JP4535376B2 - Styrenic resin laminated foam sheet, method for producing the same, and molded product thereof - Google Patents

Description

  The present invention relates to a styrene-based resin laminated foam sheet, a method for producing the same, and a molded product thereof, and in particular, a styrene-based resin laminated foam sheet used for thermoforming a packaging container such as raw fish or raw meat or a heat insulating lid, and the laminated foam. The present invention relates to a molded product such as a tray obtained from a sheet or a lid of a take-out lunch container.

  Polystyrene resin foam sheets are easy to process into containers, and the resulting containers are light and moderately rigid, and are therefore widely used as food containers. However, since the container made of polystyrene resin foam sheet is water-repellent and does not absorb water, if you put raw meat or raw fish in this container, the gravy from the raw meat or raw fish will accumulate at the bottom of the container. There was a drawback of making it look bad.

  Conventionally, a multilayer polystyrene-based resin foam and a container have been provided (Patent Document 1).

JP 2001-212914 A

  The technology described in the above publication is a multilayer polystyrene resin foam obtained by laminating a polystyrene resin foam having an open cell ratio of 40% or less and a polystyrene resin foam having water absorption, and blood accumulated in the bottom of a container Has the action and effect of absorbing gravy.

  However, this multi-layer polystyrene resin foam has poor moldability such as a foamed portion having a water absorption property (first foam) due to poor molding elongation due to thermoforming and cracks on the surface. Moreover, since it was extruded at a high resin temperature, the brittleness was large, the molded product was easily broken, and the strength was not sufficient. Furthermore, since it is made of polystyrene resin that tends to become closed-cell foams, variations in water absorption are likely to occur, and when an inorganic gas is used as a foaming agent in order to increase the open-cell ratio, the appearance of the foam is It deteriorated and the range of manufacturing conditions narrowed, making stable manufacturing difficult. Also in water absorption, the water absorption performance of gaseous water such as water vapor was not sufficient.

  An object of the present invention is to provide a laminated foam sheet, a method for producing the same, and a molded product thereof that can obtain a molded product having excellent moldability, less brittleness, excellent strength, and excellent water absorption performance.

In order to solve the above-mentioned problems, the laminated foam sheet of the present invention has a surfactant activity with respect to 100 parts by weight of a mixed resin obtained by adding a hydrogenated product of a copolymer of styrene and conjugated diene to a styrene resin and a polyolefin resin. A first foam having water absorption obtained from a resin composition containing 0.5 to 5 parts by weight of an agent and a second foam mainly composed of closed cells made of styrene resin are laminated. A laminated foam sheet having a density of 0.05 to 0.2 g / cm ³ and an open cell ratio of 40% or more was obtained.

  As a result, the first foam has excellent water absorbability and excellent moldability, and the laminated foam sheet of the present invention has less brittleness, excellent strength, and excellent appearance with excellent water absorption without variation. It is a laminated foam sheet from which a molded product can be obtained.

  In addition, since the resin composition of the first foam can be co-extruded while suppressing the resin temperature, it is possible to prevent brittleness, prevent cracking of the molded product, and improve strength. Furthermore, even if it is mainly made of polystyrene resin, which is likely to become a closed cell foam, a stable open cell rate can be obtained, variation in water absorption is unlikely to occur, and open cell rate can be achieved without using an inorganic gas as a foaming agent. Can be high. Therefore, it becomes the laminated foam sheet which was excellent in the external appearance of the foam, and was excellent in the moldability, and can ensure stable manufacture. Moreover, it can be set as the strong molded article which was excellent also in water absorption performance. In particular, since water absorption performance of gaseous water such as water vapor is also obtained, not only for food trays, but especially for molded products that are prone to water vapor from cooked food, such as lids for take-out lunch containers. Preferably used.

  That is, when a laminated foam sheet is made of a styrene-based resin alone, it tends to be a closed cell foam. Therefore, in order to obtain a foam having a high open cell ratio, the extrusion resin temperature is increased or the foaming agent is used. An inorganic foaming agent having poor compatibility with the styrene resin is used, or a large amount of inorganic powder is used. However, when the extrusion resin temperature is set to a high temperature, the foam tends to be brittle, and when a laminated foam sheet is produced by coextrusion with excellent productivity, the first high temperature in the mold is used. As a result of the resin of the foam raising the resin temperature of the second foam, the closed cell property of the second foam is lowered, and the secondary foamability and strength are lowered. As a result, the obtained laminated foam sheet has poor moldability, and the molded product has low strength. If an inorganic foaming agent is used, extrusion tends to be unstable, the width of the extrusion conditions becomes narrow, and productivity may be reduced. When a large amount of inorganic powder is used, the bubbles become too fine and the strength of the foam is reduced, or residual ash is increased in the case of thermal recycling.

In the laminated foam sheet of the present invention, the surfactant is added in an amount of 0.5 to 5% by weight with respect to 100 parts by weight of a mixed resin obtained by adding a hydrogenated copolymer of styrene and a conjugated diene and a polyolefin resin to a styrene resin. The first foam having water absorption obtained from the resin composition containing part and the second foam mainly composed of closed cells made of styrene resin are laminated, and the density is 0.05 to 0.2 g. / Cm ³ , by using a laminated foam sheet having an open cell ratio of 40% or more, it is possible to use only hydrocarbons excellent in compatibility with the resin as the foaming agent, and the closed cells of the second foam The first foam can be extruded as a foam having a high water absorbency by setting the resin temperature at which the property is less deteriorated, and the laminated foam sheet of the present invention can be obtained with high productivity by coextrusion. it can.

