JP2005246822A - Multi-layer foamed resin molding and its production method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a multi-layer foamed resin molding which is light in weight, reduced in strength lowering, and excellent in shading properties, thermal insulation properties, etc., and a method for producing the molding. <P>SOLUTION: In the multi-layer foamed resin molding, inside and outside outer layers (a and e) and the thick-walled middle part (c) of the molding are non-foamed layers. Parts held between the outer layers (a and e) and the middle part (c) are formed from foamed layers (b and d). In at least one of the foamed layers (b and d), the middle part (c) side and the outer layers (a and e) are changed in the average diameter of bubbles. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a resin foam molded article having a multilayer structure and a method for producing the same.

Thermoplastic resin foam-molded products are widely used in various applications regardless of the type of raw resin for the purpose of reducing the weight of the product, improving heat insulation, and imparting soundproofing. In this foamed molded product made of thermoplastic resin, it is desirable to increase the foaming ratio of the molded product and reduce the specific gravity from the viewpoint of improving the functionality such as weight reduction, but as the foaming ratio increases, Since the strength is reduced, the expansion ratio is restricted from the viewpoint of strength in industrial applications.

  On the other hand, there has been proposed a technique for reducing the strength caused by increasing the foaming ratio or improving the strength by miniaturizing the bubbles of the foam molded product. This technique is called microcellular plastic, and its details are described in US Pat. No. 4,473,665 and JP-A-6-506724. Specifically, in this method, (1) in a high-pressure vessel, a thermoplastic resin is impregnated with an inert gas such as nitrogen or carbon dioxide under a high pressure or in a supercritical state, and then (2) the gas is introduced. The impregnated thermoplastic resin is taken out from the high-pressure vessel, heated to a temperature equal to or higher than the glass transition temperature (Tg) of the thermoplastic resin with an oil bath or the like, and (3) nucleation is induced to cause bubble growth. A foamed molded product having bubbles is obtained.

  Furthermore, it is well known to produce a multilayer structure foam molded product or a so-called tilted foam molded product in which the cell diameter is changed in a slanted manner by an injection molding method or an extrusion molding method. For example, Japanese Patent Laid-Open No. 10-119078 discloses that the ratio of the bubble diameter between the inside and the surface of the foam obtained by pouring polyphenylene ether containing a chemical foaming agent into the cavity and changing the size of the cavity in multiple stages is 2. The manufacturing method of the foam-molded article which is the above is described. Japanese Patent Application Laid-Open No. 11-291374 discloses a spindle shape that is long in the thickness direction at the center of the sheet by containing a pyrolytic chemical foaming agent only in a certain layer constituting the multilayer sheet and foaming the foaming agent. Presented is a method for producing a molded product in which bubbles are formed in a nearly spherical shape on the sheet surface.

  Furthermore, Japanese Patent Laid-Open No. 2001-113653 discloses a technique for disposing polypropylene having a long chain branch in a non-foamed surface layer in a three-layer polyolefin extruded sheet including a foamed layer for the purpose of improving the vacuum formability of the sheet. Is described. It is described that a multi-layer sheet of five layers can be manufactured by bonding two sheets. Japanese Patent Laid-Open No. 2002-363324 discloses a sheet having bubbles in which the bubble diameter changes in an inclined manner within the sheet cross-section by extruding a plastic mixed with gas and exposing each surface of the sheet to different temperatures. A manufacturing method is described.

  However, in the method described in the above-mentioned U.S. Patent Specification, although an improvement in strength reduction of the foamed molded article is seen, it is insufficient on an industrial level, and since the heat insulation is proportional to the expansion ratio, excellent heat insulation is achieved. For the purpose of imparting the property, there is a problem similar to the conventional one that the strength decreases when the expansion ratio is increased. As a method for producing a multilayer molded product or an inclined foam molded product that can be industrially used, there is a coextrusion molding method as described in JP-A-2001-113653. However, a multi-layer foam molded article having a three-layer structure is common, but in order to obtain a multi-layer foam molded article having five or more layers, according to the conventional method, bonding using a welding method or an adhesive is required. In the case of the welding method, there are problems such as deformation of the foam by heating and secondary foaming. In the case of using an adhesive, the strength may be reduced at a portion in contact with the adhesive. It is difficult to adjust and maintain each layer to a uniform thickness and to control the average cell diameter of the foam layer in multi-layer foam molded products of five layers or more. In addition, the foam layer is divided into a high foam layer and a low foam layer. It is impossible to make different. When air bubbles are controlled, there is a problem that productivity at the time of producing a foam molded product cannot be increased, and a large amount of capital investment is required.

