JP6077898B2 - Polystyrene resin foam sheet for thermoforming - Google Patents

Description

  The present invention relates to a novel thermoplastic resin foam sheet for thermoforming having a plurality of streaks on the surface and a method for producing the same.

  Thin polystyrene-based resin foam sheets with a thickness of about 0.5 to 10 mm are excellent in light weight, heat insulation and thermoformability, so that they can be used in tray containers, instant noodle containers, lunch boxes, natto containers, etc. It is widely used as an original sheet (polystyrene resin foam sheet for thermoforming) for processing food distribution packaging materials and the like.

  Among them, polystyrene resin foam sheets for thermoforming that have a patterned appearance on the surface are superior in appearance and have a high-class feeling, so that consumer needs have increased and are currently being produced in large quantities. .

  Conventionally, as such polystyrene-based resin foam sheets, for example, the following (1) to (3) are known.

(1) A pattern printed directly on the surface of a polystyrene resin foam sheet (Patent Document 1).
(2) A film in which a pattern is printed on the surface of a polystyrene-based resin foam sheet, which is laminated with an adhesive or the like (Patent Document 2).
(3) A layered or strip-shaped polystyrene resin foam layer laminated on the surface of a polystyrene resin foam sheet by a coextrusion method (Patent Document 3).

JP 2007-7966 A Japanese Patent Laid-Open No. 5-38752 JP 2003-94896 A

However, if the pattern is directly printed on the surface of the foamed sheet of (1), there is a risk that the ink and the package will be in direct contact with each other, so the application is limited or a film is laminated on the printing surface. There was a difficulty that it was necessary.
In addition, the production required two processes, a process for producing a foam sheet as a raw fabric and a process for printing a pattern thereon.

  In the case where the film on which the pattern is printed on the surface of the foamed sheet of (2) is laminated with an adhesive, the ink used for applying the pattern is on the inner surface side of the film. Although there is no fear of touching, the manufacture of the foam sheet, which is the original fabric, and the process of manufacturing a film, the process of printing a pattern on this, and the step of bonding the printed film to the original fabric sheet, etc. It required many processes.

  (3) Coextruded streaky or strip-like foam layer on the outer peripheral surface of the foam core layer requires high thermoformability such as tray containers, instant noodle containers, lunch boxes and food containers such as natto containers. This was not a consideration of thermoformability as an original sheet for food distribution packaging materials.

Thus, the conventional polystyrene-based resin foam sheet for thermoforming having a pattern has a great difficulty, has an excellent appearance, and satisfies various physical properties such as lightness, surface smoothness, and thermoformability, and is practical. There was a strong demand for the development of a new polystyrene-based resin foam sheet for thermoforming. However, at present, no satisfactory proposal has been made.
The present invention has been made to solve such problems, and is a practical new thermoforming polystyrene that has excellent appearance and satisfies various physical properties such as lightness, surface smoothness, and thermoformability. An object of the present invention is to provide a resin foam sheet and an efficient production method thereof.

  As a result of diligent research to solve the above-mentioned problems, the inventors of the present invention have a light weight, excellent thermoformability, and can be easily and inexpensively manufactured. The inventors have found a polystyrene-based resin foam sheet and have completed the present invention.

  That is, according to this invention, the novel polystyrene-type resin foam sheet for thermoforming to which the streak pattern as described in the following <1>-<3> was provided is provided.

<1> An apparent density of 0.04 to 0.35 g / cm ³ and a thickness of 0.5 to 0.5, in which a plurality of polystyrene resin layers containing a colorant are laminated on at least one surface of a polystyrene resin foam layer by coextrusion. A 10 mm thermoplastic resin foam sheet for thermoforming, wherein the polystyrene resin layer has a streak shape along the extrusion direction and is formed adjacent to each other in the width direction. The cell wall thickness of the outermost surface portion on the layer laminate surface side is 50 μm or less, and the maximum height of the contour curve of the surface on the resin layer laminate surface side of the foam sheet is 60 μm or less. Resin foam sheet.
<2> The polystyrene-based resin foam for thermoforming as described in <1>, wherein a surface layer density from the surface to a thickness of 200 μm is 0.15 g / cm ³ or more on the resin layer lamination surface side of the foamed sheet. Sheet.
<3> The weight of the laminated resin per one resin layer is 0.01 to 0.6 g / m per 1 m in the extrusion direction, and the average center distance between adjacent resin layers is 2 to 30 mm. <1> or <2> The polystyrene-based resin laminated foam sheet for thermoforming according to <2>.

  The polystyrene-based resin foam sheet for thermoforming of the present invention is excellent in appearance, light weight, and thermoformability, and unlike conventional products, the manufacturing cost can be greatly reduced, and it can be produced extremely advantageously industrially. It is. Therefore, the demand is widely expected as a raw sheet for thermoforming of food distribution packaging materials such as tray containers, instant noodle containers, bento containers, natto containers and rice cakes.

It is explanatory drawing of the typical polystyrene-type resin foam sheet of this invention. It is explanatory drawing of the manufacturing method of the typical polystyrene-type resin foam sheet of this invention. It is explanatory drawing of the typical cyclic | annular die | dye used by this invention.

(Polystyrene resin laminated foam sheet for thermoforming)
FIG. 1 is a schematic cross-sectional view in the thickness direction of a polystyrene-based resin laminated foam sheet (hereinafter also simply referred to as a foam sheet) 1 for thermoforming according to the present invention.

  The foamed sheet 1 has a streak shape formed by coextrusion of a polystyrene resin resin layer 3 (hereinafter also simply referred to as a resin layer) containing a colorant on at least one surface of a polystyrene resin foam layer 2 (hereinafter also simply referred to as a foam layer). A plurality of layers are stacked.

  Here, for example, as shown in FIG. 1, the streak means a linear or belt-like pattern formed in the longitudinal direction that is the extrusion direction.

  In FIG. 1, the foamed sheet has been described with an example in which the resin layer is laminated on one side of the foamed layer, but the resin layer may be laminated on both the front and back sides of the foamed layer.