(Resin for the first foam)
Examples of the resin used for the first foam having water absorption include a styrene resin, a hydrogenated copolymer of styrene and conjugated diene, and a polyolefin resin.

  Examples of the styrenic resin used in the first foam of the present invention include styrene homopolymers, copolymers of styrene and other monomers, rubber-modified polystyrene, and the like. These polystyrene resins may be used alone or in combination of two or more.

Examples of other monomers to be copolymerized with styrene include α-methylstyrene, methacrylic acid, acrylic ester, methacrylic ester, acrylonitrile, maleic anhydride and the like.
Rubber-modified polystyrene has a structure in which rubber is dispersed in the form of particles in a polystyrene matrix, and polystyrene is further dispersed in the rubber particles. The rubber particles have various forms such as a salami shape and a core shell shape, and each rubber particle may be used alone, or two or more kinds of rubber particles may be mixed and used.
The rubber-modified polystyrene is preferably used in combination with a polystyrene-based resin other than rubber-modified polystyrene and other synthetic resins in order to ensure the weather resistance of the foam.

Moreover, the standard of the preferable resin selection for manufacturing a foam is 1-7 g / 10min for the melt mass flow rate of a polystyrene-type resin. A polystyrene-based resin having a melt mass flow rate lower than 1 g / 10 min is not preferred because the load on the extruder increases and the productivity decreases during extrusion foaming. When the foamed sheet exceeds 7 g / 10 min, it is difficult to obtain a low-density foam sheet, or the optimum foaming temperature for obtaining an open-cell foam and the crystallization temperature of the polyolefin resin are close. This is not preferable because the control range becomes narrower.
In addition, the measuring method of the melt mass flow rate in this invention is as follows.
JIS K 7210: 1999 “Plastics—Test Methods for Melt Mass Flow Rate (MFR) and Melt Volume Flow Rate (MVR) of Thermoplastic Plastics” Method B was used for measurement.
Fill a cylinder of a measuring device (semi-auto melt indexer (manufactured by Toyo Seiki Seisakusho Co., Ltd.)) with resin sample 3-8g, and compress the material using a filling rod.The polyethylene resin has a test temperature of 190 ° C and a test load. 21.18N, polystyrene resin was measured at a test temperature of 200 ° C. and a test load of 49.03 N, and polypropylene resin was measured at a test temperature of 230 ° C. and a test load of 21.18 N. The preheating time for each measurement was 4 minutes. The number of times was 3, and the average value was defined as the melt mass flow rate of the resin.

  In the present invention, a hydrogenated product of a copolymer of styrene and conjugated diene is used. A copolymer of styrene and a conjugated diene that has not been hydrogenated is not preferred because the foam and its molded product are likely to be deteriorated due to the double bond in the molecule, resulting in problems in long-term storage. In this respect, in the present invention, the hydrogenated copolymer of styrene and conjugated diene is preferably saturated as much as possible, but is not limited to a fully saturated structure. However, a fully saturated structure or a hydrogenated product of a copolymer of styrene and conjugated diene that is substantially similar to this is preferred.

  As a hydrogenated product of a copolymer of styrene and conjugated diene, a hydrogenated product of a block of styrene and conjugated diene or a random copolymer is preferable. In particular, those having a durometer type A hardness (HDA) value of 30 to 90 described in JIS K 7215 are preferred. Examples of the conjugated diene include conjugated dienes having 4 to 10 carbon atoms such as butadiene, isoprene, and 2-ethylbutadiene. Preferred hydrogenated styrene-conjugated diene copolymers include hydrogenated styrene-isoprene block copolymers, hydrogenated styrene-butadiene block copolymers, and hydrogenated styrene-butadiene random copolymers. It is. The fully saturated structure of these copolymers includes, for example, styrene-ethylene-butylene copolymer, styrene-ethylene-butylene-styrene block copolymer, styrene-ethylene-propylene copolymer, styrene-ethylene-propylene-styrene block. Such as a copolymer. These copolymers may be used alone or in combination of two or more.

Further, in the present invention, by adding the hydrogenated copolymer of styrene and conjugated diene, even when the polyolefin resin is mixed with the polystyrene resin, it is a homogeneous foam under a wide range of extrusion conditions. What has a high open cell ratio can be easily obtained, and the obtained foam is a compatibilizing effect of polystyrene resin and polyolefin resin by the hydrogenated product of copolymer of styrene and conjugated diene. As a result, impact resistance is improved and brittleness is improved. Further, by adding a hydrogenated copolymer of styrene and conjugated diene, the brittleness of the foam caused by deterioration with time can be suppressed.

  Furthermore, in order to enhance the brittleness improvement effect by the hydrogenated product of the copolymer of styrene and conjugated diene, as described above, the durometer described in JIS K 7215 in the hydrogenated product of the copolymer of styrene and conjugated diene is used. It is preferable to use a type A hardness (HDA) value of 90 or less. More preferably, the HDA value is 30 to 80, and the HDA value is particularly preferably 50 to 80 in terms of strength retention and brittleness improvement effect. By increasing the brittleness improvement effect, the brittleness of the foam can be further suppressed, leading to an improvement in impact resistance. In addition, in the hydrogenated product of the copolymer of styrene and conjugated diene having an HDA value of less than 30, the strength decreases. When the value of HDA exceeds 90, the brittleness improving effect is reduced and the impact resistance of the foam becomes insufficient.

  In the present invention, the value of durometer type A hardness (HDA) is determined using JIS K 7215: 1986 “plastic durometer hardness using a durometer ASKER A type manufactured by Kobunshi Keiki Co., Ltd. and a constant pressure loader to which a load of 10 N is applied. The measurement was performed in accordance with the method described in “Test Method”. At that time, 12 samples of 30 mm × 50 mm × 4 mm were prepared as a measurement sample, and an average of 6 measurements as a measurement sample having a thickness of 8 mm was obtained by stacking two pieces of this value. The value of the durometer type A hardness (HDA) of the resin It was.

