JP5457072B2 - Method for extruding laminated foamed sheet using polyolefin resin - Google Patents

Description

  The present invention relates to a method for extruding a polyolefin-based resin laminated foam sheet, and more specifically, in producing a polyolefin-based multilayer foam sheet having excellent rigidity, impact resistance, container moldability, lightness, etc., the bubbles are independent. A method for producing a polyolefin-based multilayer foam sheet that is fine and has a good appearance and excellent secondary moldability of a laminated foam container with high production efficiency, and a foaming performance with a low open cell ratio obtained by the production method. Relates to a good multilayer foam sheet.

  Foamed resin sheets have been widely used for industrial materials and daily necessities. However, in recent years, the demand for polyolefin foam sheets has increased, and it has been widely used in various applications such as vehicles, heat insulating materials, building materials, and daily necessities. It's being used. Among them, it is heavily used as a thermoforming material for producing various food and drink containers and trays.

As a basic method for producing a polyolefin foam sheet, a polyolefin resin is melt-kneaded with a foaming agent in an extruder, and this foamable melt-kneaded product is extruded into a sheet form from a die at the tip of the extruder, and the foamable melt-kneaded An extrusion foaming method for foaming a product is well known (for example, Non-Patent Document 1).
Recently, in order to further improve container moldability, rigidity, heat resistance, and the like, a technique of multilayering foam sheets has been developed (Patent Document 1, etc.).

In the production of extruded foam sheets, when multilayering is performed by laminate extrusion molding, the resin viscosity balance of each layer, the state of resin merging at the merging portion of each layer, and the foamable melt-kneaded product are extruded from an extruder. When a slight change occurs in various points such as die tip pressure, the foamed state of the melt-kneaded product changes greatly, and this phenomenon is excellent when manufacturing an extruded foamed multilayer sheet of polyolefin resin with excellent properties. It is an important factor or problem.
In particular, when extruding a polyolefin-based resin in a multilayer configuration, the appearance and bubble state of the foam-molded sheet are greatly affected by the temperature and pressure of each layer resin and its control method. Bubbles become coarse or many continuous bubbles are generated, which not only affects the secondary processability of the foam sheet, but also affects the uneven thickness of the sheet by changing the expansion ratio. The production efficiency is greatly hindered.
This tendency becomes conspicuous when a foamed resin layer is provided in the center layer and a non-foamed resin layer containing a filler having a large shear heat generation is disposed on both outer sides thereof, and the viscosity and temperature of the non-foamed resin layer containing the filler are increased. The pressure and the like also have a great influence on the foamed state of the foamed resin layer.

By the way, when molding a foamed resin sheet by extrusion melting, the temperature and pressure of the resin in the vicinity of the die cause the molding, so it is well known to specify the temperature and pressure of the molten resin in the vicinity of the die. (For example, Patent Document 2), and various studies have been conducted in extrusion laminated foam molding. For example, a molten resin in which a foamable resin is dissolved is introduced into a mold at a resin pressure equal to or higher than a gas pressure at the time of dissolution, Next, a method has been proposed in which laminate bonding is enhanced by extruding into a sheet from a die tip at a temperature near the crystallization peak temperature at the time of cooling while cooling and foaming (Patent Document 3).
However, in extrusion layered foam molding, the temperature of the extruded molten resin is comprehensive from the standpoint of suppressing the generation of open cells, making the cells dense, improving the appearance and secondary formability of the sheet, and improving production efficiency. There is still no way to control the pressure.

Japanese Patent Publication No. 7-98349 (refer to the claims) Japanese Unexamined Patent Publication No. 2007-136966 (see abstract and claim 6) Japanese Patent Application Laid-Open No. 2001-205760 (see abstract and claim 7 of claims)

FOAM EXTRUSION (Principle and Practice), S. T. Lee, TECHNOMIC PUBLISHING Co. Inc., 2000.

  In view of the technical situation in extrusion laminated foam molding described in the background art, the present invention provides a molten polypropylene resin containing a foamable gas and a molten polyolefin resin containing a filler in extrusion lamination foam molding. To develop molding methods that control the temperature and pressure of the resin and their correlation to suppress the generation of open cells and make the cells dense, improve the appearance and secondary formability of the sheet, and improve production efficiency. Is a problem to be solved by the invention.

  In order to solve the problems of the present invention, the present inventor has considered the pressure and temperature control technology in the conventional extruded molten resin, and suppresses the generation of open cells and increases the densification of the bubbles. Considering the correlation of pressure and the control method, it is possible to know the conditional elements useful in the process, and the present invention has been realized.

