JP2003276128A - Biaxially stretched styrene resin laminated sheet - Google Patents

Abstract

(57) [Problem] To provide a biaxially stretched styrene-based resin laminated sheet excellent in transparency and capable of being deep-drawn without generating raindrops during secondary molding. SOLUTION: As both surface layers, a styrene-based copolymer (a1) obtained by copolymerizing a styrene-based monomer and an ethylenically unsaturated carboxylic acid as essential components, and a hydrogenated petroleum resin (a2 )) And a surface layer (A) containing
And a biaxially stretched styrene-based resin laminated sheet having an intermediate layer (B) containing a styrene-based resin (b1) as an intermediate layer sandwiched between these surface layers.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a biaxially stretched styrenic resin sheet, and more particularly to a deep draw molding for secondary molding without impairing the transparency of the biaxially stretched styrene resin sheet. The present invention relates to a biaxially stretched styrene resin laminated sheet capable of improving the properties and suppressing the generation of raindrops.

[0002]

2. Description of the Related Art Biaxially oriented polystyrene sheets are often used for packaging lightweight food packaging containers and other articles because of their excellent environmental hygiene, stiffness, transparency, moldability and recoverability. There is. As the secondary molding method, a sheet and a hot plate are heated by contact, and a softened sheet is pressed into a mold by pressurization from the hot plate, so-called, so-called contact heating type pressure molding method is generally used. It is used. This forming method is suitable for forming an oriented biaxially stretched sheet because a strong pressure is applied in addition to preventing orientation shrinkage by sandwiching the sheet between the outer frame and the hot plate. However, in this secondary molding method, it is difficult to control the temperature of the hot plate at the initial stage of the secondary molding or when the molding conditions are changed, the mold reproducibility deteriorates when the hot plate temperature is low, and the hot plate temperature rises too much. In addition, there was a defect that a pattern called raindrop (raindrop-like spots) was generated at an excessively heated portion due to the orientation relaxation phenomenon of the sheet.

To compensate for this drawback, Japanese Patent Laid-Open No. 2-23993
In JP-A No. 3 (1994), a biaxially stretched sheet uses a styrene-methacrylic acid copolymer as a surface layer and polystyrene as an intermediate layer, thereby expanding a moldable temperature range and, as a result, at the time of secondary molding. There is disclosed a technique for preventing the generation of raindrops due to the temperature disturbance of the hot plate.

Further, in a biaxially stretched styrene resin laminated sheet having the same layer constitution, Japanese Patent Application Laid-Open No. 11-2271
No. 23, the use of a styrene-methacrylic acid copolymer having a methacrylic acid content of 1 to 4% by weight for the surface layer and a polystyrene containing mineral oil for the intermediate layer provides excellent transparency and results in recovery. A technique that can be reused and prevents the generation of raindrops due to temperature disturbance of the hot plate during secondary molding is disclosed.

However, the biaxially stretched styrenic resin laminated sheets described in JP-A-2-239933 and JP-A-11-227123 can certainly suppress the generation of raindrops during secondary molding, but During molding, due to the heat resistance of the surface layer, the surface layer is less likely to expand than the intermediate layer.Therefore, in sheet molded products with deep drawing, the sheet surface layer cannot fully expand due to insufficient heat and cracks. And a whitening phenomenon occurs in the sheet molded product.

[0006]

The problem to be solved by the present invention is to provide a biaxially stretched styrenic resin laminate which is excellent in transparency and which enables deep drawing without generating rain drops during secondary molding. To provide a seat.

[0007]

Means for Solving the Problems The inventors of the present invention have made extensive studies to solve the above problems, and found that styrene-
In the biaxially stretched styrene resin laminated sheet using an ethylenically unsaturated carboxylic acid copolymer and a styrene resin for the intermediate layer, a styrene monomer and an ethylenically unsaturated carboxylic acid are used as the surface layer. Together with the styrene-based copolymer (a1) obtained by copolymerization as an essential component,
It has been found that the laminated sheet having the surface layer (A) containing the hydrogenated petroleum resin (a2) can prevent rain drop during secondary molding and further enables deep drawing. The invention was completed.

