JP4906363B2 - Method for producing polypropylene resin foam - Google Patents

Description

The present invention relates to a method of manufacturing a foamed polypropylene resin having a high magnification 10 times or more foamed magnification.

  Polyolefin resin composition foams are characterized by their excellent performance and cost balance, as well as the recyclability of resins that are inherently required. Widely used for cushioning materials. For example, in a heat insulating building material application, a polypropylene-based resin or a foam of a polyethylene-based resin is applied to the inside of a floor or wall of a building and is widely accepted in the market as a very useful material.

  In particular, foams of polypropylene resin compositions exhibit superior mechanical properties such as heat resistance, bending strength, and tensile strength compared to foams of polyethylene resin compositions, and have recently been widely marketed in various fields. Is a material that has been spreading, and many methods for its production have been studied and implemented.

  There are two major methods for producing a polypropylene resin foam, that is, a bead method and an extrusion method. The polypropylene-based resin foam obtained by the bead method has a problem that the average cell system is as large as about 200 to 500 μm, and, for example, a heat-resistant building material cannot be obtained with sufficient thermal performance. In addition, the bead method is a batch production method, and has a drawback in that the manufacturing cost is increased in terms of the number of processes and in that continuous production is not possible.

  Furthermore, when using a polypropylene resin foam as a building material such as a flooring material for a general house or a public facility having a slightly large building area, the length is, for example, about 2 to 3 m from the viewpoint of workability. A board is often used. However, in the case of the bead method, it is necessary to go through an in-mold steam molding process, and the size of the foam obtained is greatly limited by the size of the mold that can be loaded on the molding apparatus. There was a problem that it was difficult to create a long plate of 2 m to 3 m.

  On the other hand, in the case of an extrusion method, it is manufactured by putting a polypropylene resin composition into an extruder and foaming using a gas foaming agent such as carbon dioxide. A method for producing a foam with bundled strands is described. It is described that in this extrusion method, continuous production is possible and a molded body having an arbitrary length can be obtained.

  Further, in Patent Document 2, when the foamable resin is extruded and foamed, a large number of extrusion holes are arranged in a die attached to the tip of the extruder, and an appropriate interval between the extrusion holes is set as the diameter of the extrusion hole. It is defined by a relational expression with a desired expansion ratio, and a method for obtaining a foam by fusing the obtained strand (strip) foam group together with a shaping device is disclosed.

In Patent Document 3, a thermoplastic resin containing a foaming agent is extruded from a die, and in the process of proceeding with the extruded resin, the resin discharged from the die is foamed into a foam, and then the foam is cooled. The foam surface below the softening point, and then soften the foam surface again, there is a solidified foam layer under the softened surface layer, and then the softened surface is pressed to reduce the cross-sectional area, A method of extruding a foam having a hard surface, which is then cooled, is disclosed.
Japanese Patent Publication No. 35-10518 JP-A-61-57325 Japanese Patent Laid-Open No. 54-4964

  However, in the method described in Patent Document 1, when a polypropylene resin foam is obtained using this method, when a so-called polypropylene resin composition containing a general-purpose polypropylene resin as a main component is used, There is a problem in the melt physical properties such as and the processing temperature dependence of the melt physical properties, a sufficient foaming ratio cannot be obtained, and it is practically difficult to stably produce a high-magnification foam as a strand bundling body. Had the problem.

  The method described in Patent Document 2 has a problem that the bending strength is not sufficient because a crack easily breaks in a direction parallel to the arrangement of the thin string-like strand foam group.

  Furthermore, although the method described in Patent Document 3 describes that a stiff layer can be formed on the surface of the thermoplastic resin foam, when producing an unfoamed layer on the surface of the foam under random conditions, Had various problems. That is, if the resin skin layer on the surface of the foam is too thin, the degree of reinforcing the bending strength of the foam is small, the strength cannot be improved sufficiently, and the resin skin layer on the surface of the foam is too thick. And the density of the whole foam formed from the internal foam layer and the surface resin skin layer becomes too large, and there is a problem that the characteristics such as the light weight, high strength and texture of the foam surface are lost.

In view of the above problems, the object of the present invention is to have a sufficient bending strength in a direction perpendicular to the arrangement of the thin string-like sland foam groups in the strand-bound foam, and to have a high strength without easily bending and breaking. In addition, it is a method for producing a high-foamed polypropylene resin composition that maintains the lightness by minimizing the foam density, which is an advantage of a high-magnification foam having a foaming ratio of 10 times or more , and is recyclable, inexpensive and stable. It is to provide a method capable of continuous production .

