JPH0885192A - Laminated sheet - Google Patents

Abstract

PURPOSE: To obtain a laminated sheet, good in molding property and prominent in the surface luster, by preventing drawdown upon molding. CONSTITUTION: A laminated sheet is constituted of an ethylene-propylene copolymer, containing 1-4wt.% of ethylene, or an ethylene-butene-propylene copolymer, containing 0.5-3.0wt.% of ethylene and 4-15wt.% of butene-1 and is prepared by a method wherein a biaxially oriented polyolefin film, having the degree of elongation in the tensile strength of 5kg/mm<2> in MD direction of 30-250% or preferably 50-130% and having the elastic modulus in tension of 80-130kg/mm<2> or preferably 90-120kg/mm<2> in MD direction is laminated on a polypropylene sheet.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a laminated sheet having improved surface gloss and thermoformability which can be used for food packaging containers such as lunch boxes, food packs and the like, and general packaging containers.

[0002]

2. Description of the Related Art In the field of thermoforming, there is known a laminated sheet obtained by laminating an unstretched polypropylene film (hereinafter referred to as a CPP film) on a polypropylene sheet. The CPP film used here is used for the purpose of imparting gloss to the surface of the molded product. However, the original gloss of the CPP film is lowered in the sheet forming temperature range, and there is a drawback that a desired high gloss molded article cannot be obtained. In addition, when pressing or vacuum forming a sheet, a phenomenon in which the central portion of the sheet hangs after heating (hereinafter referred to as drawdown) occurs. A CPP film was also used as a method for reducing this drawdown, but its effect was insufficient.

It is an object of the present invention to provide a laminated sheet which prevents drawdown and has good moldability and surface gloss.

[0004]

The present inventors have continued to study a polyolefin film laminated on a polypropylene sheet. As a result, it has been found that when the biaxially stretched polyolefin film laminated on the polypropylene sheet has appropriate elasticity and elongation, it is possible to prevent drawdown and produce a glossy laminated sheet with good moldability.

That is, the present invention provides (1) an ethylene-propylene copolymer having an ethylene content of 1 to 4% by weight, or an ethylene content of 0.5 to 3.0% by weight and butene.
1 Content of 4-15 wt% ethylene-butene-propylene copolymer, MD direction tensile strength 5 kg / mm
^A biaxially stretched polyolefin film having an elongation of 30 to 150% in 2 and a tensile modulus of elasticity in the MD direction of 80 to 130 kg / mm ² (2) a polypropylene sheet, which is laminated. Is.

Japanese Unexamined Patent Publication (Kokai) No. 3-288641 discloses a method for obtaining a laminated sheet by laminating a biaxially oriented polypropylene film (hereinafter referred to as an OPP film) on a polypropylene sheet having a smectic structure in a crystalline state. There is. However, the physical properties of the biaxially stretched polypropylene film are not specifically disclosed. However, it is described that the OPP film has a stretching ratio of 1.2 to 7 times, preferably 1.5 to 5 times in both the longitudinal and transverse directions. However, at such a stretching ratio, it is used in the present invention. It is not possible to obtain a biaxially stretched polypropylene film having a specified elastic modulus and elongation.

The biaxially stretched polyolefin film used in the present invention is an ethylene-propylene copolymer having an ethylene content of 1 to 4% by weight, or an ethylene content of 0.5 to 3.0% by weight and butene. 1 content 4-15
It is composed of an ethylene-butene-propylene copolymer (hereinafter, simply referred to as a polyolefin-based copolymer) in a weight percentage. The ethylene-propylene copolymer used in the present invention is a random copolymer having an ethylene content of 1 to 4% by weight, preferably 1.5 to 2.5% by weight,
The ethylene-butene-propylene copolymer has an ethylene content of 0.5 to 3.0% by weight and a butene-1 content of 4 to 15% by weight, preferably an ethylene content of 1.0.
˜2.0% by weight, butene-1 content is 7 to 10% by weight.