That is, according to the present invention, both surface layers are hydrogenated with a styrene copolymer (a1) obtained by copolymerizing a styrene monomer and an ethylenically unsaturated carboxylic acid as essential components. An intermediate layer (B) containing a styrene resin (b1) as an intermediate layer sandwiched between the surface layer (A) and the petroleum resin (a2). The present invention provides a biaxially stretched styrene resin laminated sheet characterized by having.

The present invention will be described in detail below. The surface layer (A) of the biaxially stretched styrene resin laminated sheet of the present invention is
A styrene-based copolymer (a1) obtained by copolymerizing a styrene-based monomer and an ethylenically unsaturated carboxylic acid as essential components, and a hydrogenated petroleum resin (a2) are configured as essential components. .

Here, as the styrene-based copolymer (a1), for example, an ethylenically unsaturated carboxylic acid of 0.5 to
Examples thereof include styrene-based copolymers obtained by copolymerization in the range of 15% by weight. Styrene-based copolymer (a
As the ethylenically unsaturated carboxylic acid constituting 1),
For example, acrylic acid, methacrylic acid, maleic anhydride,
Examples thereof include itaconic acid, and among them, methacrylic acid is preferable. In addition, these ethylenically unsaturated carboxylic acids,
For example, a (meth) acrylic acid alkyl ester such as methyl (meth) acrylate or stearyl (meth) acrylate may be used in combination. The styrene copolymer (a
Among 1), a styrene-methacrylic acid copolymer in which methacrylic acid is used as the ethylenically unsaturated carboxylic acid is particularly preferable from the viewpoint of heat resistance and oil resistance.

Further, the styrene-based copolymer (a1)
A biaxially stretched styrenic resin laminate that has a wide moldable temperature range, can suppress raindrops, has good deep drawability, has excellent transparency, and can collect and reuse scrap and sheet product waste. Since a sheet is obtained, a styrene-based copolymer obtained by copolymerizing with an ethylenically unsaturated carboxylic acid such as methacrylic acid in a range of 1 to 4% by weight is preferable.

The weight average molecular weight of the styrene-based copolymer (a1) is not particularly limited, but the transparency and deep drawability are good, and the moldable temperature range is further expanded. It is preferably 200,000 to 350,000, since a sheet that can suppress drop effectively can be obtained.

The hydrogenated petroleum resin (a2) used in the present invention includes petroleum unsaturated hydrocarbons such as cyclopentadiene, indene, methylstyrene,
Examples of the resin include hydrogenated petroleum resins obtained by polymerizing vinyltoluene and the like as raw materials, and resins in which polar groups such as hydroxyl groups are added. As such a hydrogenated petroleum resin (a2), for example, Alcon of Arakawa Chemical Industry Co., Ltd. or the like can be used.

The above-mentioned hydrogenated petroleum resin (a2)
Among them, heat resistance and deep drawability are good,
Since it is possible to effectively suppress the occurrence of raindrops and the whitening phenomenon of the molded product at the time of secondary molding, the softening points 110 to 150
Those having a softening point of 120 to 145 ° C. are particularly preferable.

The weight ratio (a1) / (a2) of the styrene-based copolymer (a1) and the hydrogenated petroleum resin (a2) in the surface layer (A) is such that rain drop is prevented and deep drawing is performed. Because a sheet that has both properties is obtained, 9
It is preferably 9/1 to 80/20, and particularly 9
Particularly preferably, it is 7/3 to 88/12.

Further, as the surface layer (A), the loss tangent (t
an δ) The maximum peak value temperature (Tmax) is preferably 6.5 to 25 ° C. higher than the loss tangent maximum peak value temperature measured by the dynamic viscoelasticity of the constituents of the intermediate layer (B).
It is particularly preferable that the temperature is higher by 0 to 20 ° C.