  Thus, the requirements of the basic configuration of the present invention (invention-specific matters) are condition elements that specify and correlate the temperature and pressure of each layer of the extruded molten resin in extrusion lamination foam molding. Specifically, A polypropylene resin (A) containing a foaming gas and a polyolefin resin (B) containing a filler are melt-kneaded in separate screw-type extruders, laminated through a merged portion, and supplied to a molding die. In the method for producing a laminated foam sheet by discharging from a die outlet, the resin temperature at the screw tip of the foamable gas-containing molten polypropylene resin is (T1) and the resin pressure is (P1), and the filler-containing molten polyolefin When the resin temperature at the screw tip of the resin is (T2) and the resin pressure is (P2), T1 is a crystal of polypropylene resin The temperature Tc is adjusted to 30 to 70 ° C., P1 is 15 to 30 MPa, P2 is 10 to 30 MPa, the relationship 0.8 ≦ P1 / P2 ≦ 1.8 is satisfied, and the resin temperature T2 is T1-20 ≦ T2 ≦ T1 + 40 It is a manufacturing method of a lamination foam sheet which satisfies.

As an additional condition or embodiment, the temperature of the die is controlled by an electric heater and / or a heat medium circulation, the temperature T3 of the heat medium satisfies T1-100 <T3 <T1-50, and contains a foaming gas. The MFR of the polypropylene resin used for the layer (230 ° C., 2.16 kg load; MFR1) and the MFR of the polyolefin resin containing the filler (temperature 230 ° C., 5.0 kg load; MFR2) satisfy MFR1 <MFR2. In the polypropylene-based resin used for the foamable gas-containing layer, the melt tension Y satisfies Y> 7.4446 (MFR) ^−0.7419 , the foamable gas is carbon dioxide, and contains carbon dioxide It is a manufacturing method of an extrusion lamination foaming sheet which laminates a polyolefin resin (B) containing a filler on both outer sides of a propylene resin (A) to do
Further, a laminated foamed sheet produced by any one of the above-mentioned laminated foamed sheet production methods, having a continuous cell ratio of 20% or less with respect to the total bubbles, and a polyolefin resin laminate formed by molding the laminated foamed sheet A container is also an embodiment.

  According to the present invention, the polypropylene resin (A) containing a foamable gas and the polyolefin resin (B) containing a filler are melt-kneaded and laminated foam molded according to the new and basic requirements described in paragraph 0010. At the same time, it is a useful and significant invention that realizes a molding technique that suppresses the generation of open cells and densifies the bubbles, improves the appearance and secondary formability of the sheet, and further improves the production efficiency. This is demonstrated by the data of each example described later and the comparison between each example and each comparative example.

  In the above, the means for solving the problems of the present invention have been outlined along with the background of the creation of the present invention and the basic configuration and features of the present invention. From the perspective of the whole invention, the present invention is composed of the following invention unit groups, and the invention of [1] is a basic invention, and the inventions below that embody the basic invention. Or, it is an embodiment. (The invention group as a whole is collectively referred to as “the present invention”.)

[1] A polypropylene resin (A) containing a foaming gas and a polyolefin resin (B) containing a filler are melt-kneaded in separate screw extruders and laminated through a merged portion into a molding die. In the method for producing a laminated foam sheet by supplying and discharging from a die outlet, the filler temperature at the screw tip of the foamable gas-containing molten polypropylene resin is (T1) and the resin pressure is (P1), and the filler When the resin temperature at the screw tip of the contained molten polyolefin resin is (T2) and the resin pressure is (P2), T1 is adjusted to the crystallization temperature Tc + 30 to 70 ° C. of the polypropylene resin, and P1 is 15 to 30 MPa, P2 is 10-30 MPa, satisfies the relationship 0.8 ≦ P1 / P2 ≦ 1.8, and T2 is T1-20 ≦ T2 ≦ T1 + 0 meets, further, the temperature of the die is controlled by an electric heater and / or heating medium circulation, the temperature T3 of the heating medium satisfies T1-100 <T3 <T1-50, polypropylene used for the foaming gas containing layer The MFR (230 ° C., 2.16 kg load; MFR1) of the resin (A) and the MFR (temperature 230 ° C., 5.0 kg load; MFR2) of the polyolefin resin (B) containing the filler are MFR1 <MFR2 The manufacturing method of a laminated foam sheet characterized by having the following relationship .

[ 2 ] The foamable gas is carbon dioxide, and the polyolefin resin (B) containing a filler is laminated on both outer surfaces of the polypropylene resin (A) containing carbon dioxide . method for producing a laminated foam sheet definitive one.

  When extruding and foaming a molten polypropylene resin containing a foamable gas and a molten polyolefin resin containing a filler, by controlling the temperature and pressure of the molten resin and their correlation, the generation of open cells is suppressed. It is possible to suppress the air bubbles, improve the appearance and secondary formability of the sheet, and further improve the production efficiency.

  Although the present invention has been described in accordance with the basic configuration and features of the present invention as means for solving the problems, the embodiments of the invention of the present invention group described above will be specifically described below in detail. explain.

1. Molten polypropylene resin containing foamable gas (A)
As the molten polypropylene resin (A) used in the present invention, any known polypropylene resin is used.
In particular, from the viewpoint of maintaining the cell shape when foaming is performed in the subsequent step, a polypropylene satisfying a melt tension Y satisfying Y> 7.4446 (MFR) ^−0.7419 is preferable. Here, this formula is a formula showing the dependence of MFR and melt tension of polypropylene having a general molecular weight distribution. Generally, polypropylene for foaming has a higher melt tension than this formula. As a method for producing such polypropylene, long-chain branching is imparted by irradiating polypropylene with an electron beam, or long-chain branching is imparted by modification in an extruder in the presence of peroxide and a crosslinking monomer, or multistage polymerization. And a method of improving the melt tension by adding a high molecular weight component.

