JPS5876230A - Manufacture of polypropylene resin foamed particle - Google Patents

Abstract

PURPOSE:To improve the heat resistance, cushioning property and strength of a molded body, by incorporating a volatile foaming agent or an inorganic gas into foamed particles that are prepared by cutting polypropyrene resin foamed strands, and heating the particles so that they are further allowed to foam. CONSTITUTION:A polypropylene resin is mixed with a foaming agent at high temperatures under high pressures using an extruder, and a cellular strand having a foaming rate of 1.1-20, an open cell rate of 30% or below and a cell diameter of 0.6mm. or below is extruded from a die into a low pressure zone. The cellular strand is cut into foamed partilces, a volatile foaming agent or inorganic gas is incorporated therein, and the foamed particles are heated further to be allowed to foam in steps so that foamed particles having a foamed ratio of 10-50 is obtained. As the foaming agent used in extrusion foaming, are mentioned azodicarboxylic amides, etc. and as the volatile foaming agent are mentioned propane, dicyclotetrafluoloethane, etc.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a method for producing foamed polypropylene resin particles that can be applied to a method of heating resin particles containing a blowing agent and molding them into pre-expanded particles to obtain a molded article of a desired shape. , Further details 1-< relate to a method for producing foamed polypropylene resin particles for obtaining a foamed molded product having excellent heat resistance, low density, and excellent cushioning properties and strength.

Conventionally, polystyrene and polyethylene have been widely used as base resins for foam molded products formed by in-mold foam molding. When polystyrene is used as a base resin, it is excellent in terms of foaming agent retention, processability, and rigidity, but on the other hand, it is inferior in brittleness, physical properties at low temperatures, and chemical and oil resistance. When used as a foam, foaming agent retention, processability, and rigidity are inferior, but a product that is flexible, strong, and has excellent low-temperature properties and chemical resistance can be obtained. As described above, both have advantages and disadvantages, and currently they are used differently depending on the purpose. Particularly major drawbacks of both are that polystyrene foam has a low heat resistance temperature of 9 (lc or less) and is brittle and easily broken, while polyethylene foam has a low heat resistance temperature of 90°C or less. Due to the softness of the raw material resin, polyethylene, the foaming ratio that exhibits properties suitable for use as a cushioning material is relatively low, resulting in high raw material costs.

In view of the above-mentioned current situation, the present inventors have developed a product that has flexibility, toughness, low-temperature properties, and chemical resistance comparable to that of foamed polyethylene, and has a high heat resistance temperature of 100°C or higher, which is relatively high. The present invention has been completed as a result of extensive research in order to find a raw material resin and a method for producing foamed particles thereof that provide properties suitable for use as a cushioning material at high magnification.

That is, in the present invention, polypropylene resin is mixed with a foaming agent under high temperature and pressure using an extruder, etc., and the foaming ratio is 1.
1 to 20 times, Renzu bubble rate 80 cm or less, bubble diameter 0.6 m
After extruding the foamed strand in a low-pressure region and forming it into foamed particles, a volatile blowing agent or inorganic gas is added to impart foaming ability and heated, resulting in a two-stage process. Perform foaming after the eyes,
The present invention relates to a method for producing highly expanded particles of polypropylene resin which are foamed in multiple stages to obtain expanded particles with an expansion ratio of 10 to 50 times.

The blowing agents used for extrusion foaming in the present invention include (5) chemical blowing agents that decompose with heat and generate gas, such as azodicarbonamide, dinitrone pentamethylene tetrami/,
p-toluenesulfonyl hydrazide, etc., and ◎ boiling point -5
0-100°C hydrocarbons or halogenated hydrocarbons, such as propane, butane, penta/, hexane, heptane, or dichlorofluoromethane, dichlorofluoromethane, trichloromonofluoromethane, dichloromethane, monochloromethane, Foaming agents include dichlorotetrafluoroethane, trichlorotrifluoroethane, perfluorocyclobutane, and the like, and both groups of blowing agents can be used alone or in combination.

