JPH0859876A - Expandable polypropylene resin particle - Google Patents

Abstract

PURPOSE: To provide expandable polypropylene resin particles which can give a foam which is prevented from causing chipping, cracking, etc., of the particles around the cut part by dispersing specified base resin particles in a dispersion medium in a sealed container, feeding a volatile blowing agent into the container, heating the entire mixture, and releasing the mixture into a low-pressure zone. CONSTITUTION: A propylene/2-8 C α-olefin copolymer is mixed with at least one ethylene copolymer selected from among an ethylene/α-olefin copolymer resin of a density of 0.87-0.93g/cm<3> , an ethylene/α-olefin copolymer rubber of a Mooney viscosity of 15-90 and an ethylene copolymer containing 3-30wt.% unsaturated ester or ether as a comonomer to obtain a polypropylene resin having a bending rigidity (JIS-K7106) of 4000-8000kg/cm<2> . A base resin prepared by mixing this resin with 0.05-3.0wt.% metal salt of a fatty acid and 0.05-2.0wt.% fatty acid amide is dispersed in a dispersion medium, and the resulting dispersion is placed in a sealed container. A volatile blowing agent is fed to the container and the resulting mixture is heated to or above the softening point of the base resin and released into a low-pressure zone.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to expanded polypropylene resin particles. More specifically, the molded product obtained by fusing the particles is cut or punched to form a cushioning packaging material or display. The present invention relates to a polypropylene-based resin foamed particle suitable for producing a molded product which is free from chipping or cracking of particles around the blade portion and peeling or wrinkling of the cut surface when creating characters and the like.

[0002]

2. Description of the Related Art In-mold foam moldings of polyolefin resins such as polypropylene and polyethylene are superior to polystyrene foam moldings in heat resistance, chemical resistance, impact resistance and compression elastic recovery, and are cores for bumpers. Material, helmet core material,
It is used in various containers and packaging containers.

Among them, polypropylene has higher heat resistance, impact resistance, and rigidity than polyethylene, and in order to obtain the same cushioning performance and strength, a higher expansion ratio can be set, which is economically advantageous and widely used. in use. The above products are generally molded using a mold that matches the intended final shape, but if there is little demand for products of that shape or if the delivery time is uncertain, each shape will have its own shape. Since it is too costly to manufacture the combined mold and to replace the mold, machine processing such as slice cutting and press cutting from the plate-shaped molded body, or combining two or more cut products to obtain the final shape. Is the current situation.

[0004]

When the foamed molded product is cut or punched, the polypropylene-based foam is unlikely to undergo extreme cracking as in the polystyrene-based foam, but particles around the edge of the blade are formed. There is a problem that chips and cracks occur, and the cut surface has plucking and wrinkles called "pulling deviation", especially the smaller the bubble diameter, the stronger the tendency, and the product value is low However, there is a problem in that various problems are caused due to the blistering and the like.

The present invention has been made in view of the above conventional problems, and even if cutting or punching is performed,
It is intended to provide a polypropylene-based resin expanded particle suitable for producing a molded product which suppresses the occurrence of chipping or cracking of particles around the insert blade portion and does not cause peeling or whipping on the cut surface.

[0006]

Means for Solving the Problems As a result of various studies to solve the above-mentioned problems, the present inventors have surprisingly found that
By adding to the resin adjusted to a specific rigidity range, in combination with an additive known to reduce the cell diameter in the production of expanded particles by heated steam (batch type expansion method), the above-mentioned object is achieved. We have found that we can achieve it.

That is, the polypropylene resin expanded particles of the present invention are prepared by dispersing base resin particles containing polypropylene resin as a main component in a dispersion medium in a closed container, and then supplying a volatile foaming agent into the closed container. A polypropylene resin foamed particle obtained by heating the dispersion liquid to a temperature equal to or higher than the softening point of the base resin, and then releasing the dispersion liquid into an atmosphere of a pressure lower than the pressure in the closed container, The base resin has a bending rigidity of 4 measured according to JIS K7106.
000 to 8000 kg / cm ² , and the base resin particles contain 0.05 to 3.0% by weight of a metal salt of a fatty acid and 0.05 to 2.0% by weight of a fatty acid amide. .