In the above ethylene-propylene copolymer and ethylene-butene-propylene copolymer,
When the amount of ethylene or the amount of butene-1 is less than the above range, the film itself becomes too hard, and the elongation at MD tensile strength of 5 kg / mm ² is 30 to 150%.
And the tensile elastic modulus in the MD direction is 80 to 130 k.
It is not preferable because a film of g / mm ² cannot be obtained. When the ethylene content or the butene-1 content is more than the above range, the gloss is insufficient like the CPP film, and drawdown frequently occurs, which is not preferable.

The polyolefin-based copolymer used in the present invention is in a range that does not impair its physical properties, for example, 5
Α-other than ethylene, butene and propylene within mol%
An olefin may be included as a copolymerization component. Also, a mixture of the above polyolefin copolymers or a mixture of the above polyolefin copolymers with other polyolefins can be used. When the polyolefin-based copolymers are mixed with each other, the mixing ratio is arbitrary. When the polyolefin-based copolymer and the other polyolefin are mixed, it is preferable that the content of the polyolefin-based copolymer is 70% by weight or more and the content of the other polyolefin is 30% by weight or less in order to obtain the effects of the present invention. . Examples of other polyolefins include polyethylene, polypropylene and polybutene.

The melt index of the polyolefin-based copolymer and the mixture thereof used in the present invention is not particularly limited, but in order to impart good film moldability, it is 0.5-10 g / 10 minutes, and further 1-7 g. It is preferably in the range of / 10 minutes.

The biaxially stretched polyolefin film used in the present invention has a tensile strength of 5 kg / mm in the MD direction.
^{2 has} an elongation of 30 to 150%, preferably 80 to
130% and the tensile elastic modulus in the MD direction is 80 to 130.
kg / mm ^2, preferably 90~120kg / mm ^2. The MD direction is the winding direction of the biaxially stretched polyolefin film. MD direction tensile strength 5kg / m
the elongation at m ² is less than 30%, or
If the tensile elastic modulus in the MD direction is larger than 130 kg / mm ² , the OPP film is insufficient in elongation if the molded product has a large drawing, resulting in poor moldability, which is not preferable. On the other hand, the elongation at a tensile strength of 5 kg / mm ² in the MD direction is greater than 150%, or the tensile elastic modulus in the MD direction is 80 kg / mm ²
If it is smaller than the above range, the gloss is insufficient as in the CPP film, and drawdown occurs, which is not preferable.

The biaxially stretched polyolefin film used in the present invention is biaxially stretched. MD is the draw ratio
It should be 3 to 4 times, and preferably 3.5 to 3.8 times. Further, it should be in the range of 8 to 12 times in the TD direction, and preferably in the range of 8.5 to 10.5. When the draw ratio in the MD direction is less than 3 times or the draw ratio in the TD direction is less than 8 times, the elongation in MD direction tensile strength 5 kg / mm ² exceeds 150% and the tensile elastic modulus is 80 kg / mm. ^{It is} less than ^2, which is not preferable. When the draw ratio in the MD direction exceeds 4 times, or when the draw ratio in the TD direction exceeds 12 times, MD
Elongation at 5kg / mm ² in tensile strength is 30%
And the tensile elastic modulus exceeds 130 kg / mm ^2, which is not preferable.

The thickness of the biaxially stretched polyolefin film used in the present invention is not particularly limited, but in consideration of moldability, it is preferably 15 to 120 μm, more preferably 20 to 50 μm.

The biaxially stretched polyolefin film used in the present invention may be a monolayer film or a laminated film having two or more layers. By using a laminated film, it is possible to impart physical properties such as adhesiveness, heat sealability, and gas barrier property. In the case of a laminated film, it is preferable that the thickness of the film laminated on the biaxially oriented polyolefin film of the present invention is 20% or less of the laminated film because the performance is not impaired.