  Examples of the polyolefin resin used in the present invention include a polyethylene resin and a polypropylene resin. The polyethylene resins include high density polyethylene (HDPE), medium density polyethylene (MDPE), low density polyethylene (LDPE), very low density polyethylene (VLDPE), linear low density polyethylene (LLDPE), polyethylene copolymer. Examples of the polypropylene resin include polypropylene (PP) and polypropylene copolymer (PPc). These polyethylene resins and polypropylene resins may be used alone or in admixture of two or more.

Among the polyolefin-based resins, it is preferable to select high-density polyethylene or polypropylene-based resin in order to easily increase the open cell ratio of the foam. This is considered because the resin crystallization temperature is close to the foaming temperature of the mixed composition. Moreover, when the polyolefin resin in the mixed composition is crystallized, the surface of the foam deteriorates due to crystallization on the surface of the foam. Therefore, it is desirable to set the foaming temperature to be higher than the crystallization temperature of the polyolefin resin. However, with regard to polystyrene resins, except for some engineering plastics, it is necessary to lower the foaming temperature to near the crystallization temperature of general polypropylene resins when trying to obtain a low-density foam with little brittleness. In the present invention, high-density polyethylene is particularly preferable as the polyolefin-based resin because the foaming temperature is easily set higher than the crystallization temperature. Here, the high density polyethylene means an ethylene resin having a density of 0.942 g / cc or more. In addition, the density of ethylene-type resin means what was measured using A method (underwater substitution method) prescribed | regulated in JIS K7112: 1999 "The measurement method of the density of non-foaming plastics and specific gravity".
Polyolefin resin is considered to have the effect of increasing the open cell ratio of the foam, but it tends to be difficult to increase the open cell ratio if it is too mixed with the polystyrene resin during kneading. On the other hand, if the mixing is too bad, the appearance of the foam tends to deteriorate. The preferred melt mass flow rate of the polyolefin resin in the present invention is 2 to 10 g / 10 min for a polyethylene resin and 3 to 15 g / 10 min for a polypropylene resin.
The method for measuring melt mass flow rate in the present invention is as described above.

  The composition ratio of the hydrogenated product of the copolymer of polystyrene resin, styrene and conjugated diene, and the mixed resin composition of polyolefin resin is 100 to 50% by weight, and the polystyrene resin is 50 to 94% by weight. The hydrogenated copolymer of styrene and conjugated diene is preferably 5 to 49% by weight, and the polyolefin resin is preferably 1 to 10% by weight.

If the ratio of the polystyrene resin is more than 94% by weight, it is difficult to form open cells and the water absorbability is lowered, which is not preferable. If the extruded resin temperature is further increased to form open cells, the foam becomes brittle. On the other hand, when the proportion of the polystyrene-based resin is less than 50% by weight, the strength of the obtained molded product is lowered. When the hydrogenated amount of the copolymer of styrene and conjugated diene exceeds 49% by weight, the resin viscosity is excessively lowered, the stability of extrusion foaming is lowered, and the cost is increased. Conversely, if the amount of hydrogenated copolymer of styrene and conjugated diene is less than 5% by weight, it is difficult to form open cells, and the effect of improving the compatibility between the polyolefin resin and the styrene resin is reduced. The appearance of the sheet may deteriorate. If the polyolefin resin exceeds 10% by weight, the rigidity of the foam is lowered and the strength is lowered. When the amount is less than 1% by weight, it is difficult to form open cells.
The mixing ratio of the particularly preferred mixed resin composition is 52 to 88% by weight of polystyrene resin, 10 to 40% by weight of hydrogenated copolymer of styrene and conjugated diene, and 2 to 8% by weight of polyolefin resin. It is.

When a surfactant is added to the mixed resin composition having the above composition, a foam having a high open cell ratio easily absorbs water. Surfactants include anionic surfactants such as alkyl sulfonates, alkylbenzene sulfonates, sulfosuccinic acid ester salts, sulfuric acid ester salts and phosphoric acid ester salts, or primary to tertiary alkylamine salts and quaternary ammonium salts. Cationic surfactants such as can be used. The anionic surfactant is more preferred because of its great hydrophilicity-imparting effect on the mixed resin having the above composition, and alkyl sulfonates and sulfosuccinic acid ester salts are particularly preferred. These surfactants may be used alone or in combination of two or more.

  The addition amount of the surfactant is suitably 0.5 to 5 parts by weight with respect to 100 parts by weight of the mixed resin composition, and if the addition amount of the surfactant is less than 0.5 parts by weight, The ability to absorb water is reduced, and if it exceeds 5 parts by weight, the extrusion becomes unstable due to the added surfactant, or the surfactant bleeds out on the surface of the resulting foam, causing foaming. There is a problem that the surface of the body or the molded product is slimy and the surfactant is transferred to the packaged object, which is not preferable. The particularly preferred addition amount of the surfactant is 1 to 3 parts by weight with respect to 100 parts by weight of the mixed resin.

  As the foaming agent that can be used in the present invention, any of known chemical foaming agents and physical foaming agents can be used. Examples of chemical foaming agents include decomposition types such as azodicarbonamide and reaction types such as sodium bicarbonate-citric acid. Examples of the physical blowing agent include hydrocarbons such as propane, butane and pentane, inert gases such as nitrogen and carbon dioxide, ethers such as dimethyl ether and diethyl ether, halogenated hydrocarbons such as tetrafluoroethane, chlorodifluoroethane and difluoroethane. Etc. These foaming agents may be used alone or in combination of two or more. However, since inert gas may lower the extrusion stability, narrow the extrusion condition width, and reduce productivity, it is preferable to use only an organic physical foaming agent. Particularly preferred is butane mainly composed of isobutane which has a low secondary foaming property and a large effect of maintaining secondary foamability during thermoforming.

