JPH10119037A - Preparation of polyolefin-based resin particle and prefoamed particle - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for preparing a polyolefin-based prefoamed particle having a favorable moldability at an in-mold molding by a method wherein a small and uniformly shaped polyolefin-based resin particle can be prepared by an under-water cutting system. SOLUTION: A polyolefin-based resin particle is manufactured by extruding a polyolefin-based resin under melted state through a die nozzle having a bore below 2mm at the flow rate of 0.5-8kg/hr per one bore with an extruder in the hot water having the temperature of 65-95 deg.C prepared by adding a calcium tertiary phosphate as a hard water-soluble inorganic matter and an anionic surfactant having the electric charge opposite to the electric charge on the surface of the above-mentioned inorganic matter such as an n-paraffin sodium carbonate sulfonate, sodium dodecylbenzenesulfonate or the like or a kaolin as a hardly water-soluble inorganic matter and a cationic surfactant having the electric charge opposite to the electric charge on the surface of the above-mentioned inorganic matter such as an alkyltrimethyl ammonium chloride, dialkyl dimethyl ammonium chloride, benzalkonium chloride or the like and then cut with a cutter blade. Finally, the prepared polyolefin- based resin particle is pre-foamed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to polyolefin resin particles used for the production of in-mold foamed polyolefin resin particles used for cushioning packaging materials, boxes, heat insulating materials, bumper core materials for automobiles and the like. The present invention relates to a method for producing expanded particles.

[0002]

2. Description of the Related Art The pre-expanded particles used for producing an in-mold expanded molded article of a polyolefin resin are usually 0.5 to 10 mg.
/ Particles of resin particles. In this case, the pre-expanded particles do not knead and melt the resin particles again,
Since it is manufactured by foaming as it is, the shape of the resin particles before prefoaming greatly affects the shape of the prefoamed particles. If the resin particles are too large, the pre-expanded particles will have a large particle size, and the filling of the thin portion of the mold will be poor. In addition, if the resin particle shape is not uniform, when the pre-expanded particles are formed, the expansion ratio varies for each particle. Variations increase, which is not preferable in terms of production efficiency or buffer design. Furthermore, if there is residual strain (residual stress) in the resin particles, the pre-expanded particles may become flat due to stress relaxation in the pre-expanded particle manufacturing process. Adversely affect For this reason, the resin particles used in the production of the pre-expanded particles need to have a uniform and small shape and a constant residual strain, and more preferably a small residual strain. Methods for producing such resin particles include a strand cut method, an underwater cut method, and the like.

[0003] In the case of the strand cut method, the residual distortion of the resin particles is large, and when the pre-expanded particles are produced, a large shrinkage occurs in the extrusion direction of the resin particles, and the shape of the pre-expanded particles changes greatly. For this reason, in order to obtain pre-expanded particles of a desired shape with small variation, the optimum resin particle production conditions are determined by grasping the rate of change of the shape of the resin particles in the pre-expanded particle production step in advance, and this condition is determined. Must be reproduced exactly. However, in practice, it is difficult to stably and strictly reproduce the resin particle production conditions, and the yield must be low. In addition, a great deal of pre-examination is required to change the raw material resin, a long distance is required to install the resin particle manufacturing equipment, and the productivity is relatively low because there is a limit in increasing the number of strands, There are problems such as many strand breaks.

As a method for producing resin particles by an underwater cut method, there are methods disclosed in JP-A-61-195808 and JP-A-1-234212. In these methods, although there is no large shrinkage in the extrusion direction as in the case of the strand cut method, when formed into pre-expanded particles, large cavities may be generated or may be non-spherical, so that pre-expanded particles are stably obtained. And it is not always a satisfactory method. As a method for solving such a problem, the present inventors have proposed that a discharge rate per hole is 0.5 to 8 kg / Hr, a die nozzle having a diameter of less than 2 mm is 5 to 90 ° C., and a resin temperature is 140 to 140 ° C.
A method of extruding a molten resin into warm water at 220 ° C. lower has been found (JP-A-8-90556).

