JP6980588B2 - Biaxially stretched polypropylene laminated sheet and molded body - Google Patents

Description

The present invention relates to a sheet obtained by biaxially stretching a propylene resin laminate and a molded body obtained by thermoforming the sheet.

A packaging container in which a sheet is thermoformed by a method such as vacuum compressed air molding is used for accommodating various foods. Biaxially stretched polystyrene sheets and amorphous polyethylene terephthalate sheets are used for this sheet from the viewpoints of rigidity, transparency, thermoformability and the like, and in recent years, the use of polypropylene sheets has also been studied.

Generally, polypropylene is inferior in transparency and rigidity to polystyrene and polyethylene terephthalate. However, since the transparency and rigidity are improved by the stretching process, it is an effective means to use a biaxially stretched polypropylene sheet as a sheet for thermoforming.

Regardless of whether it is stretched or unstretched, the crystalline polypropylene sheet has a narrower thermoforming processing temperature range than the amorphous biaxially stretched polystyrene sheet and the amorphous polyethylene terephthalate sheet. Since the thermoformable temperature of a crystalline polypropylene sheet is in a limited and narrow range near the melting point of polypropylene, a slight underheating causes insufficient mold reproduction, or even a slight overheating causes a sharp decrease in extensional viscosity. The tearing and charring of the sheet surface occur. Especially in the production method for mass production such as vacuum pressure forming, there is a certain limit to uniformly and uniformly heat the sheet, so expanding the thermoforming temperature range of the polypropylene sheet itself is stable production. It is a problem to be solved in order to secure the sex.

The following Patent Document 1 describes a biaxially stretched polypropylene sheet for thermoforming made of a propylene-based resin produced by a metallocene catalyst. It is described that the transparency can be improved and the thermoforming temperature range of the sheet can be widened by appropriately blending a propylene resin having a low melting point. However, when a propylene-based resin having a low melting point by copolymerizing an α-olefin such as ethylene or reducing the stereoregularity is blended in the entire sheet, the rigidity of the sheet and the thermoformed product thermoformed from the sheet are obtained. Is significantly reduced.

Japanese Unexamined Patent Publication No. 2006-328300

An object of the present invention is to provide a biaxially stretched polypropylene laminated sheet having excellent rigidity and transparency and a wide thermoforming temperature range, and a molded body obtained by thermoforming the sheet.

The biaxially stretched polypropylene laminated sheet according to the present invention includes a main layer and surface layers located on both sides of the main layer, and the melting point of the surface layer is 165 ° C. or higher, and the melting point of the main layer is higher than the melting point of the surface layer. It is low, the melting point difference between the surface layer and the main layer is 3 ° C. or more and 9 ° C. or less, the total thickness of the sheet is 100 μm or more and 500 μm or less, and the ratio of the thickness of one side of the surface layer to the total thickness of the sheet is 3% or more and 18% or less. The ratio of the total thickness of the surface layer to the total thickness of the sheet is 6% or more and 28% or less, and the haze is 2.5% or less.

In particular, the surface layer contains a nucleating agent of 800 ppm or more and 1900 ppm or less, the main layer contains no nucleating agent or contains a nucleating agent of 800 ppm or less, and the Mw / Mn of the main layer is 7 or more and 14 or less. Is preferable.

Further, it is preferable that the thickness / thinness accuracy is 12% or less and the tensile elastic modulus is 1800 MPa or more.

Further, the molded body according to the present invention is a thermoformed sheet of these sheets.

The biaxially stretched polypropylene laminated sheet according to the present invention is excellent in rigidity and transparency, and can be thermoformed in a wide range of processing temperatures.

FIG. 3 is a partially enlarged cross-sectional view of a biaxially stretched polypropylene laminated sheet according to an embodiment of the present invention.

Hereinafter, a biaxially stretched polypropylene laminated sheet (hereinafter, simply referred to as a sheet) according to an embodiment of the present invention and a molded product using the same will be described. FIG. 1 shows a cross-sectional view of a main part of the sheet in the present embodiment. The sheet includes a main layer 1 and a first surface layer 2a and a second surface layer 2b located on the front and back sides of the main layer 1, respectively. The first and second surface layers 2a and 2b are collectively referred to as surface layers 2a and 2b without particular distinction. The main layer 1 may be a single layer or a multilayer.

