JPS5865734A - Foamed polypropylene resin particles and preparing same - Google Patents

Abstract

PURPOSE:To prepare the titled foamed particles, with heat resistance, yielding a foam product with a low density, shock-absorbing properties, and great strength, by incorporating a specific foaming agent in PP resin particles and allowing to foam in multiple steps. CONSTITUTION:PP resin particles (ethylene content 1-10wt%; MI 0.1-20; Vicat softening pt. (load 1kg) 100-150 deg.C) selected from propylene/ethylene random copolymer and propylene/ethylene/butene random terpolymer are impregnated with a low b.p. org. compd. foaming agent (e.g. butane) to allow to expand 3-20 times the original volume with heat. The foamed particles are impregnated with a low b.p. org. compd. (e.g. dichlorodifluoromethane) or an inorg. gas (e.g. N2 gas), and the resulting mixt. is allowed to foam with heat, yielding a foamed PP resin particles, expansion 10-50 times the original volume; closed cell content >=65%.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to foamed polypropylene resin particles that can be applied to a method of heating resin particles containing a blowing agent to form pre-expanded particles and molding them to obtain a molded article of a desired shape. It is. More specifically, the present invention relates to foamed polypropylene resin particles and a method for producing the same for obtaining a foamed molded product having excellent heat resistance, low density, and excellent cushioning properties and strength.

Polystyrene and polyethylene are commonly used as base resins for foam molded products formed by in-mold molding.

When polystyrene is used as the base resin, it has excellent foaming agent retention, processability, and rigidity, but it is brittle.

Low-temperature properties and chemical resistance are poor, but when polyethylene is used as a base resin, foaming agent retention, processability,
Although the rigidity is poor, it is flexible and strong, and has excellent low-temperature properties and chemical resistance. As described above, both have advantages and disadvantages, and the current situation is that they are used differently depending on the purpose. The major disadvantages of both are that polystyrene foam has a low heat resistance and is brittle and easily breaks, while polyethylene foam has a low heat resistance and is soft due to the raw material polyethylene. Therefore, the foaming ratio, which exhibits physical properties suitable for use as a cushioning material, is relatively low, resulting in high raw material costs.

In view of the current situation as described above, the inventors of the present invention have developed a product with flexibility, toughness, and low-temperature properties comparable to those of foamed polyethylene.

As a result of intensive research to find a raw material resin that has chemical resistance, high temperature resistance, and physical properties suitable for use as a cushioning material at relatively high magnification, and a method for producing foamed particles thereof,
The present invention has now been completed.

That is, in the present invention, the closed cell ratio is 65 coefficient or more.

The present invention relates to expanded polypropylene resin particles characterized by an expansion ratio in the range of 10 to 50 times, and a method for producing the same.

The closed cell ratio in the present invention is the ratio of closed cells (cells separated and sealed by cell partition walls) to the total number of cells, and the expansion ratio is the ratio of the volume of foamed particles to the volume of resin particles before foaming. It refers to how many times the number is. These measurements are performed as follows.

d: Density of resin (1/crn8) W: Weight of foamed grain sample ■ = Volume of foamed grain sample ■ = Air comparison hydrometer (for example, Toshiba Peckman, air comparison hydrometer model 930) f: Using If the true volume closed cell ratio of the measured expanded particle sample is less than 65 width, the expansion pressure of the expanded particles during molding is insufficient, so a molded product with good fusion bonding cannot be obtained.
Moreover, the appearance of the molded body is impaired and the cushioning performance is also deteriorated.

The polypropylene resin particles used in the present invention are preferably random copolymers of propylene and ethylene or random terpolymers of propylene, ethylene, and butene. Foaming is possible using a polypropylene homopolymer or a block copolymer of propylene and ethylene, but a uniform cell structure cannot be obtained and the expansion ratio is difficult to increase. On the other hand, random copolymer of propylene and ethylene also haflopylene, ethylene.

When a random terpolymer of butene is used.

Expanded particles with a uniform cell structure and a high expansion ratio can be obtained. The reason for this is not yet clear, but random copolymerization of monomers such as ethylene and butene lowers the crystallinity of polypropylene and improves its viscoelasticity in the foaming temperature range. It can be boiled.

