WO2006046685A1 - Method of cleaning pre-expanded particle - Google Patents

Abstract

A method of cleaning pre-expanded particles, which is an efficient cleaning method for which a small detergent or liquid-detergent amount suffices. This is a method for cleaning pre-expanded particles obtained by introducing thermoplastic resin particles, an aqueous dispersion containing a dispersant and a dispersant aid, and a blowing agent into a pressure vessel, heating the contents and maintaining a given pressure and a given temperature to impregnating the resin particles with the blowing agent, and then discharging the contents into a low-pressure atmosphere. The method is characterized by comprising separating the aqueous dispersion from the pre-expanded particles, subsequently adding a liquid detergent to the pre-expanded particles, and then separating the liquid detergent containing the dispersant from the pre-expanded particles.

Description

 Specification

 Cleaning method of pre-expanded particles

 Technical field

 [0001] The present invention relates to a method for washing pre-expanded particles used in the production of an in-mold foam molded article of thermoplastic resin.

 Background art

 [0002] Preliminary foamed thermoplastic resin particles were obtained by dispersing thermoplastic resin particles in water containing a dispersant in a pressure vessel, then adding a foaming agent, and maintaining the high temperature and high pressure to impregnate the foaming agent. Thereafter, it is known that it is produced by a method of releasing in a low-pressure atmosphere (hereinafter referred to as pressure-reducing foaming method).

 [0003] In the above-described method, in order to prevent fusion of the resin particles under high temperature and high pressure, a dispersant such as a poorly water-soluble inorganic compound (hereinafter also referred to as an inorganic dispersant!) And a surface active Dispersing aids such as agents are used, but some of the dispersants remain on the surface of the pre-expanded particles even after being released into a low-pressure atmosphere under high temperature and high pressure. Hereinafter, the dispersant that remains and adheres to the pre-expanded particles is also referred to as the adhering dispersant.

 [0004] When the amount of the adhering dispersant is large, when the obtained pre-expanded particles are filled in a mold and heated by steam or the like to form an in-mold expanded molded product, poor fusion between the pre-expanded particles is caused. Because of this, it is usually necessary to remove the adhering dispersant after pre-foaming.

 [0005] As a method for removing the adhering dispersant, Patent Document 1 uses an aqueous solution of a water-soluble compound having a functional group capable of binding to the surface of the dispersant and a hydrophilic functional group as a cleaning agent. However, it describes only the addition of a cleaning solution to a dispersant containing pre-expanded particles, and describes and suggests specific steps. It has not been.

 Patent Document 1: JP-A-10-120819

 Disclosure of the invention

 Problems to be solved by the invention

However, the conventional method requires a large amount of water, a cleaning agent and a cleaning liquid, There is a problem that the cost of the strike and wastewater treatment becomes high.

 Means for solving the problem

 [0007] Therefore, the present inventors have sought an efficient cleaning method that requires a small amount of a cleaning agent and a cleaning liquid, and have completed the present invention.

 That is, according to the present invention, thermoplastic resin particles, an aqueous dispersion containing a dispersant and a dispersion aid, and a foaming agent are charged in a pressure vessel, and the temperature is raised to a resin particle with a predetermined pressure and a predetermined temperature. A method of washing pre-foamed particles obtained by impregnating a foaming agent and then releasing it under a low-pressure atmosphere. After separating the aqueous dispersion from the pre-foamed particle force, the cleaning liquid is added to the pre-foamed particles. Then, the present invention relates to a method for cleaning pre-expanded particles, wherein a cleaning liquid containing a dispersant is separated from the pre-expanded particles. Preferably, as an embodiment, the present invention relates to the method for cleaning pre-expanded particles described above, wherein the cleaning liquid is added, and then the cleaning liquid containing the dispersant is separated from the pre-expanded particles, and then water is further added. The second of the present invention relates to pre-expanded particles obtained by the above-described cleaning method.

 The invention's effect

 [0009] According to the method of the present invention, the adhering dispersant can be efficiently removed by using only a small amount of water, a cleaning agent and a cleaning liquid.