[0005]

However, as a result of further research, when pre-expanded particles produced from resin particles produced by the underwater cut method are molded in a mold, the moldability is poor, that is, the pre-expanded particles are inferior. It was found that there was a problem that the inter-welding became worse. Furthermore, it was found that the tensile properties greatly involved in the fusion also deteriorated at the same time. Therefore, in the present invention, when producing resin particles by an underwater cut method, a method capable of producing polyolefin resin particles having a uniform shape and small size, and producing pre-expanded particles having good moldability during in-mold molding. The aim is to provide a method.

[0006]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies to achieve the above object, and as a result, the discharge amount per die nozzle hole, the die nozzle diameter, and the cooling water when the molten resin is extruded from the extruder. It has been found that the above-mentioned problem can be solved by setting the water temperature within a certain range, and the present invention has been completed.

That is, according to the present invention, a poorly water-soluble inorganic substance and a molten polyolefin resin are discharged from a die nozzle having a diameter of less than 2 mm at a discharge rate of 0.5 to 8 kg / Hr using an extruder. A method for producing polyolefin-based resin particles, characterized by extruding into a hot water at 65 to 95 ° C. to which a surfactant having a charge opposite to that of the poorly water-soluble inorganic material is added, and cutting with a cutter blade in the warm water; And a method for producing pre-expanded polyolefin-based resin particles, which comprises pre-expanding the polyolefin-based resin particles produced by the above method.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The discharge amount per die nozzle hole is set based on extrusion stability, production amount, and the like. Although it depends on the viscosity of the resin during extrusion and the shape of the die, if it exceeds 8 kg / Hr, the flow of the molten resin in the die nozzle will not be stable, and resin particles of a satisfactory shape cannot be obtained. Further, depending on the capacity of the extruder, in consideration of a practical production scale and extrusion stability, 0.5 kg / Hr or more, preferably 2 kg / Hr or more is appropriate.

The diameter of the die nozzle is set in consideration of the die well in order to obtain resin particles of a desired size. Generally, resin particles required to obtain polyolefin-based resin pre-expanded particles of a desired size are controlled by the weight per particle, and the weight is usually 0.2 to 10 mg.
/ Grain. Therefore, the diameter of the die nozzle is suitably less than 2 mm. The die nozzle diameter is the diameter of the land tip of the die nozzle.

[0010] The size of the resin particles is from 0.2 to 10
mg / grain, preferably in the range of 0.5-6 mg / grain. When the size of the resin particles is less than 0.2 mg / particle, it is necessary to reduce the discharge amount per die nozzle hole, and the productivity is reduced. In order to ensure productivity, it is necessary to reduce the diameter of the die nozzle holes and increase the number of die nozzle holes. However, doing so decreases the distance between the holes and increases the fusion between the resin particles. In addition, when the discharge amount per hole is reduced, the heat generated by shearing with the inner wall of the die nozzle is reduced, and the nozzle is easily clogged. In addition, the size of the resin particles is 10 m.
If the amount exceeds g / particle, the particle diameter becomes large when the pre-expanded particles are used. If the diameter of the pre-expanded particles is large, the filling property into a thin portion is deteriorated during in-mold molding, and a satisfactory molded product may not be obtained. The peripheral speed of the cutter blade at this time is 10
m / sec or more, preferably 15 m / sec or more. If the peripheral speed of the cutter blade is lower than 10 m / sec, the shape of the resin particles becomes irregular and may not be a desirable shape, and the resin particles may be fused to each other. The peripheral speed of the cutter blade means the peripheral speed at the position of the die nozzle.

