JPH11100468A - Hydrous polyolefin-based resin composition and pre-expanded particle comprising the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain pre-expanded particles for providing an expanded molding product in a mold, preferably usable for a structural member such as a shock absorber for automobile, etc., requiring a low contraction coefficient, low strain and dimensional accuracy of molding product, heat insulating building material, etc., without using a volatile blowing agent. SOLUTION: This hydrous polyolefin-based resin composition comprises a polyolefin-based resin and a (meth)acrylic acid-based resin salt and has 1-50% water content. Pre-expanded particles obtained by pre-expanding particles from the resin composition with <=50 μm dispersion particle diameters of the (meth) acrylic acid resin salt by using water as a blowing agent, having an apparent expansion ratio of 5-60 times, 80-100% closed cell ratio, 50-100 μm average cell diameter and a specific peak in a DSC curve are produced and used.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a water-containing polyolefin resin composition and pre-expanded particles produced therefrom. More specifically, for example, the present invention relates to a water-containing polyolefin-based resin composition used for producing pre-expanded particles which can be preferably used as a raw material of an in-mold foam molded article, and to pre-expanded particles produced therefrom.

[0002]

2. Description of the Related Art Generally, if the cell diameter of pre-expanded polyolefin resin particles used for in-mold foam molding is too small, the pre-expanded particles can be obtained by in-mold foam molding. Molded products tend to have high shrinkage after in-mold foam molding, and are prone to problems such as distortion of the shape of the molded product (commonly referred to as sink or warp in the industry), and the commercial value of the molded product And the productivity of molded products is reduced.

[0003] Therefore, as pre-expanded particles which have a small shrinkage rate after the in-mold foam molding and do not distort the shape of the molded article,
Carboxyl group-containing polymer 0.1 to 10 with respect to 100 parts (parts by weight, hereinafter the same) of polyolefin resin.
Is used as the base resin and has a cell diameter of 200
A pre-expanded polyolefin resin particle having a diameter of from 500 to 500 μm has been proposed (JP-A-62-115042).

[0004] The pre-expanded polyolefin resin particles have an excellent effect that the molded article after in-mold foam molding has a small shrinkage and does not distort the shape of the molded article.

However, the production of the pre-expanded polyolefin-based resin particles requires a volatile foaming agent, and thus has the disadvantage of increasing the cost. In addition, hydrocarbons such as butane and pentane used as volatile foaming agents, halogenated hydrocarbons such as chlorofluorocarbon (trichlorofluoromethane, dichlorodifluoromethane, etc.), and carbon dioxide are preferably not used from the environmental point of view. .

Therefore, a method has been proposed in which an inorganic gas other than carbon dioxide and water, which are not volatile foaming agents such as hydrocarbons and halogenated hydrocarbons, which are preferably not used from the environmental viewpoint, are used as the foaming agent.

For example, a resin composition obtained by kneading a decomposable foaming agent such as sodium bicarbonate in a base resin in an extruder at a temperature at which the decomposable foaming agent does not decompose is mixed in an airtight container using water or the like as a dispersion medium. At a temperature not lower than the decomposition temperature of the decomposition type foaming agent for a predetermined time, and the inorganic gas (oxygen, nitrogen, helium, neon, carbon dioxide, air, etc.)
A method has been proposed in which one end of the container is opened while the inside of the container is pressurized with a mixture of two or more kinds, and the contents are discharged under a lower pressure atmosphere than the inside of the container to obtain pre-expanded particles (Japanese Patent Application Laid-Open No. 60-1985). -252637).

However, in this method, it is difficult to melt-knead a polypropylene resin or the like having a substantially high softening temperature because the decomposition-type foaming agent may be decomposed in an extruder, and the expansion ratio and the like are also low. limited.

Also, a mixture of a polypropylene resin composition containing an inorganic substance such as aluminum hydroxide and / or calcium carbonate and an aqueous medium is placed in a closed container and heated at a temperature not lower than the softening point of the resin composition. A method has been proposed in which an inorganic gas (normal temperature gas such as nitrogen, air, carbon dioxide, argon, etc.) is used and released into a low-pressure atmosphere to obtain pre-expanded particles (Japanese Patent Application Laid-Open No. 61-4738). .

However, even with this method, only those having a limited expansion ratio can be obtained.