 Brief Description of Drawings

FIG. 1 is a flowchart of a pre-expanded particle manufacturing apparatus according to an embodiment of the present invention.

 Explanation of symbols

 [0011] 1 pressure vessel

 2 Aqueous dispersion medium (dispersant, dispersion aid)

 3 Wax particles

 4 Valve

 5 nozzles

 6 Separator

7 Spraying device for cleaning solution 8 Water spraying equipment

 9 Pre-expanded particle product storage tank

 BEST MODE FOR CARRYING OUT THE INVENTION

 [0012] In the present invention, a thermoplastic resin particle, an aqueous dispersion containing a dispersant and a dispersion aid, and a foaming agent are charged in a pressure-resistant container, and the temperature is raised to give the resin particle a predetermined pressure at a predetermined temperature. This is a method of washing pre-expanded particles obtained by impregnating a foaming agent and then releasing it under a low-pressure atmosphere.

 [0013] From the discharge part of the pressure vessel, an aqueous dispersion containing a pre-expanded particle and a dispersant and a dispersion aid is simultaneously released. In the cleaning method of the present invention, the aqueous dispersion is separated from the pre-foamed particles, and then the cleaning liquid is added to the pre-foamed particles. The above-mentioned aqueous dispersion contains an excessive dispersant, and if the cleaning liquid is added without being separated and removed, the cleaning agent may be consumed by the dispersant in the aqueous dispersion.

 [0014] In the step of washing the pre-foamed particles of the present invention, it is desirable to wash continuously after the pre-foaming from the viewpoint that the cleaning effect becomes high and the process can be shortened!

 [0015] In order to separate the pre-foamed particle force of the aqueous dispersion, a known separator can be used. For example, only the aqueous dispersion can be discharged to the outside by meshing a part of the wall of the duct that sends the released pre-expanded particles to the subsequent process. In addition, for example, a commonly used centrifugal dehydrator may be used, but is not limited thereto.

 [0016] It is ideal that the cleaning agent's efficiency surface force be completely separated from the pre-foamed particles so that no aqueous dispersion remains, but this increases the equipment cost and power cost of the separator. Therefore, it is realistic that the remaining amount of the aqueous dispersion is adjusted so that the cost can be balanced.

 [0017] Weight of pre-expanded particles containing aqueous dispersion W (g), pre-foamed containing aqueous dispersion

 1

 Put particles W (g) in a mesh container or net bag, etc., and air blow with a wind speed of 30 mZs or more.

1

 If the weight W (g) of the pre-expanded particles, which are completely removed from the aqueous dispersion by blowing away so that no surface moisture remains, the remaining amount of the aqueous dispersion, ie the liquid content X (%), is

 0 1

X = (W-W) / W X IOO

 1 1 0 0

It is expressed. In the present invention, the remaining amount of the aqueous dispersion, that is, the liquid content X is preferably 100% or less and 1% or less.

 1

 Furthermore, the aqueous dispersion is separated from the pre-foamed particles so that it is more preferably 50% or less and 10% or more. After separating the aqueous dispersion from the pre-foamed particles in this way, the cleaning liquid is added. By adding a cleaning liquid to the pre-expanded particles, the dispersant attached to the pre-expanded particles can be removed. More specifically, (1) the cleaning agent comes into contact with the dispersant adhering to the surface of the pre-expanded particles, and (2) the surface force of the pre-expanded particles is peeled off by the action of this cleaning agent, and the aqueous phase is separated. Dissolve, and (3) remove the aqueous phase in which the dispersant is dissolved by pre-expanded particle force separation and removal, and remove the inorganic dispersant adhering to the pre-expanded particles through t ヽ ぅ step.

 [0019] The method of adding the cleaning liquid to the pre-expanded particles is not particularly limited to these, but it is desirable and convenient to make the cleaning liquid uniformly contact with the surface of the pre-expanded particles without any unevenness. As a method, for example, a method in which pre-expanded particles are immersed in a cleaning liquid, or a shower nozzle or a spray nozzle is installed in a duct that sends discharged pre-expanded particles to a subsequent process, and fine droplets of cleaning liquid are collected from a nozzle cover. Can be applied to the pre-expanded particles. When a shower nozzle or spray nozzle is installed inside the duct that sends the discharged pre-expanded particles to the subsequent process, and a method in which fine droplets of the cleaning liquid are sprayed onto the pre-expanded particles, a smaller amount is used. This is preferable because it can be cleaned with a cleaning solution.

