JP2011016914A - Foamed polypropylene resin particle and molded product of foamed particle made of the foamed particle - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide foamed polypropylene resin particles that can be heat-molded under a low steam pressure, does not leave any resin deposit on a surface of a molding die in molding, is excellent in fusibility between the foamed particles and is capable of yielding a smooth-surfaced, highly flexible molded product of foamed particles, and the smooth-surfaced, highly flexible molded product of the foamed polypropylene resin particles.SOLUTION: The foamed polypropylene resin particles are multilayered foamed particles obtained by expanding multilayered resin particles comprising a core layer and a coating layer formed from a polypropylene resin, provided that the weight ratio of the core layer to the coating layer is from 99.5:0.5 to 80:20. Regarding the polypropylene resin forming the core layer and the polypropylene resin forming the coating layer, the difference in their melting points falls within a specific range, the ratio of amounts of partial melting heat within the temperature range equal to or higher than the melting point falls within a specific range, the difference in their flexural modulus falls within a specific range, and the flexural modulus of the polypropylene resin forming the core layer is equal to or smaller than a prescribed value.

Description

  The present invention relates to expanded polypropylene resin particles, and in particular, polypropylene that can be molded with a low heating steam pressure, has heat resistance, and has a smooth surface and excellent flexibility. The present invention relates to a foamed resin foam particle and a foamed particle molded body comprising the foamed particle.

Polypropylene-based foamed resin particles can be molded into various shapes according to the application, and have excellent mechanical properties, heat resistance, shock-absorbing properties, and workability. Widely used in absorbent materials.
However, in the polypropylene resin expanded particles, when the melting point of the polypropylene resin is 135 ° C. or higher, a high heating steam pressure is required to sufficiently fuse the expanded particles when the expanded particles are molded in the mold. Become. For this reason, the service cost required for shaping | molding becomes high. Conventionally, as a method of lowering the heating steam pressure at the time of in-mold molding, a method of covering the surface of the polypropylene resin foamed particles with a low melting point resin has been performed.

  For example, Patent Document 1 includes a foamed core layer made of a crystalline thermoplastic resin, an ethylene polymer having a melting point lower than that of the thermoplastic resin, and a substantially non-foamed coating layer. It is described that the formed expanded particles can be molded by a general-purpose molding machine having a low mold closing pressure.

  Patent Document 2 discloses a polypropylene resin expanded particle composed of a core layer formed of a highly rigid polypropylene resin and a coating layer formed of a polypropylene resin having a melting point lower than that of the core layer. It is described that a foamed molded article having rigidity and heat resistance can be obtained.

Japanese Patent No. 3418081 JP 2004-68016 A

However, in the foamed particle molded body molded using the foamed particles described in Patent Document 1, the core layer and the coating layer of the foamed particles are formed because the core layer and the coating layer are composed of a combination of different resins. There is a problem that peeling easily occurs between the two. Further, the foamed particles have a problem in recyclability because the core layer and the coating layer are made of different resins.
Furthermore, since the melting point difference between the core layer and the coating layer is large, there is a large temperature difference between the temperature at which the coating layers of the expanded particles are fused together and the temperature at which the core layer is secondarily foamed. For this reason, if the core layer is molded at a high heating steam pressure in order to sufficiently secondary foam, the coating layer softens and the molded body adheres to the surface of the molding die, resulting in inferior molding processability. It was.

In the foamed particle molded body in which the foamed particles described in Patent Document 2 are molded in-mold, a highly rigid core layer is sufficiently secondary foamed by a high heating steam pressure in order to obtain a molded body with good surface smoothness. There is a problem that it exceeds the general pressure resistance (0.4 MPa) of the molding machine used for the conventional expanded polypropylene resin particles.
On the other hand, when molding is performed at a heating steam pressure within the pressure resistant performance range of the conventional molding machine, there is no major problem in the fusion between the foam particles, but the secondary foaming of the core layer becomes insufficient, As a result, voids are generated between the particles on the surface of the molded body, resulting in poor surface smoothness. In addition, such a molded body is easily cracked on the surface of the molded body, leaving a problem in flexibility.

  The present invention can be molded at a steam pressure lower than the heating steam pressure required for heat molding of conventional polypropylene resin foamed particles, and there is no resin adhesion to the mold surface during molding, and the foamed particles Polypropylene resin foam particles having excellent fusion properties between them, a smooth surface, and a foamed particle molded article excellent in flexibility, and polypropylene resin foam particles having a smooth surface and excellent flexibility It aims at providing a molded object.

  As a result of diversified examinations from various viewpoints to achieve the above-mentioned problems, the polypropylene resin that satisfies the specific ranges of the melting point, heat of fusion, and flexural modulus of the polypropylene resin forming the multilayer resin particles The foamed particles formed by foaming the multilayer resin particles, which are resins, have excellent fusion properties between the foamed particles, and can be heat-molded with a low heating steam pressure, without resin adhesion to the mold, The foamed particle molded body obtained by thermoforming the foamed particles was found to have a smooth surface and excellent flexibility, and the present invention was made based on this.

That is, the present invention is [1] a multilayer resin particle comprising a core layer and a coating layer formed of a polypropylene resin, wherein the weight ratio of the core layer to the coating layer is 99.5: 0.5 to 80:20. Polypropylene-based resin foamed particles, which satisfy the following requirements (a-1) and / or (a-2), and (b) and (c) .
(A-1) The resin melting point Tc (° C.) of the polypropylene resin forming the core layer and the resin melting point Ts (° C.) of the polypropylene resin forming the coating layer are expressed by the following formula (1). Satisfied.
(Equation 4)
1.5 ≦ Tc−Ts ≦ 30 (° C.) (1)
(A-2) In the DSC endothermic curve obtained by heat flux differential scanning calorimetry of the polypropylene resin forming the core layer, the partial melting heat amount in the temperature range equal to or higher than the resin melting point (Tc) of the core layer is expressed as Ec (J / g), and the partial melting heat amount in the temperature range equal to or higher than the resin melting point (Tc) of the core layer in the DSC endothermic curve obtained by heat flux differential scanning calorimetry of the polypropylene resin forming the coating layer Is Es (J / g), Ec and Es satisfy the following formula (2).
(Equation 5)
0 ≦ Es / Ec ≦ 0.7 (2)
(B) The bending elastic modulus of the polypropylene resin forming the core layer: Mc (MPa) and the bending elastic modulus of the polypropylene resin forming the coating layer: Ms (MPa) are expressed by the following formula ( Satisfy 3). And
(Equation 6)
Mc-Ms ≦ 500 (MPa) (3)
(C) The bending modulus of elasticity of the polypropylene resin forming the core layer: Mc (MPa) is 1100 MPa or less.
[2] The polypropylene resin expanded particle according to [1], wherein the polypropylene resin forming the core layer has a melting point: Tc (° C.) of 150 ° C. or less.
[3] Foamed particles having an apparent density of 12 g / L to 50 g / L obtained by filling the foamed particles according to [1] or [2] in a molding die and heat-molding Molded body.
Is the gist.

