JP2003041017A - Polypropylene thermoforming sheet laminating film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a polypropylene thermoforming sheet laminating film excellent in molding accuracy, molding cycle, rigidity of moldings, molding stability, and dimensional stability of the moldings. SOLUTION: This polypropylene thermoforming sheet laminating film is a polypropylene oriented film satisfying the following (a) to (d) in a flowing direction of the film and a direction perpendicular to the following direction. (a) >=100% of a tensile elongation at break at 120 deg.C, (b) generating temperature of a thermal shrinking force >=95 deg.C, (c) <=0.03 N/4 mm width of the thermal shrinking force at 120 deg.C, (d) <=0.8 N/4 mm width of the maximum thermal shrinking force.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a novel polypropylene-based thermoforming sheet laminating film. Specifically, a polypropylene thermoformed sheet laminate that has excellent molding accuracy, molding cycle, rigidity and molding stability of the molded product, and dimensional stability of the molded product when laminated on a polypropylene-based sheet and thermoformed as a thermoforming sheet. Film.

[0002]

2. Description of the Related Art Currently, polyolefin sheets, particularly polypropylene sheets and expanded polypropylene sheets, are used for food packaging containers such as bento containers, trays and bowl containers, and general packaging containers. Used in place of the polystyrene-based sheet, its usage is increasing.

These containers are generally manufactured by thermoforming methods such as vacuum forming and pressure forming. The thermoforming method is a method of heating a sheet with an infrared heater or the like and then bringing the sheet into close contact with a mold by an external force such as mechanical force, vacuum, or compressed air to form the sheet.

In the above thermoforming, when the sheet is heated, a phenomenon in which the central portion of the sheet hangs (hereinafter referred to as drawdown) occurs. Then, when heating is further continued, a force acts to return the central portion of the sheet to the position before molding due to heat shrinkage, and the molding is performed at the time when the sheet comes closest to the position before heating.

Generally, the larger the drawdown, the more difficult it is to return to the position before molding, the longer the time required to return, and the more likely the molded product is to have uneven thickness and wrinkles.

Therefore, the degree of the drawdown is important in the molding cycle and molding accuracy. Also, moldability,
The molding cycle, molding accuracy, rigidity of molded products, molding stability, and dimensional stability after molding are not limited to the drawdown described above, but also tensile stress, tensile elongation at break, and heat shrinkage force at the time of molding a heated sheet. Also depends on.

That is, if the tensile stress during heating is insufficient, the draw-down cannot be improved and the molding cycle cannot be shortened. Further, when the sheet is brought into close contact with the mold during molding, the thickness of the molded product is not uniform. A phenomenon called uneven thickness occurs and the rigidity also decreases.

When the tensile stress is excessive, the molding cycle is shortened, but the sheet is difficult to adhere to the mold during molding, the molding precision is lowered, and the desired shape of the molded product cannot be obtained. .

If the tensile elongation at break during heating is insufficient, cracking occurs during molding of a container or the like.

Further, regarding the heat shrinkage force, when the generated temperature related to the heat shrinkage force of the sheet to be molded is low, and the heat shrinkage force at the time of heating is high, stable moldability cannot be obtained.
There is a problem that the dimensional stability of the molded product is poor.

Conventionally, as a thermoformed sheet used in such a thermoforming method, for example, for imparting a high-class feeling by imparting luster to a packaging container which is a molded article or preliminarily printing, for example, An unstretched polypropylene film (hereinafter referred to as a CPP film) on a polypropylene sheet.
A thermoformed sheet obtained by stacking the above has been generally adopted.

However, the thermoformed sheet in which the CPP film is laminated has a problem that the drawdown during thermoforming is large and the forming cycle is long.

Therefore, in order to solve the above problem, CP
It has been proposed to laminate a biaxially oriented polypropylene film to the thermoformed sheet instead of the P film. For example,
JP-A-3-288641 discloses a method of improving drawdown by laminating a biaxially stretched film made of highly crystalline polypropylene as a raw material on a polypropylene sheet having a smectic structure in the crystalline state.

However, although the drawdown of the biaxially oriented polypropylene film can be improved, the molding accuracy is not sufficient and there is still room for improvement.