Also, when producing multi-layer foam molded products by co-extrusion molding method, the raw material resin is suitable for polyolefin resin with excellent meltability and low heat shrinkage, but polyester type such as aromatic polyester and aliphatic polyester. If it is a resin, there is a risk of thermal shrinkage during heat welding, and it is difficult to bond them together. None of the techniques described in these known documents are intended to suppress strength reduction due to foaming and to improve heat insulation. There is no description or suggestion of a method for improving the sexiness.
US Pat. No. 4,473,665 JP-T 6-506724 Japanese Patent Laid-Open No. 10-119078 JP-A-11-291374 JP 2001-113653 A JP 2002-363324 A

The present invention solves the above-mentioned conventional problems, and by forming a multilayer structure composed of a foam layer and a non-foam layer inside the resin foam molded product, the strength is hardly reduced, and the light shielding property, sound insulation property, The present invention has been completed as a result of intensive studies aimed at providing a resin foam-molded product having excellent heat insulation and gas barrier properties. The object of the present invention is as follows.
1. Multi-layer structure with excellent light-shielding properties, sound-insulating properties, heat insulation properties, gas barrier properties, etc. To provide a resin foam molded product.
2. To provide a method for producing a resin foam-molded article having a multilayer structure that is lightweight, has a very low strength reduction, and has excellent light shielding properties, sound insulation properties, heat insulation properties, gas barrier properties, and the like.

  In order to solve the above-described problems, in the first invention, in the resin foam molded product having a multilayer structure, the outer layers (a, e) on the front and back sides and the central thickness portion (c) of the molded product are non-foamed layers, A portion sandwiched between (a, e) and the central portion (c) is composed of a foam layer (b, d), and at least one foam layer of the foam layer (b, d) has a thick central portion (c). Provided is a resin foam-molded article having a multilayer structure characterized in that the average cell diameter is changed between the side and the outer layer (a, e).

  In the second invention, in manufacturing a resin foam molded product having a multilayer structure, a step of manufacturing an unfoamed intermediate molded product in which an inert gas of a thermoplastic resin is dissolved, the unfoamed intermediate molded product is heated. The present invention provides a method for producing a resin foam molded article having a multilayer structure, characterized by comprising a step of stretching.

  Furthermore, in the third invention, in producing a resin foam molded article having a multilayer structure, first, a process of producing an intermediate molded article using a thermoplastic resin as a raw material, the intermediate molded article is subjected to a temperature condition below the softening point of the raw resin. From the step of contacting with a pressurized inert gas and dissolving on the wall surface of the intermediate molded product, the step of returning to normal pressure under a temperature condition below the softening point of the raw material resin, and the step of heating and stretching the intermediate molded product There is provided a method for producing a resin foam-molded article having a multilayer structure.

The present invention has the following particularly advantageous effects, and its industrial utility value is extremely great.
1. The resin foam-molded product having a multilayer structure according to the present invention is lightweight because the wall surface of the resin foam-molded product is formed into a multilayer by a high foam ratio layer and a low foam layer.
2. The resin foam molded product having a multilayer structure according to the present invention is excellent in strength because the wall surface of the resin foam molded product is formed into a multilayer by a high foam ratio layer and a low foam layer.
3. The resin foam molded article having a multilayer structure according to the present invention is excellent in heat insulating property because the wall surface of the resin foam molded article is formed into a multilayer by a high foam ratio layer and a low foam layer.
4). According to the manufacturing method according to the present invention, it is relatively easy to manufacture a resin foam-molded article having a multilayer structure that is made of a high-foaming ratio layer and a low-foaming layer, is lightweight, and has very little strength reduction. Can do.