The polypropylene resin foamed particles of the present invention are excellent in fusion property between the foamed particles and secondary foamability, and can be heat-molded by lowering the heating steam pressure required at the time of molding.
Further, the foamed particle molded body obtained by molding the foamed particles of the present invention in a mold is a foamed particle molded body having a smooth surface and excellent flexibility, and is suitable for an impact absorbing material, various packaging materials, buffer materials, and the like. In particular, it is suitable as a packaging material or a cushioning material.

An example of the DSC curve of raw material resin which forms the multilayer expanded particle of this invention is shown. An example of the curve by the micro thermo mechanical measurement which shows the softening point of the core layer part of the multilayer expanded particle of this invention and a coating layer part is shown. An example of the 1st time DSC curve of an expanded particle is shown. An example of the 2nd DSC curve of an expanded particle is shown.

The polypropylene resin multilayer expanded particle of the present invention comprises a core layer and a coating layer formed of a polypropylene resin, and the weight ratio of the core layer to the coating layer is 99.5: 0.5 to 80:20. Multi-layer foamed particles (hereinafter sometimes simply referred to as “foamed particles”) formed by foaming multi-layer resin particles.
The foamed particles include a core layer portion formed by foaming a polypropylene resin of a core layer of the multilayer resin particles, and a substantially non-foamed cover layer portion formed of a polypropylene resin of a coating layer of the multilayer resin particles. Become.

  The requirements of the above (a-1) and (a-2) are important in achieving the object of the present invention to obtain foamed particles that can be molded at a low steam pressure during the steam molding of the foamed particles. One of the requirements. In addition, the molded article obtained by molding the foamed particles of the present invention in the mold is excellent in flexibility and surface smoothness. It is important in that it becomes a molded body.

Specifically, (a-1) has a resin melting point Tc (° C.) of the polypropylene resin forming the core layer and a resin melting point Ts (° C.) of the polypropylene resin forming the coating layer. The above formula (1) is satisfied.

(A-2) is a DSC endothermic curve specific to the raw material resin obtained by heat flux differential scanning calorimetry of the core layer resin, as shown in FIG. 1, and as shown in FIG. In the DSC endothermic curve specific to the raw material resin obtained by measuring the heat flux differential scanning calorimetry of the resin of the coating layer as Ec (J / g), the partial melting heat quantity in the temperature range above the resin melting point (Tc) is shown in FIG. When the partial heat of fusion in the temperature range equal to or higher than the resin melting point (Tc) of the core layer as shown in b) to (c) is Es (J / g), the above formula (2) is satisfied. .

  Melting point difference between the melting point of the polypropylene resin forming the core layer of the multilayer resin particle: Tc (° C.) and the melting point of the polypropylene resin forming the coating layer of the multilayer resin particle: Ts (° C.): When Tc-Ts is too large, when the foamed particles are molded in the mold, the resin forming the coating layer portion of the foamed particles is softened and melted, so that the fusion property is lowered or molded at the time of molding. There is a risk of resin adhering to the mold surface.

Moreover, it is preferable that the said resin melting | fusing point difference is the range of following formula (4), More preferably, it is the range of following formula (5).
(Equation 7)
5 ° C. ≦ Tc−Ts ≦ 25 ° C. (4)
(Equation 8)
7 ° C. ≦ Tc−Ts ≦ 20 ° C. (5)

As the melting point of the polypropylene resin forming the core layer and the coating layer, a value obtained by a heat flux differential scanning calorimetry method (DSC method) based on JIS K 7122 (1987) is adopted.
That is, when producing multilayer resin particles, 2 to 4 mg of polypropylene resin used as a raw material for the core layer is collected, and 10 ° C./min from room temperature (10 to 40 ° C.) to 220 ° C. by a heat flux differential scanning calorimeter. The temperature was raised at a rate of 10 ° C / min from 220 ° C to 40 ° C and then increased again at a rate of 10 ° C / min from 40 ° C to 220 ° C. Do warm. The peak temperature of the DSC endothermic curve peak at the second temperature rise obtained by such measurement is defined as the melting point. When there are two or more endothermic curve peaks, the peak temperature of the endothermic curve peak having the highest peak intensity is adopted as the melting point.

If the difference in melting point between the polypropylene resin forming the core layer and the coating layer of the multilayer resin particles is within the above range, the melting point of the coating layer is relatively low, so the fusibility of the expanded particles is good. It becomes. In addition, during in-mold molding, the resin that forms the coating layer portion of the expanded particles is not excessively softened and melted, the resin does not adhere to the molding die surface, and the surface smoothness is even better. A foamed particle molded body is obtained.
Moreover, it is preferable to select suitably the polypropylene resin which has formed the coating layer of the multilayer resin particle so that it may become the above-mentioned range.

  The partial melting heat quantity Ec in the temperature range equal to or higher than the resin melting point (Tc) of the core layer is substantially 0 (zero) J / g as shown in FIG. When the partial heat of fusion Ec increases, the DSC curve becomes broader on the high temperature side, and molding on the high temperature side is necessary, so that the secondary foamability of the obtained foamed particles may be low.

  In the resin of the coating layer, when the partial melting heat quantity Es does not satisfy the relationship of the above formula (2) and Es / Ec is too large, the core layer and the coating layer at or above the resin melting point of the core layer. It means that the crystal melting behavior of the resin forming the resin is close. As will be described later, when a foaming method is performed such that a high temperature peak is formed in the resin of the core layer in the foaming step, a high temperature peak is also formed in the resin crystal of the coating layer if Es / Ec is too large. As a result, the melting temperature of the resin of the coating layer increases. As a result, a large number of crystals that form high-temperature peaks are mixed on the surface of the expanded particles, and it becomes difficult to melt the crystals on the expanded particle surface at a low steam pressure. The mutual fusion property is relatively low, and the intended purpose of the present invention may not be achieved.

If Es / Ec is within the above range, even if a high temperature peak is formed in the resin of the core layer in the foaming step, the influence of the coating layer on the resin is small, and the coating layer has good fusion properties. The value of Es / Ec is
(Equation 9)
0 ≦ Es / Ec ≦ 0.5 (6)
It is preferable that
(Equation 10)
0 ≦ Es / Ec ≦ 0.3 (7)
More preferably.

  As described above, the melting point (Tc) of the polypropylene resin of the core layer employs a value obtained by a heat flux differential scanning calorimetry (DSC method) based on JIS K 7122 (1987).

  Further, the DSC endothermic curve for calculating the partial heat quantity of the polypropylene resin of the core layer and the DSC endothermic curve for calculating the partial heat quantity of the polypropylene resin of the coating layer are the methods for measuring the melting point of the polypropylene resin of the core layer described above. A DSC endothermic curve at the second temperature increase obtained in the same manner is used.