  Examples of the air conditioner that can be used in the present invention include inorganic fillers such as talc, mica, mica, and montmorillonite, organic fine particles such as fluororesin, or decomposable chemical foaming agents such as azodicarbonamide, sodium bicarbonate-citric acid, and the like. A reactive chemical foaming agent can be used. These bubble regulators may be used alone or in combination of two or more. The addition amount of the bubble regulator is 0.1 to 5 parts by weight with respect to 100 parts by weight of the mixed resin.

  In addition, other known additives such as a colorant, a stabilizer, a filler, a lubricant, an additive, and a dispersant can be appropriately added to the foam of the present invention.

(Resin for second foam)
The same styrenic resin used for the second foam can be used for the first foam.

(Density of laminated foam sheet)
The density of the laminated foam sheet is preferably 0.05 to 0.2 g / cm ³ . If the density is small, the strength is insufficient. If the density is high, lightness and heat insulation are insufficient.

Although there is no restriction | limiting in particular about the density of each foam, It is preferable that it is the said range for the same reason. That is, the density of the first foam is from 0.05 g / cm ^{3 to} 0.2 g / cm ³ and the density of the second foam is from 0.05 g / cm ^{3 to} 0.2 g / cm ^3. It is the laminated foam sheet which is the following.

The density of the laminated foamed sheet was calculated by measuring the volume V (cm ³ ) of the sample and using the following formula from the weight W (g) of the sample.
Foam sheet density (unit: g / cm ³ ) = W / V
For each density of the first foam and the second foam, the mass per unit area of the laminated sheet is measured, and the mass of each foam is calculated from the ratio of the extrusion amount of each foam. Multiply by thickness to calculate density.

(Open cell ratio of laminated foam sheet)
The open cell ratio of the laminated foam sheet is 40% or more, and preferably 40 to 80%. If it is less than 40%, the water absorption performance is insufficient. If it exceeds 80%, the strength is insufficient. 50 to 80% is more preferable, and 50 to 70% is particularly preferable.

The open cell ratio in the present invention was measured according to the measuring method described in ASTM D2856-87.
A test piece of 25 mm in the extruding direction and 25 mm in the width direction is cut out from the foam sheet, and the test pieces are stacked with the closest number of thicknesses to 25 mm, and the apparent volume is accurately measured using a caliper. Next, the volume of the overlapped test piece is measured by the 1-1 / 2-1 atmospheric pressure method using an air comparison type hydrometer 1000 type (manufactured by Tokyo Science Co., Ltd.). Calculate from each measured value using the following formula.
Open cell ratio (volume%) = (apparent volume−volume measured with an air-based hydrometer) / apparent volume × 100

  The first foam in the present invention preferably has an open cell ratio of at least 60%. If the open cell ratio of the first foam is lower than 60%, there is little connection between the bubbles inside the foam, and there are many closed cell walls that prevent water from being absorbed, Absorbability of the like is reduced. A particularly preferable open cell ratio of the first foam is 70% or more. If the open cell ratio of the first foam is 70% or more, water-like substances can be easily absorbed and the water absorption rate is also improved. However, the upper limit of the open cell ratio is preferably 90% or less. If it exceeds 90%, the strength reduction of the sheet and the molded product is increased, which is not preferable.

  In addition, the measurement of the open cell ratio of a 1st foam cuts off the sample for a measurement with a file or a razor blade from a laminated sheet with a file or a razor blade, and measures by the said method.

The second foam of the present invention is mainly composed of closed cells. “Consisting mainly of closed cells” means that the closed cell ratio is 50% or more. The higher the closed cell ratio, the stronger the foam and the better the secondary foamability. Therefore, it is preferable that the closed cell ratio is as high as possible. The closed cell ratio can be measured by the same method as the measurement of the open cell ratio.
In other words, the open cell ratio is preferably less than 30%, more preferably less than 20%, and particularly preferably less than 15%. The smaller the open cell ratio, the stronger the foam, and the higher the secondary foaming rate at the time of molding, which is preferable because a strong molded product can be obtained.

  In addition, the measurement of the open cell rate of a 2nd foam cuts off the sample for a 1st foam with a file or a razor blade from a lamination sheet, cuts out the sample for a measurement, and measures by the said method.

The closed cell rate (%) and the open cell rate (%) of each of the laminated foam sheet, the first foam, and the second foam are calculated as follows.
Closed cell ratio = 100 × {Measured volume of foam with air comparison hydrometer− (Mass of foam / resin density)} / apparent volume of open cell = 100 × (apparent volume of foam− (Measurement volume of the foam with an air comparison type hydrometer) / apparent volume of the foam Note that the closed cell rate = 100− (open cell rate + ratio occupied by the resin).

(Water absorption of laminated foam sheet)
The water absorption of the laminated foam sheet is preferably 0.03 g / cm ² or more. If it is less than 0.03 g / cm ² , the water absorption performance is insufficient.

The measuring method of the water absorption amount of the laminated foam sheet is as follows. A sample having a length of 4 cm, a width of 4 cm, and a total thickness is cut out from the laminated foam sheet, and its weight Wo is measured. Next, the sample is immersed in water and fixed so that the sample does not float up, left in that state for 1 hour, then taken out from the water, the adhered water on the sample surface is wiped off, and the weight W of the sample is measured. And let the value calculated | required by the following formula be the amount of water absorption of a sample.
Water absorption (g / cm ² ) = (W−Wo) / 16
This is performed for 10 samples cut out from arbitrary locations, and the arithmetic average value is taken as the water absorption amount of the laminated foamed sheet.