  In addition, another object of the present invention is to provide a method for producing a foamed polypropylene resin composition that is recyclable, inexpensive, and can be stably continuously produced.

As a result of diligent research to achieve the above object, the present invention has reached the present invention characterized by the following gist.
(1) A method for producing a polypropylene resin foam comprising a surface skin layer and an internal foam layer having the same composition and satisfying the following formula (1), wherein the melt tension at 230 ° C. is 5 to 30 g: to 100 parts by weight of the polypropylene resin composition comprising a certain polypropylene resin, supercritical carbon dioxide and including the foaming agent mixed 4 to 20 parts by weight, and melt-kneaded using an extruder to該混container, die A multi-hole die having a diameter of 0.1 to 0.7 mm is passed through, extruded and foamed at a pressure loss of 6 to 20 MPa to bundle the strands, and the resulting foam is then subjected to the following (formula 2) and ( formula ) 3) A method for producing a polypropylene resin foam, characterized by heating and pressing at a temperature and pressure satisfying the above.
D / 20E ≦ Z ≦ D / 2E (Expression 1)
(However, the thickness of the surface skin layer that is Z: 0.15 to 1.5 mm, D: the thickness of the internal foam layer that is 10 to 50 mm (mm), E: the magnification of the internal foam layer that is 10 to 60 times)
Tm ≦ K ≦ Tm + 20 (Equation 2)
0.5 ≦ S <0.95 (Expression 3)
(However, K: Surface temperature of foam (° C.), Tm: Melting point (° C.) of polypropylene resin composition measured at 10 ° C./min using DSC, S: Compression rate = after pressing Foam height (cm) / foam height before pressing (cm))
( 2 ) The method for producing a polypropylene resin foam according to the above (1), wherein the surface temperature of the foam during heating and pressing is 165 to 195 ° C.

According to the present invention, the foaming ratio has excellent extrusion foamability at a high ratio of 10 times or more, exhibits sufficient bending strength, is excellent in light weight and strength balance and design, and is stably inexpensive. can be produced, manufacturing method of recycling is also possible polypropylene resin foam is provided.

  The polypropylene resin composition in the polypropylene resin foam of the present invention preferably contains a polypropylene resin having a melt tension of 5 to 30 g at 230 ° C. Here, the melt tension can be determined using a capillograph at a measurement temperature of 230 ° C., an extrusion speed of 10 mm / min, and a take-up speed of 3.1 mm / min. If the melt tension is less than 5 g, cell breakage is likely to occur during foaming, and it is difficult to obtain a foam having high flexibility and high foaming ratio. On the other hand, when the melt tension exceeds 30 g, sufficient cells do not grow at the time of foaming, and it is difficult to obtain a foam having high flexibility and high foaming ratio. The melt tension is preferably 6.5 to 20 g, and more preferably 7.5 to 10 g.

Further, the polypropylene resin preferably satisfies the following formula (3) in relation to the melt tension at 230 ° C. and the melt flow rate (MFR) at 230 ° C.
Log (MT)> − 1.33 log (MFR) +1.2 (Formula 3)

  In the present invention, when the melt tension and MFR of the polypropylene resin satisfy the above formula (I), the melt fluidity of the resin increases simultaneously with the increase of the melt tension, and the resin pressure at the time of extrusion during foaming is increased. It is held properly. Moreover, since sufficient elongation of the film forming the cell at the time of foaming can be obtained and a high-magnification foam can be easily obtained, it is excellent in thermal performance and extremely suitable.

  In order to satisfy the above relationship, the polypropylene resin preferably has a melt flow rate (MFR) of 0.1 to 30 g / min, particularly 0.5 to 15 g / min.

  In the present invention, as the polypropylene resin, other resins can be used in combination with the polypropylene resin having the melt tension and MFR. However, even when other resins are used in combination, the polypropylene resin having the specific melt tension, and preferably the specific MFR, is preferably contained in an amount of 50% by mass or more, particularly 80% by mass or more. . When the content of the polypropylene resin is less than 50% by weight, the foaming ratio of the obtained foam is lowered, the flexibility is impaired, the cell diameter is enlarged, the heat insulation performance is lowered, and the mechanical strength is reduced. And heat resistance may be insufficient.

