JP2000281809A - Bi-axially stretched styrene-based resin sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a bi-axially stretched styrene-based resin sheet excellent in transparency and peeling property, and having a good appearance. SOLUTION: This bi-axially stretched styrene-based resin sheet consists of a resin composition containing a styrene resin and 50-500 ppm spherical synthesized silicon dioxide having 1-15 μm volume-average particle diameter (d50 value) and <=2.0 particle diameter distribution (d90/d10 value).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a biaxially stretched styrene-based resin sheet which has a low pressure increase due to clogging of a screen mesh in an extruder and the frequency of mesh replacement is small, thereby improving extrusion stability and productivity.

[0002]

2. Description of the Related Art Biaxially stretched styrene resin sheets are widely used in the field of food packaging because of their transparency and stiffness. But,
The biaxially stretched sheet is formed into a container, and when a food or the like is filled in a container in which a large number of containers are stacked, there has been a problem that the peelability between the containers is poor and the work efficiency is reduced. for that reason,
Conventionally, silicone oil has been applied to one side of a sheet as a release agent. Also, the container is filled with hot food, or after filling the food, store it in the refrigerator,
There has been a problem that water droplets adhere to the surface of the container and significantly reduce the commercial value of the container. For this purpose, a surfactant such as sucrose fatty acid ester or polyglycerin fatty acid ester is applied as an antifogging agent. However, the sheet coated with these coating agents is shipped as a product after being wound on a roll, so the core is pressed from the periphery, especially at the core, and is applied to both sides of the sheet. There is a problem in that the transfer to the sheet on the opposite side where the agent and the release agent are in contact causes the sheet appearance to deteriorate and the antifogging property to decrease.

As a method for solving this problem, when a synthetic rubber is added to a styrenic resin and biaxially stretched,
Improving appearance defects due to sheet blocking by projecting the rubber on the sheet surface (Japanese Patent Publication No. 57-2013)
5 gazette). However, when synthetic rubber is biaxially stretched, it is necessary to add a large amount of rubber in order for the rubber to be flat and exhibit a sufficient blocking effect,
Transparency may decrease.

In addition, when a synthetic silicon dioxide is added to a styrene resin and the sheet is biaxially stretched, the silicon dioxide is projected on the sheet surface to improve the uniform application property of the silicon oil (Japanese Patent Publication No. Hei 6 (1994)). Japanese Unexamined Patent Publication No. 6-855) discloses that a styrene-grafted diene rubber is added to improve the uniform application property of silicone oil. However, the general amorphous silicon dioxide used in these prior arts having an irregular shape, when present in the molten resin of an extruder, forms secondary aggregates by hydrogen bonding due to hydroxyl groups on the surface of the silicon dioxide fine particles. However, it has been pointed out that the pressure increases due to clogging of the screen mesh and the frequency of replacing the mesh increases, thereby reducing productivity.

Further, synthetic silicon dioxide having a small particle size does not exhibit a sufficient anti-blocking effect, and synthetic silicon dioxide having a very large particle size damages the surface of the sheet when transported in a sheet roll state, and has an adverse effect on appearance. This causes a problem that foreign matter is seen on the upper surface. In addition, it has been pointed out that if these synthetic silicon dioxides having different particle diameters are mixed and the particle diameter distribution is widened, a great defect in sheet quality is caused.

[0006] In order to solve such a problem, the present invention uses a spherical synthetic silicon dioxide having an optimized volume average particle size and particle size distribution, thereby increasing pressure due to clogging of a screen mesh in an extruder and the frequency of mesh replacement. Low extrusion, good extrusion stability and productivity, excellent sheet transparency and releasability, decrease in antifogging property due to transfer of antifogging agent to the opposite sheet due to blocking, damage during sheet roll transport It is intended to improve.

[0007]

According to the present invention, there is provided a styrenic resin having a volume average particle diameter (d50 value) of 1 to 15 μm,
Provided is a biaxially stretched styrene resin sheet comprising a resin composition containing 50 to 500 ppm of spherical synthetic silicon dioxide having a particle size distribution (d90 / d10 value) of 2.0 or less.
The ppm indicating the content of the spherical synthetic silicon dioxide is on a weight basis.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION The spherical synthetic silicon dioxide used in the present invention is synthesized by the reaction of sodium silicate and an acid, and is spherical to prevent secondary aggregation.

The volume average particle diameter (d50 value) is from 1 to 15
μm, preferably 2 to 10 μm. Volume average particle size is 1μ
When it is not less than m, a sufficient anti-blocking effect can be exhibited, and when it is not more than 15 μm, it is possible to prevent the appearance of the sheet from being impaired or to prevent the sheet surface from being damaged during transport of the sheet roll.

The particle size distribution (d90 / d10 value) is as follows:
0 or less, preferably 1.85 or less. When the particle size distribution is 2.0 or less, a sufficient anti-blocking effect is exhibited, and furthermore, it is possible to prevent the appearance of the sheet from being impaired and to prevent the sheet surface from being damaged during transport of the sheet roll.