At this time, the resin to be laminated is not limited to polyolefin, and a known resin can be adopted depending on the physical properties imparted to the laminated film. For example, in the case of imparting heat sealability, a resin that melts at a temperature lower than that of the polyolefin-based copolymer used in the present invention, for example, an ethylene content of 4 to 8 wt% and a melt index of 4 to 12 is used.
A g / 10 min ethylene-propylene random copolymer may be laminated.

Further, in order to impart a gas barrier property, an ethylene-vinyl alcohol copolymer, for example, "Eval", trade name of Kuraray Co., Ltd., is interposed on one side of the film by an adhesive resin by a coextrusion method or the like. It can also be laminated. In this case, it is preferable that the surface on which the ethylene-vinyl alcohol copolymer is laminated is the outer surface in order not to impair the effects of the present invention.

Known additives such as an antioxidant, a crystal nucleating agent, a heat stabilizer, a release agent, a slip agent, an antiblocking agent and an antistatic agent may be used in various resins used in the present invention. You can As the antiblocking agent, silica, natural zeolite, synthetic zeolite, kaolin, talc, silicone resin, silicone rubber, fused silica,
Fine particles such as melamine resin and acrylic resin may be used. These fine particles are preferably spherical, and more preferably rubber-based, which is softer than the polyolefin-based copolymer. As the slip agent, higher fatty acid amide type can be used, but it should be noted that if added in a large amount, there is a risk of whitening of the film and loss of transparency and gloss. Generation of static electricity can be suppressed by adding an appropriate amount of antistatic agent. When the corona treatment is performed, the effect is further improved and the printability can be imparted, and the laminate processability in the case of performing extrusion lamination (direct lamination) or dry lamination with a sheet can also be imparted.
When an appropriate amount of antifogging agent is added, the polyolefin-based copolymer used in the present invention easily exhibits an antifogging effect.

The biaxially stretched polyolefin film used in the present invention is not particularly limited, but can be produced, for example, by the following method. First, a polyolefin-based copolymer is melted and kneaded in an extruder,
It is cooled and solidified into a sheet on a cooling roll with a die.
The obtained sheet is heated in a longitudinal stretching machine and stretched 3 to 4 times, and subsequently heated in a transverse stretching machine and then stretched 8 to 12 times in the width direction. After transverse stretching, at a temperature slightly higher than the stretching temperature, 5
It is preferable to relax the content by about 15% because the heat shrinkage can be low.

As the polypropylene sheet laminated with the above-mentioned biaxially stretched polyolefin film, known polypropylene sheets can be used without any limitation. As polypropylene, a propylene homopolymer, an α-olefin other than propylene, for example, a random, block or graft copolymer in which 20% by weight or less of ethylene, butene-1, pentene-1 and the like and 80% by weight or more of propylene are used. , And also mixtures of these.

As the polypropylene sheet, for example, a polypropylene foam sheet, a filler-blended sheet, or a stretched sheet can be used. As the above-mentioned filler, known fillers such as talc, mica, calcium carbonate, magnesium carbonate, silica and glass can be adopted. The filling amount of these fillers is not particularly limited, but is preferably in the range of 5 to 50% by weight in order to impart heat resistance and improve mechanical strength of the laminated sheet. In addition, examples of the above-mentioned stretched sheet include a uniaxially stretched sheet, a biaxially stretched sheet, a rolled sheet and the like.

The thickness of the polypropylene sheet is not particularly limited, but considering the formability, it is preferably 0.2 to 1 mm, more preferably 0.3 to 0.5 mm.

The method for laminating the biaxially oriented polyolefin film and the polypropylene sheet is not particularly limited, but known methods such as extrusion laminating method and dry laminating method are used.

[0023]

The laminated sheet of the present invention has almost no drawdown, good moldability and excellent surface gloss.
Therefore, the laminated sheet of the present invention can be suitably used in the field of food packaging and general packaging.

[0024]

EXAMPLES Examples and comparative examples are given below to specifically describe the present invention, but the present invention is not limited to these examples. The physical properties of the films in the following examples and comparative examples were measured by the following methods.