  Examples of other resins contained in the present invention together with the above-mentioned specific melt tension and preferably a polypropylene resin having a specific MFR include, for example, a polyethylene homopolymer or copolymer, a propylene homopolymer, A copolymer of propylene and an α-olefin other than propylene copolymerizable with the propylene is exemplified. The α-olefin in this case is not particularly limited. For example, ethylene, 1-butene, 1-pentene, 1-hexene, 4-methyl-1-pentene, 1-heptene, 1-octene, etc. Is mentioned. These other resins may be used alone or in combination of two or more.

  Among the above-mentioned other resins, a propylene homopolymer having a relatively large molecular weight, a copolymer of propylene and ethylene mainly composed of propylene, because of its excellent extrusion foamability and performance of the obtained foam. A mixed resin of a polypropylene resin and a polyethylene resin is preferably used.

  The specific polypropylene resin used in the present invention and the other resin used together with the polypropylene resin are preferably substantially linear. In the present invention, the term “linear” means that each molecular chain of a propylene polymer (propylene polymer) constituting a polypropylene resin is copolymerized with a propylene monomer as a constituent unit thereof. The α-olefin monomer is an aggregate of substantially one polymerized in a string. Thereby, since it has substantially no cross-linking structure such as chemical cross-linking or electron beam cross-linking or graft structure such as long-chain branching, manufacturing and quality control are relatively easy. In addition, the molecular structure is hardly deteriorated even with repeated thermal histories received in processes such as re-pelletizing performed at the time of recycling.

  The polypropylene resin foam of the present invention is foamed using a foaming agent containing at least carbon dioxide. Carbon dioxide is preferably mixed and foamed in a supercritical state. In the foaming, the foaming agent containing carbon dioxide in a supercritical state is preferably 4 to 20 parts by weight, particularly preferably 5 to 15 parts by weight, with respect to 100 parts by weight of the polypropylene resin composition. It is. If the amount of carbon dioxide used is less than 4 parts by mass, the foaming ratio tends to decrease. If it exceeds 20 parts by mass, large voids due to excess carbon dioxide are likely to be generated in the foam, resulting in heat insulation performance. Decrease or expansion ratio is reduced, and flexibility is impaired.

  The polypropylene resin composition used in the present invention contains the polypropylene resin having the specific physical properties described above, but the polypropylene resin composition is necessary as long as it does not hinder achievement of the object of the present invention. Corresponding to phenolic, phosphorus, amine, sulfur and other antioxidants (anti-aging agents); heat stabilizers; light stabilizers; ultraviolet absorbers; phosphorus, nitrogen, halogen, antimony, etc. One or more of various additives such as a flame retardant, a lubricant, a metal harm-preventing agent, an antistatic agent, a filler, a colorant, a cell nucleating agent, and a crystal nucleating agent may be added.

  The cell nucleating agent is not particularly limited, but includes talc, calcium carbonate, clay, kaolin, mica, magnesium oxide, zinc oxide, carbon black, glass, quartz, silica, alumina, nobicularite, hydrated alumina. , Iron, iron oxide, silicon dioxide, titanium oxide and the like.

  The crystal nucleating agent is not particularly limited, and generally includes a rosin-based, sorbitol-based, or phosphate ester salt-based crystal nucleating agent. The rosin crystal nucleating agent is not particularly limited as long as it is a rosin resin, and examples thereof include dibenzylidene sorbitol (DBS) manufactured by Shin Nippon Rika Co., Ltd. and the like. The phosphoric acid ester salt nucleating agent is not particularly limited, and examples thereof include NA-11 manufactured by Asahi Denka Kogyo Co., Ltd. These crystal nucleating agents may be used alone or in combination.

  The polypropylene resin foam of the present invention uses a foaming apparatus having an extruder and a die attached to the tip, a polypropylene resin composition containing a polypropylene resin having the above specific properties, and a supercritical state. It is produced by mixing with a blowing agent containing at least carbon dioxide and melt extrusion at a temperature of preferably 160 to 250 ° C. When the melt extrusion temperature is less than 160 ° C, the dissolution and diffusion of supercritical carbon dioxide into the resin is poor, and conversely, when it exceeds 250 ° C, degradation such as molecular chain breakage due to heat of the polypropylene resin starts to occur. Absent.

