JP4360609B2 - Production method of polystyrene resin foam sheet for thermoforming, polystyrene resin foam sheet for thermoforming - Google Patents

Description

The present invention relates to a method for producing a polystyrene resin foam sheet for thermoforming relates to a polystyrene resin foam sheet for thermoforming.

  Polystyrene resin foam sheets have excellent thermoformability, the appearance of the resulting molded products are beautiful, light weight and excellent heat insulation, etc., so they have been used in large quantities as thermoforming foam sheets for food containers in recent years. Has been. Such a polystyrene resin foam sheet is obtained by heating and melting a polystyrene resin in an extruder, adding a foam control agent such as a foaming agent or talc to the melted resin, kneading with the molten resin, and then from the extruder at atmospheric pressure. It is manufactured by a method such as extrusion and foaming. Conventionally, industrial butane has been widely used as the foaming agent because it is inexpensive and has excellent secondary formability when thermoforming a foam sheet.

  However, when industrial butane containing about 70% of normal butane is used as a foaming agent, the dissipation rate of normal butane contained as a foaming agent in the polystyrene resin foam sheet is high, so foaming in the foamed sheet The remaining amount of the agent is extremely lowered in a short period. If the foaming agent residual amount in the foamed sheet is too much or too little, good thermoforming cannot be performed, and if the foaming agent residual amount in the foamed sheet becomes too small, when the foamed sheet is thermoformed As a result, the expansion of the foamed sheet due to heating during thermoforming is referred to as “secondary foaming”. The molded product of “next foaming thickness” is not obtained. For this reason, there has been a problem that the thermoforming suitability period (hereinafter referred to as sheet life) capable of obtaining the desired secondary foam thickness when thermoforming the foam sheet is short.

  In order to solve such a problem, a method of using a foaming agent in which the ratio of normal butane which is rapidly dissipated from the foamed sheet is 0 to 30% by weight and the ratio of isobutane which is slowly dissipated is 100 to 70% by weight. (Patent document 1), normal butane is used in an amount of more than 30% by weight to 50% by weight and isobutane is less than 70% by weight to 50% by weight, and a specific relationship is established between the overall density of the foamed sheet and the surface layer density. A method of extrusion foaming (Patent Document 2) and the like has been proposed.

Japanese Patent Publication No. 5-42977 JP-A-7-165969

  However, the method of Patent Document 1 using a foaming agent having a large isobutane content has a problem that the content of isobutane in the obtained foamed sheet is large and the rate of dissipation of isobutane from the polystyrene resin foamed sheet is slow. For this reason, it takes time until the amount of the foaming agent in the foamed sheet is reduced to an appropriate amount for thermoforming. If thermoforming is performed before that, molding obtained by thermoforming the foamed sheet by the plasticizing effect of isobutane. Surface roughness occurred in the product, and such a molded product was not suitable as a product because the appearance was impaired and the printability on the surface of the molded product was also reduced. For this reason, a long aging period is required to reduce the amount of foaming agent in the foamed sheet to an amount suitable for thermoforming, and it must be stocked for a long time for aging after the foamed sheet is manufactured. Due to this cost, a new problem has arisen that the cost of the molded product is high.

  On the other hand, the method described in Patent Document 2 uses a foaming agent having a high ratio of normal butane that is quickly dissipated from the foamed sheet as compared with the method of Patent Document 1, so that the aging period can be shortened. By controlling the surface layer density within a specific range with respect to the total density of the foam and relatively increasing the surface layer density, surface roughness of the foamed sheet during thermoforming can be prevented. However, this method still has the following two problems.

  The first problem is that in the winter season, a ripening period of about 2 weeks is insufficient and 3 to 4 weeks are required. This problem is due to the fact that normal butane has a faster permeation rate to polystyrene resins than isobutane, but is about 1/8 faster than the permeation rate of air to polystyrene resins. It is. As a result, in summer, the residual amount of normal butane decreased to a range where thermoforming was possible in an aging period of about 2 weeks, but in winter, it took 3 to 4 weeks to decrease to a range where thermoforming was possible.

  The second problem is that after aging for about 2 weeks, the secondary foam thickness and thermoformability change greatly in the winding direction and width direction of the foamed sheet wound in a roll shape, and the stability of thermoforming is lacking. In addition, the thickness of the obtained molded product is greatly different for each molded product, and the quality stability is lacking. The second problem is that the remaining amount of the foaming agent is reduced in the outer part of the foam sheet wound in a roll shape, whereas the remaining foaming agent is present in the part wound from the center of the roll. A large amount is considered as a cause. In addition, the remaining amount of the foaming agent is decreased on the width direction end portion side of the foam sheet, whereas the remaining amount of the foaming agent is large in the center portion in the width direction.

  That is, isobutane has a very low permeation rate with respect to the polystyrene resin, so that it hardly dissipates outside the foamed sheet even during the aging period, whereas normal butane gradually foams during the aging period. In order to dissipate out of the sheet, the remaining amount of foaming agent is large at the outer side (in contact with the outside air) wound in a roll shape and the inner part (portion from the center of the roll) wound in the roll shape. The difference is considered to be the cause of the difference in thermoformability and secondary foam thickness.

  Also, since the permeation rate of normal butane to polystyrene resin is about 1/8 that of air, the rate at which air enters the foam sheet is faster than the rate at which the amount of normal butane in the foam sheet decreases. The internal pressure in the air bubbles may be greater than atmospheric pressure, and the secondary foam thickness and thermoforming of the foam sheet wound in a roll shape on the outside, inside and middle (the part between the outside and inside of the roll) It is thought to be a cause of the change of sex.

  That is, when the internal pressure in the bubbles on the outer side in the width direction of the foam sheet wound in a roll shape becomes atmospheric pressure or more, the foam sheet expands slightly due to the influence of the pressure, and the adjacent foam sheets are tightened and sealed together. As a result, the gas is prevented from flowing through between the foam sheets. As a result, normal butane in the foam sheet located in the middle portion of the roll is less likely to escape through the gap between the contact surfaces of the foam sheet and the foam sheet, and air is less likely to enter the foam sheet. For this reason, the normal butane content and the air at the intermediate portion of the roll of the foam sheet and the portion wound outwardly, and at the end portion in the width direction and the central portion in the width direction even at the same location in the extrusion direction of the foam sheet. It is thought that the content will vary greatly.