The polypropylene resin used in the present invention is a polypropylene homopolymer or a copolymer of propylene and other vinyl monomers, but it is preferable that the foamed particles have a high fusion property during foam molding and a temperature that is too high during foam molding. In view of this, random copolymers of propylene and ethylene, and random terpolymers of propylene/ethylene/butene are preferred.

In the present invention, when the blowing agent is a chemical blowing agent of group (5), the mixing of the polypropylene resin and the blowing agent under high temperature and high pressure using an extruder or the like is performed by blending the polypropylene resin with the chemical blowing agent, This can be achieved by supplying the foaming agent to an extruder, and when the foaming agent is a volatile foaming agent of the group (c), it can be achieved by pressurizing the foaming agent through a barrel hole provided in the middle of the extruder.

The foaming ratio of the extruded foam strand of the present invention is 1.1 to 20
However, if the expansion ratio exceeds 20 times, the shape of the bubbles becomes distorted, and the bubble diameter becomes large and tends to become uneven. If the expansion ratio is less than 1.1 times, the degree of foaming is too low. This is because foaming in the second and subsequent stages becomes difficult. Preferably it is 1.5 to 10 times, more preferably 1.5 to 5 times. The foaming ratio can be controlled by selecting the type and amount of the foaming agent used.

The open cell ratio of the extruded foam strand of the present invention is 30 or less, but this is because if the open cell ratio exceeds 30, the foaming ratio will not increase in the second and subsequent stages of foaming, and is preferably 2 (1% or less.

The open cell rate also depends on the type and amount of the blowing agent used, but once the type and amount of the blowing agent is determined, the extrusion foaming temperature is lowered as much as possible and the viscosity of the polypropylene resin melt is increased. By this, a foamed strand with a low open cell ratio can be obtained.

The cell diameter of the extruded foam strand of the present invention is 0.6 ym or less; however, if the cell diameter exceeds 0.6 mb,
When the foaming ratio increases further in the foaming stages after the stage, the cell diameter also expands, and in some cases, the bubble diameter increases to 1.0.
It can be more than 1m long. If the cell diameter is 1.0a or more, the flexibility and cushioning properties of the foamed molded product will deteriorate. Therefore, the cell diameter of the extruded foam strand is 0.6 mm or less, preferably 0.3 mm or less.

The bubble diameter depends on the type and amount of the blowing agent used and the extrusion foaming temperature, and by adjusting these conditions, the bubble diameter can be reduced to 0.6 m or less, but preferably, for example, talc, calcium carbonate, silica, A nucleating agent such as a mixture of sodium chloride and citric acid may be added to the suitable polypropylene resin.

The porous die for extrusion foaming used in the method of the present invention has a cross-sectional shape of a circle, a rectangle, a triangle, a square, a star, or the like. For the purpose of using the foamed particles obtained by extrusion foaming for in-mold foam molding, a porous die with a circular cross section is preferable because it increases the filling efficiency of the foamed particles, and the cross-sectional diameter is in the range of 0.1 to 10 m. . The cross-sectional diameter is 0.
If it is less than 1 m, it will be difficult to manufacture the die, the die pressure during extrusion foaming will be too high, and the cross-sectional diameter will be 10 m.
If the extrusion foaming exceeds this value, the foamed particles obtained by extrusion foaming will be too large, and depending on the molded product, it may be impossible to mold the curvature or thin wall part when molding the foamed particles obtained from the second and subsequent foaming steps. This is not desirable. Preferred cross-sectional diameters range from 1 to 5 NL.

The number of holes in the multi-hole die ranges from 2 to 100, preferably from 3 to 20. If the number of holes in the multi-hole die is less than 2, the number of extruded foam particles obtained will decrease, and if it exceeds 100, the holes will be spaced quite closely, although it depends on the die dimensions.
This is because foams extruded from adjacent holes fuse together. Note that the cross-sectional area and number of holes of the porous die can be appropriately determined depending on the scale of the extruder and the amount of extrusion.