Here, the loss tangent (ta) of the dynamic viscoelasticity measurement
nδ) Maximum peak value temperature (Tmax) is a test method (JIS K-7198, A) concerning temperature dependence of dynamic viscoelasticity.
Loss tangent (tan δ) maximum peak value temperature (Tmax) measured by the method). The maximum peak value temperature (Tmax) of the constituent components of the surface layer (A) is 6.5 to 25 ° C., particularly preferably 10 ° C., higher than the maximum peak value temperature of the constituent components of the intermediate layer (B).
By increasing the temperature by -20 ° C, a sheet excellent in deep drawability can be obtained without generating raindrops while maintaining good transparency and appearance.

Next, the intermediate layer (B) of the biaxially stretched styrene resin laminated sheet of the present invention may be a resin layer containing the styrene resin (b1). Styrene resin (b
Examples of 1) include polystyrene, styrene-butadiene-styrene block copolymer, styrene-isoprene-butadiene-styrene block copolymer (SIB).
S), rubber-containing polystyrene (high-impact polystyrene, HIPS), styrene-based ionomer resin, styrene-based elastomer, and mixtures thereof.
Polystyrene is preferable because a sheet having a deep drawability and a good transparency when formed into a sheet can be obtained.

The weight average molecular weight of such a styrene resin (b1) is not particularly limited, but the loss tangent (ta) of the constituent components of the intermediate layer (B) measured by dynamic viscoelasticity (ta).
nδ) The maximum peak value temperature (Tmax) is lower than that of the surface layer (A).
It is preferably in the range of 10,000 to 400,000.

Further, as a method of adjusting the loss tangent maximum peak value temperature in the dynamic viscoelasticity measurement of the constituents of the intermediate layer (B) to be lower than that of the surface layer (A), preferably 6.5 to 25 ° C. It is not particularly limited, and examples thereof include addition of additives such as mineral oil, plasticizer, and lubricant, adjustment of molecular weight at the production stage of styrene resin, adjustment by blending styrene resins having different fluidity, and the like.

In the biaxially stretched styrenic resin laminated sheet of the present invention, a method for adjusting the loss tangent maximum peak value temperature of the dynamic viscoelasticity measurement of the constituents of the intermediate layer (B) to be lower than that of the surface layer (A) is as a method. It is particularly effective to adjust by adding mineral oil, and especially adding mineral oil to the styrene resin obtained by adjusting the molecular weight in the production stage improves the strength of the molded product while reducing the maximum peak value temperature. It is preferable because it can be held. The amount of mineral oil added is preferably in the range of 0.1 to 3 parts by weight with respect to 100 parts by weight of the styrene resin (b1).

In the biaxially stretched styrenic resin laminated sheet of the present invention, the surface layer (A) and the intermediate layer (B) have a melt flow rate of their constituents in order to improve the sheet surface condition. It is preferable that the difference in (MFR) value is within twice.

The biaxially stretched styrenic resin laminated sheet of the present invention may have a structure in which an intermediate layer (B) sandwiched between both surface layers (A) is arranged, and usually (A) layer /
Although it has a three-layer structure of layer (B) / layer (A), surface layer (A)
5 layer structure of (A) layer / (B) layer / (A ') layer / (B) layer / (A) layer, in which (A') layer having the same structure as above is added,
Layer / (B) Layer / (A ′) Layer / (B) Layer / (A ′) Layer /
A seven-layer structure of (B) layer / (A) layer may be used.

Further, the manufacturing method is not particularly limited as long as these laminates are biaxially stretched as a whole, and for example, the surface layer (A) is formed on both surfaces of the intermediate layer (B). ) May be adhered by an adhesive, but a method by hot melt coextrusion is preferable.

