JP6208445B2 - Polypropylene film for thermoforming sheet lamination - Google Patents

Description

The present invention relates to a polypropylene film for thermoforming sheet lamination. Specifically, thermoformed sheet lamination with excellent flatness and glossiness, and excellent molding accuracy, molding cycle, and molded product rigidity when thermoformed by laminating on a thermoforming sheet such as a polystyrene sheet or polypropylene sheet. For polypropylene film.
In particular, since the flatness is remarkably improved, it is a polypropylene-based film for laminating thermoformed sheets having excellent printability.

For food packaging containers such as lunch boxes, trays and bowl containers, and general packaging containers, polyolefin sheets, in particular, polypropylene sheets, polypropylene sheets and foamed polypropylene sheets with high heat resistance due to the widespread use of microwave ovens are used. These thermoformed sheets are rarely used alone, and in the case of polystyrene-based sheets, polystyrene is weak against oil, and when used in foods containing oil, there are problems such as opening holes in containers when heated in a microwave oven. For this reason, an unstretched polypropylene film is laminated. Further, most of such thermoformed sheets are preliminarily printed on an unstretched polypropylene film to be glossed or laminated for the purpose of improving design and giving a high-class feeling.

The thermoformed sheet laminated with unstretched polypropylene film has a problem that the center part of the sheet hangs down due to heating during molding, so-called drawdown is large, and the molding cycle is long. In order to solve the above problem, it has been proposed to laminate a biaxially stretched polypropylene film instead of an unstretched polypropylene film (see Patent Document 1). By laminating a biaxially stretched polypropylene film, drawdown can be improved and surface gloss can be imparted. In particular, among biaxially stretched films, a film produced by tubular simultaneous biaxial stretching, in particular, has a good balance between longitudinal and lateral tensile elongation and shrinkability, and has excellent formability (patent) Reference 2).

However, biaxially stretched polypropylene films for laminating thermoformed sheets often use high crystalline polypropylene as a raw material. In tubular simultaneous biaxial stretching, uneven stretching tends to occur even if the stretching ratio is increased, and the thickness accuracy is low. It is inferior and has a problem that tarmi is often seen in the obtained film. Therefore, when printing is performed, problems such as wrinkles and ink loss due to tarmi and pitch shift due to meandering of the original film occur, and the printability is not fully satisfactory.

By the way, by adding a nucleating agent, a method of imparting gloss to a polypropylene sheet, a foamed polypropylene sheet, or imparting transparency to an unstretched polypropylene film is widely known. None of them are used for the purpose of improving the thickness accuracy (see Patent Document 3).

JP 2003-41017 A JP 2007-160700 A JP 2008-62524 A

An object of the present invention is to provide a film for laminating a polypropylene-based thermoformed sheet that is excellent in stretching stability and flatness, has both printability and formability, and has little thickness unevenness.

As a result of intensive studies, the present inventors have stretched a film in which a nucleating agent is added to a polypropylene-based resin to solve the above-mentioned problems. It was found that the flatness was imparted.

That is, the present invention
(1) Thermoforming sheet lamination obtained by biaxially stretching a mixture consisting of a propylene-based resin and a nucleating agent and having a half crystallization time of less than 60 seconds at a stretching ratio of 3 to 7 in both length and width the film.
(2) The propylene resin is a mixture of two or more of a propylene homopolymer and an ethylene-propylene copolymer having an ethylene content of 2.6% by weight or more, and the film for laminating a system thermoforming sheet according to (1) above (3) The biaxial stretching method is a tubular simultaneous biaxial stretching method, wherein the system thermoforming sheet laminating film according to (1) and (2) (4) is a multilayer film of at least 3 or more The film for laminating thermoformed sheets according to (1), (2) and (3), wherein the anti-blocking agent is added to the surface layer in an amount of 500 to 2000 ppm or the slip agent is added to the entire layer in an amount of 500 to 2000 ppm.

The stretched film for laminating a thermoformed sheet of the present invention is thin and uneven even when the crystallinity is increased by adding a nucleating agent, the crystal is refined, and a highly crystalline polypropylene is biaxially stretched tubularly. And has the characteristics of excellent flatness, printability, glossiness, and moldability.

Embodiments of the present invention will be described below.

