JPH034573B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing an olefin resin foam, and particularly to a method for producing an olefin resin foam with high rigidity.

The olefin resin foam is produced by putting an olefin resin in an extruder, melting it, impregnating it with a blowing agent, and extruding it from a die. Olefin resins include homopolymers of ethylene or propylene and their copolymers, as well as copolymers with other monomers that can be copolymerized with ethylene or propylene, such as copolymers of ethylene and vinyl acetate. was used. These resins are generally rich in flexibility and elasticity, and have good chemical resistance and oil resistance, but have low rigidity and poor shape retention. As a blowing agent, propane,
Aliphatic hydrocarbons such as butane and halogenated aliphatic hydrocarbons such as methyl chloride and dichlorodifluoromethane are used, and extrusion is also performed with the addition of a crosslinking agent to improve foaming. However, if the degree of crosslinking is increased, it cannot be extruded, and if the degree of crosslinking is decreased, the foam has poor rigidity and poor shape retention.

On the other hand, a styrene resin can also be made into a foam by putting it in an extruder and melting it, press-fitting a foaming agent for ethylene resin, and extruding it from a die. Styrenic resins have strong rigidity and good shape retention, but have the disadvantage of poor chemical resistance and oil resistance. Therefore, styrene resin foams have advantages and disadvantages that are completely opposite to those of the above-mentioned olefin resins. Therefore, by mixing olefin resin and styrene resin,
Compensating for the deficiencies of both resins, foaming this mixture appears to yield a foam free of all of the aforementioned deficiencies.

However, olefin resins do not mix well with styrene resins. It is possible to mix a small amount of styrene resin with olefin resin, but as mentioned above, if you try to mix them in equal weight proportions to the extent that they compensate for each other's shortcomings, the two resins will not mix uniformly. This causes phase separation. Therefore, if this were to be made into a foam, not only would the surface have a fluffy appearance, resulting in a foam with a poor appearance, but also the foaming ratio would be low, making it difficult to obtain a good foam. I can't. Therefore, the above-mentioned drawbacks of olefin resin foams cannot be improved by mixing styrene resins as in the past.

On the other hand, it is known to mix a special resin called a mutually impregnated polymer with an olefin resin to form a foam. The mutually impregnated polymer referred to herein is a type of graft polymer obtained by polymerizing a state in which a styrene monomer is permeated into an olefin resin.

However, the interimpregnated polymer used here was not crosslinked. This is because only a combination of benzoyl peroxide and tertiary butyl perbenzoate was to be used as a polymerization initiator. It has been found that when other polymerization initiators are used in combination, such as benzoyl peroxide and dicumyl peroxide, the resulting interimpregnated polymer becomes crosslinked. When a moderately crosslinked one is selected from the crosslinked mutually impregnated polymers thus obtained and added to the olefin resin, the resulting composition can be extruded and foamed in the same way as the olefin resin alone. It was confirmed that a foam with excellent physical properties could be obtained. This invention was made based on such knowledge and confirmation.

This invention involves adding and mixing a mutually impregnated polymer of olefin and styrene with a gel concentration of 5-50%, which is obtained by polymerizing a styrene monomer infiltrated into an olefin resin. death,
The present invention relates to a method for producing an olefin resin foam, which comprises melting this mixture in an extruder, impregnating it with a blowing agent, and extruding it from a die.

Since the most important feature of this invention is that a mutually impregnated polymer is added to an olefin resin to form a mixture, the mutually impregnated polymer will be explained first.

The term "interimpregnated polymer" generally refers to a polymer obtained by polymerizing a certain monomer in a state in which another monomer is infiltrated into the polymer. That is, it is a kind of graft polymer. The mutually impregnated polymer used in this invention is obtained by polymerizing a styrenic monomer while permeating the styrene monomer into an olefin resin obtained by polymerizing or copolymerizing an olefin. This is a polymer obtained by Such polymers are disclosed in, for example, JP-A No. 54-106576 (Japanese Patent Publication No. 59-14493).
It is already known as described in .

In these publications, the mutually impregnated polymer is mixed alone with a blowing agent and extruded to form a foam.

However, it was not possible to use the mutually impregnated polymer in combination with other resins. JP-A-52-121669 states that, as mentioned above, a mutually impregnated polymer may be mixed with an olefin resin, but in order to perform extrusion foaming, the mutually impregnated polymer is mixed with the olefin resin. It remained uncrosslinked. Therefore, these publications do not teach that a crosslinked interimpregnated polymer is mixed with an olefinic resin and then extruded and foamed.

Olefin resins are used as materials to make mutually impregnated polymers, but as olefin resins,
In addition to polyethylene, polypropylene, and ethylene/propylene copolymers, ethylene/vinyl acetate copolymers, ethylene/vinyl chloride copolymers, ethylene/methyl methacrylate copolymers, and the like can be used. These olefin resins are used in the form of spheres or pellets. The particle size is preferably 6 to 30 mesh.