The requirement (b) is the difference between the flexural modulus of the polypropylene resin forming the core layer: Mc (MPa) and the flexural modulus of the polypropylene resin forming the coating layer: Ms (MPa). Is required to be 500 MPa or less. When the difference between Mc and Ms is too large, there is a possibility that peeling occurs between the core layer portion and the coating layer portion of the expanded particles. When peeling occurs between the core layer portion and the coating layer portion, there is a possibility that it is impossible to obtain foamed particles capable of reducing the molding pressure. In addition, molding processability is deteriorated, for example, a coating layer peeled off at the time of molding adheres to a molding die. Furthermore, the obtained in-mold foam molded article may be inferior in surface smoothness. On the other hand, even in the case where no peeling is observed, the expanded particles using a resin having a large difference in flexural modulus have a poor balance between the fusion property and the secondary foamability at the time of molding, and the secondary foamability is lowered. There is a risk of forming foamed particles.

  The bending elastic modulus of the polypropylene resin forming the coating layer: Ms is the difference between the bending elastic modulus of the resin forming the core layer and the bending elastic modulus of the resin forming the coating layer: Mc−Ms It is appropriately selected so as to be 500 or less. Difference in flexural modulus: When Mc-Ms exceeds 500, as described above, there are problems in terms of peeling of the coating layer and the core layer of the foamed particles, surface smoothness and flexibility of the foamed particle molded body. May occur.

  The difference in flexural modulus: Mc-Ms is preferably 280 MPa or less. Within the above range, the resin forming the coating layer and the core layer has a good balance between the fusibility during foam molding and the secondary foamability, and the number of particle gaps on the surface of the molded body should be reduced. Can do.

The requirement (c) requires that the flexural modulus: Mc (MPa) of the polypropylene resin forming the core layer be 1100 MPa or less. When the flexural modulus of the polypropylene resin forming the core layer: Mc is too high, the core layer portion is formed by molding at a low steam pressure, even if the fusion between the foamed particles is good. Since the formed polypropylene resin has a high flexural modulus, there is a possibility that a molded article having excellent flexibility cannot be obtained. The bending elastic modulus is preferably 1000 MPa or less.

In addition, said bending elastic modulus is measured based on the measuring method as described in JISK7171 (1994).
The flexural modulus was as follows: a test piece having a thickness of 4 mm, a width of 10 mm, and a length of 80 mm was left in a thermostatic chamber at room temperature of 23 ° C. and a humidity of 50% for 24 hours or more, and then the fulcrum distance was 64 mm and the indenter radius R ₁ was 5. It was measured and calculated by an autograph AGS-10kNG (manufactured by Shimadzu Corporation) tester under the conditions of 0 mm, radius R _{2 of the} support base of 5.0 mm, test speed of 2 mm / min, room temperature of 23 ° C. and humidity of 50%. The arithmetic average value (5 points or more) is adopted.

  The polypropylene resin forming the core layer of the multilayer resin particle of the present invention is, for example, a propylene homopolymer or a propylene component unit of 60 mol% or more, preferably 80 mol% or more of propylene and another comonomer. One of the copolymers, or a mixture of two or more selected from these polymers may be mentioned.

  Examples of the copolymer of propylene containing 60 mol% or more of the propylene component and other comonomers include, for example, propylene-ethylene random copolymer, propylene-ethylene block copolymer, propylene-butene random copolymer. And propylene-ethylene-butene random copolymer.

  To the polypropylene resin forming the core layer, a synthetic resin other than the polypropylene resin and / or a synthetic rubber and / or an elastomer is added within a range not impairing the intended effect of the present invention. can do. The total amount of synthetic resin other than polypropylene resin, synthetic rubber, and elastomer is preferably 35 parts by weight or less, more preferably 25 parts by weight or less, and still more preferably 10 parts with respect to 100 parts by weight of polypropylene resin. More preferably, it is 5 parts by weight or less.

  Examples of the synthetic resin other than the polypropylene resin include high-density polyethylene, medium-density polyethylene low-density polyethylene, linear low-density polyethylene, linear ultra-low-density polyethylene, ethylene-vinyl acetate copolymer, ethylene- Examples thereof include ethylene resins such as acrylic acid copolymers, ethylene-acrylic acid ester copolymers, and ethylene-methacrylic acid ester copolymers, and styrene resins such as polystyrene and styrene-maleic anhydride copolymers.

  Examples of the synthetic rubber include ethylene-propylene rubber, ethylene-1-butene rubber, propylene-1-butene rubber, styrene-butadiene rubber and hydrogenated products thereof, isoprene rubber, neoprene rubber, and nitrile rubber. Examples of the elastomer include a styrene-butadiene block copolymer, a styrene-isoprene-styrene block copolymer, and hydrogenated products thereof.

  In the polypropylene resin of the core layer, various additives can be contained as desired. Examples of such additives include antioxidants, ultraviolet light inhibitors, antistatic agents, flame retardants, metal deactivators, pigments, dyes, nucleating agents, and bubble regulators. Examples of the air conditioner include inorganic powders such as zinc borate, talc, calcium carbonate, borax, and aluminum hydroxide.

  The content of these additives is 20 parts by weight or less, preferably 15 parts by weight or less, more preferably 10 parts by weight or less, and further 5 parts by weight or less based on 100 parts by weight of the polypropylene resin forming the core layer. It is preferable that In particular, the content of the air conditioner is preferably 0.005 to 1 part by weight when the average cell diameter of the expanded particles is 20 μm to 300 μm.

  The polypropylene resin forming the coating layer of the multilayer resin particles of the present invention is a polypropylene resin that forms a core layer except that the polypropylene resin is selected so as to satisfy the above-mentioned requirements. The same is illustrated.

  In the propylene-based resin forming the coating layer, the same additive as the additive added to the core layer can be contained as necessary, like the polypropylene-based resin of the core layer. The content thereof is approximately 30 parts by weight or less, preferably 15 parts by weight or less, more preferably 10 parts by weight or less, and particularly preferably 5 parts by weight or less with respect to 100 parts by weight of the resin of the coating layer. The lower limit of the addition amount is approximately 0.01 parts by weight.

The melting point of the propylene-based resin forming the core layer is such that it is possible to cause the secondary foaming of the core layer to be performed at a low steam pressure during heating molding of the foamed particles, and has flexibility. From the viewpoint of obtaining a foam molded article having excellent surface smoothness, it is preferably 150 ° C. or lower, and preferably 135 to 145 ° C.
On the other hand, the lower limit of the melting point of the polypropylene-based resin forming the core layer is preferably 115 ° C. or higher from the viewpoint of softening and melting of the surface of the expanded particles in consideration of the resin forming the coating layer. .