The nucleating agent used for the purpose of imparting good flatness, which is a feature of the present invention, is not particularly limited, and is suitably used, such as an inorganic type or a polymer type. The nucleating agent is added so that the half crystallization time is less than 60 seconds, preferably 30 seconds or less, more preferably 20 seconds or less, with respect to the entire layer. In the case of 60 seconds or more, since the crystal size becomes large, the thickness accuracy is significantly lowered. For example, in the case of a polypropylene-based crystallization accelerator which is a resin having a nucleating effect, it is preferably added so that the total layer is 0.05 to 0.15% by weight.

The term “half crystallization time” as used in the present invention is defined as the time to reach 50% heat when the area between the DSC heat curve and the baseline in the isothermal crystallization process (115 ° C.) is the total heat. To do.

The polypropylene resin used for the film is a mixture of at least two of a propylene homopolymer and an ethylene-propylene copolymer.
The ethylene content of the ethylene-propylene copolymer is preferably 2.6% by weight or more, more preferably 3% by weight or more.
When the ethylene content is less than 2.6% by weight, the stability of the bubbles is lacking, non-uniform stretching is likely to occur, and the thickness accuracy is likely to be lowered.

The ethylene content of the propylene-ethylene copolymer can be measured using a nuclear magnetic resonance apparatus described later.

The melting point when the propylene homopolymer and the ethylene-propylene copolymer are mixed is preferably 145 ° C. to 170 ° C. in order to maintain heat resistance during microwave heating.

About this mixture, it is preferable to mix ethylene-propylene copolymer in 20 to 50% of range. When the mixing ratio is less than 20%, necking becomes remarkable and the thickness accuracy is remarkably lowered. If it exceeds 50%, the thermal shrinkage of the film tends to increase, and there is a possibility that the thermal shrinkage causes the width shrinkage or the printing pattern deformation.

Next, the manufacturing method of the invention is shown.
In order to obtain a polypropylene-based laminated film by tubular simultaneous biaxial stretching using the resin, it is preferable to stretch the film so that the longitudinal and lateral stretching ratios are 3 to 8 times and the area ratio is 9 to 64 times. Tenter biaxial stretching is performed at a large stretching ratio of TD 10 times or more, so that a good thickness is obtained. However, tubular simultaneous biaxial stretching is difficult to stretch TD 10 times or more, and good thickness cannot be obtained. When the MD or TD draw ratio is smaller than 3, the thickness accuracy is remarkably reduced due to the occurrence of non-uniform stretching, and the occurrence of tarmi becomes significant. In particular, in the case of industrial production, the product yield is poor and a sufficient yield cannot be obtained. Moreover, the gloss of a film is also inferior. When the draw ratio of MD or TD is larger than 8 times, the tensile elongation decreases and deep drawing becomes difficult.

The film taken out from the stretching apparatus is relaxed to MD, heat-treated, then opened in two sheets, and wound on a winder.

The film of the present invention may be a single layer or a multilayer. The film of the present invention is subjected to heat treatment in order to relax the orientation due to stretching and to impart a low shrinkage rate and elongation. The heat treatment temperature is more effective as the temperature is closer to the melting point of the mixed resin. However, the higher the temperature is, the more the film is fused. In this case, a multilayer film of at least three layers is formed, and an anti-blocking agent is added to the surface layer, or a slip agent is added to the whole layer at 500 ppm to 2000 ppm, so that the melting point of 135 ° C. to 150 ° C. is closer to the melting point. Heat treatment is possible. When the anti-blocking agent or slip agent is less than 500 ppm, film fusion occurs at a high temperature, and the film cannot be cut up and down. On the other hand, if the temperature is low, the orientation imparted by the tubular stretching cannot be sufficiently relaxed and the moldability is poor. If the anti-blocking agent or slip agent exceeds 2000 ppm, adhesion to the roll due to dropping off occurs during printing.

The anti-blocking agent and slip agent used in the present invention are not particularly limited. If the anti-blocking agent is inorganic, talc, zeolite, silica, etc., polymer beads are preferably used if organic, If it is a slip agent, a fatty acid amide, a fatty acid glycerol ester compound, etc. are used suitably.

It should be noted that additives such as antistatic agents and antioxidants may be added to these propylene resins as necessary.

As for the thickness of the film of this invention, 10-20 micrometers is preferable. In the case of an unstretched polypropylene film, a thickness of 20 μm or more, preferably 25 μm or more is required for heat resistance and suppression of drawdown, but in the film of the present invention, sufficient heat resistance and suppression of drawdown are achieved with 10 to 20 μm. It is because it is obtained.