As a result of intensive studies to solve the above problems, the present inventors have found that at least one selected from isobutane, normal pentane, and isopentane, carbon dioxide, water, ether having a boiling point of 140 ° C. or lower, and dialkyl carbonate having a boiling point of 140 ° C. or lower. Previously proposed a method for producing a polystyrene-based resin foam sheet using a physical foaming agent mainly composed of a mixed foaming agent containing at least one selected from the above (Japanese Patent Application No. 2002-28740). . This method is a suitable method for obtaining a foam sheet having a thickness of 0.5 to 5 mm and an apparent density of 70 to 150 kg / m ³ and excellent thermoformability. also apparent density a foam sheet in excess of 150 kg / m ^3, with the thermoforming aging period of about 2 weeks is possible, thermoformability due to the difference in the site of the foam sheet was aged wound into a roll stabilized In addition, a stable secondary foam thickness can be obtained, which makes it possible to obtain a molded product with excellent thickness uniformity between molded products obtained from the same roll, and a long-life polystyrene-based polystyrene resin. The present inventors have found a method capable of obtaining a foam sheet and have completed the present invention.

The present invention
(1) A polystyrene resin and a physical foaming agent are heated and kneaded in an extruder to form a foamable molten resin, and the foamable molten resin is extruded and foamed to give a thickness of 0.5 to 3.0 mm. In a method for obtaining a foamed sheet having a density of more than 150 kg / m ³ and 420 kg / m ³ or less, a mixed physical foaming agent comprising 50 to 95 mol% of isobutane and 5 to 50 mol% of carbon dioxide or / and water (however, The total amount of foaming agent contained in the mixed physical foaming agent composed of the foaming agent is 100 mol%.) The physical foaming agent having a main component of isobutane addition amount per 1 kg of polystyrene resin is represented by the following formula (1) A method for producing a polystyrene-based resin foam sheet for thermoforming, which is added so as to satisfy the above relationship.
30 (mol / m ³ ) ≦ α × d ≦ 65 (mol / m ³ ) (1)
(Where α is the amount of isobutane added per 1 kg of polystyrene resin (mol / kg), and d is the apparent density (kg / m ³ ) of the foam sheet.)
(2) In a foam sheet having a thickness of 0.5 to 3.0 mm, an apparent density of more than 150 kg / m ³ and 420 kg / m ³ or less, the foam sheet has a temperature of 23 ° C. and a relative humidity of 50% immediately after the foam sheet is produced. When moving to the atmosphere and aging, the ratio of isobutane to the total organic physical foaming agent remaining in the foamed sheet is 90 to 100 mol% after 30 minutes from the start of aging until aging for 90 days, And a polystyrene-based resin foam sheet for thermoforming, characterized in that an amount of isobutane that satisfies the relationship of the following formula (2) remains:
30 (mol / m ³ ) ≦ β × d ≦ 60 (mol / m ³ ) (2)
(Where β is the amount of residual isobutane (mol / kg) in the foamed sheet relative to 1 kg of polystyrene-based resin, and d is the apparent density (kg / m ³ ) of the foamed sheet.)
(3) The polystyrene-based resin foam sheet for thermoforming as described in (2) above, wherein the polystyrene-based resin comprises 90 to 30% by weight of polystyrene and 10 to 70% by weight of polyphenylene ether;
(4) A polystyrene-based resin foam sheet for thermoforming as described in (2) or (3) above, wherein a thermoplastic resin film is laminated on one side or both sides,
Is the gist.

  In the method for producing a polystyrene-based resin foam sheet for thermoforming according to the present invention, a specific amount of isobutane having a permeation rate with respect to a polystyrene resin that is extremely slower than air, and a specific amount having a permeation rate with respect to the polystyrene resin that is several times faster than air. The foaming sheet obtained by the method of the present invention has a aging period because the foaming agent mainly composed of a mixed physical foaming agent composed of carbon dioxide and / or water is added so that the amount of isobutane added falls within a specific range. Is shortened and thermoforming becomes possible in the aging period of about 2 weeks even in winter. Moreover, even in the aging period of about 10 days to 2 weeks, a molded product with a constant quality is obtained because there is very little variation in thermoformability due to the difference in the part in the winding direction and width direction of the foam sheet wound in a roll shape. Obtainable.

  The polystyrene-based resin foam sheet for thermoforming of the present invention has a specific range of thickness, a specific range of apparent density, a specific range of physical foaming agent total residual amount, a specific range of isobutane residual amount, The foam sheet of the present invention has a long sheet life. Further, the entire foamed sheet wound in a roll and aged is highly uniform in secondary foamability during thermoforming, and the surface of the foamed sheet does not become rough during thermoforming. For this reason, molded articles such as containers obtained by thermoforming the polystyrene resin foam sheet of the present invention have effects such as small variations in thickness between molded articles, good surface condition, and uniform quality. .

    In the method for producing a polystyrene resin foam sheet for thermoforming according to the present invention, the polystyrene resin is heated, melted and kneaded in an extruder, and further a physical foaming agent is press-fitted into the extruder and kneaded to obtain a foamable molten resin. The foamable molten resin is extruded from a high pressure region to a low pressure region in an extruder to obtain a polystyrene-based resin foam sheet for thermoforming (hereinafter simply referred to as a foam sheet). The foamable molten resin is extruded from a high pressure region to a low pressure region in an extruder through an annular die attached to the tip of the extruder and foamed into a cylindrical shape, and then the cylindrical foam is cut in the extrusion direction to form a sheet. It is preferable that the foamed sheet can be efficiently manufactured. However, in the present invention, the foamable molten resin may be extruded and foamed through a T die attached to the tip of the extruder.

