JP3087404B2 - Polypropylene-based multilayer sheet - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is excellent in transparency and thermoforming for use in food packaging such as meat trays, cosmetic packaging, medical equipment packaging, and PTP packaging used for packaging pharmaceutical tablets and capsules. The present invention relates to a polypropylene-based multilayer sheet having improved properties, particularly vacuum formability.

[0002]

2. Description of the Related Art Polypropylene resins generally used in the field of thermoforming have superior properties such as heat resistance, water vapor transmission resistance, impact resistance, light weight, and no pollution as compared with vinyl chloride resins and polystyrene resins. However, since the sagging of the polypropylene resin during thermoforming is large, a molding method has been specified, and it has hardly been used in fields where transparency is required due to the opacity of the molded product.

[0003] In recent years, however, various proposals have been made regarding improvement of transparency. JP-A-49-14575 proposes to obtain a molded article having high transparency by melting and quenching a polypropylene sheet to form a smectic structure, and molding this at a temperature lower than its melting point. In order to effectively obtain a smectic structure by quenching, it is effective to use a polypropylene resin having a melt flow rate (MFR) of about 10. However, in this case, the sheet sags greatly during thermoforming, and can be formed only by pressure forming.

On the other hand, in order to solve the sagging phenomenon of the sheet at the time of thermoforming, a method of laminating another resin sheet without sagging as described in Japanese Patent Application Laid-Open No. Sho 51-57661, or Japanese Patent Application Laid-open No. As described in JP-A-68864, there is a method in which rolling is performed and a pressing pressure is applied at a temperature lower than the crystal melting point to form.

[0005] However, as described in JP-A-51-77561, if another type of resin sheet is laminated, the sagging of the polypropylene resin can be prevented, but the transparency is inferior, though it is obtained. Also, molding by pressure molding as described in JP-A-54-68864 has a problem in versatility due to problems such as molding cycle and complexity of the molding machine.

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to provide a multilayer sheet which is free from sagging during molding and has good transparency and moldability.

[0007]

Means for Solving the Problems In view of the above situation, the present inventors have made intensive studies and as a result, have found that a multilayer sheet made of polypropylene having a specific crystal structure and an ethylene-based thermoplastic resin has caused a problem. They have found that they can be solved and have completed the present invention.

[0008] That is, the present invention relates to a polypropylene-based multilayer sheet in which a polypropylene layer having a smectic crystal structure and an ethylene-based thermoplastic resin layer are laminated. Hereinafter, the present invention will be described in detail.

In the present invention, in defining the amount of smectic crystals necessary for maintaining transparency and moldability, a calorific value (hereinafter ΔHt) based on the thermal transition behavior of smectic crystals determined by DSC is used.

It has been known that a smectic crystal transforms to an α crystal in a solid state when heated in a temperature range of 60 ° C. or more, and this transition is known to be an exothermic transition (V. Vittoria). , J. Macromo
l. Sci. , B28, 489, 1989).

[0011] The exothermic peak determined by DSC, the area of which decreases as the transition proceeds,
By using ΔHt as an index, the amount of smectic crystals contained in the polypropylene layer can be relatively quantified and evaluated.

In the DSC measurement, the exothermic peak appears on the lower temperature side than the melting peak of the α-crystal, but on the lower temperature side further than the exothermic peak, an endothermic peak considered to be based on the melting of the microcrystal appears (A. Ficera). and
R. Zannetti, Macromol. Che
m. 176, 1885, 1975). These two peaks tend to shift to higher temperatures due to thermal history,
Depending on the molding conditions, each peak appears close to each other. Therefore, in determining ΔHt from the DSC chart, separation of each peak is important. In the ΔHt measurement method in the present invention, each peak is separated by drawing a baseline in consideration of the above matters.

In order that the polypropylene sheet of the present invention can be vacuum-formed while maintaining transparency, the ΔHt of the polypropylene crystal part is at least 4% or more, preferably at least 4%, compared to the ΔHt of the sheet composed of almost 100% smectic crystals. Needs to be 10% or more.

The polypropylene polymer used in the polypropylene layer having a smectic structure used in the present invention is a homo- or copolymer of propylene containing 75% by weight or more of propylene as a constitutional unit. As the copolymer component, ethylene and C 4-20 (preferably 4-
8) The α-olefin and the like may be mentioned, but may further contain an unsaturated organic acid or a derivative thereof as long as the transparency is not impaired. A system blended with a homopolymer or a copolymer may contain a petroleum resin.
Examples of petroleum resins that can be used here include, for example,
No. 1-91955, molecular weight 500-50
And aliphatic and alicyclic petroleum resins having a softening point of 50 to 170 ° C.