  In addition, the resin pressure (pressure loss) in the immediate vicinity of the die opening in the extruder is preferably 6 to 20 MPa, and it is preferable that the resin pressure be extruded and foamed. In particular, the pressure loss is more preferably 7 to 15 MPa. When the pressure loss is less than 6 MPa, carbon dioxide in a supercritical state dissolved in the polypropylene resin composition is easily vaporized inside the extruder and inside the die, and foaming occurs inside the apparatus. Bubbles, excessive growth, a decrease in expansion ratio, and a significant decrease in appearance are undesirable. On the other hand, if the pressure loss exceeds 20 MPa, large shearing tends to be applied to the cell during cell formation in foaming, which is undesirable because cell foaming and cell structure non-uniformity occur. Such imperfect cell structure is a major obstacle to exhibiting sufficient thermal performance when the foam is used as, for example, a heat insulating material.

  The extrusion discharge amount in the extruder is preferably 1 to 1000 kg / hr. In particular, the extrusion discharge amount depends on the specifications of the extruder, but is preferably about 1 to 50 kg / hr for a type having a relatively small screw diameter, and about 20 for a type having a relatively large screw diameter. -1000 kg / hr is preferred. If the discharge amount is too large or too small, it will be difficult to maintain a pressure loss suitable for foaming at the die part, and it will not be possible to obtain a foam with sufficient magnification, or the cell may break. To do.

  For the extruder to be used, two screws having a screw diameter (D) of preferably 40 to 80 mm and a screw length (L) of (L / D) of preferably 15 to 40 are connected in series. A tandem extruder constructed on the basis of combination is preferred. By using a tandem type extruder, the resin pressure loss condition and the discharge amount of the die part suitable for foaming can be controlled independently by the number of rotations of each screw, and the characteristics of the polypropylene resin of the present invention described above are A foam with excellent characteristics can be produced.

  The shape of the die used in the extruder is not limited, but the number, shape, and thickness of the openings are designed so that the pressure loss per opening is 6 to 20 MPa as described above. Preferably, for example, a multi-hole die is used. By selecting a die that satisfies such conditions, a foam that is satisfactory in performance can be obtained.

Moreover, it is preferable that the die opening part in an extruder is circular from a viewpoint of the external appearance property of the molded object after extrusion foaming, and the easiness of shape adjustment , and the diameter of an opening part is 0.1-0.7 mm . The depth of the die is preferably 0.1 to 20 mm, and a plurality of openings are preferably provided on the front surface of the die. If the diameter of the opening is less than 0.1 mm, the strand diameter of the foam structure is too small, and it is not preferable because it easily breaks during take-up. On the other hand, if it exceeds 2.0 mm, the diameter of the strand is too large, and board-like post-molding for producing smoothness becomes difficult.

In the method for producing a polypropylene resin foam according to the present invention, a polypropylene resin composition containing a polypropylene resin is mixed with a foaming agent containing at least carbon dioxide in a supercritical state, melt-kneaded using an extruder, and a die is obtained. The strands that have been passed through and foamed are converged, and the strand-converged foam needs to be heated and pressed at a temperature and pressure that satisfy the following (Equation 2) and (Equation 3).
Tm ≦ K ≦ Tm + 20 (Equation 2)
0.5 ≦ S <0.95 (Expression 3)
(However, in the formula, K: surface temperature of foam (° C.), Tm: melting point (° C.) of polypropylene resin measured by DSC using a temperature rising condition of 10 ° C./min, S: compression rate = after pressing Foam height (cm) / foam height before pressing (cm))

  The heating / pressing method at the temperature and pressure satisfying the above (Formula 2) and (Formula 3) is not particularly limited, but a vertical sandwiching roll and a vertical sandwiching belt conveyor are preferably used. These upper and lower sandwiching rolls and sandwiching conveyors can heat and pressurize the foam of the polypropylene resin composition by using hot air or an internal circulation type heat medium in combination.

In the present invention, Tm ≦ K ≦ Tm + 20 . For example, taking a foam of a polypropylene resin composition mainly composed of a homopolypropylene resin as an example, the melting point as the resin melting temperature is about 165 ° C., and the surface temperature K of the polypropylene resin foam is 165 ℃ ~1 8 5 ℃, preferably such that 165 to 180 ° C., a hot air temperature, air volume condition, and / or heat medium temperature, flow rate condition is preferably used. If the surface temperature K at this time is lower than 165 ° C., the surface of the polypropylene resin foam does not melt, a surface skin layer cannot be formed, and only a strand-bound foam having a low mechanical strength can be obtained. Can not. Further, the surface temperature K is greater than 1 8 5 ° C. At this time, or significantly reduced magnification of the foam surface of the polypropylene-based resin foam too thick is excessively melted too surface skin layer, rolling There arises a problem that problems in operation of the apparatus such as melting and adhering to a roll or a sandwiching conveyor and being difficult to peel off easily occur.