  The polystyrene resin used in the present invention is a styrene homopolymer resin, a styrene copolymer resin obtained by copolymerization of styrene and other monomers, a styrene homopolymer resin or / and a styrene copolymer resin and styrene. -A mixture with a butadiene block copolymer, a rubber-modified styrene resin (impact polystyrene resin) obtained by polymerizing a styrene monomer in the presence of a rubber-like polymer, or the above-mentioned polystyrene resin and other Examples thereof include a polystyrene resin or a polystyrene resin composition having a styrene component ratio of 50% by weight or more, such as a mixture with a resin. However, only a mixture of polystyrene resin and polyphenylene ether is a polystyrene resin or polystyrene resin composition having a styrene component ratio of 25% by weight or more. When the brittleness improvement of a polystyrene-type resin is requested | required, it is preferable to use the mixture of 90-30 weight% of polystyrene and 10-70 weight% of polyphenylene ether. Examples of other monomers that can be copolymerized with styrene constituting the styrene-based copolymer include acrylic acid, methacrylic acid, maleic anhydride, butadiene, acrylonitrile, and the like, but butadiene is preferable.

  In the method of the present invention, the physical foaming agent is a mixed physical foaming agent containing 50 to 95 mol% of isobutane, 5 to 50 mol% of carbon dioxide and water selected from water (provided that isobutane and water or / And the total amount of carbon dioxide is 100 mol%). A polystyrene resin foam sheet obtained using a physical foaming agent mainly composed of such a mixed physical foaming agent has an aging period shorter than the summer (for example, 2 weeks) even in the winter when an aging period longer than the summer is required. The following is possible: thermoforming is possible, and even during a short aging period, there is little variation in thermoformability due to the difference in position in the winding direction and width direction of the foamed sheet wound in a roll, and the thickness between molded products There is an advantage that a molded product with small variation can be obtained and the sheet life of the foamed sheet is also long. Such an advantage is very advantageous when the foamed sheet is stored or aged in a state of being wound in a roll shape, and the longer the length of the foamed sheet in one roll (the larger the diameter of the roll). More useful. The length of the foam sheet in one roll is preferably 150 m or more, more preferably 160 to 650 m, and still more preferably 180 to 450 m.

  On the other hand, carbon dioxide and water constituting the mixed physical foaming agent together with isobutane have an extremely high permeation rate for polystyrene resins and several times faster than the permeation rate of air for polystyrene resins (the rate of permeation rate of air to polystyrene resins). Therefore, most of them are dissipated from the foamed sheet immediately after the foamed sheet is produced, and are not gradually dissipated out of the foamed sheet during the aging period like normal butane. For this reason, the amount of remaining foaming agent does not differ greatly between the portion located outside the roll of the sheet wound in a roll shape and the portion located inside, and the amount of remaining foaming agent in the longitudinal and width directions of the sheet is also uniform. It will be something. This is presumed to be due to the following phenomenon. In other words, most of the carbon dioxide and water escape from the foam sheet at a speed much faster than the speed at which air penetrates into the foam sheet immediately after the foam sheet is manufactured. Will also be in a reduced pressure state. For this reason, the tightening state of the foam sheet is somewhat loosened, and air efficiently circulates through the gap between the contact surfaces of the foam sheet and the foam sheet. This facilitates air permeation into the foam sheet and is quick. Most of the air permeates into the foam sheet at the time (approximately 10 days after production), and the amount of air is stabilized. On the other hand, since isobutane has a far slower release than normal butane, the isobutane content is almost constant for a long period of time (approximately half a year after production) immediately after production, regardless of where it is in the roll. As described above, the amount of air and isobutane in the foamed sheet is stabilized early in the manufacturing process, and the amount of residual foaming agent in the longitudinal and width directions of the sheet can be reduced anywhere in the roll by maintaining it for a long period of time. It will be uniform.

  When the proportion of isobutane in the mixed physical foaming agent of isobutane and carbon dioxide or / and water is less than 50 mol% (when the proportion of carbon dioxide or / and water exceeds 50 mol%), The secondary foam thickness is small. The ratio of isobutane and carbon dioxide or / and water in the mixed foaming agent is preferably 60 to 95 mol% of isobutane and 40 to 5 mol% of carbon dioxide or / and water, but the sheet life is long and the foam sheet is stored. From the point that a sufficient secondary foaming thickness can be obtained even after 40 days have passed after production in the summer when the temperature is inevitably high, in particular, isobutane is 70 to 95 mol%, carbon dioxide and / or water is 30 to 5 mol%. It is preferable to include. On the other hand, when the proportion of isobutane in the mixed physical foaming agent exceeds 95 mol% (when the proportion of carbon dioxide or / and water is less than 5 mol%), the foam sheet can be thermoformed by the plasticizing effect of isobutane. There is a possibility that the range of temperature and heating time is narrowed and thermoformability is lowered. In other words, the surface of the foamed sheet may be roughened if it is heated too much, but if the heating time is shortened by virtue of being overheated, the heating will be insufficient, the foamed sheet will be torn, or the mold will be molded according to the shape of the mold. The inconvenience that the product cannot be obtained is likely to occur. Moreover, it may take too much time for the amount of air in the foam sheet to stabilize. In order to avoid such inconvenience, the proportion of isobutane in the mixed physical foaming agent is preferably 90 mol% or less, preferably 75 to 90 mol% of isobutane, 10 to 25 mol% of carbon dioxide and / or water.