(Thickness of laminated foam sheet)
The thickness of the laminated foam sheet is 0.5 to 4.0 mm, and the ratio of the thickness of the first foam having water absorption and the thickness of the second foam is the thickness of the first foam: second foam. The thickness is preferably 4.0: 1 to 1: 1. If it is less than 0.5 mm, heat insulation and strength are insufficient. If it exceeds 4.0 mm, the moldability deteriorates. 0.8-3.5 mm is more preferable.

  Further, if the thickness of the first foam: the thickness of the second foam is larger than 4.0: 1, the second foam is thinned, the secondary foamability is lowered, and the strength of the molded product may be insufficient. . If it is less than 1: 1, the water absorption performance is insufficient. 3.5: 1 to 1: 1 are more preferable, and 3.0: 1 to 1: are particularly preferable.

  The thickness of the laminated foam sheet, the first foam, and the second foam was measured by measuring the thickness (mm) at 10 locations in the width direction with a thickness gauge (Sickness Gauge ID-TYPE manufactured by Mitutoyo Co., Ltd.). Was the thickness of the foamed sheet.

  The thickness ratio is measured by taking a vertical cross-sectional photograph of the laminated foam sheet, drawing a straight line in the thickness direction, and measuring the thickness ratio of each foam on the straight line. This was performed at five arbitrary positions in the width direction, and the arithmetic average was taken as the thickness ratio of each foam. This thickness ratio was multiplied by the thickness of the laminated sheet to obtain the thickness of each foam. A laminated foam sheet produced by co-extrusion is easy to measure if a colorant is added to one of the foams during production. If the extrusion conditions are established, a colorless laminated foam sheet can be obtained by removing the colorant. In addition, the said vertical cross-section photograph and the enlarged photograph of the thickness before and behind water absorption of the said colored laminated foam sheet can be image | photographed, for example using the microscope VH-5000 of KEYENCE.

  The secondary foaming ratio of the laminated foam sheet is preferably 1.2 times or more. If it is less than 1.2 times, the moldability is poor and the strength of the molded product tends to be insufficient. For this purpose, it is preferable to lower the open cell ratio of the second foam so that the secondary foam ratio is 1.8 times or more.

The measuring method of the secondary foaming rate is as follows.
After measuring the thickness T1 (primary thickness) of the laminated foamed sheet 14 days after production, the laminated foamed sheet is heated in a heating tank of a molding machine and subjected to secondary foaming, and the thickness T2 after heating is measured. The amount of heating was changed, and the secondary foaming rate (maximum secondary foaming rate) at which T2 / T1 was maximized in a state in which melting due to overheating was not observed on the surface of the laminated foamed sheet was obtained, and this was determined as the secondary foaming rate It was.
Specifically, after measuring the thickness (T1) of the laminated foam sheet 14 days after production, the laminated foam sheet was manufactured by Tosei Sangyo Co., Ltd .: Model FM-3A (single-shot) molding machine, and the ambient temperature was adjusted. Set the upper 175 ± 5 ° C. and lower 165 ± 5 ° C., change the heating seconds at 1 second intervals, and T2 / T1 is maximum when the laminated foam sheet surface is not melted by overheating The secondary foaming rate was obtained.
The secondary foaming ratio of the second foam is taken by taking a vertical cross-sectional photograph of the measurement sample from which the maximum secondary foaming ratio was obtained, measuring the thickness and thickness ratio in the same manner as described above, and dividing by the thickness before heating. Calculated.

  The laminated foamed sheet of the present invention can be formed into a molded product such as a food tray, a fruit and vegetable tray, a lid for take-out lunch, etc. by forming the sheet by a conventionally known thermoforming method such as vacuum forming or pressure forming. Since the strength of the molded product may not be sufficiently secured if the thickness of the side wall of the package storage part of the molded product and the thickness of the bottom of the package storage unit are not uniform, the foam of the present invention is a match mold. It is preferable to form by vacuum forming.

In the present invention, if an opening leading to the inside of the first foam of the present invention is provided immediately after extrusion foaming or simultaneously with molding or before molding, water can be efficiently passed from the foam surface to the inside thereof. Can be absorbed. For example, the opening is formed by passing a foam sheet through a roll between pins, a method of forming an opening at the same time as foam molding using a mold provided with a pin, and simultaneously trimming a molded product. Various methods such as a method of making a hole can be adopted. The opening may be formed by scraping the surface layer of the first foam in addition to the hole penetrating the first foam and the hole not penetrating the first foam.
In addition, as a hole of the said opening part in this invention, a hole diameter of 0.1-1 mm and 1-10 pieces / cm < ² > are preferable. If the hole diameter is less than 0.1 mm or less than 1 piece / cm ² , the water absorption efficiency is lowered, and if the hole diameter exceeds 1 mm or more than 10 pieces / cm ² , the strength of the foam or molded product is lowered. To do.

(Production method)
A known coextrusion foaming equipment can be used for the production of the laminated foam sheet of the present invention. As such facilities, there are those described in JP-A-9-141773, JP-A-6-238788, and the like.

  FIG. 1 is a schematic view showing an example of a laminated foam sheet manufacturing apparatus according to the present invention. FIG. 2 is a schematic enlarged cross-sectional view of the confluence mold shown in FIG.