In this case, it is preferable that the thicknesses of the surface layers (A) on both surfaces are approximately equal to each other since a sheet which does not cause distortion in the molded product after the secondary molding can be obtained. Further, the thickness of one surface layer (A) is preferably 0.5 to 7% of the total thickness of the sheet, since a sheet having a wide moldable temperature range can be obtained.
The range of 0.5 to 2.3% is particularly preferable because a sheet having a better appearance such as a deep-drawn portion during secondary molding can be obtained. Further, the total thickness of the surface layers (A) on both surfaces is preferably in the range of 1 to 14%, and particularly preferably in the range of 1 to 4.6% because a sheet having better mold reproducibility can be obtained. Further, as described above, in the case of 5 or more layers including the (A ') layer having the same constitution as the surface layer (A), the total thickness of the (A) layer and the (A') layer is 70% of the total thickness of the sheet. The following range is preferable.

The biaxially stretched styrenic resin laminated sheet of the present invention is a slip agent, an antistatic agent, a release agent, an antifogging agent, which is commonly used for general biaxially oriented polystyrene sheets, within a range that does not impair the effects of the present invention. , A colorant, an antibacterial agent, etc. may be contained in the intermediate layer (B) or the surface layer (A), or may be coated on the surface layer (A). Among these, the slip agent and the antifogging agent are preferably used because the surface condition of the sheet can be maintained well and the effect of the present invention becomes more remarkable. Examples of the slip agent include silica and crosslinked polymer beads, and examples of the antifogging agent include glycerin fatty acid ester and sorbitan fatty acid ester.
Examples thereof include sucrose fatty acid ester. Furthermore, beauty,
In order to impart functionality and the like, printing may be performed on the front surface of the sheet, or a resin film having functionality such as barrier properties, antibacterial properties, and heat sealing properties may be laminated.

The biaxially stretched styrene resin laminated sheet of the present invention can be easily molded into a desired container, lid material, etc. by pressure molding with a die having a predetermined shape under the same conditions as the conventional biaxially stretched polystyrene sheet. Obtainable. Further, it is also possible to mold by a vacuum pressure forming method or a vacuum forming method.

[0028]

EXAMPLES The present invention will be described in detail below with reference to examples and comparative examples, but the present invention is not limited to these examples and is not intended to be limited thereto.

Each characteristic value is measured by the following method.
An evaluation was made.・ Loss tangent (tan δ) maximum peak value temperature (Tma
x): According to JIS-K7198, Method A, the mixed resin used for the surface layer (A) and the polystyrene used for the intermediate layer (B) were measured. -Softening point: The softening point of the hydrogenated petroleum resin was measured according to JIS-K5902. -Transparency: Based on JIS-K7105, the haze value of the biaxially stretched styrene-based resin laminated sheet was measured and evaluated according to the following criteria. Judgment criteria ○: Less than 3%, △: 3 to 5%, ×: 5% or more

Secondary moldability: A biaxially stretched styrene resin laminated sheet was molded using the following molding machine and mold, and the occurrence of rain drops and the occurrence of whitening were evaluated. Mold 1 was used for the evaluation of rain drop generation, and mold 2 was used for the whitening evaluation. Molding machine: Contact heating type pneumatic molding machine (manufactured by Kansai Automatic Molding Machine Co., Ltd.) Heating time: 3 seconds Molding pressure: 0.4 MPa Molding temperature: 130 ° C Rain drop evaluation mold 1: Length x width x depth = 180 x 80 × 8 mm box-shaped mold Judgment criteria Visually check for rain drops. Without rain drop: ○, With rain drop: × Whitening evaluation mold 2: Vertical × horizontal × depth = 78 × 8 × 8 mm box-shaped mold Criteria Criteria visually confirmed occurrence of whitening. No whitening: ○, Whitening: ×