  In the present invention, the physical foaming agent used for foaming the polystyrene-based resin is mainly composed of a mixed physical foaming agent composed of the above isobutane and carbon dioxide or / and water (isobutane and carbon dioxide in the mixed physical foaming agent). Or / and the sum of water is 80 mol% to 100 mol%), preferably 85 mol% or more, more preferably 90 mol% or more, and most preferably 95 mol% or more. Examples of other blowing agents that can be used in combination with a mixed physical blowing agent of isobutane and carbon dioxide or / and water include, for example, normal pentane, isopentane, carbon dioxide, As with water, dimethyl ether, ethyl methyl ether, diethyl ether, methyl chloride and the like, which are early dissipative blowing agents, are used. In addition, propane, normal butane and the like can be used. However, the use of foaming agents such as normal butane, which has a permeation rate of about 1/8 of that of polystyrene resin, and propane having a permeation rate of the same level should be avoided as much as possible or as little as possible. Specifically, the normal butane content in the mixed physical foaming agent is preferably 0 to 10 mol%, more preferably 0 to 5 mol%. In addition, chemical foaming agents can also be used as other foaming agents, but when using chemical foaming agents, it is preferable to use only a small amount as a foam control agent that reduces the bubble size, specifically, 0.01-1 weight part is preferable with respect to 100 weight part of polystyrene-type resin.

  As a reference, Table 1 shows the permeation rates of various foaming agents when the permeation rate of air to polystyrene resin is 100.

(Table 1)

  In the method of the present invention, a physical foaming agent is added so that isobutane in an amount satisfying the following formula (1) is added to the foamable molten resin.

30 (mol / m ³ ) ≦ α × d ≦ 65 (mol / m ³ ) (1)
Where α is the amount of isobutane added (kg / kg) to 1 kg of polystyrene resin used for extrusion foaming, and d is the apparent density (kg / m ³ ) of the foamed sheet obtained by extrusion foaming. More than (kg / m ³ ) and 420 (kg / m ³ ) or less.

When α × d is less than 30 (mol / m ³ ), even if a foam sheet having an intended apparent density is obtained, a sufficient secondary foam thickness at the time of thermoforming may not be obtained. It becomes difficult to obtain a molded product faithful to the mold. On the other hand, when it exceeds 65 (mol / m ³ ), even if a foam sheet having the desired apparent density is obtained, β × d described later is present exceeding 60 (mol / m ³ ) even during thermoforming. As a result of the increased content of isobutane dissolved in the polystyrene resin constituting the foamed sheet, the surface becomes rough during heating during thermoforming (polystyrene resin is plasticized due to the excessive presence of organic volatile foaming agent). It becomes more sensitive to heat than necessary, and bubbles on the surface are destroyed during heating, and the appearance is remarkably deteriorated). From such a viewpoint, the lower limit of α × d is preferably 32 (mol / m ³ ) or more, more preferably 35 (mol / m ³ ) or more, and the upper limit thereof is preferably 60 (mol / m ³ ) or less. (Mole / m ³ ) or less is more preferable.

  In order to adjust the bubble diameter of the foamed sheet, a cell regulator is usually added to the foamable molten resin obtained by adding a physical foaming agent to a polystyrene resin and melt-kneading. Examples of the air conditioner include talc, kaolin, mica, silica, calcium carbonate, barium sulfate, titanium oxide, clay, aluminum oxide, bentonite, diatomaceous earth and the like, or sodium bicarbonate, monosodium citrate, and the like. Illustrated. These bubble regulators are usually used alone, but may be used in combination of two or more. Since the inorganic powder used as the bubble adjusting agent has a larger effect of reducing the bubble diameter of the foam sheet as the particle size is smaller, the inorganic powder having a smaller particle diameter can reduce the bubble diameter of the foam sheet with a smaller amount of use. From this viewpoint, the average particle diameter (centrifugal sedimentation method) of the inorganic powder is preferably 30 μm or less, more preferably 20 μm or less, and further preferably 15 μm or less. However, the smaller the average particle size, the higher the processing cost and the higher the price of the inorganic powder, so 0.1 μm is preferable as the lower limit. Among the inorganic powders, talc is most preferable because it has a large effect of reducing the bubble diameter and is inexpensive.

  In the foamable molten resin, various additives such as a nucleating agent, an antioxidant, a thermal stabilizer, an antistatic agent, and conductivity imparting are added as necessary, as long as the object of the present invention is not significantly impaired. Agents, weathering agents, ultraviolet absorbers, flame retardants, inorganic fillers, and the like can be added. These additives and the above-mentioned air conditioner may be added when the polystyrene-based resin is melted in the extruder to prepare a foamable molten resin, but may be previously contained in the polystyrene-based resin.

The method of the present invention is a method of obtaining a polystyrene-based resin foam sheet having a thickness of 0.5 to 3.0 mm, an apparent density of more than 150 kg / m ³ and 420 kg / m ³ or less, preferably a thickness of 0.8 to 2.5 mm. is suitable for obtaining a foamed sheet of apparent density 150 kg / ^{m 3} super ~350kg / ^{m 3.} Such an apparent density range and thickness range are important factors in obtaining a sharp molded product faithful to the mold.

Polystyrene resin foam sheet thickness 0.5~3.0mm of the present invention, preferably 0.8～2.5Mm, apparent density 150 kg / ^{m 3} Super ~420kg / ^{m 3.} If the thickness of the foamed sheet is less than 0.5 mm, the strength of the molded product obtained by thermoforming may be reduced too much, and if the thickness exceeds 3.0 mm, the thermoformability will deteriorate and the molded product will be deteriorated. There is a risk of uneven thickness. When the apparent density is 150 kg / m ³ or less, there is a possibility that a sharp molded product having a shape as in the mold cannot be obtained, and the strength of the obtained molded product may be lowered. On the other hand, when the apparent density exceeds 420 kg / m ³ , there is a possibility that the characteristics of the foam such as lightness, heat insulation, and buffering properties may be lost. The apparent density of the foamed sheet is particularly preferable when it is 150 to 350 kg / m ^{3, since} it is excellent in thermoformability and is particularly excellent in lightness, heat insulation, and mold transferability.

  In the foamed sheet of the present invention, it is necessary that the proportion of the total organic physical foaming agent remaining is 90 to 100 mol% and that isobutane in an amount satisfying the following formula (2) remains.

30 (mol / m ³ ) ≦ β × d ≦ 60 (mol / m ³ ) (2)
(Where β is the amount of residual isobutane (mol / kg) in the foamed sheet relative to 1 kg of polystyrene-based resin, and d is the apparent density (kg / m ³ ) of the foamed sheet.)