Further, a mixture of a resin composition containing a water-soluble inorganic substance such as borax and, for example, an aqueous medium is placed in a closed container, and a high-pressure inorganic gas (chitter) at a temperature higher than the softening point of the resin composition. A method of obtaining pre-expanded particles by releasing the same under a low-pressure atmosphere using carbon, carbon dioxide, argon, air or the like at a normal temperature (Japanese Patent Laid-Open No. 3233/1991).
No. 47).

However, without using a volatile foaming agent,
When only inorganic gas is used as a foaming agent, it must be held for a long time with high-pressure inorganic gas, and when inorganic gas such as nitrogen or air other than carbon dioxide is used,
After all, only those with a limited expansion ratio can be obtained.

Therefore, in recent years, development of polyolefin resin pre-expanded particles having desired characteristics at low cost and using only an inorganic gas which does not adversely affect the environment without using a volatile foaming agent which has been conventionally required, and at a low cost. Is eagerly awaited.

[0014]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned prior art, and has been made in order to obtain polyolefin resin pre-expanded particles having desired characteristics without using a volatile foaming agent. Containing a polyolefin-based resin and a (meth) acrylic acid-based resin salt and having a water content of 1
A water-containing polyolefin resin composition in which the dispersion particle size of the (meth) acrylic acid resin salt contained in the resin composition is 50 μm or less. The water-containing polyolefin-based resin composition according to claim 1, wherein the water-containing polyolefin-based resin composition according to claim 1 contains a filler in an amount of 10 parts or less based on 100 parts of the polyolefin-based resin. 2) The hydrated polyolefin resin composition according to claim 2, wherein the filler is talc (Claim 3), and the hydrated polyolefin resin according to claim 1, 2 or 3, wherein the polyolefin resin is a polypropylene resin. A composition (claim 4);
The water-containing polyolefin resin composition according to claim 1, wherein the (meth) acrylic acid-based resin salt is an ionomer-based resin obtained by crosslinking the molecules of an ethylene- (meth) acrylic acid copolymer with metal ions. 5) The water-containing polyolefin resin composition according to claim 5 wherein the metal ion is an alkali metal ion (Claim 6), and the pre-foamed particles obtained from the water-containing polyolefin resin composition according to claim 1 Foamed particles, having an apparent expansion ratio of 5 to 60 times,
80-100% closed cell ratio and 50-50 average cell diameter
DSC curve obtained by a differential scanning calorimeter of the pre-expanded particles (provided that the pre-expanded particles 1 to 3 mg
At a heating rate of 10 ° C./min by a differential scanning calorimeter.
In a DSC curve obtained when the temperature is raised to 0 ° C., a peak (high-temperature peak) appears on the higher temperature side than the intrinsic peak of the water-containing polyolefin resin composition, and the melting energy of the peak on the high-temperature side is 4.0 mJ. Pre-expanded particles characterized by having a crystal structure of at least / mg or more (claim 7), and the pre-expanded particles according to claim 7, wherein the water-containing polyolefin-based resin composition contains a filler. Regarding item 8).

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION The water-containing polyolefin-based resin composition of the present invention is a polyolefin-based resin composition containing a polyolefin-based resin and a (meth) acrylic acid-based resin salt. ５０50%.

The polyolefin resin is a main component of the pre-expanded particles, and is a component mainly used for imparting a desired mechanical strength to an arbitrary molded article. , And more than 70%
It is a resin containing 0% or less and containing 50% or less, more preferably 30% or less and 0% or more of a monomer unit copolymerizable with an olefin monomer. Since the olefin monomer unit is contained in an amount of 50% or more, a molded article having light weight and excellent in mechanical strength, workability, electrical insulation, water resistance, and chemical resistance can be obtained. The monomer unit copolymerizable with the olefin monomer has adhesiveness,
It is a component used for modifying transparency, impact resistance, gas barrier properties, antistatic properties, etc., improving moldability, shortening the molding cycle, and the like. % Or more, more preferably 5% or more.

Specific examples of the olefin monomer include:
Ethylene, propylene, butene, pentene, hexene,
Examples thereof include α-olefin monomers having 2 to 8 carbon atoms such as heptene and octene, and cyclic olefins such as norbornene-based monomers. Of these, ethylene and propylene are preferred because they are inexpensive and the physical properties of the obtained polymer are improved. These may be used alone,
More than one species may be used in combination.