  Moreover, about the compression rate S of a foam, 0.5 <= S <0.95 is preferable. As described above, the compression rate S is defined as (height of foam after pressing (cm) / height of foam before pressing (cm)). The foam height after pressing here refers to the height of the foam after passing through a roll or a vertically sandwiched belt conveyor, and the foam height before pressing refers to the height of the foam before passing through the roll or the like. Say. If the compression ratio S is less than 0.5, the deformation due to pressing is too large, causing problems such as excessive deformation of the cell structure, complete melting and solidification of the end portion, and the compression ratio S is 0.95 or more. It is not preferable because the pressure is hardly applied and the surface skin cannot be shaped smoothly. Especially, it is suitable that the compression rate S satisfies 0.6 ≦ S <0.9.

  Also, the above heating. The surface of the sandwiching roll and / or the sandwiching conveyor used for pressurization may have a beautifully polished surface, or a mesh pattern, a texture pattern, some pattern, a pattern, a character , Etc. may be transferred. Further, the formation of the skin layer in the polypropylene resin foam by the roll surface and / or the conveyor surface may be performed only on one side of the foam, or preferably on both sides. Even when the skin layer is formed on only one side, there is an effect of strengthening the bending strength in the direction perpendicular to the extrusion direction, but preferably when the skin layer is formed on both sides, the bending strength in the direction perpendicular to the extrusion direction is improved. This is preferable because the reinforcing effect is remarkably improved.

In the polypropylene resin foam of the present invention obtained as described above, the internal foam layer and the surface skin layer are formed from a polypropylene resin having the same composition. The thickness Z of the surface skin layer in the foam needs to satisfy the following formula (1) in relation to the thickness D of the internal foam layer and the expansion ratio E of the internal foam layer.
D / 20E ≦ Z ≦ D / 2E (Formula 1)
(Wherein, Z: thickness of surface skin layer (mm), D: thickness of internal foam layer (mm), E: foaming ratio of internal foam layer)

  When the thickness Z of the surface skin layer of the polypropylene resin foam is larger than D / 2E, the mass of the surface skin layer portion of the foam becomes too large with respect to the degree of reinforcement of the bending strength of the resulting foam, and as a result, the entire foam As the density becomes too large. Moreover, even if Z is changed more greatly than D / 2E, the degree of reinforcement of the bending strength does not change so much as in the case of Z = D / 2E, and the obtained effect is poor.

  Further, if the thickness Z of the surface skin layer of the foam is smaller than D / 20E, the reinforcing effect of bending strength is poor. When the thickness Z of the surface skin layer is D / 20E ≦ Z ≦ D / 2E, the increase in weight due to the increase in the surface skin layer is not significant with respect to the degree of reinforcement of the bending strength obtained, and it is lightweight and high strength. This is preferable because the properties as a foam are maintained.

The thickness D of the internal foam layer of the polypropylene resin foam of the present invention is preferably substantially 10 to 50 mm. When the thickness D of the internal foam layer is smaller than 5 mm, the thickness is too thin, and the number of strand stages in the thickness direction in the configuration as the strand-focused foam is reduced. For example, when a strand bundling body is composed of one strand in the thickness direction, the strand mutual fusing property, the instability of the structure and strength, and the strand bundling are easily broken.

On the other hand, if the thickness D of the internal foam layer exceeds 50 mm, the thickness is too thick, and the number of strand stages in the thickness direction in the configuration of the strand-focusing foam increases. The difference becomes so large that wrinkles and sink marks due to local differences in contraction are likely to occur. Further, the foam layer thickness D is substantially in the case of 10 to 50 mm, originating foam layer when the thickness D is within this range, the thickness direction of the strands stages in the construction of a strand converging body is appropriate, stable dimensional accuracy A good strand bundle can be manufactured.

The thickness Z of the skin layer of the polypropylene resin foam of the present invention is 0.15 to 1.5 mm, although it is determined by the thickness of the internal foam layer and the expansion ratio in the above (Formula 1). When the skin layer is less than 0.15 mm, it is difficult to uniformly cover the foam surface with the skin layer, and the effect of enhancing the bending strength is poor. If the skin layer exceeds 1.5 mm, the skin layer part is thick enough to be perceived sensibly, so that not only the texture is impaired, but also chip processing in construction work is difficult and heat insulation is inferior.