As the styrenic monomer used to make the interimpregnated polymer, various types of vinyl aromatic monomers can be used. For example, styrene, methylstyrene, ethylstyrene, halogenated styrene, α-methylstyrene, etc. can be used.

To make interimpregnated polymers, a polymerization initiator is required to polymerize the styrenic monomers. The polymerization initiator may be added to the styrenic monomer in advance, but if it is added in advance, the styrenic monomer should be infiltrated into the olefin polymer immediately after addition. It is necessary to The polymerization initiator can also be added after being dissolved in a solvent that does not interfere with the polymerization of the styrenic monomer, for example, an organic solvent such as benzene or toluene. As the polymerization initiator, it is necessary to select specific ones from known oil-soluble organic peroxides and use them in appropriate combinations. For example, it is necessary to use dicumyl peroxide in combination with tertiary butyl peroxide, benzoyl peroxide, lauroyl peroxide, and the like. The amount of the polymerization initiator is suitably 0.2 to 2.0% by weight based on the styrene monomer.

To make the interimpregnated polymer, the olefinic resin is dispersed in an aqueous medium, and the styrenic monomer is impregnated in suspension and polymerized. Dispersants are used in the aqueous medium to maintain it in suspension. As the dispersant, polyvinyl alcohol, methylcellulose, calcium phosphate, calcium pyrophosphate, etc. are used, and these dispersants are added in a proportion of 0.01 to 5% by weight based on water.

A styrenic monomer and a polymerization initiator are added to the aqueous suspension of olefinic resin thus prepared. The mixing ratio of olefin resin and styrene monomer is as follows, assuming that the sum of both is 100 parts by weight.
The former is 90 to 10 parts by weight, while the latter is 10 to 90 parts by weight, and is appropriately selected within that range. Among these, preferred is 30 to 70 parts by weight of the styrene monomer to 70 to 30 parts by weight of the olefin resin.

The styrenic monomer is polymerized in the presence of a specific polymerization initiator while penetrating into the olefin resin, and the styrenic monomer polymerizes between the monomers.
The polymer molecules constituting the olefin resin are crosslinked to produce a graft polymer. The cross-linked mutually impregnated polymer contains a portion that is insoluble in organic solvents. In fact, a mutually impregnated polymer obtained by infiltrating and polymerizing a styrene monomer into polyethylene contains a considerable amount of components that do not dissolve in hot toluene. Thus, the proportion of components that do not dissolve in hot toluene in the mutually impregnated polymer is called the gel concentration. Gel concentration is considered to be an index representing the degree of crosslinked structure.

Specifically, the gel concentration is measured as follows. That is, a certain amount of the mutually impregnated polymer was immersed in boiling toluene for 16 hours, then cooled, and the undissolved matter was dried under reduced pressure in an oven at 120°C for 3 hours. The ratio of dry insoluble matter to the mutually impregnated polymer was expressed as a percentage, and this was taken as the gel concentration. In the method of this invention, gels with a gel concentration of 5 to 50% as measured in this manner are used. Among them, gel concentration
10-30% is desirable.

In the method of this invention, the above-mentioned inter-impregnated polymer is added to and mixed with the olefinic resin. The olefin resin in this case is not limited to a homopolymer of olefin, but also includes a copolymer of olefin and a copolymer of olefin and another monomer that can be copolymerized with olefin. The mixing ratio is preferably such that, when the total weight is 100 parts, the mutual impregnating polymer accounts for 90 to 10 parts by weight, and the olefin resin accounts for 10 to 90 parts by weight. The reason for this is that if the amount of mutually impregnated polymer is less than 10 parts by weight, there is no effect of adding it, whereas if it is more than 90 parts by weight, it cannot be said that the olefin resin was used. Within the above ratios, the inter-impregnated polymer can be added to the olefinic resin and mixed together uniformly. Among these, a polymer containing a large amount of styrene monomer is used as the inter-impregnated polymer, and as the amount of the inter-impregnated polymer is further increased, the mixture becomes more rigid.

In this invention method, a mixture of an olefinic resin and a co-impregnated polymer is fed to an extruder and heated and melted within the extruder. Further, a blowing agent is included in this melt in the extruder, or it is thoroughly mixed with a blowing agent mixed in advance. In this way, a foaming agent-containing resin is produced, and this is extruded from a nozzle attached to the tip of the extruder. With regard to the inclusion of these blowing agents and extrusion from an extruder, the mixture of olefinic resin and interimpregnated polymer does not differ significantly from conventional olefinic or styrenic resins. The only difference is that since the mutually impregnated polymer is added, it is easier to foam than when only the olefin resin is extruded.