Specific examples of the monomer copolymerizable with the olefin monomer include vinyl alcohol esters such as vinyl acetate, and alkyl groups having 1 to 6 carbon atoms such as methyl methacrylate, ethyl acrylate and hexyl acrylate. Examples thereof include (meth) acrylic acid alkyl esters, vinyl alcohol, methacrylic acid, and vinyl chloride. Of these, vinyl acetate is adhesive, flexible,
Methyl methacrylate is preferred in terms of low-temperature properties, and methyl methacrylate is preferred in terms of adhesiveness, flexibility, low-temperature properties, and thermal stability.
These may be used alone or in combination of two or more.

The melt index (MI) of the polyolefin resin is, for example, 0.5 to 30 g / 10 min for a polypropylene resin, and more preferably 1 to 10 g / min.
10 minutes is preferable, and the flexural modulus (JIS K
7203) is, for example, 5,000 to 20,000 kgf / cm ² for polypropylene-based resin,
000~16000kgf / cm ^2, as the melting point, for example, one hundred and twenty-five to one hundred and sixty-five ° C. in polypropylene resin, more preferably from one hundred thirty to one hundred and sixty-five ° C.. When the MI is less than 0.5 g / 10 min, the melt viscosity is too high to obtain pre-expanded particles having a high expansion ratio, and the MI is less than 30 g / 10 min.
If the amount exceeds the above range, the melt viscosity with respect to the elongation of the resin at the time of foaming is low, and the foam tends to break, and the open cell ratio tends to increase. Further, when the bending strength is less than 5000 kgf / cm ² , the mechanical strength of the molded article composed of the pre-expanded particles is low to provide as a product, and it is 20,000 kgf / cm ^2.
If it exceeds cm ² , the physical properties of the pre-expanded particles tend to be rigid but brittle, and cannot be used for molding. Further, when the melting point is less than 125 ° C., when the polypropylene resin is used, the ethylene content is high, and when the property of the polypropylene resin is not reflected in the pre-expanded particles and exceeds 165 ° C., the prepared pre-expanded The molding pressure of the particles tends to be high, and the molding equipment tends to be extremely expensive.

Specific examples of the polyolefin resin include, for example, an ethylene-propylene random copolymer,
Polypropylene resins such as ethylene-propylene-butene terpolymer, polyethylene-polypropylene block copolymer, and homopolypropylene; low-density polyethylene, medium-density polyethylene, high-density polyethylene, linear low-density polyethylene, ethylene-vinyl acetate Copolymer,
Polyethylene resins such as ethylene-methyl methacrylate copolymer; polybutene, polypentene and the like. The polyolefin-based resin may be used in a non-crosslinked state, or may be used after being crosslinked by peroxide or radiation. These may be used alone or in combination of two or more. Among the polyolefin-based resins, the polypropylene-based resin is easy to obtain pre-expanded particles having a high expansion ratio, and the molded article composed of the obtained pre-expanded particles has good mechanical strength and heat resistance. It can be preferably used in the present invention.

The (meth) acrylic acid-based resin salt has a water content of 1 to 50% when the composition of the present invention is water-containing, and the water impregnated in the water-containing polyolefin resin composition is used as a foaming agent. The (meth) acrylic acid-based resin and the metal ion form a salt.

In the (meth) acrylic acid-based resin salt, the (meth) acrylic acid-based resin is (meth) acrylic acid 0.1%.
1 mol% or more, further 10.0 mol% or more and 100 mol% or less, ethylene 0 mol% or more and 99.9 mol% or less, further preferably 90.0 mol% or less. And copolymerizable monomers (eg (meth)
Methyl acrylate, butyl (meth) acrylate and i-butyl (meth) acrylate) up to 10 mol%,
Further, it is a resin obtained by (co) polymerizing 5 mol% or less.

The (meth) acrylic acid is a monomer used to convert a (meth) acrylic resin into a hydrophilic polymer by introducing a carboxyl group into the (meth) acrylic resin and converting it into a salt. And ethylene is a monomer used to improve the compatibility with the polyolefin-based resin. Further, if necessary, a copolymerizable monomer can be obtained (meth ) A monomer used for adjusting the properties of the acrylic resin.

Among the (co) polymerization ratios of the monomers forming the (meth) acrylic acid-based resin, ethylene 50 to 9
9 mol%, more preferably 90 to 96 mol%, 1 to 50 mol% of (meth) acrylic acid, furthermore 4 to 10 mol%, and if necessary, a monomer copolymerizable with these 0
In the case of copolymerized from 10 to 10 mol%, furthermore, from 0 to 5 mol% (so-called ionomer resin component), since it contains a large amount of ethylene units, it has good compatibility with the polyolefin resin, It is preferable because a certain water content required in the present invention can be obtained.

