JP2001001384A - Method for producing extruded foam bundle of polypropylene resin - Google Patents

Abstract

(57) [Problem] To provide a polypropylene resin extruded thin strip convergent body having a high closed cell ratio and a high expansion ratio. SOLUTION: A mixture composed of a specific polypropylene resin and a foaming agent whose elongational viscosity measured in a molten state rapidly rises as the strain amount increases is melt-kneaded in an extruder,
After adjusting the temperature of the mixture to a temperature suitable for foaming, the strip is extruded and foamed at a low temperature and a low pressure from an extrusion die having a large number of small holes. The present invention relates to a method for producing a bundle of extruded foamed specific polypropylene resin strips, characterized by having a structure in which foamed strips are bundled and fused together.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a strip bundle extruded foam made of a specific polypropylene resin obtained by an extrusion facility. More specifically, the present invention melt-kneads, in an extruder, a mixture of a specific polypropylene resin and a foaming agent, in which the elongational viscosity measured in a molten state rises sharply as the strain increases, and the mixture is foamed. After adjusting the temperature to a suitable temperature, the strip is extruded and foamed at a low temperature and low pressure from an extrusion die having a large number of small holes, and is introduced into a cylindrical device while the foamed strip is softened. The present invention relates to a method for manufacturing a bundle of extruded specific polypropylene resin foam strips, which has a structure in which foam strips are bundled and fused.

[0002]

2. Description of the Related Art A foamable thermoplastic resin is extruded from an extrusion die having a large number of small holes, and while the extruded resin strip is foaming and still softening, the resin strip is converged and fused. The method of producing a foam by letting it be extruded is generally referred to as strand extrusion. The production of a foam by this method is described, for example, in Japanese Patent Publication No. 35-10518.
Although this publication describes that any thermoplastic resin can be similarly used, it is not so. For example, a styrene-based resin such as polystyrene can easily obtain a foam by strand extrusion, but an olefin-based resin such as polyethylene or polypropylene cannot easily obtain a foam by the above method. Because polypropylene is a linear resin and causes a sharp drop in viscosity when melted,
Since the foamed cells cannot be retained and are easily broken, it is difficult to obtain a product having a high closed cell ratio and a high expansion ratio according to the conventional method. Therefore, in order to extrude and foam a polypropylene resin like a polystyrene resin, it is necessary to expand the extrudable temperature range of the polypropylene resin and to increase the melt viscoelasticity in a temperature range equal to or higher than the melting point. For this purpose, attempts have been made to increase the molecular weight of the polypropylene resin and to copolymerize it with another olefin. Modification of the resin by these means has given good results to the extrusion processability of the non-foamable sheet and the physical properties of the molded article of the non-foamed sheet. Did not.

[0003]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a polypropylene resin extruded foam bundle having a high closed cell ratio and a high expansion ratio.

[0004]

Means for Solving the Problems The inventors of the present invention have made intensive studies to solve the above-mentioned problems, and as a result, have found that a specific polypropylene resin whose elongational viscosity measured in a molten state increases sharply as the strain amount increases. A mixture comprising a foaming agent is melt-kneaded in an extruder, and the mixture is adjusted to a temperature suitable for foaming, and then extruded and foamed from a die for extrusion having a number of small holes under low temperature and low pressure, While the foamed strip is softened, it is introduced into a cylindrical device and the foamed strip is focused and fused to produce a bundle of extruded polypropylene resin foam having a small cell diameter and a high expansion ratio. They have found what they can do and have completed the present invention.

A first aspect of the present invention is to melt-knead a mixture of a specific polypropylene resin and a foaming agent in which an elongational viscosity measured in a molten state sharply rises with an increase in strain, and melt-knead the mixture in an extruder. Is adjusted to a temperature suitable for foaming, and then the strip is extruded and foamed at a low temperature and a low pressure from an extrusion die having a large number of small holes. The present invention relates to a method for producing a bundle of extruded foamed specific polypropylene resin strips, which has a structure in which foamed strips are introduced and fused. In the second aspect of the present invention, the specific polypropylene resin is a linear polypropylene resin, a styrene monomer, an isoprene monomer, and 1,3.
2. A specific polypropylene resin extruded foam bundle according to claim 1, comprising a modified polypropylene resin obtained by melt-kneading at least one monomer selected from butadiene monomers and a radical polymerization initiator. And a method for producing the same.