The cause of this is that the biaxially stretched film of crystalline polypropylene has too large a molecular orientation due to stretching, an excessive tensile stress at the time of thermoforming, a small tensile elongation at break, and a heat shrinkage force. It is considered that the generated temperature is low and the heat shrinkage force at the time of heating is large, so that it cannot sufficiently adhere to the mold.

Against this background, the inventors of the present invention have a small tensile stress and a large tensile elongation, which are obtained under a relatively low drawing condition of an area draw ratio of 4 to 30 times.
A thermoformed sheet having improved molding accuracy by laminating an axially stretched polypropylene film (Japanese Patent Laid-Open No. H11-111240).
-170455).

However, the sheet laminated with the film obtained by the above-mentioned low stretching proposed by the present inventors is excellent in molding accuracy and rigidity of a molded product,
There was still room for improvement in molding stability and dimensional stability of molded products.

[0018]

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a thermoformed sheet laminate which is excellent in molding accuracy and rigidity of a molded product and has improved molding cycle, molding stability and dimensional stability of the molded product. Is to provide a film for use.

[0019]

Means for Solving the Problems The present inventors have conducted extensive research to achieve the above object. As a result, the tensile rupture elongation at the time of heating the stretched film using the polypropylene resin is high, and by using the stretched film set to a specific heat shrinkage force as a film for thermoforming sheet lamination, molding The inventors have found that the molding cycle, molding stability, and dimensional stability of a molded product can be effectively improved with almost no reduction in accuracy, and have completed the present invention.

That is, the present invention is a polypropylene-based stretched film, characterized in that the following (a) to (d) are satisfied in the film flow direction and the direction perpendicular to the film flow direction. Film for laminating thermoformed sheets. (A) the tensile elongation at break at 120 ° C is 100% or more,
(B) The heat shrinkage generation temperature is 95 ° C. or higher, and (c) 120
Heat shrinkage force at ℃ is 0.03N / 4mm width or less,
(D) The maximum heat shrinkage force is 0.8 N / 4 mm width or less.

[0021]

BEST MODE FOR CARRYING OUT THE INVENTION The polypropylene-based thermoforming sheet laminating film of the present invention is a stretched film having a tensile elongation at break of 100% or more at 120 ° C. in the film flow direction and the direction perpendicular to the film flow direction. Is very important in combination with the heat shrinkage force requirement described below.

That is, when the tensile elongation at break at 120 ° C. is less than 100% in the film flow direction or the direction perpendicular to the film flow direction, molding accuracy and high molding stability cannot be obtained. Further, in the film flow direction and the direction perpendicular to the film flow direction, even if the tensile breaking elongation at 120 ° C. is 100% or more, the drawdown is large unless it is a stretched film, preferably a biaxially stretched film. In addition, the molding cycle becomes longer and the rigidity of the molded product decreases. The preferred range of the tensile elongation at break of the stretched film at 120 ° C. is 10
It is 0 to 500%.

Further, the polypropylene thermoforming sheet laminating film of the present invention has a heat shrinkage force generation temperature of 95 ° C. or higher, preferably 100 ° C. or higher in the film flow direction and the direction perpendicular to the film flow direction. It is necessary that the heat shrinkage force at 120 ° C. is 0.03 N / 4 mm width or less, preferably in the film flow direction and the direction perpendicular to the film flow direction.
0.02 N / 4 mm width or less, and further, the maximum heat shrinkage force is 0.8 N / 4 mm width or less, preferably 0.6 N / 4 mm width or less in the film flow direction and the direction perpendicular to the film flow direction. It is necessary to be.

That is, if the temperature at which the heat shrinkage is generated is less than 95 ° C., the dimensional stability of the molded product after molding is poor. For example, the molded product is largely deformed after being heated in a microwave oven. The upper limit of the heat shrinkage force generation temperature is not particularly limited, but in the stretched film using a polypropylene resin, the heat shrinkage force generation temperature is preferably 95 to 145 ° C. If the temperature at which the heat shrinkage force is generated exceeds 145 ° C., the drawdown during thermoforming tends to be large, and it is difficult to shorten the molding cycle.