The polypropylene resin used in the present invention is a homopolymer of propylene, α having 2 to 8 carbon atoms.
-Propylene / α-olefin copolymers obtained by copolymerizing olefins and the like are used.
A propylene / butene-1 copolymer containing 20% by weight is preferred. Also, with polypropylene resin, the density is 0.8
7 to 0.93 g / cm ³ of ethylene / α-olefin copolymer resin, ethylene / α-olefin copolymer rubber having Mooney viscosity of 15 to 90, unsaturated ester or unsaturated ether of 3 to 30% by weight A polypropylene-based resin composition comprising one or more ethylene-based copolymers selected from copolymerized ethylene-based copolymers, and in particular, the main component polypropylene-based resin is α having 2 to 8 carbon atoms.
-Olefins, more preferably those composed of the above composition which is a propylene / butene-1 copolymer containing 5 to 20% by weight of butene-1 are preferable because of excellent buffering performance, impact resistance and heat resistance. .

The flexural rigidity of these base resins measured according to JIS K7106 is 4000 to 8000 kg /
cm ² , preferably 5000 to 7500 kg / cm ² . If the flexural rigidity is too low, the molded product obtained by using the obtained expanded particles has large flexibility and tensile elongation, and cracks and chips during cutting are less likely to occur, but the compressive strength of the molded product is low. Therefore, it becomes impossible to reduce the weight of the molded body, and it is necessary to increase the thickness of the cushioning material.
As a result, the number of products stored per package is reduced, which is not economical.

Further, if the bending rigidity is too high, the flexibility and tensile elongation of the molded article molded using the obtained expanded particles decrease, and during cutting, chipping of particles around the insert edge part and There is a tendency for cracks to occur and for the insert to be depressed, resulting in a poor appearance. In the present invention, the density is 0.87 to 0.93 g / cm ³ mixed with the polypropylene resin.
As the ethylene / α-olefin polymer resin, the ethylene / α-olefin polymer resin is obtained by copolymerizing ethylene with one or more α-olefins such as propylene, butene-1, pentene-1, octene-1, and 4-methylpentene-1. Things are used.

As the ethylene / α-olefin copolymer rubber having a Mooney viscosity of 15 to 90, ethylene and one or more of α-olefins such as propylene, butene-1, pentene-1 are randomly selected. A low crystalline or amorphous rubbery copolymer obtained by copolymerization with
A copolymer of a diene monomer may be used as the third component.

Unsaturated ester or unsaturated ether is 3 to.
As the ethylene copolymer copolymerized with 30% by weight, an ethylene copolymer containing vinyl acetate, ethyl acrylate or the like is used. The Mooney viscosity of ethylene / α-olefin copolymer rubber is JIS K630.
0, using an L-shaped rotor at a test temperature of 100 ° C. for 1 minute of preheating, and a rotor operating time of 4 minutes (ML1 + 4,100
(° C). The bending rigidity is JIS
It is measured according to K7106.

In the present invention, the above-mentioned base resin is
A specific amount of fatty acid metal salt and fatty acid amide is added. Examples of the fatty acid metal salt used include calcium stearate, zinc stearate, magnesium stearate,
Examples thereof include metal salts of fatty acids having 12 to 30 carbon atoms such as lead stearate, calcium laurate, zinc laurate, calcium ricinoleate, and zinc ricinoleate.

Examples of the fatty acid amide used include fatty acid amides having 12 to 30 carbon atoms such as stearic acid amide, oleic acid amide and erucic acid amide. Of these, a combination of calcium stearate and stearic acid amide or erucic acid amide is preferable because of its good compatibility with the base resin.

The metal salt of a fatty acid is 0.05 to 3.1 parts by weight, preferably 0.5 to 3.1 parts by weight, based on 100 parts by weight of the base resin.
By adding 2.0 parts by weight, 0.0
5 to 3.0% by weight is contained. If the content is too small, there is a problem that the effect of improving pluckiness and blistering is small, and if it is too large, the bleed out of the additive to the surface of the foam particles increases, and the problem of poor fusion bonding of the molded body occurs. There is.

Further, the fatty acid amide is 0.05 to 2.0 parts by weight, preferably 0.1 to 100 parts by weight of the base resin.
.About.1.0 parts by weight to give a base resin of 0.1.
It is contained in an amount of 05 to 2.0% by weight. If the content is too small, there is a problem that the effect of improving pluckiness and blistering is small, and if it is too large, the bleed out of the additive to the surface of the foam particles increases, and the problem of poor fusion bonding of the molded body occurs. There is. In the case of mechanical cutting processing such as punching cutting, these fusion defects cause the foamed particles around the insert edge part of the molded product to be easily chipped or cracked, and in severe cases, the strength of the molded product decreases. cause.

