JP2012144285A - Packaging sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a new packaging material having shock-absorbing properties, flexibility, waterproofness, and easiness of opening, all at the same time, to be suitable for packaging CDs, DVDs, books or the like.SOLUTION: The packaging sheet is formed of a foamed styrene-based resin sheet containing polystyrene and polyolefin, and biaxially stretched.

Description

  The present invention relates to a packaging sheet used for packaging CDs, DVDs, books, miscellaneous goods, clothes, and the like when mailed or delivered to homes.

  In recent years, online shopping via the Internet has become popular, and a business model in which CDs, DVDs, books, miscellaneous goods, clothing, etc. are purchased on websites and these products are delivered to buyers by mail or home delivery has become widespread. ing. In such a business model, the packaging and transportation of merchandise is generally carried out by mail or home delivery by packaging with a packaging material having cushioning properties so as not to damage the merchandise.

  As packaging materials for this type of application, packaging with paper products (kraft paper) is currently in practical use, but the protective properties (buffer properties) of the contents are insufficient, so plastic bubbles It was necessary to carry out double packaging, in which the contents were packaged with a buffer sheet and then packaged with the above-mentioned kraft paper, which could not be said to be efficient.

  In addition, Patent Document 1 discloses that a long sheet of a plastic bubble sheet is folded in half along a substantially center line thereof, and is subjected to heat sealing in a transverse direction at a predetermined interval, so that the fold line is the bottom and the sheet Disclosed is a perforated continuous packaging bag having a cushioning performance by a plastic foam sheet, wherein a continuous body of a bag having an opening on an end side is formed, and a perforation for cutting is formed in the heat seal portion. Has been.

  Patent Document 2 discloses the use of a foam sheet made of a mixture of an olefin polymer, a styrene polymer and a compatibilizer as a packaging material.

JP-A-11-1278 JP 2000-204185 A

  Considering packaging and transporting CDs, DVDs, books, miscellaneous goods, clothing, etc., as packaging materials used for this purpose, in addition to cushioning to protect these products from impacts, to package products of various shapes It is desirable to have flexibility, water resistance that prevents water from entering, and ease of opening that can be easily opened by tearing by hand.

  Therefore, the present invention intends to provide a new packaging material having such buffering properties, flexibility, water resistance, and ease of opening.

  The present invention proposes a packaging sheet comprising a foamed styrene resin sheet containing polystyrene and polyolefin and biaxially stretched.

  The packaging sheet proposed by the present invention is made of a foamed styrene-based resin sheet containing polystyrene and polyolefin and biaxially stretched, and thus has buffering properties, flexibility, water resistance, and ease of opening. Suitable as a packaging sheet. For example, this packaging sheet can be cut into a rectangular shape of appropriate size, and two sheets can be stacked and sealed on two or three sides, and then the product can be placed and the remaining sides sealed to wrap the product. For example, it can be used for packaging when mailing or delivering a CD, DVD, book, miscellaneous goods, clothing, or the like.

  Next, the present invention will be described based on exemplary embodiments, but the present invention is not limited to the embodiments described below.

<This resin sheet 1>
A resin sheet (referred to as “the present resin sheet 1”) according to an embodiment of the present invention contains polystyrene and polyolefin, and has a single-layer structure composed of a foamed styrene-based resin sheet that is biaxially stretched. This is a resin sheet.

(polystyrene)
Polystyrene is not particularly limited as long as it is a styrene resin. For example, when (A) is a polystyrene resin not containing a rubber component and (B) is a polystyrene resin containing a rubber component, (A) alone, (B) alone, or (A) and (B) Any of the mixtures may be used.

  Typical examples of the polystyrene-based resin (A) not containing a rubber component include polystyrene such as general-purpose polystyrene (hereinafter sometimes referred to as “GPPS”). Furthermore, styrene, alkyl styrene (for example, o-, m-, p-methyl styrene, p-ethyl styrene, pt-butyl styrene), α-alkyl styrene (for example, α-methyl styrene, α-ethyl styrene). ) Aromatic vinyl compound homopolymers, copolymers of these monomers, styrene- (meth) acrylic acid ester copolymers (for example, styrene-butyl acrylate copolymers), styrene- ( Also included are (meth) acrylic acid copolymers. These can be used alone or in combination of two or more. Also when (A) is used in combination with (B), (A) can be used in combination of two or more.

  Among these, as (A), GPPS is preferable. Of the above (A), (A) other than GPPS is preferably used alone or in combination of two or more in a range having compatibility with GPPS.

  Among GPPS, GPPS having a melt flow rate in the range of 0.5 to 20 g / 10 min at a temperature of 200 ° C. and a load of 5 kg is preferable, and GPPS in the range of 2 to 10 g / 10 min is particularly preferable. By using such GPPS, melt kneading and extrusion foaming at a relatively low temperature can be performed more easily.

  On the other hand, as the polystyrene resin (B) containing a rubber component, for example, HIPS, which is a representative of a graft type copolymer, and a styrene-butadiene-styrene block copolymer, which is a representative of an ABA type block copolymer (hereinafter, referred to as “polystyrene type resin”). Styrene-isoprene-styrene block copolymer (hereinafter sometimes referred to as “SIS”), and the like.

  Examples of the rubber component used in the production of (B) include non-styrene rubbers such as butadiene rubber, isoprene rubber, acrylic rubber, and butadiene-isoprene rubber; and styrene rubbers such as styrene-butadiene rubber and styrene-isoprene rubber. Can be mentioned. Among them, butadiene rubber is preferable, and among butadiene rubbers, a high cis type having a high content of cis-1,4 structure is preferable from the viewpoint of thermal stability than a low cis type having a low content.