(Apparent density of the foam sheet of the present invention)
The apparent density of the foamed sheet of the present invention is 0.04 to 0.35 g / cm ³ . If the apparent density is too low, it may be difficult to maintain strength as a thermoforming foam sheet. From the above viewpoint, the lower limit of該見seat density is more preferably 0.05 g / cm ^3, most preferably from 0.07 g / cm ^3.
On the other hand, if the apparent density is too high, it may be difficult to maintain the lightness of the molded product. From the above viewpoint, the upper limit of the apparent density is more preferably 0.21 g / cm ³ , and still more preferably 0.15 g / cm ³ .

(Thickness of the foam sheet of the present invention)
The thickness of the foam sheet of the present invention is 0.5 to 10 mm. When the thickness of the foam sheet is too thin, the foam sheet has low rigidity and may not be used as a container. On the other hand, when the thickness of the foamed sheet is too thick, there is a risk that thermoforming such as a decrease in mold reproducibility becomes difficult.

  From the above viewpoint, the foamed sheet of the present invention has a more preferable thickness of 0.7 mm to 5 mm, and a further preferable thickness of 1 mm to 3 mm.

(Cell wall thickness at the outermost surface of the foam sheet)
The cell wall thickness of the outermost surface portion on the resin layer lamination surface side of the foamed sheet is 50 μm or less. When the cell wall thickness of the outermost surface portion exceeds 50 μm, the surface unevenness becomes severe, which may affect the moldability of the foamed sheet. From the above viewpoint, the cell wall thickness of the outermost surface portion is preferably 45 μm or less, and more preferably 40 μm or less.

  The cell wall thickness at the outermost surface portion of the resin layer laminated surface in the foamed sheet means the thickness from the foamed sheet surface to the inner surface of the first cell wall in the thickness direction of the foamed sheet. In addition, by the said measuring method, it measures without distinguishing a foamed layer part and a resin layer part.

  For the maximum value of the measured values obtained, the arithmetic average value at five locations is defined as the cell wall thickness of the outermost surface portion. In the foam sheet of the present invention, the fact that the cell wall thickness of the outermost surface portion is 50 μm or less has the feature that the resin layer is formed very thin. Moreover, the cell wall thickness of the outermost surface portion requires that at least a portion where thermoforming is performed on the foamed sheet satisfies the above range.

(Maximum height of the contour curve of the foam sheet surface)
The maximum height of the contour curve on the surface of the foam sheet on the resin layer laminated surface side of the foam sheet of the present invention is 60 μm or less. When the maximum height of the contour curve on the surface of the foamed sheet exceeds 60 μm, the unevenness of the surface of the foamed sheet becomes severe, and the moldability of the foamed sheet and the appearance of the foamed sheet may be deteriorated. From the above viewpoint, the maximum height is preferably 50 μm or less, and more preferably 45 μm or less.

  The maximum height of the contour curve on the surface of the foam sheet is an uneven contour curve element in the width direction of the foam sheet formed by the foam layer and the resin layer on the surface of the foam sheet in accordance with JIS B0601 (2001). Specified as the height of. Specifically, it can be measured using a surf coder SE1700α manufactured by Kosaka Laboratory Ltd. In addition, the maximum height of the contour curve on the surface of the foam sheet requires that at least a portion where thermoforming is performed on the foam sheet satisfies the above range.

  In the present invention, a streaky pattern is formed by a coextrusion method, and the resin layer is appropriately stretched at the time of extrusion foaming, so that the rigidity is improved and the foam has excellent thermoformability while being excellent in appearance. It becomes a sheet.

(Total basis weight of foam sheet)
The total basis weight of the foam sheet is preferably 70~600g / ^{m 2.} If it is in the said range, it will become a foam sheet which has the rigidity suitable for thermoforming and is excellent in lightweight property. It said total basis weight is more preferably ^{100~500g / m 2, 120~400g / m} 2 is more preferable.

As a measuring method of the total basis weight of the foamed sheet, a test piece having a width of 250 mm was cut out over the entire width of the foamed sheet, and the weight (g) of the test piece was the area of the test piece (sheet width (mm) × 250 mm). Dividing and converting to the weight (g) of the laminated foam sheet per 1 m ² , this was defined as the basis weight “t” (g / m ² ) of the laminated foam sheet.

The surface layer density of the surface portion from the surface to 200 μm on the resin layer lamination surface side of the foamed sheet is preferably 0.15 g / cm ³ or more. If it is in the said range, it will become a heat-molding foam sheet with favorable moldability. From the above viewpoint, the surface layer density is more preferably 0.16 g / cm ³ or more, and further preferably 0.17 g / cm ³ or more.

  The surface layer density is measured as follows. A 200 μm portion is sliced from the surface of the foamed sheet, cut into test pieces having a width of 5 mm and a length of 20 mm, and the weight and thickness of the test piece are measured with a gauge. Divide the weight of the test piece by the volume of the test piece and convert the unit to obtain the surface layer density. The said measurement is performed about 10 places of equal intervals in the width direction of the said foam sheet, and it is set as the surface layer density of those arithmetic mean values.

(Resin layer)
On at least one surface of the polystyrene resin foam layer, a plurality of polystyrene resin layers containing a colorant are laminated in a line shape in the extrusion direction by coextrusion. In addition, the resin layer formed by being laminated on the foamed layer in the foamed sheet does not necessarily have to be convexly formed from the surface of the foamed layer, and the resin layer portion is embedded in the foamed layer as shown in FIG. It is preferable to form in the shape.

(Total amount of resin layers)
The total amount of the resin layer is appropriately set so that a streaky pattern of the resin layer is exposed in the extrusion direction on the surface of the foam layer, but is preferably in the range of ^{2 to} 50 g / m ² . In the foam sheet of the present invention, it is easy to form a non-foamed resin layer by forming a thin resin layer in the above range. In view of the above, the total laminate weight of the resin layer is more preferably from 5 to 40 g / ^{m 2,} further preferably 10 to 30 g / ^{m 2.} In addition, the total lamination amount of a resin layer is the total lamination amount of the resin layer formed in the stripe form which exists in the unit area of a foamed sheet.

The total lamination amount of the resin layers is obtained by the following equation (1), where L (kg / hr) is the discharge amount of the resin layer extruder, the sheet take-up speed M (m / min), and the total sheet width N (m). be able to.
Total amount of resin layers (g / m ² ) = L × 10 ³ / (M × N × 60) (1)

(Average distance between resin centers)
It is preferable that the average center-to-center distance between adjacent resin layers laminated in a streak is 2 to 30 mm so that a streak pattern is exposed in the extrusion direction of the foam sheet. If it is in the said range, it will become a foam sheet excellent in the external appearance.