  Hereinafter, the present invention will be described in detail. The raw material resin of the resin foam molded article having a multilayer structure according to the present invention is a thermoplastic resin. Thermoplastic resins include polystyrene, rubber-reinforced polystyrene, styrene resins such as ABS resin and AS resin, acrylic resins such as polymethyl methacrylate, olefin resins such as polyethylene and polypropylene, polyvinyl chloride resins, and polyvinylidene chloride. Resin, polyvinyl alcohol resin, polyester resin such as aromatic polyester, aliphatic polyester, alicyclic polyester, polyamide resin, polycarbonate resin, norbornene resin, fluorine resin, polyethersulfone, polysulfone, polyimide, Polyetherimide, polyetherketone, polyetheretherketone, polyarylate, triacetylcellulose, poly-4 methylpentene-1, polyurethane, polybutene, polyacetal, polyph Niren'okishido, natural rubber, synthetic rubbers, and thermoplastic elastomers. These may be used alone or as a mixture.

  Various kinds of resin additives that do not impair the effects of the present invention can be blended with the raw material thermoplastic resin. Examples of resin additives include foam nucleating agents, colorants such as pigments and dyes, heat stabilizers, light stabilizers, mold release agents, preservatives, ultraviolet absorbers, plasticizers, lubricants, flame retardants, and conductivity imparting. Agents, antistatic agents, crystal nucleating agents and the like. These resin additives may be one kind or two or more kinds.

  Examples of the method for producing a resin foam molded article having a multilayer structure according to the present invention include the following three methods: Method A, Method B and Method C. In Method A, first, an unfoamed intermediate molded product in which an inert gas of a thermoplastic resin is dissolved (or impregnated) is manufactured in a first step (hereinafter abbreviated as A1 step). Then, in the second (hereinafter abbreviated as A2 step), the unfoamed intermediate molded product is stretched under heating.

  In order to produce an unfoamed intermediate molded product in which an inert gas is dissolved, the molten resin is pushed into the sealed space filled with the inert gas as an intermediate molded product, and the surface of the intermediate molded product is brought into contact with the inert gas to be inert. Dissolve the gas. In the step A1, the unfoamed intermediate molded product has an inert gas dissolved on the surface thereof, but is in an unfoamed state. The sealed space means a sealed space such as an injection mold cavity or a hollow mold cavity.

  In the present invention, the intermediate molded product is a sheet, a box-shaped container, a bottle-shaped container, a tube or a tube. Sheets as intermediate molded products are injection molding dies, extrusion T dies, etc., containers as intermediate molded products are injection molding dies, tubes or tubes as intermediate molded products are for hollow molding dies and extrusion molding Can be molded by. Examples of the sheet as the foamed molded product in the present invention include a light shielding sheet, a heat shielding sheet, and a sound insulating sheet. Box-shaped containers include food containers that are heat-treated in a microwave oven, and bottle-shaped containers include cosmetics, cosmetics, and pharmaceuticals that require light-shielding in addition to uses for drinking water and health drinks. Used in such fields. Examples of the tube or tube include a roll of OA equipment and a tube for medical equipment. When the final foamed molded product is a sheet, a box-shaped container, a tube or a tube, the intermediate molded product is a sheet, a box-shaped container, a tube or a tube. , A parison. In addition, in the following description, it demonstrates in detail based on the example which manufactures a bottle-shaped container for convenience.

  Examples of the inert gas filled in the sealed space include inorganic gases and organic gases. These inert gases are not particularly limited as long as they are in a gaseous state at normal temperature and normal pressure and can be dissolved (infiltrated) into the wall surface of the intermediate molded product. Specific examples of the inorganic gas include carbon dioxide, nitrogen, argon, neon, helium, oxygen and the like. Specific examples of the organic gas include chlorofluorocarbon gas and low molecular weight hydrocarbon gas. These inert gases may be one kind or a mixture of two or more kinds. Among the above inert gases, inorganic gases are preferable, and carbon dioxide and nitrogen are particularly preferable from the viewpoint of impregnation with respect to the wall surface of the intermediate intermediate molded product.

  In step A1, the higher the pressure of the inert gas that fills the sealed space, the more the inert gas dissolves in the intermediate molded product in the molten state. Is practical, preferably 10 MPa or less. The sealed space is preferably sealable with a metallic packing. If the air remaining in the sealed space is replaced with the inert gas used before pushing the parison as the intermediate molded product, the concentration of the inert gas becomes high, and dissolution in the intermediate molded product in the molten state becomes faster, which is preferable. . It is preferable that the inert gas is uniformly contacted with the surface of the parison and dissolved, but for products that are difficult to uniformly dissolve on the surface, the location where the expansion ratio may be low in one product. This can be dealt with by providing a gate. The amount of inert gas dissolved on the surface can be adjusted by the type of inert gas, pressure, temperature, type of resin, temperature of the intermediate molded product in a molten state, contact time between the two, and the like.