  The softening point of the core layer portion of the foamed particle of the present invention: Nc (° C.) is preferably higher than the softening point of the coating layer portion of the foamed particle: Ns (° C.). In the case described above, the fusion property between the foamed particles and the secondary foamability are improved, and the molded product obtained by molding the foamed particles in a mold is further excellent in flexibility and surface smoothness. Become. Further, when the softening point temperature of the coating layer portion is relatively high, the fusion property of the obtained foamed particles is lowered, and the softening of the resin proceeds excessively. Resin adhesion may occur.

Further, the softening point of the core layer portion and the covering layer portion is expressed by the following formula (8).
(Equation 11)
Nc-Ns ≦ 70 ° C. (8)
It is preferable that the above relationship is satisfied, and if it is within the above range, the physical properties of the core layer portion and the coating layer portion of the expanded particles are balanced, and the fusibility and secondary expandability of the expanded particles become better.

  The softening point of the core layer portion of the expanded particles: Nc is preferably 170 ° C. or lower. If the softening point of the core layer portion is 170 ° C. or lower, the secondary foaming of the core layer portion is sufficiently performed with a low steam pressure, regardless of a conventional pressure-resistant molding machine for molding polypropylene resin foam particles. It is possible to obtain expanded particles that are more excellent in fusion between particles. Furthermore, there is no space between the particles on the surface of the foamed molded product obtained from the foamed particles, and the foamed molded product has flexibility and excellent surface smoothness.

  In the present invention, the softening point of the coating layer portion of the multilayer expanded particle is preferably 80 ° C. or higher. If it is the said range, the foamed particle molded object which does not impair the original heat resistance as the whole polypropylene resin foam particle can be obtained.

  The softening point was measured using a micro thermo mechanical measurement (hereinafter sometimes referred to as μTA), a micro thermal analysis system “2990 type micro thermal analyzer” manufactured by T.A. From 250 to 250 ° C. under a temperature rising rate of 10 ° C./second.

  The micro-thermo-mechanical measurement for the coating layer portion of the expanded particles is performed by measuring expanded particles (if one expanded particle is too large as it is, for example, by cutting it into half, etc.) The test piece cut out from the sample is fixed to the sample stage of the apparatus, and then the probe tip (covering the expanded particles) is directed toward a randomly selected location on the surface of the expanded particles constituting the expanded particles or the expanded particle molded body. The portion to be brought into contact with the layer portion has a tip portion of 0.2 μm in length and width) and is brought into contact with the expanded particles. Then, the probe tip comes into contact with the coating layer, the temperature is raised, and the softening point of the coating layer is measured. Thereafter, the coating layer portion melts, but the probe tip is further heated to reach the core layer portion, and the softening point of the core layer portion is measured.

  FIG. 2 shows an example of the μTA curve of the coating layer portion and the core layer portion of the foam particles constituting the foam particles or the foam particle molded body, and using these drawings, the coating layer portion of the foam particles A method for obtaining a steep inflection point derived from the softening of the crystal will be described.

In FIG. 2, a curve Cm is an example of a μTA curve for multilayer expanded particles. The curve Cm shows at least two steep displacement amounts (Cm1) having a steep displacement amount originating from the coating layer portion on the low temperature side and steep regions (Cm2) having a steep displacement amount originating from the core layer portion on the high temperature side. It has the field which shows. In each of the Cm1 and Cm2 regions, two tangents to the curve Cm before and after the temperature with a steep displacement are created, which are defined as a tangent BL and a tangent TL, respectively. The inflection point N is an intersection of the tangent line BL and the tangent line TL. This intersection was defined as a softening point N.
The inflection point by the micro thermomechanical measurement is measured by increasing the measurement temperature of the apparatus at a constant rate of 10 ° C./second. The temperature of the inflection point is the intersection of the tangents of the descending positions of the regions before and after the steep amount of displacement due to the softening of the crystal in the curve of the displacement and temperature due to the softening of the crystal.

  In the present invention, the DSC curve obtained by heat flux differential scanning calorimetry of the expanded particles includes an endothermic curve peak inherent to the polypropylene resin (hereinafter referred to as “inherent peak”) and an endothermic curve on the higher temperature side than the endothermic curve peak. A peak (hereinafter referred to as [high temperature peak]), and the heat quantity of the endothermic curve peak on the high temperature side is preferably 1 J / g or more and 40 J / g or less, and more preferably 3 J / g to 35 J / g, In particular, it is preferably 5 J / g to 30 J / g. Such expanded particles are suitable expanded particles for thermoforming.

  If the amount of heat at the high temperature peak is too small, the steam pressure at the time of molding can be lowered, but the compression strength and energy endotherm of the resulting foamed particle molded body may be reduced. On the other hand, if the amount of heat at the high temperature peak is too large, expanded particles with the target expansion ratio cannot be obtained, or the secondary foamability during molding is suppressed, and a molded body cannot be obtained unless the molding pressure is increased. There is a risk that.

  The amount of heat at the high temperature peak is preferably 3% or more, more preferably 5% or more, further 8% or more, and particularly preferably 10% or more with respect to the total amount of heat of all endothermic curve peaks. Further, the upper limit is preferably 70% or less, more preferably 60% or less, and particularly preferably 50% or less.

  Moreover, it is preferable that the sum total (total calorie | heat amount) of all the endothermic curve peaks of the expanded particle in this invention is 40-100 J / g. If the amount of heat is too small, physical properties such as compression may be reduced. On the other hand, when the amount of heat is too large, there is a possibility that the foamed particle molded body has a poor secondary foaming property during molding and has many gaps.

The total calorific value of the endothermic curve peak and the calorific value of the high temperature peak are measured as follows by a measuring method based on JIS K7122 (1987).
First, 2 to 10 mg of foamed particles are collected, and the temperature is increased from room temperature (10 to 40 ° C.) to 220 ° C. at a rate of 10 ° C./minute using a heat flux differential scanning calorimeter. An example of the first DSC curve obtained by such measurement is shown in FIG.

  In the DSC curve of FIG. 3, an intrinsic peak a derived from the polypropylene resin constituting the expanded particles and a high temperature peak b appear, and the amount of heat of the high temperature peak b corresponds to the peak area. It can be obtained as follows.

  First, a straight line (α−β) connecting a point α corresponding to 80 ° C. on the DSC curve and a point β on the DSC curve corresponding to the melting end temperature T of the expanded particles is drawn. The melting end temperature T is a temperature corresponding to the intersection of the DSC curve on the high temperature side of the high temperature peak b and the high temperature side baseline.

Next, a straight line parallel to the vertical axis of the graph is drawn from the point γ on the DSC curve corresponding to the valley between the intrinsic peak a and the high temperature peak b, and the point intersecting the straight line (α−β) is represented by σ. To do. The area of the high-temperature peak b is the portion surrounded by the curve of the high-temperature peak b portion of the DSC curve, the line segment (σ-β), and the line segment (γ-σ) (the portion hatched in FIG. 3). Area, which corresponds to the amount of heat at the high temperature peak.
In addition, the total heat amount of all endothermic curve peaks in this specification is represented by the area of the portion surrounded by the DSC curve and the straight line (α-β) in FIG. 3, and this is the total heat amount of the endothermic curve peak. Equivalent to.