  Furthermore, the coefficient of variation Cv of the distance between the centers of the adjacent resin layers is preferably 25 or less, more preferably 20 or less, and further preferably 15 or less.

In this specification, the coefficient of variation Cv of the distance between the centers of adjacent resin layers refers to the percentage of the value obtained by dividing the standard deviation (mm) of the distance between the centers by the average center distance molded product (mm). It is an index representing the degree of variation from the value. Note that the standard deviation V of the center-to-center distance is obtained by the following equation (2).
V = {Σ (Ti−Tav) ² / (n−1)} ^1/2 (2)
In the above formula (1), Ti represents the measured value of the distance between the centers, Tav represents the average distance between the centers, n represents the number of measurements, and Σ was calculated for each measured value (Ti-Tav) ² Indicates that all are added.
The variation coefficient Cv is obtained by the following equation (3).
Cv (%) = (V / Tav) × 100 (3)

  Further, from the viewpoint of becoming a uniform laminated foam sheet without thickness unevenness, in the distance between the centers of the adjacent resin layers, the relationship between the maximum value and the minimum value is preferably maximum value / minimum value ≦ 7, The maximum value / minimum value ≦ 6 is more preferable, and the maximum value / minimum value ≦ 5 is further preferable.

(About colorants)
The resin layer contains a colorant. As the colorant, inorganic or organic pigments or dyes can be used. For example, examples of organic pigments include monoazo, condensed azo such as chromoftal red, anthraquinone, isoindolinone, heterocyclic, perinone, quinacridone, perylene, thioindigo, dioxazine, Examples include phthalocyanine-based, nitroso-based, phthalocyanine pigments, and organic fluorescent pigments. Examples of inorganic pigments include titanium oxide, carbon black, titanium yellow, iron oxide, ultramarine blue, cobalt blue, calcined pigment, metallic pigment, mica, pearl pigment, zinc white, precipitated silica, cadmium red and the like. Examples of organic dyes include anthraquinone series, heterocyclic series, perinone series, basic dyes, acid dyes, and mordant dyes. Among these, the use of an inorganic pigment is preferable because it can be produced at low cost. Moreover, a coloring agent can also be used in mixture of 2 or more types.
In particular, when used for food containers, it is preferable to select and use a polyolefin hygiene association registered product from the above.

  When the colorant is iron oxide or a tea-based colorant containing iron oxide, for example, a colorant composed of a mixture of iron oxide, carbon black, and titanium oxide, the resin layer has a tea-based color. Presenting a wood-tone or grid-like pattern, so that a laminated foamed sheet capable of forming a more luxurious container can be obtained.

(Advantages of polystyrene resin foam sheet for thermoforming according to the present invention)
Unlike conventional products, the polystyrene-based resin foam sheet for thermoforming according to the present invention is a foam sheet in which a streak pattern is formed, and has excellent appearance, light weight, thermoformability, and surface smoothness. It is.

  Therefore, as a raw material sheet for thermoforming such as food distribution packaging materials such as tray containers, instant noodle containers, bento containers, natto containers and rice cakes with excellent safety, streaks, such as wood grain, high quality, The demand is widely expected.

  Further, since the production is extremely simple, unlike the conventional products, the production cost can be greatly reduced, and there are many advantages such that the production can be industrially extremely advantageous.

  The resin layer is formed in order to give a streak pattern, but also contributes to improving the strength of the foam sheet. Therefore, it is preferable that the resin layer is formed as a non-foamed layer from the viewpoint of improving the physical properties of the molding sheet and the molded product obtained by molding it. Note that the non-foamed layer may locally be a part of which bubbles are formed.

Next, the preferable manufacturing method of the foam sheet which concerns on the said invention is demonstrated.
The method for producing a foamed sheet of the present invention includes a polystyrene resin (B), a colorant, a volatile plasticizer, and a foamed layer forming resin melt obtained by kneading a polystyrene resin (A) and a physical foaming agent. It is preferable that a plurality of resin melts for forming a resin layer obtained by kneading are co-extruded after being stacked in a line shape.
In this case, the weight of the laminated resin per 1 m of each resin layer is 0.01 to 0.6 g / m, and a plurality of polystyrene resin layers are formed in stripes on at least one side of the polystyrene resin foam layer. It is preferable to do.

An example of the manufacturing method of the foam sheet of this invention is shown in FIG.
As shown in FIG. 2, the method for producing a foamed sheet of the present invention is obtained by coloring a polystyrene resin (B) and a colored resin melt for foaming layer formation by kneading a polystyrene resin (A) and a physical foaming agent. It is preferable to obtain a desired foamed sheet by laminating a plurality of resin melts for forming a resin layer obtained by kneading an agent and a volatile plasticizer and coextruding them.

(Resin melt for resin layer formation)
First, the polystyrene-based resin (B) 4 and the colorant 5 constituting the resin layer 3 and other additives added as necessary are supplied to the first extruder, heated and melted to obtain the volatile plasticizer 6. Add and melt knead to obtain a polystyrene resin melt for forming a resin layer (resin melt 7 for forming a resin layer).
As the polystyrene resin melt for forming the resin layer, a kneaded material such as a polystyrene resin, a colorant, an additive added as necessary, a volatile plasticizer, and the like is used.

(About the polystyrene resin (B) constituting the resin layer)
Examples of the polystyrene resin (B) include polystyrene, impact polystyrene, styrene-acrylonitrile copolymer, styrene-butadiene-acrylonitrile copolymer, styrene-acrylic acid copolymer, and styrene-methacrylic acid copolymer. Styrene-methyl methacrylate copolymer, styrene-ethyl methacrylate copolymer, styrene-methyl acrylate copolymer, styrene-ethyl acrylate copolymer, styrene-maleic anhydride copolymer, polystyrene-polyphenylene ether Examples thereof include a copolymer and a mixture of polystyrene and polyphenylene ether.

  For these resins, depending on the desired purpose, polypropylene resins such as propylene homopolymer and ethylene-propylene copolymer, polyethylene resins such as high density polyethylene and low density polyethylene, styrene-conjugated diene block copolymer A polymer containing a polymer such as a thermoplastic elastomer such as a coalescence or a hydrogenated product thereof, or a rubber such as ethylene-propylene rubber or butadiene rubber in an amount of 40% by weight or less can be used.