As the blowing agent, aliphatic hydrocarbons, cycloaliphatic hydrocarbons, halogenated aliphatic hydrocarbons, and thermally decomposable solid compounds can be used. Examples of aliphatic hydrocarbons include propane, butane, pentane, etc.; examples of cycloaliphatic hydrocarbons include cyclopentane, cyclohexane; and examples of halogenated aliphatic hydrocarbons. ,
Methyl chloride, ethyl chloride, dichlorodifluoromethane, trichlorofluoromethane,
Examples of thermally decomposable solid compounds include azodicarbonamide and N,N'-dinitrosopentamethylenetetramine. These blowing agents are used in the range of 1-30% by weight based on the resin mixture. Among the foams mentioned above, it is preferable that the thermally decomposable foaming agent is mixed with the resin before the resin is supplied to the extruder, and the other foaming agents are press-fitted into the molten resin in the extruder. It is preferable.

As for the extruder used in the method of this invention and the nozzle attached to its tip, those conventionally used for foaming olefin resins can be used as they are.

According to the method of this invention, a mutually impregnated polymer of olefin and styrene obtained by polymerizing a styrene monomer infiltrated into an olefin resin is used, and this is added to the olefin resin and mixed. Therefore, both can be mixed in exactly the desired ratio, and as a result, a uniform composition can be obtained as a whole. In addition, the composition obtained in this way has the characteristics of olefin resin, which has good flexibility, elasticity, chemical resistance, and oil resistance, and the characteristics of styrene resin, which is easy to foam, has strong rigidity, and has good shape retention. It has the characteristics of resin. Moreover, at that time, by adjusting the mixing ratio of the olefin resin and the mutually impregnated polymer, and furthermore the ratio of the styrene monomer in the mutually impregnated polymer,
It is possible to increase the amount of olefin to strongly express the characteristics of the above-mentioned olefin-based resin, or conversely, to increase the amount of styrene to strongly express the characteristics of the styrene-based resin. Additionally, this composition can be foamed more easily than conventional common olefinic resins. Also, gel concentration 5
Since the -50% co-impregnated polymer is used, the chemical resistance of the composition is improved compared to the case where the gel concentration is zero, that is, when a non-crosslinked co-impregnated polymer is used. Thus, the method of the present invention provides a great advantage in that it is possible to obtain an improved olefinic resin foam that has high rigidity and good shape retention.

Next, the details of the method of this invention will be explained with reference to Examples. In the following, parts simply mean parts by weight.

Example 1 In this example, polyethylene was used as the olefin resin, and a polymer obtained by impregnating polyethylene with styrene monomer was used as the mutually impregnated polymer.

The interimpregnated polymer was produced as follows.
Dissolve 0.9 parts of magnesium pyrophosphate and 0.04 parts of sodium dodecylbenzenesulfonate in 200 parts of water,
80 parts of low-density polyethylene was added and dispersed, and this was heated to 80°C, and a mixture of 120 parts of styrene monomer, 1 part of benzoyl peroxide, and 1 part of dicumyl peroxide was added to this for 6 hours. Then, it was gradually added dropwise. After adding
Raise the temperature to 90℃, hold at this temperature for 2 hours, and then
The temperature was raised to 130°C and maintained at this temperature for 4 hours to polymerize the styrene monomer infiltrated into the polyethylene. Next, the polymer was cooled to room temperature, separated, washed with water and dried to obtain a mutually impregnated polymer containing 40% by weight of ethylene and 60% by weight of styrene. The gel concentration of this polymer was 20%.

Add 20 parts of high-density polyethylene (Mitsui Hi-Zex 7000F) and 0.5 part of finely powdered talc to 80 parts of the above-mentioned mutually impregnated polymer, mix uniformly, put this mixture into an extruder with a diameter of 115 mm, and melt it at 200 ° C. A foaming agent was press-injected into the extruder to form a foamed sheet. Butane was used as the blowing agent, and the blowing agent was press-injected at a ratio of 5 parts to 100 parts of the resin.

At the tip of the extruder, a die with an annular slit with a diameter of 190 mm and a thickness of 0.7 mm is installed, and the resin is extruded from the die and foamed at a temperature of 135°C, cooled by sliding on the surface of a mandrel with a circumference of 2080 mm, and formed into a cylindrical shape. A foamed sheet was obtained. This cylindrical foam sheet was cut open to obtain two foam sheets. This foam sheet is thick
It was 2.5 mm wide, 1020 mm wide, and 0.08 g/cc in density, had good surface conditions and bubble conditions, did not crack when bent, and was flexible and semi-rigid.