[0011] The resin temperature at the time of extrusion is 180 to 320 ° C, preferably 200 to 280 ° C. 180 ° C resin temperature
If it is less than 3, the resin has a high viscosity and is difficult to extrude. When the resin temperature is 32
If the temperature exceeds 0 ° C., thermal decomposition of the resin occurs.

Further, if the temperature of the cooling water from which the resin is extruded is less than 65 ° C., the moldability when producing pre-expanded particles produced from the obtained resin particles in a mold is poor. On the other hand, if the temperature exceeds 95 ° C., a boiling state occurs, and bubbles of water vapor are mixed in the cooling water, and the agglomerate particles in which a plurality of resin particles are fused rapidly increase, which is not preferable because the production efficiency decreases. If the temperature of the cooling water is increased even if the temperature does not exceed 95 ° C., agglomerate particles start to be generated, and the production efficiency is reduced. Therefore, in the present invention, in order to reduce the agglomerate particles, a poorly water-soluble inorganic substance and a surfactant having a charge opposite to the surface of the poorly water-soluble inorganic substance are added to warm water as cooling water. Here, the poorly water-soluble inorganic substance refers to a powdery inorganic substance that is not substantially dissolved in neutral water, for example, powdered inorganic substances such as tertiary calcium phosphate, magnesium carbonate, calcium carbonate, kaolin, bentonite, and the like. And powdered clays. The surface of these poorly water-soluble inorganic substances is generally charged to either positive or negative. Therefore, when a surfactant having a charge (ion) opposite to that of the surface of the poorly water-soluble inorganic substance is added to the warm water to which the poorly water-soluble inorganic substance is added, the surfactant dissolves the hydrophilic group (charge ion) of the poorly water-soluble inorganic substance. A hydrophobic group is coordinated to the surface of the inorganic inorganic material with the aqueous phase side. As a result, the vicinity of the surface of the poorly water-soluble inorganic material is hydrophobized, the affinity with the resin particles is improved, the dispersing power is improved, the occurrence of agglomerate particles during the production of the resin particles is prevented, and the production efficiency is reduced. Thus, resin particles can be produced without any need. Therefore, as the combination of the poorly water-soluble inorganic substance and the surfactant, when the poorly water-soluble inorganic substance is tribasic calcium phosphate whose surface is positively charged, the anionic surfactant is used. In the case of kaolin which is charged to a negative polarity, a cationic surfactant is effective.

Further, it is preferable to use, as the third calcium phosphate, slurry calcium phosphate synthesized by a wet method and not subjected to a drying step by heating. This is because the calcium phosphate slurry has a higher surface charge density than the heated and dried calcium phosphate, so that the amount of the surfactant adsorbed on the surface of the calcium phosphate particles is large, the vicinity of the surface is made more hydrophobic, and the affinity with the resin particles is increased. It is presumed that the property becomes higher. Furthermore, since a drying step by heating has not been performed, aggregation between particles is small and the particle size is small. This is presumed to be due to the fact that the resin particles are more uniformly dispersed in water to enhance the shielding effect between the resin particles.

As the anionic surfactant, n-
It is preferable to use either sodium paraffin sulfonate or sodium dodecylbenzene sulfonate alone or in combination. As the cationic surfactant, any of penzalkonium chloride, dialkyldimethylammonium chloride and alkyltrimethylammonium chloride is preferably used alone or in combination of two or more.