  As the polystyrene resin (B) constituting the resin layer, for example, the melt viscosity η1 is set to 600 to 1400 Pa · s so that a uniform resin layer having a narrow width is laminated on at least one surface of the foam layer. It is preferable to use one having a viscosity of 700 to 1300 Pa · s, more preferably 800 to 1200 Pa · s.

(Volatile plasticizer)
In the method for producing a foamed sheet of the present invention, when the resin melt for forming a resin layer and the resin melt for forming a foam layer are co-extruded, the melt elongation of the resin melt for forming the resin layer at an appropriate foaming temperature. In order to make the elongation of the resin melt for forming the resin layer correspond to the elongation of the resin melt for forming the polystyrene-based resin foam layer, a plasticizer may be added to the resin melt for forming the resin layer. preferable.

  As said plasticizer, it is preferable to use the volatile plasticizer which dissipates from a foam sheet after foam sheet manufacture. In the state where the volatile plasticizer is present in the resin melt for forming the resin layer, it is possible to reduce the melt viscosity of the polystyrene resin and form a resin melt suitable for foaming by coextrusion. After extrusion foaming, it is volatilized from the resin layer and can be easily removed from the resin layer. Therefore, if a volatile plasticizer is used, the plasticizer blended in the resin layer does not come into contact with food or the like, which is preferable from the viewpoint of food hygiene.

In addition, a volatile plasticizer is preferably used because the plasticizer remains after extrusion and there is no possibility of lowering the rigidity of the resin layer.
In addition, if it is the addition amount of the grade which does not produce the physical property fall of the polystyrene-type resin which comprises a resin layer, a normal plasticizer can also be used, and the addition amount is preferably less than 3%, and less than 2% It is more preferable that

  Examples of the volatile plasticizer include aliphatic hydrocarbons having 2 to 7 carbon atoms, halogenated aliphatic hydrocarbons having 1 to 3 carbon atoms, aliphatic alcohols having 1 to 4 carbon atoms, or 2 to 8 carbon atoms. Those composed of one or more selected from the following aliphatic ethers are preferably used.

  Examples of the aliphatic hydrocarbon having 2 to 7 carbon atoms exemplified in the volatile plasticizer include ethane, propane, normal butane, isobutane, normal pentane, isopentane, isohexane, cyclohexane and heptane.

  Examples of the halogenated aliphatic hydrocarbon having 1 to 3 carbon atoms include methyl chloride, ethyl chloride, 1,1,1,2-tetrafluoroethane, and 1,1-difluoroethane.

  Examples of the aliphatic alcohol having 1 to 4 carbon atoms include methanol, ethanol, propanol, butanol, isopropyl alcohol, isobutyl alcohol, sec-butyl alcohol, and tert-butyl alcohol.

  Examples of the aliphatic ether having 2 to 8 carbon atoms include methyl ether, ethyl ether, propyl ether, isopropyl ether, methyl ethyl ether, methyl propyl ether, methyl isopropyl ether, methyl butyl ether, methyl isobutyl ether, and methyl amyl ether. Methyl isoamyl ether, ethyl propyl ether, ethyl isopropyl ether, ethyl butyl ether, ethyl isobutyl ether, ethyl amyl ether, ethyl isoamyl ether, vinyl ether, allyl ether, methyl vinyl ether, methyl allyl ether, ethyl vinyl ether, ethyl allyl ether.

  The boiling point of the volatile plasticizer is preferably 120 ° C. or lower, more preferably 80 ° C. or lower because it easily evaporates from the resin layer. When the boiling point of the volatile plasticizer is within this range, the volatile plasticizer is volatilized naturally from the resin layer by the heat after co-extrusion and the subsequent gas permeation at room temperature, and is naturally removed. The lower limit of the boiling point is approximately -50 ° C.

  The volatile plasticizer is preferably added in an amount of 0.15 mol / kg to 1.4 mol / kg with respect to the total amount of the styrene resin 4 and the colorant 5, and 0.2 mol / kg to 1.2 mol / kg. It is more preferable to add. If it is in the said range, the resin melt for resin layer formation favorable will be obtained.

  The resin melt for forming a resin layer is preferably coextruded so as to form a non-foamed resin layer. As a method of forming a non-foamed resin layer, the addition amount of the volatile plasticizer is set in the above range, and a method of not adding a cell regulator to the resin melt for resin layer formation, the resin layer is rapidly cooled after coextrusion. It is preferable to suppress foaming by a method or the like.

(About colorants)
The above-mentioned colorant is blended in the resin layer forming resin melt. The colorant can be added as a master batch.

  Moreover, in this invention, although it is essential to contain a coloring agent in a resin layer, a coloring agent can also be contained in a foaming layer. In terms of appearance, the resin layer is preferably darker in the resin layer and the foamed layer. Further, in the lightness (L value) of the foamed sheet measured with a spectroscopic color difference meter, the difference between the maximum value and the minimum value of the lightness is preferably 2 or more, more preferably 5 or more, and 10 or more. More preferably.

(Other additives)
Various additives may be added to the resin layer forming resin melt.
Examples of the various additives include antioxidants, heat stabilizers, weathering agents, ultraviolet absorbers, flame retardants, fillers, antibacterial agents, and the like.

(Polystyrene resin melt for forming a foam layer (resin melt for forming a foam layer))
Separately, the polystyrene-based resin (A) 8 constituting the foam layer and other additives such as a bubble adjusting agent added as necessary are supplied to the second extruder, heated and melted and kneaded, and the physical foaming agent 9 And then kneaded to obtain a polystyrene-based resin melt for forming a foam layer (resin melt for forming a foam layer) 10.

(Polystyrene resin (A))
There is no restriction | limiting in particular as polystyrene-type resin (A) which comprises the foaming layer 3, The thing similar to the above-mentioned polystyrene-type resin (B) which comprises the resin layer can be used.
The melt viscosity η2 of the polystyrene resin 8 is preferably 800 to 2000 Pa · s, more preferably 1000 to 1700 Pa · s, and further preferably 1200 to 1500 Pa · s. If it is in the said range, a favorable foamed layer can be formed.