  The resin (A) may contain not only the above high melt tension polypropylene alone, but also general polypropylene, or other polymer components such as polyethylene, polystyrene, and elastomer as long as the foamability is not impaired. Fillers such as talc, calcium carbonate, and silica, and auxiliary additives commonly used in polyolefins as required, such as antioxidants, neutralizers, heat stabilizers, light stabilizers, UV absorbers, antifogging An agent, a slip agent, an antiblocking agent, an antibacterial agent, a colorant, a flame retardant, and the like can be blended.

2. Foamable Gas and Foaming Action As the foamable gas used in the present invention, ordinary foamable gases such as volatile hydrocarbons and ethers are used, and carbon dioxide gas is particularly preferably used.
There are two methods for containing carbon dioxide: a method in which carbon dioxide gas is directly injected into the extruder, and a chemical foaming agent that generates carbon dioxide gas by chemical pyrolysis and added in advance, and kneading in the extruder. The method of doing is mentioned.

The method of injecting carbon dioxide directly into the extruder is to provide a gas supply port in the extruder cylinder and compress the carbon dioxide with a diaphragm metering pump or the like at a predetermined pressure when the polypropylene resin is plasticized. It is a method of injecting, kneading with a subsequent extruder screw, and diffusing the gas. In this case, it is preferable to add talc, calcium carbonate, citric acid, sodium bicarbonate and a mixture thereof as the foam nucleating agent.
In addition, a chemical foaming agent that chemically decomposes and generates carbon dioxide gas is added in advance, and the method of kneading in the extruder is chemical foaming in the form of a masterbatch at the stage of supplying polypropylene resin to the extruder. In this method, the agent is added by a method such as dry blending, the chemical foaming agent is decomposed while plasticizing and kneading in an extruder, and carbon dioxide is contained in molten polypropylene.

The types of chemical foaming agents are azodicarbonamide, dinitrosopentamethylenetetramine, azobisisobutyronitrile, P, P'-oxybisbenzenesulfonylhydrazide, citric acid, which decomposes and generates a gas such as carbon dioxide. And sodium bicarbonate.
Of these, citric acid, sodium bicarbonate, or a mixture thereof is preferably used because carbon dioxide is sufficiently generated and there are few residues in the extruder. These may be added to the polypropylene resin as they are, or a resin having a melting point lower than the decomposition temperature, for example, kneaded at a predetermined concentration in a low density polyethylene or the like and added as a master batch. preferable.

  The expansion ratio (X) of the foamable gas-containing molten polypropylene resin (A) such as carbon dioxide gas is 1.5 to 6 times, preferably 1.5 to 4 times. If it is less than 1.5 times, the lightweight property as a foam sheet is impaired, and the advantage of weight reduction cannot be obtained. If it exceeds 6 times, the state of fine bubbles cannot be maintained, continuous bubbles are formed, and problems occur in subsequent container molding. For the expansion ratio, the supply amount of carbon dioxide gas or the like or the amount of the chemical foaming agent is adjusted so as to obtain a desired expansion ratio.

3. Molten polyolefin resin containing filler (B)
Non-foamed polyolefin resin used as a resin composite material containing a filler is a normal polyolefin resin, and representative examples include high-density polyethylene, low-density polyethylene, linear low-density polyethylene, and homopolypropylene. , Ethylene or an α-olefin / propylene random copolymer having 4 or more carbon atoms, ethylene or an α-olefin / propylene block copolymer having 4 or more carbon atoms, ethylene propylene rubber, ethylene propylene diene rubber, and the like.
Among these, in view of coextrusion properties, high density polyethylene, low density polyethylene, linear low density polyethylene, homopolypropylene, propylene ethylene block copolymer, propylene ethylene random copolymer, and mixtures thereof are preferable, and extrusion is more preferable. Homopolypropylene, propylene ethylene block copolymer, propylene ethylene random copolymer, and a mixture thereof are used in order to suppress heat generation at the time.

The filler used in this resin composite material is used to improve various physical properties such as impact strength and heat resistance of polyolefin resin. As such filler, inorganic and organic fillers are used. Yes, inorganic fillers include talc, calcium carbonate, silica, diatomaceous earth, alumina, titanium oxide, magnesium oxide, aluminum hydroxide, magnesium hydroxide, calcium silicate, glass beads, bentonite, glass flakes, glass fiber, carbon Fiber, aluminum powder, molybdenum sulfide, boron fiber, potassium titanate, calcium titanate, hydrotalcite, carbon fiber, pumice powder, mica, calcium phosphate, aluminum phosphate, etc. PMMA beads are used as organic fillers , Cellulose fiber, polyamide fiber, aramid fiber Polyester fibers, rice hulls, wood powder, bean curd refuse, tapioca powder, rice flour, etc. kenaf fibers.
Of these, inorganic fillers are preferable from the viewpoint of improving physical properties, handling, odor, and price, and talc and calcium carbonate are more preferable from the viewpoint of improving physical properties, price, and odor.