On the other hand, (meth) acrylic acid 50 to 100 mol%, further 96 to 100 mol%, ethylene 0 to 50 mol%
Mol%, more preferably 0 to 4 mol%, and if necessary, 0 to 10 mol% of a monomer copolymerizable therewith,
Further, in the case of copolymerized from 0 to 5 mol% (resin component of poly (meth) acrylate polymer),
Since it contains a large amount of (meth) acrylic acid units, a polymer having a high hydrophilicity can be obtained by converting a carboxyl group into a salt, and thus it is preferable in that a small amount of use increases the water content.

Further, 70 to 99 mol% of the ethylene unit, 1 to 30 mol% of the (meth) acrylic acid unit and, if necessary, a monomer having a copolymerizability with these are used.
Resin salt (ionomer resin) containing from 5 to 5 mol%, 70 to 100 mol% of (meth) acrylic acid unit, 0 to 30 mol% of ethylene unit and copolymerizable with these if necessary. When a resin salt containing a monomer (0 to 5 mol%) (poly (meth) acrylate-based polymer) is used in combination, the (meth) acrylic acid-based resin salt has good compatibility with the polyolefin-based resin. It is preferable because they are compatible with each other and have a high water content. When used in combination, the proportion of the ionomer resin is preferably 70 to 90%, and the content of the poly (meth) acrylate polymer is preferably 10 to 30% from the viewpoint of not impairing the compatibility with the polyolefin resin.

The metal ions for converting the (meth) acrylic acid resin into a metal salt include, for example, alkali metal ions such as sodium ion and potassium ion, and transition metal ions such as zinc ion. . Since the amount of metal ions introduced (degree of ionization) depends on the amount of carboxyl groups contained therein, it cannot be unconditionally limited, but usually, it is necessary to obtain the water content necessary to obtain pre-expanded particles having desired characteristics. Is a carboxyl group 10
40 mol% or more with respect to 0 mol%, further 60 mol%
It is preferable that this is the case. The upper limit is 100 mol%.

Specific examples of the (meth) acrylic acid-based resin salt include, for example, an alkali metal ion such as sodium ion and potassium ion, and a zinc ion such as zinc ion between ethylene- (meth) acrylic acid copolymer molecules. Ionomer resins crosslinked with transition metal ions, poly (meth) acrylates such as sodium polyacrylate, sodium polymethacrylate, potassium polyacrylate, potassium polymethacrylate, zinc polyacrylate, and zinc polymethacrylate Polymers. These may be used alone or in combination of two or more. Among the (meth) acrylic acid-based resin salts, ethylene-
Ionomer resins in which the molecules of the (meth) acrylic acid copolymer are crosslinked with alkali metal ions such as sodium ions and potassium ions or metal ions such as zinc ions, especially ionomer resins in which the metal ions are alkali metal ions. It is preferable because it has excellent dispersibility in a polyolefin-based resin and a desired high water-content water-containing polyolefin-based resin composition can be obtained by using a relatively small amount.

The water content at the time of the water content is the water content under the water vapor pressure at the melting point of the polyolefin resin (the temperature at the top of the melting peak as measured at a heating rate of 10 ° C./min by DSC). Yes, specifically, it is obtained as follows.

That is, 50 g of the water-containing polyolefin resin composition particles, 150 g of water, 0.5 g of powdery basic tribasic calcium phosphate and 0.03 g of sodium n-paraffin sulfonate were placed in a 300 cc pressure-resistant ampoule as a dispersant. Then, heat treatment is performed for 3 hours in an oil bath set to the melting point of the polyolefin resin used after sealing. After cooling to room temperature, the resin was taken out, washed thoroughly with water to remove the dispersant, and the weight (X) of the water-containing particles of the obtained water-containing polyolefin resin composition from which the adhering water was removed was determined. After drying in an oven set at a temperature 20 ° C. higher than the melting point of the resin for 3 hours, and cooling to room temperature in a desiccator, the weight (Y) was determined.
Formula (I):

[0031]

(Equation 1)

Means a value determined in accordance with In addition,
Even when the water-containing polyolefin-based resin composition contains components other than the polyolefin-based resin and the (meth) acrylic acid-based resin salt, for example, a filler, the water content in the present invention is not limited to the polyolefin-based resin and the (meth) acrylic-based resin. It is a value obtained as a ratio of the water content to the total amount of the acid-based resin salt.