 [0020] The cleaning liquid used in the present invention refers to a liquid that can remove the dispersant and the like adhering to the pre-expanded particles, and typically refers to a liquid containing a cleaning agent.

 [0021] The substance used as the cleaning agent can be used without particular limitation as long as it has been conventionally used. For example, a water-soluble compound described in JP-A-10-120819 has at least one functional group capable of binding to the surface of a dispersant and one hydrophilic functional group in the molecule. High cleaning efficiency is preferable.

 [0022] When the dispersant is an inorganic dispersant, the functional group capable of binding to the surface of the inorganic dispersant has an ionicity opposite to the ionicity of the surface of the inorganic dispersant. It is a functional group that can ionically bond to a surface. The hydrophilic functional group is a polar group or a dissociating group that forms a weak bond with a water molecule by electrostatic interaction or hydrogen bond, and exhibits affinity for water.

[0023] To explain based on a specific example, for example, the surface of the used inorganic dispersant is positively banded. In the case of tricalcium phosphate, which is charged, functional groups that can bind to the surface of the inorganic dispersant include key-on functions such as phosphate groups (ions), carboxyl groups (ions), and kaate ions. A water-soluble compound that contains a hydrophilic functional group such as a phosphate group (ion), a carboxyl group (ion), a kalate ion, or an alcoholic hydroxyl group in the molecule as a cleaning agent. used. Specifically, water-soluble condensed phosphates such as sodium pyrophosphate, sodium tripolyphosphate and sodium hexametaphosphate; water-soluble phosphates such as sodium tertiary phosphate and potassium tertiary phosphate; Mixtures of phosphates and water-soluble phosphates; water-soluble silicates such as sodium metasilicate and sodium orthokeate; water-soluble ethylene diamine tetraacetates such as ethylene diamine 4 acetic acid 2 sodium, ethylene diamine 4 acetic acid 4 sodium; Water-soluble citrates such as acid soda; water-soluble tartrate such as sodium tartrate; mixtures of water-soluble hydroxy carbonates such as water-soluble citrate and water-soluble tartrate; sodium polyacrylate . These may be used alone or in combination of two or more. Of these, the cleaning effect is greater! / ヽ The water-soluble condensed phosphate is preferred, and the pH of the sodium hexametaphosphate aqueous solution is around 7.5, which is easier to handle and more preferred than point power.

[0024] Further, for example, in the case of kaolin in which the surface of the inorganic dispersant used is negatively charged, amino groups (ions), quaternary ammonium ions, functional groups capable of binding to the surface of the inorganic dispersant, It contains cationic functional groups such as pyridinium groups, and hydrophilic functional groups such as amino groups (ions), quaternary ammonium ions, pyridinium groups, and alcoholic hydroxyl groups as hydrophilic functional groups. A water-soluble compound contained in the molecule is used as a cleaning agent. Specifically, water-soluble polypyridyl-um compounds such as poly-4-vinyl-N-ethylpyridylum bromide; polyoxyethylene alkylamines; ethylenediamin tetraacetic acid 2 sodium, ethylenediamin tetraacetic acid 4 sodium, etc. Ethylene diamine amine acetate; ethylene diamine amine hydrochloride etc. are used. These may be used alone or in combination of two or more. Of these, ethylenediamine hydrochloride is preferred because of its greater cleaning effect.

[0025] Thus, the molecule has one or more functional groups that can bind to the surface of the inorganic dispersant used, preferably 2 or more and 500 or less, and one hydrophilic functional group in the molecule. More Alternatively, when a water-soluble compound having 2 or more and 500 or less is used as a cleaning agent, the adhering and dispersing agent can be efficiently cleaned.

