JP4907118B2 - Method for producing polypropylene resin pre-expanded particles - Google Patents

Description

  The present invention relates to a method for producing polypropylene resin pre-expanded particles, and more specifically, when the particles are released from a high-temperature and high-pressure sealed container into a low-pressure atmosphere, the pre-expanded particles are less fused, The present invention relates to a production method capable of obtaining polypropylene resin pre-expanded particles with good productivity.

  Polypropylene resin in-mold foam molded products have superior chemical resistance, heat resistance, buffer performance, and compression strain recovery performance compared to polystyrene resin in-mold foam molded products. Compared to polyethylene resin in-mold foam molded products. Even so, since it is excellent in heat resistance and compressive strength, it is widely used as a buffer packaging material, a returnable box, and an automobile member.

  In particular, as buffer packaging materials of various shapes, they can be molded flexibly and without cutting work in accordance with the shape of products and members to be included, so that they are widely used from electronic machines to industrial materials.

  As a method for producing pre-expanded polypropylene resin particles for in-mold foam molding, by releasing into a low-pressure atmosphere from a high-temperature and high-pressure container, when foaming, by contacting with steam or air of 60 ° C. or higher, Methods for increasing the expansion ratio and suppressing variations in expansion ratio of pre-expanded particles are known (Patent Documents 1 and 2). However, when contacted with water vapor or air of 60 ° C. or higher in a low-pressure atmosphere as described above, there is a problem that the pre-expanded particles are easily fused with each other, although the variation in expansion ratio can be reduced.

  Due to the wide demand for in-mold foam moldings obtained by heat-molding polypropylene resin pre-expanded particles, products with a beautiful mold shape with thinner parts and a small amount of steam heating are eagerly desired, For this purpose, a polypropylene resin having many crystals that are easily melted at a low temperature is being used.

  However, when such a resin is used and released into the low-pressure and high-temperature atmosphere from the high-temperature and high-pressure vessel as described above, there is a problem that the pre-expanded particles are easily fused. The fused pre-foamed particles are usually removed by a sieve such as a shifter, which not only reduces the yield, but if the amount of fused pre-foamed particles is large, the granulation ability is lowered. In the worst case, it may lead to blockage of the granulation pipe, which is a big problem in production.

On the other hand, for pre-expanded particles produced using a polypropylene resin composition containing a crystal nucleating agent, increase rigidity (Patent Document 3) or prevent shrinkage of pre-expanded particles after pre-expansion (Patent Document 4). In the case of a high expansion ratio of 15 times or more with addition of a small amount of about 0.01 to 0.1% by weight, there is almost no effect of improving the rigidity, and the pre-expanded particles are fused. Is not released under a high temperature atmosphere when releasing the pre-expanded particles from the sealed container under a low pressure. There was no problem with the fusion. The problem regarding the fusion of the pre-expanded particles generated by using water as a foaming agent and releasing it in a high-temperature atmosphere is not mentioned in the production of the pre-expanded particles using a different foaming agent (Patent Document 4).
JP-A-11-106546, JP 2002-338724 A Japanese Patent Laid-Open No. 5-179049 Japanese Patent Laid-Open No. 5-156065

  The objective of this invention is providing the manufacturing method of the polypropylene resin pre-expanded particle which can manufacture stably the polypropylene resin pre-expanded particle for in-mold foam-molding with favorable productivity.

  In view of the above circumstances, the present inventors have made extensive studies and as a result, obtained the following knowledge. That is, by using a polypropylene resin composition containing a crystal nucleating agent in a method for producing polypropylene pre-foamed particles that releases particles made of a polypropylene resin composition from a high temperature and high pressure sealed container under a low pressure and high temperature atmosphere. The inventors have found that pre-foamed particles can be produced stably and with high yield by preventing fusion of the pre-foamed particles even under conditions where the pre-foamed particles are easily fused together, and the present invention has been completed.