  The isobutane in the foaming agent added to the polystyrene resin during the production of the foamed sheet is the foamable molten resin or foamed sheet until the foamed sheet is obtained by extruding and foaming the foamable molten resin from the extruder. There is almost no escape from the inside, and the escape from the obtained foamed sheet is very slow. For this reason, the amount of isobutane added in the foamable molten resin: α (mol / kg) and the amount of isobutane remaining in the foamed sheet: β (mol / kg) have some dispersal during production, etc. After that, the sheet gradually escapes from the foam sheet at an extremely slow speed, so β is slightly smaller, but only a slight decrease is observed for 4 months from the first day of production, and there is no significant change. When the residual amount of isobutane in the foamed sheet is less than the lower limit obtained from the above formula (2), as described above, a sufficient secondary foam thickness cannot be obtained in thermoforming, and when the amount exceeds the upper limit, Surface roughness is likely to occur during heating during thermoforming. Further, even when the residual amount of isobutane is within the range determined from the above formula (2), when the amount is less than 90 mol% with respect to the total amount of the organic foaming agent remaining in the foamed sheet (that is, an organic physical foaming agent other than isobutane) In the case where the residual amount exceeds 10 mol%), this causes a variation in thickness between molded products in the same roll. From this point of view, the organic physical foaming agent remaining in the foam sheet after 240 hours of production, which is a time when air penetrates into the bubbles of the sheet and the amount of air in the bubbles is generally stabilized over the entire roll. Of these, the proportion of isobutane is preferably 90 mol% or more, more preferably 92 mol% or more, and still more preferably 95 to 100%. Further, the residual amount of isobutane at that time is preferably in the range of 5 to 20 g per kg of the foam sheet.

In addition, the thickness of the foam sheet in this specification refers to the arithmetic average value of each measured value obtained by measuring the thickness at 10 locations at equal intervals over the entire width of the foam sheet. The apparent density of the foamed sheet is a value (g / cm ³ ) obtained by dividing the weight (g) per unit area (1 cm ² ) of the foamed sheet by the thickness (cm) of the foamed sheet, kg / m Calculated by converting to ³ units.

  The remaining amount of the organic physical foaming agent in the foamed sheet is determined by placing the measurement sample collected from the foamed sheet in a sample bottle with a lid containing toluene and stirring to dissolve the foaming agent in the foamed sheet in toluene. Then, the toluene in which the blowing agent is dissolved can be collected with a microsyringe and subjected to gas chromatography analysis, which can be determined by an internal standard method.

  The foamed sheet of the present invention has an open cell ratio of 0 to 15%, more preferably 0 to 10%, which is excellent in secondary foamability during thermoforming, and the mechanical strength and thickness of the resulting molded product. It is preferable from the point of being particularly good in uniformity.

The open cell ratio (%) in the present specification is a value obtained in the following manner in accordance with ASTM D-2856-70 (Procedure C), and is the true value of the measurement sample using an air pycnometer. The volume Vx (cm ³ ) is obtained, the apparent volume Va (cm ³ ) is obtained from the outer dimension of the measurement sample, and can be calculated by the following equation (3). The true volume Vx is the sum of the volume of the resin in the measurement sample and the volume of the closed cell portion.

  Open cell ratio (%) = {(Va−Vx) / (Va−W / ρ)} × 100 (3)

In the above formula (3), W is the weight (g) of the measurement sample, and ρ is the density (g / cm ³ ) of the base resin constituting the foamed sheet. The dimensions of the measurement sample in the measurement of the open cell ratio are 25 mm in length, 25 mm in width, and 40 mm in thickness. In the present invention, a single sample cannot be obtained with a size suitable for the thickness of the above-mentioned measurement sample. Therefore, when a plurality of samples are overlapped, the thickness is closest to 40 mm but does not exceed 40 mm. Measure multiple samples at the same time with an air pycnometer. The sampling location of the measurement sample is a location randomly selected from the portions excluding the 50 mm portions from the both ends in the width direction of the foam sheet, the number of measurements from one roll is 10, and the open cell ratio is obtained for each of them. Is calculated as the open cell ratio of the foamed sheet of the present invention.

  In the foam sheet of the present invention, the average cell diameter in the thickness direction of the foam sheet: X, the average cell diameter in the extrusion direction of the foam sheet (MD): Y, the average cell diameter in the width direction of the foam sheet: Z, Those satisfying the relation expressed by the following formulas (a) to (c) are preferable.

      0.3 ≦ X / Y ≦ 1.0 (a)

      0.3 ≦ X / Z ≦ 1.0 (b)

    60 μm ≦ (X + Y + Z) / 3 ≦ 100 μm (c)

  A foamed sheet having bubbles in such a shape that the values of X / Y and X / Z satisfy the above ranges is excellent in thermoformability and mechanical strength of the resulting molded product. However, when one or both of X / Y and X / Z is less than 0.3, flat bubbles are formed, and the mechanical strength of a molded product obtained by thermoforming the foamed sheet may be reduced. There is. On the other hand, a foam sheet in which one or both of X / Y and X / Z exceeds 1.0 may cause a large drawdown of the sheet during thermoforming. Average cell diameter in the thickness direction of the foamed sheet: ratio of X and average cell size in the extrusion direction: Y: X / Y, average cell size in the thickness direction: ratio of X and average cell size in the width direction: Z ratio: X / More preferably, each Z is 0.4 to 0.8.

  The average cell diameter in the thickness direction: X, the average cell diameter in the extrusion direction: Y, and the average cell diameter in the width direction: Z are obtained by observing the vertical section in the extrusion direction and the vertical section in the width direction of the foam sheet with a microscope. Can be sought. In order to obtain the average cell diameter in the extrusion direction: Y, first, a vertical cross section along the extrusion direction of the foam sheet is magnified and photographed with a microscope or the like. In the vicinity of the back surface, a horizontal line corresponding to a length of 2 mm before enlargement is drawn. Next, the number n of bubbles intersecting with each line segment (n includes those in which a part of the bubbles intersects with the line segment) is obtained, and each line is calculated according to the calculation formula: [2 / (n-1)]. The average bubble diameter per bubble in the minute is obtained from each of the three line segments drawn near the surface, in the center in the thickness direction, and near the back surface, and the average bubble diameter of each obtained bubble is calculated. Let the arithmetic mean value be Y (mm).