 [0026] The concentration of the cleaning agent in the cleaning liquid varies depending on the type of the dispersing agent and the dispersing aid, and the concentration and remaining amount of the excess dispersing agent contained in the aqueous dispersion, but it is preferable. Is 5 to 50000 ppm, more preferably 20 to 5000 ppm. In order to reduce the cost of cleaning agents, it is preferable to keep the concentration of the cleaning solution to the minimum necessary.

 [0027] Further, the temperature of the cleaning liquid is preferably 50 to 95 ° C from the viewpoint that variation in magnification of the pre-expanded particles can be reduced.

 [0028] The amount of the cleaning liquid is preferably 0.05 L or more and 5 L or less, more preferably 0.1 L or more and 1 L or less, per kg of pre-expanded particles. In order to reduce the cost of the cleaning agent and the amount of waste water to be treated, it is preferable to keep the amount of cleaning liquid to the minimum necessary. On the other hand, if the amount of the cleaning liquid is too small, it may be difficult to uniformly add to all the pre-expanded particles.

 [0029] In the method described in JP-A-10-120819, 5 to 40 L, more preferably 10 to 30 L are required per kg of pre-expanded particles. For example, when washing with only water (or warm water), 40-80L is required. In the cleaning method of the present invention, the amount of cleaning liquid is much smaller and economical.

 [0030] In the cleaning method of the present invention, after adding the cleaning liquid to the pre-foamed particles, the cleaning liquid containing the dispersant (hereinafter referred to as the adhesion liquid) is separated.

 In order to separate the adhesion liquid from the pre-expanded particles, a known separator may be used. For example, a commonly used centrifugal dehydrator may be used, and a part of the wall of the duct that sends the discharged pre-foamed particles to the subsequent process is meshed in the same manner as the method of separating and removing the aqueous dispersion. By doing so, only the adhered liquid can be discharged to the outside.

 [0032] If the adhering liquid remains attached to the pre-expanded particles, the adhering liquid contains a dispersant dissolved in the aqueous phase, and this dispersing agent is used when the pre-expanded particles are dried. May adhere to the pre-expanded particles again, and the amount of dispersant adhering to the pre-expanded particles may increase. Therefore, it is preferable that the remaining amount of the adhesion liquid is small.

 [0033] The weight W (g) of the pre-expanded particles containing the adhesion liquid, the pre-expanded particles containing the aqueous dispersion

 2

Put W (g) in a mesh container or mesh bag, etc., and blow it with an air blow with a wind speed of 30 m / s or more. Assuming that the weight W (g) of the pre-expanded particles that have been completely removed by blowing away so that no surface moisture remains, the remaining amount of the adhering liquid, ie the liquid content X (%), is

 0 2

 X = (w-w) / w X IOO

 2 2 0 0

 It is expressed. In the present invention, the remaining amount of the adhering liquid, that is, the liquid content X is preferably 50% or less,

 2

 The adhering liquid is separated from the pre-expanded particles so that it is more preferably 20% or less, particularly preferably 10% or less.

 [0034] A more preferable cleaning method of the present invention is to add the cleaning liquid as described above, and then to separate and remove the adhering liquid, and then add water to the pre-expanded particles. Then, by separating the adhering liquid again after that, the dispersant in the adhering liquid remaining in the pre-expanded particles is diluted, and the final adhering dispersant can be further reduced.

 [0035] The method of adding water is not particularly limited to these, but, as in the case of adding a cleaning liquid, water can be uniformly and uniformly applied to the surface of the pre-foamed particles. For example, a simple method is to immerse the pre-foamed particles in water, or install a shower nozzle or spray nozzle inside the duct that sends the discharged pre-foamed particles to the subsequent process. Another method is to spray fine water droplets onto the pre-expanded particles. The amount of water used is a method that employs a method in which a shower nozzle or spray nozzle is installed inside the duct that sends the discharged pre-expanded particles to the subsequent process, and fine water droplets are sprayed onto the pre-expanded particles. A smaller amount is often preferable.