  When using the A method, the unfoamed parison is stretched under heating in the step A2 after the step A1. By heating and stretching the parison, the strength of the foamed molded product is improved, and at the same time, the structure of the foamed layer formed on the parison surface is changed. The foamed layer reduces the weight of the foam molded product and improves the heat insulating property of the foam molded product. That is, the non-foamed layer of the wall surface center layer is stretched to cause molecular orientation, which contributes to improving the strength of the foam molded product. Moreover, the foam layer on the surface is crushed by the heating at the time of stretching and the stretching after the heating, and changes smoothly like a non-foamed layer. Bubbles remain in the lower layer (inside) of the smooth non-foamed layer, and the bubbles have a smaller average bubble diameter in the surface layer and a larger average bubble diameter in the central layer.

  The temperature heated in this A2 process shall be more than the softening point of the raw resin of unfoamed parison. The heating time is preferably set to such an extent that the unfoamed intermediate molded product can be stretched. To stretch the unfoamed parison, it is possible to blow air into the heated parison. Since the inert gas is dissolved in the unfoamed parison, the wall surface is foamed in the A2 step of stretching under heating. The inert gas dissolved on the wall forms foam by forming closed cells on the wall, but since the dissolved inert gas is more on the surface side, the bubble diameter is larger on the surface side, and the bubble is smaller on the inside of the wall surface, Since bubbles on the surface are destroyed by stretching, a non-foamed layer is formed. In the present invention, the softening point means a melting peak temperature (Tpm) measured by a differential scanning calorimeter (DSC) in accordance with JISK7121 in the case of a crystalline resin, and in the case of an amorphous resin. , And means a glass transition temperature (Tmg) measured according to JISK7121.

  The draw ratio can be selected in the range of 1.1 to 10 times. If the draw ratio is less than 1.1, the purpose of improving the strength, weight reduction and heat insulation of the foam molded product is not achieved, and if the draw ratio is 10 times or more, the strength of the foam molded product is reduced. Since the manufacturing apparatus becomes complicated and the manufacturing process becomes complicated, neither is preferable.

  In the method B for producing a foamed molded article having a multilayer structure according to the present invention, the inert gas is brought into contact with a pressurized inert gas on the wall surface of the unfoamed parison between the steps A1 and A2 in the method A. A step of dissolving (hereinafter abbreviated as B3 step) and a step of returning to normal pressure under a temperature condition below the softening point of the raw material resin (hereinafter abbreviated as B4 step) can be added. By adding the B3 step, the amount of inert gas dissolved in the wall surface of the unfoamed parison can be increased. In this B3 process, an unfoamed parison in which an inert gas is dissolved on the wall surface through the above-mentioned A1 process, an intermediate molded product is put in a pressure vessel, and an inert gas is injected into the pressure vessel and pressurized to perform intermediate molding. This means that the wall surface of the product is brought into contact with an inert gas.

  The temperature in the step B3 for dissolving the inert gas on the wall surface of the unfoamed parison is selected in the temperature range from room temperature to the softening point (Tmg or Tpm) of the raw material resin. When the temperature is below room temperature, the inert gas is difficult to dissolve on the parison wall surface, and when the temperature is too high, the shape of the parison is destroyed, which is not preferable. The reason why the inert gas is pressurized in the step B3 is to increase the amount of the inert gas dissolved in the parison wall. The higher the pressure of the inert gas, the larger the amount of impregnation on the parison wall surface, but this is not preferable because the apparatus becomes large. The pressure of the inert gas is preferably selected in the range of normal pressure to 40 MPa. The contact time between the parison wall and the inert gas is the size of the parison, the thickness of the wall, the type of inert gas, the pressure when contacting, the temperature when contacting, and the foam molded product to be finally obtained. The foam layer can be selected in the range of several minutes to several hours depending on the form (foaming ratio, bubble density, bubble size) and the like.