Such fillers have high physical properties such as bending strength, impact strength, heat resistance and dimensional change rate not only for use as industrial parts materials such as automobile parts but also for daily use products such as food containers. It is effective for exhibiting in dimensions.
In addition, the resin composite material includes auxiliary additives generally used in polyolefins as required, for example, antioxidants, neutralizers, heat stabilizers, light stabilizers, ultraviolet absorbers, antifogging agents, A slip agent, an antiblocking agent, an antibacterial agent, a colorant, a flame retardant, and the like can be blended.
In addition, up to 50% by weight, crushed material such as ear loss and skeleton generated when the laminated foam sheet of the present invention is obtained, or styrene-based elastomer, petroleum resin or cycloolefin as necessary as a modifier. Various resin materials such as polyethylene resin, petroleum wax, ethylene-vinyl acetate copolymer, maleic acid-modified polypropylene, ethylene-vinyl alcohol copolymer, polyethylene terephthalate, polystyrene, ABS, etc. It can also be blended in a range that does not inhibit the above.

4). Extrusion lamination foaming method (1) Extrusion method of polypropylene resin (A) Polypropylene resin (A) containing foamable gas and polyolefin resin (B) containing filler are melted in separate extruders. As the extruder for extruding the molten polypropylene resin (A) containing the foamable gas when kneaded, joined and laminated, any single type single screw extruder, twin screw extruder, dandem type extruder, etc. In view of avoiding molecular cutting due to shear history, a single screw extruder is preferable in any method. Any of the above extruders for polyolefin resin (B) containing a filler may be used, but a single screw extruder is preferred.
In addition, an extruder having a water-cooled or oil-cooled cylinder temperature control is preferable because each extruder can accurately reflect temperature adjustment. As for the aperture, it is selected according to the thickness ratio of the foamed layer and the non-foamed layer of the obtained sheet, but when the discharge amount is increased by high rotation with a small diameter, it becomes difficult to adjust the resin temperature by shearing heat generation, It is preferable to extrude with a large diameter and low rotation.

The set temperature is selected so that the resin temperature at the screw tip described below can be reached. Generally, when a physical foaming agent is used, the gas inlet is used. The setting is set as high as about 150 to 250 ° C. Thereafter, the nominal temperature is gradually lowered and is set to about 150 to 200 ° C. at the final screw tip.
The screw tip resin temperature (T1) of the polypropylene resin (A) containing the foaming gas satisfies the relationship of T1 = Tc + 30 to 70 ° C. when the crystallization temperature of the polypropylene resin (A) is (Tc). is necessary.
This is necessary to increase the cooling rate after casting from the die outlet after extrusion and to maintain the resin viscosity at a high level. If this condition is exceeded, the foamed foam sheet that is finally obtained is coarse. There is a problem that the continuous bubbles increase, the appearance of the sheet deteriorates, and the subsequent moldability of the container becomes poor. On the other hand, if the temperature is lower than this temperature, the resin starts to solidify in the flow path and cannot be extruded. This temperature is adjusted by the above-mentioned screw cylinder set temperature and cylinder cooling conditions.

  Here, the crystallization temperature was measured using a differential scanning calorimetry (DSC) apparatus manufactured by Seiko Co., Ltd. in accordance with JIS-K7121 “Plastic Transition Temperature Measurement Method”. A 5 mg sample was taken and held at 200 ° C. for 10 minutes, and then crystallized to 40 ° C. at a cooling rate of 10 ° C./min. The maximum exothermic peak temperature of the DSC curve obtained at this time was taken as the crystallization temperature.

The screw tip resin pressure of the molten polypropylene resin (A) containing the foamable gas needs to be adjusted to 15 to 30 MPa. If it is less than 15, it becomes difficult to maintain the resin pressure at the tip of the die, and the formation of bubbles is coarse and continuous. When a gear pump such as a helical gear pump is used, the supply pressure to the die can be improved as compared to the screw tip pressure, but this is also not preferable because the resin transport pressure to the gear pump becomes low. On the other hand, if it exceeds 30, it causes heat generation of the resin in the extruder, and it becomes difficult not only to adjust to a preferable extrusion temperature, but also an overload is applied to the screw and the motor, which may cause a problem of breakage.
The pressure adjustment method may be any method, but examples include adjustment based on the discharge amount of the extruder, adjustment using a screw-type pressure valve installed at the tip of the screw, and pressure adjustment method using a gear pump.

