JP2008055695A - Laminated foamed polypropylene resin sheet - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a laminated foamed polypropylene resin sheet which is excellent in lightweight properties, heat resistance, appearance, etc., and can appropriately be molded into a bowl having high mouth rigidity in all directions. <P>SOLUTION: The laminated foamed polypropylene resin sheet keeps a polyolefin resin film overlying at least one side of a foamed polypropylene resin sheet having a density of 90-145 kg/m<SP>3</SP>and a basis weight of 0.30-0.45 kg/m<SP>2</SP>through a non-foamed polypropylene resin layer. The polyolefin resin film is a high-density polyethylene resin film having a tensile elongation at break of at least 100%. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a polypropylene-based resin laminated foam sheet that is excellent in deep drawability and can be suitably molded into a bag excellent in lightness, rigidity, heat resistance, appearance, and the like.

  Foamed sheets made of thermoplastic resin are generally lightweight and have good heat insulation properties, and can be easily obtained by thermoforming such as match mold molding. Widely used. And in the shape of bowls such as instant noodle containers, a polystyrene resin laminated foam sheet in which a polystyrene resin non-foamed film is laminated on the surface of the polystyrene resin foam sheet is thermoformed from the viewpoint of lightness, heat insulation, mechanical strength, etc. Molded products obtained in this way are widely used. However, the molded product of the polystyrene-based resin laminated foamed sheet can be suitably used when cooking by pouring hot water, but when it is heated using a microwave oven due to insufficient heat resistance, deformation, etc. It sometimes caused problems.

  On the other hand, polypropylene-based resin laminated foam sheets are excellent in heat resistance and oil resistance, and can be applied to microwave oven heating, so they are used in pasta containers for convenience stores. However, the conventional polypropylene-based resin laminated foam sheet can be suitably molded into a relatively shallow molded body such as a pasta container, but a deep molded body such as a bowl does not have rigidity. there were.

  In general, a melted / softened polypropylene-based resin has a strong tackiness (stickiness), and therefore tends to stick to a mold in thermoforming such as match mold molding, and hardly slip on the mold surface. This effect is particularly noticeable in deeply shaped molded bodies such as wrinkles, and the side of the molded body is greatly stretched, so that the container rigidity tends to be low.

  On the other hand, biaxially stretched polypropylene resin film, which is often used in conventional polypropylene resin laminated foam sheets, has relatively good slipperiness with the mold, but is not good for deep drawing molding such as ridges because of poor elongation. There was a problem of tearing.

  Up to now, attempts have been made to laminate films on both sides of polypropylene resin foam sheets, mainly for the purpose of improving the rigidity of deep foam containers by increasing the rigidity of laminated foam sheets or increasing the container thickness (e.g., patents Reference 1) and attempts to define the thickness of a polypropylene resin foamed sheet before and after heating (for example, Patent Document 2) have been made. Although these attempts have improved the rigidity level of the container, there are cases where sufficient rigidity cannot be obtained depending on the shape of the container. In addition, since the moldability cannot be sufficiently improved by these attempts, there is a direction that lacks a sense of rigidity when the mouth of the molded body is pushed from the left and right, and there is still anxiety even when holding the container with one hand. For this reason, further improvement on the moldability has been required.

On the other hand, attempts have been made to laminate a polyethylene resin on a polypropylene resin foam sheet for the purpose of improving impact resistance at low temperatures (for example, Patent Document 3), but the non-foamed layer is a polyethylene resin layer. Therefore, the reinforcement effect of rigidity was low, and heat resistance was lacking
JP 2005-305849 A JP 2006-89638 A JP 2002-59521 A

  An object of the present invention is to provide a polypropylene-based resin laminated foam sheet that is excellent in light weight, heat resistance, appearance, and the like, and that can be suitably molded into a bag having high rigidity in any direction.

  As a result of earnest research to obtain the above foam sheet, the inventors have found a method of laminating a film made of a high-density polyethylene resin on a polypropylene resin foam sheet, and have reached the present invention.

That is, in the present invention, the polyolefin resin film is not expanded on at least one surface of a polypropylene resin foam sheet having a density of 90 to 145 kg / m ³ and a basis weight of 0.30 to 0.45 kg / m ^2. A polypropylene resin laminated foam sheet laminated through layers, wherein the polyolefin resin film is a high density polyethylene resin film having a tensile elongation at break of 100% or more. The thickness of the high-density polyethylene resin film is preferably 10 to 30 μm.