 [0036] The amount of water to be added is preferably 0.05 L or more and 5 L or less, more preferably 0.1 L or more and 1 L or less, per kg of pre-expanded particles. In order to reduce the amount of wastewater to be treated, it is preferable to keep the amount of water added to the minimum necessary. On the other hand, if the amount of water is too small, it may be difficult to add uniformly to all the pre-expanded particles. Further, the temperature of the water to be added is preferably 50 to 95 ° C. from the viewpoint that the variation in magnification of the pre-foamed particles can be reduced.

[0037] The method for separating the adhesion liquid from the pre-foamed particle force may be the same as the method for separating the adhesion liquid after adding the cleaning liquid. In the present invention, the adhering liquid is separated from the pre-expanded particles so that the remaining amount of the adhering liquid is preferably 50% or less, more preferably 20% or less, and particularly preferably 10% or less. [0038] If the adhering liquid remains attached to the pre-expanded particles, when the pre-expanded particles are dried, the dispersant in the adhering liquid adheres again to the pre-expanded particles and adheres to the pre-expanded particles. There is a possibility that the dispersing agent to increase. Therefore, it is preferable that the remaining amount of the adhesion liquid is small.

 [0039] The amount of the pre-expanded particle adhesion dispersant can be measured by a known method. For example, if you know that liquid phase chromatography (HPLC) or high decomposition temperature can be used, use inorganic dispersants! The method of doing is mentioned. For example, when the dispersant is tribasic calcium phosphate, an aqueous solution (colorimetric solution) containing ammonium metavanadate, ammonium molybdate and nitric acid and a predetermined amount of pre-expanded particles are placed in a conical beaker and allowed to react for a predetermined time. The liquid phase obtained can be quantified by measuring the absorbance at 4 lOnm with a spectrophotometer.

 [0040] Also, when the dispersing agent is kaolin, a predetermined amount of pre-expanded particles are taken in a crucible and heated until completely incinerated with a gas burner, and the weight of ash remaining before pre-expanding The amount of adhering dispersant can be determined by measuring the ash weight of the particles.

 [0041] The pre-cleaning process will be described below. In the present invention, the conventional force is also known. That is, an aqueous dispersion containing thermoplastic resin particles, an inorganic dispersant and a dispersion aid and a foaming agent are charged in a pressure vessel, and the temperature is raised to a predetermined pressure. Pre-foamed particles are produced by a method in which a foaming agent is impregnated with a foaming agent at a predetermined temperature and then released in a low-pressure atmosphere (depressurization foaming method).

 [0042] The apparatus used as the pressure vessel is not particularly limited as long as it can withstand the pressure and temperature in the preliminary foaming step. For example, an autoclave pressure vessel is a specific example.

 [0043] The pre-expanded particles are produced by releasing a mixture of the thermoplastic resin particles and the aqueous dispersion medium in an atmosphere lower than the internal pressure of the pressure vessel. The above-mentioned atmosphere means a space including the scattering trajectory of the released aqueous dispersion (pre-expanded particles and aqueous dispersion medium). Say. Further, a discharge pipe having a normal valve is disposed between the pressure vessel and the discharge portion.

[0044] In the discharge section, a diaphragm is generally used for adjusting the discharge time and making the expansion ratio uniform. It is preferable to use it. Among them, the use of an orifice plate is preferable because it can keep the outflow rate constant, obtain pre-expanded particles with high magnification and little variation in magnification, and has a simple structure. The orifice plate is a concept including an orifice type, a nozzle type, a bench type, and the like, and these may be combined.

 [0045] Examples of the thermoplastic resin include low density polyethylene, medium density polyethylene, high density polyethylene, linear low density polyethylene, polypropylene homopolymer, ethylene propylene random copolymer, propylene-butene random copolymer. Examples thereof include polymers, ethylene propylene-butene random copolymers, polybutene, and polystyrene. These may be used alone or in combination of two or more.

 [0046] In addition, cell nucleating agents, antioxidants, weathering agents, antistatic agents, flame retardants, lubricants, crystal nucleating agents, and the like may be added to these thermoplastic resins.

 [0047] The dispersant and the dispersion aid used in the pressure-reducing foaming method in the previous period are used for preventing the fusion of the thermoplastic resin particles in the pressure vessel.