In the method of the present invention, the device for cutting the strand-shaped foam extruded from the multi-hole die of the extruder into strips to form foamed particles is a rotary pelletizer device used in a normal pellet cutter. be done. It is preferable to use the pelletizer device as close to the porous die as possible.

This is because if a foamed strand extruded from a multi-hole die is cut into particles as close to the die as possible, the cut foamed particles still have an expansion foaming capacity, so new skin is formed on the cut surface. Since a layer is formed, when used as foamed particles for in-mold foaming, an extremely favorable result is obtained in terms of complete filling of the fused interface between the particles.

Note that it is preferable that the pelletizer device has a variable rotation speed of the cutter blade. This is because the longitudinal length of the foam particles can be cut to a desired size by adjusting the rotation speed.

In the present invention, the low-pressure region usually means under atmospheric pressure, but also includes under reduced pressure.

The open cell ratio in the present invention refers to the ratio of open cells to all cells, and the expansion ratio refers to how many times the volume of foamed particles is compared to the volume before foaming. These measurements are performed as follows.

d: Resin density (P/cA) W: Weight of expanded particle sample (y) V: Volume of expanded particle sample (c4) ■: Air comparison hydrometer (for example, Toshiba Beckman, air comparison hydrometer 930) true volume of the expanded particle sample (cli) −v open cell ratio (chi) = xio.

■ Expansion ratio (times), -V/- Furthermore, in the present invention, polypropylene resin is extruded into strands through a porous gouer, the foamed strands are cut to form foamed particles, and then a volatile blowing agent or The present invention provides a method for producing foamed polypropylene resin particles, which is characterized in that foaming is carried out in multiple stages by incorporating an inorganic gas to impart foaming ability and heating to perform foaming in the second and subsequent stages.

Polypropylene has greater rigidity and strength than polyethylene, and when producing foam with the same cushioning performance, it can be made with a lower density than polyethylene, which reduces raw material costs and is economically advantageous. However, technology to foam polypropylene to a high degree is required. The method of the present invention solves this technical problem by carrying out foaming in multiple stages. In other words, in the first stage, foaming is performed to form foamed particles with a relatively low magnification by an extrusion foaming method, and then the foamed particles are volatilized. It is characterized in that it contains a foaming agent or an inorganic gas to impart foaming ability and performs second and subsequent foaming by heating. Similar foaming methods are known for polyethylene (JP-A-54-81475, JP-A-54-52169, JP-A-55-27801, etc.), but originally polyethylene was impregnated with a foaming agent and then expanded in one step. However, it is possible to foam to a predetermined high magnification, and the main purpose of this foaming method is to reduce variations in the foaming magnification. However, in the case of polypropylene, the blowing agent type,
Even if the amount of foaming agent impregnated is selected, it is difficult to achieve a high degree of foaming in one stage of foaming, and the desired high foaming ratio can only be obtained by the method of the present invention.

Volatile blowing agents used in the second and subsequent stages of foaming of the present invention include hydrocarbons or halogenated hydrocarbons with a boiling point of -50 to 50°C, such as linear hydrocarbons such as propane, butane, and pentane; Halogenated hydrocarbons such as monochloromethane, dichloromethane, monochloroethane, trichloromonofluoromethane, dichlorodifluoromethane, dichloromonofluoromethane, trichlorotrifluoroethane, dichlorotetrafluoroethane, etc., preferably Dichlorodifluoromethane, propane, dichlorotetrafluoroethane, etc. or a mixture thereof.

As a method of imparting foaming ability for the second and subsequent stages to the foamed particles obtained in the first stage extrusion foaming, a volatile blowing agent may be included in the foamed particles, and an inorganic gas is foamed under a pressurized atmosphere. It may be contained within the particles.