That is, in the present invention, particles made of a polypropylene resin composition are dispersed in an aqueous dispersion medium in a closed container, the particles are heated to a temperature equal to or higher than the softening temperature of the polypropylene resin composition, and water as a dispersion medium is added. In the method for producing pre-expanded polypropylene resin particles, the polypropylene resin is pre-expanded by impregnating the particles as a foaming agent and then releasing into an atmosphere at a pressure lower than the internal pressure in the sealed container and 80 ° C. or higher. A method for producing pre-expanded polyolefin resin particles, characterized in that the composition contains at least one crystal nucleating agent selected from an organic phosphorus crystal nucleating agent, an aluminum crystal nucleating agent, and a sorbitol crystal nucleating agent. About.

As a preferred embodiment, in the measurement of polypropylene resin pre-expanded particles by differential scanning calorimetry, it has two melting points, the low-temperature side melting point is 143 ° C. or less, and the low-temperature melting crystal content ratio is 90% or less. relates to a manufacturing method of polypropylene resin pre-expanded particles of the wherein, as another preferred embodiment, the polypropylene resin composition contains at least one member selected from compounds having a hydrophilic polymer, a triazine skeleton And a method for producing the pre-expanded polypropylene resin particles described above.

  According to the present invention, in a method for producing polypropylene-based pre-expanded particles in which particles made of a polypropylene-based resin composition are released from a high-temperature / high-pressure sealed container under a low pressure and an atmosphere of 80 ° C. or higher, the polypropylene-based polypropylene containing a crystal nucleating agent By using the resin composition, it is possible to prevent the pre-expanded particles from being fused to each other, and to provide the manufacture of the pre-expanded particles having a stable and high yield and a high expansion ratio.

  As the polypropylene resin constituting the polypropylene resin pre-expanded particles of the present invention, as long as it contains propylene as a monomer in an amount of 80% by weight or more, more preferably 85% by weight or more, and further preferably 90% by weight or more. The composition and the synthesis method are not particularly limited, for example, propylene homopolymer, ethylene-propylene random copolymer, propylene-butene random copolymer, ethylene-propylene block copolymer, ethylene-propylene-butene ternary. A copolymer etc. are mentioned.

  Examples of the crystal nucleating agent contained in the polypropylene resin composition in the present invention include 2,2-methylenebis (4,6-di-tert-butylphenyl) phosphate and bis (4-tert-butylphenyl) phosphate. Organic phosphorus crystal nucleating agents such as sodium, organoaluminum crystal nucleating agents such as hydroxy-di (tert-butylbenzoic acid) aluminum, sorbitol such as bis (p-ethylbenzylidene) sorbitol, bis (4-methylbenzylidene) sorbitol It is preferable that it is 1 type (s) or 2 or more types among type | system | group crystal nucleating agents. Among these crystal nucleating agents, an organophosphorus crystal nucleating agent is preferable from the viewpoint of the effect of addition amount, and at least one kind containing sodium 2,2-methylenebis (4,6-di-tert-butylphenyl) phosphate. More preferably.

  Although the effect on the added amount of various crystal nucleating agents is different, the total amount of the crystal nucleating agent is preferably 0.001 to 0.5 parts by weight, preferably 0.005 to 0 parts by weight with respect to 100 parts by weight of the polypropylene resin. More preferred is 3 parts by weight or less. When the total amount of the crystal nucleating agent is less than 0.001 part by weight, it is difficult to obtain the effect of the present invention, and when it is more than 0.5 part by weight, the effect as a foam cell nucleating agent is strengthened, May be too fine. The method for adding the crystal nucleating agent is not particularly limited, but when a polypropylene resin is thermoformed into particles by a conventionally known method, the crystal nucleating agent may be added and melt-kneaded. The resin particles granulated with a high concentration of the agent may be adjusted and mixed so as to have a desired ratio and then melt-kneaded.

  The polypropylene resin composition in the present invention is not particularly limited as the resin melting point, preferably 130 ° C. or higher and lower than 170 ° C., more preferably 135 ° C. or higher and lower than 165 ° C., and further preferably 140 ° C. or higher and lower than 160 ° C.