The water content is 1 to 50% as described above, but is preferably 3 to 30%. If the water content is too low, the apparent expansion ratio will be less than 5 times, and if it is too high, the dispersibility of the particles in the aqueous dispersion medium will decrease. In this case, the particles are aggregated, and it is difficult to obtain uniform pre-expanded particles.

The proportion of the polyolefin resin and the (meth) acrylic acid resin salt used in the water-containing polyolefin resin composition of the present invention is not particularly limited as long as the water content is within a predetermined range when water is contained. No,
Since it differs depending on the type of each component used, etc., it cannot be specified unconditionally.
The amount of the (meth) acrylic acid-based resin salt is 0.05 part or more, more preferably 0.5 part or more, 30 parts or less, and further 10 parts or less. If the amount of the (meth) acrylic acid-based resin salt is too small, a water-containing polyolefin-based resin composition having a predetermined water content tends to be difficult to obtain. Production stability and foaming characteristics during the production of pre-expanded particles become poor, and it becomes difficult to impart excellent mechanical strength and heat resistance to the molded product obtained from the pre-expanded particles, and suppress dimensional changes during water absorption Tends to be difficult to perform.

The dispersed particle size of the (meth) acrylic resin salt in the water-containing polyolefin resin composition of the present invention is 50 μm or less, and preferably 30 μm or less. When the dispersed particle size of the (meth) acrylic acid-based resin salt exceeds 50 μm, the water-containing water cannot be uniformly dispersed in the water-containing polyolefin-based resin composition,
Pre-expanded particles having a high expansion ratio and a uniform cell diameter cannot be obtained. The lower limit of the dispersed particle size of the (meth) acrylic acid-based resin salt is 1.0 μm, and further 10.0 μm.
Is preferable because it hardly changes the physical properties of the polyolefin resin.

The dispersion particle size is determined by cutting particles (pellets) from the water-containing polyolefin resin composition into thin films using a diamond cutter in two directions, ie, the cross-sectional direction and the side direction of the cylindrical pellets. The two samples prepared in this manner are stained by the RuO ₄ staining method, measured using a transmission electron microscope (JEM-1200EX manufactured by JEOL Ltd.), and imaged as a photograph.

The method for reducing the dispersed particle size of the (meth) acrylic acid-based resin salt to 50 μm or less is not particularly limited, and any method may be used as long as the dispersed particle size is 50 μm or less. In addition to the method of giving a force, it is preferable that a unit from a (meth) acrylic acid-based resin salt and a polyolefin monomer to be dispersed is contained in the (meth) acrylic acid-based resin salt as a copolymer.

As described above, the water-containing polyolefin-based resin composition of the present invention contains a filler to obtain pre-expanded particles having a high expansion ratio and to provide a cell nucleating agent for the pre-expanded particles. Is also good.

The filler is roughly classified into an inorganic filler and an organic filler.

Specific examples of the inorganic filler include talc, calcium hydroxide and calcium carbonate. These inorganic fillers may be used alone or in combination of two or more. Among these inorganic fillers, talc is preferred because it gives pre-expanded particles having uniform cells and high expansion ratio.

The organic filler is not particularly limited as long as it is solid at a temperature equal to or higher than the softening temperature of the polyolefin resin. Specific examples of the organic filler include a fluororesin powder, a silicone resin powder, and a thermoplastic polyester resin powder.
These organic fillers may be used alone or in combination of two or more.

The average particle size of the filler is such that pre-expanded particles having uniform cells and a high expansion ratio are produced, and a molded article having excellent mechanical strength and flexibility is obtained from the pre-expanded particles. 0.1-50 μm, further 1-10
It is preferably μm. When the average particle diameter exceeds 50 μm, the bubble diameter tends to be too large, and when the average particle diameter is less than 0.1 μm, it is difficult to form foam nucleus points, and the moldability tends to deteriorate.

The amount of the filler is preferably at least 0.01 part, more preferably at least 0.1 part based on 100 parts of the polyolefin resin, in order to obtain the effect of the use. 10 parts or less, more preferably 5 parts or less, in order to develop excellent fusion properties when molding the pre-expanded particles and obtain a molded article having excellent mechanical strength and flexibility from the pre-expanded particles. It is preferred that

The polyolefin-based resin composition containing the polyolefin-based resin, the (meth) acrylic acid-based resin salt, and a filler optionally added is usually prepared by using an extruder, a kneader, a Banbury mixer, a roll, or the like. It is preferable to melt-knead and then shape the particles into a desired particle shape that can be easily used for preliminary foaming, such as a columnar shape, an elliptical columnar shape, a spherical shape, a cubic shape, and a rectangular parallelepiped shape. The particles obtained are usually 0.9
４4.5 mg / grain.