The heat shrinkage force at 120 ° C. is 0.0
Over 3N / 4mm width, maximum heat shrink force is 0.8N / 4m
When the width exceeds m, the molding stability during molding is poor, and the dimensional stability of the molded product after molding is poor. This is because the temperature at which the heat shrinkage is generated is low and the heat shrinkage is large, the stretched film shrinks due to the heating temperature during thermoforming, and the elongation of the film required at the time of molding is It is presumed that the molded product is inferior in molding stability because of the action of making it difficult to stretch, and that the molded product is largely deformed when it is reheated after molding in a microwave oven or the like. The preferable range of the heat shrinkage force at 120 ° C. is −0.05 to 0.03 N / 4 mm width, and the maximum shrinkage force is preferably the range of 0.05 to 0.8 N / 4 mm width.

The polypropylene resin used in the above film is not particularly limited as long as it can satisfy the tensile elongation at break and the heat shrinkage force. For example, propylene homopolymer, ethylene-propylene copolymer, ethylene. -Propylene-butene copolymer, propylene-α-
Examples thereof include olefin copolymers. Of these, a propylene homopolymer and an ethylene-propylene copolymer are particularly preferable. The ethylene content is preferably in the range of 0 to 5% by weight, more preferably 0 to 2.5% by weight. When the ethylene content exceeds 5% by weight, the heat shrinkage force of the film tends to be large, and the molding stability may be poor. Further, the deformation of the molded product is likely to be large when reheated in a microwave oven or the like after molding.

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

In addition, the MFR of the above polypropylene resin
Is 0.1 to 50 g / 10 minutes, preferably 0.2 to 10 g / 10 minutes in consideration of the film-forming property.
More preferably, the range of 0.3 to 4 g / 10 minutes is 12
It is preferable for increasing the tensile elongation at break at 0 ° C.

The polypropylene resin, which is a raw material resin used in the polypropylene thermoforming sheet laminating film of the present invention, may be mixed with other resins as long as the characteristics of the obtained film are not significantly changed. it can.

The resin that can be mixed is not particularly limited, but generally, a polyolefin wax, a polyolefin elastomer, or a hydrocarbon resin such as a petroleum resin or a terpene resin can be used. Further, these resins can be used as a mixture of two or more kinds.

Further, the raw material resin for the film for laminating a polypropylene-based thermoformed sheet of the present invention contains, if necessary, an antistatic agent, an antifogging agent, an antiblocking agent, an antioxidant, a light stabilizer and a crystallization nucleating agent. Known additives such as lubricants, surfactants, colorants, antibacterial agents, etc. may be added. Furthermore, the polypropylene-based thermoforming sheet laminating film of the present invention preferably has the following properties.

The polypropylene thermoforming sheet laminating film of the present invention has a tensile elastic modulus in the MD direction of 1300MP.
It is preferably more than a, more preferably more than 1400 MPa. Tensile elastic modulus in MD direction is 1300
When the pressure is equal to or lower than MPa, workability may be poor when laminating the film and the sheet, for example, when thermally laminating the film and the sheet.

The thickness of the polypropylene-based thermoforming sheet laminating film used in the present invention is 10 to 60 μm in consideration of the forming accuracy of the thermoforming sheet obtained by laminating the film and the thermoforming property such as forming cycle. It is preferable that it is 15 to 50 μm.

The method for producing the film for laminating a polypropylene-based thermoformed sheet of the present invention is not particularly limited, but considering thermoformability, a method of sequential biaxial stretching or simultaneous biaxial stretching is preferable.

In the case of the above-mentioned sequential biaxial stretching method, for example, 60
To 160 ° C., preferably 130 to 155 ° C., and then stretched in the MD direction with a roll, and then stretched in the TD direction in a tenter heated to 120 to 195 ° C., preferably 140 to 165 ° C., and 0 to TD direction. 140% while relaxing 20%
The heat treatment may be performed at 190 ° C., preferably 155 to 185 ° C. At this time, taking into consideration the molding stability and the dimensional stability of the molded product after molding, it is preferable to stretch at a high temperature within a range where the thickness accuracy and the film appearance are good.