  When the polypropylene-based resin laminated foam sheet according to the present invention is used for thermoforming, it is difficult to stick when it comes into contact with a mold, so that it can be easily stretched uniformly, and a crease having a high mouth rigidity in any direction can be obtained.

Polypropylene-based resin laminated foam sheets are easy to stick because of their strong tackiness when they come into contact with a mold in thermoforming. And due to anisotropy of heat elongation and shrinkage, drawdown during preheating, etc., there is a direction of low rigidity at the mouth of the molded body because uneven stretching occurs if the sticking to the mold is different in the middle of molding. There is a tendency.
On the other hand, the polypropylene resin laminated foam sheet of the present invention is thermoformed by laminating a high density polyethylene resin film via a polypropylene resin non-foamed layer on at least one surface of the polypropylene resin foam sheet. The sticking to the metal mold | die is reduced, and the site | part extended too much is reduced.

  When the polypropylene-based resin laminated foam sheet of the present invention is molded in a direction in which the high-density polyethylene-based resin is on the outer side of the molded body, sticking to the female mold opening (corresponding to the molded body mouth) is suppressed, Since it is easy to draw in the portion (which does not become a molded body) uniformly, the rigidity of the mouth becomes uniform, and the compression strength of the molded body also improves.

On the other hand, when the polypropylene resin laminated foam sheet of the present invention is molded in such a direction that the high density polyethylene resin film side is the inside of the molded body, sticking to the male mold tip (corresponding to the bottom of the molded body) is suppressed. Since the portion pushed by the mold also uniformly turns to the side wall, the rigidity of the mouth becomes uniform and improves.
Since the above effects do not adversely affect each other, when a high-density polyethylene-based resin film is laminated on both surfaces, a container having particularly excellent rigidity can be obtained.

The high-density polyethylene-based resin film in the present invention is mainly composed of high-density polyethylene having a density of 950 to 970 kg / m ³ , and if necessary, low-density polyethylene, linear low-density polyethylene, and ethylene-α olefin copolymer. Polyolefin resins such as polypropylene and additives such as stabilizers and lubricants may be blended.

  The blending amount of the polyolefin-based resin blended as necessary is preferably 20% by weight, more preferably 10% by weight or less, since the heat resistance and the slipperiness that are characteristic of high-density polyethylene are not impaired. .

  The high-density polyethylene-based resin film in the present invention has a tensile elongation at break according to JIS K7127 of 100% or more in both the extrusion direction and the width direction so that the film does not tear at the time of thermoforming the laminated foam sheet. Furthermore, it is necessary to be 150% or more.

In addition, the thickness of the high-density polyethylene-based resin film in the present invention is 10 to 30 μm in order not to be damaged at the time of thermoforming the laminated foamed sheet, and not to impair the heat resistance and lightness of the container obtained by thermoforming. Furthermore, it is necessary to be 15 to 25 μm.
Examples of the high-density polyethylene resin film having the above characteristics include TK polyethylene film manufactured by Towa Chemical Co., Ltd., HD film manufactured by Tamapoly Co., Ltd., and the like.

  Moreover, you may print a character, a pattern, etc. on the high-density polyethylene-type resin film in this invention for the purpose of providing designability.

  In the present invention, the polypropylene resin foam sheet and the high density polyethylene resin film are laminated via a polypropylene resin non-foamed layer. The lamination method is preferably an extrusion lamination method.

  Examples of the polypropylene resin constituting the polypropylene resin non-foamed layer include a propylene homopolymer, a block copolymer of propylene and another monomer, or a random polymer of propylene and another monomer. However, the polypropylene homopolymer is preferable from the viewpoint of high rigidity and low cost.

  The polypropylene-based resin non-foamed layer has a high density polyethylene, a low density polyethylene, a linear low density polyethylene, an ethylene-propylene copolymer, an ethylene-butene copolymer, as long as the effects of the present invention are not impaired. A butene-based resin or the like may be blended.