  The rubber component content is calculated by measuring the diene content by potentiometric titration using iodine monochloride, potassium iodide and sodium thiosulfate standard solution, and calculating the diene content as the rubber component content. Analytical methods are described in, for example, the Japan Society for Analytical Chemistry, Polymer Analysis Research Roundtable, “New Edition Polymer Analysis Handbook”, Kinokuniya (1995 edition), p. 659 “(3) Rubber content”, measured by this method and defined as the value so measured.

  The content of the rubber component in (B) is preferably 3 to 50% by mass, more preferably 4% by mass or more and 40% by mass or less, and more preferably 5% by mass with respect to the whole (B). It is particularly preferable that the amount is 30% by mass or less.

(B) is preferably a HIPS or SIS copolymer having a melt flow rate in the range of 0.5 to 20 g / 10 min at a temperature of 200 ° C. and a load of 5 kg, and more preferably 2.0 g / 10 min or more or 10 g / 10. HIPS and SIS that are less than or equal to a minute are more preferable. In particular, the above HIPS is preferable. (B) can be used alone or in combination with (A).
(B) can be used alone or in combination of two or more. Even when (B) is used in combination with (A), (B) can be used in combination of two or more. By using such a polystyrene-based resin, melt kneading and extrusion foaming at a relatively low temperature are possible.

  The content of a preferable rubber component with respect to the entire resin sheet 1 is 0 to 50% by mass, more preferably 1% by mass or more and 40% by mass or less, and more preferably 2% by mass or more or 20% by mass or less. Is particularly preferred. By containing the rubber component, the sheet can be provided with flexibility, buffering property, and tear strength. On the other hand, when the content of the rubber component is too large, not only the extrusion stability and stretching stability during production are deteriorated, but also the rigidity of the produced sheet may be unnecessarily lowered. The above (A) and / or (B) may be used so that the content of the rubber component falls within the above range.

(Polyolefin)
By blending polyolefin with polystyrene, flexibility can be increased, packaging wrinkles and misalignment can be made difficult when products are put, and it can be made suitable for packaging applications.

The polyolefin used for the resin sheet 1 may be an olefin homo- or copolymer.
Examples of olefins include ethylene, propylene, 1-butene, isobutene, 4-methyl-1-butene, 1-pentene, 3-methyl-1-pentene, 1-hexene, 1-heptene, 1-octene and the like. Can do. Of these olefins, ethylene or propylene is particularly preferred.
Moreover, the copolymer (a random copolymer, a block copolymer, etc. are included) of the said olefin and a copolymerizable monomer may be sufficient. In this case, examples of the copolymerizable monomer include (meth) acrylic acid; (meth) acrylic acid esters such as methyl (meth) acrylate, ethyl (meth) acrylate, butyl (meth) acrylate; vinyl acetate, Examples thereof include vinyl esters such as vinyl propionate; cyclic olefins such as norbornene, ethylidene norbornene, cyclopentene, cyclopentadiene and cyclohexene; dienes such as butadiene, isoprene and 1,4-pentadiene.
These copolymerizable monomers can be copolymerized with olefins alone or in combination of two or more.

  Among these, from the viewpoints of imparting flexibility to the resin sheet 1 and easy availability, preferred polyolefins include polyethylene that is a homopolymer of ethylene, polypropylene that is a homopolymer of propylene, and an ethylene vinyl acetate copolymer. Of these, it is preferable to use one or more of them in combination.

  Polyolefin may be blended with polystyrene alone or as pellets kneaded with other resins. Moreover, you may mix | blend as a masterbatch containing a foaming agent.

(Content ratio)
The content ratio of polystyrene and polyolefin is 50 to 99.5 parts by mass of polystyrene with respect to 100 parts by mass of the total amount of polystyrene and polyolefin from the viewpoint of imparting buffering properties, flexibility, water resistance, and ease of opening to the sheet. It is preferable to contain 0.5 to 50 parts by mass of polyolefin. Among them, it is particularly preferable to contain 1 part by mass or more and 20 parts by mass or less of polyolefin, and it is more preferable to contain 2 parts by mass or more and 10 parts by mass or less of polyolefin. The polystyrene content in the sheet is desirably 50 to 99.5% by weight.

(Other ingredients)
The resin sheet 1 may contain a compatibilizing agent, but the content thereof is set to 0.000 parts by mass with respect to 100 parts by mass of the total amount of polystyrene and polyolefin from the viewpoint of burnt foreign matter and gelation due to oxidation at high temperature. It is preferably less than 1 part by weight, particularly less than 0.08 part by weight, and more preferably less than 0.05 part by weight (including 0 part by weight).

  Examples of the compatibilizing agent include a styrene monomer-conjugated diene copolymer to which a random copolymer of a styrene monomer and a conjugated diene is added, a hydrogenated copolymer of a block copolymer, and the like. A polymer etc. can be mentioned.

  The hydrogenated styrene monomer-conjugated diene copolymer includes not only (a) a hydrogenated copolymer in which a random or block copolymer of a styrene monomer and a conjugated diene is hydrogenated. (B) A hydrogenated copolymer of a random or block copolymer of a styrene monomer and one or more α-olefins is also included.

  The styrenic monomer includes the monomers exemplified above. The hydrogenated styrene monomer-conjugated diene copolymer may be modified with maleic anhydride, (meth) acrylic acid, (meth) acrylic acid ester, glycidyl (meth) acrylate, or the like.

  Preferred hydrogenated styrene monomer-conjugated diene copolymers include styrene monomers such as hydrogenated styrene-butadiene random or block copolymers, hydrogenated styrene-isoprene random or block copolymers, and a carbon number of 4 Examples thereof include hydrogenated products of copolymers with -6 to conjugated dienes.