[0006]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Although the reason why the foamability of a polypropylene-based resin is remarkably improved in the present invention is not clear, a specific viscosity-dependent melt viscosity is considered to be smaller than that of an ordinary polypropylene-based resin. This is considered to be due to the use of the polypropylene-based resin, that is, the polypropylene-based resin whose elongational viscosity measured in a molten state sharply increases as the strain amount increases. In the present invention, the characteristic that the elongational viscosity measured in a molten state sharply increases as the strain amount increases will be described below. As a method of evaluating this characteristic, for example, a strand-shaped resin molded product having a diameter of about 3 mm is used as a sample, and both ends of the sample are sandwiched by rotary clamps, and the temperature of the sample is maintained at a temperature at which the sample is completely melted. And
This sample is stretched at a constant strain rate, the stress generated between the chucks is measured over time, and the elongational viscosity is determined from the relationship between the stress and the cross-sectional area of the sample at that time. That is, the elongational viscosity is represented by the following equation.

[0007]

(Equation 1) (Where η _e is the elongational viscosity, σ is the stress per sectional area, γ
Indicates the strain rate. Γ is given by

[0008]

(Equation 2) Where L is the length of the sample and t is the time. ) This elongational viscosity is plotted over time. At this time, the elongational viscosity gradually increases as the measurement time elapses, and from a certain measurement time, the one in which the rate of increase in the elongational viscosity sharply increases compared to that time has a specific elongation property. I can say.

[0009] In addition, in the relationship line representing the relationship between the measurement time and the extensional viscosity obtained by taking the logarithm of the measurement time on the horizontal axis and taking the logarithm of the extensional viscosity on the vertical axis, the extensional viscosity at the initial stage of measurement of the relationship line is The slope of the straight line drawn from the portion where the elongational viscosity rises most steeply with the passage of the measurement time is 1.2 to the slope of the straight line drawn from the portion that rises relatively slowly with the passage of the measurement time. It is preferably at least 1.5 times, more preferably at least 1.5 times. Note that the slope of each straight line drawn from the above curve is obtained by the following equation.

[0010]

(Equation 3) The measurement temperature is equal to or higher than the temperature at which the polypropylene-based resin melts, and may be arbitrarily selected from a temperature range below the temperature at which the polypropylene-based resin starts to thermally decompose.
It is preferable to set the temperature in the range of 250 ° C. Further, it is generally preferable to set the strain rate in the range of 0.01 to 0.5 / sec.

The specific polypropylene resin that can be used in the present invention is a polypropylene resin whose elongational viscosity measured in a molten state sharply increases as the amount of strain increases. Examples of such a resin include irradiating a linear polypropylene resin with radiation, or a normal linear polypropylene resin, a radical polymerization initiator, a styrene monomer, an isoprene monomer and 1,1. Examples thereof include a polypropylene resin having a branched structure obtained by a method such as melting and mixing a monomer selected from 3-butadiene monomers. In particular, at least one monomer selected from ordinary linear polypropylene resins, radical polymerization initiators, styrene monomers, isoprene monomers and 1,3-butadiene monomers can be produced at a low cost. Modified polypropylene resins obtained by melt mixing are preferred.

The linear polypropylene resin used as a raw material of the modified polypropylene resin may be any one of a propylene homopolymer, a copolymer, particularly a block copolymer and a random copolymer. Of these, propylene copolymers and propylene homopolymers containing 75% by weight or more of propylene are particularly preferred. The copolymerizable monomers in the polypropylene copolymer include, in addition to ethylene, butene-1, isobutene,
Pentene-1,3-methyl-butene-1, hexene-
1,3-methyl-pentene-1, 4-methyl-pentene-1, 3,4-dimethyl-butene-1, heptene-1,
3-methyl-hexene-1, octene-1, decene-1
Α-olefins having 4 to 12 carbon atoms; cycloolefins such as cyclopentene and norbornene.