(1) Tensile strength and elongation The sample was cut into a strip with a width of 10 mm, and the measurement length was 40 mm.
Was recorded on a chart paper at a tensile speed of 300 mm / min and a chart speed of 300 mm / min. The elongation of 5 kg / mm ² was read from the base point.

(2) Tensile elastic modulus The sample was cut into strips with a width of 10 mm, and the measurement length was 20 mm.
The rising angle was recorded on the chart paper by a tensile tester at a tensile speed of 20 mm / min and a chart speed of 2000 mm / min. A perpendicular line was drawn at a point 20 mm from the base point, the strength at the intersection with the tangent line was read, and the tensile elastic modulus was calculated by the following formula.

Tensile elastic modulus (kg / mm ² ) = [strength (k
g) x sample length (mm) x chart speed (mm / min)] ÷
[Pulling speed (mm / min) x 20 mm x Film thickness (mm) x Film width (mm)] (3) Amount of sagging Far infrared rays with a laminated sheet sandwiched between clamp frames (300 mm x 300 mm) with the film side facing up. Heater 30
The laminated sheet was set at 0 ° C. and heated from above and below. The sheet drooped once, and the amount of drooping of the central portion of the sheet was measured 5 seconds after the sheet drooped back.

(4) Formability Bento container (length 200 mm, width 220 mm, height 35 m)
m) vacuum-formed container partition (width 2m
m, height 25 mm) was set as 100%, and the moldability was evaluated from the height of the partition part of the molded product under each condition.

Example 1 Ethylene content 2.2% by weight, melt index 2.
100 parts by weight of an ethylene-propylene copolymer of 2 g / 10 minutes, 0.2 parts by weight as an antioxidant (BHT), glycerin monostearate and N, N 'as an antistatic agent.
0.1 parts by weight of bis (2-hydroxyethyl) stearylamine, 0.01 parts by weight of erucic acid amide, 0.04 parts by weight of calcium stearate, average particle diameter 2 μm
0.1 part by weight of the silicone rubber fine particles was added and melt-kneaded to obtain a raw material for a biaxially stretched film. This raw material was melt-extruded at 260 ° C. using a T-die type extruder, and a 1.35 mm sheet was formed on a casting roll at 40 ° C. This sheet was preheated with a heating roll at 125 ° C. and stretched 3.5 times in the machine direction. Then, the film was stretched 9 times in the transverse direction in a transverse stretching machine heated to 145 ° C., and then relaxed in the transverse direction by 7% at 150 ° C. in a heat setting zone of the transverse stretching machine. The thickness of the obtained film was 40 μm. The strength, elongation, tensile modulus, and talc-containing polypropylene sheet of the film thus obtained (thickness: 0.45 m
m, talc content 30 wt%), the amount of sag of the laminated sheet laminated by the extrusion laminating method, the moldability, and the surface gloss of the film surface of the molded product were measured. The results are shown in Table 1.

Example 2 Ethylene content 1.3% by weight, butene-1 content 8.0
% By weight and 100 parts by weight of ethylene-butene-1-propylene copolymer having a melt index of 5.0 g / 10 min.
Same as Example 1 except that the resin containing the same additives as in Example 1 was melt extruded at 240 ° C. using the same T-die type extruder to form a sheet of 1.02 mm on a casting roll at 30 ° C. Biaxial stretching was performed under the conditions. The thickness of the obtained film was 30 μm. The film thus obtained was laminated to the same polypropylene sheet used in Example 1. The results are shown in Table 1.

Example 3 Ethylene content 2.5% by weight, melt index 6.
A mixture of 80 parts by weight of an ethylene-propylene copolymer at 0 g / 10 minutes and 20 parts by weight of a propylene homopolymer at a melt index of 2.0 g / 10 minutes with the same additives as in Example 1 was also subjected to T-die type extrusion. Melt extruding at 250 ° C using a machine and 1.3 on a casting roll at 35 ° C.
Biaxial stretching was performed under the same conditions as in Example 1 except that a 5 mm sheet was used. The thickness of the obtained film is 40 μm
Met. The film thus obtained was laminated to the same polypropylene sheet used in Example 1. The results are shown in Table 1.