The stretching ratio is preferably 20 to 47 times, and preferably 25 to 45 times, in order to obtain the film thickness accuracy, the tensile elongation at break and the heat shrinkage force specified in the present invention. Is more preferable. That is, when the area draw ratio is less than 20 times, the obtained stretched film is inferior in thickness accuracy and inferior in suitability for lamination with a sheet. When the area stretching ratio is larger than 47 times,
The stretched film obtained has a small tensile elongation at break and a large heat shrinkage force, which is unfavorable because the molding stability and the dimensional stability of the molded product are poor. Further, the stretching ratio in each of the film flow direction and the direction perpendicular to the film flow direction is preferably in the range of 3 to 10 times, and more preferably 3.5 to 9.5 times. . When any one of the draw ratios is less than 3 times, the unevenness of the drawing results in poor thickness accuracy, and when any of the draw ratios is 10 or less.
When it is more than double, the tensile elongation at break of the obtained stretched film is small, and the heat shrinkage force tends to be large, so that the molding stability and the dimensional stability of the molded product are deteriorated, which is not preferable.

The polypropylene-based thermoforming sheet laminating film of the present invention may be a multi-layered film within the scope of the present invention depending on its use. For example, in order to improve suitability for heat lamination, a method of laminating a polyolefin resin having a melting point of about 60 to 150 ° C. on the surface layer of the film, or matting or roughening the surface of the film to make the molded article matte Therefore, a method of laminating a polyethylene resin, an ethylene-polypropylene block copolymer, or the like on the surface of the film may be used. In that case, the thickness of the layer to be laminated is not particularly limited, but is preferably in the range of 0.1 to 20% of the whole.

The polypropylene thermoforming sheet laminating film of the present invention can be laminated on a polypropylene resin sheet to form a thermoforming sheet.

The polypropylene resin constituting the propylene resin sheet is not particularly limited, and a homopolymer of propylene and a copolymer of propylene as a main constituent unit with an α-olefin other than propylene are generally used. .

As the polypropylene resin sheet, known ones can be used without any limitation. For example, a polypropylene resin simply molded into a sheet, a composition in which a filler is mixed with a polypropylene resin molded into a sheet (filler-containing sheet), and a polypropylene resin foamed into a sheet. (Foamed sheet) and the like.

Other forms of these sheets include a non-stretched sheet, a uniaxially stretched sheet, a biaxially stretched sheet, a rolled sheet and the like. Among them, the nonstretched sheet is preferable in consideration of thermoformability. .

Further, the thickness of the thermoforming sheet is not particularly limited, but in consideration of thermoformability, it is 0.2 to 3 mm.
Is preferred.

The lamination mode of the polypropylene thermosetting sheet laminating film of the present invention and the polypropylene resin sheet is not particularly limited as long as the thermoforming sheet laminating film is laminated on at least one side of the polypropylene resin sheet. .

As a method for laminating the laminated sheet, a known method that does not significantly change the characteristics of the polypropylene-based thermoforming sheet laminating film can be used without particular limitation. For example, extrusion laminating method, thermal laminating method,
A method such as a dry laminating method can be used. More specifically, a method of laminating a polypropylene resin on the polypropylene thermoforming sheet laminating film of the present invention set on a chill roll is recommended.

The polypropylene-based thermoforming sheet laminating film of the present invention can be suitably used as a thermoforming sheet for lunch boxes, trays, bowls and other food containers, general containers and the like by laminating with the polypropylene sheet. .

Further, as the thermoforming method, generally used is a method of heating, followed by vacuum forming, pressure forming, vacuum pressure forming, and the like, followed by shaping in a mold such as a mold and then cooling. . Of these, vacuum pressure molding is particularly preferable.

[0047]

EFFECT OF THE INVENTION The polypropylene-based thermoforming sheet laminating film of the present invention is excellent in molding accuracy, molding cycle, rigidity of molded articles, molding stability, when forming a thermoforming sheet.
It has excellent characteristics that the dimensional stability of the molded product is excellent.

[0048]

EXAMPLES The present invention will be described below with reference to examples and comparative examples, but the present invention is not limited to these examples. In the following examples and comparative examples,
The resins used as the raw material resin for the film are shown in Table 1.