On the other hand, for the average cell diameter in the width direction: Z, a vertical section along the width direction of the foam sheet was magnified and photographed with a microscope or the like. In addition, a horizontal line corresponding to a length of 2 mm before enlargement is drawn in the vicinity of the back surface, and the value obtained by the same operation as the operation for obtaining the average bubble diameter Y in the extrusion direction is defined as Z (mm). . Further, the average cell diameter: X in the thickness direction is determined by an enlarged vertical sectional view in the extrusion direction. First, in a vertical cross-sectional enlarged view of the measurement sample in the extrusion direction, a straight line is drawn over the entire thickness of the foamed sheet to obtain the number n ₂ of bubbles intersecting the straight line, and the calculation formula: [thickness of foamed sheet / The value obtained from n ₂ ] is X (mm).

  The foam sheet of the present invention may be laminated with a non-foamed thermoplastic resin sheet or film on one or both sides thereof, and when a non-foamed sheet or film is laminated, the thermoformability, rigidity, tear strength, etc. are improved. This is preferable. A laminated sheet in which a sheet or film is laminated on one or both sides of a foamed sheet is a method in which a foamed sheet and a sheet or film are produced in separate processes, and these are laminated with heat or an adhesive, and foamed by extrusion foaming. It can be obtained by an extrusion laminating method in which a film or sheet is extruded and laminated on the sheet from another extruder, a co-extrusion method in which a foamable molten resin and a non-foamable thermoplastic molten resin are coextruded.

  Examples of the thermoplastic resin constituting the sheet or film include high-density polyethylene, low-density polyethylene, linear low-density polyethylene, polyethylene resins such as ethylene-vinyl acetate copolymer, polystyrene such as polystyrene and high-impact polystyrene. Resin, polypropylene resin, polyester resin and the like. Of these thermoplastic resins, polystyrene resins that can be directly heat bonded to the foamed sheet are preferable.

  Although there is no restriction | limiting in the thickness of the sheet | seat and film laminated | stacked on the said foamed sheet, Usually, it is 0.01-0.3 mm. If the thickness is too thin, the effect of improving the physical properties of the sheet by laminating a non-foamed sheet or film may be insufficient, and if it is too thick, the lightness may be reduced and the economy may be deteriorated. is there.

  The foamed sheet of the present invention can be thermoformed using a mold comprising a male mold and / or a female mold. The thermoforming methods include vacuum forming, pressure forming, and free drawing forming, plug and ridge forming, ridge forming, matched mold forming, straight forming, drape forming, reverse draw forming, and air slip forming. , Plug assist molding, plug assist reverse draw molding and the like, and molding methods combining these. This thermoforming method is a preferable method because a molded product can be obtained continuously in a short time.

  The molded product obtained by thermoforming from the foamed sheet of the present invention is suitably used for applications such as trays, baskets, lunch boxes and cups.

Hereinafter, the present invention will be described in more detail with reference to examples.
Examples 1-5, Comparative Examples 1-3
The resin shown in Table 2 or 3 and 1 part by weight of talc are put into a first extruder having a diameter of 90 mm and heated, melted and kneaded, and then the physical foaming agent shown in Table 2 or Table 3 is added to the first extruder. The mixture was pressed and kneaded. Next, the melt-kneaded product was cooled in a second extruder having a diameter of 120 mm connected to the first extruder, extruded from an annular die having a diameter of 110 mm at the resin temperature shown in Table 2 or Table 3, and foamed into a cylindrical shape. Next, the cylindrical foam is taken along the side surface of a columnar cooling device having a diameter of 333 mm, cut in the extrusion direction to form a foam sheet, and this is made into a foam sheet having a length of 200 m using a rod-shaped rotary body having a diameter of 266 mm. The portion was wound up into one roll and pulled out from the rod-like rotating body to obtain a foam sheet roll. This operation was repeated to obtain a plurality of roll bodies.

The resins shown in Tables 2 and 3 are as follows. In the table, PS is polystyrene, PPE is polyphenylene ether, and SBS is styrene-butadiene-styrene copolymer.
HH32: Polystyrene (made by Idemitsu Petrochemical Co., Ltd.)
PKN4752: Modified polyphenylene ether (manufactured by GE Plastics, Inc., PS / PPE = 30/70)
Toughprene 125: Styrene-butadiene-styrene copolymer (manufactured by Asahi Kasei)

The thickness (mm), basis weight (g / m ² ), apparent density d (kg / m ³ ), β × d (mol / m) of the foamed sheets obtained in Examples 1 to 5 and Comparative Examples 1 to ^{3 3} ), secondary foaming ratio A, secondary foaming ratio B, surface roughness of the foamed sheet at the time of thermoforming, foam sheet quality stability Q and Q 'at the time of thermoforming are shown in Tables 4 to 7 together.