The film of the present invention has better moldability as the tensile elongation is larger, and a container contour as obtained from the mold can be obtained. Specifically, if the tensile elongation is 120% or more for both MD and TD, a polypropylene film having good moldability can be obtained. A film in which both MD and TD are 120% or more can be obtained by producing a film by the method described above.

Since the film of the present invention has good flatness and thickness accuracy, it is excellent in printability. The printing method can be used without particular limitation as long as it is a printing method used for a film.

The film for laminating a thermoformed sheet of the present invention is laminated on a sheet used for molding a resin sheet such as an olefin resin, a resin foam resin sheet, etc., and is thermoformed to produce food such as a lunch box, a tray, a bowl container, etc. It can be used for packaging containers and general packaging containers.

The lamination method is not particularly limited, and the lamination can be performed by a known method. For example, there are methods such as a heat laminating method, dry laminating, and extrusion laminating.

The method for thermoforming a sheet laminated with a film using the present invention is not particularly limited, and thermoforming methods such as vacuum forming, pressure forming, and drawing can be used.

Hereinafter, the present invention will be described in more detail. However, the present invention is not limited to these examples.

In addition, each physical property measurement shown in a present Example was performed with the following method.
1. The ethylene content of copolymerization was measured under the following conditions using a nuclear resonance frequency of 67.8 MHz.
Measurement mode: H-complete, coupling pulse width: 7.0 microseconds (C45 degrees)
Pulse repetition time: 3 seconds Integration frequency: 10,000 times Solvent: Orthodichlorobenzene / heavy benzene mixed solvent (90/10 vol%)
Sample concentration: 120 mg / 2.5 ml Solvent measurement temperature: 120 ° C.
2. Film thickness: measured according to JIS-Z1709.
3. Bubble stability: Bubble stability was evaluated according to the following criteria.
<Bubble stability evaluation criteria>
○: No problem.
Δ: Slightly distorted.
X: Yure big punk.
4). Stretch uniformity: The stretch uniformity of the film was evaluated according to the following criteria.
<Elongation uniformity>
○: Necking is not observed at the stretching start point.
Δ: Some necking is observed.
X: Necking is observed at the stretching start point, and white streaks are observed in the obtained film.
5. Flatness: The flatness of the film was evaluated according to the following criteria. In addition, it was judged that the film with meandering in the flatness caused the meandering of the film during printing or the occurrence of ink loss due to wrinkles.
<Flatness standard>
○: No tarmi is seen on the film, or almost no tarmi is seen.
Δ: Tarmi is seen in the film, but it becomes inconspicuous if it is stretched lightly.
X: Talmi is observed on the film, and it remains even when lightly stretched. Thickness R: The thickness R of the film was evaluated according to the following criteria. In addition, it was judged that the larger the thickness unevenness, the more the meandering of the film occurs during printing, or the occurrence of ink loss due to wrinkles.
<Standard>
○: Thickness variation when the thickness is measured in the width direction of the film is 0 to 3 μm
Δ: Thickness variation when the thickness is measured in the width direction of the film is 4 to 6 μm
X: Thickness unevenness when the thickness is measured in the width direction of the film is 7 μm or more. Crystallization time: About 8 to 10 mg of sample was weighed, enclosed in an aluminum pan, and heated at a pitch of 10 ° C./1 min from room temperature to 230 ° C. in a nitrogen flow of 20 ml / min with a differential calorimeter. Hold at these temperatures for 10 minutes. Then, it is cooled to 115 ° C. at 100 ° C./min and held at these temperatures for 10 minutes. The half crystallization time 1 / 2T is determined from the DSC curve obtained here.
The time for reaching the isothermal crystallization temperature from 115 ° C. was T0, the time for the crystallization peak area to be ½ was T1, and the half crystallization time was calculated by the following equation.
Half crystallization time 1 / 2T = T1-T0
8). Tensile elongation: Using an autograph, the tensile elongation of MD and TD was measured on a film having a width of 15 mm under the conditions of a tensile speed of 200 mm / min and a distance between chucks of 100 mm. The elongation was evaluated according to the following criteria. In addition, it was judged that the higher the tensile elongation, the better the moldability, and if the tensile elongation was 120% or more in the container molding, it was judged that a container outline as in the mold was obtained.
<Standard>
○: Both MD and TD have an elongation of 120% or more. Δ: Both MD and TD, or one of the elongations is 100 or more and less than 120%. ×: Both MD and TD have an elongation of less than 100%.