 [0048] The dispersant can be used without particular limitation as long as it has been used in the past. Specific examples thereof include inorganic salts such as tricalcium phosphate, magnesium carbonate and calcium carbonate, and clays such as bentonite and kaolin. Of these, tricalcium phosphate is preferable because of its strong dispersion power. Moreover, the point power which does not pollute the environment where kaolin has a strong dispersion power is also preferable. The surface of these dispersants is usually positive or negative! /, Or slightly charged! /.

[0049] The dispersing aid is a component used for the purpose of improving the affinity between the thermoplastic resin particles and the dispersing agent to increase the dispersing power, and is particularly limited as long as it has been used conventionally. It can be used without. Specific examples include anionic surfactants such as sodium dodecylbenzene sulfonate, sodium paraffin sulfonate, higher alcohol sodium sulfate, sodium alkylnaphthalene sulfonate, benzalkonium chloride, alkyltrimethylammonium chloride, and dialkyl chloride. Forces such as dimethylammonium thionic surfactants. Among these, n-paraffin sulfonic acid soda gives good dispersibility and is easy to biodegrade, and salty benzalcoum is preferred to give good dispersibility. [0050] When the dispersion aid is used, a surfactant having a charge opposite in sign to the surface charge of the dispersant is usually used. For example, in the case of a triphosphate calcium salt whose surface is positively charged, an anionic surfactant such as sodium n-paraffin sulfonate or sodium dodecylbenzene sulfonate is usually used. In the case of kaolin in which the surface of the dispersant is negatively charged, a cationic surfactant such as benzalkonium chloride or dialkyldimethylammonium chloride is usually used. Of these, a combination of tricalcium phosphate and sodium n-paraffin sulfonate is preferable because it shows a good dispersibility.

 [0051] As described above, normally, the dispersing agent and the dispersing aid are used in combinations having different signs of charges. By doing so, the hydrophilic group (ionic group) of the dispersing aid interacts with the surface of the dispersing agent, and the dispersing agent surface is hydrophobized by the hydrophobic group of the dispersing aid, so that the hydrophobic thermoplastic resin is hydrophobic. The interaction force with the particle surface is improved. In other words, the dispersing aid acts as a binder between the thermoplastic resin particles and the dispersing agent to increase the dispersing power.

 [0052] In the present invention, known foaming agents such as a volatile foaming agent, an inorganic gas, and water are not particularly limited.

 [0053] Specific examples of the volatile blowing agent include aliphatic hydrocarbons such as propane, isobutane, normal butane, isopentane, normal pentane, and hexane; alicyclic compounds such as cyclobutane, cyclopentane, and cyclohexane. Hydrocarbons: Halogenated hydrocarbons such as trichloromonochloromethane, dichlorofluoromethane, dichlorotetrafluoroethane, trichlorodifluoroethane and the like. These can be used alone or in combination.

 [0054] Examples of the inorganic gas include economical points, productivity, safety, environmental compatibility, etc., as well as carbon dioxide, nitrogen, air, or inert gas, water vapor, oxygen, It is preferable to use an inorganic gas containing a small amount of hydrogen, ozone, etc., but nitrogen and air are more preferable because the effect of reducing variation in magnification is great.

 [0055] When water is used as a foaming agent, it is preferable to use a thermoplastic polymer in combination with a hydrophilic polymer.

[0056] Further, the temperature at which thermoplastic rosin particles are impregnated with a volatile foaming agent and subjected to decompression foaming. The pressure varies depending on the type of thermoplastic resin particles used and the desired expansion ratio.

1S At temperatures above the soft melting point of the resin used, the temperature is usually 100 to 150 ° C, the pressure is about 0.5 to 3.0 MPa, and the prefoaming ratio is about 5 to 40 times.

 [0057] As a preferred embodiment of the present invention, the apparatus shown in Fig. 1 is used as follows.

 In addition, hereinafter, unless otherwise specified, it is based on weight.