Although these additives are mixed by kneading as described in detail below, most of the added amount is contained in the resin without loss. The base resin used in the present invention includes other additives such as attack polypropylene, wax,
Resins with plasticizing effects such as petroleum resins, antioxidants, ultraviolet absorbers, lubricants, antistatic agents, flame retardants, fillers, metal deactivators, pigments, dyes, crystal nucleating agents, etc., as needed. Can be included. The amount to be contained is determined in consideration of economical efficiency and required quality, but in general, it is 1 in the base resin.
It is 7% by weight or less, preferably 5% by weight or less. For the above additives and the additives used in the present invention, generally solid mixing by kneading is used. For example, the mixture is kneaded using a screw type extruder, a Banbury mixer, a mixing roll or the like, and granulated into particles of an appropriate size. In this case, any method such as a strand cutting method, an underwater cutting method, a freeze pulverization method, and a melt spraying method may be used.

In the present invention, the expanded particles are produced by the Docan method (Patent Office, March 63, Ed., Illustrated IPC).
That is, the base resin particles are dispersed in a dispersion medium in a closed container,
Then, a volatile foaming agent is supplied into the closed container, the dispersion is heated to a temperature equal to or higher than the softening point of the resin particles, and then the dispersion liquid is discharged into an atmosphere having a pressure lower than the pressure in the closed container. It

At this time, it is preferable to pressurize the inside of the container with air or nitrogen gas to facilitate the discharge. As a volatile swelling agent,
For example, butane, pentane, hexane, heptane and other aliphatic hydrocarbons, trichlorofluoromethane, dichlorofluoromethane, tetrachlorodifluoroethane, dichlorotetrafluoromethane, methylene chloride, halogenated hydrocarbons such as ethyl chloride. These are used alone or in combination of two or more. In addition, air, nitrogen gas, carbon dioxide gas, or other inorganic gas may be used to impart foamability to foam. The addition amount of the volatile expansion agent varies depending on the type of expansion agent and the intended bulk density of the expanded particles, but is usually 10 to 80 relative to 100 parts by weight of the resin particles.
Parts by weight.

As the dispersant for dispersing the resin particles in water, aluminum oxide, titanium oxide, calcium carbonate,
Inorganic suspension agents such as basic magnesium carbonate, tribasic calcium phosphate, magnesium pyrophosphate; polyvinyl alcohol, methylcarboxycellulose, water-soluble polymeric protective colloid agents such as N-polyvinylpyrrolidone; sodium dodecylbenzenesulfonate, alkane sulfone Anionic surfactants such as acid soda, sodium alkyl sulfate ester, sodium olefin sulfate ester, acylmethyl taurine, sodium dialkyl sulfosuccinate and the like can be mentioned.

Among these, it is preferable to use tricalcium phosphate having a particle size of 0.01 to 0.8 micron in combination with sodium dodecylbenzenesulfonate as a suspension aid. This fine tricalcium phosphate is obtained by reacting phosphoric acid in water at a ratio of 0.60 to 0.67 mol with respect to 1 mol of calcium hydroxide. The amount of water as the dispersion medium is 100 to 100 parts by weight of the resin particles.
It is 0 part by weight, preferably 200 to 500 parts by weight. 1
If the amount is less than 50 parts by weight, resin particles are likely to block each other during heating and pressurization. If it exceeds 1000 parts by weight, the production of expanded beads is reduced, which is not economical.

When a gaseous or liquid foaming agent is supplied to a dispersion of polypropylene resin particles dispersed in water with a dispersant in a closed container and heated to a temperature above the softening point of the resin, this heating As a result, the pressure in the container rises. At this time, the foaming agent is impregnated into the resin particles. Then, by discharging the resin particles together with the dispersion medium through a slit provided in the lower part of the closed container, a discharge port such as a nozzle, under a low-pressure atmosphere (generally at atmospheric pressure) from the closed container, the polypropylene resin foamed particles are can get.

In this case, in order to maintain the internal pressure in the container during discharging, it is preferable to supplement the inorganic gas or the foaming agent from the outside. Further, in the production of this expanded particle,
Before or after filling the foaming agent into the closed container,
It is preferable to supply an inorganic gas such as nitrogen, helium, argon, carbon dioxide, or air into the closed container to apply pressure.

The inorganic gas may be supplied before or after heating the dispersion liquid. Supply of an inorganic gas such as air, nitrogen gas, helium, argon or carbon dioxide gas into the closed container facilitates the impregnation of the foaming agent into the resin particles, and is useful for obtaining low density polypropylene resin expanded particles.
Further, there is an advantage that the pressure difference when releasing the contents in the container under a low pressure is increased and the foaming efficiency is increased.