It is preferable to perform the second and subsequent foaming stages using an inorganic gas, since the cell structure is more uniform than when a volatile foaming agent is used. As an inorganic gas, for example, an inorganic gas whose main component is nitrogen, such as air, is advantageous because it is low in cost.
Carbon dioxide alone can also be used.

When using the method of the present invention to obtain high-magnification foamed particles by foaming polypropylene resin foam particles obtained in the first stage of extrusion foaming in multiple stages from the second stage onwards, increasing the number of foaming stages will result in a higher It is advantageous to obtain a foaming ratio, and the variation in the foaming ratio is reduced, but when considering the manufacturing economy required for foaming equipment and foaming, it is 2 to 5' stage, including extrusion foaming. Preferably in 2 to 3 stages,
Furthermore, it is particularly advantageous to obtain expanded particles of the desired expansion ratio in two stages. In this case, it is preferable that the foamed particles obtained by the first stage extrusion foaming have an expansion ratio of 1.1 to 20 times, and the foamed beads of the second stage have an expansion ratio of 10 to 50 times. It should be noted that the relationship between the expansion ratio of the foamed particles obtained by the first-stage extrusion foaming and the expansion ratio of the foamed particles obtained after the second-stage foaming is not uniquely determined; It depends on the method of imparting foaming ability, that is, the type and amount of the volatile blowing agent or inorganic gas used to impart foaming ability in the second stage.

In the present invention, methods for incorporating a foaming agent consisting of a volatile foaming agent in order to perform foaming in the second and subsequent stages include (1)
Any of a method of impregnating in a liquid phase, (2) a method of impregnating in a gas phase, and (3) a method of impregnating in an aqueous dispersion system can be adopted. However, in the case of liquid phase impregnation (1), if a blowing agent with a high solvent capacity for the resin is used, components in the resin will be extracted into the liquid phase, and the amount of blowing agent used will be large, resulting in increased costs. It has the disadvantage that it takes a long time. In the case of (3) impregnation using an aqueous dispersion system, there is a drawback that the foamed particles must be separated from water after the impregnation is completed, which complicates the process. On the other hand, in the case of (2) gas phase impregnation, there are no drawbacks as mentioned above, and the expanded particles can be taken out as they are after impregnation and subjected to the foam molding process, which is advantageous because the process can be simplified.

Furthermore, since polypropylene resin has inferior heat stability compared to polyethylene, relatively large amounts of compounding agents such as antioxidants are added, and in order to prevent these compounding agents from being lost through extraction etc. Particularly preferred is impregnation.

The expanded polypropylene resin particles obtained by the method of the present invention are further given foaming ability during in-mold foam molding by further containing an inorganic gas, and then filled into a mold and heated. As a result, a high-magnification foam molded product having a uniform cell structure, good fusion between foam particles, and a smooth surface can be obtained.

Heating conditions during heat foaming and in-mold foam molding vary depending on the type of resin and foaming agent, but when using steam as the heating medium, the steam temperature is 110 to 160°C and the heating time is about 10 seconds to 3 minutes. It can be done within a range. In this case, the foaming machine and molding machine used are those normally used for foaming and molding polyethylene, and may be used as they are or with some modification.

As described above, the method of the present invention is a method for producing high expansion ratio foam particles by a multi-stage foaming method of polypropylene resin, in which the first stage foam is continuously extruded as a foam strand using an extruder, and then this It is characterized by cutting into foamed particles, and has the advantage that foamed polypropylene resin particles can be obtained extremely efficiently compared to the conventional method of impregnating with a blowing agent and then heating and foaming.

The foam molded article produced by in-mold foam molding of the polypropylene resin foam particles finally obtained by the method of the present invention is
Compared to foamed polyethylene molded products, due to the properties of polypropylene resin, it has a higher heat resistance temperature of over 100°C, has a relatively low density, has excellent strength and cushioning properties, and has flexibility and temperature control properties comparable to those of foamed polyethylene molded products. , has chemical resistance,
In particular, it is suitably used as a cushioning material, a heat insulating material, a packaging material, etc.