(Physical foaming agent)
Examples of the physical foaming agent include aliphatic hydrocarbons having 2 to 7 carbon atoms, such as ethane, propane, normal butane, isobutane, normal pentane, isopentane, isohexane, cyclohexane, heptane, methyl chloride, ethyl chloride, 1,1. 1,2-tetrafluoroethane, 1,1-difluoroethane, etc., halogenated aliphatic hydrocarbons having 1 to 3 carbon atoms, methanol, ethanol, propanol, butanol, isopropyl alcohol, isobutyl alcohol, sec-butyl alcohol, tert -C1-C4 aliphatic alcohols such as butyl alcohol, or methyl ether, ethyl ether, propyl ether, isopropyl ether, methyl ethyl ether, methyl propyl ether, methyl isopropyl ether, Butyl butyl ether, methyl isobutyl ether, methyl amyl ether, methyl isoamyl ether, ethyl propyl ether, ethyl isopropyl ether, ethyl butyl ether, ethyl isobutyl ether, ethyl amyl ether, ethyl isoamyl ether, vinyl ether, allyl ether, methyl vinyl ether, methyl allyl ether, Examples thereof include organic physical foaming agents such as aliphatic ethers having 2 to 8 carbon atoms such as ethyl vinyl ether and ethyl allyl ether, and inorganic physical foaming agents such as nitrogen and carbon dioxide.

  The above-mentioned physical foaming agents can be used in combination of two or more. Among the above, the physical foaming agent is preferably an organic physical foaming agent from the viewpoint of compatibility with the polystyrene resin (A) and foaming efficiency, and among them, normal butane, isobutane, or a mixture thereof is the main component. Is preferred.

  The addition amount of the physical foaming agent is appropriately adjusted according to the apparent density of the foamed sheet and the like, but is generally 0.15 to the polystyrene resin (A) constituting the foamed layer. It is preferably 1.8 mol / kg, more preferably 0.3 to 1.5 mol / kg, still more preferably 0.4 to 1.2 mol / kg.

  In addition, as a foaming agent, foaming agents other than a physical foaming agent can also be used together.

(Bubble conditioner)
As the bubble adjusting agent, either an organic type or an inorganic type can be used.
Examples of the inorganic foam regulator include boric acid metal salts such as zinc borate, magnesium borate, and borax, sodium chloride, aluminum hydroxide, talc, zeolite, silica, calcium carbonate, sodium bicarbonate, and the like.

  Examples of the organic air conditioner include sodium phosphate-2,2-methylenebis (4,6-tert-butylphenyl), sodium benzoate, calcium benzoate, aluminum benzoate, and sodium stearate. A combination of citric acid and sodium bicarbonate, an alkali salt of citric acid and sodium bicarbonate, or the like can also be used as the bubble regulator. These bubble regulators can be used in combination of two or more.

  In addition, the amount of the cell regulator added to the foamed layer forming resin melt 10 is 0.05 to 10 parts by weight, preferably 0.2 parts by weight, per 100 parts by weight of the polystyrene resin constituting the foamed layer. The amount is 5 parts by weight or less.

(Other additives)
Various additives may be added to the foamed layer forming resin melt 10.
Examples of the various additives include antioxidants, heat stabilizers, weathering agents, ultraviolet absorbers, flame retardants, inorganic fillers, antibacterial agents, and colorants. In addition, when mix | blending a coloring agent, it is preferable from a viewpoint of improving the texture of a laminated foam sheet to adjust the kind and compounding quantity of a coloring agent so that it may become lighter than a resin layer.

(Coextrusion of resin melt 10 for forming foam layer and resin melt 7 for forming resin layer)
Next, the foamed layer forming resin melt 10 and the resin layer forming resin melt 7 are respectively adjusted to appropriate temperatures as described later, and then introduced into the annular die 13. The resin melt 7 for forming the resin layer is laminated on the outer peripheral surface of the resin melt 10 for forming the foam layer in the die so as to form a plurality of streaks in the extrusion direction, and then coextrusion and the foam layer are performed. By foaming the forming resin, a cylindrical laminated foam in which the resin layer 3 is formed in a streak shape on the surface of the foam layer 2 is manufactured.
In the coextrusion method, it is preferable that the temperature of the foam layer forming resin melt and the resin layer forming resin melt be as close as possible to obtain a foam sheet having a higher closed cell ratio.

  When a plurality of resin melts for forming a resin layer are linearly laminated in the extrusion direction and co-extruded with the resin melt for forming a foam layer, the weight of the laminated resin per 1 m in the extrusion direction for each resin layer (Hereinafter, sometimes referred to as resin amount) and the average center distance of the resin layer (hereinafter also referred to as pitch) are noted.

That is, when a plurality of resin melts for forming a resin layer are streaked in the extrusion direction and co-extruded with the resin melt for forming a foam layer, the weight of the laminate resin per 1 m in the extrusion direction per each resin layer Is preferably 0.01 to 0.6 g / m, and a plurality of polystyrene resin layers are preferably formed in a streaky manner on at least one surface of the polystyrene resin foam layer.
When the amount of the laminated resin is within the above range, it becomes easy to form a streak pattern, and a foam sheet with small thickness unevenness can be obtained without the adjacent resin layers overlapping.
From the above viewpoint, the resin amount is preferably 0.02 to 0.5 g / m, more preferably 0.03 to 0.4 g / m, and 0.04 to 0.3 g / m. More preferably.

The weight of the laminated resin per 1 m in the extrusion direction per each resin layer is X (Kg / hr) for the discharge amount of the resin layer, Y (m / min) for the take-up speed of the foam sheet, and per foam sheet full width. The number Z of resin layers can be obtained by the following equation (4).
(X × 10 ³ ) / (Y × Z × 60) (4)

Moreover, in a foam sheet, it is preferable that the average center distance of adjacent resin layers is 2 to 30 mm, and a plurality of polystyrene resin layers are formed in a streak shape on at least one surface of the polystyrene resin foam layer.
If the average center-to-center distance between adjacent resin layers is within the above range, adjacent resin layer forming resin melts may overlap to form a streak pattern, or the streak pattern may be too wide. A good foam sheet can be obtained without deteriorating the appearance. From the above viewpoint, the average center distance is preferably 2 to 25 mm, more preferably 3 to 15 mm.