  The high temperature peak b is observed in the first DSC curve measured as described above, but not in the second DSC curve. In the second DSC curve, as shown in FIG. 4, only an endothermic curve peak (inherent peak a) unique to the polypropylene resin constituting the expanded particles is recognized. In the second DSC curve, in the heat flux differential scanning calorimetry, after obtaining the first DSC curve, the temperature was lowered to 40 ° C. at 10 ° C./min, and again to 220 ° C. at 10 ° C./min. It is a DSC curve obtained when the temperature is raised at.

  The multilayer resin particles comprising the core layer and the coating layer of the present invention are known per se, for example, Japanese Patent Publication No. 41-16125, Japanese Patent Publication No. 43-23858, Japanese Patent Publication No. 44-29522, JP, It can be produced by a coextrusion method described in Japanese Patent Laid-Open No. 60-185816. In general, a core layer forming extruder and a coating layer forming extruder are used and connected to a coextrusion die. Melting and kneading the required resin components and additives as necessary in the core layer forming extruder, and melt kneading the required resin components and additives as necessary in the coating layer forming extruder To do. Each melt-kneaded product is merged in the die to form a multilayer structure comprising a cylindrical core layer and a coating layer covering the outer surface of the core layer. Multi-layer resin particles are produced by extruding into strands from the holes and cutting with a pelletizer such that the weight of the resin particles becomes a predetermined weight.

  Examples of the shape of the multilayer resin particles used in the present invention include a columnar shape, a rugby ball shape, and a spherical shape. Foamed particles obtained by foaming such multilayer resin particles have a columnar shape, a rugby ball shape, or a spherical shape according to the shape of the resin particles before foaming.

  The average weight per multilayer resin particle is preferably 0.01 to 10.0 mg, particularly preferably 0.1 to 5.0 mg. The average weight of the expanded particles can be adjusted by adjusting the average weight per one resin particle for obtaining the expanded particles to the average weight per one expanded foam particle. If the average weight per one of the foamed particles is too small, the foaming efficiency is deteriorated. Therefore, the average weight per one of the foamed particles is also 0.01 to 10.0 mg, particularly 0.1 to 5.0 mg. Is preferred.

  In the multilayer resin particles of the present invention, the resin forming the core layer and the resin forming the coating layer are in a weight ratio of 99.5: 0.5 to 80:20, preferably 96: 4 to 90:10 is desirable. If the weight ratio of the resin forming the coating layer of the multilayer resin particles is too small, the thickness of the coating layer portion of the foamed particles is too thin, and the effect of improving the fusion property cannot be obtained, and the fusion between the foamed particles is not achieved. There is a risk of becoming insufficient. On the other hand, if the weight ratio of the resin forming the coating layer is too large, the resin forming the coating layer may easily foam. Furthermore, since the ratio of the resin component having a low melting point and low flexural modulus increases, the mechanical properties of the foamed particle molded body may be easily lowered. Therefore, the weight ratio of the resin forming the core layer of the multilayer resin particles (that is, the core layer portion of the expanded particles) and the resin forming the coating layer (that is, the coated layer portion of the expanded particles) is within the above range. As a result, there is no air bubble in the vicinity of the fusion interface between the expanded particles, and the fusion strength between the expanded particles is increased, so that the expanded molded article is excellent in mechanical strength.

  Regarding the thickness of the coating layer of the multilayer resin particles of the present invention, when the multilayer resin particles are foamed, bubbles are less likely to be generated in the coating layer portion, and from the viewpoint of the strength of the foamed molded product, the thinner one is preferable. Although it is preferable, if it is too thin, the effect of improving the fusing property between the expanded particles cannot be expected, and it becomes difficult to sufficiently cover the core layer portion. Therefore, the thickness of the coating layer of the multilayer resin particles is desirably 5 to 500 μm, and more preferably 10 to 100 μm. In addition, the thickness of the coating layer portion of the expanded particles is desirably 0.1 to 200 μm, and more preferably 0.5 to 50 μm.

The thickness of the coating layer of the multilayer resin particles is measured as follows. The multilayer resin particles are divided into two equal parts, and the cross section thereof is enlarged so that the entire cross section enters under the microscope, and the entire circumference of the coating layer is measured by a photograph taken with an optical microscope in the bisecting vertical cross section. Specifically, a straight line is drawn on the photograph so that the cross section is approximately bisected, and a straight line is drawn so as to be perpendicular to the straight line. The average is taken as the thickness of the coating layer of one multilayer resin particle. These operations are combined and measured with 10 multilayer resin particles, and the arithmetic average value is taken as the thickness of the coating layer in the multilayer resin particles. The thickness of the coating layer portion of the expanded particles is also measured by the same method.
In addition, when it is difficult to understand the thickness of the coating layer of the multilayer resin particles, it is preferable to produce the multilayer resin particles by previously adding a colorant to the resin constituting the coating layer.

  In the foamed particles of the present invention, the multilayer resin particles comprising the core layer and the coating layer are dispersed in an aqueous medium (usually water) in a pressurized container (for example, an autoclave), and if desired, a dispersant. After adding a required amount of foaming agent and stirring under heating to impregnate the resin particles with the foaming agent, the contents together with the aqueous medium from the pressurized container are lower than the internal pressure of the container (larger (This method is hereinafter referred to as a dispersion medium releasing foaming method). It is preferable to release by applying back pressure in the container at the time of this release.

  In particular, when obtaining expanded particles with a high expansion ratio, the expanded particles obtained by the above-described method are cured under normal atmospheric pressure, and then filled into a pressurizable sealed container so that air or the like can be removed. After performing an operation of increasing the internal pressure of the expanded particles by pressurizing with an active gas, the expanded particles are taken out from the container and heated with steam or hot air to obtain expanded particles with a high expansion ratio. (This is hereinafter referred to as two-stage foaming).

  In the present invention, a physical foaming agent is used as the foaming agent and is not particularly limited. For example, aliphatic hydrocarbons such as n-butane, i-butane and a mixture thereof, n-pentane, i-pentane, n-hexane and the like. , Organic physical foaming agents such as halogenated hydrocarbons such as trichlorofluormethane, dichlorofluoromethane, tetracolorofluoroethane, and dichloromethane, and inorganic gases such as carbon dioxide, nitrogen, and air, or a mixture of two or more. Can be used. Among these foaming agents, it is preferable to use a foaming agent mainly composed of an inorganic gas such as carbon dioxide, nitrogen, or air, and more preferably carbon dioxide. In the present invention, the above-mentioned inorganic gas as a main component means that the inorganic gas blowing agent is contained in 50 mol% or more, preferably 70 mol% or more, more preferably 90 mol% or more in 100 mol of the total physical blowing agent. Means that. In addition, when using an organic physical foaming agent, it is preferable to use n-butane, i-butane, n-pentane, and i-pentane from the viewpoint of compatibility with the polyolefin resin and foamability.