The melt flow index (MI) of the linear polypropylene resin is preferably 0.2 or more in view of workability at 230 ° C. and a load of 2.16 kg according to JIS K7210. From the viewpoint of maintaining the melt viscosity of the linear polypropylene resin at the time of melting to an extent suitable for foaming, it is preferably 20 or less, particularly preferably 10 or less.

The radical polymerization initiator is generally a peroxide or an azo compound. In the present invention, the radical polymerization initiator having a hydrogen abstracting ability with respect to the polymer molecule of the linear polypropylene resin is used. Is preferred.

Examples of the radical polymerization initiator include peroxides and azo compounds. Specific examples thereof include ketone peroxides such as methyl ethyl ketone peroxide and methyl acetoacetate peroxide;
1-bis (t-butylperoxy) -3,3,5-trimethylcyclohexane, 1,1-bis (t-butylperoxy) cyclohexane, n-butyl-4,4-bis (t-butylperoxy) Peroxy ketals such as valerate, 2,2-bis (t-butylperoxy) butane; permethane hydroperoxide, 1,1,
3,3-tetramethylbutyl hydroperoxide,
Hydroperoxides such as diisopropylbenzene hydroperoxide and cumene hydroperoxide; dicumyl peroxide, 2,5-dimethyl-2,
5-di (t-butylperoxy) hexane, α, α'-
Bis (t-butylperoxy-m-isopropyl) benzene, t-butylcumyl peroxide, di-t-butyl peroxide, 2,5-dimethyl-2,5-di (t
Dialkyl peroxides such as -butylperoxy) hexine-3; diacyl peroxides such as benzoyl peroxide; di (3-methyl-3-methoxybutyl) peroxydicarbonate, di-2-methoxybutylperoxydicarbonate and the like T-butyl peroxy octate, t-butyl peroxy isobutyrate, t-butyl peroxy laurate, t-butyl peroxy-3,5,5-trimethylhexanoate, t-butyl peroxy octanoate Butylperoxyisopropyl carbonate, 2,5-dimethyl-2,5-di (benzoylperoxy) hexane, t-butylperoxyacetate, t-butylperoxybenzoate, di-t-
One or more organic peroxides such as peroxyesters such as butyl peroxyisophthalate are exemplified. Among these, those having a high hydrogen abstracting ability are particularly preferable. As such a radical polymerization initiator,
For example, 1,1-bis (t-butylperoxy) -3,
3,5-trimethylcyclohexane, 1,1-bis (t
-Butylperoxy) cyclohexane, n-butyl-
4,4-bis (t-butylperoxy) valerate,
Peroxyketals such as 2,2-bis (t-butylperoxy) butane; dicumyl peroxide, 2,5-
Dimethyl-2,5-di (t-butylperoxy) hexane, α, α′-bis (t-butylperoxy-m-isopropyl) benzene, t-butylcumyl peroxide, di-t-butylperoxide, Dialkyl peroxides such as 2,5-dimethyl-2,5-di (t-butylperoxy) hexyne-3; diacyl peroxides such as benzoyl peroxide; t-butylperoxyoctate, t-butylperoxyiso Butyrate, t-butylperoxylaurate, t-butylperoxy-3,5,5-trimethylhexanoate, t-
Butyl peroxyisopropyl carbonate, 2,5-
One or two of peroxyesters such as dimethyl-2,5-di (benzoylperoxy) hexane, t-butylperoxyacetate, t-butylperoxybenzoate and di-t-butylperoxyisophthalate;
More than seeds.

The styrene monomer, isoprene monomer and 1,3-butadiene monomer may be used alone or in combination. When used in combination, the usage ratio is arbitrary. The amount of the monomer (or monomer mixture) is preferably 0.1 to 50 parts by weight based on 100 parts by weight of the raw material linear polypropylene resin. Further, the amount is preferably 0.1 to 20 parts by weight from the viewpoint of compatibility with the raw material resin.