  The melt index of the polypropylene resin in the present invention is not particularly limited as long as the pre-expanded particles can be produced, and is preferably 0.2 g / 10 min or more and 50 g / 10 min or less, and preferably 1 g / 10 min or more and 30 g / min. More preferably, it is 10 min or less. When the melt index is within this range, it is easy to achieve both high secondary foamability and good dimensionality. When the melt index is less than 0.2 g / 10 min, the melt viscosity is too high and it is difficult to obtain highly foamed pre-expanded particles, and when it is greater than 50 g / 10 min, the melt viscosity with respect to the elongation of the resin during foaming is too low. , Easy to break. The melt index may be adjusted, for example, by using an organic peroxide.

  A synthetic resin other than the polypropylene resin may be added to the polypropylene resin as long as the effects of the present invention are not impaired, so that the base resin may be used. Synthetic resins other than polypropylene resins include high density polyethylene, medium density polyethylene, low density polyethylene, linear low density polyethylene, linear ultra low density polyethylene, ethylene-vinyl acetate copolymer ethylene-acrylic acid. Examples thereof include ethylene resins such as copolymers and ethylene-methacrylic acid copolymers, and styrene resins such as polystyrene and styrene-maleic anhydride copolymers.

  It is preferable to add one or more compounds among the hydrophilic polymer and the compound having a triazine skeleton to the polypropylene resin of the present invention. In the present invention, the hydrophilic polymer refers to an ethylene-acrylic acid-maleic anhydride terpolymer, an ethylene- (meth) acrylic acid copolymer, and an ethylene- (meth) acrylic acid copolymer crosslinked with a metal ion. Examples thereof include carboxyl group-containing polymers such as ionomer resins. These may be used alone or in combination of two or more. In particular, an ethylene ionomer resin obtained by crosslinking an ethylene- (meth) acrylic acid copolymer with an alkali metal ion such as sodium ion or potassium ion is preferable because it provides a good water content and good foamability. Further, an ethylene ionomer resin obtained by crosslinking an ethylene- (meth) acrylic acid copolymer with potassium ions is more preferable because it gives a larger average cell diameter.

  The amount of the hydrophilic polymer used is not particularly limited depending on the kind of the hydrophilic polymer, but it is preferably 0.01 parts by weight or more and less than 20 parts by weight with respect to 100 parts by weight of the polypropylene-based resin. More preferred is less than 5 parts by weight. If it is less than 0.01 parts by weight, it is difficult to obtain pre-expanded particles having a high expansion ratio, and if it is 20 parts by weight or more, the heat resistance and mechanical strength may be greatly reduced.

  In the present invention, the compound having a triazine skeleton preferably has a molecular weight per unit triazine skeleton of 300 or less. Here, the molecular weight per triazine skeleton is a value obtained by dividing the molecular weight by the number of triazine skeletons contained in one molecule. When the molecular weight per unit triazine skeleton exceeds 300, variation in foaming ratio and variation in cell diameter may be noticeable. Examples of the compound having a molecular weight per unit triazine skeleton of 300 or less include melamine (chemical name 1,3,5-triazine-2,4,6-triamine), ammelin (1,3,5-triazine-2- Hydroxy-4,6-diamine), ammelide (1,3,5-triazine-2,4-hydroxy-6-amine), cyanuric acid (1,3,5-triazine-2,4,6-triol) ), Tris (methyl) cyanurate, tris (ethyl) cyanurate, tris (butyl) cyanurate, tris (2-hydroxyethyl) cyanurate, melamine isocyanuric acid condensate and the like. These may be used alone or in combination of two or more. Among these, it is preferable to use melamine, isocyanuric acid, and melamine / isocyanuric acid condensate in order to obtain pre-expanded particles having a high expansion ratio with small variations in expansion ratio and cell diameter.

  Furthermore, if necessary, for example, cell nucleating agents such as talc, antioxidants, metal deactivators, phosphorus processing stabilizers, UV absorbers, UV stabilizers, fluorescent brighteners, metal soaps, etc. Stabilizers or crosslinkers, chain transfer agents, lubricants, plasticizers, fillers, reinforcing agents, pigments, dyes, flame retardants, antistatic agents, etc. are added to the base resin to the extent that the effects of the present invention are not impaired. It is good also as a system resin mixture.