  The average center-to-center distance is defined as the distance from the central part of the resin layer to the central part of the adjacent resin layer (the length of the perpendicular to the extrusion direction) between adjacent resin layers in the entire width of the foam sheet. The

  In the annular die, the resin melt for forming the resin layer passes through the flow passages of a plurality of holes for forming the resin layer arranged on the circumference, and the resin melt for forming the resin layer is slit for forming the resin layer. It is preferable to use one having a structure that can be laminated in a streak pattern on the outer peripheral surface of the resin melt for forming a foam layer.

  The resin layer forming slit processed in the annular die is not particularly limited as long as the streaky pattern of the resin layer is formed on the outer peripheral surface of the foam layer. The width is preferably 0.4 to 6.0 mm, more preferably 0.5 to 5.0 mm, and still more preferably 0.6 to 4.0 mm. If it is said slit width, the resin layer of the width of 0.5-20 mm in general, Preferably 0.8-15 mm will become easy to be formed in a foam sheet.

  In addition, in the laminated portion of the resin melt for forming a resin layer and the resin melt for forming a foam layer, the average center length between adjacent slits is preferably 1 to 12 mm, and preferably 2 to 11 mm. Adjacent resin layers do not overlap each other, and this is more preferable from the viewpoint of forming a good resin layer.

  In the production method of the present invention, since the resin melt for forming the foam layer is foamed during coextrusion, it is expanded in the width direction, so that the average center of the streaky resin layer is larger than the slit width in the annular die. The distance between them is increased. The above widening is defined as the blow-up ratio. In addition, by controlling the blow-up ratio of the foam sheet (the value obtained by dividing the diameter of the mandrel by the diameter of the die outlet) and the take-up speed, the foam sheet is stretched, so that the shrinkage ratio suitable for a laminated foam sheet for thermoforming ( (Length change before and after heating).

  In addition, regarding the laminated foam sheet of the present invention, in consideration of the fact that both end portions are not thermoformed, a plurality of polystyrene resin layers are formed in a streak shape at 80% or more of the entire width of the laminated foam sheet. It only has to be done.

  In the production method of the present invention, when a plurality of resin melts for resin layer formation are laminated in the extrusion direction and coextruded with the resin melt for foam layer formation, the extrusion direction for each resin layer The weight of the laminated resin per meter is 0.01 to 0.6 g / m, and the average center distance between adjacent resin layers is 2 to 30 mm, and the polystyrene resin layer is streaked on at least one surface of the polystyrene resin foam layer. It is preferable to form a plurality of them. In order to obtain a foamed sheet in the above range, for example, the foamed sheet is adjusted by stretching the foamed sheet by controlling the blow-up ratio of the foamed sheet (the value obtained by dividing the diameter of the mandrel by the diameter of the die outlet) or the take-off speed. be able to.

  A cylindrical laminated foam extruded from an annular die after a plurality of resin melts for forming a resin layer are linearly laminated in the extrusion direction and co-extruded with the resin melt for forming a foam layer is circularly The polystyrene-based resin laminated foam sheet of the present invention can be obtained by passing the sample on a columnar cooling device and cooling it, and cutting the cylindrical laminated foam into a sheet.

  Hereinafter, the polystyrene-based resin laminated foam sheet for thermoforming of the present invention will be described in more detail with reference to examples. However, the present invention is not limited to the examples.

  As the production apparatus, a tandem type foam layer forming extruder comprising a first extruder having a barrel inner diameter of 90 mm and a second extruder having a barrel inner diameter of 120 mm connected to the first extruder is used. A co-extrusion apparatus in which an annular die for coextrusion (lip diameter 67 mm, gap 0.6 mm) is attached to the outlet of the nozzle, and a third extruder for forming a resin layer on one side (inner diameter 65 mm) is connected to the annular die for coextrusion Was used.

  The polystyrene resin for forming a foam layer shown in Tables 1 and 2 and talc (weight% shown in the table as a weight ratio with respect to the total amount of polystyrene resin and talc) as a cell nucleating agent are supplied to the first extruder and heated, melted and kneaded. Then, butane was injected in an amount shown in Table 2, adjusted to a resin temperature suitable for foaming in the second extruder, and formed into a resin melt for forming a foamed layer and introduced into an annular die for coextrusion. .

At the same time, a polystyrene resin for forming a resin layer and a brown inorganic pigment mainly composed of iron oxide are supplied to the third extruder, heated, melted and kneaded, and then injected with a volatile plasticizer to form a resin layer forming resin. It was made into a melt and introduced into an annular die for coextrusion.
In the annular die for coextrusion, the resin melt for forming the foam layer is joined by joining the resin melt for forming the foam layer flowing in a cylindrical shape and the resin melt for forming the resin layer formed from the slit-like inner lip. A resin melt for forming a resin layer was laminated on the product and coextruded into a cylindrical shape, then taken through a 270 mmφ mandrel (blow-up ratio 4) and cut to obtain a laminated foam sheet of the present invention. The resin layer was laminated on one side of the foamed layer in a non-foamed state.

Tables 1 and 2 show the manufacturing conditions, the design shape of the slit-shaped die, the physical properties of the laminated foam sheet, and the like in Examples and Comparative Examples.
In Tables 1 and 2, raw material PS resins (1) and (2) used for the foam layer and the resin layer mean the following polystyrene resins.
PS resin (1): PS Japan 680: Melt viscosity 930 Pa · s
PS resin (2): GX154 manufactured by PS Japan Co., Ltd .: Melt viscosity 1430 Pa · s
In addition, the melt viscosity of the polystyrene resin is based on JIS K 7199, using a flow property measuring machine of Capillograph 1D (manufactured by Toyo Seiki Seisakusho Co., Ltd.) under conditions of a temperature of 200 ° C. and a shear rate of 100 seconds− ¹ . It is a measured value.
Moreover, the following were used as a coloring agent.
Colorant (1) PS-M-SSCA11N7470BR manufactured by Dainichi Seika Kogyo Co., Ltd.
Colorant (2) SBF-T-3775 manufactured by Resino Color Industry Co., Ltd.