The surface layers 2a and 2b are made of a propylene-based resin having a melting point of 165 ° C. or higher. The main layer 1 is made of a propylene-based resin having a melting point of 3 ° C. to 9 ° C. lower than that of the surface layers 2a and 2b. The thickness / thinness accuracy of the sheet is preferably 12% or less. The tensile elastic modulus of the sheet is preferably 1800 MPa or more. The haze of the sheet is preferably 2.5% or less. The image sharpness of the sheet by the transmission method is preferably 60% or more. The range of the moldable temperature at the time of thermoforming the sheet is preferably 8 ° C. or higher.

The propylene-based resin constituting the surface layers 2a and 2b may have a melting point of 165 ° C. or higher, and includes a propylene homopolymer, a random copolymer of propylene and an α-olefin, and the like. Here, as the α-olefin, ethylene, butene-1, penten-1, hexene-1, octene-1, 4-methyl-pentene-1, and the like can be used. Of these, the propylene homopolymer is most preferable. If the melting points of the surface layers 2a and 2b are lower than 165 ° C., the melting point of polypropylene constituting the main layer 1 is lowered, and at the same time, the rigidity of the entire sheet is lowered, which is not preferable.

The propylene-based resin constituting the main layer 1 preferably has a melting point lower than that of the propylene-based resins constituting the surface layers 2a and 2b by 3 ° C. to 9 ° C., and a propylene homopolymer, a propylene-α-olefin copolymer, or the like is preferable. included. Here, as the α-olefin, ethylene, butene-1, pentene-1, hexene-1, octene-1, 4-methyl-pentene-1, and the like can be used. Of these, a propylene-α-olefin copolymer is preferable, and a random copolymer with ethylene is most preferable.

<Melting point difference>
The melting point difference between the surface layers 2a and 2b and the main layer 1 is preferably 3 ° C to 9 ° C. If the melting point difference between the surface layers 2a and 2b and the main layer 1 exceeds this range, the thickness and thinness accuracy of the sheet during biaxial stretching is lowered. When the thickness / thinness accuracy is lowered, in the processing temperature range on the low temperature side in thermoforming, partial mold reproduction is insufficient in the thick part, and extremely thin wall is likely to occur in the thin part, and as a result, the moldable temperature of the sheet is likely to occur. It tends to narrow the range. On the contrary, even when the melting point difference is smaller than the above range, the melting point of the main layer 1 does not change from the melting points of the high melting points surface layers 2a and 2b, so that the moldable temperature range on the low temperature side in thermoforming is narrowed. Prone.

<MFR>
The polypropylene MFR used for the surface layers 2a and 2b is 1 to 30 g / 10 minutes, preferably 2 to 20 g / 10 minutes, and the polypropylene MFR used for the main layer 1 is 1 to 15 g / 10 minutes, 2 to 10 g / min. 10 minutes is preferable. When the MFR is within the above range, the processability when the laminate before stretching is extruded is excellent.

<Ethylene content>
When ethylene is copolymerized, the ethylene content is 1.0% by weight or less, preferably 0.1 to 0.6% by weight or less. When the ethylene content is in this range, transparency and rigidity are well balanced.

<Mw / Mn>
The Mw / Mn of polypropylene constituting the main layer 1 is preferably 7 or more and 14 or less. If the Mw / Mn of polypropylene constituting the main layer 1 is less than 7, the thickness / thinness accuracy at the time of biaxial stretching tends to decrease, and as a result, the thermoforming temperature range of the sheet tends to be narrowed.

<Nuclear agent>
The surface layers 2a and 2b preferably contain a crystal nucleating agent. The content of the nucleating agent in the surface layers 2a and 2b is preferably 800 ppm to 1900 ppm. When the amount of the nucleating agent contained in the surface layers 2a and 2b is less than 800 ppm, the haze value increases and the image sharpness of the sheet decreases. When the amount of the nucleating agent contained in the surface layers 2a and 2b exceeds 1900 ppm, the crystallization speed of the surface layers 2a and 2b increases, and the thickness and thinness accuracy at the time of biaxial stretching tends to decrease. As a result, the thermoformed temperature range of the sheet tends to be narrowed.