  In addition, foaming agents, fillers, dispersants, anti-blocking agents, slip agents, dispersion aids, internal lubricants, lubricants, thermal stabilizers, antioxidants, hydrolysis inhibitors, UV rays, as described below, as necessary. Absorber, Light Resistant, Crystal Nucleating Agent, Mold Release Agent, Flame Retardant, Plasticizer, Antifogging Agent, Reinforcing Agent, Extender, Antibacterial Agent, Antifungal Agent, Pigment, Dye, Colorant, Surface Wetting Agent, Flow It may contain a property improver, a thickener, a surfactant other than the antistatic agent, an inorganic filler, an organic filler, carbon black, ketjen black, graphite, a reinforcing agent, and the like.

(Foaming ratio)
The expansion ratio of the resin sheet 1 is preferably in the range of 1.1 to 5.0 times.
If the expansion ratio is 1.1 times or more, flexibility, buffering properties, sheet surface appearance and the like can be maintained, while if the expansion ratio is 1.5 times or less, deterioration of the sheet surface appearance, mechanical Strength (impact strength, tear strength, etc.) can be maintained.
From this viewpoint, the foaming ratio of the resin sheet 1 is more preferably 1.6 times or more and 4.5 times or less, and particularly preferably 2.5 times or more or 4.2 times or less.

  This expansion ratio (P) is the density (Q) of the foam sheet measured in accordance with JIS K7222 and the density of the foam material in an unfoamed state measured in accordance with the D method of JIS K7112 ( From R), it is a value obtained by P = R / Q.

  The expansion ratio can be controlled by the type of foaming agent and its blending amount, as well as the resin temperature, resin pressure, etc. during extrusion. The resin sheet can achieve the above expansion ratio while keeping other physical properties good. In particular, even if the expansion ratio is large (for example, 4.0 times or more), the mechanical strength can be kept good.

  In order to foam the resin sheet, a method of extruding by adding a chemical foaming agent, a method of extruding while injecting a foaming gas raw material, a method of extruding a resin impregnated with a liquid foaming gas raw material, etc. Can be applied.

Examples of the foaming agent include volatile foaming agents such as propane, butane, pentane, and hexane; ammonium carbonate, ammonium bicarbonate, sodium bicarbonate, sodium citrate, azo compounds (azobisisobutyronitrile, azodicarbonamide, diazo Aminobenzene, etc.), sulfonyl hydrazide compounds (benzenesulfonyl hydrazide, p-toluenesulfonyl hydrazide, diphenyloxy-4,4′-bissulfonylhydrazide, etc.), nitroso compounds (N, N′-dinitrosopentamethylenetriamine, etc.), etc. In addition to chemical foaming agents (decomposable foaming agents), examples thereof include foaming gas raw materials such as carbon dioxide and nitrogen gas, and liquid foaming gas raw materials such as water.
These foaming agents may be used alone or in combination of two or more.

  In addition, when using a chemical foaming agent, the resin pellet (masterbatch) which mixed the chemical foaming agent and resin may be created, and you may use as resin containing a foaming agent. As resin used for a masterbatch, the above-mentioned polystyrene and polyolefin can be mentioned.

(Stretch ratio)
The draw ratio of the resin sheet 1 is longitudinal (sheet flow direction or extrusion direction (also referred to as “MD”)) and lateral direction (sheet flow direction or direction perpendicular to the extrusion direction (also referred to as “TD”)). Both of the draw ratios are preferably 1.1 to 5.0 times, and more preferably 1.1 to 3.0.
If the draw ratio exceeds 5.0 times, the improvement of the mechanical properties due to stretching is saturated, so it is not efficient to stretch beyond this, while if the draw ratio is too small, the mechanical strength (impact strength, It is preferable that the draw ratios of both MD and TD are in the above range since the tear strength is likely to be reduced and easily broken. From such a viewpoint, the draw ratio in the resin sheet 1 is more preferably 1.2 times or more and 3.0 times or less for both MD and TD, and among them, 1.5 times or more and 2.9 times or less. Even more preferably.
When extruding a mixture of polystyrene and polyolefin, it is generally known that mechanical properties are usually lowered when a compatibilizer is not added. However, even if a compatibilizing agent is not added, a good sheet can be obtained in which mechanical properties do not deteriorate even if a compatibilizing agent is not added by biaxially stretching the sheet after forming the sheet.

Here, the “stretch ratio” is a ratio at which the length of the straight line written on the test piece of the biaxially stretched sheet changes before and after shrinkage. Specifically, the following formula, that is, stretch ratio = Y / Z The value (unit [times]) calculated by. Y means the length of the test piece of the biaxially stretched sheet, and Z represents the length of the test piece before stretching.
In this formula, Y and Z are obtained by indicating the length [mm] of a straight line drawn on MD and TD using a ruler and a writing instrument on a test piece of a biaxially stretched sheet, and Z is 140 ° C. The length of the straight line [mm] after the test piece is immersed in the silicone oil bath for 10 minutes and contracted is shown.

(Closed cell rate)
The closed cell ratio of the resin sheet 1 is preferably 0.5 to 27%.
When the closed cell ratio is 27% or less, it is possible to prevent a situation in which the repulsive force of the bubbles is over and difficult to process during the bending process when using the packaging, and the closed cell ratio is 0. If it is 5% or more, it is possible to prevent the bubbles from being too few and the shock-absorbing property against external impacts from being insufficient.
Therefore, from this viewpoint, the closed cell ratio of the resin sheet 1 is more preferably 0.7% or more or 25% or less, and more preferably 0.9% or more or 10% or less. preferable.