Various physical properties of the foam sheets shown in Tables 4 to 7 were determined as follows.
(1) β × d
Immediately after manufacturing the roll body, the roll body was moved to a curing chamber having an atmosphere of a temperature of 23 ° C. and a relative humidity of 50%, and after 30 minutes, a foamed sheet sample was cut out from the central part of the outermost peripheral part of the roll body in the sheet width direction. . Place 1g of this sample in a sample bottle with a lid containing toluene, add cyclopentane as an internal standard, close the lid and stir well to dissolve the organic physical foaming agent in the foamed sheet in toluene. The concentration (wt%) of isobutane in the sample was calculated from the peak area of the gas chromatogram obtained by gas chromatography analysis using the following formula (4) and converted to mol / kg. Subsequently, β × d (mol / m ³ ) was calculated.
Similarly, β × d (mol / m ³ ) was calculated for the roll body after 10 days aging and the roll body after 90 days aging in the same curing room as in the case after 30 minutes. In Comparative Example 3, β × d (mol / m ³ ) calculated from the residual concentration of isobutane was shown as β in Table 5. However, in the item (), the residual concentration of normal butane was β and β × The result of calculating d (mol / m ³ ) is shown for reference.

x _i = (F _i × A _i × W _s × 100) ÷ (A _s × W _sm ) (4)
x _i : Weight% concentration of physical foaming agent in sample F _i : Correction coefficient A _s : Peak area of standard material A _i : Peak area of foaming agent W _s : Weight of standard material W _sm : Sample weight

The measuring machine was GC-14B manufactured by Shimadzu Corporation and measured under the following conditions.
(A) Column: Shimadzu Corporation column Silicone DC550 20% on Chromosorb W AW-DMCS 60/80 mesh, 4.1 m × 3.2 mm
(B) Column temperature: 40 ° C
(C) Detector temperature: 180 ° C
(D) Inlet temperature: 180 ° C
(E) Detector: FID
(F) Carrier gas: nitrogen 140 ml / min.
(G) Sample volume: 2 μl

(2) Measurement of secondary foaming ratio The roll body of the foamed sheet was aged for 10 days immediately after production in an atmosphere at a temperature of 23 ° C. and a relative humidity of 50%. After completion of aging, a 260 mm × 260 mm test piece was cut out from the outermost periphery of the roll body, and the thickness was measured. Next, using a thermostat made by Tabai Espec Co., Ltd .: Perfect Oven Original PH-200, the circumference of the above test piece is fixed to a wooden frame with an inner dimension of 200 mm in length and 200 mm in width. 30) for 27 seconds to cause secondary foaming, and after cooling to room temperature (23 ° C.), the thickness (thickness assuming a secondary foaming thickness, here referred to as secondary foaming thickness) was measured. A value obtained by dividing the secondary foaming thickness by the thickness of the test piece before heating was defined as a secondary foaming ratio A.
A test piece of 260 mm × 260 mm was cut out from the center part in the width direction of the foam sheet in the middle part of the roll body (the part 120 m long from the roll winding outer end of the foam sheet having a length of 200 m toward the core side). Under the same conditions as the test piece cut out from the outermost peripheral part of the roll body, the second foaming was performed by heating and secondary foaming, and the secondary foaming thickness was divided by the thickness of the test specimen before heating. The magnification was B.
Further, a 260 mm × 260 mm test piece was cut out from the end of the roll sheet in the width direction of the intermediate portion of the roll body, and the test piece was heated under the same conditions as those of the test piece cut out from the outermost peripheral portion of the roll body to obtain a secondary A value obtained by foaming and dividing the secondary foaming thickness by the thickness of the test piece before heating was designated as the secondary foaming ratio C.

(3) Quality stability Q10 and Q10 ′
Another roll body manufactured under the same conditions as the manufacturing conditions of each example was aged for 10 days immediately after the production in the atmosphere of 23 ° C. and 50% relative humidity immediately after the production, as described above. For this roll body, the absolute value of the difference “A−B” between the secondary foaming ratio A at the outermost peripheral portion of the roll body and the secondary foaming ratio B at the intermediate portion of the roll body is obtained, and foaming is performed by the following formula (5). The quality stability Q after aging in a state where the sheet was rolled up was determined.
Further, the absolute value of the difference “C−B” between the secondary foaming ratio C at the widthwise end of the intermediate part of the roll body and the secondary foaming ratio B at the center part in the widthwise direction of the intermediate part of the roll body is obtained, The quality stability Q ′ after aging in a state in which the foamed sheet was wound into a roll was obtained by the equation (6).
In addition, quality stability Q10 and Q10 'means that the smaller the absolute value, the smaller the difference in secondary foaming ratio and the more stable the quality.

      Quality stability Q10 = (| (A−B) | / A) × 100 (5)

      Quality stability Q10 '= (| (CB) | / C) × 100 (6)

(4) Quality stability Q90 and Q90 ′
Another roll body manufactured under the same conditions as the manufacturing conditions of each example was aged for 90 days immediately after manufacture in an atmosphere of 23 ° C. and 50% relative humidity immediately after manufacture, as described above. For this roll body, the quality stability Q90 and Q90 are the same as the quality stability Q10 and Q10 ′ except that the secondary foaming ratios A, B, and C are respectively changed to secondary foaming ratios D, E, and F described later. 'Sought.

(5) Long life property Another roll body manufactured under the same conditions as the manufacturing conditions of each example was subjected to 90 days from immediately after the manufacture in the atmosphere of 23 ° C. and 50% relative humidity immediately after the manufacture, as described above. Aged. About this roll body, the secondary foaming ratio D of the outermost periphery part, the secondary foaming ratio E of the foam sheet width direction center part of the intermediate part of a roll body, and the foam sheet width direction end of the intermediate part of a roll body are similar to the above. The secondary foaming ratio F of the part was determined, and those in which D, E, and F all satisfy the following secondary foaming ratio were evaluated as x that did not satisfy any one of ◯, D, E, and F. In addition, although the minimum of the secondary foaming ratio requested | required according to the basic weight of a foam sheet differs, the following reference | standard was employ | adopted in this example.
Foam sheet basis weight 350 g / m ² : 1.6 times or more Foam sheet basis weight 290 g / m ² : 1.8 times or more Foam sheet basis weight 250 and 240 g / m ² : 2.0 times or more

(6) Surface roughness of foam sheet during thermoforming The roll body of the foam sheet is placed in an atmosphere at a temperature of 23 ° C. and a relative humidity of 50% immediately after production, and the width direction of the intermediate part of the roll body after aging for 10 days from production. Cut out the test piece from the center, and after secondary foaming under the same conditions as the measurement of the secondary expansion ratio, observe the surface of the test piece,
No surface roughness: ○
Surface roughness: ×
As evaluated.