The amount of the water-insoluble inorganic substance and the surfactant used as described above is in the range of 0.3 to 5% by weight of the poorly water-soluble inorganic substance and 0.003 to 1.0% by weight of the surfactant. The addition is preferable from the viewpoint of the balance between the effect of preventing agglomeration and the cost. When the addition amount of the poorly water-soluble inorganic substance is less than 0.3% by weight, there is no effect of reducing the agglomerate particles, and when it exceeds 5% by weight, the viscosity of the warm water as the cooling water increases and the cooling water is circulated. Not only does a high-output pump be required to perform this operation, but strainers are usually installed in the cooling water circulation line to remove resin debris, etc. It will be easier. Furthermore, excessive addition leads to an increase in raw material costs. On the other hand, if the amount of the surfactant added is less than 0.003% by weight, there is no effect of reducing the agglomerate particles.
If it exceeds 0% by weight, the effect of reducing agglomerate particles saturates, and excessive addition leads to an increase in raw material costs,
Bubbling of cooling water increases, a large amount of defoamer is required,
This is also not preferable because it leads to an increase in raw material costs.
In addition, when the amount of the surfactant is too large relative to the poorly water-soluble inorganic substance, the effect of reducing the agglomerate particles (dispersing power) may be lost. This is because the surface of the poorly water-soluble inorganic material is hydrophilized by coordinating the surfactant (micellar double coordination) with the surface of the poorly water-soluble inorganic material that has been hydrophobicized by the coordination of the surfactant. By losing affinity with the particles.

Furthermore, it is preferable to add an antifoaming agent to the warm water. This is because the surfactant added to the warm water as the cooling water is present in the water in a partially free state, and the cooling water is generally circulated and used, so the foam may be foamed in the circulation line. That's why. As the defoaming agent, a silicon-based defoaming agent is preferable, and the addition amount of the surfactant in warm water is 0.003 to 1.0.
When it is% by weight, it is preferable to add an antifoaming agent in the range of 0.1 to 1.5% by weight. If the amount of the defoaming agent is less than 0.1% by weight, the defoaming ability is not sufficient, and if it exceeds 1.5% by weight, the dispersing power of the poorly water-soluble inorganic substance and the surfactant tends to decrease. It is.

Examples of the polyolefin resin used in the present invention include low-density polyethylene, medium-density polyethylene, high-density polyethylene, linear low-density polyethylene, polypropylene homopolymer, ethylene-propylene random copolymer, and propylene-butene random. Copolymer, ethylene propylene-butene random copolymer,
Poly (butene-1) and the like can be used, and these can be used alone or in combination of two or more, but are not limited thereto.

The pre-expanded polyolefin resin particles in the present invention can be obtained by expanding the polyolefin resin particles obtained as described above to about 5 to 60 times by a known method as described below. After stirring the polyolefin-based resin particles and the volatile foaming agent together with water and a dispersing agent in a pressure-resistant container and raising the temperature to near the melting point of the resin particles to pressurize, open the valve provided at the bottom of the pressure-resistant container. And releasing the aqueous dispersion and the resin particles into a low-pressure atmosphere (usually atmospheric pressure range). Polyolefin-based resin particles contain a volatile foaming agent in advance, put the resin particles in a pressure vessel having a stirrer, and, if necessary, stir with a small amount of an anti-fusion agent, etc.
A method in which water vapor or the like is introduced from one end of a container and foamed.

[0019]

The present invention will be described below in more detail with reference to Examples and Comparative Examples.

[Examples 1 to 10, Comparative Examples 1 to 5; Production of polyolefin resin particles] Werner & PFL
A nozzle of a die (number of nozzles: 9) mounted at the tip of an extruder using an underwater cut type co-rotating twin screw extruder ZSK70 (70 mmφ screw) manufactured by EIDERE
6. A melt composed of 100 parts by weight of an ethylene-propylene random copolymer (melting point: 145 ° C.), 0.01 part by weight of talc as a nucleating agent and other components is discharged per die hole from a nozzle diameter of 0.8 mm). The amount is 3.6 kg /
As a ratio of Hr, a cutter blade (a number of blades) that is extruded into warm water at each temperature to which a poorly water-soluble inorganic substance, a surfactant and an antifoaming agent shown in Table 1 are added, and rotates at a peripheral speed of 19 m / sec in proximity to the die 12) and separated from the circulating warm water to produce resin particles. The weight per obtained resin particle was 1.7 to 1.9 mg. The agglomeration rate and shape of the obtained resin particles were evaluated by the following methods, and the results are shown in Table 1.