The closed cell ratio can be measured using a dry automatic densimeter (Accumic 1340) manufactured by Shimadzu Corporation according to the following procedures (1) to (5). The same applies to the closed cell ratio described later.
Procedure (1) The resin sheet 1 is cut into strips having a length of 39 mm and a width of 12.5 mm. The number of strips is adjusted so that the sheet thickness is about 12.5 mm when the strips are stacked. For example, in Example 1, since the sheet thickness was 0.75 mm, 17 strips were used. Stacked thickness 12.75mm.
Procedure (2) The cut strip is accommodated in a sample cell, and the sample volume (Vp1) is measured with a dry automatic densimeter.
Procedure (3) The strip after measurement is cut six times in the vertical direction to produce a strip with a length of 39 mm and a width of 1.79 mm. For example, in Example 1, all 17 strips were cut 6 times.
Procedure (4) All the cut strips are accommodated in a sample cell, and the sample volume (Vp2) is measured with a dry automatic densimeter.
Procedure (5) The closed cell ratio S (average value of N = 3) is obtained based on the following formula.
S (%) = Vc / Vg × 100
Vc = Vg-W / D-Voc
Voc = 1 / A (A · Vp1-Vp2)

Vc: volume of only closed cells (cm ³ )
Vg: geometric volume (volume calculated from external dimensions) (cm ³ )
W: Sample weight of the cut strip (g)
D: Sample density (g / cm ³ )
Voc: Volume of open bubbles (cm ³ )
A: Ratio of side area before and after cutting of strips (sum of side areas of each strip after cutting / sum of sides of cut out strips)
Vp1: Sample volume (cm ³ ) of the cut strip
Vp2: Sample volume of the strip after cutting (cm ³ )

(Production method)
The resin sheet 1 can be prepared by mixing polystyrene, polyolefin, and other raw materials such as a foaming agent as necessary, extruding to form a sheet and foaming, and then biaxially stretching. .
More specifically, polystyrene, polyolefin, and other raw materials such as a foaming agent as necessary are melted and kneaded by an extruder, supplied to the base while being extruded, and continuously heated by heating above the decomposition temperature of the foaming agent at the base outlet. For example, the sheet may be formed into a sheet while being extruded and foamed, and then continuously and sequentially biaxially stretched by, for example, longitudinal stretching by a roll stretching method or the like, followed by lateral stretching by a tenter method or the like.

<This resin sheet 2>
A resin sheet (referred to as “present resin sheet 2”) according to an embodiment of the present invention is a biaxially stretched resin sheet composed of three or more layers including an inner layer and an outer layer. Is a foamed resin layer containing polystyrene and polyolefin, and the outer layer is a resin layer containing polystyrene.
Since the above three layers only have to be provided, a resin layer may be appropriately interposed between the outer layer and the inner layer.

(Inner layer)
The composition and expansion ratio of the inner layer of the resin sheet 2 are preferably the same as those of the resin sheet 1 described above. That is, it is preferable to form the outer layer on the front and back sides of the resin sheet 1 before stretching, and biaxially stretch to obtain the resin sheet 2.

(Outer layer)
The outer layer is preferably a resin layer containing polystyrene as a main component from the viewpoint of adhesion to the inner layer and imparting rigidity, and it is preferable to further mix components appropriately according to the purpose. For example, in order to further increase flexibility, the above polyolefins and compatibilizers are added to polystyrene, or nonionic, anionic, cationic surfactants and polyethers are added to polystyrene to impart antistatic properties. Examples thereof include adding an ester amide, and adding an ionomer to polystyrene in order to impart heat sealability. The amount of polystyrene in the resin layer is preferably 50 to 99.5% by weight.
In addition, when a foaming agent is blended in the outer layer, the printability of the ink is lowered. Therefore, it is preferable not to blend a foaming agent in the outer layer. Also, from the viewpoint of increasing strength and rigidity, the outer layer is a non-foamed layer. Is preferred.

(Preferred laminated structure)
As a more preferred configuration example, polystyrene (for example, HIPS), preferably a polyolefin (for example, PE) is further contained on one or both sides of an inner layer composed of a foamed resin layer containing polystyrene (for example, HIPS) and polyolefin (for example, PE). A sheet formed by laminating an outer layer made of a foamed resin layer and biaxially stretching is preferred.

(Layer ratio)
The mass ratio per unit area of the inner layer and the outer layer (total) is inner layer: outer layer (total) = 50: 50 to 99: 1 from the viewpoint of the balance between buffer properties, flexibility, water resistance and ease of opening. Among them, 60:40 or more or 95: 5 or less is more preferable, and among them, 70:30 or more or 90:10 or less is more preferable.

(Stretch ratio)
Like the resin sheet 1, the draw ratio of the resin sheet 2 is preferably 1.1 to 5.0 times for both MD and TD, and is 1.2 times or more and 3.0 times or less. More preferably, the ratio is more preferably 1.5 times or more or 2.9 times or less.
When extruding a mixture of polystyrene and polyolefin, it is generally known that when no compatibilizer is added, mechanical properties are lowered, and in the case of multiple layers, the layers are easily peeled off. However, even if a compatibilizing agent is not added, a good sheet can be obtained in which mechanical properties do not deteriorate even if a compatibilizing agent is not added by biaxially stretching the sheet after forming the sheet.

(Closed cell rate)
The closed cell ratio of the resin sheet 2 is preferably 0.5 to 27%. When the closed cell ratio is 27% or less, it is possible to prevent a situation in which the repulsive force of the bubbles is over and difficult to process during the bending process when using the packaging, and the closed cell ratio is 0. If it is .5 or more, it is possible to prevent a shortage of air bubbles and insufficient buffering against external impacts.
Therefore, from this viewpoint, the closed cell ratio of the resin sheet 2 is more preferably 0.7% or more or 25% or less, and more preferably 0.9% or more or 10% or less. preferable.

(Production method)
The raw materials constituting each layer may be mixed, coextruded to form a laminated sheet and foamed, and then biaxially stretched as described above. Specifically, it can be co-extruded using a general-purpose die with a feed block, a multi-manifold die, or the like.
Moreover, after forming the sheet | seat which comprises each layer and making it foam, this may be made to laminate | stack by methods, such as heat lamination and dry lamination.