The pre-expanded particles from the water-containing polyolefin resin composition may be, for example, a water-containing polyolefin resin containing the polyolefin resin, a (meth) acrylic acid resin salt, and, if necessary, a filler. The particles from the composition are dispersed in an aqueous dispersion medium in a closed container, and the particles are heated to a temperature equal to or higher than the softening temperature of the polyolefin resin, and the water content of the water-containing polyolefin resin composition is 1 to 50%. Then, one end of the closed container is released, and the water-containing particles and the aqueous dispersion medium are released in an atmosphere having a pressure lower than the internal pressure of the closed container, usually under atmospheric pressure, to foam the water-containing particles. It is obtained by doing.

The water content of the water-containing polyolefin resin composition when it is water-containing is 1 to 50%, preferably 3 to 30%.
Therefore, the water content of the particles is also 1 to 50%, preferably 3
~ 30%.

The temperature equal to or higher than the softening point is defined as the melting point of the polyolefin resin used, which is -40 ° C. or higher, preferably higher than the melting point, preferably lower than the melting point + 30 ° C., and more preferably higher than the melting point + 2.
It is a temperature of 0 ° C. or less. When the temperature is lower than the softening temperature, the crystals do not melt and foam hardly occurs, and
If the melting point is higher than + 30 ° C., the pre-expanded particles become open cells.

The particles are dispersed in an aqueous dispersion medium in the closed container. At this time, tribasic calcium phosphate, basic magnesium carbonate, basic zinc carbonate,
Calcium carbonate and the like, and a small amount of a surfactant such as sodium dodecylbenzenesulfonate, sodium n-paraffinsulfonate, sodium α-olefin sulfonate, and the like can be used.

As a typical example of the aqueous dispersion medium, water can be mentioned.
It may contain one or more of ethyl alcohol and glycerin.

The pre-expanded particles using the water-containing polyolefin resin composition thus obtained have an apparent expansion ratio of 5%.
~ 60 times, preferably 7-45 times, closed cell rate 80-1
A DSC curve obtained by measuring the pre-expanded particles with a differential scanning calorimeter (preferably, 94 to 100%, and an average cell diameter of 50 to 500 μm, preferably 200 to 300 μm). 1-3m
g at a heating rate of 10 ° C./min by a differential scanning calorimeter.
In a DSC curve obtained when the temperature is raised to 20 ° C., a peak (high-temperature peak) higher than the intrinsic peak of the water-containing polyolefin resin composition appears, and the melting energy of the high-temperature side peak is 4.0 mJ. / Mg or more.

When the apparent expansion ratio is less than 5 times,
The flexibility and cushioning properties of the obtained molded article become insufficient, and if it exceeds 60 times, the mechanical strength and heat resistance of the obtained molded article become insufficient. Further, when the closed cell ratio is less than 80%, the secondary foaming power is insufficient, so that poor fusion occurs at the time of molding, and the mechanical strength of the obtained molded body is reduced. Further, the average bubble diameter is 50 μm.
If it is less than m, problems such as distortion of the shape of the obtained molded article occur, and if it exceeds 500 μm, the mechanical strength of the obtained molded article decreases.

The high temperature peak is an endothermic peak which appears on the DSC curve at a temperature higher than the temperature at which an intrinsic endothermic characteristic of the polyolefin resin appears, and is distinguished by the following method.

That is, the DSC curve obtained when 4.0 to 6.0 mg of the sample was heated from room temperature to 220 ° C. at a rate of 10 ° C./min was used as the first DSC curve, To 10 ° C / min at a cooling rate of 40 ° C
The temperature is lowered to around 220 ℃ again at a heating rate of 10 ℃ / min.
The DSC curve obtained when the temperature was raised to
An SC curve is used. The peak peculiar to the polyolefin resin is generally found in the first DSC curve and the second DSC curve.
It also appears in the curve, and the temperature of the peak apex is 1st and 2nd
There may be a slight difference at the time, but the difference is less than 5 ° C,
Usually it is less than 2 ° C.

On the other hand, the high temperature peak in the present invention is the first peak.
It is an endothermic peak that appears on the higher temperature side than the above-mentioned intrinsic peak on the second DSC curve. Pre-expanded particles in which this high-temperature peak does not appear in the DSC curve have poor in-mold moldability, making it difficult to obtain a good molded product. Even when a high temperature peak appears, the melting energy of the high temperature peak is 4.0.
If it is less than mJ / mg, the shrinkage during molding is large.