The volume average particle diameter (d50) and particle diameter distribution (d90 / d10 value) of the spherical synthetic silicon dioxide are as follows:
The evaluation was performed by a laser diffraction particle size distribution measuring method. d50
Is a volume average particle diameter corresponding to a cumulative product value of 50% in the cumulative frequency distribution, d90 is a volume average particle diameter corresponding to a cumulative product value of 90% in the cumulative frequency distribution,
d10 is a volume average particle diameter corresponding to a cumulative product value of 10% in the cumulative frequency distribution.

The content of the spherical synthetic silicon dioxide in the resin composition is 50 to 500 ppm, preferably 100 to 30 ppm.
It is 0 ppm. When it is 50 ppm or more, a sufficient antiblocking effect is exhibited, and when it is 500 ppm or less, the transparency of the sheet is not impaired.

The styrene resin used in the present invention includes styrene, alkylstyrene (o-, m- and p-methylstyrene, p-ethylstyrene, p-isopropylstyrene, butylstyrene, pt-butylstyrene, etc.), α
-Alkylstyrene (α-methylstyrene, α-ethylstyrene, etc.), halostyrene (, o-, m- and p-chlorostyrene, bromostyrene, fluorostyrene, etc.), di-, tri-, tetra- and pentahalo-substituted styrene , Β-halo-substituted styrene (α-bromostyrene, β
-Chlorostyrene, β-bromostyrene, etc.) or a homopolymer or copolymer of a styrene monomer selected from the group or a mixture thereof. In addition, copolymerization of these styrene monomers with copolymerizable monomers, that is, acrylonitrile, alkyl (meth) acrylates such as (meth) acrylic acid, maleic acid or maleimide anhydride maleimide, and the like. It may be a combination or a mixture thereof.

A styrene-butadiene copolymer containing 60 to 85% by weight of a styrene monomer as a raw material can be added to the styrene resin. The amount of the styrene-butadiene copolymer to be added is preferably 0.1 to 1.5% by weight, more preferably 0.5 to 1.0% by weight in terms of butadiene as a raw material. Butadiene concentration of 0.
When the content is 1% by weight or more, it is possible to prevent cracks and powder from being generated when the sheet is punched, and to prevent a fitting portion of a container formed from the sheet from cracking. When the content is 1.5% by weight or less, the rigidity and transparency of the container obtained from the sheet are not impaired.

In order to improve the moldability of the biaxially stretched styrene resin sheet, the resin composition is preferably used in an amount of 0.05%.
To 2.0% by weight, more preferably 0.2 to 1.0% by weight
Plasticizers such as mineral oil may be added in the range described above.

In the resin composition, various stabilizers, ultraviolet absorbers, phosphorus-based, sulfur-based or hindered phenol may be used as long as the transparency, strength, moldability and the like of the biaxially stretched styrene-based resin sheet are not impaired. Contains antioxidants, fillers such as calcium phosphate, barium sulfate, talc, zeolite and divinylbenzene cross-linked beads, coloring agents, lubricants such as fatty acid esters, antistatic agents, styrene-butadiene block copolymer, and other additives. May be.

The biaxially oriented styrene resin sheet of the present invention is prepared by placing a screen mesh having a mesh structure of 200/400/200 mesh in a single screw extruder at 220 ° C.
After extrusion molding from a T-die, a method of stretching can be applied.

The stretching method is, for example, stretching at a stretching temperature of 110 to 135 ° C. in a biaxial direction (MD direction and TD direction) by 1.5 to 5.0 times, respectively. When the stretching ratio is 1.5 times or more, the toughness of the sheet is improved, and when the stretching ratio is 5.0 times or less, even when the container is formed by the vacuum forming method and / or the pressure forming method, the sheet thickness is uneven. Never happen. Stretching is desirably performed almost uniformly in the range of 2.0 to 3.0 times in each of the biaxial directions.

The biaxially stretched styrene resin sheet of the present invention has a shrinkage stress measured in accordance with ASTM D-1504 of preferably 1 to 10 kg / cm ² , more preferably 3 to 7 kg / cm ² . Shrinkage stress is 1kg / cm ²
In the above case, sufficient impact strength and bending strength can be obtained, and 1
When it is 0 kg / cm ² or less, the moldability is not impaired.

In the biaxially stretched styrene resin sheet of the present invention, the total amount of volatile components in the sheet is preferably less than 0.4% by weight, more preferably less than 0.2% by weight. Volatile components are unreacted styrene-based monomers, dimers, trimers, and other solvents used in the polymerization reaction, such as toluene, xylene, and ethylbenzene, and can be measured by gas chromatography. . When the total amount of volatile components in the resin composition is less than 0.4% by weight,
Volatile components are prevented from floating on the sheet surface and unevenly distributed in an oil film form, thereby reducing the commercial value of the sheet.

The biaxially stretched styrenic resin sheet of the present invention can be subjected to a corona discharge treatment at 40 to 60 dyne / cm.
After adjusting the surface tension, a releasing agent such as a silicone oil emulsion can be applied to both surfaces uniformly by using a releasing agent alone and in combination with an antifogging agent and an antistatic agent. Further, a release agent may be applied on one side and an antifogging agent may be applied on the other side. The coating amount of the release surface and the antifogging surface was 10 to 150 mg / m ² , respectively.
Is preferable.