<Physical properties of the resin sheets 1 and 2>
What is necessary is just to adjust the thickness of this resin sheet 1 and 2 according to the objective. When used as a packaging material, that is, a sheet for forming a packaging bag, the thickness is preferably 0.1 mm to 1.5 mm, particularly preferably 0.3 mm or more or 1.3 mm or less. More preferably, it is 4 mm or more or 1.0 mm or less.

The tear strength of the resin sheets 1 and 2 is preferably 15 N / mm or less, particularly preferably 10 N / mm or less, and more preferably 7 N / mm or less, from the viewpoint of being easily tearable by hand. .
Similarly, from the viewpoint of tearing straight from either the MD or TD side, the ratio of MD and TD tear strength is MD: TD = 1: 3 to 3: 1. In particular, MD: TD = 1: 2.5 to 2.5: 1 is preferable, and MD: TD = 1: 2 to 2: 1 is particularly preferable. When the ratio is out of the above range, when tearing by hand, the tearing direction may be bent, and it may be difficult to open. Such a ratio of the tear strength of MD and TD can be adjusted by setting the composition, the stretching ratio of MD and TD, and the temperature condition during stretching in the resin sheets 1 and 2.

<Uses of the present resin sheets 1 and 2>
The resin sheets 1 and 2 can be suitably used as a packaging material sheet.
For example, a packaging bag can be formed by cutting this resin sheet or 2 into a rectangular shape, stacking two sheets, and sealing the three sides.
Moreover, this resin sheet 1 or 2 is cut into a rectangular shape, two sheets are stacked, two or three sides are sealed, the product is stored between the sheets, and the remaining sides are sealed to wrap the product. be able to.
Since this resin sheet 1 or 2 has cushioning properties, flexibility, water resistance, and ease of opening, it can be packaged according to the shape of the product as the contents, and the product can be removed from impact or water intrusion. It has a feature as a packaging material that can be protected and can be easily opened by hand.

(Self-adhesive adhesive)
When the resin sheets 1 and 2 are used as packaging materials, it is preferable that a self-adhesive adhesive is attached to at least a part or the entire surface of one side of the resin sheets 1 and 2.

Self-adhesive adhesive means a resin that only adheres to each other without heating when the adhesive surfaces are stacked and pressed with a certain amount of force. Natural rubber-based adhesives are typical examples. It is.
However, the self-adhesive adhesive applied to one side of the resin sheets 1 and 2 is preferably an adhesive having a composition obtained by blending natural rubber material with styrene butadiene rubber.
Adhesives made of natural rubber or adhesives that are only modified from methyl methacrylate (MMA) of natural rubber-based materials have poor compatibility with polystyrene and cause stringing when tearing and opening. An adhesive having a composition in which styrene-butadiene rubber is blended with a natural rubber-based material, or an adhesive having a composition in which natural rubber-based material is MMA-modified and further blended with styrene-butadiene rubber is used for such stringing. This is particularly preferable because no phenomenon occurs.

(Total light transmittance)
When the resin sheets 1 and 2 are used as packaging materials, the total light transmittance of the resin sheets 1 and 2 is preferably 20% or less, more preferably 19% or less, and most preferably 18% or less. Is more preferable.
In order to reduce the total light transmittance of the sheet to 20% or less, for example, ink may be applied to one side of the resin sheets 1 and 2 to provide light shielding properties.
Further, light shielding properties can be imparted to the sheet by kneading a pigment such as titanium oxide into the sheet.
By providing light shielding properties in this way, the contents of the product are not seen through, and thus confidentiality can be maintained.

As a preferable packaging sheet, a sheet obtained by applying a self-adhesive adhesive on the entire surface of one side of the resin sheets 1 and 2 and applying an ink on the other side of the resin sheet 1 and 2 to impart light shielding properties can be exemplified.
Such a packaging sheet, for example, is stacked on top and bottom two so that the surfaces to which the self-adhesive adhesive is applied face each other, presses the right and left side edges to bond and seal, and cuts into a rectangle with an appropriate length. A packaging bag can be formed by pressing the other side and adhesively sealing it.
In addition, for example, the upper and lower two sheets are overlapped so that the surface to which the self-adhesive adhesive is applied faces, adhesively seals by pressing both side edges in the flow direction of the sheet, and puts the product between the two sheets, A product can be packaged by cutting it into a rectangular shape by appropriately cutting it in the flow direction of the sheet, and pressing the other two sides for adhesive sealing. In this case, the self-adhesive adhesive has a property that it does not adhere to the product even when pressed.

<Explanation of words>
In the present specification, when expressed as “X to Y” (X and Y are arbitrary numbers), unless otherwise specified, “X is preferably greater than X” or “preferably Y”. It also includes the meaning of “smaller”.
In addition, when expressed as “X or more” (X is an arbitrary number) or “Y or less” (Y is an arbitrary number), it is “preferably greater than X” or “preferably less than Y”. Includes intentions.

  EXAMPLES Hereinafter, although an Example demonstrates this invention in detail, this invention is not limited to a following example, unless the summary is exceeded. The raw materials used in the examples described below were raw materials having the following characteristics. The evaluation items and the evaluation method of the packaging sheet are as described below.

[raw materials]
GPPS: General polystyrene with a melt flow rate (MFR) measured under the conditions of a temperature of 200 ° C. and a load of 5 kg of 3.5 g / 10 min (manufactured by PS Japan, trade name: HH102, rubber component content: 0% by mass) ).
HIPS: Impact polystyrene having an MFR measured under the same conditions as above, 3.0 g / 10 min (manufactured by PS Japan, trade name: HT478, rubber component content: 9% by mass).
PP: General polypropylene (trade name: EA9, manufactured by Nippon Polypro Co., Ltd.) having an MFR of 0.5 g / 10 min measured under the same conditions as above.