The high-temperature peak is considered to be due to the presence of a crystal structure different from the structure appearing as the intrinsic peak. Although the high-temperature peak appears in the first DSC curve, the temperature was raised under the same conditions. It does not appear in the second DSC curve. Therefore, the structure that appears as a high temperature peak is that which is present in the pre-expanded particles themselves.

When the polyolefin-based resin is a polypropylene-based resin, the characteristic peak exists in a range of about 145 to 165 ° C., the high-temperature peak exists in a range of about 160 to 180 ° C., and the temperature difference between the characteristic peak and the high-temperature peak. Is about 10 to 20 ° C.

Since the pre-expanded particles from the water-containing polyolefin-based resin composition of the present invention have a closed cell ratio of 80% or more, if necessary, the pre-expanded particles are heated and pressed in a pressure vessel for a certain period of time. After the air impregnation is performed by the treatment, the mixture may be filled in a molding die, and may be heated and foamed by steam heating to produce a foamed molded product according to the mold.

The foamed article thus obtained has a small dimensional shrinkage and a small shape deformation, so that it has extremely high commercial value.

[0059]

EXAMPLES Next, the present invention will be described based on examples and comparative examples, but the present invention is not limited to only these examples.

The evaluation methods performed in the examples and comparative examples are summarized below.

(Dispersion particle size of (meth) acrylic acid-based resin salt) Measured by the method described above.

(Water content of water-containing particles) Measured by the method described above.

(Apparent Expansion Ratio) Gently put the obtained pre-expanded particles into a beaker having a capacity of 1 liter until they can be worn, and apply no vibration to the pre-expanded particles with a flat plate. The weight of the pre-expanded particles is measured, and the apparent density is calculated. Next, the density of the resin composition particles (pellets) used to obtain the pre-expanded particles is divided by the apparent density, and the obtained value is defined as the apparent expansion ratio.

(Closed cell ratio) The closed cell volume of the obtained pre-expanded particles was determined using an air-comparison hydrometer (model 930, manufactured by BECKMAN), and the closed cell volume was separately measured by a submerged method. The closed cell ratio is calculated by dividing by the obtained apparent volume.

(Average cell diameter) From the obtained pre-expanded particles, 30 pre-expanded particles were arbitrarily taken out, and JIS
The cell diameter is measured according to K6402, and the average cell diameter (d) is calculated.

(Variation of Bubble) The ratio U of the average bubble diameter (d) to the standard deviation (σ) representing the variation of the bubble diameter is calculated from U (%) = (σ / d) × 100. The smaller U is, the more uniform the bubbles are. The value of U was classified and evaluated according to the following criteria. ：: The value of U is less than 35% Δ: The value of U is 35 to 45% ×: The value of U exceeds 45%

(Measurement of intrinsic peak temperature, high-temperature peak temperature, and calorie of high-temperature peak) The first and second DSC curves are obtained by the above-described method, and the intrinsic peak temperature of the first DSC curve is obtained. In addition, it is on the higher temperature side than the intrinsic peak, and exists in the first DSC curve but is in the second DS curve.
The temperature of the peak not present in the C curve is determined. The calorific value (mJ / mg) of the high-temperature peak can be determined by (area of the high-temperature peak on the chart (cm ² ) × heat amount per 1 cm ^{2 of the} chart (mJ / mg)) / measured sample weight (mg).

Examples 1 to 6 Ethylene-propylene random copolymer as a polyolefin resin (density 0.91 g / cm ³ , ethylene content 3.1%, melting point 145 ° C., MI = 7 g / 10 min) 10
The amount of the (meth) acrylic acid-based resin salt (an ionomer-based resin obtained by crosslinking the molecules of an ethylene-methacrylic acid copolymer with sodium ions in the amount shown in Table 1 with respect to 0 parts, and 95 mol% of ethylene units and methacrylic acid An acid unit consisting of 5 mol% of acid units, in which 60 mol% of methacrylic acid units form a salt, MI = 0.9 g / 10 min, melting point 90 ° C.) and talc as an inorganic filler (average particle size 9 2.0 μm) and fed to a 50 mmφ single screw extruder. The mixture was melt-kneaded using a full flight type screw and a dalmage type screw having a higher kneading capacity than the full flight type screw, and then a 2.2 mmφ cylindrical die was used. More extruded,
After cooling with water, cut with a cutter and obtain particles (pellets) from the columnar water-containing polyolefin-based resin composition (1.8 mg /
Grain).