< Reference Example 1>
The composition of propylene-based mixed resin and nucleating agent shown in Table 1 was melt kneaded at 170 ° C. to 270 ° C. with an extruder and coextruded downward from an annular die maintained at 240 ° C. The formed tubular molten resin was cooled by passing through the water tank while sliding the outer surface of the cylindrical cooling mandrel in which the cooling water circulated on the inner side, and an unstretched film was obtained. It leads to the tubular non-stretched film in Ji Yubura biaxial stretching device, folded into two and cooled to 40 ° C. below with stretched MD3.2 times and TD3.4 times. Next, this stretched film was guided to a roll heat treatment apparatus and heat-treated at 145 ° C., and the film was cut into upper and lower stages and then wound on one roll. Stretching bubble stability during stretching is good, there is no vertical movement of the stretching point or swinging of the stretching tube, and there is no necking or white streaks, so-called leftovers, and non-uniform stretching. There was no state. The stretched film thus obtained had good thickness accuracy and flatness, and had a tensile elongation of 120% or more, and therefore was judged to be excellent in printability and moldability.

<Example 2>
An unstretched film was obtained in the same manner as in Reference Example 1 with the configuration of the propylene mixed resin and the nucleating agent shown in Table 1. It leads to the tubular non-stretched film in Ji Yubura biaxial stretching device, folded into two and cooled to 40 ° C. below with stretched MD6.5 times and TD6.5 times. Next, this stretched film was guided to a roll heat treatment apparatus and heat-treated at 150 ° C., and the film was cut into upper and lower stages and then wound on one roll. The stability of the stretched bubble during stretching was good, there was no vertical movement of the stretching point, rocking of the stretching tube, and no nonuniform stretching state such as necking was observed. The stretched film thus obtained had good thickness accuracy and flatness, and had a tensile elongation of 120% or more, and therefore was judged to be excellent in printability and moldability.

<Example 3>
An unstretched film was obtained in the same manner as in Reference Example 1 with the constitution of the propylene-based mixed resin and the nucleating agent shown in Table 1. It leads to the tubular non-stretched film in Ji Yubura biaxial stretching device, folded into two and cooled to 40 ° C. below with stretched MD5.5 times and TD5.5 times. Next, this stretched film was guided to a roll heat treatment apparatus and heat-treated at 150 ° C., and the film was cut into upper and lower stages and then wound on one roll. The stability of the stretched bubble during stretching was good, there was no vertical movement of the stretching point, rocking of the stretching tube, and no nonuniform stretching state such as necking was observed. The stretched film thus obtained had good thickness accuracy and flatness, and had a tensile elongation of 120% or more, and therefore was judged to be excellent in printability and moldability.

<Example 4>
An unstretched film was obtained in the same manner as in Reference Example 1 with the constitution of the propylene-based mixed resin and the nucleating agent shown in Table 1. It leads to the tubular non-stretched film in Ji Yubura biaxial stretching device, folded into two and cooled to 40 ° C. below with stretched MD6.0 times and TD6.0 times. Next, this stretched film was introduced into a roll heat treatment apparatus and heat-treated at 148 ° C., and the film was cut into upper and lower stages and then wound on one roll. The stability of the stretched bubble during stretching was good, there was no vertical movement of the stretching point, rocking of the stretching tube, and no nonuniform stretching state such as necking was observed. The stretched film thus obtained had good thickness accuracy and flatness, and had a tensile elongation of 120% or more, and therefore was judged to be excellent in printability and moldability.

< Reference Example 5>
With the configuration of the propylene-based mixed resin and the nucleating agent shown in Table 1, 500 ppm of the antiblocking agent was added to the surface layer, and 500 ppm of the lubricant was added to all layers, and a stretched film was obtained under the same production conditions as in Reference Example 1. Even at a heat treatment temperature of 145 ° C. as in Reference Example 1, the film could be cut up and down without any problem. The stretched film thus obtained had good thickness accuracy and flatness, and had a tensile elongation of 120% or more, and therefore was judged to be excellent in printability and moldability.