[0049]

[Table 1]

Table 2 shows thermoforming sheets used in Examples and Comparative Examples.

[0051]

[Table 2]

The physical properties of resins and films in the following examples and comparative examples were measured by the following methods.

(1) Copolymerization composition: JNM-GSX-270 ( ¹³ C-nuclear resonance frequency 67.8 MHz) manufactured by JEOL Ltd. was used and measured under the following conditions.

Measurement mode: ¹ H-complete decoupling pulse width: 7.0 microseconds (C45 degrees) Pulse repetition time: 3 seconds Integration frequency: 10000 times Solvent: Orthodichlorobenzene / deuterated benzene mixed solvent (90 / 10% by volume) Sample concentration: 120 mg / 2.5 ml Solvent measurement temperature: 120 ° C. The attribution of the peak in the methyl group region is A. Zambelli et al [M
acromolecules 13, 267 (1980)].

(2) Melt Mass Flow Rate (MFR) MFR at 230 ° C. was measured according to JIS K6758.

(3) Heat Shrinkage Using a TMA / SS150C manufactured by Seiko Denshi Kogyo Co., Ltd., a film sample having a width of 4 mm and a chuck distance of 10 mm were used.
The film was immersed in a heating medium set at 20 ° C., the temperature was raised at a temperature rising rate of 10 ° C./min until the film was melted, and the shrinkage force was measured in a state where a chuck distance of 10 mm was maintained. The temperature at which the heat shrinkage occurred, the heat shrinkage at 120 ° C., and the maximum heat shrinkage were read.

(4) Tensile rupture elongation at 120 ° C. Using an Autograph AD-500G manufactured by Shimadzu Corporation, a film sample having a width of 10 mm was immersed in a heating medium set at 120 ° C., and the sample temperature was 120 ° C. ± 1. The measurement was started when the temperature reached ℃. Pulling speed 300 mm / min, chuck distance 5
The tensile elongation at break in the MD direction and the TD direction was measured under the condition of 0 mm.

(5) The far-infrared heater was set to 300 ° C. by sandwiching the laminated sheet in a drawdown clamp frame (500 mm × 500 mm), and the thermoformed sheet of the sample was heated from above and below. Measure the length from the position before heating of the center of the sheet to the lowest point of sag,
It evaluated according to Table 3.

[0059]

[Table 3]

(6) Moldability (molding accuracy) As for the thermoformed sheet of the sample, a heater temperature of 300 to 430 ° C., a degree of vacuum of 70 mmHg, and a degree of air pressure were measured by using a Cosmic molding machine FK-0431-40 manufactured by Asano Laboratory Ltd. 3k
Tray (length 200 mm, width 250 m) at g / cm ² .
m, height 20 mm) was vacuum-pressure molded.

Partition of tray (width 3 mm, height 1
The height of 15 mm (5 mm) was set to 100%, and the molding accuracy was evaluated from the height of the partition part after molding. The evaluation has four levels as shown in Table 4.

[0062]

[Table 4]

(7) Molding stability Using the molding machine and mold described in (6) above, molding is performed for 5 times.
The test was repeated 0 times, and the cracks (film cracks) of the molded product were visually determined, and the defective rate was calculated.

[0064] Defect rate (%) = (number of cracked molded products / 50) x 100

[0065]

[Table 5]

(8) Molding cycle As for the thermoformed sheet of the sample, using a Cosmic molding machine FK-0431-40 manufactured by Asano Laboratory Co., Ltd., from the start of preheating at a heater temperature of 300 to 430 ° C. (mold transfer) The time (sec) was measured. The mold used was the same tray mold as used in the moldability evaluation, and the shortest preheating time required for the moldability evaluation in Table 4 to be ◯ or above was the molding cycle.

(9) Rigidity of molded product Using an autograph AD-500G manufactured by Shimadzu Corporation, using a molding machine described in (6) above, a bowl container (opening 135 × 135 mm, bottom 90 × 90 mm, high) 55m
m, no partition), the yield point strength was measured when the bottom was compressed at a speed of 50 mm / min, and was defined as the rigidity of the molded product.