(7) Rigidity evaluation The roll body of the foam sheet is placed in an atmosphere at a temperature of 23 ° C. and a relative humidity of 50% immediately after manufacture, and 10 cm in length from the center in the width direction of the outermost periphery of the roll body after aging for 10 days from manufacture. , A sample having a width of 2.5 cm was prepared, and in accordance with JIS K7203, the test speed was 10 mm / min. Perform a bending test at
Flexural modulus 25 MPa or more: ○
Flexural modulus less than 25 MPa: ×
As evaluated.

(8) Impact resistance (dirt impact test)
The roll body of the foam sheet is placed in an atmosphere at a temperature of 23 ° C. and a relative humidity of 50% immediately after the production, and after curing for 10 days from the production, a test piece is cut out from the center in the width direction of the middle part of the roll body. Dart impact test is performed according to the law, 50% fracture energy is obtained,
50% destruction energy 250mJ or more: ○
50% fracture energy 100 mJ or more and less than 250 mJ: △
50% destruction energy less than 100 mJ: ×
As evaluated.

The results of Examples and Comparative Examples show the following.
As for the results of Examples 1 to 5, as a result of producing a low foamed polystyrene resin foam sheet with α × d within the range of the present invention, β × d could be within the range of the present invention. In addition to isobutane as a foaming agent at the time of manufacture, as a result of using a small amount of water or carbon dioxide, both in the early stage after 10 days of aging and after a considerable period of time after 90 days of aging, both are stable in quality. Can be found to be expensive. Moreover, it turns out that high secondary foaming performance is maintained over a long period of time. In addition, the foamed sheets of Examples 2 to 4 in which a polyphenylene ether resin was mixed with polystyrene resin improved the brittleness, which is a defect of the low foamed polystyrene resin foam sheet, compared with the foamed sheet of Example 1 (impact resistance) It can be seen that it has been improved). Moreover, it turns out that the brittleness improvement effect in the foamed sheets of Examples 2 to 4 also has rigidity that cannot be achieved in Example 5 in which a polystyrene resin is mixed with a styrene-based thermoplastic elastomer.
On the other hand, Comparative Example 1 is contrasted with Example 1 and is an example in which the addition amount of isobutane is reduced and the lack of foaming power is compensated by increasing the addition amount of water. As a result, α × d is less than the range of the present invention. Since the foamed sheet thus obtained has β × d below the lower limit of the range of the present invention, there is no problem in quality stability, but the secondary foaming ratio cannot be increased, resulting in long life. It was also inferior.
Comparative Example 2 was compared with Example 2 and was produced by increasing the amount of isobutane added and lowering the foaming temperature by that amount. As a result, α × d exceeded the scope of the present invention. It was a condition. The foamed sheet thus obtained has no problem in terms of quality stability and long life, but β × d exceeds the upper limit of the range of the present invention even after 10 days (the content of isobutane is too large). For this reason, surface roughness was generated by heating during thermoforming.
Comparative Example 3 is contrasted with Example 3, and shows an example in which the amount of isobutane added is reduced without using carbon dioxide, and the lack of foaming power is compensated with normal butane. As a result, although β × d based on the residual concentration of isobutane was within the scope of the present invention, it was affected by normal butane, and after 10 days of aging, air was present in the middle portion of the roll sheet in the width direction of the foam sheet. The penetration was insufficient, the secondary foaming ratio at that portion was extremely small, and quality stability was lacking. In addition, even after 90 days of aging, the normal butane is affected by the normal butane, and the normal butane is greatly diffused at the outermost peripheral portion of the roll body, the secondary foaming ratio at that portion is greatly reduced, and the long life property is insufficient. It became a thing.

Claims (4)

A polystyrene resin and a physical foaming agent are heated and kneaded in an extruder to obtain a foamable molten resin, and the foamable molten resin is extruded and foamed to obtain a thickness of 0.5 to 3.0 mm and an apparent density of 150 kg. / ^{m 3} greater than the 420 kg / ^{m 3} process to obtain the following foam sheet, isobutane 50-95 mol% and carbon dioxide and / or water 5-50 mole percent of a mixed physical foaming agent (however, the blowing agent The total amount of the foaming agent contained in the mixed physical foaming agent is 100 mol%.) With the physical foaming agent having the main component, the addition amount of isobutane per 1 kg of the polystyrene resin satisfies the relationship of the following formula (1): A method for producing a polystyrene-based resin foam sheet for thermoforming, characterized by being added in a satisfactory manner.
30 (mol / m ³ ) ≦ α × d ≦ 65 (mol / m ³ ) (1)
(Where α is the amount of isobutane added per 1 kg of polystyrene resin (mol / kg), and d is the apparent density (kg / m ³ ) of the foam sheet.) In a foam sheet having a thickness of 0.5 to 3.0 mm, an apparent density of more than 150 kg / m ³ and 420 kg / m ³ or less, the foam sheet is placed in an atmosphere at a temperature of 23 ° C. and a relative humidity of 50% immediately after the foam sheet is manufactured. When moving and ripening, the ratio of isobutane to the total organic physical foaming agent remaining in the foamed sheet is 90 to 100 mol% after 30 minutes from the start of aging until aging for 90 days, and the following ( 2) A polystyrene-based resin foam sheet for thermoforming, wherein an amount of isobutane satisfying the relationship of the formula remains.
30 (mol / m ³ ) ≦ β × d ≦ 60 (mol / m ³ ) (2)
(Where β is the amount of residual isobutane (mol / kg) in the foamed sheet relative to 1 kg of polystyrene-based resin, and d is the apparent density (kg / m ³ ) of the foamed sheet.)   The polystyrene resin foam sheet for thermoforming according to claim 2, wherein the polystyrene resin comprises 90 to 30% by weight of polystyrene and 10 to 70% by weight of polyphenylene ether.   The polystyrene-based resin foam sheet for thermoforming according to claim 2 or 3, wherein a thermoplastic resin sheet or film is laminated on one side or both sides.