  1 and 5 are extruders constituting a tandem extruder for the first foam, 2 is a hopper for charging the first foam resin mixture, 3 is a blowing agent supply port, and 4 is a connecting pipe. 6 is a single-screw extruder for the second foam, 7 is a hopper for charging the resin mixture for the second foam, 8 is a foaming agent supply port, 9 is a confluence mold, and 10 is an annular mold. The molten resin mixture 21 for the first foam and the resin mixture 22 for the second foam, which are adjusted to the proper foaming temperature by the respective extruders, are laminated by the joining mold 9 and extruded from the annular mold 10. It cools with the air ring 11 and the cooling mandrel 12, and becomes a cylindrical laminated foam. This foam is cut | disconnected by the cutter 15 and 16 attached to the rear part of the mandrel in the take-up direction of a sheet | seat, and a laminated foam sheet is obtained. In addition, 13 is a take-up roll and 14 is a take-up roll.

Since the first foam has a high open cell ratio and is soft and easily crushed, it is preferable to extrude the second foam with the second foam layer inside (mandrel 12 side). Further, it is preferable that air is blown onto the surface of the sheet when it is extruded from the mold 10 for cooling. In addition, it is preferable to extrude by setting the difference between the resin temperature of the first foam injected into the confluence mold 9 and the resin temperature of the second foam to less than 10 ° C. In order to increase the open cell ratio of the first foam by using the first foam as the resin mixture, the resin temperature is not excessively increased, and an inorganic foaming agent is not used as a foaming agent. It can be produced stably with a high open cell ratio at a low resin temperature setting. Thereby, there is little influence on the resin temperature of a 2nd foam, and it can be set as the 2nd foam with a high closed cell property.
When the resin is a polystyrene resin, the extrusion resin temperature of the second foam varies depending on the degree of polymerization of the resin, the ratio of foaming, and the like. It is done.

For the water-absorbent first foam, 78.9% by weight of a polystyrene resin (“XC-515” melt mass flow rate 1.3 g / 10 min, manufactured by Dainippon Ink & Chemicals, Inc.), a copolymer of styrene and a conjugated diene Hydrogenated product (“SS9000” manufactured by Asahi Kasei Co., Ltd.) 15.8% by weight, high-density polyethylene resin (manufactured by Nippon Polyethylene Co., Ltd., HJ565W density 0.968 g / cm ³ , melt mass flow rate 5.0 g / 10 min) 5.3% by weight 100 parts by weight of a mixed resin composition containing 10 parts by weight of a product name Elestmaster S-520 (polystyrene resin masterbatch containing 20% by weight of an alkylsulfonic acid surfactant manufactured by Kao Corporation) as a surfactant, air bubbles A mixed raw material in which 0.6 parts by weight of talc is mixed as a regulator is used as a first extruder having an inner diameter of 115 mm and a second extruder having an inner diameter of 150 mm. It was fed to the hopper of the first extruder linked tandem extruder. The maximum cylinder temperature of the extruder is 220 ° C., 3.5 parts by weight of butane (isobutane / normal butane = 70/30) is press-fitted and kneaded as a foaming agent, and the foamable molten mixture is cooled in the second extruder. The resin temperature was adjusted to 161 ° C. and flowed into the confluence mold at an extrusion rate of 150 kg / hr.

On the other hand, for the second foam, 0.7 parts by weight of talc was mixed as a foam regulator with respect to 100 parts by weight of polystyrene resin (“HRM-12” melt mass flow rate 5.5 g / 10 min manufactured by Toyo Styrene Co., Ltd.). The mixture is supplied to a hopper of a single-screw extruder having an inner diameter of 115 mm, the cylinder temperature of the extruder is set to 230 ° C., and 4.0 parts by weight of butane (isobutane / normal butane = 70/30) is injected and kneaded as a blowing agent. After cooling, the resin temperature of the foamable molten mixture was adjusted to 154 ° C. and flowed into the confluence mold at an extrusion rate of 100 kg / hr.
The resin merged in the merge mold is poured into an annular mold having a diameter of 175 mm, extruded into a cylindrical shape from a slit having a thickness of 0.45 mm, taken along a cooling mandrel having a diameter of 670 mm, and attached to the rear part of the mandrel. The cylindrical foam was cut with two cutters to obtain two upper and lower laminated foam sheets. Air was blown into and out of the foam immediately after exiting the slit to cool the foam surface. The laminated foam sheet of Example 1 shown in Table 1 and FIG. 3 was obtained.

  FIG. 3 is a diagram (magnification 25 times) according to the cross-sectional enlarged electron micrograph of Example 1. FIG. 4 is a diagram (magnification 50 times) according to the microscope of Example 1 in which the water absorption state of Example 1 is shown in a colored state. The cross-sectional enlarged electron micrograph was obtained with a scanning electron microscope (S-3000N, manufactured by Hitachi, Ltd.), and the microscope used was a microscope VH-5000 manufactured by KEYENCE.

  A laminated foam sheet was produced in the same manner as in Example 1 except that the take-up speed was 1.33 times.

Hydrogenated polystyrene resin (Dainippon Ink & Chemicals Co., Ltd. “XC-515” melt mass flow rate 1.3 g / 10 min) 80% by weight for water-absorbent first foam, copolymer of styrene and conjugated diene Mixed resin composition containing 15% by weight of product ("SS9000" manufactured by Asahi Kasei Co., Ltd.) and 5% by weight of high-density polyethylene resin (HJ565W density 0.968 g / cm ³ , melt mass flow rate 5.0 g / 10 min manufactured by Nippon Polyethylene Co., Ltd.) For 100 parts by weight, 2 parts by weight of the trade name “Denon 3200” (manufactured by Maruhishi Oil Chemical Co., Ltd., sodium alkyl sulfonate surfactant containing sodium stearate) as a surfactant, and 0.6% by weight of talc as a foam regulator. The first part of the tandem extruder in which the mixed raw material is mixed with the first extruder having an inner diameter of 115 mm and the second extruder having an inner diameter of 150 mm. Feed to the hopper of the extruder. The maximum cylinder temperature of the extruder is 220 ° C., 3.5 parts by weight of butane (isobutane / normal butane = 70/30) as a blowing agent is press-fitted and kneaded, and the foamable molten mixture is cooled in the second extruder. The resin temperature was adjusted to 165 ° C. and flowed into the confluence mold at an extrusion rate of 200 kg / hr.