  As the amount of the inert gas dissolved in the parison wall in Step B3 increases, the expansion ratio can be increased, the bubble density can be increased, and more bubbles with a small average diameter can be formed. The inert gas that dissolves on the parison wall surface has a larger amount of dissolution toward the wall surface and a smaller amount of dissolution toward the inside of the wall surface. It is preferable to adjust the inert gas so that it does not reach the center layer in the thickness direction of the wall surface. This is because a non-foamed layer is formed at the center of the wall surface to maintain the strength of the foamed molded product. In order to prevent the inert gas from reaching the center layer of the wall surface, when the impregnation distance of the inert gas is x, the diffusion coefficient of the inert gas on the wall surface is D, and the dissolution time is t, x = sqrt ( Dt), t may be set so that x is smaller than the dimension reaching the center of the wall surface.

  The inert gas may be in a normal gas state, but is preferably contacted in a supercritical state. The supercritical state means a state above the critical temperature and critical pressure. For example, in the case of carbon dioxide, the supercritical state is a state where the temperature is 30 ° C. or higher and the pressure is 7.3 MPa or higher. Inert gas in the supercritical state has characteristics that it has a lower viscosity than that in the liquid state and has high diffusibility to the resin wall surface, and has a higher density than the normal gas state. In addition, it is preferable because the parison wall surface can be impregnated with an inert gas quickly. The amount of inert gas dissolved in the wall surface affects the foam layer shape (foaming ratio, bubble density, bubble size) of the foam molded product. It is preferable to confirm the optimum conditions by experiments in advance and set the manufacturing conditions.

  In order to produce a resin foam-molded article having a multilayer structure according to the B method, the pressure is returned to normal pressure under the temperature condition below the softening point of the raw material resin in the next step B4. In this B4 process, when the inert gas dissolved in the parison wall surface in the B3 process is returned from the pressurized state to the normal pressure, the inert gas dissolved in the parison wall surface is foamed and scattered outside the wall surface. Is used. The form of the foamed layer formed on the parison wall surface (foaming ratio, bubble density, bubble size) is the wall temperature, inert gas pressure, dissolved amount of inert gas, time to return to normal pressure (speed), etc. Depends on.

  The temperature of this B4 process shall be chosen in the temperature range below the softening point of raw material resin from normal temperature. When the raw material resin is an amorphous thermoplastic resin, the glass transition temperature Tg or lower is preferable, and when the raw material resin is a crystalline thermoplastic resin, the melting point Tm or lower is preferable. When the pressure of the inert gas in step B3 is high and the time for returning to normal pressure is short, the inert gas dissolved in the wall surface suddenly scatters out of the wall surface, so that bubbles having a large diameter are formed. Even if the pressure of the inert gas in the step B3 is high, if the time for returning to the normal pressure is long, the inert gas that has permeated the wall surface does not abruptly splash outside the wall surface, so that bubbles having a small diameter are formed.

  Next, a procedure for producing a resin foam molded article having a multilayer structure by the C method will be described. This method C is a step of producing an intermediate molded product from a thermoplastic resin as a raw material (hereinafter abbreviated as C1 step), and this intermediate molded product is subjected to a pressurized inert gas under a temperature condition below the softening point of the raw material resin. A step of contacting and dissolving on the wall surface of the intermediate molded product (hereinafter abbreviated as C2 step), a step of returning to normal pressure under a temperature condition below the softening point of the raw material resin (hereinafter abbreviated as C3 step), and It consists of the process (henceforth C4 process) of heat-drawing the said intermediate molded product.

  In the C1 process in the method C, a parison as an intermediate molded product is manufactured by an injection molding machine. When the C method is used, since the parison is formed without filling the injection mold with the inert gas in the cavity, the obtained parison is different from the parison obtained by the A method in that the inert gas is not dissolved. The C2 step in the C method can be performed by the same method as the B3 step in the B method, and the C3 step in the C method can be performed by the same method as the B4 step in the B method. Is omitted.

  The resin foam molded article having a multilayer structure obtained by the above method is a multilayer resin foam molded article having a five-layer structure in which the outermost layer is a non-foamed layer and the non-foamed layer and the foamed layer are alternately arranged in the thickness direction. is there. The foamed molded product having a five-layer structure has the outer layer (a, e) side and the central layer (c) formed of a non-foamed layer, and contributes to improving the strength, heat resistance, and gas barrier properties of the foamed molded product. The foamed layers (b, d) contribute to the light shielding property, heat insulating property, weight reduction and the like of the foam molded product.