  The amount of the above physical foaming agent added is appropriately selected according to the type of polypropylene resin, the type of foaming agent, the apparent density (expanding ratio) of the target foamed particles, etc. For example, when carbon dioxide is used as a physical foaming agent, 0.1 to 30 parts by weight, preferably 0.5 to 15 parts by weight, more preferably 1 to 10 parts by weight with respect to 100 parts by weight of the polypropylene resin. Part is used.

In addition, as a dispersant, inorganic substances that are hardly soluble in water such as aluminum oxide, tricalcium phosphate, magnesium pyrophosphate, zinc oxide, kaolin, mica,
Examples thereof include water-soluble polymeric protective colloid agents such as polyvinylpyrrolidone, polyvinyl alcohol, and methylcellulose. Anionic surfactants such as sodium dodecylbenzenesulfonate and sodium alkanesulfonate can also be used.

  As a specific method for adjusting the high temperature peak in the dispersion medium releasing foaming method, when the multilayer resin particles are dispersed in an aqueous medium and heated, the melting end temperature (Tce) of the polypropylene resin in the core layer is not exceeded. To a temperature lower than the melting point (Tc) of the resin by 20 ° C. or more and stopped at an arbitrary temperature (Ta) within the range of less than the melting end temperature (Tce), and a sufficient time at the temperature (Ta), Preferably, the temperature is maintained for about 10 to 60 minutes, and then heated to a temperature (Tb) within the range of 15 ° C. lower than the melting point (Tc) to the melting end temperature (Tce) + 10 ° C., and stopped at that temperature. It is preferable that the multilayer resin particles are released from the inside of the sealed container under a low pressure and foamed after being held for a sufficient time, preferably about 10 to 60 minutes.

  In the dispersion medium releasing foaming method, it is preferable to set the temperatures Ta and Tb and the holding time as described above, because the size of the high temperature peak of the foamed particles is mainly the above for the resin particles when the foamed particles are produced. This is because it depends on the temperature Ta, the holding time at the temperature, the temperature Tb, the holding time at the temperature, and the rate of temperature increase.

  In general, the amount of heat at the high temperature peak of the expanded particles tends to increase as the temperature Ta or Tb decreases within the above temperature range or as the holding time increases. Usually, 0.5-5 degreeC / min is employ | adopted for the temperature increase rate in the said foaming process. By repeating the preliminary experiment in consideration of these points, it is possible to easily and accurately know the production conditions of the expanded particles exhibiting a desired high temperature peak heat quantity.

  In addition, the temperature adjustment range at the time of foaming of the resin particle demonstrated above is a suitable temperature range at the time of using an inorganic type physical foaming agent as a foaming agent. When an organic physical foaming agent is used in combination, the appropriate temperature range tends to shift to a lower temperature side than the above temperature range depending on the type and amount of use.

  The foamed particles of the present invention obtained by the above method have a multilayer structure in which a foamed core layer portion having fine bubbles and a substantially non-foamed coating layer portion are formed on the surface thereof. The above-mentioned expanded particles preferably have an apparent density of 18 to 80 g / L from the viewpoint of physical properties of the expanded molded article.

  The apparent density of the expanded particles is measured as follows. A foamed particle group with a weight W (g) is submerged in a graduated cylinder containing water using a wire mesh, and the volume V (L) of the foamed particle group is obtained from the rise in the water level, and the weight of the foamed particle group is foamed. The value obtained by dividing by the volume of the particle group (W / V) is obtained by converting the unit to g / L.

  The average cell diameter of the foamed particles of the present invention is preferably 50 to 900 μm from the viewpoints of secondary foamability and mold transferability of the foamed particles. Furthermore, the average bubble diameter is preferably 20 μm or more, more preferably 25 μm or more and 30 μm or more. On the other hand, the upper limit is preferably 300 μm or less, more preferably 250 μm or less, and even more preferably 200 μm or less, from the viewpoint of the strength against compression stress and the appearance smoothness of the foamed molded product to be obtained.

  The average cell diameter of the expanded particles is measured by enlarging a section obtained by dividing the expanded particles into two equal parts under the microscope so that the entire section is included, and photographing the section. On the photograph taken, draw a straight line so that the cross section is approximately bisected, and the value obtained by dividing the length of the straight line by the number of all the bubbles in contact with the straight line is the average bubble diameter of one foamed particle. 20 foamed particles were measured, and the arithmetic average value was taken as the average cell diameter of the foamed particles.

The method for producing a foamed molded article obtained by molding the foamed particles of the present invention into a mold can be produced by a known in-mold molding method.
For example, using a pair of conventional molds for molding expanded particles in a mold, filling the expanded mold cavity with expanded particles under atmospheric pressure or reduced pressure, and closing the mold to reduce the mold cavity volume by 5 to 70% Then, a method using a reduced pressure molding method (for example, Japanese Examined Patent Publication No. Sho 46-38359) in which a heating medium such as steam is supplied into the mold and heated to heat and expand the foamed particles. In addition, the foamed particles are pre-pressurized with a pressurized gas such as air to increase the pressure in the foamed particles, and the secondary foamability of the foamed particles is increased to maintain the secondary foamability. A pressure molding method (for example, Japanese Patent Publication No. 51-22951) in which foamed particles are filled in a mold cavity under reduced pressure, the mold is closed, and then a heating medium such as steam is supplied into the mold to heat-fuse the foamed particles. Etc.). In addition, after filling foamed particles pressurized above the pressure into a cavity pressurized above the atmospheric pressure with compressed gas, a heating medium such as steam is supplied into the cavity to heat-fuse the foamed particles. It can also be molded by a filling molding method (for example, Japanese Patent Publication No. 4-46217). In addition, after filling foam particles with high secondary foamability into a pair of mold cavities under atmospheric pressure or reduced pressure, a heating medium such as steam is supplied and heated to heat-fuse the foam particles. It can also be molded by a normal pressure filling molding method (for example, Japanese Patent Publication No. 6-49795) or a method combining the above methods (for example, Japanese Patent Publication No. 6-22919).

The density of the foamed particle molded body produced from the foamed particles of the present invention can be arbitrarily set depending on the purpose, but from the viewpoint of being a foamed molded body having flexibility, it is in the range of 12 g / L to 50 g / L. It is preferably 12 g / L to 30 g / L.
The density of the foamed particle molded body is calculated by dividing the weight (g) of the test piece cut out from the molded body by the volume (L) obtained from the outer dimension of the test piece.

  Hereinafter, the present invention will be described with reference to examples and comparative examples.

The polypropylene resins used in the examples and comparative examples are shown in Table 1 below.