Random copolymers of propylene and ethylene or random terpolymers of tahablobylene, ethylene, and butene are
Ethylene content 1-10 wt.
C, 2,16kQ) 0.1 to 201 and Vicat softening point (JIS-K 7206. Load [q) 100 to 15
Preferably, the temperature is 0°C. If the ethylene content is less than 1% by weight, it becomes close to a homopolymer, making it impossible to obtain a uniform cell structure and making it difficult to increase the expansion ratio. When the ethylene content exceeds 10% by weight, the rigidity and strength, which are characteristics of polypropylene, decrease and the material becomes close to that of low-density polyethylene. If the MI is less than 0.1, the fluidity during foaming will be poor and foaming will be difficult; if the MI exceeds 20, the fluidity will be too high and the foaming ratio will increase, and the foam will shrink after foaming. It becomes easier to do. Although the Vicat softening point has a strong correlation with the ethylene content, it is an important index from the viewpoints of foaming temperature range, strength, and heat resistance.

If the Vicat softening point (load 1 kti) is less than 100°C, the heat resistance and strength will be poor, and if it exceeds 150°C, the foaming temperature will be too high, making it impractical. In addition, atactic polymers with 8 to 1
It is preferable to contain 0 weight gold.

Furthermore, in the present invention, polypropylene resin particles contain a blowing agent made of a low-boiling point organic compound, and after performing the first stage of foaming by heating, the polypropylene resin particles are converted to a low-boiling point organic compound.

A compound or an inorganic gas is added to impart foaming ability, and the second and subsequent stages of foaming are performed by heating.

The present invention provides a method for producing expanded polypropylene resin particles characterized by foaming in multiple stages.

Polypropylene is more rigid than polyethylene.

When producing a foam with greater strength and the same cushioning performance, polypropylene can be economically advantageous due to lower density and reduced raw material costs compared to polyethylene. A technology to foam the foam to a high degree is required.

The method of the present invention solves this technical problem and is characterized by performing one foaming in multiple stages to obtain foamed polypropylene resin particles with a high expansion ratio and a high closed cell ratio.

A similar foaming method is also used for polyethylene (Japanese Patent Laid-Open No. 1987-
81475.54-52169.55-27801)
However, it is possible to foam polyethylene to a predetermined expansion ratio even in one foaming process, and the main purpose of such a foaming method is to reduce the variation in expansion ratio.

However, in the case of polypropylene, even if one blowing agent type, one blowing agent impregnated amount, etc. are selected, it is difficult to achieve a high degree of foaming with one foaming, and the desired high expansion ratio can only be obtained by the method of the present invention. .

The blowing agent consisting of a low-boiling organic compound used in the present invention is a hydrocarbon or a chlorogenated hydrocarbon with a boiling point of 150 to 50°C, such as propane, butane, pentane, monochloromethane, dichloromethane, etc. , monochloroethane, trichloromonofluoromethane, dichloroμsifμoμmethane, dichloromonofluoromethane, trichloroμtrifluoroμethane, dichlorotetrafluoroethane. When trying to obtain foamed particles with a high expansion ratio, it is advantageous to increase the expansion ratio in the first stage of foaming because the number of times of foaming in the second and subsequent stages is reduced. In order to do it efficiently.

It is desirable that the first stage expanded particles have a uniform cell structure and a high closed cell ratio. The closed cell ratio of the first stage expanded particles is preferably 8C1 or more.

As the blowing agent used for the first stage of foaming, among the blowing agents listed above, those that have an appropriate solvent ability for the polypropylene resin used, such as propane, butane, and dichlorotetrafluoroethane, have shown good results. give. In the second and subsequent stages of foaming, use a solvent that does not have a very large solvent capacity for the propylene resin used, such as dichlorodifluoromethane.

Dichlorotetra 7M ethane and propane are preferred.

If the acid agent ability for the propylene resin used is too large, one foamed granule will shrink during impregnation with the foaming agent, and a high expansion ratio will not be obtained even if foamed.