Further, the polypropylene used in the present invention has a melt flow rate (M) in accordance with JIS-K6758.
FR, 230 ° C., 2.16 Kg) is 20 g / 10 min or less, preferably in the range of 15 g / 10 min to 2 g / 10 min.

The ethylene thermoplastic resin used in the present invention includes, for example, low-density polyethylene, medium-density polyethylene, high-density polyethylene, linear low-density polyethylene, ethylene-vinyl acetate copolymer, ethylene-
Completely or partially saponified vinyl acetate copolymer, ethylene-acrylic acid copolymer, various metal salts of ethylene-acrylic acid copolymer, ethylene-methacrylic acid copolymer, various types of ethylene-methacrylic acid copolymer Metal salt of
Ethylene-acrylic acid ester copolymer, ethylene-acrylic acid ester-maleic anhydride terpolymer, ethylene-methacrylic acid ester copolymer, etc., alone or in a mixture of any ratio, are particularly preferred. 10 g of melt flow rate (MFR, 190 ° C., 2.16 kg / 10 minutes) based on JIS-K6760
/ 10 minutes or less. This MFR is 10g / 10
If the amount exceeds the above range, the drawdown at the melting point of the smectic structure of polypropylene is large, and the effect of improving the moldability is not sufficient.

The above-mentioned ethylene-based thermoplastic resin may contain various additives which are usually added to the ethylene-based thermoplastic resin as needed, such as a nucleating agent, an antioxidant, a heat stabilizer, an anti-fogging agent, Inhibitors, slip agents, ultraviolet absorbers, heavy metal stabilizers (copper damage inhibitors), coloring agents, and the like can be used in combination. Further, to the composition of the present invention, other additional components, for example, an inorganic filler such as talc and calcium carbonate, a flame retardant, a flame retardant auxiliary agent and the like are added to the extent that the object of the present invention is not significantly impaired. You can also.

The smectic structure referred to in the present invention means that when X-ray diffraction is measured at a diffraction angle (2θ) in the range of 10 to 30 degrees, two lines are present only at around 14.6 degrees and around 21.2 degrees. A structure in which a typical peak appears. In order to make such a sheet, the polypropylene composition is melt-extruded from a die at a temperature 40 ° C. or more higher than its melting point,
It is necessary to immediately cool to below 60 ° C.

In the polypropylene layer of the present invention, various additives which are usually added to the polypropylene as required, such as nucleating agents, antioxidants, heat stabilizers, antifogging agents, antistatic agents, slip agents, ultraviolet rays An absorbent, a heavy metal stabilizer (a copper damage inhibitor), a coloring agent, and the like can be appropriately used in combination. Further, to the composition of the present invention, other additional components such as an inorganic filler such as talc and calcium carbonate, a flame retardant, a flame retardant auxiliary agent, etc. may be added to the extent that the object of the present invention is not significantly impaired. Can be.

[0020] The polypropylene-based multilayer sheet of the present invention basically comprises two types, a polypropylene layer (A) and an ethylene-based thermoplastic resin layer (B). Resin having high gas impermeability can be formed. Various resins can be used as the resin having high gas impermeability for forming the C layer. For example, ethylene-vinyl alcohol copolymer, nylon 1
2, nylon 11, nylon 6, nylon 6-10, polyvinylidene chloride resin, polyvinyl chloride-polyvinylidene chloride copolymer, polyacrylonitrile resin, polyethylene terephthalate, polybutylene terephthalate, and the like.

When the adhesion between the layer C and the resin used for the layer A or the layer B is poor, a layer D made of an adhesive resin can be formed if necessary. Although various adhesive resins can be used, a polyolefin adhesive resin is particularly preferable. For example, unsaturated carboxylic acid-modified polyolefin, maleic anhydride-modified polyolefin, saponified ethylene-vinyl acetate copolymer, unsaturated carboxylic acid copolymer, ethylene-vinyl acetate-glycidyl methacrylate terpolymer, ethylene-acryl Acid copolymers, ethylene-ethyl acrylate copolymers, ethylene-methacrylic acid copolymers and the like can be mentioned. Also,
Since the thickness composition ratio of the multilayer sheet of the present invention varies depending on the function, application, and manner of lamination, it cannot be uniquely defined.

The multilayer sheet of the present invention can be manufactured by a general multilayer extrusion method, for example, a T-die extrusion method, an inflation method, an extrusion lamination method and the like.