Further, the magnification E internal foam layer of the foamed polypropylene resin body is virtually Ru der 10-60 times less. When the magnification ratio E of the foamed layer is less than 10 times, a major feature of the foam, lightweight is not sufficient to volume, will per unit volume cost, which is the main market for foam insulation building materials, automobiles It can hardly be used as a material for member use, buffer material use and the like. When the foam layer magnification E exceeds 60 times, the cell membrane constituting the foam becomes too thin, the cell structure becomes inhomogeneous and unstable, and as a result, the mechanical properties such as compressive strength, which is a characteristic of the foam, are large. A decrease occurs. Especially, the magnification E of the internal foam layer is substantially more preferably 20 to 60 times. When the magnification E of the internal foam layer is within this range, a strand bundle having a density useful in the market as a foam and having a uniform and fine cell structure can be produced.

  The expansion ratio of the internal foam layer in the polypropylene resin foam of the present invention is the expansion ratio of the substantially foamed portion excluding the surface skin layer in the foam. Therefore, for example, for a foam that has not been provided with a skin layer, the expansion ratio of the internal foam layer is substantially the same as the expansion ratio of the foam itself.

  In order to describe the present invention more specifically, examples are given below, but the present invention is not limited to these examples.

Example 1
A polypropylene resin A having an MFR at 230 ° C. of 3.3 (g / 10 min) and a melt tension at 230 ° C. of 7.6 g is supercritical carbon dioxide supply machine (manufactured by Kawata Corporation) Product name: CO2-3) carbon dioxide supply line is installed, and the tandem type single with a die 1 (8 × 48 multi-hole die with an opening diameter of 0.5 mm) attached to the tip of the second stage It supplied to the screw extruder (KGT-50-65 by Kawata Co., Ltd.).

  In the extruder, the carbon dioxide supply amount is set to 1.2 kg / hour, and the extrusion amount is adjusted by the screw rotation speed of the first-stage extruder so as to contain 6 parts by mass with respect to 100 parts by mass of the polypropylene resin A. In addition, by adjusting the screw rotation speed of the second-stage extruder so that the resin pressure (pressure loss) at one part of the die is 8.7 MPa, the foam surface untreated product of the polypropylene resin A is obtained by extrusion foaming. Obtained.

  For the untreated foam surface 1 of the polypropylene resin A, two heating rolls with a mirror-finished surface are prepared in the immediate vicinity of the die exit of the extruder, the distance between which can be changed. The polypropylene-based resin A foam surface untreated product 1 is passed between the rolls, and the surface of the polypropylene-based resin foam when the upper and lower rolls pass is kept at around 170 ° C. (melting point of the polypropylene-based resin A + 5 ° C.), After sufficiently heating and rolling for about 10 seconds until the compression skin (foam height after pressing / foam height ratio before pressing: S) is 0.8 and the foam skin layer melts to form a skin layer Then, size adjustment and cutting were performed using a take-up roll and a cutting device, surface treatment was performed, and a foam of polypropylene resin A having surface skin layers on both upper and lower surfaces was obtained.

Example 2
The surface of the polypropylene resin foam when passing through the upper and lower rolls is kept at around 175 ° C. (melting point of polypropylene resin A + 10 ° C.), heated and rolled for about 10 seconds with a compression ratio of 0.8, and then taken up. Except having carried out dimension adjustment and cutting using the roll and the cutting apparatus, it implemented similarly to Example 1, and obtained the foam of the polypropylene resin A which has a surface skin layer only on the upper surface.

Example 3
A sandwich type in which a mesh sheet (made of Teflon) is wound in the vicinity of the die outlet of the extruder, adjusted by the screw speed of the second-stage extruder so that the resin pressure at one part of the die in the extruder becomes 8.8 MPa. A belt conveyor was prepared, and the produced foam-surface untreated product 2 of the polypropylene resin A was allowed to pass through both belt conveyors. After the surface of the polypropylene resin foam when passing through the sandwiched belt conveyor is kept at around 165 ° C. (melting point of the polypropylene resin composition A), and after sufficiently heating and rolling for about 10 seconds at a compression ratio of 0.8 A foam of polypropylene resin A having a surface skin layer only on the upper surface was obtained by carrying out in the same manner as in Example 1 except that the dimensions were adjusted and cut using a take-up roll and a cutting device.