 [0058] In an autoclave-type pressure-resistant container 1, 150 to 500 parts of water and 0.2 to 3 parts of tribasic calcium phosphate as an inorganic dispersant for 100 parts of polyolefin resin (melting point Tm ° C), dispersion aid N-paraffin sulphonate as an agent 0. 001-0. 1 part and 5-30 parts of isobutane as a volatile foaming agent are charged and heated to (1¾1 10) to (1¾1 + 10) ° 〇, 1.0 The resin particles are impregnated with a foaming agent at a constant temperature and pressure within a range of ˜3.0 MPa, and then discharged from the discharge nozzle 5 under atmospheric pressure to obtain pre-expanded particles.

 [0059] The released pre-expanded particles and the aqueous dispersion are separated and removed by the separator 6 until the remaining amount of the aqueous dispersion reaches 50 to 10%, and then an aqueous solution containing 20 to 5000 ppm sodium hexametaphosphate is obtained. Spray at a temperature of 50 to 95 ° C and spray from the spray nozzle 7 so that the amount of cleaning liquid per kg of pre-foamed particles is 0.1 to LL. Next, the adhering liquid is separated and removed through the separator 6 so that the remaining amount of the adhering liquid is 10% or less.

 [0060] Next, 0.1 to 1 L of water per kg of pre-foamed particles is added by spraying from the spray nozzle 8 at a temperature of 50 to 95 ° C, and then the remaining amount of the adhering liquid is passed through the separator 6. Separate and remove the adhering liquid to 10% or less. The pre-expanded particles thus washed are obtained in the product storage tank 9. Example

 [0061] Hereinafter, the method of the present invention will be described in more detail based on Examples and Comparative Examples.

 [Example 1]

Ethylene-propylene random copolymer (melting point: 146 ° C, MI value: 9gZlO) 100 parts of polypropylene-based resin, ethylene ionomer copolymer with ethylene ion (meth) acrylic acid copolymer as a hydrophilic polymer 2 parts of fat (trade name: High Milan SD100, manufactured by Mitsui Dupont Polychemical Co., Ltd.) and melamine as a compound having a triazine skeleton and a molecular weight of 300 or less per unit triazine skeleton (trade name: melamine, manufactured by BASF) 1 0.15 parts of talc (average particle size 8 μm) as an inorganic filler, and carbon black as a colorant. 2. Melt and knead 6 parts with a 50 mm φ single screw extruder, extrude into a strand shape from a cylindrical die with a diameter of 2.2 mm φ, water cool, and cut with a cutter. Got.

[0063] In an autoclave pressure vessel 1 (capacity 3. Om ³ ), 100 parts (8 OOKg) of the obtained resin particles, 200 parts of water, and 0.75 part of calcium triphosphate as an inorganic dispersant. Then, 0.01 parts of n-paraffin sulfonic acid sodium was added as a dispersion aid, and the temperature in the pressure vessel was heated to 156 ° C. with stirring. After that, the pressure inside the pressure vessel is increased to 2.6 MPa with compressed air, held at the temperature inside the vessel for 30 minutes, and then the nozzle 4 at the bottom of the vessel is opened to open orifice 5 (opening diameter 3.6πιπι φ, numerical aperture 5 Pre-expanded particles were discharged through a hole) in a steam saturated atmosphere at 100 ° C.

 [0064] The released pre-expanded particles and the aqueous dispersion are separated and removed through the separator 6 until the remaining amount of the water-washed dispersion reaches 30%, and then the aqueous solution containing 5000 ppm sodium hexametaphosphate is removed at a temperature of 95 ° C. At C, the spray solution was sprayed from the spray nozzle 7 so that the amount of the cleaning liquid per kg of the pre-foamed particles was 0.5 L. Next, the adhering liquid was separated and removed through the separator 6 so that the remaining amount of the adhering liquid was 5% or less. The pre-expanded particles thus cleaned were obtained in the product storage tank 9. The amount of the adhering dispersant in the pre-expanded particles obtained was 450 ppm.