Hereinafter, the present invention will be explained in detail with reference to Examples.

Example 1 1.0 parts by weight of talc was added as a nucleating agent to a foaming extrusion equipment in which a 4,0 extruder and a 50ψ extruder were connected, which had 114 barrel holes containing 1 ml of volatile foaming agent in the middle of the barrel. A random copolymer of propylene and ethylene (M'
I9, 1Ji4.5 mol% containing ethylene) at about 5kyZ
Butane was fed as a foaming agent through the barrel hole of a 40 ψ extruder at a speed of about 0.7 mm and 9 amps. The tip of the 50ψ extruder has a cross section of 1 and a circular shape of 2.
A multi-hole die having four holes of ψm/m was installed, and a pellet and cutter with a four-wheel blade were provided adjacent to the multi-hole die. As a result, the foamed strand extruded from the porous gouer was used with a pellet cutter to obtain foamed polypropylene resin particles having a substantially circular cross section and a cylindrical shape with an approximate size of 4 m pieces x 5 am. The foamed particles and foaming ratio are approximately 1
0 times, the open cell ratio was 8.5%, the cell diameter was about 0.3 mm, and it had a uniform cell structure.

The foamed particles were heated to 711 (degrees 80℃, 11 min force 25 icq)
/d (gauge) nitrogen addition + UE, kept under atmosphere for 4 hours to impregnate nitrogen into the foamed particles, then 2-5 kg
Foamed particles with an expansion ratio of approximately 25 times were obtained by heating and foaming with water vapor at a volume of 1/2 cm for 30 seconds.

The foamed particles are heated again at a temperature of 25 kq/cd and a pressure of 25 kq/cd.
The foamed particles were held in a pressurized nitrogen atmosphere for 3 hours to impregnate nitrogen into the foamed particles, and then filled into a mold for 2.5kg/c-
The molded product obtained by heating with water vapor for 40 seconds has a density of about 0.
It was a molded article with a smooth surface in which each particle was well fused at a rate of 0.023 fl/am.

Example 2.3.4 As blowing agents, dichlorodifluoromethane, dichlorotetrafluoroethane, and a mixture of equal weights of dichlorodifluoromethane, tritalolmono 7, and fluoromethane were used in the amounts listed in the attached table. Otherwise, extrusion foaming was performed in the same manner as in Example 1 to obtain polypropylene resin 5 bright foam particles,
Then, after the second stage foaming by the method described in Example 1,
The molding process was carried out after considering the molding instructions. These results are shown in Table 1.

Example 5 A random terpolymer of propylene, ethylene, and butene (MI
6. Polypropylene resin foam particles having an approximately circular cross section and cylindrical dimensions of approximately 3 ψ mm x 3.5 mm were prepared in substantially the same manner as in Example 1, except that ethylene content (ethylene content: approximately 3 to 4 mol%) was used. Obtained.

The foaming ratio of the foamed particles is approximately 2.3 times, and the open cell ratio is 6.
%, and the bubble diameter was about 0.2 mm. The foamed particles were kept in a nitrogen pressurized atmosphere at a temperature of 80°C and a pressure of 25 kg/aJ (gauge) for 5 hours to impregnate nitrogen into the foamed particles, and then heated with water vapor of 2.6 k4/t:rlt for 40 hours. By heating for seconds and foaming, foamed particles with an expansion ratio of about 20 times were obtained. The expanded particles are heated again at a temperature of s o '
c.

The foamed particles were impregnated with nitrogen by holding them under a nitrogen pressurized atmosphere of 25 pc9/cm for 3 hours, and then filled into a mold in step a and heated with 2.5 kg/d steam for 40 seconds. The molded article obtained had a density of approximately 0.02□5 g/c+#, a smooth surface, and a flexible body.