  The polypropylene resin particles are dispersed in water in a pressure vessel using a conventionally known method, for example, to form a propylene resin dispersion, and the dispersion is preferably a melting point of the polypropylene resin particles. The polypropylene resin particles are impregnated with water by heating to a temperature in the range of −25 ° C. to + 25 ° C., more preferably −10 ° C. to + 10 ° C. and pressurizing with an inorganic gas such as nitrogen or air. While keeping the temperature and pressure inside the container constant, the polypropylene-based pre-expanded particles are produced by releasing the dispersion of the polypropylene resin particles and water in a lower pressure atmosphere than in the container. When discharging into a low-pressure atmosphere, the low-pressure atmosphere needs to be maintained at 80 ° C. or higher in order to increase the expansion ratio, and is preferably maintained at 90 ° C. or higher and 100 ° C. or lower with high-temperature air or water vapor. . When the temperature is less than 80 ° C., pre-expanded particles having a high expansion ratio cannot be obtained, and the pre-expanded particles shrink due to the effect of cooling the pre-expanded particles immediately after expansion. When the temperature exceeds 100 ° C., it may be difficult to prevent the pre-foamed particles from being fused.

  There are no particular limitations on the sealed container at the time of producing the pre-foamed particles, and any container that can withstand the pressure and temperature in the container at the time of producing the pre-foamed particles may be used. For example, an autoclave type pressure-resistant container may be mentioned.

  In the preparation of the dispersion, as a dispersant, for example, inorganic dispersants such as tribasic calcium phosphate, basic magnesium carbonate, calcium carbonate, and so on, for example, sodium dodecylbenzenesulfonate, sodium n-paraffinsulfonate, α-olefin It is preferable to use a dispersion aid such as sodium sulfonate. Among these, the combined use of tricalcium phosphate and sodium dodecylbenzenesulfonate is more preferable. The amount of dispersant and dispersion aid used varies depending on the type and the type and amount of polypropylene resin used, but usually 0.2 to 3 parts by weight of the dispersant is added to 100 parts by weight of water. It is preferable to add 0.001 to 0.1 parts by weight of a dispersion aid. Moreover, in order to make a polypropylene resin particle favorable in the dispersibility in water, it is preferable to use normally 20-100 weight part with respect to 100 weight part of water.

  The expansion ratio of the polypropylene resin pre-expanded particles obtained by the above production method is 5 to 50 times, preferably 7 to 45 times.

  Moreover, once the pre-expanded particles of 5 times to 35 times are manufactured, the pressure in the pre-expanded particles is made higher than the normal pressure by pressurizing the pre-expanded particles in a sealed container and impregnating with nitrogen, air, etc. Then, the foamed particles may be heated by steam or the like to obtain two-stage foamed pre-foamed particles 50 times or more by a method such as a two-stage foaming method for further foaming.

  Here, the pre-expanded particles thus obtained have two melting point peaks in the DSC curve obtained by differential scanning calorimetry, the lower melting point (hereinafter referred to as the low temperature side melting point) is 143 ° C. or lower, and the low temperature melting is performed. The crystal content ratio is preferably 90% or less, more preferably the low-temperature melting point is 140 ° C. or less and the low-temperature melt crystal content ratio is 70% or less. When the low-temperature melting point is higher than 143 ° C., or when the low-temperature melting crystal content ratio exceeds 90%, the pre-expanded particles are molded into the mold having thin-walled parts in the mold or by a small amount of steam heating. It is difficult to form a molded article with a beautiful appearance when molding. The lower limit for the stable production of pre-expanded particles and the ability to maintain moldability during in-mold molding using the pre-expanded particles is desirably a low-temperature melting point of 130 ° C. and a low-temperature melting crystal ratio of 60%.