[0023]

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

The evaluation method of the obtained sheet is described below. (1) Amount of sag The amount of sag at the center of the sheet when the sheet surface temperature was heated to 135 ° C. by a heater with the sheet interposed between clamp frames (230 mm × 330 mm) was measured. (2) Haze Measured according to JIS-K6782. (3) Gloss According to JIS-Z8741, the angle was measured at 60 ° -60 °. (4) Transition Heating Value (ΔHt) Using RDC220 manufactured by Seiko Denshi Kogyo, the temperature was measured at a rate of temperature increase of 20 ° C./min, and the measurement temperature range was −10 ° C. to 250 ° C. in a nitrogen atmosphere.

Example 1 (A) Polypropylene resin (manufactured by Tosoh Corporation: Tosoh Polypro J5100A, homopolypropylene, MFR10)
g / 10 minutes), (B) ethylene-vinyl acetate copolymer (manufactured by Tosoh Corporation: Ultracene UE631, MFR)
1.5 g / 10 min) was melt-extruded from a die at 240 ° C. with a thickness ratio of 300 μ / 100 μ / 300 μ in the configuration of (A) / (B) / (A), and then rapidly cooled with cold water of 10 ° C. X-ray diffraction pattern (diffraction by X-ray analyzer JDX-11PA manufactured by JEOL Ltd.) of the polypropylene layer of the polypropylene-based multilayer sheet having a thickness of 0.7 mm in which the polypropylene crystal part of the layer has a 100% smectic structure is shown in FIG. Show. In addition, D of this polypropylene layer
FIG. 2 shows the SC measurement results. Table 1 summarizes the measurement results of the amount of sag, haze, and gloss using this multilayer sheet.

Example 2 The polypropylene-based multilayer sheet obtained in Example 1 was
X of the polypropylene layer of the polypropylene-based multilayer sheet having a thickness of 0.7 mm in which a heat treatment was performed at 0 ° C. for 30 minutes to make the polypropylene crystal part a mixture of smectic crystals and α crystals.
The line diffraction pattern is shown in FIG. FIG. 4 shows the result of DSC measurement of the polypropylene layer. In order to separate the three peaks appearing on the DSC chart of FIG.
The baseline was drawn with reference to the DSC curve of the α-crystal polypropylene layer shown in FIG. This baseline is shown by a broken line in FIG. From the obtained DSC chart, the area of the portion surrounded by the exothermic peak and the baseline was determined as ΔHt, and the amount of the smectic crystal was quantified in comparison with ΔHt of the polypropylene layer of Example 1 and summarized in Table 1. Table 1 summarizes the measurement results of the amount of sag, haze, and gloss using this multilayer sheet.

Example 3 (A) Polypropylene resin (manufactured by Tosoh Corporation: Tosoh Polypro J5100A, homopolypropylene, MFR10)
g / 10 minutes), (B) ethylene-vinyl acetate copolymer (manufactured by Tosoh Corporation: Ultracene UE630, MFR)
(1.5 g / 10 min) was melt-extruded from a die at 240 ° C. with a thickness ratio of 300 μ / 100/300 μ in the configuration of (A) / (B) / (A), and then rapidly cooled with cold water at 10 ° C. 0.7mm with a smectic layer
To obtain a polypropylene-based multilayer sheet having a thickness of Table 1 summarizes the measurement results of the amount of sag, haze, and gloss using this multilayer sheet.

Example 4 (A) Polypropylene resin (manufactured by Tosoh Corporation: Tosoh Polypro J5100A, homopolypropylene, MFR10)
g / 10 minutes), (B) an ethylene-vinyl acetate copolymer (manufactured by Tosoh Corporation: Ultracene UE635, MFR)
2.4 g / 10 min) was melt-extruded from a die at 240 ° C. with a thickness ratio of 300 μ / 100 μ / 300 μ in the configuration of (A) / (B) / (A), and then rapidly cooled with cold water at 10 ° C. 0.7mm with a smectic layer
To obtain a polypropylene-based multilayer sheet having a thickness of Table 1 summarizes the measurement results of the amount of sag, haze, and gloss using this multilayer sheet.

Example 5 (A) Polypropylene resin (manufactured by Tosoh Corporation: Tosoh Polypro J5100A, homopolypropylene, MFR10)
g / 10 minutes), and (B) a partially saponified ethylene-vinyl acetate copolymer (manufactured by Toso Co., Ltd .: Mersen H6501;
MFR 5.0 g / 10 min) was melt-extruded from a die at 240 ° C. with a thickness ratio of 300 μ / 100 μ / 300 μ in the configuration of (A) / (B) / (A), and then quenched with 10 ° C. cold water. A 0.7 mm thick polypropylene-based multilayer sheet having a smectic structure of the polypropylene layer was obtained. Table 1 summarizes the measurement results of the amount of sag, haze, and gloss using this multilayer sheet.