It is preferable that the main layer 1 does not contain a nucleating agent. Alternatively, even if the main layer 1 contains a nucleating agent, its content is preferably 800 ppm or less. When the amount of the nucleating agent contained in the main layer 1 exceeds 800 ppm, the crystallization speed of the main layer 1 increases, which tends to cause a decrease in thickness and thinning accuracy during biaxial stretching. As a result, the thermoformed temperature range of the sheet tends to be narrowed.

The crystal nucleating agent is preferably selected from nonitol-based nucleating agents, sorbitol-based nucleating agents, phosphate ester-based nucleating agents, triaminobenzene derivative nucleating agents, carboxylic acid metal salt nucleating agents, and xylitol-based nucleating agents. In particular, in order to maintain transparency after thermoforming, it is more preferable to use a nonitol-based nucleating agent or a sorbitol-based nucleating agent. In addition, these crystal nucleating agents can be used alone or in combination of two or more.

The sheet may contain other additives other than the crystal nucleating agent. Examples of other additives include antioxidants, neutralizers, chlorine absorbers, heat stabilizers, light stabilizers, UV absorbers, internal lubricants, external lubricants, antiblocking agents, antistatic agents, antifogging agents. , Flame retardants, dispersants, copper damage inhibitors, plasticizers, crosslinkers, peroxides, oil spreads and other conventional additives commonly used for polyolefins such as organic and inorganic pigments.

An antistatic agent, an anti-fog agent, a lubricant, or the like can be applied to the surface of the sheet. Here, as the anti-fog agent, sucrose fatty acid ester, polyglycerin fatty acid ester, water-soluble polymer and the like can be used, and as the lubricant, silicone oil and the like can be used.

<Thickness>
The total thickness T of the sheet is preferably 100 to 500 μm, particularly preferably 130 to 350 μm. Considering the practical rigidity of the molded product, 100 μm is appropriate as the lower limit of the total thickness T of the sheet. If a sheet having a total thickness T of more than 500 μm is to be obtained, the chuck holding the sheet in between is likely to come off during biaxial stretching, and biaxial stretching is likely to be impossible.

The ratio of the thickness on one side of the surface layers 2a and 2b to the total thickness T of the sheet is preferably 3% to 18%. The ratio of the thickness of one side of the surface layers 2a and 2b to the total thickness T of the sheet is the ratio of the thickness T2a of the first surface layer 2a to the total thickness T of the sheet and the thickness T2b of the second surface layer 2a to the total thickness T of the sheet. Is the ratio of. When the one-sided thickness of the surface layers 2a and 2b having a high melting point is less than 3%, that is, the ratio of the thickness T2a of the first surface layer 2a to the total thickness T of the sheet and the thickness of the second surface layer 2a to the total thickness T of the sheet. If one of the ratios of T2b is less than 3%, the surface of the sheet is likely to be charred during thermoforming, and as a result, the moldable temperature range on the high temperature side is narrowed. On the contrary, if the thickness of one side of the surface layers 2a and 2b having a high melting point exceeds 18%, the moldable temperature range on the low temperature side is narrowed.

The ratio of the total thickness (T2a + T2b) of both surface layers 2a and 2b to the total thickness T of the sheet is preferably 6% to 28%. The lower limit of 6% or more depends on the above-mentioned one-sided thickness of 3% or more. When the total thickness of the surface layers 2a and 2b having a high melting point exceeds 28%, the thermoforming temperature range on the low temperature side is narrowed. Further, as the composition ratio of the polypropylene layer having a high melting point increases, the thickness / thinness accuracy at the time of biaxial stretching decreases, which is not preferable.

<Stretching ratio>
The stretch ratio of the sheet is preferably 3 to 6 times in both vertical and horizontal directions. If the draw ratio is less than 3 times, the effect of improving the rigidity by the stretching process is not sufficient, and if the draw ratio exceeds 6 times, thermoforming becomes difficult.

<Evaluation method>
<Melting point measured by differential scanning calorimeter (DSC)>
After weighing a 3.0 mg sample, it is sealed in an aluminum pan, and the temperature is raised to 210 ° C. in a nitrogen stream supplied at 20 ml / min with a differential scanning calorimeter (model: DSC-60, manufactured by Shimadzu Corporation). It is held at this temperature for 3 minutes and then cooled to 30 ° C. at a cooling rate of 10 ° C./min. Next, the peak temperature showing the maximum endothermic process in the endothermic curve obtained when the temperature was raised to 210 ° C. at a heating rate of 10 ° C./min was defined as the melting point.