  The thickness of the polypropylene resin non-foamed layer in the present invention is preferably 30 μm to 200 μm, more preferably 50 μm to 150 μm, from the viewpoint of adhesiveness, lightness, or rigidity. When the thickness of the polypropylene resin non-foamed layer is less than 30 μm, the adhesion between the polypropylene resin foam sheet and the high density polyethylene resin film tends to be impaired, or the effect of increasing the rigidity of the foam sheet of the present invention tends to be small. . When the thickness of the polypropylene resin non-foamed layer exceeds 200 μm, it tends to be difficult to achieve a preheat balance between the foamed layer and the non-foamed layer in thermoforming.

  The polypropylene-based resin foam sheet in the present invention is obtained by extrusion-foaming a polypropylene-based resin. However, as a polypropylene-based resin as a base material, a linear sheet is used because a foam sheet is easily obtained because of high melt tension. A polypropylene resin (hereinafter also referred to as “raw polypropylene resin”) that is irradiated with an electron beam to introduce long chain branching (for example, HMS-PP manufactured by Sun Allomer Co., Ltd.), or raw polypropylene It is preferable to employ a modified polypropylene resin obtained by melt-kneading an isoprene monomer and a radical polymerization initiator with respect to a resin. In particular, a modified polypropylene resin obtained by melting and kneading a raw material polypropylene resin, an isoprene monomer and a radical polymerization initiator is preferable from the viewpoint that it can be produced at low cost.

  As the raw material polypropylene resin in the present invention, a copolymer obtained by copolymerizing another monomer that can be copolymerized with propylene may be used. Examples of other monomers that can be copolymerized with propylene include ethylene, butene-1, α-olefin, cyclic olefin, diene monomer, and vinyl monomer. Of these monomers, ethylene or butene-1 is preferred because it is inexpensive.

  If necessary, other resins or rubbers may be added to the polypropylene resin as the base resin in the present invention as long as the effects of the present invention are not impaired. The amount of other resin or rubber added to the polypropylene resin as the base resin varies depending on the type of this resin or the type of rubber, as long as it is within the range not impairing the effects of the present invention as described above. Usually, it is preferably about 25 parts by weight or less.

  In the polypropylene resin as the base resin in the present invention, if necessary, an antioxidant, a metal deactivator, a phosphorus processing stabilizer, an ultraviolet absorber, an ultraviolet stabilizer, a fluorescent brightening agent, Effects of the present invention include stabilizers such as metal soaps and antacid adsorbents, or additives such as crosslinking agents, chain transfer agents, nucleating agents, lubricants, plasticizers, fillers, reinforcing materials, pigments, dyes, and flame retardants. You may add in the range which does not impair.

  The polypropylene resin foam sheet in the present invention is obtained by, for example, melting and kneading a polypropylene resin, a nucleating agent, and a resin and additives blended as necessary in an extruder, press-fitting the foaming agent, and then resin in the extruder. After cooling and adjusting the temperature to a suitable foaming temperature, a circular die having an annular lip is used and extruded from the lip of the die into atmospheric pressure (that is, foaming is performed by releasing pressure) to obtain a cylindrical foam. Then, after stretching and cooling with a cylindrical cooling cylinder (mandrel) installed inside the cylindrical foam so as to cool from the inner surface side of the cylindrical foam, a sheet shape obtained by cutting open and obtaining a foam sheet It is easily manufactured by the method of making. Further, if necessary, air may be blown from the inside and outside of the cylindrical foam before the cooling cylinder or at the position of the cooling cylinder.

  Examples of the blowing agent in the present invention include aliphatic hydrocarbons, alicyclic hydrocarbons, halogenated hydrocarbons, inorganic gases, water, and the like, and one or more of them are used in combination. Also good. Although the addition amount of a foaming agent changes with kinds of foaming agent and the density of the target foam sheet, 0.5-10 weight part is preferable with respect to 100 weight part of polypropylene resin, and 1-5 weight part is more. preferable.

  Examples of the nucleating agent in the present invention include sodium bicarbonate-citrate mixture, organic acid metal salt, talc and the like, and one or more of them may be used in combination. The addition amount of the nucleating agent varies depending on the type of the nucleating agent and the number of cells in the target foam sheet, but is usually preferably 0.01 to 3 parts by weight with respect to 100 parts by weight of the polypropylene resin. .