Example 2 Example 2 The mutually impregnated polymer was prepared using the same material composition as 30 parts of low-density polyethylene, 170 parts of styrene monomer, 1.4 parts of benzoyl peroxide, and 0.5 parts of dicumyl peroxide. A product obtained by operating in exactly the same manner as in 1 was used. This interimpregnated polymer had a gel concentration of 8%.

20 parts of this mutually impregnated polymer, 80 parts of low-density polyethylene (Yukalon HE-30 manufactured by Mitsubishi Yuka Co., Ltd.) and 0.5 parts of finely powdered talc were uniformly mixed, and this mixture was passed through two extruders with diameters of 50 mm and 65 mm. 30 kg is supplied per hour to an extrusion device with connected tables, melted at 200℃,
A blowing agent was press-fitted into the extruder having a diameter of 50 mm. The blowing agent is trichlorofluoromethane to 100 parts of resin.
A mixture of 20 parts of dichlorodifluoromethane and 10 parts of dichlorodifluoromethane was used and extruded at a resin temperature of 105°C.

At the tip of the extruder, a cap with a slit of 2 mm thick and 50 mm wide is installed, and the outlet is connected to the cap so that the outlet dimension is the same as the thickness.
A molding passage with a diameter of 50 mm, a width of 80 mm, and a length of 110 mm was provided, and the inner surface was coated with fluororesin.

The resin extruded through the slits of the die was foamed and shaped in the molding passage, yielding a foamed board with a thickness of 50 mm and a width of 130 mm with good appearance and bubble condition. This foam board had a density of 0.02 g/cc, which was high in rigidity for an olefin resin.

Example 3 The material composition for making the mutually impregnated polymer was 50 parts of ethylene/vinyl acetate copolymer resin,
The same procedure as in Example 1 was used except that 150 parts of styrene monomer, 1.2 parts of benzoyl peroxide, and 1.0 part of dicumyl peroxide were used. This interimpregnated polymer had a gel concentration of 15%.

20 parts of low-density polyethylene (Yukalon HE-30 manufactured by Mitsubishi Yuka Co., Ltd.) and 0.5 parts of finely powdered talc were uniformly mixed with 80 parts of this mutually impregnated polymer, and the same extrusion equipment as in Example 2, die and molding equipment were used. The extrusion operation was carried out using a channel. However, the blowing agent used was a mixture of 7 parts of dichlorodifluoromethane and 7 parts of methyl chloride per 100 parts of the resin.
Extrusion was carried out at a resin temperature of 110°C.

The resulting foam has a thickness of 55 mm, a width of 150 mm, and a density
It was 0.028 g/cc, had good appearance and cell condition, and had high rigidity for a polyolefin foam.

Example 4 In this example, the same interimpregnated polymer as used in Example 2 was used. To 20 parts of this mutually impregnated polymer, 80 parts of polypropylene (Noblen MH-8 manufactured by Mitsubishi Yuka) and 2.0 parts of finely powdered talc.
and a small amount of brown pigment, and this mixture was fed at a rate of 12 kg per hour to an extrusion device consisting of two extruders, one with a diameter of 40 mm and one with a diameter of 50 mm.
It is melted at a temperature of ℃, and in the middle of the extrusion device, butane (a blowing agent) is injected at a ratio of 5 parts to 100 parts of resin.
The resin was extruded at a temperature of 170°C.

As for the cap, small holes with a diameter of 1.6 mm are lined up in two rows, upper and lower, with an interval of 10 mm, and the small holes are 3 mm in each row.
A total of 96 small holes were used, with 48 small holes lined up at intervals of . In addition, the exit dimensions are 13mm thick, 150mm wide, 30mm long and close to the base.
A molding passage with a 50 mm passage and a fluororesin lining was provided on the inside.

The resin extruded from the small hole of the nozzle is foamed, focused and fused in the molding passage, and then compressed and shaped by a molding frame and roll group to form a product with a thickness of 12 mm and a width of 150 mm.
A foam board with no internal voids was obtained with a density of 0.18 g/cc. This foam board has a structure in which the resin extruded from each small hole becomes a string, and the strings are closely connected without any gaps. Although it had the feel of an olefin resin, it was highly rigid.

Comparative Example A foamed sheet was obtained in exactly the same manner as in Example 1, except that dicumyl peroxide was not used. The interimpregnated polymer obtained here had a gel concentration of zero and was not crosslinked at all. The resulting foamed sheet had a wall thickness of 2.3 mm, a width of 980 mm, a density of 0.09 g/cm ³ , poor surface smoothness, coarse air bubbles, and poor bending flexibility.

Claims (1)

[Claims] 1 Gel concentration 5- obtained by polymerizing styrene monomer infiltrated into olefin resin
A mutually impregnated polymer of 50% olefin and styrene is added to and mixed with an olefin resin, and this mixture is melted in an extruder, impregnated with a blowing agent, and extruded from a die. A method for producing an olefin resin foam.