As a method of imparting foaming ability to the foamed particles obtained in the first stage of foaming, the above-mentioned low-boiling point organic compound may be contained in the foamed particles, but an inorganic gas may be added to the foamed particles under a pressurized atmosphere. It may be included. It is preferable to perform the second and subsequent foaming steps using an inorganic gas, since the cell structure is more uniform than when using a low boiling point organic compound. As the inorganic gas, for example, an inorganic gas containing nitrogen as a main component, such as air, is advantageous because of its low cost.

When attempting to obtain foamed particles by foaming polypropylene resin particles in multiple stages using the method of the present invention, increasing the number of foaming stages is advantageous in obtaining a high expansion ratio, and also reduces the variation in the expansion ratio of the foamed particles. becomes smaller.

When considering the foaming equipment required for foaming and the economical efficiency of production, the number of steps is 2 to 5, preferably 2 to 8.Furthermore, it is particularly preferable to obtain foamed particles with a desired expansion ratio in two steps. It's advantageous. In the case of two stages, it is preferable that the expansion ratio of the expanded particles in the first stage of foaming is 8 to 20 times, and the expansion ratio of the foamed particles in the second stage of foaming is 10 to 50 times. When trying to obtain foamed particles with a high expansion ratio, it is advantageous to increase the expansion ratio in the first stage as described above, but if you try to increase the expansion ratio in the first stage beyond 20 times, foaming will occur. This is not preferable because it causes a decrease in the closed cell ratio of the grains. Furthermore, if the first stage foaming ratio is less than 3 times, the second stage foaming, especially foaming using an inorganic gas, becomes difficult.

In this way, by increasing the first stage expansion ratio from 3 to 20 times, a second stage expansion ratio of 10 to 50 times can be obtained.

In the present invention, methods for incorporating a blowing agent made of a low-boiling organic compound into particles in order to perform the first and second stage foaming include (1) impregnation in a liquid phase;
Either (2) a method of impregnation in a gas phase or (3) a method of impregnation in an aqueous dispersion system can be used. In the case of (1) liquid phase impregnation, if a blowing agent with a high solvent capacity for the resin is used, the components in the resin will be extracted into the liquid phase, and the amount of blowing agent used will be large, increasing costs. There is a drawback. In the case of (3) impregnation using an aqueous dispersion system, there is a drawback that it is necessary to separate each particle from water after completion of impregnation, which complicates the process. On the other hand, in the case of 2) gas phase impregnation, there is no such drawback, and the particles can be taken out as they are after impregnation and subjected to the foaming process, which is advantageous because the process can be simplified. Furthermore, since polypropylene resin has poor thermal stability compared to polyethylene etc., relatively large amounts of compounding agents such as antioxidants are added, and care must be taken to ensure that these compounding agents are not lost through extraction etc. Phase impregnation is particularly preferred.

The foamed polypropylene resin particles obtained by the method of the present invention are further imparted with foaming ability by the method of containing an inorganic gas as described above, and are then filled into a mold and heated to form a uniform cell structure. It is possible to obtain a molded product with good fusion between particles and a smooth surface.

Heating conditions during foaming and molding vary depending on the type of resin and blowing agent, but when using steam as the heating medium, the steam temperature is 110 to 160°C, and the heating time is 10 seconds to 3.
This can be done within a range of about minutes. The foaming machine and molding machine used in this case are those normally used for foam molding of polyethylene.

It can be used as is or with some modification.

The molded product obtained in this way has a higher heat resistance than a foamed polyethylene molded product due to the characteristics of the polypropylene resin, does not lose its strength and cushioning properties even at a relatively low density, and has the same properties as a foamed polyethylene molded product. It has flexibility, low-temperature properties, and chemical resistance, and is particularly suitable for use as cushioning materials, insulation materials, and packaging materials.

The present invention will be explained below with reference to Examples.