<Agglomeration ratio>
g and collect the agglomerate particles. The weight of the divided agglomerate particles is W ₁ (g), and the weight of the resin particles without fusion is W ₂ (g). Agglomeration rate (%) = (W ₁ ) / (W ₁ + W ₂ ) × 100

<Resin Particle Shape> Visually evaluated according to the following criteria. ：: Almost spherical. Δ: Slightly deviated from the sphere, but may become sphere after foaming. X: Not spherical, and there is no possibility of becoming spherical after foaming.

[0023]

[Table 1]

Examples 11 to 22, Comparative Examples 6 to 11; Production of Pre-expanded Particles and In-Mold Expanded Molded Article
To 10 or 100 parts by weight of the resin particles obtained in Comparative Examples 1 to 5, 5 to 10 parts by weight of isobutane as a volatile foaming agent, 2 parts by weight of powdery basic tribasic calcium phosphate as a dispersant, and sodium n-paraffin sulfonate 0 .03
A part by weight was charged together with 300 parts by weight of water into a pressure-resistant container, the temperature in the container was maintained at 142 ° C., and the pressure in the container was adjusted to 20 kg / cm ² by additional press-fitting of isobutane. afterwards,
While maintaining the temperature and pressure in the vessel constant while press-fitting isobutane, the valve at the bottom of the pressure vessel was opened and the aqueous dispersion was discharged under atmospheric pressure through an orifice plate to obtain pre-expanded particles. The expansion ratio and shape of the obtained pre-expanded particles were evaluated. Table 2 shows the results. In the evaluation of the shape of the pre-expanded particles in the table, “○” indicates a substantially spherical shape, and “×” indicates a shape deviated from a spherical shape.

The pre-expanded particles are pressurized with air to give an internal pressure of 1.7 kg / cm ² ,
It was filled in a m × 300 mm × 300 mm mold and molded at a predetermined vapor pressure shown in Table 2. The obtained molded body was dried in an oven at 80 ° C. for 12 hours, then gradually cooled to room temperature, and the fusion rate, the molded body density and the tensile properties were evaluated by the following methods. Table 2 shows the results.

<Fusion Ratio> The formed body was divided along a crack having a depth of about 5 mm into the surface of the formed body with a knife, the cross section was observed, and the ratio of the number of broken particles to the total number of particles was determined. , Fusion rate. ◎: fusion rate of 80% or more ：: fusion rate of 60 to less than 80% △: fusion rate of 50 to less than 60% ×: fusion rate of less than 50% Usually, the level of the fusion rate that is satisfactory as a molded article is: It is at least 60% or more.

<Tensile Properties> Cut out into dumbbells having a thickness of 20 ± 0.5 mm, a width of 25 ± 0.5 mm, and a distance between marked lines of 50 ± 0.5 mm at 20 ° C. so that the surface layer of the molded body does not remain.
After leaving in the room for more than 24 hours, pulling speed 500mm
/ Min, a tensile test is performed at a measurement temperature of 20 ° C., the magnitude of the force f (Kg) at the breaking point and the moving distance L (c) between the marked lines
m) is measured, and the tensile strength and the tensile elongation are calculated by the following equations. Tensile strength (Kg / cm ² ) = f / (D × H) Tensile elongation (%) = (L−L ₀ ) / L ₀ × 100 where D, H, and L ₀ are the thickness, Width,
This is the distance between the marked lines, and the unit is cm.