The amount of the radical polymerization initiator to be added is 0.05 to 5 parts by weight based on 100 parts by weight of the raw material linear polypropylene resin in view of optimizing the melt viscosity of the modified polypropylene resin and being economical. Parts by weight are preferred.

The starting polypropylene resin may contain, if necessary, an antioxidant, a metal deactivator, a phosphorus-based processing stabilizer, an ultraviolet absorber, an ultraviolet stabilizer, a fluorescent brightener, a metal soap, an antacid absorber. Additives such as stabilizers or cross-linking agents, chain transfer agents, nucleating agents, lubricants, plasticizers, fillers, reinforcing agents, pigments, dyes, flame retardants, antistatic agents, etc. within a range that does not impair the purpose of the present invention. It may be added.

Such raw material linear polypropylene resin, styrene monomer, isoprene monomer and 1,3-
The method of mixing and melt-kneading at least one kind of monomer selected from butadiene monomers, a radical polymerization initiator and other optional materials to be added as needed are not particularly limited. At least one monomer selected from a linear polypropylene resin, a styrene monomer, an isoprene monomer, and a 1,3-butadiene monomer, a radical polymerization initiator, and other After mixing the additive materials, it may be melt-kneaded, or after melt-kneading the linear polypropylene-based resin and the optional materials to be added as necessary, a styrene monomer, an isoprene monomer and 1, At least one monomer selected from 3-butadiene monomers,
The radical polymerization initiators may be mixed simultaneously or separately, collectively or separately, and then melt-kneaded.

The melt kneading apparatus includes a roll,
Kneaders such as co-kneaders, Banbury mixers, Brabenders, single-screw extruders, twin-screw extruders, twin-screw surface renewers,
Examples of such devices include a horizontal stirrer such as a multi-shaft disk device or a vertical stirrer such as a double helical ribbon stirrer, which can heat a polymer material to an appropriate temperature and knead it while applying an appropriate shear stress. Of these, especially uniaxial or 2
A screw extruder is preferred in terms of productivity. In addition, the melt-kneading may be repeated a plurality of times in order to sufficiently and uniformly mix the respective materials.

As described above, it is possible to produce a specific polypropylene resin having a characteristic that the elongational viscosity measured in a molten state according to the present invention rapidly increases as the strain amount increases. As an example of the method for producing a foam of the present invention, a method for obtaining a foam by melt-kneading a specific polypropylene resin and a foaming agent in an extruder, adjusting the mixture to a temperature suitable for foaming, and extruding the mixture. After adding or press-fitting a foaming agent to a specific polypropylene resin in a molten state, the mixture is retained in a cooling mixer adjusted to a temperature suitable for foaming, and then extruded to obtain a foam. Method. The extruder is not particularly limited as long as it can heat a specific polypropylene-based resin in a molten state and can knead it while applying an appropriate shear stress, and may be a single-screw or twin-screw extruder. Further, these extruders may be used in combination with two, three or multiple stages in series. In particular, a two-stage tandem-type extruder is more preferable from the viewpoint of uniforming the mixture composition of a specific polypropylene resin and a foaming agent and productivity.

As the foaming agent, for example, propane,
Aliphatic hydrocarbons such as butane, pentane, hexane and heptane; alicyclic hydrocarbons such as cyclobutane, cyclopentane and cyclohexane; chlorodifluoromethane, difluoromethane, trifluoromethane, trichlorofluoromethane, dichloromethane, dichlorofluoromethane, Dichlorodifluoromethane, trichlorofluoromethane, chloromethane, chloroethane, dichlorotrifluoroethane, dichlorofluoroethane, chlorodifluoroethane, dichloropentafluoroethane, tetrafluoroethane, difluoroethane, pentafluoroethane, trifluoroethane, dichlorotetrafluoroethane, trichloro Trifluoroethane, tetrachlorodifluoroethane, chloropentafluoroethane, perfluorocyclobutane What halogenated hydrocarbons; carbon dioxide, nitrogen, inorganic gases such as air; one or two or more of such water.