Example 1 Propylene-ethylene random copolymer (density 0.
909/cm8. M I = 9, ethylene content 4
~ 5 壬, Vicat softening point 119 ° C) pellets 100 parts by weight In-butane saturated steam and temperature 8 ° C 1 pressure 10
kg/art! The particles were brought into contact for 4 hours, impregnated with 28 parts by weight of n-butane, and heated and foamed with 1.0 kg/di steam for 40 seconds to obtain foamed particles with an expansion ratio of 18 times. The cell structure of these particles is uniform.

The closed cell ratio was 91.

The foamed particles were held in a nitrogen pressurized atmosphere at a temperature of 80°C and a pressure of 25 kQA for 4 hours to impregnate nitrogen into the foamed particles. , 5 kq/d of steam for 30 seconds to obtain foamed particles with an expansion ratio of 36 times. The cell structure of these particles is uniform, and the closed cell ratio is 9.
I was in charge 2.

The foamed particles were heated again at a temperature of 80°C and a pressure of 25kq/li.
The foamed particles were held in a nitrogen pressurized atmosphere for 3 hours to impregnate nitrogen, and then filled into a mold at 2.5 kfl/etl.
The molded product obtained by heating with 1 of water vapor for 40 seconds has a density of 0,
016 (At 17am8, each particle was well fused and the molded product had a smooth surface.

Example 2 Same as Example 1 except that the impregnated pellet in Example 1 in which the amount of n-butane impregnated was 28 parts by weight was left in the atmosphere and the impregnated amount of n-butane was 10 parts by weight. It was conducted under the following conditions.

The foaming ratio of the foamed particles obtained in the first stage of foaming was 5.
．． The expansion ratio of the foamed particles obtained in the second stage of foaming after nitrogen impregnation was 21 times. After impregnating the expanded particles with nitrogen again, the resulting molded product had a density of 0.028 Q/am'' and each particle was well fused.

The foamed particles with an expansion ratio of 21 times obtained in the second stage of foaming were again impregnated with nitrogen, and a third stage of foaming was carried out to obtain foamed particles with an expansion ratio of 42 times. This was similarly molded to obtain a molded product having a density of 0.0149/cma.

Example 3 In Example 2, expanded particles with an expansion ratio of 5.1 times obtained in the first stage foaming were used. This foamed particle 100
The weight part was brought into contact with saturated vapor of dichlorotetrafluoroethane at a temperature of 80° C. and a pressure of 10 kg/cr for 7 t for 4 hours to impregnate the heavy portion of dichlorotetrafluoroethane f81. This'x 2.8 kq/crA of water vapor
The mixture was heated and foamed for 0 seconds to obtain foamed particles with an expansion ratio of 25 times.

Example 4 The foamed particles obtained in the first stage of foaming in Example 2 and having a foaming ratio of 5.1 times are used. This foamed particle to
o parts by weight of dichlorodifluoromethane were brought into contact with saturated vapor of dichlorodifluoromethane at a temperature of 80° C. and a pressure of 25 kqlcr for 4 hours to impregnate i'8'9ift parts of dichlorodifluoromethane. This was heated and foamed for 40 seconds with water vapor of 2.8 kl/l to obtain foamed particles with an expansion ratio of 21 times.

Example 5 Propylene-ethylene random copolymer (density 0.9
0 f/am8. M I =9. Ethylene content 4
5, Vicat softening point 119°C) 100 parts by weight of pellets was heated to 80°C in dichlorotetrafluoroethane.
C. Impregnated with 23 parts by weight of dichlorotetrafluoroethane by liquid-phase immersion treatment at pressure IQ# (7 meters) for 4 hours.
The foamed particles were foamed to obtain foamed particles 5 times the size of foamed I. The foamed particles were held in a nitrogen pressurized atmosphere at a temperature of 80° C. and a pressure of 25 kg/ctl for 4 hours to impregnate the expanded particles with nitrogen. By heating and foaming with water vapor of .5 kti/crl for 30 seconds, foamed particles with a single expansion ratio of 32 times were obtained.

The cell structure of these particles was uniform, and the cell diameter was smaller than that of Example 1. Further, the closed cell ratio was 93%.

Example 6 The following table shows a series of results obtained under the same conditions as in Example 1 except that the polypropylene resin used was changed.