  The melt flow rate (MFR) was measured under conditions of 230 ° C. and a load of 21.17 N in accordance with JIS K7210 (1976). In the case of a polyethylene resin, the measurement was performed under the conditions of 190 ° C. and a load of 21.17 N.

Example 1
An extruder in which a die for forming a multilayer strand was attached to the outlet side of a core layer forming extruder having an inner diameter of 65 mm and a coating layer forming extruder having an inner diameter of 30 mm was used.
The core layer forming extruder and the coating layer forming extruder are each supplied with the propylene-based resin for forming the core layer and the coating layer shown in Table 1 at the ratio shown in Table 2, and melted. Kneaded. The melt-kneaded product is introduced into the above-mentioned multilayer strand forming die, joined in the die, and formed into two layers (coating layer / core layer structure) from the pores of the die attached to the tip of the extruder The extruded strand was cooled with water, cut with a pelletizer to a weight of approximately 1 mg, and dried to obtain multilayer resin particles.
In addition, zinc borate was supplied to the polypropylene-based resin of the core layer so that the content of zinc borate was 1000 ppm by weight as a bubble regulator.

  1 kg of the obtained multilayer resin particles are charged into a 5 L sealed container together with 3 L of water as a dispersion medium, and 0.3 parts by weight of kaolin as a dispersant and a surfactant (trade name) with respect to 100 parts by weight of the multilayer resin particles. : Neogen, manufactured by Daiichi Kogyo Seiyaku Co., Ltd., sodium dodecylbenzenesulfonate) 0.2 parts by weight (as an active ingredient) and 0.01 parts by weight of aluminum sulfate were added, and carbon dioxide as a blowing agent in a sealed container. And heated to the foaming temperature shown in Table 2 under stirring, and maintained at that temperature for 15 minutes to adjust the high-temperature peak calorific value (obtained from the endothermic curve by DSC measurement). Thereafter, the contents of the container were discharged together with water under atmospheric pressure to obtain expanded particles having an apparent density of 60 g / L. The high expansion ratio (low density) expanded particles were produced under the conditions shown in Table 2 using a two-stage expansion method. That is, first, foamed particles with an apparent density of 72 g / L were obtained, and then the foamed particles were filled into another sealed container and heated with steam after the pressurizing step to obtain multilayer foamed particles with an apparent density of 29 g / L.

  The obtained multilayer foamed particles were filled into a flat plate mold having a length of 250 mm, a width of 200 mm, and a thickness of 50 mm, and subjected to in-mold molding by pressure molding by steam heating to obtain a plate-like foamed particle compact. In the heating method, steam is supplied for 5 seconds with the drain valves on both sides open, and after preliminary heating (exhaust process), one heating is performed at a pressure 0.04 MPa (G) lower than the main heating pressure, Further, after one-way heating in the opposite direction at a pressure lower than the main heating pressure by 0.02 MPa (G), the minimum molding steam pressure shown in Table 2 (note that the minimum molding steam pressure refers to filling the mold with foam particles). When heated with steam, the foamed particles are heated at the lowest steam pressure at which a foamed molded product having a smooth surface and excellent flexibility can be obtained by secondary foaming and fusion within the mold. After the heating was completed, the pressure was released, and water cooling was performed until the surface pressure due to the foaming force of the molded body became 0.04 MPa (G), and then the mold was opened and the molded body was taken out from the mold. The obtained molded body was cured in an oven at 80 ° C. for 12 hours and then gradually cooled to room temperature to obtain a polypropylene resin foam molded body. The physical properties of the foamed molded product were evaluated, and the results are shown in Table 2.

Examples 2 and 3
Multilayer resin particles are produced in the same manner as in Example 1 except that the polypropylene resin forming the core layer is replaced with the resin shown in Table 2. The resin particles are expanded in the same manner as in Example 1 and expanded. A molded body was obtained. The physical properties are shown in Table 2.

Example 4
Multilayer resin particles were produced in the same manner as in Example 1 except that the polypropylene resin forming the coating layer was changed to the resin shown in Table 2, and the resin particles were expanded in the same manner as in Example 1 and expanded. A molded body was obtained. The physical properties are shown in Table 2.

Example 5
Multilayer resin particles were produced in the same manner as in Example 1 except that the polypropylene resin forming the coating layer was changed to the resin shown in Table 2, and the resin particles were expanded in the same manner as in Example 1 and expanded. A molded body was obtained. The physical properties are shown in Table 2.
The difference in flexural modulus of the propylene-based resin forming the multilayer resin particles was 300 MPa, and a molded body in which the gaps between the foamed particles were slightly recognized was obtained, but the object of the present invention was achieved. .

Example 6
Multilayer resin particles were produced in the same manner as in Example 1 except that the polypropylene resin forming the coating layer was changed to the resin shown in Table 2, and the resin particles were expanded in the same manner as in Example 1 and expanded. A molded body was obtained. The physical properties are shown in Table 2.
The difference in melting of the propylene-based resin forming the multilayer resin particles is 6 ° C., the fusing property is slightly lower than that of the foamed particles of Example 1, and cracking occurs even when the test piece is bent 90 degrees. Although not formed into a molded product that cracks when bent 180 degrees, the object of the present invention was achieved.

Example 7
Multilayer resin particles were produced in the same manner as in Example 1 except that the polypropylene resin forming the coating layer was changed to the resin shown in Table 2, and the resin particles were expanded in the same manner as in Example 1 and expanded. A molded body was obtained. The physical properties are shown in Table 2.
The propylene-based resin forming the multilayer resin particles has a large melting point difference, and the resin rarely adhered to the mold during molding, but the object of the present invention was achieved.

Example 8
Except for changing the ratio between the coating layer and the core layer as shown in Table 2, multilayer resin particles were produced in the same manner as in Example 1, and the resin particles were expanded in the same manner as in Example 1 and expanded. A molded body was obtained. The physical properties are shown in Table 2.
Since the weight ratio of the coating layer is large, the resin rarely adhered to the mold during molding, but the object of the present invention was achieved.

Example 9
In the same manner as in Example 1, the foamed particles obtained under the conditions shown in Table 2 were subjected to in-mold molding as they were without carrying out the two-stage foaming treatment to obtain a foam molded article. The physical properties are shown in Table 2.
Since the foaming ratio of the molded body is low, cracking does not occur even if the test piece is bent 90 degrees, but when it is bent 180 degrees, the molded body has cracked, but the object of the present invention is achieved. there were.

Example 10
Except for changing the ratio between the coating layer and the core layer as shown in Table 2, multilayer resin particles were produced in the same manner as in Example 8, and the resin particles were expanded as in Example 1, and A foam molded product was obtained. The physical properties are shown in Table 2.