Foaming agent-1: A master batch based on polyethylene and containing 10% by mass of a foaming agent having a decomposition temperature of 155 ° C. (trade name: Polyslen EE105, manufactured by Eiwa Kasei Kogyo Co., Ltd.).
Foaming agent-2: Masterbatch (made by Eiwa Kasei Kogyo Co., Ltd., trade name: Polyslen ES405) containing 40% by mass of a foaming agent having a decomposition temperature of 155 ° C. based on polystyrene.
Foaming agent-3: A master batch (trade name: Polyslen EV405D, manufactured by Eiwa Kasei Kogyo Co., Ltd.) containing 40% by mass of a foaming agent having a decomposition temperature of 155 ° C. based on an ethylene vinyl acetate copolymer (EVA).

Adhesive-1: A natural rubber latex having a solid content of 58%, which is modified by graft polymerization of natural rubber latex with methyl methacrylate (MMA) (trade name: CS-200, manufactured by Regex Corp.).
Adhesive-2: Natural rubber latex having a solid content of 50%, which is obtained by graft polymerization of natural rubber latex with methyl methacrylate (MMA) and further blended with styrene butadiene rubber latex.

[Sheet evaluation items]
The following evaluation is based on a sheet in a state where no adhesive is laminated.

(1) Tensile modulus (unit: MPa): Flexibility Test piece type 2 (width 10 mm; MD and TD) based on JIS K7127 was prepared from the packaging sheets obtained in Examples and Comparative Examples, and Toyo Seiki Using “Autograph DSS2000” manufactured by the company, the measurement was performed under the conditions of an initial clamp distance of 5 cm and a tensile speed of 10 mm / min, and the tensile elastic modulus (unit: MPa) was obtained. About MD and TD, the average value in five test pieces made into each long side was computed.
When this value is less than 1000 MPa, the flexibility is judged as “good” and indicated as “O”, and when the value is 1000 MPa or more, the sheet is hard and is not suitable for processing for packaging, and judged as “poor”. Is displayed.

(2) Tear strength (unit: N / mm): easy tearability From the packaging sheets obtained in the examples and comparative examples, test pieces having a size of 50 mm x 64 mm were measured and the MD of each sheet (sheet extrusion direction). Was made with 5 as the long side and 5 pieces with TD (the direction perpendicular to the extrusion direction of the sheet) as the long side. An incision of 13 mm is cut from the central edge of the end side (50 mm) side of these test pieces in parallel with the long side, and the indicated value when torn using a “light load tear tester” manufactured by Toyo Seiki Co., Ltd. A value obtained by dividing the indicated value by the thickness [mm] of the initial test piece was taken as the tear strength (unit: N / mm). About MD and TD, the average value in five test pieces made into each long side was computed.
When this value is MD: TD = 3: 1 to 1: 3, it can be torn almost straight regardless of whether it is torn from either the MD or TD side. ”Is displayed, and when it is torn from the high tear strength side of MD and TD, it is not straight and it is bent, and“ x ”is displayed.

(3) Closed cell ratio (unit:%): bending workability From the packaging sheets obtained in the examples and comparative examples, a test piece having a size of 39 mm x 12.5 mm becomes a sheet thickness of about 12.5 mm. The number of sheets was cut out. These test pieces were subjected to volume measurement using a “dry automatic densimeter (Acpic 1340)” manufactured by Shimadzu Corporation, and the value obtained by dividing the obtained closed cell volume by the geometric volume was determined as the closed cell rate (unit: %). The average value of three tests was calculated for each. For details, see also the above-mentioned item of closed cell ratio.
If this value is 0.5% to 27.0%, it is possible to prevent a situation in which the repulsive force of the bubbles wins and the processing becomes difficult at the time of bending processing when using the packaging, Since it is possible to prevent the shock-absorbing property from being externally insufficient due to too few bubbles, the bending workability is judged as “good” and displayed as “◯”, and when it falls out of this range, “inferior” It was judged and “×” was displayed.

(4) Total light transmittance (unit:%): light shielding property From the packaging sheets obtained in the examples and comparative examples, five test pieces having a size of 50 mm × 50 mm were prepared and in accordance with JIS K7105, Japan. The average value of five test pieces was calculated using a “turbidity meter NDH2000” manufactured by Denshoku.
This average value was defined as the total light transmittance (unit:%). When this value is 20% or less, the contents cannot be recognized when packaging, so the light-shielding property is judged as “good” and “○” is displayed, and those exceeding 20% are judged as “poor” Is displayed as “×”.

(5) Opening performance:
A test piece having a size of 150 mm × 150 mm was prepared from the packaging sheets obtained in the examples and comparative examples, and the surfaces to which the self-adhesive adhesive was adhered were stacked face-to-face to form a bag. An end portion of 30 mm in the direction was pressed with a press at 7 MPa for 10 seconds to produce an envelope-shaped sample.
The envelope-shaped sample was opened by tearing it with a bare hand, and the state of the adhesive when opened was visually confirmed to be the opening performance.
If the adhesive on the opened surface is inconspicuous and clean, it is judged as “good” and displayed as “O”, and if the adhesive on the opened surface pulls the thread, it is “slightly inferior” “△” was determined and “Δ” was displayed, and those in a state where the adhesive had already been peeled before opening were determined as “poor” and indicated as “x”.

(6) Foaming ratio (unit: times)
From the sheet obtained in the example described below, the density (Q) measured according to JIS K7222 and the density (R) in a state where the sheet measured according to JIS K7112 is not foamed are expanded. The magnification (unit: times) was determined as the foaming magnification P = R / Q.
The expansion ratio P is not a ratio of density before and after foaming of only the foamed resin layer, but is a ratio of density before and after foaming of the entire sheet.