Claims (1)

[Claims] (1) Closed cell ratio is 65 coefficients or more and one foaming ratio is 10 to 5.
Polypropylene resin foam particles characterized by being in the range of 0 times. (2) The foamed polypropylene resin particles are random copolymers of propylene and ethylene. The expanded polypropylene resin particles according to claim (1), which are random terpolymers of lopylene, ethylene, and butene. (3) Random copolymer of 7" propylene and ethylene, random terpolymer of propylene, ethylene, and butene has an ethylene content of 1 to 10, an MI (melt flow index) of 0.1 to 20, and a Vicat softening point. (Load: 1#g) Polypropylene resin foam particles according to claim 2, which are in the range of 100 to 150°C. The foamed polypropylene resin particles according to claim (3), wherein the polymer contains an atactic polymer having a weight ratio of 8 to 10. r5) The polypropylene resin particles contain a blowing agent made of a low boiling point organic compound, After the first stage of foaming is performed by heating, a low boiling point organic compound or inorganic gas is added to impart foaming ability.The second stage and subsequent stages of foaming are performed by heating, resulting in multi-stage foaming. (6) The polypropylene resin foam according to claim 5, wherein the foamed polypropylene resin particles are a random copolymer of propylene and ethylene or a random terpolymer of propylene, ethylene, and butene. Method for producing foamed resin particles. (7) A random copolymer of propylene and ethylene or a random terpolymer of propylene, ethylene, and butene has an ethylene content of 1 to 10%, and 87II
(Melt flow index) 0°1 to 20 and Vicat softening point (load 1 kq) 100 to 150°C (7) The method for producing polypropylene resin foam particles according to claim (6). (8) A random copolymer of propylene and ethylene or a random or terpolymer of propylene, ethylene, butene contains a 7-tactic polymer having a weight of 3 to 10 tz. A method for producing expanded polypropylene resin particles. (9) A blowing agent consisting of a low-boiling organic compound that is contained in the polypropylene resin particles for the first stage of foaming, and a low-boiling organic compound that is contained in the expanded polypropylene resin particles for the second and subsequent stages of foaming. 5. The method for producing expanded polypropylene resin particles according to claim 5, wherein the hydrocarbon having a boiling point of -50 to 50°C is a halogenated hydrocarbon or a mixture thereof. 00 Claim (9), wherein the blowing agent made of a low-boiling organic compound contained in the polypropylene resin particles for the first stage of foaming is propane, butane, dichlorotetrafluoroethane, or a mixture thereof. The method for producing the polypropylene resin foam particles described above. 0η Hydrocarbons or halogenated hydrocarbons with a boiling point of -50 to 50°C to be contained in the polypropylene resin foam particles for the second and subsequent foaming steps are propane, dichlorotetrafluoroethane, dichloroN-difluoro! The method for producing expanded polypropylene resin particles according to claim (9), which is remethane or a mixture thereof. The method for producing expanded polypropylene resin particles according to claim (5), wherein the inorganic gas is an inorganic gas containing nitrogen as a main component. 0 East After the polypropylene resin particles contain a foaming agent made of a low-boiling point organic compound and perform the first stage of foaming by heating, the second and subsequent stages contain an inorganic gas to impart foaming ability and then heating. A method for producing expanded polypropylene resin particles according to claim (5), which comprises foaming in multiple stages. (2) A blowing agent made of a low-boiling point organic compound is contained in polypropylene resin particles, the first stage of foaming is performed by heating, and then an inorganic gas is added to the foamed particles to impart foaming ability, and then by heating A method for producing expanded polypropylene resin particles according to claim α1, in which a second stage of foaming is performed and the foaming is performed in two stages. 0θ The expansion ratio of foamed particles in the first stage of foaming is 3~
39. The method for producing expanded polypropylene resin particles according to claim 39, wherein the expansion ratio of the expanded particles in the second stage of expansion is 10 to 50 times. 0Q The method for producing foamed polypropylene resin particles according to claim (5), wherein the blowing agent made of a low boiling point organic compound is impregnated in a gas phase.