Comparative Example 1
A multilayer resin particle was produced in the same manner as in Example 1 except that a resin having a high melting point of the coating layer and a large Es value was used with respect to the core layer of the example. The expanded particles and the expanded molded body were obtained by the above operations. Table 3 shows the evaluation results of physical properties.
The resulting foamed molded article is not flexible because the melting point difference of the resin forming the core layer and the coating layer and the partial melting calorie ratio are not satisfactory, and the resin fusion property of the non-foamed coating layer is insufficient. The molded product was inferior to.

Comparative Example 2
The multilayer resin particles, the expanded particles, and the expanded molded body were obtained by the same operation as in Example 1 except that a resin having a higher flexural modulus than that of the polypropylene resin used for forming the core layer portion used in Example 4 was used. Obtained. Table 3 shows the evaluation of physical properties.
The obtained foamed molded article had high rigidity and was inferior in flexibility. Furthermore, since the bending elastic modulus of the core layer is high, the appearance of the surface of the molded body was lowered below the pressure resistance (0.40 MPa) of the molding machine used for molding the conventional polypropylene resin foam particles.

Comparative Example 3
In Comparative Example 2, when the steam pressure during molding was increased and molding was performed, the mutual fusion property and surface smoothness between the expanded particles were satisfactory, but the rigidity of the resin forming the core layer was high. Therefore, the flexibility of the foamed molded product was inferior.

Comparative Example 4
Multilayer resin particles, expanded particles, and expanded molded articles were obtained by the same operation as in Example 1 except that a resin having a higher flexural modulus than that of the polypropylene resin used to form the core layer used in Example 7 was used. . Table 3 shows the evaluation of physical properties.
Since the melting point difference between the coating layer and the core layer is large, a high molding pressure is required, the resin easily adheres to the mold during molding, and the molding processability is poor.

Comparative Example 5
Foamed particles and a foamed molded article were obtained by the same operation as in Example 1 except that the coating layer of Example 1 was changed to a polyethylene resin. Table 3 shows the evaluation of the physical properties.
Moreover, the difference in the flexural modulus of the resin forming the core layer and the coating layer was large, and the surface smoothness was poor. Further, since the melting point difference between the sheath cores is large, the resin easily adheres to the mold during molding, and the molding processability is poor.

Comparative Example 6
Expanded particles and a foamed molded article were obtained in the same manner as in Comparative Example 4 except that the resin forming the coating layer in Comparative Example 4 was changed to the resin shown in Table 3. The physical property evaluation is shown in Table 3.
Since the resin forming the core layer has a high flexural modulus, it is inferior in flexibility. Further, since the difference in flexural modulus between the coating layer and the core layer is large, the surface smoothness is also inferior. Further, since the melting point difference between the sheath cores is large, the resin easily adheres to the mold during molding, and the molding processability is poor.

Comparative Example 7
Multilayer resin particles, foamed particles, and foamed molded articles were obtained in the same manner as in Example 2 except that the resin forming the coating layer in Example 2 was changed to the resin shown in Table 3. The physical property evaluation is shown in Table 3.
The difference in the flexural modulus of the resin forming the core layer and the clothing layer was large, the surface smoothness of the molded product was inferior, and the flexibility was inferior.

  The foamed molded product was evaluated as follows.

(Surface smoothness)
The appearance of the foamed particle molded body was visually evaluated according to the following criteria.
(Double-circle): The surface of a molded object is smooth, the melt | fusion between foamed particles is favorable, and there is almost no space | gap between particles.
A: The surface of the molded body is smooth, but a slight gap between the expanded particles is observed.
(Triangle | delta): The surface of a molded object is smooth, but the space | gap between expanded particles is conspicuous.
X: The smoothness of the surface of a molded object is lacking, the space | interval between expanded particles is conspicuous, or the fusion | melting between space | gap is inadequate.

(Flexibility)
A test piece having a length of 195 × width 50 × thickness 10 mm was cut out from the central portion of the foamed particle molded body, and the crackability when the test piece was bent so as to be substantially equally divided in the thickness direction was evaluated.
(Double-circle): Even if it bends 180 degree | times, it does not produce a crack (circle): It does not produce a crack even if it bends 90 degree | times.
Δ: Even if bent 90 degrees, it does not crack but cracks.
X: It cracks when bent 90 degrees.

(Adhesion to mold)
Judgment was made based on whether or not the resin adhered to the mold after molding under the conditions described in Table 3.
A: Adhesion is not recognized.
○: Adhesion is rarely observed.
Δ: Partial adhesion is observed.
X: Adhere.

Curves from Cm micro thermomechanical measurements
Cm1 Steep region of displacement derived from the coating layer
Cm2 Steep region of displacement derived from the core layer
BL, TL tangent
Softening point of Ns coating layer
Nc Core layer softening point a Inherent peak on DSC curve b High temperature peak on DSC curve α Point corresponding to 80 ° C on DSC curve β Point corresponding to melting end temperature γ Intrinsic peak and high temperature peak on DSC curve Valley δ Intersection with straight line α-β T Melting end temperature Tm Melting point Te Melting end temperature

Claims (3)

Multilayer foamed particles obtained by foaming multilayer resin particles comprising a core layer and a coating layer formed of a polypropylene resin and having a weight ratio of the core layer to the coating layer of 99.5: 0.5 to 80:20 The expanded polypropylene resin particles satisfy the following requirements (a-1) and / or (a-2), and (b) and (c).
(A-1)
The resin melting point Tc (° C.) of the polypropylene resin forming the core layer and the resin melting point Ts (° C.) of the polypropylene resin forming the coating layer satisfy the following formula (1).
(Equation 1)
1.5 ≦ Tc−Ts ≦ 30 (° C.) (1)
(A-2)
In the DSC endothermic curve obtained by heat flux differential scanning calorimetry of the polypropylene resin forming the core layer, Ec (J / g) is a partial melting heat amount in a temperature range equal to or higher than the resin melting point (Tc) of the core layer. In the DSC endothermic curve obtained by heat flux differential scanning calorimetry of the polypropylene resin forming the coating layer, the partial melting heat amount in the temperature range equal to or higher than the resin melting point (Tc) of the core layer is Es (J / When g), Ec and Es satisfy the following formula (2).
(Equation 2)
0 ≦ Es / Ec ≦ 0.7 (2)
(B) The bending elastic modulus of the polypropylene resin forming the core layer: Mc (MPa) and the bending elastic modulus of the polypropylene resin forming the coating layer: Ms (MPa) Satisfy (3).
(Equation 3)
Mc-Ms ≦ 500 (MPa) (3)
(C) The bending modulus of elasticity of the polypropylene resin forming the core layer: Mc (MPa) is 1100 MPa or less. The polypropylene resin expanded particles according to claim 1, wherein the polypropylene resin forming the core layer has a resin melting point: Tc (° C) of 150 ° C or less.
  An expanded particle molded body having an apparent density of 12 g / L to 50 g / L, which is obtained by filling the expanded particles according to claim 1 or 2 in a molding die and heat molding.

Images