□Comparative Example 1 In Example 1, the amount of butane used for extrusion foaming was
．． The procedure was the same as in Example 1, except that the amount of water was supplied at a rate of 6 to 9 hours. The foamed polypropylene resin particles obtained here were foamed particles with approximate dimensions of 5φ x 6mm, with an expansion ratio of about 25 times, an open cell ratio of 35%, and a cell size of 0.7 in the order of non-uniformity. Ta. The foamed particles were heated at a temperature of 80°C and a pressure of 25kg/C.
The foamed particles were held in a pressurized nitrogen atmosphere for 4 hours to impregnate nitrogen into the foamed particles, and then heated and foamed with 2.5 to 9/cd water vapor for 40 seconds, resulting in a foaming ratio of approximately 32 times. The origin of
Foam particles were obtained. The foamed particles were heated again at 80°C and at a pressure of 25k.
After impregnating the foamed particles with nitrogen by holding them in a nitrogen pressurized atmosphere of tiAa (gauge) for 3 hours, they were filled into a mold for forming.2.
The molded product obtained by heating with water vapor of 5 to 9/(?-) for 40 seconds has a density of 0.026 g/crl and has an uneven surface.
The fusion between the foamed particles was poor and could not be put to practical use.

Chapter 1 Table “HaB58-76230<7>

Claims (9)

[Claims] (1) Polypropylene resin □ is mixed with a foaming agent under high temperature and pressure using an extruder, etc., and the foaming ratio is 1.
Extruded into a low pressure region as a foamed strand with a cell diameter of 1 to 20 times, an open cell ratio of 30% or less, and a cell diameter of 0.6 or less,
Next, the foamed strands are cut to form foamed particles, and the foamed particles are made to contain a volatile foaming agent or an inorganic gas to give them foaming ability, and are heated to carry out the second and subsequent foaming steps. A method for producing expanded polypropylene resin particles, which comprises foaming the particles to obtain expanded particles with an expansion ratio of 10 to 50 times. (2) The polypropylene resin is a propylene and ethylene norandom copolymer or a random terpolymer of hapropylene, ethylene, and butene.
) The method for producing expanded polypropylene resin particles as described in item 1. (3) The foaming agent used for extrusion foaming is a chemical foaming agent that decomposes with heat and generates gas, or has a boiling point of 50 to 100'L:
The method for producing foamed polypropylene resin particles according to claim (1), which is a hydrocarbon, a halogenated hydrocarbon, or a mixture thereof. (4) The volatile blowing agent contained in the polypropylene resin foam particles for the second and subsequent foaming steps has a boiling point of -50
The method for producing expanded polypropylene resin particles according to claim (1), wherein the polypropylene resin foam particles are hydrocarbons or halogenated hydrocarbons having a temperature of -50°C. (5) The method for producing expanded polypropylene resin particles according to claim (4), wherein the volatile blowing agent is propane, di-chlorotetra-fluoroethane, dichlorodifluoromethane, or a mixture thereof. (6) The method for producing expanded polypropylene resin particles according to claim (1), wherein the inorganic gas is a mixed gas containing nitrogen as a main component. (7) Polypropylene resin foam 1 obtained by extrusion foaming
The method for producing expanded polypropylene resin particles according to claim 1, wherein the particles are made to contain an inorganic gas in the second and subsequent stages to impart foaming ability and are foamed in multiple stages by heating. (8) The foamed polypropylene resin particles obtained by extrusion foaming are made to contain an inorganic gas to impart foaming ability, and are heated to carry out the second stage of foaming. 7) The method for producing expanded polypropylene resin particles as described in section 7). (9) When incorporating a volatile blowing agent into the polypropylene resin foam particles obtained by extrusion foaming, the polypropylene resin foam particles according to claim (1) are impregnated in the gas phase. Manufacturing method. OI The method for producing expanded polypropylene resin particles according to claim (1), wherein a nucleating agent is added to the polypropylene resin during extrusion foaming.