The addition amount (kneading amount) of the blowing agent varies depending on the type of the blowing agent and the target expansion ratio, but may be in the range of 2 to 30 parts by weight with respect to 100 parts by weight of the specific polypropylene resin. preferable.

In order to control the cell diameter of the foam to an appropriate size, if necessary, sodium bicarbonate may be used.
A foam nucleating agent such as citric acid or talc or mica may be used in combination. Usually, the addition amount of the foam nucleating agent used as needed is preferably 0.01 to 1 part by weight based on 100 parts by weight of the specific polypropylene resin composition.

The diameter and shape of the hole of the die attached to the tip of the extruder are not limited. For example, the shape can be selected from a round shape, a square shape, a polygonal shape, a slit, and other shapes. You can choose.

The foam of the present invention is a bundle of strips having a high closed cell ratio and a high expansion ratio, and is useful for cushioning materials, heat insulating materials, and other uses.

[0027]

Next, the present invention will be described in detail with reference to examples, but the present invention is not limited to only these examples. 1) Measurement of closed cell ratio Measured by air pycnometer according to the method described in ASTM D-2856 2) Measurement of foam density Measured according to JIS-K6767. 3) Cross-sectional area Slice the cross-section of the foam and project it on paper. The foam was cut along the cross-sectional shape, and the cross-sectional area of the foam was calculated from the weight and the specific gravity of the paper. 4) Cell diameter AS in the extrusion direction, width direction and thickness direction of the foam
The measurement was performed according to TM D3576. In the following Examples and Comparative Examples, the relationship between the elongational viscosity measured in a molten state of a specific polypropylene-based resin or a normal linear polypropylene-based resin and the measurement time (strain amount) was measured by the following method. . The polypropylene-based resin pellets are filled into a capillary having an orifice having a diameter of 3 mm, melted at 200 ° C., and extruded to obtain a strand-like sample having a length of about 180 mm. Using this sample, the relationship between the elongational viscosity and the measurement time (strain amount) is measured at 180 ° C. and a strain rate of 0.05 / sec using a Melten rheometer manufactured by Toyo Seiki Co., Ltd. At this time, the elongational viscosity is measured by dividing the stress by the cross-sectional area of the sample measured by the charge-coupled device.

For example, in FIG. 1, the specific polypropylene-based resin shows a tendency that the elongational viscosity increases with a gentle slope immediately after the start of the measurement, and thereafter the elongational viscosity rapidly increases. A relatively flat portion of the relationship line at the initial stage of the measurement of the slope of the portion where the extensional viscosity rises sharply (the slope of the straight line drawn from the portion where the extensional viscosity rises most steeply as the measurement time elapses) (The ratio of a specific elongational viscosity) to the inclination (the inclination of a straight line drawn from a portion where the elongational viscosity rises relatively slowly as the measurement time elapses) was determined. (Example 1) Ethylene random polypropylene (Hypol B230 manufactured by Grand Polymer Co., Ltd., MI = 0.
5 g / 10 minutes, 100 parts by weight of ethylene 3% by weight, 1,1-di (t-butylperoxy) -3,3,5-trimethylcyclohexane (manufactured by NOF CORPORATION, Perhexa 3M) as a radical polymerization initiator 1 minute half-life temperature 147
C) 0.5 part by weight, a stabilizer (Irganox B225 manufactured by Ciba Geigy) 0.2 part by weight, and a blended oil (Super Ease manufactured by Koshigaya Kasei Co., Ltd.) 0.05 part by weight was mixed with a superfloter. Stir and mix. The mixture was put into a hopper opening of a 44 mm twin-screw extruder at 50 kg / hr using a measuring feeder, and an attached liquid feed pump (manufactured by Nikkiso Co., Ltd.) was supplied at a rate of 1.25 kg / hr of isoprene. Diaphragm: Model C22X-08F-
Using 14D1D and a discharge pressure of 50 kgf / cm2), 2.5 parts by weight of isoprene was injected from the middle of the extruder cylinder. 180 ° C before injecting isoprene and 200 ° C after injecting isoprene
Extruding the mixture at 150 rpm with the temperature set to
A specific polypropylene resin was produced.