Example 1
According to the manufacturing conditions shown in Table 1, a polystyrene resin (B), a colorant (1), and a volatile plasticizer are added to a foamed layer-forming resin melt obtained by kneading a polystyrene resin (A) and a physical foaming agent. A laminated foam sheet was obtained by laminating a plurality of resin melts for forming a resin layer obtained by kneading and coextrusion. The colorant (1) was added as a master batch so that the amount of the colorant (1) added was 0.9 parts by weight with respect to 100 parts by weight of the polystyrene resin (B). Further, the resin layer forming resin melt is composed of a number of resin layer forming holes (groove width 0.6 mm, depth) arranged on the circumferential outer edge of the flow path of the foam layer forming resin melt in the annular die. Co-extruded through a flow path of 2.1 mm (170 slits). Table 1 shows the characteristics and the like of the obtained laminated foam sheet.

(Example 2)
The conditions of Table 1 were obtained by co-extrusion through the flow paths of numerous resin layer forming holes (groove width 1.1 mm, depth 2.2 mm and 90 slits) arranged on the circumference of the annular die. A laminated sheet was obtained in the same manner as in Example 1 except for the above. In addition, to the resin melt for forming the foam layer, the colorant (2) is added as a master batch, and the amount of the colorant (2) added is 0.5 parts by weight with respect to 100 parts by weight of the polystyrene resin (A). It added so that it might become. Table 1 shows the characteristics and the like of the obtained laminated foam sheet. Similar to Example 1, a uniform streak-like resin layer was formed on the entire surface, and the foam sheet was good with few surface irregularities.

(Example 3)
A sample was obtained in the same manner as in Example 2 except that the weight of the laminated resin per meter in the extrusion direction per each resin layer was 0.19 g / m and the conditions shown in Table 1 were used. Table 1 shows the characteristics and the like of the obtained laminated foam sheet. Similar to Example 1, a uniform streaky resin layer was formed on the entire surface, and the foam sheet was good with few surface irregularities.

Example 4
A sample was obtained in the same manner as in Example 1 except that the resin layer forming holes (groove width 1.3 mm, depth 3.1 mm, 53 slits) were co-extruded and the conditions shown in Table 1 were applied. Table 1 shows the characteristics and the like of the obtained laminated foam sheet. Although the surface of the foamed sheet was slightly uneven, the foamable sheet for thermoforming had good moldability.

(Example 5)
The conditions of Table 1 were obtained by co-extrusion through the flow paths of numerous resin layer forming holes (groove width 1.5 mm, depth 3.5 mm and 40 slits) arranged on the circumference of the annular die. A sample was obtained in the same manner as in Example 1 except for the above. Table 1 shows the characteristics and the like of the obtained laminated foam sheet. Although the surface of the foam sheet was slightly uneven, the foam sheet for thermoforming had good moldability.

(Example 6)
A sample was obtained in the same manner as in Example 2 except that the weight of the laminated resin per 1 m of the resin layer was 0.33 g / m and the conditions shown in Table 1 were used. Table 1 shows the characteristics and the like of the obtained laminated foam sheet. The obtained foamed sheet can easily approach the average center distance between adjacent resin layers, but it can be recognized as a streak pattern and has good thermoformability.

(Example 7)
A sample was obtained in the same manner as in Example 4 except that the weight of the laminated resin per 1 m of the resin layer was 0.40 g / m and the conditions shown in Table 1 were used. Table 1 shows the characteristics and the like of the obtained laminated foam sheet. The obtained laminated foam sheet is difficult to be cooled because of the large weight of the laminated resin, and the thickness unevenness becomes slightly conspicuous due to the influence of the resin layer, but the maximum height of the contour curve on the surface of the foam sheet is 50 μm or less. As a foam sheet for molding, it was a good range.

(Example 8)
Many resin layer forming holes (groove width changed from 0.6 mm to 0.8 mm, 1.0 mm, depth 1.2 mm, 170 slits) arranged on the circumference of the annular die A foamed sheet was obtained in the same manner as in Example 1 except that the conditions shown in Table 1 were used. Table 1 shows the characteristics and the like of the obtained laminated foam sheet. Even if the groove width of the slit was changed, a streak pattern could be formed, and a foam sheet with few surface irregularities was obtained.

Example 9
Through a flow path of a large number of resin layer forming holes (170 slits having a groove width changed from 0.6 mm to 0.8 mm and 1.0 mm) arranged on the circumference of the annular die of Example 8 Then, coextrusion and the speed of the take-up machine and the amount of the foaming agent were adjusted to obtain a foamed sheet. Table 1 shows the characteristics and the like of the obtained laminated foam sheet. Similar to Example 8, even when the groove width of the slit was changed, a streak pattern could be formed, and a foam sheet with few surface irregularities was obtained.

(Comparative Example 1)
If the maximum height of the contour curve on the surface of the foam sheet exceeds 60 μm, the thin-walled portion of the foam sheet will further expand during thermoforming, resulting in a decrease in strength of the molded product, and is not suitable for a thermoforming sheet. became. The foam sheet was produced in the same manner as in Example 1 except for the conditions shown in Table 2.

(Comparative Example 2)
When the cell wall thickness of the outermost surface of the foamed sheet was too thick and 68 μm, it was difficult to form a streak pattern, and a foamed sheet for thermoforming could not be obtained. This is probably because the resin melts for forming the resin layer merged, and the cell wall thickness on the outermost surface became thick, and a resin layer with a uniform streak pattern could not be formed. The foam sheet was produced in the same manner as in Example 1 except for the conditions shown in Table 2.

(Comparative Example 3)
When the maximum height of the contour curve on the surface of the foam sheet exceeds 60 μm, the thickness unevenness of the foam sheet becomes severe, and the maximum height of the contour curve on the surface of the foam sheet exceeds 50 μm. Occasionally, the thin part of the foamed sheet was further extended, resulting in a decrease in strength of the molded product, which was not suitable for a thermoforming sheet. The foam sheet was produced in the same manner as in Example 1 except for the conditions shown in Table 2.

In Tables 1 and 2, each characteristic was measured and evaluated as follows.

(Thermoformability)
Thermoformability was evaluated as follows.
○ ... Good formability (no molding defects)
X: The molded product shows a decrease in strength due to the formation of irregularities in the foam sheet.