  In the resin foam molded article having a multilayer structure obtained by the above method, the outer layers (a, e) of the front and back and the thickness center part (c) of the molded article are non-foamed layers, and the foamed layers (b, d) It is preferable that at least one of the bubbles is composed of bubbles having different average bubble diameters. In particular, both of the bubble average diameters of the foam layers (b, d) are large on the thick central portion (c) side, and the outer layer (a E) The side is preferably small. Among them, the bubbles contained in the foamed layer (b, d) are provided with a gradient in the foaming ratio as the average diameter of the large bubbles is more than twice that of the small bubbles, which improves strength, weight reduction, heat insulation, etc. It is preferable from the viewpoint. In order to remarkably improve the heat insulation, it is preferable that the average diameter of the large bubbles is at least three times that of the small bubbles, and the inclination is provided up to 50 times.

  In the present invention, the non-foamed layer refers to a layer in which only bubbles having an average bubble diameter of less than 0.1 μm are observed when a cross section (SEM) of the foamed molded product is observed with a scanning electron microscope magnified 60 times. The foam layer refers to a layer in which bubbles having an average bubble diameter of 0.1 μm or more are observed when a cross section of the foam molded product is observed with a scanning electron microscope magnified 60 times. In the present invention, the average bubble diameter is the length of the individual bubbles in the xz cross section, where y is the method of stretching the wall surface of the molded product, x is the direction orthogonal to the stretching direction, and z is the thickness direction of the wall surface. When the average of the axis and the short axis is taken as the diameter of the bubble unit, it means the average value of the diameters of all the bubbles including at least a part in the unit area. Specifically, after taking a photograph of the cross section of the foam molded product, the average cell diameter is statistically processed by a commercially available image processing software (for example, trade name: Win Roof, manufactured by Mitani Corporation). Can be calculated.

  The thickness of each layer of the resin foam molded product having a multilayer structure varies depending on the physical properties to be imparted to the foam molded product. For example, by increasing the thickness of the non-foamed layer (c) of the center layer, the strength, heat resistance, and light shielding properties can be improved. Furthermore, by reducing the thickness of the non-foamed layer (c) of the center layer, the weight can be reduced and the heat insulation can be improved. In order to obtain a foam-molded product with greatly improved heat insulation, it is preferable to use 30% or more of the entire wall thickness as the foam layer. In order to improve the heat resistance, when the raw material resin is a crystalline resin, it is preferable that the foamed molded product has a high crystallinity, and the crystallinity is preferably 5% or more, and more preferably 10% or more. Moreover, in order to improve heat resistance, the thickness of the center non-foamed layer (c) is in the range of 10% to 90%, more preferably in the range of 20% to 50% of the entire wall thickness.

  As mentioned above, although the resin foam molded product was demonstrated based on the method of manufacturing a hollow blow product according to this invention method, a sheet | seat, a tube, a pipe | tube, etc. can also be made into a foam molded product in the procedure similar to the above. When the intermediate molded product is a sheet, the intermediate molded product can be stretched by a tenter or the like, and when the intermediate molded product is a tube or a tube, air is blown into these.

  EXAMPLES Hereinafter, although this invention is demonstrated in detail based on an Example and a comparative example, this invention is not limited to a description example below, unless the summary is exceeded.

[Example 1]
Using a multilayer stretch blow machine injection molding machine (manufactured by Nissei ASB Co., model: ASB-50TH), polyethylene terephthalate {manufactured by Nihon Unipet, PET for bottles, softening point (Tmg) 80 ° C} A parison with a length of 100 mm, an outer diameter of 25 mm, and a wall thickness of 4 mm under the conditions of a raw material resin, a cylinder temperature of 280 ° C., an injection of 1.5 seconds, a pressure holding of 16.5 seconds, a cooling of 10 seconds, and a mold temperature of 15 ° C. (Internal volume 30 ml) was prepared. No bubbles were observed on the parison wall. Next, this intermediate molded product was placed in a pressure-resistant container having a capacity of 1000 ml, the atmospheric temperature was set to 25 ° C., carbon dioxide pressurized to 25 MPa was injected, and this temperature and pressure were maintained for 2 hours. Thereafter, under normal temperature, pressurized carbon dioxide was returned to normal pressure over 5 minutes to obtain a parison having carbon dioxide dissolved on the wall surface.