[0028]

[Table 2]

As is clear from the results shown in Tables 1 and 2, the polyolefin resin was mixed with a poorly water-soluble inorganic substance and a surfactant having a charge opposite to the surface of the poorly water-soluble inorganic substance.
By extruding into hot water at ~ 95 ° C, it is possible to efficiently produce resin particles having a preferable spherical shape while suppressing the generation of agglomerate particles, and the pre-expanded particles produced from these resin particles are: The moldability during in-mold foam molding is good, and a good in-mold molded article can be obtained even with a low molding pressure. On the other hand, as in Comparative Examples 1 and 2,
When the temperature of the hot water at the time of resin extrusion is lower than 65 ° C., the agglomeration rate at the time of resin particle production is relatively low and the particle shape is good, but Comparative Examples 6, 7 and 10, 11
As is apparent from the above, the pre-expanded particles produced from the resin particles have poor moldability during in-mold foam molding, have a low fusion rate in the molded body, and have a good in-mold molded body unless the molding pressure is increased. Can not get. Further, as is apparent from Comparative Example 3, when the temperature of the hot water is high, not only the poorly water-soluble inorganic substance and the surfactant are not added, but also the occurrence of agglomeration becomes remarkable, and it is not possible to obtain resin particles having a preferable shape. . Further, when the temperature of the hot water exceeds 95 ° C., as is apparent from the results of Comparative Examples 4 and 5, even if a poorly water-soluble inorganic substance and a surfactant are added to the hot water, the generation of agglomerate particles is suppressed. It is not possible to obtain resin particles having a preferable shape. From the above, the effect of the method for producing polyolefin resin particles and pre-expanded particles of the present invention has been clarified.

[0030]

As described above, according to the present invention, polyolefin resin particles having a uniform and small shape and polyolefin resin pre-expanded particles having good moldability during in-mold molding are obtained by the underwater cut method. , And can be manufactured efficiently.

Claims (11)

[Claims] 1. A hardly water-soluble inorganic substance and a hardly water-soluble inorganic substance, wherein an extruder is used to discharge a molten polyolefin resin from a die nozzle having a diameter of less than 2 mm at a discharge rate per hole of 0.5 to 8 kg / Hr. Extruded into 65-95 ° C. hot water to which a surfactant having a charge opposite to the surface is added,
A method for producing polyolefin-based resin particles, comprising cutting with hot water using a cutter blade. 2. The method for producing polyolefin resin particles according to claim 1, wherein the poorly water-soluble inorganic substance and the surfactant added to the warm water are a tribasic calcium phosphate and an anionic surfactant. 3. The method for producing polyolefin-based resin particles according to claim 2, wherein the third calcium phosphate is a slurry calcium phosphate synthesized by a wet method and not subjected to a drying step. 4. The method for producing polyolefin resin particles according to claim 2, wherein the anionic surfactant is sodium n-paraffin sulfonate and / or sodium dodecylbenzene sulfonate. 5. The method for producing polyolefin resin particles according to claim 1, wherein the poorly water-soluble inorganic substance and the surfactant added to the warm water are kaolin and a cationic surfactant. 6. The method for producing polyolefin-based resin particles according to claim 5, wherein the cationic surfactant is at least one selected from alkyltrimethylammonium chloride, dialkyldimethylammonium chloride, and benzalkonium chloride. 7. The addition amount of the poorly water-soluble inorganic substance is from 0.3 to
5% by weight, and the amount of the surfactant added is 0.003 to 1.
The method for producing polyolefin-based resin particles according to any one of claims 1 to 6, which is 0% by weight. 8. The silicone-based antifoaming agent 0.1 to 0.1 in said warm water.
The method for producing polyolefin-based resin particles according to any one of claims 1 to 7, wherein 1.5% by weight is added. 9. A method for producing pre-expanded polyolefin resin particles, wherein the polyolefin resin particles produced by the method according to claim 1 are pre-expanded. 10. A water-insoluble inorganic substance produced by an underwater cut method, weighing 0.2 to 10 mg / particle, and a surfactant having a charge opposite to that of the surface of the poorly water-soluble inorganic substance adhered to the surface. Polyolefin resin particles. 11. Pre-expanded polyolefin resin particles obtained by pre-expanding the polyolefin resin particles according to claim 10.