Comparative Example 1
The same tandem single-screw extruder as used in Example 1 for polypropylene resin B (homopolypropylene resin) having an MFR at 230 ° C. of 6 g / 10 min and a melt tension at 230 ° C. of 1.8 g. The carbon dioxide supply amount is set to 1.2 kg / hour, and the extrusion amount is adjusted by the screw speed of the first-stage extruder so as to contain 6 parts by mass with respect to 100 parts by mass of the polypropylene resin. The foam 4 of a polypropylene resin composition was obtained by adjusting the screw rotation speed of the second-stage extruder so that the resin pressure at the die 1 site was 4.5 MPa and extrusion foaming.

Comparative Example 2
A sandwich-type belt conveyor wound with a mesh sheet (made of Teflon) is prepared in the immediate vicinity of the die outlet of the extruder, and the both surfaces of the foam conveyor are allowed to pass slowly through the foam surface, and the surface is 200 ° C. (polypropylene resin A The melting point of the resin is maintained at around 35 ° C.), and the compression rate is set to 80%. The foam skin layer is sufficiently heated and rolled for about 10 seconds until the skin layer is melted to form a skin layer. A foam was obtained in the same manner as in Example 1 except that the adjustment and cutting were performed and the heating surface treatment was performed.

Comparative Example 3
The resin pressure at the die 2 (8 × 48 row multi-hole die with an opening diameter of 0.8 mm) is adjusted to 5.1 MPa by adjusting the screw speed of the second-stage extruder, and extrusion foaming is performed. To obtain a foam and prepare a sandwich type belt conveyor wound with a mesh sheet (made of Teflon), and slowly pass the produced polypropylene resin A foam surface untreated product 3 of both belt conveyors. The surface is kept near 130 ° C. (melting point of polypropylene resin A−35 ° C.), and the compression rate is 80%. The foam skin layer melts and forms a skin layer for about 10 seconds. After that, a foam was obtained in the same manner as in Example 1 except that dimensional adjustment and cutting were performed using a take-up roll and a cutting device, followed by heating surface treatment.

Comparative Example 4
The same tandem single-screw extruder as used in Example 1 for polypropylene resin B (homopolypropylene resin) having an MFR at 230 ° C. of 6 g / 10 min and a melt tension at 230 ° C. of 1.8 g. Supplied. In the extruder, the carbon dioxide supply rate is set to 1.2 kg / hour, and the extrusion amount is adjusted by the screw rotation speed of the first-stage extruder so as to contain 6 parts by mass with respect to 100 parts by mass of the polypropylene resin. The foam of the polypropylene resin composition was obtained by adjusting the screw rotation speed of the second-stage extruder so that the resin pressure at 1 part of the die was 4.5 MPa and extrusion foaming.

  A sandwich-type belt conveyor wound with a mesh sheet (made of Teflon) is prepared, and the produced polypropylene-based resin B foam surface untreated product 4 is slowly passed through both belt conveyors. The melting point of the polypropylene resin B is kept in the vicinity of −5 ° C., the compression rate is 80%, and the foam skin layer is sufficiently heated and rolled for about 10 seconds until the foam skin layer is melted to form the skin layer. A foam was obtained in the same manner as in Example 1 except that dimensional adjustment and cutting were performed using an apparatus.