  Next, the above parison is set in a mold of a stretch blow molding machine, the parison surface is heated by an infrared heater for 69 seconds to a surface temperature of about 110 ° C., and then allowed to cool for about 23 seconds to have a parison surface temperature of about 100 ° C. Then, 3 MPa of compressed air was injected to obtain a five-layered bottle-shaped container having a length of 200 mm, an outer diameter of 60 mm, and an average wall thickness of 1 mm and an internal volume of 500 ml. The wall surface of this bottle-shaped container was cut in a direction perpendicular to the length direction, and the cross-section was magnified 60 times with a scanning electron microscope, and a photograph was taken.

  In FIG. 1, a, c and e are non-foamed layers, and b and d are foamed layers. The thickness of the a layer was 20 μm, the thickness of the b layer was 120 μm, the thickness of the c layer was 1000 μm, the thickness of the d layer was 350 μm, and the thickness of the e layer was 50 μm. In both the b layer and the d layer of the foam layer, the closer to the non-foam layer a and e layers, the smaller the bubble diameter, and the closer to the center non-foam layer (c layer), the larger the bubble diameter, and The layer is tilted. As a result of observing a photograph taken with a scanning electron microscope, the average diameter of the large bubbles in the d layer was about 200 μm, and the average diameter of the small bubbles in the b layer was 70 μm.

  The obtained bottle-shaped container was filled with 500 ml of 10 ° C. cold water, immersed in warm water held at 60 ° C. to the neck of the container, and the time until the temperature of the cold water filled in the bottle-shaped container reached 40 ° C. was measured. However, it was 10 minutes and 30 seconds. For comparison, when a similar test was performed on a bottle-shaped container of the same capacity, which was made of PET for bottles and the entire wall surface was composed of a non-foamed layer, the filled water reached 40 ° C. in 5 minutes. This test shows that the heat insulating property of the foamed molded product according to the present invention is significantly superior to the molded product having a non-foamed layer wall surface.

[Example 2]
In the example described in Example 1, except that the time for storing the parison in the high-pressure vessel was changed to 5 hours, carbon dioxide was dissolved in the same procedure as in the same example, and returned to normal pressure in the same procedure, A parison whose wall surface was impregnated with carbon dioxide was obtained. A pressure of 3 MPa was injected into the obtained parison in the same procedure as in Example 1 to obtain a five-layered bottle-shaped container having an internal volume of 500 ml. As a result of observing the foamed layer in the same procedure as in Example 1, the average diameter of the large bubbles in the d layer was about 250 μm, and the average diameter of the small bubbles in the b layer was 100 μm.

[Comparative Example 1]
In the example described in Example 1, except that the time for storing the parison in the high-pressure vessel was changed to 24 hours, carbon dioxide was dissolved in the same procedure as in the same example, and returned to normal pressure in the same procedure, A parison whose wall surface was impregnated with carbon dioxide was obtained. The obtained parison was injected with 3 MPa of compressed air in the same procedure as in Example 1 to obtain a five-layered bottle-shaped container, but the parison burst during the pressurized air injection. The wall surface of the ruptured bottle-like container was foamed to the center layer. The cause of the parison rupture is presumed to be that carbon dioxide had reached the central layer of the parison wall because the carbon dioxide impregnation time was long.

[Comparative Example 2]
In the example described in Example 1, carbon dioxide was dissolved in the same procedure as in the same example, and the carbon dioxide was dissolved in the same procedure, and returned to normal pressure in the same procedure to obtain a parison in which carbon dioxide was dissolved in the wall surface. This parison was heated by being immersed in an oil bath heated to 120 ° C. for 5 minutes. Subsequently, a pressure of 3 MPa was injected in the same procedure as in Example 1 to obtain a bottle-like container, but the parison burst during the pressure injection. The wall surface of the ruptured bottle-shaped container has a five-layer structure as in Example 1, but the average diameter of large bubbles in the d layer was about 1000 μm, and the average diameter of small bubbles in the b layer was 25 μm. In this example, the parison was ruptured because the parison was heated and stretched in separate steps.