[0022]

EXAMPLES The present invention will be described in more detail with reference to the following Examples, but it should not be construed that the invention is limited thereto. Each measurement method described below is as follows.

(1) Easiness of clogging in a mesh Using a single-screw extruder with a mesh configuration of 200/400/200 mesh and a protrusion amount of 5 kg / hour, a resin to which a predetermined amount of synthetic silicon dioxide has been added is heated to 220 ° C. 5kg
Extrusion, pressure increase and clogging of the mesh were confirmed. ：: Pressure rise, clogging of mesh. ×: No increase in pressure and no clogging of the mesh.

(2) Peelability A sheet-shaped single-pressure air forming machine (manufactured by Asano Laboratories) is used to form a cup-shaped container (opening diameter 90 × bottom diameter 60 × depth 50 m).
m) were obtained, and twenty of them were stacked with their openings facing down.
The height when a load of 2 kg was placed on the stacked cup-shaped containers was defined as [A], and the height when the load was removed was defined as [B], and the recovery rate was calculated as follows. Recovery rate = {([B]-[A]) / [A]} × 100 ：: Recovery rate of 30% or more. ：: Recovery rate of less than 20 to 30%. Δ: Recovery rate of less than 10 to 20%. X: Recovery rate of less than 10%.

(3) Transparency The haze of the outermost surface portion of the sheet roll was measured using a haze measuring machine with a suga tester (sheet thickness 180 μm).
Criteria). A: 0.5% or less. ：: more than 0.5 to 1.0%. Δ: More than 1.0 to 1.5%. X: More than 1.5%.

(4) Anti-fogging property The sheet of the core portion is cut into a size of 100 × 150 mm.
The sheet was adhered to the opening of a transparent acrylic container containing hot water, and the state of water droplets attached to the sheet was visually evaluated. ：: Water droplets formed a uniform liquid film, and the contents were clearly visible. ：: Water droplets form a substantially uniform liquid film, and the contents are relatively visible. Δ: Water droplets became uneven, and the contents were slightly hard to see. ×: Water droplets were uneven and the contents were not visible at all.

Examples 1 to 3 Synthetic silicon dioxide having the properties shown in Table 1 was prepared using a styrene resin (Daicel Styrol # 31, Daicel Chemical Industries, Ltd.).
And extruded into a sheet. Next, the film is stretched 2.5 times in the MD and TD directions at a stretching temperature of 125 ° C., and corona discharge treatment is performed on both surfaces at 60 dyne / cm. A sucrose fatty acid ester was applied as a clouding agent to a dry weight of 30 mg / m ² . Then 1
It was dried at 00 ° C. and wound up on a roll to obtain a biaxially stretched styrene resin sheet having a thickness of 180 μm. The shrinkage stress of this sheet was 5 kg / cm ² .

Example 4 Using the resin compositions shown in Table 1, a biaxially stretched styrene resin sheet having a thickness of 180 μm was obtained in the same manner as in Examples 1 to 3. The shrinkage stress of this sheet was 5 kg / cm ² . The styrene-butadiene copolymer used had a styrene content of 76% by weight.

Example 5 A biaxially oriented styrene resin sheet having a thickness of 180 μm was obtained in the same manner as in Example 4 using the resin compositions shown in Table 1. The shrinkage stress of this sheet was 5 kg / cm ² .

Comparative Examples 1 to 5 Using the resin compositions shown in Table 1, the same procedures as in Examples 1 to 3 were carried out.
A 180 μm thick biaxially stretched coated sheet was obtained. The shrinkage stress of this sheet was 5 kg / cm ² .

[0031]

[Table 1]

[0032]

The biaxially stretched styrene resin sheet of the present invention uses a spherical synthetic silicon dioxide having an optimized volume average particle size and particle size distribution to reduce pressure increase due to clogging of a screen mesh in an extruder. The frequency of mesh replacement is low, and extrusion stability and productivity are good. Further, the sheet was excellent in transparency and releasability, and the appearance defect due to blocking, the decrease in antifogging property due to the movement of an antifogging agent or the like to the opposite sheet, and the occurrence of scratches during transportation were also improved.

Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat II (reference) // B29K 25:00 B29L 7:00 F term (reference) 4F071 AA22 AB26 AD02 AD06 AE22 AH04 BB06 BB08 BC01 4F210 AA13 AA47 AB17 AE01 AG01 AG03 QC05 QG01 QG18 QW17 QW50 4J002 BC021 BC031 BC052 BC061 BC071 DJ016 FA086 FD016 FD206 GG00

Claims (2)

[Claims] A styrene resin and a volume average particle diameter (d)
50 value) is 1 to 15 μm and the particle size distribution (d90 / d1)
0 value) is 50 to 50, which is 2.0 or less.
A biaxially stretched styrene resin sheet comprising a resin composition containing 0 ppm. 2. A styrene-butadiene copolymer containing 60 to 85% by weight of styrene, having a butadiene concentration of 0.1 to 0.1%.
The biaxially stretched styrene resin sheet according to claim 1, which contains 1.5% by weight.