Example 6 (A) Polypropylene resin (Toso-Polypro J5100A, homopolypropylene, MFR10, manufactured by Tosoh Corporation)
g / 10 min), (B) linear low density polyethylene (manufactured by Toso Corporation: Nipolon-LF10, MFR 0.8 g /
(10 minutes) is (A) / (B) / (A) and the thickness ratio is 300 μ / 100 μ / 300 μ.
After being melt-extruded at 10 ° C., the mixture was quenched with cold water at 10 ° C. to obtain a 0.7 mm thick polypropylene-based multilayer sheet having a smectic polypropylene layer. Table 1 shows the measurement results of the amount of sag, haze, and gloss using this multilayer sheet.
Summarized in

Example 7 (A) Polypropylene resin (manufactured by Tosoh Corporation: Tosoh Polypro J5100A, homopolypropylene, MFR10)
g / 10 minutes), (B) ethylene-acrylic acid copolymer (manufactured by Dow Chemical: Primacol 1320, MFR
2.5 g / 10 min) was melt-extruded from a die at 240 ° C. with a thickness ratio of 300 μ / 100 μ / 300 μ in the configuration of (A) / (B) / (A), and then quenched with 10 ° C. cold water. 0.7 with a polypropylene layer having a smectic structure
A polypropylene-based multilayer sheet having a thickness of mm was obtained. Table 1 summarizes the measurement results of the amount of sag, haze, and gloss using this multilayer sheet.

Example 8 (A) Polypropylene resin (Toso-Polypro J5100A, manufactured by Toso Corporation, homopolypropylene, MFR10)
g / 10 minutes), (B) a metal salt of an ethylene-methacrylic acid copolymer (manufactured by Mitsui Polychemicals: Himilan 1707,
(MFR 0.9 g / 10 min) in a configuration of (A) / (B) / (A) with a thickness ratio of 300 μ / 100 μ / 300 μ, melt extrusion at 240 ° C. from a die, and rapid cooling with 10 ° C. cold water. A 0.7 mm thick polypropylene-based multilayer sheet having a smectic structure of the polypropylene layer was obtained. Table 1 summarizes the measurement results of the amount of sag, haze, and gloss using this multilayer sheet.

Comparative Example 1 Polypropylene resin (homopolypropylene, MFR10
g / 10 min) from a die at 240 ° C.
This was quenched with 10 ° C. cold water to obtain a polypropylene single-layer sheet having a thickness of 0.7 mm with a polypropylene layer having a smectic structure. Using this single-layer sheet, the measurement results of the amount of sag, haze, and gloss are summarized in Table 1.

Comparative Example 2 The polypropylene-based multilayer sheet obtained in Example 1 was
FIG. 6 shows the X-ray diffraction pattern of the polypropylene layer of the sheet which was heat-treated at 0 ° C. for 1 hour to make all the polypropylene crystal parts of the polypropylene layer α-crystal. FIG. 5 shows the results of DSC measurement of the polypropylene layer. Table 1 summarizes the measurement results of the amount of sag, haze, and gloss using this multilayer sheet.

[0035]

[Table 1]

[0036]

According to the present invention, there is provided a polypropylene-based multilayer sheet comprising a polypropylene having a smectic crystal structure and at least one other layer made of an ethylene-based thermoplastic resin. Exothermic peak based on the transition from the smectic crystal to the α-crystal at a lower temperature side than the melting peak of the crystal, and the caloric value is 4% of the same calorific value that the polypropylene crystal part of the polypropylene sheet almost completely has a smectic structure.
% By using the polypropylene-based multi-layer sheet of the present invention as described above, (1) drooping is greatly improved, and vacuum forming becomes possible. (2) A molded article having excellent surface gloss and transparency is obtained. (3) Can be molded at a low temperature. (4) The heat resistance of the molded article is the same as when a normal polypropylene sheet is used. It has become possible to use such excellent sheets.

[Brief description of the drawings]

FIG. 1 shows X of a polypropylene layer used in Example 1.
It is a figure which shows a line diffraction pattern.

FIG. 2 shows D of a polypropylene layer used in Example 1.
It is a figure showing an SC measurement result.

FIG. 3 shows the X of the polypropylene layer used in Example 2.
It is a figure which shows a line diffraction pattern.

FIG. 4 shows the D of the polypropylene layer used in Example 2.
It is a figure showing an SC measurement result.

FIG. 5 shows the D of the polypropylene layer used in Comparative Example 2.
It is a figure showing an SC measurement result.

FIG. 6 shows the X of the polypropylene layer used in Comparative Example 2.
It is a figure which shows a line diffraction pattern.

Claims (1)

(57) [Claims] 1. A polypropylene-based multilayer sheet comprising a laminate of a polypropylene layer having a smectic crystal structure and an ethylene-based thermoplastic resin layer.