  Here, the low-temperature melting crystal amount ratio in the present invention means that when a sample 4 to 10 mg is heated from 40 ° C. to 200 ° C. at a rate of 10 ° C./min in differential scanning calorimetry (DSC), The melting peak calorie α (J / g) of the melting peak (hereinafter referred to as the low temperature peak) based on the crystalline state originally possessed by the base resin of the expanded particles and the melting peak (hereinafter referred to as the high temperature side) from the peak. When the melting peak calorie β (J / g) of the high-temperature peak is defined as the ratio (α / (α + β)) of the total melting peak of the low-temperature peak calorie (hereinafter referred to as the low-temperature DSC peak ratio). ) FIG. 1 shows a schematic diagram of a DSC chart obtained under the above conditions.

  In order to make the pre-expanded polypropylene resin particles obtained by the production method of the present invention into an in-mold foam molded article, for example, a) Pressurizing the foamed particles with an inorganic gas to impregnate the particles with an inorganic gas, A method in which the inner pressure of the particles is applied, and then filled into a mold and heat-sealed with steam or the like (Japanese Examined Patent Publication No. 51-22951). B) Resilience of the particles by compressing the expanded particles with gas pressure and filling the mold. A method of heating and fusing with steam or the like (Japanese Patent Publication No. 53-33996) can be used.

EXAMPLES Next, although this invention is demonstrated further in detail based on an Example, this invention is not limited only to these Examples.
<Measurement of foaming ratio>
The pre-foamed particle density was calculated from the weight of the pre-foamed particles used as a sample and the volume obtained by immersing the sample in ethanol in a volumetric flask, and the base resin density was divided to obtain the expansion ratio.
<Fused pre-foamed particle ratio>
Pre-expanded particles having a weight of 20 to 100 g are placed on a sieve having a mesh opening of 4.75 mm, the sieve is vibrated for 1 minute, and the weight ratio of the weight of the pre-expanded particles remaining on the sieve is calculated to obtain the fused pre-expanded particle ratio. .
Polypropylene resin a: ethylene-propylene random copolymer Melting point 149.6 ° C. Melt flow rate 7.3 g / 10 min
Polypropylene resin b: ethylene-propylene-butene random copolymer Melting point: 145.6 ° C. Melt flow rate: 9.0 g / 10 min
Polypropylene resin c: ethylene-propylene random copolymer Melting point 142.0 ° C Melt flow rate 7.0 g / 10 min
Crystal nucleating agent A: Sodium 2,2-methylenebis (4,6-di-tert-butylphenyl) phosphate Crystal nucleating agent B: Hydroxy-di (tert-butylbenzoic acid) aluminum Crystal nucleating agent C: Bis (4- Methylbenzylidene) sorbitol

Example 1
100 parts by weight of polypropylene resin a is dry blended with 0.1 parts by weight of powdered talc, 0.01 parts by weight of crystal nucleating agent A, and 0.3 parts by weight of melamine as a compound having a triazine skeleton. Extrusion was performed with a screw extruder to obtain polypropylene resin particles. 100 parts by weight (2.4 kg) of the obtained resin particles are put in a 10 L pressure vessel having a stirrer, and 2.0 parts by weight of tribasic calcium phosphate (manufactured by Ohira Chemical Industry Co., Ltd.) and sodium normal paraffin sulfonate 0 Dispersed in 200 parts by weight of water in the presence of 0.03 parts by weight. While stirring the dispersion, the dispersion was heated to 165.4 ° C., and then the internal pressure of the pressure vessel was adjusted to 2.98 MPa. Next, the discharge valve with an inner diameter of 25 mm installed at the lower part of the pressure vessel is released, and the pellet and water dispersion are brought to an atmospheric temperature of 100 ° C. with water vapor through a circular orifice with a diameter of 4 mm attached to the rear end of the discharge valve. Release into the adjusted atmosphere to obtain pre-expanded particles having an expansion ratio of 17.0 times and a low-melting crystal ratio of 72%. The fusion pre-expanded particle ratio was 0%.