On the other hand, for the second foam, 0.7 parts by weight of talc was mixed as a foam regulator with respect to 100 parts by weight of polystyrene resin (“HRM-12” melt mass flow rate 5.5 g / 10 min manufactured by Toyo Styrene Co., Ltd.). The mixture is fed to a hopper of a single-screw extruder having an inner diameter of 115 mm, the cylinder temperature of the extruder is set to 230 ° C., and 3.2 parts by weight of butane (isobutane / normal butane = 70/30) is injected and kneaded as a blowing agent. After cooling, the resin temperature of the foamable molten mixture was adjusted to 158 ° C. and flowed into the confluence mold at an extrusion rate of 100 kg / hr.
The resin merged in the merge mold is poured into an annular mold having a diameter of 175 mm, extruded into a cylindrical shape from a slit having a thickness of 0.45 mm, taken along a cooling mandrel having a diameter of 670 mm, and attached to the rear part of the mandrel. The cylindrical foam was cut with two cutters to obtain two upper and lower laminated foam sheets. The foam surface was cooled by blowing air into and out of the foam immediately after exiting the slit.

(Comparative Example 1)
For water-absorbent first foam, 95% by weight of polystyrene resin (“XC-515” melt mass flow rate 1.3 g / 10 min manufactured by Dainippon Ink & Chemicals, Inc.), high density polyethylene resin (HJ565W density 0 manufactured by Nippon Polyethylene Co., Ltd.) The product name “DENON 3200” (manufactured by Maruhishi Oil Chemical Co., Ltd., stearic acid) as a surfactant with respect to 100 parts by weight of the mixed resin composition containing 5% by weight of 968 g / cm ³ , melt mass flow rate 5.0 g / 10 min) A mixed raw material in which 2 parts by weight of a metal salt-containing sodium alkylsulfonate surfactant) and 0.6 parts by weight of talc as a foam regulator are mixed is mixed into a first extruder having an inner diameter of 115 mm and a second extruder having an inner diameter of 150 mm. Feed to the hopper of the first extruder of the connected tandem extruder. The maximum cylinder temperature of the extruder is 220 ° C., 3.5 parts by weight of butane (isobutane / normal butane = 70/30) is press-fitted and kneaded as a foaming agent, and the foamable molten mixture is cooled in the second extruder. The resin temperature was adjusted to 168 ° C. and flowed into the confluence mold at an extrusion rate of 150 kg / hr.

On the other hand, for the second foam, 0.7 parts by weight of talc was mixed as a foam regulator with respect to 100 parts by weight of polystyrene resin (“HRM-12” melt mass flow rate 5.5 g / 10 min manufactured by Toyo Styrene Co., Ltd.). The mixture is supplied to a hopper of a single-screw extruder having an inner diameter of 115 mm, the cylinder temperature of the extruder is set to 230 ° C., and 4.0 parts by weight of butane (isobutane / normal butane = 70/30) is injected and kneaded as a blowing agent. After cooling, the resin temperature of the foamable molten mixture was adjusted to 154 ° C. and flowed into the confluence mold at an extrusion rate of 100 kg / hr.
The resin merged in the merge mold is poured into an annular mold having a diameter of 175 mm, extruded into a cylindrical shape from a slit having a thickness of 0.45 mm, taken along a cooling mandrel having a diameter of 670 mm, and attached to the rear part of the mandrel. The cylindrical foam was cut with two cutters to obtain two upper and lower laminated foam sheets. Air was blown into and out of the foam immediately after exiting the slit to cool the foam surface.

(Comparative Example 2)
80% by weight of polystyrene resin (Dainippon Ink & Chemicals "XC-515" melt mass flow rate 1.3g / 10min), hydrogenated copolymer of styrene and conjugated diene ("SS9000" manufactured by Asahi Kasei) Air bubble regulator for 100 parts by weight of mixed resin composition containing 15% by weight, 5% by weight of high-density polyethylene resin (HJ565W density 0.968 g / cm ³ , melt mass flow rate 5.0 g / 10 min, manufactured by Nippon Polyethylene) The mixed raw material mixed with 0.6 parts by weight of talc was supplied to the hopper of the first extruder of the tandem extruder in which the first extruder having an inner diameter of 115 mm and the second extruder having an inner diameter of 150 mm were operated. The maximum cylinder temperature of the extruder is 220 ° C., 3.5 parts by weight of butane (isobutane / normal butane = 70/30) as a blowing agent is press-fitted and kneaded, and the foamable molten mixture is cooled in the second extruder. The resin temperature was adjusted to 161 ° C. and flowed into the confluence mold at an extrusion rate of 150 kg / hr.