 [Example 2]

 By the same method as in Example 1, the pressure-resistant container force was also released to obtain pre-expanded particles. The released pre-expanded particles and the aqueous dispersion are separated and removed to 30% of the remaining amount of the water-washed dispersion through the separator 6, and then the aqueous solution containing 5000 ppm sodium hexametaphosphate at a temperature of 95 ° C. Then, the spray liquid was sprayed from the spray nozzle 7 so that the amount of the washing liquid per 1 kg of the pre-foamed particles was 0.2 L. Next, the adhering liquid was separated and removed through the separator 6 so that the remaining amount of the adhering liquid was 5% or less.

 [0066] Next, 0.2 L of water per kg of pre-expanded particles is added by spraying from the spray nozzle 8 at a temperature of 95 ° C, and then the remaining amount of the adhering liquid is 5% or less via the separator 6 The adhering liquid was separated and removed so that The pre-expanded particles thus washed were obtained in the product storage tank 9. The amount of the adhering dispersant for the pre-expanded particles obtained was 440 ppm.

 [0067] (Comparative Example 1)

By the same method as in Example 1, the pressure-resistant container force was also released to obtain pre-expanded particles. Released Spray nozzle 7 from an aqueous solution containing 5000 ppm sodium hexametaphosphate in a mixture of the pre-expanded particles and aqueous dispersion at a temperature of 95 ° C so that the amount of cleaning liquid per kg of pre-expanded particles is 8.5 L. Added by spraying. Next, the adhering liquid was separated and removed through the separator 6 so that the remaining amount of adhering liquid was 5% or less, and washed pre-expanded particles were obtained in the product storage tank 9. The amount of the adhering dispersant in the pre-expanded particles obtained was 530 ppm.

[0068] (Measurement of amount of adhering dispersant)

Metavanadate ammonium - © arm 0.022% (wt _^0/0, hereinafter the same), ammonium molybdate - © arm 0.54% and an aqueous solution containing nitric acid 3% (Hiiroeki) 50. OML and W (g) The pre-foamed particles were placed in a co-calc beaker, stirred for 1 minute, and allowed to stand for 10 minutes. Take the obtained liquid phase in a quartz cell with an optical path length of 1. Ocm, and measure the absorbance A (—) at 410 nm with a spectrophotometer.

 [0069] For the same colorimetric solution, using the absorbance coefficient ε (gZL'cm) of tricalcium phosphate measured at 410 nm in advance,

Adhesive dispersant amount C (ppm) = 5. Ο Χ ΙΟ ⁴ · ε -A / W

 Asked.

 [0070] As described above, with the cleaning method of the present invention, it was possible to obtain pre-expanded particles with a smaller amount of the cleaning liquid and with a smaller amount of adhering dispersant than the conventionally known methods.

 [0071] According to the cleaning method of the present invention, the amount of cleaning liquid (cleaning agent) and water is very small, and the pre-expanded particles are industrially produced in large quantities while keeping the cost of the cleaning agent and waste water treatment low. Can be produced.

 [0072] Further, in the case of the above-described Examples and Comparative Examples, it is necessary to wash in a steam saturated atmosphere at 100 ° C in order to reduce the variation in the magnification of the pre-expanded particles, and the washing liquid and water are 95 ° Power required to heat up to C According to the present invention, since the amount of cleaning liquid and water can be reduced, the energy cost for heating can be kept low.

Claims

The scope of the claims  [1] A pressure-resistant container is charged with thermoplastic resin particles, an aqueous dispersion containing a dispersant and a dispersion aid, and a foaming agent, and the temperature is raised and the resin particles are impregnated with the foaming agent at a predetermined pressure and a predetermined temperature. After that, the pre-expanded particles obtained by discharging in a low-pressure atmosphere are washed. After the aqueous dispersion is separated from the pre-foamed particle force, the washing liquid is added to the pre-foamed particles, and then the dispersant is added. A method for cleaning pre-expanded particles, comprising separating the cleaning liquid containing from the pre-expanded particles.  [2] After adding the cleaning liquid and then separating the cleaning liquid containing the dispersant from the pre-foamed particles 2. The method for washing pre-expanded particles according to claim 1, wherein water is further added. [3] Pre-expanded particles obtained by the cleaning method according to claim 1 or 2.