With respect to 100 parts by weight of the specific polypropylene resin, 0.05 parts by weight of blend oil and mica (A21S; YAMAGUCHIM) as a cell nucleating agent
0.5 parts by weight (manufactured by ICA POWDER) were added and mixed with a super floater. Then, the mixture is fed to a 65-90 mmφ tandem type extruder, the first stage extruder (65 mmφ) is set to a rotation speed of 80 rpm and a temperature of 200 ° C. to melt the mixture, and then isobutane is used as a blowing agent in the specific polypropylene-based extruder. 12 parts by weight were press-mixed with 100 parts by weight of the resin composition. Next, the mixture was fed to a second-stage extruder (90 mmφ) set at a rotation speed of 10 rpm and a temperature of 140 ° C., and extruded at a discharge rate of 50 kg / hr. The extrusion dies used were those in which 40 holes, 1.5 mm in diameter, were opened in six rows at intervals of 5 mm. The resin extruded from each extrusion hole of the extrusion die progresses as a large number of fired strips, and foams and fuses with each other during fusion to form a united body having a thickness of 30 mm, a width of 200 mm, and a density of 0.0.
An extruded foam bundle of 20 g / cm2 was obtained.

[0030] (Example 2) isoprene monomer styrene monomer 10 parts by weight, the radical polymerization initiator alpha, alpha ^`- bis (t-butylperoxy -m- isopropyl) benzene (NOF Corporation The same as Example 1 except that 0.5 parts by weight was used.

Comparative Example 1 Ethylene random polypropylene (Hypol B23 manufactured by Grand Polymer Co., Ltd.)
0, MI = 0.5 g / 10 min, ethylene 3% by weight), except that it was used without modification.

Table 1 shows the formulation in the production of the specific polypropylene resin, Table 2 shows the specific elongational viscosity ratio, and Table 3 shows the properties of the extruded foam bundle.

[0033]

[Table 1]

[0034]

[Table 2]

[0035]

[Table 3] In Comparative Example 1, it can be seen that the closed cell ratio is low, and a high magnification foam is not obtained.

[0036]

According to the present invention, a mixture comprising a specific polypropylene resin composition and a foaming agent, in which the elongational viscosity measured in a molten state rises sharply with an increase in strain, is extruded and foamed by the method of the present invention. Then, it is possible to produce an extruded foam strip condensate made of a specific polypropylene resin having a high closed cell ratio and a high expansion ratio.

[Brief description of the drawings]

FIG. 1 shows the characteristics of a specific polypropylene resin and a general polypropylene resin of the present invention. In the case of a specific polypropylene resin, when the measurement time is early, △ (lo
gη _e ) / △ (logt) has a relatively flat slope, but the amount of distortion expressed by logt and time increases,
After a certain point, it rises sharply. On the other hand, a normal linear polypropylene-based resin has Δlogη _e /
The slope represented by Δlogt remains relatively flat.

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Claims (2)

[Claims] 1. A mixture comprising a specific polypropylene resin and a foaming agent whose elongational viscosity measured in a molten state rises sharply with an increase in strain is melt-kneaded in an extruder, and the mixture is suitable for foaming. After the temperature is adjusted to a temperature, the strip is extruded and foamed at a low temperature and a low pressure from an extrusion die having many small holes, and is introduced into a cylindrical device while the foamed strip is softened. A method for producing a bundle of extruded foamed specific polypropylene resin strips, characterized by having a structure obtained by condensing and fusing the fibers. 2. The method according to claim 1, wherein the specific polypropylene resin is at least one monomer selected from a linear polypropylene resin, a styrene monomer, an isoprene monomer and a 1,3-butadiene monomer. The method for producing a specific polypropylene-based resin extruded foam bundle according to claim 1, comprising a modified polypropylene-based resin obtained by melt-kneading a radical polymerization initiator.