[Example 1]
For two types and three layers through two extruders (Pura Giken Co., Ltd., vent type 65mmφ type extruder, and Ikekai Tekko Co., Ltd., tandem 115mmφ extruder) and connecting pipes attached to the tips of the respective extruders A T-die (manufactured by Pla Giken Co., Ltd.) having a surface length of 850 mm was prepared from the feed block and the distribution block (Pura Giken Co., Ltd.), and these were assembled so as to obtain a three-layer sheet.

  The combinations of raw materials and the proportions thereof were as shown in Table 1, and were uniformly mixed by a ribbon blender to obtain a dry blend product. The cylinder temperature of the two extruders was set to 190 ° C., the dry blend was melted, extruded as a three-layer unstretched sheet so as to have the sheet configuration shown in Table 1, and with a cooling roll set to 80 ° C. Quenching was performed to prepare an unstretched foam sheet in which both outer layers were foam layers and the inner layer was also a foam layer. The obtained unstretched sheet was stretched about 2.5 times in the longitudinal direction by a roll type longitudinal stretching machine, and then stretched about 2.5 times in the transverse direction by a tenter transverse stretching machine, and the thickness was 0.75 mm and the expansion ratio was 4 A 1-fold biaxially stretched foam sheet was wound up into a roll. Since the obtained sheet has the same composition of the inner and outer layers, it is a substantially single-layer sheet. The sheet was evaluated for tensile modulus and tear strength. The evaluation results are shown in Table-1.

  Next, white paint was applied to the entire surface of one side of the obtained sheet as a light-shielding treatment using a spray coating apparatus. Moreover, the adhesive-2 was apply | coated with the roll coating apparatus to the other surface whole surface of the sheet | seat, let the drying furnace pass, and it wound up in roll shape, and obtained the single layer packaging sheet. The total light transmittance and the opening performance were evaluated using the packaging sheet. The evaluation results are shown in Table 1.

  Table 1 shows the layer configuration, layer ratio, composition concentration ratio of the entire sheet, thickness, and evaluation results for the evaluation items (1) to (6) above.

[Example 2]
As shown in Table 1, a single-layer packaging sheet having a thickness of 0.71 mm and an expansion ratio of 4.1 was obtained in the same manner as in Example 1 except that the type of polystyrene and the draw ratio were changed.
Table 1 shows the evaluation results of the obtained sheets and packaging sheets.

[Example 3]
As shown in Table 1, a single-layer packaging having a thickness of 0.41 mm and a foaming ratio of 1.5 times was performed in the same manner as in Example 1 except that the raw materials and their blending ratio, the type of adhesive, and the stretching ratio were changed. A sheet was obtained.
Table 1 shows the evaluation results of the obtained sheets and packaging sheets.

[Example 4]
The outer layer forming resin is not blended with a foaming agent, the inner layer forming resin is blended with a foaming agent, and the same two extruders used in Example 1 are used. The cylinder temperature of the inner layer extruder 220 ° C., the extruder cylinder temperature for the outer layer is set to 220 ° C. and melted, extruded as a three-layer unstretched sheet in which the inner layer is foamed in the procedure of Example 1, and rapidly cooled with a cooling roll set to 80 ° C., An unstretched foam sheet was produced in which both outer layers were unfoamed layers and the inner layer was also composed of a foamed layer. The obtained unstretched sheet was stretched about 2.5 times in the longitudinal direction by a roll-type longitudinal stretching machine, and then stretched about 2.5 times in the transverse direction by a tenter lateral stretching machine. The thickness was 0.47 mm, and the foaming ratio was 1 A 7-fold biaxially stretched foam sheet was wound up in a roll shape.

As a light-shielding treatment, white paint was applied to the entire surface of one side of the obtained sheet using a spray coating apparatus. Moreover, adhesive-2 was apply | coated with the roll coating apparatus to the other surface whole surface of the sheet | seat, it let the drying furnace pass, and it wound up in roll shape, and obtained the multilayer packaging sheet.
Table 1 shows the evaluation results of the obtained sheets and packaging sheets.

[Example 5]
A multilayer packaging sheet having a thickness of 0.58 mm and a foaming ratio of 3.7 times in the same manner as in Example 4 except that the stretching ratio and the foaming ratio were changed by adjusting the stretching conditions and the temperature of the extruder in Example 4. Got.
Table 1 shows the evaluation results of the obtained sheets and packaging sheets.

[Example 6]
A multilayer packaging sheet having a thickness of 0.72 mm and an expansion ratio of 3.6 times was obtained in the same manner as in Example 4 except that the raw material composition and the stretching ratio were changed as shown in Table 1 in Example 4.
Table 1 shows the evaluation results of the obtained sheets and packaging sheets.

[Example 7]
A multilayer packaging sheet having a thickness of 0.88 mm and a foaming ratio of 3.0 was obtained in the same manner as in Example 4 except that the raw material composition and the stretching ratio were changed as shown in Table 1 in Example 4.
Table 1 shows the evaluation results of the obtained sheets and packaging sheets.

[Comparative Example 1]
In Example 1, the type and amount of the foaming agent and the draw ratio were changed as shown in Table 2, and the thickness was 0.33 mm as in Example 1 except that the polyolefin was not contained. A foam sheet having a magnification of 1.5 was wound into a roll.
As a light-shielding treatment, white paint was applied to the entire surface of one side of the obtained sheet using a spray coating apparatus. Moreover, the adhesive-2 was apply | coated with the roll coating apparatus to the other surface whole surface of the sheet | seat, let the drying furnace pass, and it wound up in roll shape, and obtained the single layer packaging sheet.
Table 2 shows the evaluation results of the obtained sheets and packaging sheets.

[Comparative Example 2]
A multilayer packaging sheet having a thickness of 0.31 mm and a foaming ratio of 1.7 times in the same manner as in Example 4 except that the type and amount of the foaming agent in the inner layer were changed and no polyolefin was contained. Got.
Table 2 shows the evaluation results of the obtained sheets and packaging sheets.