(2) Extrusion method of polyolefin-based resin (B) Molten polypropylene-based resin (A) containing a foaming gas extruded by a separate screw-type extruder and molten polyolefin-based resin (B) containing a filler If the relationship between the temperatures of the two layers satisfies the range of T1-20 ≦ T2 ≦ T1 + 40 at the screw tip, a good foam laminate can be obtained. This is for the purpose of preventing the influence of the amount of heat transferred from the non-foamed layer containing the filler to the foam layer after lamination, and the temperature of the molten polyolefin resin (B) containing the filler is the above If it is lower than T1-20, crystallization of the molten polypropylene resin (A) containing the foamable gas starts in the flow path, resulting in problems such as blockage in the flow path, which is higher than T1 + 40. In this case, the molten polypropylene resin (A) containing the foamable gas after joining and being discharged from the die is given heat from the molten polyolefin resin (B) containing the filler, (A) As a result, fine independent bubbles cannot be obtained.

The resin pressure at the screw tip of the molten polyolefin resin (B) containing the filler needs to be adjusted to 10 to 30 MPa. If it is less than 10, the flow may be uneven due to a difference in pressure balance when joining with the foamable gas-containing polypropylene resin (A) at the joining part, and the appearance may deteriorate. In addition, the extrusion stability of the filler-containing polyolefin resin becomes poor, which may be affected by thickness fluctuation such as surging. On the other hand, if it exceeds 30, it will cause heat generation of the resin in the extruder and it will be difficult not only to adjust to a preferable extrusion temperature, but also the screw and motor will be overloaded and may be damaged.
The pressure adjustment method may be any method, but adjustment by the discharge amount of the extruder, adjustment by a screw type pressure valve installed at the tip of the screw, pressure adjustment method by a gear pump, etc. may be mentioned.

As described above, P1 is 15 to 30 MPa and P2 is 10 to 30 MPa, but it is necessary to satisfy the relationship of 0.8 ≦ P1 / P2 ≦ 1.8. It is more preferable to satisfy the relationship of 1.0 ≦ P1 / P2 ≦ 1.6.
This is because the turbulent flow at the merging portion between (A) and (B) at the time of merging, the maintenance of the optimum resin temperature of the molten resin in each layer due to the decrease in the shear heat generation during the extrusion of each layer resin, Necessary for maintaining the layer composition ratio and ensuring extrusion stability to prevent surging and the like. If the relationship of P1 / P2 is less than 0.8, the resin pressure of the foam layer is lost to the resin pressure of the filler-containing layer, and the influence of turbulent flow at the merging portion occurs, and the shear heat generation of the filler-containing layer Will increase the temperature of the foam layer resin, and there will be effects such as the inability to obtain fine and independent bubbles. If it is greater than 1.8, the filler layer will be pushed by the resin pressure and the width A uniform multilayer structure cannot be maintained in the direction, affecting the extrusion stability of the filler layer, causing shear heat generation of the foam layer resin, and controlling the foam layer resin temperature is difficult.

(3) Lamination | stacking of resin (A) and resin (B) Thus, resin extruded on said conditions is laminated | stacked through a junction part. As a method for joining these layers, any method may be used as long as the layers are laminated in a molten state. For example, a multi-manifold system that is melt-kneaded in an extruder and then stacked in a die, or a feed block system (combining adapter system) that is stacked immediately before flowing into the die can be used. Block method. This is because in the multi-manifold system, the resin stays just before the die exit, and there is a pressure loss part that extends to the entire die width, and the gas dissolved in the resin generates bubbles in this part, and as a result, the foam sheet bubbles become coarse It is because it is easy to become.
In addition, as for the lamination | stacking aspect of both layers, the multilayer lamination | stacking which laminates | stacks the polyolefin resin (B) containing a filler on both the outer side surfaces of the polypropylene resin (A) containing a foamable gas is more preferable.

The molten resin that has been joined and laminated is supplied to a die and discharged from a die outlet to produce a laminated foamed sheet. As the shape of the die, any of a T-type die, a coat hanger type, and an annular die can be used.
The temperature control of the die is controlled by a generally used electric heater, but it is preferably controlled by circulation of a heat medium in order to keep the temperature of the resin constant and to reduce the temperature increase due to the pressure increase. Oil is used as the heating medium, and the mode of circulation of the heating medium can be set and adjusted outside the heater in addition to circulating the temperature-controlled oil inside the die. It is. Although the heat medium can always be flowed, it is most preferable to have a mechanism in which the valve opens and the heat medium flows when the temperature is detected by a thermocouple and is higher than the set temperature.
In this case, the heat medium temperature preferably satisfies T1-100 <T3 <T1-50 in relation to the extrusion resin temperature of the molten polypropylene resin (A) containing the foamable gas. This is necessary in the setting for appropriately maintaining the temperature of the die. When T1-50 or higher, temperature control by heating medium circulation becomes difficult, and when T1-100 or lower, the temperature is rapidly increased by heating medium circulation. The resin may be cooled and the resin may start to solidify in the die. A molten laminate that has been appropriately temperature controlled in an extruder is extruded at an appropriate die temperature to obtain a good foamed laminate.