Next, 100 parts of the obtained particles, 1.4 parts of powdery basic calcium triphosphate as a dispersant and 0.03 part of sodium n-paraffinsulfonic acid were added to 1 part of water.
50 parts were charged into a closed container and heated to 155 ° C. to make the particles water-containing. The pressure at this time is about 5.6k
g / cm ² G.

After that, the pressure in the container is reduced to 30 by compressed air.
kg / cm ² G and held for 5 minutes. Next, while maintaining the pressure in the container at 30 kg / cm ² G,
The valve at the lower part of the closed vessel was opened to release the aqueous dispersion (hydrous particles and aqueous dispersion medium) under atmospheric pressure to perform prefoaming.

The physical properties of the particles, the water-containing particles and the pre-expanded particles obtained from the resin composition include the dispersed particle diameter of the (meth) acrylic resin salt of the particles from the resin composition, the water content of the water-containing particles, and The apparent expansion ratio, closed cell ratio, average cell diameter, and cell dispersion of the pre-expanded particles were measured.
Table 1 shows the results.

Comparative Examples 1 to 3 Example 1 was repeated except that a full-flight type screw was used when preparing the water-containing polyolefin resin composition shown in Table 1.
Pre-expanded particles were obtained and evaluated in the same manner as in Examples 6 to 6. Table 1 shows the results.

[0073]

[Table 1]

From the results shown in Table 1, it can be seen that all of the pre-expanded particles obtained in Examples 1 to 6 are pre-expanded particles having a high expansion ratio, uniform fine cells, and a high closed cell ratio.

[0075]

According to the present invention, when pre-expanded particles are produced using particles from the water-containing polyolefin resin composition of the present invention, the apparent expansion ratio is 5 to 60 without using a volatile blowing agent.
Double, closed cell ratio 80-100% and average cell diameter 50-
Pre-expanded particles having a uniform average cell diameter of 500 μm are obtained. As a result, an in-mold foam molded product that has a small shrinkage ratio when formed into a molded product, excellent appearance such as appearance, excellent mechanical strength, excellent economic efficiency, and markedly improved productivity. You can get.

Therefore, the pre-expanded particles of the present invention can be used for structural members such as a vehicle shock absorber, which require dimensional accuracy,
It can be suitably used for the production of heat insulating building materials and the like, and is also useful for applications such as buffer packaging materials.

Claims (8)

[Claims] 1. A water-containing polyolefin-based resin composition containing a polyolefin-based resin and a (meth) acrylic acid-based resin salt and having a water content of 1 to 50% by weight, which is contained in the resin composition. A water-containing polyolefin-based resin composition, wherein the dispersed particle size of the (meth) acrylic acid-based resin salt is 50 µm or less. 2. The composition according to claim 1, wherein the content of the filler is not more than 10 parts by weight based on 100 parts by weight of the polyolefin resin.
The water-containing polyolefin-based resin composition as described in the above. 3. The water-containing polyolefin resin composition according to claim 2, wherein the filler is talc. 4. The water-containing polyolefin resin composition according to claim 1, wherein the polyolefin resin is a polypropylene resin. 5. The water-containing polyolefin-based resin according to claim 1, wherein the (meth) acrylic acid-based resin salt is an ionomer-based resin obtained by crosslinking the molecules of an ethylene- (meth) acrylic acid copolymer with metal ions. Composition. 6. The water-containing polyolefin resin composition according to claim 5, wherein the metal ion is an alkali metal ion. 7. Pre-expanded particles obtained by pre-expanding particles from the water-containing polyolefin-based resin composition according to claim 1, wherein the apparent expansion ratio is 5 to 60 times and the closed cell ratio is 80 to 80.
DSC curve obtained by a differential scanning calorimeter of the pre-expanded particles having 100% and an average cell diameter of 50 to 500 μm (provided that the pre-expanded particles 1 to 3 mg were measured at a heating rate of 10 ° C./min by a differential scanning calorimeter). In the DSC curve obtained when the temperature is raised to 220 ° C., a peak (high-temperature peak) appears on the higher temperature side than the intrinsic peak of the water-containing polyolefin-based resin composition, and the melting energy of the high-temperature side peak is 4.0 mJ. / Pre-expanded particles having a crystal structure of not less than / mg. 8. The pre-expanded particles according to claim 7, wherein the water-containing polyolefin resin composition contains a filler.