[Comparative Example 3]
In Example 2, a foamed sheet having a thickness of 1.04 mm and a foaming ratio of 2.2 times was wound into a roll in the same manner as in Example 2 except that biaxial stretching was changed to uniaxial stretching.
White paint was applied to the entire surface of one side of the obtained sheet using a spray coating apparatus as a light shielding treatment. Moreover, the adhesive-2 was apply | coated with the roll coating apparatus to the other surface whole surface of the sheet | seat, let the drying furnace pass, and it wound up in roll shape, and obtained the single layer packaging sheet.
Table 2 shows the evaluation results of the obtained sheets and packaging sheets.

In Tables 1 and 2, the numerical value in “sheet layer ratio ^{* 1} ” means the extrusion amount (mass) ratio of the resin composition of each layer in the outer layer / inner layer / outer layer, and “single layer / multilayer ^{* 2} In “”, “foam” means foaming, and “non” means non-foaming. The numerical value in “rubber component ^{* 3} ” means a rubber component (mass%) contained only in the sheet portion excluding the self-adhesive adhesive and paint.
Moreover, although not shown in particular, in the sheet | seat obtained in Example 1-7, content of the compatibilizing agent was 0 mass part with respect to 100 mass parts of total amounts of polystyrene and polyolefin.

(Results and discussion)
In contrast to Examples 1-7, Comparative Example 1 and Comparative Example 2 are foamed biaxially stretched sheets that are made only of polystyrene and do not contain polyolefin. Therefore, the tensile elastic modulus is high, and the packaging sheet is inferior in flexibility. It was. Moreover, since the closed cell ratio was high, bending workability was inferior.
Compared with Example 2, Comparative Example 3 is a difference between biaxial stretching and uniaxial stretching, but because it is uniaxial stretching, the aspect ratio of tear strength was large and the opening performance was inferior.

  On the other hand, Examples 1-7 are all foamed biaxially stretched sheets containing polystyrene and polyolefin, or the inner layer is a foamed resin layer containing polystyrene and polyolefin, and the outer layer is non-foamed containing polystyrene. Since it is a biaxially stretched sheet made of a foamed resin layer, it had buffering properties, folding workability, flexibility, water resistance, and unsealing performance necessary for a packaging sheet.

  Considering the above-mentioned examples and comparative examples together with the test results so far, from the viewpoint of imparting flexibility while ensuring buffering properties, bending workability, water resistance and opening performance, a single-layer foamed styrene system In the foamed resin layer constituting the inner layer of the resin sheet or the multilayer structure, it is preferable to blend the polyolefin in a proportion of 0.5 to 49 parts by mass with respect to 100 parts by mass of the total amount of polystyrene and polyolefin, and in particular, 1 part by mass or more Or it can be considered that it is more preferable to mix | blend in the ratio of 20 mass parts or less among them, 2 mass parts or more, or 10 mass parts or less.

Adhesive-1 used in Example 3 is an adhesive obtained by simply modifying a natural rubber-based material with MMA, and Adhesive-2 used in other examples is obtained by modifying a natural rubber-based material with MMA. It was an adhesive having a composition obtained by blending styrene butadiene rubber.
Comparing the two, the adhesive containing no styrene butadiene rubber had poor compatibility with polystyrene and produced a stringing phenomenon when it was torn and opened, whereas the adhesive containing styrene butadiene rubber was a yarn. There was no pulling phenomenon.
From the test results so far, it was found that an adhesive having a composition obtained by blending styrene butadiene rubber with a natural rubber material can be opened cleanly without causing a stringing phenomenon.

Claims (11)

  A packaging sheet comprising a foamed styrene resin sheet containing polystyrene and polyolefin and biaxially stretched.   The packaging sheet according to claim 1, wherein the closed cell ratio is 0.5 to 27%.   It is a packaging sheet in which a self-adhesive adhesive is attached to one side of the sheet, and the self-adhesive adhesive is an adhesive having a composition in which styrene butadiene rubber is blended with a natural rubber material. The packaging sheet according to claim 1 or 2, characterized in that   The packaging sheet according to any one of claims 1 to 3, wherein the content of the compatibilizer is less than 0.1 parts by mass with respect to 100 parts by mass of the total amount of polystyrene and polyolefin.   The packaging sheet according to any one of claims 1 to 4, wherein the ratio of the tear strength in the longitudinal direction and the transverse direction of the sheet is longitudinal direction: lateral direction = 1: 3 to 3: 1.   The packaging sheet according to any one of claims 1 to 5, wherein the longitudinal and lateral stretch ratios of the packaging sheet are 1.1 to 5.0 times.   The packaging sheet according to any one of claims 1 to 6, wherein the total light transmittance of the packaging sheet is 20% or less.   The packaging sheet according to any one of claims 1 to 7, comprising a single-layer foamed styrene resin sheet containing polystyrene and polyolefin and biaxially stretched.   A biaxially stretched packaging sheet comprising three or more layers including an inner layer and an outer layer, wherein the inner layer is a foamed resin layer containing polystyrene and polyolefin, and the outer layer is a non-sheet containing polystyrene. It is a foamed resin layer, The sheet | seat for packaging in any one of Claims 1-8 characterized by the above-mentioned.   In the foamed resin layer constituting the inner layer of the single layer foamed styrene resin sheet or multilayer structure, 50 to 99.5 parts by mass of polystyrene is contained with respect to 100 parts by mass of the total amount of polystyrene and polyolefin, and 0.5 to The packaging sheet according to claim 1, comprising 50 parts by mass.   The packaging sheet according to any one of claims 1 to 10, wherein the polyolefin is one or more selected from the group consisting of polyethylene, polypropylene, and ethylene vinyl acetate copolymer.