<Melt flow rate (MFR)>
The melt flow rate of the raw material propylene resin was measured according to JIS K7210 under the conditions of a temperature of 230 ° C. and a load of 21.18 N.

<Ethylene content in copolymer>
The ethylene content in the copolymer was 13C using JNM LA-400 (13C resonance frequency 100MHz) manufactured by JEOL Ltd. for the sample dissolved in the mixed solvent of 1,2,4-trichlorobenzene / dehydrogenated benzene. -Calculated from the values measured by the NMR method.

<Molecular weight distribution (Mw / Mn)>
The molecular weight distribution (Mw / Mn) of the polymer or copolymer is a value obtained by measuring the weight average molecular weight (Mw) and the number average molecular weight (Mn) by gel permeation chromatography and calculating Mw / Mn. .. PL GPC220 manufactured by Polymer Laboratories is used as an apparatus, 1,2,4-trichlorobenzene containing an antioxidant is used as a mobile phase, and Showa Denko UT-G (1) and UT-807 (1) are used as columns. ), UT-806M (2 pieces) connected in series, and a differential refractometer was used as a detector. The same solvent as the mobile phase was used as the solvent for the sample solution of the polypropylene composition, and the sample was dissolved at a sample concentration of 1 mg / mL for 2 hours while shaking at a temperature of 150 ° C. to prepare a measurement sample. 500 μL of the sample solution thus obtained was injected into the column, and measurements were taken at a flow rate of 1.0 mL / min, a temperature of 145 ° C., and a data acquisition interval of 1 second. A polystyrene standard sample (Shodex STANDARD, manufactured by Showa Denko KK) having a molecular weight of 580 to 7.45 million was used for column calibration, and a cubic approximation was used. The coefficients of Mark-Houkins are K = 1.21 × 10-4, α = 0.707 for polystyrene standard samples, and K = 1.37 × 10-4, α = 0. For propylene-based polymers. 75 was used.

<Sheet thickness and thickness accuracy>
For the thickness and thickness / thickness accuracy of the sheet, 200 points were measured at a pitch of 1 mm in the width direction of the sheet using a continuous thickness meter (TOF-4R05 manufactured by Yamabun Electric Co., Ltd.), and 10 sheets were measured at intervals of 20 mm in the flow direction. The average thickness A (μm) and the standard deviation σ (μm) were obtained when the minute measurement was performed, and the values obtained by the following equation were used.
Thickness / thinness accuracy [%] = (2σ / A) × 100
The smaller the thickness / thinness accuracy value, the smaller the thickness unevenness, and in the case of a stretched sheet, it means that the uniform stretchability is excellent.

<Tension modulus>
The tensile elastic modulus of the sheet was measured according to JIS K7161-1 at a tensile speed of 1 mm / min in an atmosphere at room temperature of 23 ° C.

<Image sharpness by transmission method>
The image sharpness at a comb width of 1.0 mm by the sheet transmission method was measured according to JIS K 7374. The larger the image sharpness value, the less cloudiness and the better the transparency.

<Haze>
The haze of the sheet was measured with a haze meter (model: NDH4000, manufactured by Nippon Denshoku) in accordance with JIS K 7136. The haze of the thermoformed body was measured in the same manner.

Hereinafter, examples of the present invention will be described in detail, but the present invention is not limited to the following description examples.

<Raw materials used>
Table 1 shows a list of the raw materials used.

<Preparation of test sheet>
[Examples 1 to 7, Comparative Examples 1 to 11]
A test sheet was prepared as follows. First, using the above-mentioned polypropylene material, the sheets having the layer structure shown in Tables 2 to 4 were produced as follows using a multilayer sheet molding machine (manufactured by Plastic Engineering Laboratory Co., Ltd.). Examples 1 to 7 are shown in Table 2, and Comparative Examples 1 to 11 are shown in Tables 3 and 4.