Example 4 Ethylene content 2.2% by weight, melt index 2.
70 parts by weight of an ethylene-propylene copolymer at 2 g / 10 minutes, an ethylene content of 1.3% by weight, a butene-1 content of 7.0% by weight, and a melt index of 5.0 g / 10 minutes of ethylene-butene-1-. A mixture of 30 parts by weight of the propylene copolymer and the same additives as in Example 1 was mixed with T
Biaxial stretching was performed under the same conditions as in Example 1 except that melt extrusion was performed at 260 ° C. using a die-type extruder and a 1.35 mm sheet was formed on a casting roll at 40 ° C. The thickness of the obtained film was 40 μm. The film thus obtained was laminated to the same polypropylene sheet used in Example 1. The results are shown in Table 1.

Example 5 The film obtained in the same manner as in Example 1 was laminated on a transparent polypropylene sheet (thickness: 0.4 mm) by the extrusion laminating method, and the same measurement as in Example 1 was carried out. The results are shown in Table 1.

Example 6 Except that an expanded polypropylene sheet (thickness: 0.5 mm) was used, the same procedure as in Example 5 was carried out, and the results are shown in Table 1.
It was shown to.

Comparative Examples 1 and 2 Polypropylene sheet containing talc (thickness: 0.45 m
m, talc content 30 wt%), the surface temperature of the polypropylene sheet during molding was changed as shown in Table 1, and the amount of sag, moldability and surface gloss of the molded product were measured. The results are shown in Table 1.

Comparative Example 3 The same additives as in Example 1 were blended, except that the antistatic agent was added to 1.0 part by weight to 100 parts by weight of a propylene homopolymer having a melt index of 2.0 g / 10 min. Biaxial stretching was performed under the same conditions as in Example 1 except that melt extrusion was performed at 280 ° C. using a T-die type extruder and a 1.35 mm sheet was formed on a casting roll at 35 ° C. However, since the obtained film has insufficient longitudinal stretching ratio, MD
The thickness in the direction was as large as 30 to 120 μm, and unevenness was partially mixed in a mottled area, and a film that could be used practically was not obtained.

Comparative Examples 4 and 5 A resin similar to Comparative Example 3 was biaxially stretched to obtain a longitudinal stretching ratio of 5
The same procedure as in Example 1 was performed except that the film was stretched to 00%. The thickness of the obtained film was 40 μm. The film thus obtained was laminated to the same polypropylene sheet used in Example 1. The surface temperature of the laminated sheet at the time of molding was changed as shown in Table 1, and the results were shown in Table 1.

Comparative Example 6 Ethylene content 1.3% by weight, butene-1 content 7.0
% Of ethylene-butene-1-propylene copolymer having a melt index of 5.0 g / 10 min and the same additives as in Example 1 were blended, and the same T-die type extruder was used at 210 ° C. Melt extrusion was carried out to obtain a 40 μm unstretched film on a casting roll at 30 ° C. The film thus obtained was laminated to the same polypropylene sheet used in Example 1. The results are shown in Table 1.

[0039]

[Table 1]

Claims (1)

[Claims] 1. An ethylene-propylene copolymer having an ethylene content of 1 to 4% by weight, or an ethylene content of 0.5 to 3.0% by weight and butene-1 content of 4 to 15% by weight. Of ethylene-butene-propylene copolymer having an elongation of 30 to 150% at a tensile strength of 5 kg / mm ² in the MD direction and a tensile elastic modulus of 80 in the MD direction.
A biaxially stretched polyolefin film having a weight ratio of up to 130 kg / mm ² (2) A polypropylene sheet is laminated.