In the above adjustment, the relationship between the viscosity of the molten polyolefin resin (B) containing the filler and the viscosity of the polypropylene resin (A) also affects the foamability secondarily. It is preferable that the MFR of the polypropylene resin (230 ° C. · 2.16 kg load MFR1) and the MFR of the filler-containing polyolefin resin (temperature 230 ° C. · 5.0 kg load MFR2) have a relationship of MFR1 <MFR2. If the MFR does not have the above relationship, the viscosity of the non-foamed layer will be low, and multilayer extrusion cannot be performed uniformly in the die width direction. Depending on the situation, the turbulent flow at the merged part may affect the final product. The appearance deteriorates due to the so-called flow mark or the like.
Further, the MFR1 of the foamed layer more preferably satisfies 0.5 to 10. If MFR1 is less than 0.5, heat generation due to the influence of shear becomes remarkable during extrusion, the resin temperature becomes high, and stable bubbles are not formed. When MFR1 exceeds 10, the holding force of the sheet from the die outlet to the cooling roll at the time of extrusion molding becomes weak, and there is a problem that molding cannot be performed.
In addition, MFR (unit: g / 10min) said here was measured based on JIS-K6921-2 appendix.

5. Step after Extrusion Subsequently, the foamed laminated sheet extruded from the die is cooled and solidified by a known method, for example, a polishing roll, an air knife, a mandrel, etc., and then wound by a winder or by a cutter. Cut to a predetermined dimension. There are no particular restrictions on the post-treatment after cooling and solidification, for example, corona treatment, flame treatment, flame treatment, plasma treatment and other polar group imparting treatment steps, coater roll anti-fogging agent, anti-static agent coating treatment steps, Film bonding, printing, painting, etc. can be used.
In particular, film lamination is performed by using a pre-thermoforming laminating method for pasting before secondary molding, a thermal laminating method for laminating at the time of cooling during the formation of a laminated foamed sheet, or a heating roll after cooling the laminated foamed sheet. There are methods such as warming and pasting, but any known method can be used for pasting.
The type of film to be bonded is not particularly limited, such as a CPP film, a printed film thereof, a film laminated with EVOH, etc., but it is easy to adhere to a polyolefin-based film, or a film having a polyolefin-based resin on the bonding surface, or chlorine. It is preferable to use a film coated with an ink, an adhesive, or the like mixed with a polypropylene or a low molecular weight polyolefin.

6). Closed cell and open cell The laminated foam sheet finally obtained has fine bubbles and a good laminated foam sheet with reduced open cell rate, and has good secondary moldability such as container molding.
Here, the open cell rate and the closed cell rate are indices indicating how continuous with the adjacent bubble in the cell structure, that is, whether the cell wall is broken and continuous, and is generally implemented. It is measured using an air hydrometer as shown in the example.
The values of the open cell ratio and the closed cell ratio affect the secondary processability such as the subsequent container forming. It also affects the appearance of the finished sheet. The preferred open cell ratio is 20% or less, more preferably 15% or less. When the value is larger than 20%, the part where the bubbles are continuous is depressed and the appearance of the sheet is deteriorated, and the thermal expansion preferentially occurs due to reheating in the secondary processing, and the film is broken. Occurs.

7). Use Mode of Laminated Foamed Sheet The thus obtained laminated foamed sheet is extremely suitable for secondary molding into a molded article such as a container. Examples of the molding method used for the secondary molding include a vacuum pressure forming method, a vacuum forming method, a plug forming method, a press forming method, and a double-sided vacuum forming method, which are usually any known methods.
As a molded product obtained by such a molding method, it can be applied to all fields such as stationery files, food containers, beverage cups, display cabinets, industrial industrial parts, trays and the like.

  In the following, the present invention will be described in more detail by comparing the comparative examples with examples, the configuration of the present invention will be clarified, the rationality and significance of each requirement of the configuration of the present invention, and Demonstrate the superiority of the present invention over the prior art. In addition, the evaluation method of the various performance in a present Example is described below.

MFR (unit: g / 10 min): Measured according to JIS-K6921-2 appendix. The measurement was performed under two conditions of a temperature of 230 ° C. and a 2.16 kg load and a temperature of 230 ° C. and a 5.0 kg load.
Open cell ratio (unit:%) and closed cell ratio (unit:%): Using an air pycnometer (manufactured by Toshiba Beckman, Model 930) as a measuring device, measure the air specific gravity, and determine the volume of the non-foamed layer by multiple layers. Excluded, the open cell rate and closed cell rate were measured by the following formula.
Open cell ratio = {(apparent foam layer volume−measured value) / apparent foam layer volume} × 100
Closed cell ratio = {(measured value−foam layer weight / 0.9) / apparent foam layer volume} × 100
Sheet moldability: When molding a laminated foamed sheet, it can be molded without any problem. When the obtained laminated foamed sheet is evaluated as “Good” without gloss unevenness, streaks, and roughening, each layer material is formed when molding the laminated foamed sheet. The unevenness in flow caused by poor viscosity balance was observed, and the sheet appearance was evaluated as x for visually confirming gloss unevenness, flow marks, streaks, and roughness.

