introduced at a rate of 50 kg/hour, and water vapor was discharged from exhaust port B (Japanese Patent Application Laid-open No. 1983-
104642). Cylinder temperature at deep groove part 50°C
1 The melting start part was set at 230°C, the kneading part and the vent part were set at 240°C, and the ventro Di, 02 was kneaded under a reduced pressure of 10 Torr, and then extruded to form 3.0IIIIIIlφ×3.0.
mmL (Molded into D chip Zozo.

Next, the obtained chips Z2° were supplied to the resin supply port A at a rate of 75 kg/hour, and the water slurry Y containing the conductive particles X was introduced to the introduction port C at a rate of 62.5 kg/hour, and kneaded under the above conditions. It was molded into a chip Zao.

Next, chips Z4° were supplied at a rate of 66.7 kg/hour, water slurry Y containing conductive particles X was introduced at a rate of 83.25 kg/hour, and the chips Z4 were kneaded under the above conditions. It was molded into.

Next, Chip Z. was supplied at a rate of 62.5 kg/hour, water slurry Y containing conductive particles 27% was molded.

Next, a conductive composite fiber was produced in the same manner as in Example 2 Y described in JP-A-60-224812, except that the chip Zws was used as the conductive core component. The operability of spinning and drawing was good, and the yarn quality, conductivity, and antistatic properties of the obtained conductive composite fibers were also good.

Example 6 Nylon 6 chips were supplied to the resin supply port A at a rate of 19.4 kg/hour, and a mixture of glycerin ethylene oxide/propylene oxide adduct (addition polymerization weight ratio 80/20°, average molecular weight 17.000) and dimethyl terephthalate was added. 2 kg/hour of water in which 30% by weight of the reaction product was dissolved was introduced into the inlet C.
An antistatic nylon fiber was produced in the same manner as in Example 4, except that the water vapor was introduced into the air and the water vapor was discharged from the exhaust port B. kneading,
Spinning and drawing could be operated stably. The strength of the obtained fiber was 3.28/d.

It had an elongation of 44% and good antistatic performance.

Example 7 The kneading extruder shown in Fig. 4 (double section, only twin shafts, inner diameter 60 m)
m) resin supply port A with a size of approximately 3+nmφ×311II
65 kg/hour of IIL polybutylene terephthalate chips (Mitsubishi Kasei Tubadol 5010), size approximately 31
1IIlφ x 3mmL styrene-butadiene block copolymer chip (Denka Kagaku Kogyo Denka 5TR1602
) was supplied to A' at a rate of 15 kg/hour of polystyrene bromide powder (Nissan Ferro Organic Chemical ■Pyrocheck 68PH) with an average particle size of about 0.1 mm, and the particle size distribution was 20~
A hydrothermal colloid containing 50 μm antimony pentoxide (50% by weight at 1 degree, temperature 90°C, containing 1% by weight of triethanolamine as a suspending agent) was introduced at a rate of 10 kg/hour and suctioned with a blower through a cloth filter. The water vapor was discharged. Static mixing element (inner diameter 80 m, 6 elements, length 480 m) and cylinder temperature 150°C in 2 shaft parts 1 kneading part 2b.

After kneading at 240°C, set the vent 2d and measuring part 2C at 260°C, and reduce the pressure in the ventro D to 10 Torr,
Extrude to 3.0mφX3. I made it into an OmL chip.

Various test pieces were then injection molded under normal conditions.

Injection molding could be performed stably. In addition to a high degree of flame retardancy, the test piece also had excellent impact resistance.

Example Day The same procedure as Example 1 was carried out, except that polyethylene terecrate chips were fed at a rate of 100 kg/hour, and hot water in which a blue anthraquinone dye was suspended at a concentration of 2.0% by weight was introduced at a rate of 1.5 kg/hour. A film was produced in the same manner. The obtained film was transparent and exhibited a similar blue color in all parts, and could be used as a base film for X-rays.

(Effects of the Invention) As explained in detail above, the present invention provides a novel method for producing thermoplastic resin compositions and molded articles in which fine particles of 10 μm or less and additives, particularly submicron fine particles, are dispersed at a high concentration. It provides technology.

In other words, according to the present invention, it is possible to carry out the wet processing step of fine particles directly connected to the melt-kneading step and the molding step, thereby significantly improving quality, cost, and productivity, which were difficult to solve with conventional methods. be able to. Further, the method of the present invention
It is also a method suitable for high-mix, low-volume production, and provides an industrially extremely useful polymer process.

[Brief explanation of drawings]

Figures 1 to 4 are longitudinal cross-sectional schematic diagrams of equipment suitable for carrying out the method of the present invention. Figure 1 is a twin-screw kneading extruder, Figure 2 is a single-screw extruder, and Figure 3 is a resin feed port. FIG. 4 shows an example in which a particulate matter moving layer is formed in a stationary mixing element section. Connie

Claims (1)

[Claims] 1. When melt-kneading a thermoplastic resin and fine particles, a liquid containing fine particles with a particle size of 10 μm or less is introduced into a particle transfer layer of an unmolten thermoplastic resin to move the particles. A method for producing a thermoplastic resin composition, comprising: discharging the liquid as a gas while attaching or depositing fine particles to a layer; and melting and kneading the mixture of the fine particles and the fine particles. 2. When melt-kneading a thermoplastic resin and an additive, a solution or emulsion of the additive is introduced into a particulate transfer layer of an unmolten thermoplastic resin, and the additive is attached to the particulate transfer layer. A method for producing a thermoplastic resin composition, which comprises discharging a solvent or dispersion medium as a gas while depositing the same, and then melting and kneading the mixture of the granules and additives. 3. A method for producing a molded article, which comprises molding the fine particle-dispersed thermoplastic resin composition following the melting and kneading according to claims 1 and 2. 4. Claim 1, characterized in that the gas is discharged closer to the part to which the thermoplastic resin particles are supplied than to the part to which the liquid containing fine particles, solution or emulsion of additives is introduced.
, 2. The method described in .