The expanded particles released into the atmosphere are dried (cured) in a room at 30 to 65 ° C. to remove the water adhering to the surface, and used for molding. Various known methods can be used as the molding method. A. After the foamed particles have been impregnated with a volatile foaming agent in advance to give the foamed particles a secondary foaming ability, the mold is filled and heated with steam to cause secondary foaming and the foamed particles are fused, and then the mold is cooled. , A method of obtaining a molded body. B. Put the foamed particles in a closed container, then air, inorganic gas such as nitrogen is pressed into the container to increase the pressure in the cells of the expanded particles to give a secondary foaming ability, and the particles are filled in a mold, A method of heating by steam for secondary foaming and fusing particles, and then cooling the mold to obtain a molded body (pressure aging method, Japanese Patent Publication No. 59-23731). C. The foamed particles were placed in a mold whose pressure was increased to 1.0 to 6.0 kg / cm ² G with a pressurized gas, and 0.5 kg / cm ² from the mold.
While compressing using the above-mentioned high pressurized gas, it is divided into a plurality of times and sequentially filled, the mold pressure during filling is kept at the mold pressure described above, and then the mold pressure is returned to atmospheric pressure after the completion of filling. Then heat with steam to fuse the expanded particles, the formula of the expanded particles at that time,

[0026]

[Equation 1] [In the formula, W, V, and ρ represent the following, respectively. ] W: Weight of molded product (g) V: Volume of molded product (liter) ρ: Compressibility expressed by bulk density (g / liter) of expanded particles at atmospheric pressure is controlled to 40 to 70%. After that, the mold is cooled to obtain a molded body (Japanese Patent Laid-Open No. 62-132132).
No. 5).

D. 0.5-5.0 kg / cm with pressurized gas
^In the mold boosted to ² G, 0.5 k from the mold pressure in advance
The expanded particles to which a gas internal pressure is obtained, which are obtained by pressurizing the gas for 1 hour or more using a pressured gas higher than g / cm ^{2, are} higher than the pressure inside the mold by 0.5 kg / cm ² or higher. Using the above, it is divided into a plurality of times and sequentially filled, and during filling, the in-mold pressure is kept at the above-mentioned in-mold pressure, and after completion of the filling, the in-mold pressure is returned to atmospheric pressure and then heated by steam. A method in which expanded particles are fused and the compression ratio of the expanded particles represented by the above formula is controlled to less than 40% (excluding 0%), and then the mold is cooled to obtain a molded product. E. Expanded particles themselves are filled with expanded particles having secondary expansion ability in a cavity under normal pressure, or filled in a mold under pressure and heated by steam for secondary expansion and fusion of expanded particles, then , A method of cooling a mold to obtain a molded article (Japanese Patent Laid-Open No. 128709/1987 and No. 63709/1988).
256634, JP-A-63-258939, JP-A-63-107516).

Any of the above molding methods may be used, and the molding method is selected in consideration of the properties of the expanded particles, the shape of the molded body, the density and the like.

[0029]

EXAMPLES The present invention will be described in detail below with reference to examples and comparative examples. "Parts" and "%" described in these examples are based on weight. Example 1 Propylene / Butene-1 Random Copolymer (Butene-1
Content 16.0% by weight, flexural rigidity 7500 kg / c
m ² ), 0.5 part by weight of calcium stearate and 0.1 part by weight of erucic acid amide were added to 100 parts and blended for 10 minutes with a ribbon blender, and then this mixture was melt-kneaded at 230 ° C. in an extruder. It was extruded in a strand shape to obtain a pellet.

Then, in a closed container, 600 parts of water, 100 parts of the pellet, and a third particle having a particle size of 0.3 to 0.5 micron.
Charge 1.0 part of calcium phosphate and 0.007 part of sodium dodecylbenzenesulfonate, and then supply 22 parts of butane gas into the closed container under stirring, and further nitrogen gas until the pressure in the closed container reaches 7 kg / cm ² G. Pressurized with. While stirring the contents of the closed container to 135 ° C. over about 1 hour, hold the same temperature for 10 minutes, and then open the valve installed at the bottom of the closed container and disperse from the discharge nozzle to atmospheric pressure. The liquid was discharged to cause foaming.
The expanded polypropylene resin particles thus obtained had a bulk density of 18 g / liter, an average cell diameter of 210 microns, and a closed cell rate of 87%.