(Example 2)
Instead of using the polypropylene resin used in Example 1, the polypropylene resin b was used, 0.05 part by weight of the crystal nucleating agent b, 1 part by weight of isocyanuric acid as a compound having a triazine skeleton were extruded, and the dispersion liquid was 159. Foaming was carried out in the same manner as in Example 1 except that the pre-expanded particles were discharged into the atmosphere adjusted to 90 ° C. with water vapor, adjusted to an internal pressure of 1.99 MPa, and heated to 0.8 ° C. Pre-expanded particles having a magnification of 14.5 times and a low-melting crystal ratio of 70% were obtained. The ratio of the fused pre-expanded particles was 0.5%.

Example 3
Instead of using the polypropylene resin used in Example 1, the polypropylene resin b was used, the crystal nucleating agent c was used in an amount of 0.1 part by weight instead of 0.01 part by weight, and the compound having a triazine skeleton was used. 3 parts by weight of an ethylene ionomer resin obtained by crosslinking an ethylene- (meth) acrylic acid copolymer with sodium ions was added, and the dispersion was heated to 160.5 ° C. to adjust the internal pressure of the pressure vessel to 2.00 MPa. Except for this, pre-expanded particles having the expansion ratio of 14.2 times and the low-temperature melting crystal ratio of 77% were obtained in the same manner as in Example 1. The fusion pre-expanded particle ratio was 0%.

Example 4
Instead of using the polypropylene resin used in Example 1, the polypropylene resin c was used, and 0.05 part by weight of the crystal nucleating agent c was used instead of 0.01 part by weight of the crystal nucleating agent a, and the dispersion was maintained at 154.0 ° C. By heating, adjusting the internal pressure of the pressure vessel to 3.00 MPa, and releasing the pre-expanded particles into the atmosphere adjusted to 90 ° C. with water vapor, the expansion ratio was 17.3 times by the same method as in Example 1. Pre-expanded particles having a low-temperature melting crystal ratio of 81% were obtained. The fusion pre-expanded particle ratio was 0%.

(Comparative Example 1)
In the same manner as in Example 1, except that the crystal nucleating agent a used in Example 1 was not added, and the dispersion was heated to 166.3 ° C. and adjusted to an internal pressure of 1.98 MPa in the pressure vessel, an expansion ratio of 14 Pre-expanded particles having a ratio of low-temperature melting crystal of 78% were obtained. The ratio of the fused pre-expanded particles was 25%.

(Comparative Example 2)
Except that the crystal nucleating agent b used in Example 2 was not added and the dispersion was heated to 160.5 ° C., a foaming ratio of 14.0 times and a low-temperature melting crystal ratio of 85% were obtained in the same manner as in Example 2. Pre-expanded particles were obtained. The ratio of the fused pre-expanded particles was 55%.
As shown in Examples 1 to 4 and Comparative Examples 1 and 2, it can be seen that by adding the crystal nucleating agent to the polypropylene resin, the fused pre-expanded particles can be dramatically suppressed.

Schematic diagram of DSC chart of polypropylene resin pre-expanded particles

Explanation of symbols

α Low temperature melting peak heat β High temperature melting peak heat

Claims (3)

Particles composed of a polypropylene resin composition are dispersed in an aqueous dispersion medium in a closed container, the particles are heated to a temperature equal to or higher than the softening temperature of the polypropylene resin composition, and water as a dispersion medium is used as a blowing agent in the particles. In the method for producing polypropylene resin pre-expanded particles that are pre-expanded by being discharged into an atmosphere at a pressure lower than the internal pressure in the sealed container and 80 ° C. or higher after impregnation into
The polyolefin resin preliminary , wherein the polypropylene resin composition contains one or more crystal nucleating agents selected from an organic phosphorus crystal nucleating agent, an aluminum crystal nucleating agent, and a sorbitol crystal nucleating agent A method for producing expanded particles. In the measurement of the pre-expanded polypropylene resin particles by differential scanning calorimetry, has two melting points, low temperature-side melting point of 143 ° C. or less and a low-melting crystal amount ratio is equal to or less than 90%, claim 2. A method for producing pre-expanded polypropylene resin particles according to 1. Polypropylene resin composition, characterized by containing at least one member selected from compounds having a hydrophilic polymer, a triazine skeleton, a manufacturing method of polypropylene resin pre-expanded particles according to claim 1 or 2.

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