As the processing conditions, the melting temperature and the die temperature of the extruder were set to 230 ° C., and the extruded sheet was sandwiched between metal casting drums set to 40 ° C. to prepare a laminate having a thickness of 3.2 mm. As the crystal nucleating agent, a masterbatch of a nonitol-based nucleating agent (Milllad NX8000, manufactured by Milliken Japan Co., Ltd.) was added in an appropriate amount so as to have the concentration shown in the table. The unstretched laminate prepared above was cut into a size of 120 mm × 120 mm, set in a biaxial stretching device (bruckner, KARO IV), heated in an atmosphere of 160 ° C. for 3 minutes, and stretched at a stretching speed of 100. Simultaneous vertical and horizontal stretching was performed at a stretching ratio of% / sec and a stretching ratio of 4.0 times in the vertical and horizontal directions to prepare a biaxially stretched polypropylene laminated sheet having a thickness of 200 μm.

<Sheet moldable temperature>
The thermoformable temperature of the biaxially stretched laminated polypropylene sheet was evaluated by molding a hemispherical container (molded body) using a vacuum compressed air molding machine. First, a thermocouple is attached to the surface of the sheet to be thermoformed, and this is molded in a heating furnace set to a heater temperature of 300 ° C., starting from 10 seconds and extending the heating time in 0.5 second increments. A molded container at the heating time was obtained. At this time, the sheet temperature actually measured by the thermocouple is used as the sheet processing temperature, and if the molded body at that processing temperature is not torn, the sheet surface is scorched, the mold reproduction is insufficient, or the thin wall is not formed, the processing temperature is thermoformed. The possible temperature was set. The presence or absence of tearing or charring that occurred when the sheet was heated above the thermoforming temperature was visually observed.

The overall lack of mold reproduction caused by the sheet falling below the thermoforming temperature, and the partial lack of mold reproduction and thinning caused by the uneven thickness of the sheet were determined as follows. First, the two-dimensional strain when the sheet is unfolded into a container by thermoforming is defined as follows. This two-dimensional strain is a value obtained by dividing the amount of increase in the seat area by the original seat area, and is hereinafter referred to as "surface strain".
Surface strain = (BA) / A
A: Opening area of the container B: Area of the inner surface of the container excluding the flat portion extending outward from the opening of the container By the way, the area and the thickness before and after molding have the following relationship.
A × a = B × b
a: Sheet thickness before molding
b: Thickness of the molded container That is, since the relationship of "A: B = b: a" is established, the surface strain can be converted by the following equation using the thickness before and after molding of the sheet.
Surface strain = (ab) / b
With a thickness of 200μm sheet, mold vessel ideal surface distortion on calculation is 100% (hemispherical container 60 mm. Ideal plane strain ^{100% = (2Πr 2 -Πr 2} ) / Πr 2. The ideal state molding If so, the thickness of the container will be 100 μm), and thermoforming was performed.

The thickness of the container molded at each processing temperature is measured at 5 points, and if the surface strain of all the measurement points is 95% or more and 105% or less, it is assumed that sufficient and uniform mold reproduction is performed, and the surface of the measurement points is If there is even one place where the strain is less than 95% or the surface strain exceeds 105%, it is judged that the overall mold reproduction is insufficient or the mold reproduction is non-uniform. The processing temperature of the molded product, which was generally not torn or burnt and had all surface strains at the measurement points of 95% or more and 105% or less, was defined as the thermoforming temperature.

In Tables 2 to 4, the "surface layer piece thickness ratio" is the ratio of the one-sided thicknesses of the surface layers 2a and 2b to the total sheet thickness T, and the "surface layer total thickness ratio" is the surface layer 2a, to the total sheet thickness T. The ratio of the total thickness of 2b.

<Examples 1 to 7>
As shown in Table 2, all of the sheets of Examples 1 to 7 have a thermoforming temperature range of 8 ° C. or 9 ° C., and can be thermoformed over a wide temperature range. For example, in the case of the sheet of Example 1, there is a measurement point where the surface strain is 93% at 154 ° C., and charring occurs at 163 ° C., but thermoforming is possible at 155 ° C. to 162 ° C., which is 8 ° C. A wide thermoformed temperature range was obtained. Further, the haze of the sheets of Examples 1 to 7 is 2.5% or less, particularly 2.0% or less, and the image sharpness of the sheet is 60% or more, particularly 70% or more, and is transparent. Excellent in sex. The value (haze / thickness) obtained by dividing the haze of the sheet by the total thickness T of the sheet was 10% / mm or less. Further, the thickness / thinness accuracy is 12% or less, and the thickness uniformity is excellent. The tensile elastic modulus was 1800 MPa or more, particularly 1900 MPa or more, and high rigidity was obtained. As described above, a sheet having high rigidity, excellent transparency, a uniform thickness, and a wide thermoforming temperature range was obtained.