(In-mold foam molding) The obtained foamed particles were mixed with 50
After drying and curing at ℃ for 8 hours, 2kg / c in a pressure vessel
When the internal pressure was applied for 24 hours with pressurized air of m ² G, the internal pressure of the expanded particles was 0.8 kg / cm ² G. Next, the foamed particles were filled in a mold having steam holes pressurized to 1 kg / cm ² G while being compressed with a compressed gas of 1.5 kg / cm ² G while being divided into a plurality of times, and then 2.5 k
A steam of g / cm ² G was introduced to heat and fuse, followed by cooling with water for 90 seconds, further cooling for 10 seconds, taking out the molded body from the mold, followed by drying and curing at 60 ° C. for 24 hours. The molded body had a density of 22 g / liter, had few surface gaps, and had no irregularities. Further, when it was fractured from the central part and visually observed, it was an excellent molded product in which about 80% of the cross section of the expanded particles were fused.

With respect to the compressive strength measured according to NDS Z-0504, the stress when compressing the 50% compact was 1.8 kg / cm ² . A sample with a length of 600 mm, a width of 500 mm, and a thickness of 50 mm was cut out from this molded product, and the following punching test was performed. The molded product was cut without crushing of the insert blade portion, chipping or cracking of particles around the insert blade portion, etc. The surface condition was good.

Punching test; thickness 1 mm, height 10 mm
The sample was placed on a steel blade of, and a compression platen was lowered from above to compress and cut the sample. At that time, the collapse of the blade portion, the cracks around the blade portion, and the state of the cut surface were determined according to the following criteria.

Crushing of the blade portion; ◯: Crushing of 1 mm or less from the surface of the molded product to the cut surface. Δ: There is a crush of 1 to 3 mm from the surface of the molded product to the cut surface. X: There is a crush of 3 mm or more from the surface of the molded product to the cut surface.

Cracking around the blade part; ◯: No chipping or cracking of particles around the blade part. Δ: 1 to 3 chips / chips and / or 1 cm to 3 cm cracks around the edge part. X: 4 or more chips / cuts and / or 3 cm or more cracks around the insert edge.

Cut surface condition: Good: The cut surface is smooth or only folds having a depth of 1 mm or less are present. Δ: There are folds with a depth of 1 to 2 mm. ×: There are folds with a depth of 2 mm or more. In addition, the restoration rate in the compression direction of the above compression-cut sample was 96%.

Examples 2-4 and 6-9 and Comparative Examples 1-
10 and 12 The same procedure as in Example 1 was carried out except that the base resin for the resin particles, the additive, and the foaming conditions were changed. The results are shown in Tables 1 to 4.

Examples 5, 10 and 11 and Comparative Example 11 The procedure of Example 1 was repeated except that no internal pressure was applied to the expanded beads.

[0039]

[Table 1]

[0040]

[Table 2]

[0041]

[Table 3]

[0042]

[Table 4]

[0043] Note * 1 ... A; calcium stearate * 2 ... B; erucamide * 3 ... C; stearic acid amide _{* 4 ... C 2 / C 3} ; ethylene-propylene rubber

[0044]

EFFECTS OF THE INVENTION According to the present invention, since a specific additive is used in combination, when cutting a molded product molded with the additive, chipping or cracking of particles around the edge of the blade and peeling of the cut surface may occur. It is possible to suppress the crushing of the molded body during cutting without causing the softening and the like.

Claims (4)

[Claims] 1. A base resin particle containing a polypropylene resin as a main component is dispersed in a dispersion medium in a closed container, and then a volatile foaming agent is supplied into the closed container to obtain a softening point of the base resin or higher. A polypropylene resin foamed particle obtained by heating the dispersion liquid to a temperature and then releasing the dispersion liquid under an atmosphere of a pressure lower than the pressure in the closed container, wherein the base resin is in accordance with JIS K7106. The measured flexural rigidity is 4000 to 8000 kg / cm ² , and the base resin particles contain 0.05 to 3.0% by weight of metal salt of fatty acid and 0.05 to 2.0% by weight of fatty acid amide. Polypropylene resin foamed particles characterized by the above. 2. A polypropylene resin having 2 to 8 carbon atoms.
The polypropylene-based resin expanded particles according to claim 1, which is a propylene / α-olefin copolymer obtained by copolymerizing the α-olefin. 3. A base resin, a propylene / α-olefin copolymer obtained by copolymerizing an α-olefin having 2 to 8 carbon atoms, and ethylene / α having a density of 0.87 to 0.93 g / cm ^3. -Olefin copolymer resin, Mooney viscosity 15
Ethylene-α-olefin copolymer rubber of 90 to 90, one or more ethylene copolymers selected from ethylene copolymers obtained by copolymerizing 3 to 30% by weight of unsaturated ester or unsaturated ether. The polypropylene-based resin expanded particles according to claim 1, which are composed of a united body. 4. The expanded polypropylene resin particles according to claim 1, wherein the metal salt of fatty acid is calcium stearate, and the fatty acid amide is stearic acid amide or erucic acid amide.