[Example 1]
For 100 parts by weight of polypropylene (Nippon Polypro's New Former FB5100 MFR1 = 0.9 g / 10 min crystallization temperature 120.1 ° C.) as a blowing agent, Clariant's blowing agent CF40E (bicarbonate / citric acid-based chemical foaming) The additive was adjusted so that the expansion ratio (X) was 3 times, and was mixed by dry blending to obtain a resin material for the foam layer. In addition, as a raw material for the non-foamed layer, polyolefin talc masterbatch (Nippon Polypro's Novatec PP / TX1447MB talc content 60% by weight) is 50% by weight, polypropylene (Nippon Polypro Novatec PP / BC3 MFR 10 g / 10 min) 50 What dry-blended weight% (MFR2 = 24g / 10min) was used. An extruder having a diameter of 115 mm was used as an extruder for forming a foamed layer, and an extruder having a diameter of 90 mm was used as an extruder for forming a non-foamed layer. The resin temperature and the resin pressure were measured by installing a contact thermometer and a pressure gauge in the flow path at the tip of each extruder screw. A screw-type pressure control valve was installed on the downstream side of the resin thermometer and the resin pressure gauge so that the extrusion pressure could be adjusted arbitrarily.
Layer structure is non-foamed layer / foamed layer / non-foamed layer, thickness ratio is 100 μm / 800 μm / 10
The discharge amount of each extruder was adjusted so as to be 0 μm, the flow path was distributed by a selector (set temperature 175 ° C.), and the layers were joined by a feed block. The joined resin was extruded onto the slit using a 1,300 mm wide T-die (set temperature 175 ° C.). Oil whose temperature was adjusted to 100 ° C. was circulated in the die. Thereafter, the foamed multilayer sheet was formed by cooling and solidifying with a polishing roll and winding.
Table 1 shows the results of the resin temperature and pressure at the screw tip of each layer resin and the foaming ratio, open cell rate, closed cell rate, and sheet moldability of the obtained sheet.

[Comparative Example 1]
In Example 1, the foam layer screw tip resin temperature was 20 under the extruder temperature setting condition.
Evaluation was performed in the same manner as in Example 1 except that the temperature was set to be around 0 ° C. The results are shown in Table 1. The appearance was not good because surface roughness was observed with an increase in the open cell ratio.
[Comparative Example 2]
In Example 1, evaluation was performed in the same manner as in Example 1 except that the screw tip resin temperature of the non-foamed layer was set to be around 230 ° C. under the extruder temperature setting conditions. The results are shown in Table 1. The appearance was not good because the surface roughness with the increase in the open cell ratio was noticeable.

[Comparative Example 3]
In Example 1, evaluation was carried out in the same manner as in Example 1 except that the screw tip resin pressure was set to be around 34 MPa with a pressure regulating valve installed at the foam layer screw tip. The results are shown in Table 1. The appearance was not good with some surface roughness.
[Comparative Example 4]
In Example 1, evaluation was performed in the same manner as in Example 1 except that the screw tip resin pressure was set to be close to 12 MPa with a pressure regulating valve installed at the foam layer screw tip. The results are shown in Table 1. The open cell ratio was very high, surface roughness was observed, and the appearance was not good.

[Comparative Example 5]
Example 1 except that the resin pressure at the tip of the non-foamed layer was set to 220 ° C. and the resin temperature at the tip of the non-foamed layer was set to 220 ° C. with a pressure regulating valve installed at the tip of the non-foamed layer screw. Evaluation was carried out by the same method. The results are shown in Table 1. The appearance was not good because the surface irregularities with the increase in the open cell ratio and the flow unevenness at the time of merging were noticeable.
[Comparative Example 6]
In Example 1, evaluation was carried out in the same manner as in Example 1 except that the screw tip resin pressure was set to be in the vicinity of 8 MPa with a pressure regulating valve installed at the tip of the non-foamed layer screw. The results are shown in Table 1. The appearance was not good because the surface irregularities with the increase in the open cell ratio and the flow unevenness at the time of merging were noticeable.

[Comparative Example 7]
In Example 1, the screw tip resin pressure was set to about 28 MPa with a pressure regulating valve installed at the foam layer screw tip, and the screw tip resin pressure was set to 12 MPa with a pressure regulating valve installed at the non-foamed layer screw tip. Evaluation was performed in the same manner as in Example 1 except that the setting was made to be close. The results are shown in Table 2. The flow unevenness at the time of merging was noticeable and not good.
[Comparative Example 8]
In Example 1, the screw tip resin pressure was set to about 16 MPa with a pressure regulating valve installed at the foam layer screw tip, and the screw tip resin pressure was set to 28 MPa with a pressure regulating valve installed at the non-foamed layer screw tip. Evaluation was performed in the same manner as in Example 1 except that the setting was made to be close. The results are shown in Table 2. The appearance was not good because the flow unevenness at the time of merging was noticeable.