<Comparative Example 1>
An unstretched film was obtained in the same manner as in Reference Example 1 without adding a nucleating agent to the propylene-based mixed resin shown in Table 2. The tubular unstretched film led to Ji Yubura biaxial stretching device, folded and two cooling to below 40 ° C. while stretched MD3.2 times and TD3.4 times are the same conditions as in Reference Example 1. Then it leads to the stretched film in a roll thermal treatment apparatus, heat-treated at 145 ° C., wound on respective one roll after cut open the film in the vertical stage. Stretching bubble stability during stretching was good, no vertical movement of the stretching point or rocking of the stretching tube was observed, but necking was observed at the stretching start point, and the resulting film had a white streak shape The thickness of that part was clearly thick.
The stretched film thus obtained was inferior in thickness and thinness and had a depth of 5 mm. It was judged that meandering and ink loss occurred during printing.

<Comparative example 2>
An unstretched film was obtained in the same manner as in Reference Example 1 with the constitution of the propylene-based mixed resin and the nucleating agent shown in Table 2. This tubular unstretched film was guided to a tubular biaxial stretching apparatus, cooled to 40 ° C. or lower and folded into two while stretching 2.5 times MD and 2.5 times TD. Next, this stretched film was guided to a roll heat treatment apparatus and heat-treated at 150 ° C., and the film was cut into upper and lower stages and then wound on one roll. The stretching bubble during stretching was slightly unstable, and vertical movement of the stretching point and rocking of the stretching tube were observed. Further, necking was observed at the stretching start point, and the obtained film had a white streak-like film, and the thickness of the part was clearly thick. The stretched film thus obtained was remarkably inferior in thickness and thickness, and had a depth of 10 mm. It was judged that meandering and ink loss occurred during printing.

<Comparative Example 3>
An unstretched film was obtained in the same manner as in Reference Example 1 with the constitution of the propylene-based mixed resin and the nucleating agent shown in Table 2. This tubular unstretched film was guided to a tubular biaxial stretching apparatus, cooled to 40 ° C. or lower and folded in two while stretching 8.5 times MD and 8.5 times TD. Next, this stretched film was introduced into a roll heat treatment apparatus and heat-treated at 148 ° C., and the film was cut into upper and lower stages and then wound on one roll. The stability of the stretched bubble during stretching was good, there was no vertical movement of the stretching point, rocking of the stretching tube, and no nonuniform stretching state such as necking was observed. The stretched film thus obtained was determined to have a particularly good thickness and thinness and flatness and no problem in printability, but it was determined that the formability was remarkably inferior because the elongation was significantly reduced.

<Comparative Example 5>
An unstretched film was obtained in the same manner as in Reference Example 1 with the constitution of the propylene-based mixed resin and the nucleating agent shown in Table 2. This tubular unstretched film was guided to a tubular biaxial stretching apparatus, cooled to 40 ° C. or lower and folded into two while stretching MD6.7 times and TD6.5 times. Next, this stretched film was guided to a roll heat treatment apparatus and heat-treated at 150 ° C., and the film was cut into upper and lower stages and then wound on one roll. The stretching bubbles during stretching were slightly unstable, and vertical movement of the stretching point and swinging of the stretching tube were observed, and necking was observed at the stretching start point. The stretched film thus obtained was inferior in thickness accuracy, and several 5 mm deep tarmi were found, and it was judged that meandering and ink loss occurred during printing.

<Comparative Example 6>
An unstretched film was obtained in the same manner as in Reference Example 1 with the constitution of the propylene-based mixed resin and the nucleating agent shown in Table 2. This tubular unstretched film was guided to a tubular biaxial stretching apparatus, cooled to 40 ° C. or lower and folded in two while stretching MD4.6 times and TD4.8 times. Next, this stretched film was guided to a roll heat treatment apparatus and heat-treated at 150 ° C., and the film was cut into upper and lower stages and then wound on one roll. The stretching bubbles during stretching were slightly unstable, and vertical movement of the stretching point and swinging of the stretching tube were observed, and necking was observed at the stretching start point. The stretched film obtained in this way has some white streaks, the thickness of the part is clearly thick and the thickness accuracy is inferior, and several 5 mm deep talmi is seen. Was determined to occur.

Claims (2)

It consists of a propylene resin consisting of 80-60% propylene homopolymer and 20-40% ethylene-propylene copolymer having an ethylene content of 2.6-4% by weight, and a nucleating agent. There 3 the mixture is less than 0 seconds, the Rukoto to tubular simultaneous biaxial stretching in draw ratio 3-8 times with aspect, thermoforming sheet laminated film obtained. The film for laminating thermoformed sheets according to claim 1, wherein the film is a multilayer film having at least 3 layers, and 500 to 2000 ppm of an antiblocking agent is added to the surface layer, or 500 to 2000 ppm of a slip agent is added to all layers.