Performance of polyolefin (polypropylene) -based resin composition foams obtained in Examples 1 to 3 and Comparative Examples 1 to 4 (a. Foam layer density, b. Compressive strength, c. Average cell) Diameter, d. Melt tension, e. Bending strength, f. Skin layer thickness, g. Foam layer thickness, h. Foam density, i. Melting point of polypropylene resin, j. Appearance, k. Light weight, l. Conductivity) was evaluated by the following method.
a. Foam layer density: The foam layer of the obtained foam is cut into 20 × 20 × 2 (cm) test pieces, the weight and length of each side are measured, and the foam density is determined according to the following formula: Asked.
(Foam layer density G / L) = (foam layer small piece weight G) / (foam layer small piece volume L)
b. Compressive strength: Based on JISK-6767 (polyethylene foam test method), the 25% compression hardness (kPa) of the foam was measured.
c. Average cell diameter: The foam is cut into test pieces, and the cross-sectional area is obtained from an image observed with an electron microscope (SEM) at a magnification of 50 times using an SEM super scan 220 manufactured by Shimadzu Corporation. The average cell diameter was calculated by the following formula by drawing 10 straight lines corresponding to a length of 2 mm at random and counting the number of cells on the straight line.
(Average cell diameter μm) = (2000 × 10) / (number of cells on 10 straight lines)
d. Melt tension: determined using a capillograph 1C (manufactured by Toyo Seiki Co., Ltd.) at a measurement temperature of 230 ° C., an extrusion speed of 10 mm / min, and a take-up speed of 3.1 m / min. In the measurement, an orifice having a length of 8 mm and a diameter of 2.095 mm was used.
e. Bending strength: Measured according to JIS7221-2 jig B method.
f. Skin layer thickness: The interface between the foam layer and the skin layer in the foam was expanded using an optical loupe, and the thickness of the skin layer portion was measured using a reference gauge preliminarily engraved with a length scale.
g. Foam layer thickness: The interface between the foam layer and the skin layer in the foam was enlarged using an optical loupe, and the thickness of the foam layer portion was measured using a reference gauge preliminarily engraved with a length scale.
h. Foam density: foam layer density obtained in the above-mentioned a, f. Skin layer thickness, g. From the foam layer thickness, the foam density was determined according to the following formula.
(Foam density G / L) =
(Foaming layer density G / L) × (foaming layer thickness mm) / ((skin layer thickness mm) + (foaming layer thickness mm)) + (900 G / L) × (skin layer thickness mm) / ((skin layer thickness mm) + (foamed layer thickness mm))
i. Melting point of polypropylene resin: Using a DSC measuring device (diamond DSC) manufactured by PerkinElmer, the top peak of the crystal melting heat was measured for 10 mmg of the sample at a heating rate of 10 ° C./min.
j. Appearance: The surface property of the obtained foamed board and the presence or absence of distortion due to waviness of the shape were visually observed.
k. Lightness: It was determined whether or not the foam has a density of 90 G / L or less, which greatly expands the market value as a high-magnification foam.
l. Thermal conductivity: In accordance with JIS A-1412, the obtained foam was cut into 20 × 20 × 2 (cm) test pieces, and a thermal conductivity measuring device HC-074 manufactured by Eihiro Seiki was used. The thermal conductivity was measured.
Table 1 shows the composition used in the present invention, the extrusion conditions, and the physical properties of the obtained foam.

  From the above results, the foam of Comparative Example 3 in which the thickness of the skin layer does not satisfy Formula 1 is inferior in bending strength, and Comparative Example 2 has a bending strength that is significantly impaired in terms of the lightness of the foam before treatment. The improvement effect was not outstanding. Further, Comparative Example 1 having a foaming ratio of less than 10 times at a melt tension of less than 5 g at 230 ° C. was inferior in foamability itself and could not obtain a strand-bundled foam having a satisfactory ratio and appearance. Further, Comparative Example 4 having a foaming ratio of less than 10 times can obtain a strand bundling foam having satisfactory magnification and appearance even when the skin layer satisfying the formula 1 is applied while the density is high and heavy. There wasn't. Further, the thermal conductivity showing the performance as a heat insulating material, which is one of useful uses of the foam, was inferior to that of the Examples and did not exhibit sufficient performance.

  The foam of the polypropylene resin composition of the present invention has a balance between its excellent performance and cost, particularly high bending strength and lightness, and is mainly used for heat insulating building materials, automotive parts, and packaging cushioning materials. It can be widely used for applications.

Claims (2)

A method for producing a polypropylene resin foam having the same composition and comprising a surface skin layer and an internal foam layer and satisfying the following formula (1), wherein the melt tension at 230 ° C. is 5 to 30 g: to 100 parts by weight of the polypropylene resin composition comprising a resin, the carbon dioxide in a supercritical state including blowing agent mixed 4 to 20 parts by weight, and melt-kneaded using an extruder to該混initial charge, die diameter 0. A multi-hole die having 1 to 0.7 mm is passed, extruded and foamed at a pressure loss of 6 to 20 MPa, and the strands are converged. Then, the obtained foam is expressed by the following (formula 2) and ( formula 3). A method for producing a polypropylene resin foam, characterized by heating and pressing at a filling temperature and pressure.
D / 20E ≦ Z ≦ D / 2E (Expression 1)
(However, the thickness of the surface skin layer that is Z: 0.15 to 1.5 mm, D: the thickness of the internal foam layer that is 10 to 50 mm (mm), E: the magnification of the internal foam layer that is 10 to 60 times)
Tm ≦ K ≦ Tm + 20 (Equation 2)
0.5 ≦ S <0.95 (Expression 3)
(However, K: Surface temperature of foam (° C.), Tm: Melting point (° C.) of polypropylene resin composition measured at 10 ° C./min using DSC, S: Compression rate = after pressing Foam height (cm) / foam height before pressing (cm))   The method for producing a polypropylene resin foam according to claim 1, wherein the surface temperature of the foam during heating and pressing is 165 to 195 ° C.