(10) Dimensional Stability of Molded Product 100 cc of tap water was put into the molded product using the molding machine and mold described in (6) above, wrapped with a wrap film, and then lapped in a microwave oven of 1600 W for 2 minutes. After the heat treatment, the amount of deformation of the molded product was measured. The amount of deformation is the sum of the vertical and horizontal dimensional changes of the molded product, and has three levels as shown in Table 6.

[0069]

[Table 6]

(11) Tensile elastic modulus film was cut out from the film with a width of 10 mm and a length of 100 mm in the film flow direction during film forming, and both ends of the sample were chucked by a tensile tester (Autograph: Shimadzu Corporation). Fixed in. In this case, the chuck gap in the lengthwise direction of the sample was adjusted to be 20 mm.
A tensile test was performed at a tensile speed of 20 mm / min to create a tensile stress-strain curve.

The tensile modulus was calculated by the following equation using the first linear portion of the tensile stress-strain curve.

Em = Δδ / Δε Em: Tensile modulus Δδ: Difference in stress between two points on the straight line due to the original average cross-sectional area of the sample Δε: Difference in strain between the same two points Example 1 Table 1 The resin A shown is 280 ° C. using a T-die extruder.
Was extruded into a sheet under heating and melting, cooled and solidified on a cooling roll, longitudinally stretched by a heating roll stretching machine, and then laterally stretched by a tenter stretching machine to obtain a polypropylene film.

Area draw ratio of the film, draw ratio in MD direction and TD direction, draw temperature, film thickness,
Table 7 shows the draw ratio of the film, the tensile elongation at break at 120 ° C, and the heat shrinkage force. Also, using the obtained film as a film for polypropylene thermoformed sheet lamination,
The polypropylene sheet shown in Table 2 was laminated by a heat laminating method so that the film was placed on a heat roll heated to 160 ° C. above and 190 ° C. below with the flow directions aligned, and a thermoformed sheet was obtained. Obtained.

The resulting thermoformed sheet was vacuum-pressure formed. The drawdown, molding accuracy, molding stability, molding cycle, rigidity of the molded product, and dimensional stability of the molded product of the obtained laminated sheet were measured, and the results are shown in Table 8.

Examples 2 to 12, Comparative Examples 1 to 8, except that the resins shown in Table 1 were used and the stretching ratio, stretching temperature, film thickness, and film stretching ratio were changed as shown in Table 7. Film formation, thermoforming, and evaluation were performed in exactly the same manner as in Example 1. The results are shown in Tables 7 and 8.

[0076]

[Table 7]

[0077]

[Table 8]

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Naohiko Kuramoto             1-4-5 Nishishinbashi, Minato-ku, Tokyo Sun ・             Tox Co., Ltd. (72) Inventor Koji Hirata             1-4-5 Nishishinbashi, Minato-ku, Tokyo Sun ・             Tox Co., Ltd. (72) Inventor Takeshi Nakagawa             1-4-5 Nishishinbashi, Minato-ku, Tokyo Sun ・             Tox Co., Ltd. F-term (reference) 4F071 AA20 AF15 AF20 AF61 AH05                       BB08 BC01 BC10 BC17                 4F100 AK07A AK07B AK64 BA02                       DJ01 EJ37A GB16 GB23                       JA03A JK07A JK08A JL01                       JL04 YY00A

Claims (3)

[Claims] 1. A polypropylene-based stretched film,
A film for laminating a polypropylene-based thermoformed sheet, characterized by satisfying the following (a) to (d) in the film flow direction and the direction perpendicular to the film flow direction. (A) the tensile elongation at break at 120 ° C is 100% or more,
(B) The temperature at which the heat shrinkage is generated is 95 ° C. or higher, and (c) 120
Heat shrinkage force at ℃ is 0.03N / 4mm width or less,
(D) Maximum heat shrink force is 0.8 N / 4 mm width or less 2. The tensile modulus of elasticity of the film in the machine direction is 130.
The polypropylene-based thermoforming sheet laminating film according to claim 1, which has a pressure of more than 0 MPa. 3. A laminated sheet obtained by laminating the polypropylene-based thermoforming sheet laminating film according to claim 1 or 2 and a polypropylene-based sheet.