Examples 1 to 4 Styrene-methacrylic acid copolymer (SMAA) obtained by using methacrylic acid in a content of 3% by weight, and hydrogenated petroleum resin having a softening point shown in Table 1. As the surface layer (A), and the loss tangent (tan δ) maximum peak value temperature (Tmax) of the mixed resin for the surface layer (A).
15 ° C lower polystyrene (PS) for the intermediate layer (B), one for both surface layer (A) extruder (caliber 30 mm) and one intermediate layer (B) extruder (caliber 50 mm) Supply to each, melt-knead, surface layer (A) / intermediate layer (B) /
After stacking so that the thickness ratio of the surface layer (A) is 0.8 / 98.4 / 0.8, it is melt extruded into a sheet form from a T die and cooled by a cooling roll at 90 ° C. The film was longitudinally stretched 2.5 times by stretching and then transversely stretched 2.5 times by a tenter, and both ends were cut to a thickness of 0.
A 3 mm biaxially stretched sheet, cooled by a cooling device in which two cooling rolls and an air knife are combined, and the surface layer (A) is made of a styrene-methacrylic acid copolymer, and the intermediate layer is made of polystyrene. A biaxially stretched styrene resin laminated sheet having a layer structure was obtained.

Using the obtained biaxially stretched styrene resin laminated sheet, the transparency, secondary moldability and whitening were evaluated. All were excellent in transparency and were free from raindrops and whitening. It was The results are shown in Table 1.

Comparative Example 1 For the surface layer (A), methacrylic acid was used at a content of 3% by weight instead of the mixed resin of styrene-methacrylic acid copolymer (SMAA) and hydrogenated petroleum resin. A biaxially stretched styrene-based resin laminated sheet having a two-kind three-layer structure was obtained in the same manner as in Example 1 except that only the styrene-methacrylic acid copolymer (SMAA) obtained as described above was used.

Using the obtained biaxially stretched styrene resin laminated sheet, the transparency, secondary moldability and whitening were evaluated. All were excellent in transparency and were free from raindrops. , Whitening occurred. The results are shown in Table 1.

[0035]

[0036]

INDUSTRIAL APPLICABILITY The biaxially stretched styrene resin sheet of the present invention has excellent transparency and is capable of deep drawing without causing raindrops during secondary molding.

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Claims (8)

[Claims] 1. A styrene-based copolymer (a1) obtained by copolymerizing a styrene-based monomer and an ethylenically unsaturated carboxylic acid as essential components for both surface layers, and a hydrogenated petroleum resin ( a2) and a surface layer (A) containing
And a biaxially stretched styrene-based resin laminated sheet having an intermediate layer (B) containing a styrene-based resin (b1) as an intermediate layer sandwiched between these surface layers. 2. Loss tangent (tan δ) maximum peak value temperature (Tmax) measured by dynamic viscoelasticity of surface layer (A) constituents
Is higher than the loss tangent maximum peak value temperature measured by dynamic viscoelasticity of the constituent components of the intermediate layer (B) by 6.5 to 25 ° C., the biaxially stretched styrene resin laminated sheet according to claim 1. 3. The biaxially stretched styrene resin laminated sheet according to claim 2, wherein the softening point of the hydrogenated petroleum resin (a2) is 110 to 150 ° C. 4. The weight ratio (a1 / a2) of the styrene copolymer (a1) and the hydrogenated petroleum resin (a2) is 9
The biaxially stretched styrenic resin laminated sheet according to claim 3, which is 9/1 to 80/20. 5. The styrene-based copolymer (a1) is a styrene-based copolymer obtained by copolymerization using an ethylenically unsaturated carboxylic acid in the range of 1 to 4% by weight. Biaxially stretched styrene resin laminated sheet of. 6. The surface layer (A) is a resin layer composed of a styrene-methacrylic acid copolymer and a hydrogenated petroleum resin (a2), and the intermediate layer (B) is a resin layer containing polystyrene. The biaxially stretched styrene resin laminated sheet according to any one of claims 1 to 5. 7. The biaxially stretched styrene resin laminated sheet according to claim 6, wherein the intermediate layer (B) is a resin layer containing polystyrene and mineral oil. 8. The total thickness of the laminated sheet is 100 to 500 μm.
And the thickness of one surface layer (A) constituting both surfaces is within the range of 0.5 to 7% with respect to the total thickness of the laminated sheet. The biaxially stretched styrene-based resin laminated sheet according to item 1.