[Comparative Example 9]
In Example 1, evaluation was performed in the same manner as in Example 1 except that oil whose temperature was adjusted to 150 ° C. was circulated in the die. The results are shown in Table 2. The appearance was conspicuous on the surface.
[Comparative Example 10]
In Example 1, as a foaming layer raw material, polypropylene (Nippon Polypro Newformer FB3312 MFR1 = 3.5 g / 10 min) 100 parts by weight, as a foaming agent, Clariant Foaming Agent CF40E (Baking soda / citric acid) Polyolefin talc masterbatch (Novatech PP / TX1778MB talc content 60% by weight manufactured by Nippon Polypro Co., Ltd.) as a raw material for the non-foamed layer 50% by weight, polypropylene (Novatech PP / EC9 manufactured by Nippon Polypro Co., Ltd.) Evaluation was carried out in the same manner as in Example 1 except that 50% by weight of MFR 0.5 g / 10 min (MFR2 = 0.4 g / 10 min) was used, and the results were shown in Table 2. The open cell ratio was very high, and the appearance was also rough.

[Example 2]
In Example 1, polypropylene (New Former FB51 manufactured by Nippon Polypro Co., Ltd.)
00 MFR1 = 0.9 g / 10 min) 100 parts by weight, 0.5 parts by weight of Clariant's foaming agent CF40E (bicarbonate / citric acid chemical foaming agent) is added as a foam nucleating agent, and mixed by dry blending. Using a foam layer resin material, in the middle of the foam layer extruder, carbon dioxide gas is supplied by a diaphragm supply pump, and the supply amount is adjusted so that the expansion ratio (X) of the foam layer is 5 times. did. Moreover, the temperature setting of the extruder which shape | molds a foaming layer was set so that resin temperature might be 165 degreeC, and the resin temperature of the extruder which shape | molds a non-foaming layer was set so that it might be 170 degreeC. Except for the above, evaluation was performed in the same manner as in Example 1. The results are shown in Table 2. The appearance was somewhat rough.

[Example 3]
In Example 1, 100 parts by weight of polypropylene (Novatech PP / BC4L MFR1 = 5.0 g / 10 min) manufactured by Nippon Polypro Co., Ltd. was used as a foaming agent. Chemical foaming agent) was evaluated in the same manner as in Example 1 except that the addition amount was adjusted so that the expansion ratio (X) was 3 times, and was mixed by dry blending to obtain a resin material for the foam layer. . The results are shown in Table 2. The appearance was somewhat rough.

[Example 4]
In Example 1, 100 parts by weight of polypropylene (Novatech PP / EC9 MFR1 = 0.5 g / 10 min) manufactured by Nippon Polypro Co., Ltd. was used as a foaming agent. Chemical foaming agent) was evaluated in the same manner as in Example 1 except that the addition amount was adjusted so that the expansion ratio (X) was 3 times, and was mixed by dry blending to obtain a resin material for the foam layer. . The results are shown in Table 2. The appearance was somewhat rough.

As can be seen from the data of each of the above examples, in each of the examples of the present invention, since the requirements of the configuration of the present invention (as defined in claims 1 and 2) are satisfied, the open cell ratio is 20% or less. It showed a closed cell foaming state, and the sheet formability (sheet appearance) was generally good or within an acceptable range.
In each comparative example, T1 is too high in Comparative Example 1, T2 is too high in Comparative Example 2, P1 is too high in Comparative Example 4, P1 is too low in Comparative Example 5, and T2 and P2 are in Comparative Example 5. Too high, comparative example 6 has too low P2, comparative example 7 has too high P1 / P2, comparative example 8 has too low P1 / P2, comparative example 9 has too high T3, comparative example 10 has low MFR2. Since the requirements of the configuration of the present invention are not satisfied, either or both of the open cell ratio and sheet formability (sheet appearance) were inferior.
As is clear from the data of each example and the comparison between each example and each comparative example, the rationality and significance of the requirements of the configuration of the present invention and the superiority to the conventional example are demonstrated.

Claims (2)

A polypropylene resin (A) containing a foaming gas and a polyolefin resin (B) containing a filler are melt-kneaded in separate screw-type extruders, laminated through a merged portion, and supplied to a molding die. In the method for producing a laminated foam sheet by discharging from a die outlet, the resin temperature at the screw tip of the foamable gas-containing molten polypropylene resin is (T1) and the resin pressure is (P1), and the filler-containing molten polyolefin T1 is adjusted to the crystallization temperature Tc of the polypropylene resin Tc + 30 to 70 ° C., and P1 is 15 to 30 MPa, P2 where the resin temperature at the screw tip of the resin is (T2) and the resin pressure is (P2). Is 10-30 MPa, satisfies the relationship 0.8 ≦ P1 / P2 ≦ 1.8, and T2 satisfies T1-20 ≦ T2 ≦ T1 + 40. Plus further temperature of the die is controlled by an electric heater and / or heating medium circulation, the temperature T3 of the heating medium is T1-100 <T3 <meet T1-50, polypropylene resin used in the foamable gas containing layer ( A) MFR (230 ° C., 2.16 kg load; MFR1) and MFR (temperature 230 ° C., 5.0 kg load; MFR2) of the polyolefin resin (B) containing the filler have a relationship of MFR1 <MFR2. A method for producing a laminated foam sheet, comprising: And foaming gas is a carbon dioxide gas, to both outer surfaces of the polypropylene resin (A) layer containing carbon dioxide gas, characterized by laminating the polyolefin resin (B) containing a filler, claim 1 A method for producing a laminated foamed sheet described in 1.