  Molding was performed by match mold vacuum molding using a molding machine manufactured by Asano Laboratories, product number FKS-0631-10, with a heater temperature of 330 ° C. and a heating time of 7 seconds ± 1 second. Thermoforming was performed using a tray mold having a depth of 25 mm, a stack side wall thickness of 1.5 mm, and a stacking height pitch of 2.85 mm. The minimum gap created by the upper and lower molds of the mold was 1.5 mm at the stack portion.

(Appearance evaluation)
The appearance of the foam sheet was evaluated according to the following criteria.
A streaky pattern is formed. In addition, a high-quality wood grain pattern is seen when using a tea-based colorant.
O ... A streak pattern is formed. In addition, when using a tea-based colorant, a wood grain pattern is observed, but a slight thickness unevenness is observed.
Δ: Although a streak pattern is formed, the distance between the centers of the resin layers is too far, and when using a brown colorant, it does not become a woodgrain pattern but a stripe pattern.
X: A streak pattern is not formed.

(Thickness of foam sheet)
The thickness of the foam sheet is an arithmetic average of thicknesses (mm) measured at a plurality of points (5 points or more) at equal intervals from one end part to the other end part in the width direction of the foam sheet. Obtained as a value.

(Apparent density of foam sheet)
The apparent density of the foamed sheet is the volume (cm ³⁾ determined from the external dimensions of the test piece, which is the weight (g) of the test piece, which is randomly cut out at multiple locations (preferably 5 or more) over the entire width of the foamed sheet. ) Was converted into units (g / cm ³ ) to determine the apparent density of each sample, and the average value of the obtained values was taken as the apparent density.

(Maximum height of the contour curve of the foam sheet surface)
The maximum height of the contour curve on the surface of the foam sheet was measured using a surf coder SE1700α manufactured by Kosaka Laboratory Co., Ltd. in accordance with JIS B0601 (2001). In the width direction of the foam sheet, cut out 5 pieces of 30 mm test pieces at equal intervals, place the test pieces on a horizontal base, and bring the tip of the stylus with a tip curvature radius of 2 μm into contact with the sheet surface of the test piece Then, it was moved in the width direction at a moving speed of 0.5 mm / s, and the up and down variation of the stylus was sequentially measured. The measurement length specified by the moving distance of the test piece was set to be at least three times the cut-off value (8 mm). The arithmetic average value of the five measured values obtained was taken as the maximum height of the contour curve on the foam sheet surface.

(Outermost cell wall thickness of foam sheet)
The measurement of the cell wall thickness of the outermost surface portion of the foamed sheet was performed by cutting out 10 pieces of 10 mm wide test pieces every 100 mm in the width direction of the foamed sheet, and magnifying the cross section of the test piece (digital microscope: product name: stock) The thickness was measured with a digital microscope VHX-900 manufactured by Keyence Corporation, and the thickness from the surface of the foam sheet to the inner surface of the first cell wall in the thickness direction of the foam sheet was measured. The cell wall thickness was measured by measuring the central portion of the bubble (the center in the width direction in the enlarged micrograph) for all the bubbles in the test piece. Moreover, the arithmetic average value of five places was made into the cell wall thickness of the outermost surface part about the maximum value of the obtained measured value.

(Surface density)
The surface layer density is measured by slicing a 200 μm portion from the surface of the foam sheet and cutting it into a test piece having a width of 5 mm × a length of 20 mm, and measuring the weight and thickness of the test piece with a gauge. The surface layer density was determined by dividing by the volume of the test piece and converting the unit. The said measurement was performed about 10 places of equal intervals in the width direction of the said foam sheet, and those arithmetic mean values were made into the surface layer density of the lamination | stacking surface.

(Lightness of the foam sheet surface)
The brightness of the surface of the foamed sheet was determined by cutting out test pieces having a width of 10 mm at 5 locations every 100 mm in the width direction of the foamed sheet, placing the test piece on a sample stage having a measurement range of 6 mmφ, and fixing it with a weight. A piece was covered with a dark box, and the brightness of the surface of the test piece was measured by a reflection method at intervals of 5 mm using a spectroscopic color difference meter SE2000 (manufactured by Nippon Denshoku Industries Co., Ltd.). For each of the maximum value and the minimum value of the measured values, five arithmetic average values were calculated. In terms of appearance, when the resin layer is darker in the resin layer and the foam layer, the maximum value of brightness is a measured value corresponding to the foam layer of the foam sheet, and the minimum value of brightness is the resin layer. The corresponding measured value. When measuring the foamed layer portion, the measurement was performed after slicing and removing the portion corresponding to the resin layer. When measuring the resin layer part, the test piece was measured as it was. In addition, when the width | variety of the resin layer was smaller than the measurement range, the brightness of the some test piece which cut out the resin layer part was measured.

DESCRIPTION OF SYMBOLS 1 Polystyrene resin foam sheet for thermoforming 2 Polystyrene resin foam layer 3 Polystyrene resin resin layer 4 Polystyrene resin constituting the resin layer 5 Colorant 6 Volatile plasticizer 7 Polystyrene resin melt for forming resin layer 8 Polystyrene resin constituting the foam layer 9 Physical foaming agent 10 Polystyrene resin melt for forming the foam layer 11 First extruder 12 Second extruder 13 Annular die

Claims (3)

A heat having an apparent density of 0.04 to 0.35 g / cm ³ and a thickness of 0.5 to 10 mm, in which a plurality of polystyrene resin layers containing a colorant are laminated on at least one surface of the polystyrene resin foam layer by coextrusion. A polystyrene resin foam sheet for molding,
The polystyrene-based resin layer has a streak shape along the extrusion direction , and is formed adjacent to each other in the width direction ,
The cell wall thickness of the outermost surface portion on the resin layer lamination surface side of the foam sheet is 50 μm or less, and the maximum height of the contour curve on the surface of the foam sheet on the resin layer lamination surface side is 60 μm or less. A polystyrene resin foam sheet for thermoforming. 2. The polystyrene-based resin foam for thermoforming according to claim 1, wherein a surface layer density of a portion from the surface to the thickness direction of 200 μm on the resin layer lamination surface side of the foamed sheet is 0.15 g / cm ³ or more. Sheet.   The weight of the laminated resin per resin layer is 0.01 to 0.6 g / m per meter in the extrusion direction, and the average distance between the centers of adjacent resin layers is 2 to 30 mm. Or the polystyrene-type resin laminated foam sheet for thermoforming of 2.