On the other hand, for the second foam, a mixture in which 0.7 parts by weight of talc was mixed as a foam regulator with 100 parts by weight of polystyrene resin (“HRM-12” melt mass flow rate 5.5 g / 10 min manufactured by Toyo Styrene Co., Ltd.) Is supplied to a hopper of a single-screw extruder having an inner diameter of 115 mm, the cylinder temperature of the extruder is 230 ° C. at the maximum, and 4.0 parts by weight of butane (isobutane / normal butane = 70/30) as a blowing agent is press-fitted and kneaded. After cooling, the resin temperature of the foamable molten mixture was adjusted to 158 ° C. and flowed into the confluence mold at an extrusion rate of 100 kg / hr.
The resin merged in the merge mold is poured into an annular mold having a diameter of 175 mm, extruded into a cylindrical shape from a slit having a thickness of 0.45 mm, taken along a cooling mandrel having a diameter of 670 mm, and attached to the rear part of the mandrel. The cylindrical foam was cut with two cutters to obtain two upper and lower laminated foam sheets. Air was blown into and out of the foam immediately after exiting the slit to cool the foam surface.

  As shown in Table 1, FIG. 3, and FIG. 4, the laminated foam sheets of the examples can obtain molded products having excellent water absorption performance with excellent moldability, less brittleness, excellent strength, and no variation. In particular, since the first foam is composed of a predetermined mixed resin composition, the extrusion temperature can be suppressed. Therefore, the styrene resin foam of the second foam is held at a low density, and the secondary foam is formed during molding. Since the expansion ratio can be increased, brittle fracture can be prevented while maintaining high water absorption performance, and a laminated foam sheet and a molded product thereof having high strength can be obtained.

  The present invention relates to a styrene-based resin laminated foam sheet used for thermoforming a packaging container or a heat insulating lid for raw fish or raw meat, and a molded product such as a tray or a lid of a take-out lunch container obtained from the laminated foam sheet. Can be used as

It is the schematic of an example of the manufacturing apparatus of the laminated foam sheet of this invention. It is a schematic sectional drawing of the confluence | merging metal mold | die and cyclic | annular metal mold | die of FIG. 1 is a diagram (magnification 25 times) according to an enlarged cross-sectional electron micrograph of Example 1. FIG. It is a figure (magnification 50 times) which concerns on the microscope of Example 1 which shows the water absorption state about Example 1 in the coloring state.

Explanation of symbols

1,5, Extruder 2,7 Hopper 3,8 Supply port 4 Connection pipe 6 Single screw extruder 9 Merge mold 10 Annular mold 11 Air ring 12 Cooling mandrel 13 Take-up roll 14 Take-up rolls 15, 16 Cutter 21 First Resin mixture for one foam 22 Resin mixture for second foam

Claims (9)

A mixed resin obtained by adding a hydrogenated product of a copolymer of styrene and a conjugated diene and a polyolefin resin to a styrene resin, the styrene resin being 50 to 94% by weight, and the copolymer weight of the styrene and the conjugated diene 0.5 to 5 parts by weight of a surfactant is contained with respect to 100 parts by weight of the mixed resin composed of 5 to 49% by weight of the combined hydrogenated product and 1 to 10% by weight of the polyolefin resin. A first foam having water absorption obtained by foaming a resin composition to be formed and a second foam mainly composed of closed cells made of a styrene-based resin are laminated,
A laminated foam sheet having a density of 0.05 g / cm ^{3 to} 0.2 g / cm ³ and an open cell ratio of 50 to 80% .   The first foam is made by foaming a resin composition containing 10 to 40% by weight of a hydrogenated copolymer of the conjugated diene with 100 parts by weight of the mixed resin using a hydrocarbon foaming agent. The laminated foam sheet according to claim 1 obtained. The laminated foam sheet according to claim 1 or 2, wherein the polyolefin resin is high-density polyethylene. The density of the first foam is from 0.05 g / cm ^{3 to} 0.2 g / cm ³ , the open cell ratio is from 70% to 90%, and the density of the second foam is 0.05 g / cm 2. The laminated foam sheet according to any one of claims 1 to 3, wherein cm ³ or more and 0.2 g / cm ³ or less and the open cell ratio is less than 15% . The laminated foam sheet has a thickness of 0.5 mm to 3.5 mm, and the laminated foam sheet has a water absorption amount of 0.03 g / cm ² or more. The laminated foam sheet according to claim 4, wherein the ratio of the thickness of the constituted second foam is 4.0: 1 to 1: 1. The laminated foam sheet according to claim 5, wherein a secondary foam ratio of the laminated foam sheet is 1.2 times or more . The laminated foam sheet according to any one of claims 1 to 6, wherein the hydrogenated product of a copolymer of styrene and conjugated diene has a durometer type A hardness (HDA) value of 30 to 90 . A molded product of a container molded from the laminated foam sheet according to claim 6, wherein the container is molded so that the inside of the container becomes a first foam having water absorption, and the interior of the first foam is formed on the surface thereof. 1-10 holes / cm with a hole diameter of 0.1-1 mm leading to ² Formed molded product. In the method for producing a laminated foam sheet in which a resin mixture for a first foam and a resin mixture for a second foam are injected into a confluence mold and laminated and foamed by coextrusion,
  The resin mixture for the first foam has a surfactant amount of 0.5 to 100 parts by weight of a mixed resin obtained by adding a hydrogenated product of a copolymer of styrene and a conjugated diene and a polyolefin resin to a styrene resin. A resin composition containing 5 parts by weight, wherein the styrene resin is 50 to 94% by weight, the hydrogenated copolymer of styrene and conjugated diene is 5 to 49% by weight, and the polyolefin resin is 1 10% by weight of a resin composition,
  The difference between the resin temperature of the first foam resin mixture injected into the confluence mold and the resin temperature of the second foam resin is set to less than 10 ° C., and the resin temperature of the second foam resin mixture is set to 145- A method for producing a laminated foamed sheet, characterized by co-extrusion in the range of 165 ° C.