<Comparative Examples 1 to 11>
The sheet of Comparative Example 1 is a single-layer sheet, and the sheets of Comparative Examples 2 to 11 are laminated sheets. The sheet of Comparative Example 1 had a narrow thermoformed temperature range of 5 ° C. In the sheet of Comparative Example 2, the melting point difference between the main layer 1 and the surface layers 2a and 2b was as small as 1 ° C., and the thermoforming temperature range was as narrow as 5 ° C. The sheet of Comparative Example 3 has a large melting point difference of 10 ° C. between the main layer 1 and the surface layers 2a and 2b, a poor thickness / thinness accuracy of 20%, a thermoforming temperature range of 5 ° C., and a tensile elastic modulus. Was slightly insufficient in rigidity at 1720 Mpa. In the sheet of Comparative Example 4, the surface layer piece thickness ratio in one of the surface layers 2a and 2b was as small as 2.5%, and the thermoforming temperature range was as narrow as 5 ° C. In the sheet of Comparative Example 5, the surface layer piece thickness ratio in one of the surface layers 2a and 2b was as large as 20%, and the thermoforming temperature range was as narrow as 5 ° C. The sheet of Comparative Example 6 had a large surface layer total thickness ratio of 30%, and the thermoforming temperature range was as narrow as 4 ° C. The sheet of Comparative Example 7 has a high content of nucleating agent in the surface layers 2a and 2b as high as 2000 ppm, a thermoforming temperature range as narrow as 3 ° C., and a poor thickness and thinning accuracy of 23%. The sheet of Comparative Example 8 has a low content of nucleating agent in the surface layers 2a and 2b of 500 ppm, and is transparent with haze of 2.9%, haze / thickness of 14.5%, and image sharpness of 52%. There was a problem in terms of sex. The sheet of Comparative Example 9 had a Mw / Mn of 5 in the main layer 1, had a slightly poor thickness and thinness accuracy of 15%, and had a narrow thermoforming temperature range of 5 ° C. In the sheet of Comparative Example 10, the melting points of the surface layers 2a and 2b were as low as 162 ° C., the tensile elastic modulus was 1620 MPa, and the rigidity was slightly insufficient. The sheet of Comparative Example 11 had a high content of the nucleating agent in the main layer 1 of 1000 ppm, had a slightly poor thickness and thinning accuracy of 15%, and had a narrow thermoforming temperature range of 5 ° C.

1 Main layer 2a First surface layer 2b Second surface layer T2a First surface layer thickness T2b Second surface layer thickness T Sheet total thickness

Claims (3)

It is provided with a main layer made of a propylene-based resin and a surface layer made of a propylene-based resin located on both sides of the main layer.
The melting point of the propylene-based resin on the surface layer is 165 ° C or higher, and the temperature is 165 ° C or higher.
The melting point of propylene-based resin of the main layer is lower than the melting point of the surface layer of the propylene-based resin, the melting point difference between the surface layer of the propylene resin and the main layer of propylene-based resin is at 3 ° C. or higher 9 ° C. or less,
The total thickness of the sheet is 100 μm or more and 500 μm or less.
The ratio of the thickness of one side of the surface layer to the total thickness of the sheet is 3% or more and 18% or less.
The ratio of the total thickness of the surface layer to the total thickness of the sheet is 6% or more and 28% or less.
Haze Ri der 2.5% or less,
The surface layer contains a nucleating agent of 800 ppm or more and 1900 ppm or less.
The main layer contains no nucleating agent or contains 800 ppm or less of nucleating agent.
A biaxially stretched polypropylene laminated sheet having a main layer of Mw / Mn of 7 or more and 14 or less. Thickness accuracy is 12% or less,
Tensile modulus is at least 1800 MPa, biaxially oriented polypropylene laminated sheet according to claim 1, wherein. A molded product obtained by thermoforming the sheet according to claim 1 or 2.

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