  The resin foam molded article having a multilayer structure obtained by the production method according to the present invention is a sheet, a box-shaped container, a bottle-shaped container, a tube or a tube. The sheet-like molded product obtained by the method of the present invention has a wide range of applications utilizing functions such as light shielding properties, heat insulation (heat shielding properties), sound insulation properties, light reflection properties, and gas barrier properties. Furthermore, the sheet-like molded product can obtain a box-like container that is light and excellent in heat resistance by secondary processing such as vacuum forming. Bottled containers are used as drinking water, health drinks, cosmetic containers, cosmetic containers, and pharmaceutical containers, and have excellent surface smoothness and gloss. An excellent molded product can be obtained. In addition, stored items that are easily deteriorated by light can be shielded from light by the foam layer, can maintain the temperature at an appropriate temperature rather than heat insulation, and have excellent gas barrier properties. Can do. A tube made of a hard thermoplastic resin can be used as a roll for OA equipment, and a tube made of a raw material such as natural rubber, synthetic rubber, or thermoplastic elastomer can be used as a gasket for a refrigerator or a freezer.

It is a wall surface cross-sectional enlarged view of an example of the foam-molded article which concerns on this invention.

Explanation of symbols

a: non-foamed layer b: foamed layer c: non-foamed layer in the center d: foamed layer e: non-foamed layer

Claims (13)

  In the resin foam molded product having a multilayer structure, the outer layers (a, e) on the front and back sides and the central thickness portion (c) of the molded product are non-foamed layers, and the outer layers (a, e) and the central portion (c) The sandwiched portion is composed of a foam layer (b, d), and at least one foam layer of the foam layer (b, d) is between the thick central portion (c) side and the outer layer (a, e). A foamed product made of a resin having a multilayer structure, characterized in that the average bubble diameter is changed.   The resin foam-molded article having a multilayer structure according to claim 1, wherein the resin is an aromatic polyester, an aliphatic polyester, an alicyclic polyester, a polycarbonate, or a mixture of these resins.   The resin foam-molded article having a multilayer structure according to claim 1 or 2, wherein at least one of the foam layers (b, d) is composed of bubbles having different average cell diameters.   The average cell diameter of both of the foamed layers (b, d) is such that the thickness central portion (c) side is large and the outer layer (a, e) side is small. A resin foam-molded article having the multilayer structure described.   5. The multi-layer structure according to claim 1, wherein the bubbles contained in the foamed layer (b, d) have a larger average diameter of the large bubbles than twice the average diameter of the small bubbles. Resin foam molding.   The resin foam molded article having a multilayer structure according to any one of claims 1 to 5, wherein the molded article is a sheet, a box-shaped container, a bottle-shaped container, a tube, or a tube.   In producing a resin foam molded article having a multilayer structure, it comprises a step of producing an unfoamed intermediate molded product containing an inert gas of a thermoplastic resin, and a step of stretching the unfoamed intermediate molded product under heating. A method for producing a resin foam-molded article having a multilayer structure.   After producing an unfoamed intermediate molded product, the intermediate molded product is brought into contact with a pressurized inert gas under a temperature condition below the softening point of the raw material resin to dissolve the inert gas on the wall surface of the intermediate molded product, raw material The method for producing a resin foam-molded product having a multilayer structure according to claim 7, comprising a step of returning to normal pressure under a temperature condition equal to or lower than a softening point of the resin, and a step of heating and stretching the intermediate molded product.   In manufacturing a resin foam molded article having a multilayer structure, a process of producing an intermediate molded article using a thermoplastic resin as a raw material, and this intermediate molded article is treated with a pressurized inert gas under a temperature condition below the softening point of the raw resin. It comprises a step of contacting and dissolving an inert gas on the wall surface of the intermediate molded product, a step of returning to normal pressure under a temperature condition below the softening point of the raw resin, and a step of heating and stretching the intermediate molded product A method for producing a resin foam-molded product having a multilayer structure.   The method for producing a resin foam molded article having a multilayer structure according to claim 8 or 9, wherein the inert gas brought into contact with the intermediate molded article is in a supercritical state.   The resin having a multilayer structure according to any one of claims 7 to 10, wherein the resin is an aromatic polyester, an aliphatic polyester, an alicyclic polyester, a polycarbonate, or a mixture of these resins. A method for producing a foamed molded product.   The method for producing a resin foam molded article having a multilayer structure according to any one of claims 7 to 11, wherein a draw ratio is in a range of 1.1 to 10 times.   The method for producing a resin foam molded article having a multilayer structure according to any one of claims 7 to 12, wherein the molded article is a sheet, a box-shaped container, a bottle-shaped container, a tube or a tube.

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