The density of the polypropylene resin foam sheet in the present invention is preferably 90 to 145 kg / m ³ because it is easy to secure the thickness of the molded body and the molded body has high rigidity.
The basis weight of the polypropylene resin foam sheet in the present invention is preferably 0.30 to 0.45 kg / m ² because it is lightweight and economically advantageous, and the molded body has high rigidity.

Since the polypropylene resin foam sheet in the present invention has good heat insulation and excellent surface properties, the number of bubbles present in the thickness direction in the cross section of the foam sheet is preferably 5 / thickness or more, more preferably 8 / thickness or more. preferable.
The closed cell ratio of the polypropylene resin foam sheet used in the present invention is preferably 60% or more, and more preferably 70% or more. When the closed cell ratio is less than 60%, it is difficult to secure the range of thickness increase of the present invention, and the resulting molded article may have poor rigidity.

  Examples of thermoforming of the polypropylene resin laminated foam sheet in the present invention include plug molding, matched mold molding, straight molding, drape molding, plug assist molding, plug assist reverse draw molding, air slip molding, snapback molding, Examples include reverse draw molding, free drawing molding, plug and ridge molding, and ridge molding. Matched mold molding is preferred because of its excellent mold shape transferability, good appearance, and high rigidity. preferable.

  Examples of the present invention and comparative examples are shown below, but the present invention is not limited to such examples.

  In the examples and comparative examples, the polypropylene foam sheet and the method for producing the laminated foam sheet, the production of the molded article for evaluation, and the evaluation method for the molded article are as follows.

(Example 1)
[Method for producing foam sheet]
As a base resin for the foam sheet, 100 parts by weight of homopolypropylene (PL500A, melt flow rate 3 g / 10 min at 230 ° C.) manufactured by Sun Allomer Co., Ltd., 0.25 parts by weight of radical polymerization initiator (t-butylperoxybenzoate) and Pellets of modified polypropylene resin were obtained by melt-kneading 0.5 parts by weight of isoprene at a resin temperature of 200 ° C. with a twin screw extruder.

A blend of 100 parts by weight of the modified polypropylene resin and 0.6 parts by weight of a cell nucleating agent master batch (manufactured by Eiwa Kasei Kogyo Co., Ltd., EE275F) with stirring by a ribbon blender is supplied to a 90-125 mmφ tandem extruder. And melted in a first stage extruder (90 mmφ) set to 200 ° C., and then, isorich butane (iso / normal = 85/15) as a foaming agent was used with respect to 100 parts by weight of the foamed sheet base resin. 3.5 parts by weight of the mixture was press-fitted and cooled in a second stage extruder (125 mmφ) set at 160 ° C., and extruded from a circular die (caliber 127 mmφ) at a discharge rate of 80 kg / hour under atmospheric pressure. The cylindrical foam to be discharged is molded from the periphery with a mandrel while being molded with a cylindrical cooling cylinder (mandrel) having an outer diameter of 335 mmφ and a main body length of 800 mm (external portion is 338 mmφ, with an enlarged portion of 40 mm in length). While blowing with air at 3 m ³ / min and drawing at a take-up speed of 3.9 m / min, stretching and cooling to obtain a cylindrical foam, this is cut with a cutter to obtain a width of 1035 mm, a density of 108 kg / m ³ , A polypropylene resin foam sheet having a closed cell ratio of 83%, a basis weight of 0.33 kg / m ² , a thickness of 3.1 mm, and 10 cells / thickness was obtained.

[Method for producing laminated foam sheet]
A high-density polyethylene-based resin film (TK polyethylene film, tensile fracture elongation: 500% / 300% (extrusion direction / width direction), thickness: 25 μm, width: 1000 mm) manufactured by Towa Kako Co., Ltd. A polypropylene-based resin-laminated foamed sheet was obtained by pressure-bonding and laminating via a homopolypropylene manufactured by Sun Allomer Co., Ltd. (PM600A, melt flow rate 10 g / 10 min at 230 ° C.) melt-extruded from the die at a resin temperature of 230 ° C. The linear velocity at the time of producing the laminated foam sheet was 20 m / min, and the height of the T die was adjusted so that the homopolypropylene extruded from the T die was pressed in contact with the film and the foam sheet within 2 seconds. . The polypropylene resin non-foamed layer in the obtained laminated foamed sheet had a thickness of 90 μm and a width of 1200 mm.

  The tensile breaking elongation of the film was measured according to JIS K7127 using a test piece having a total length of 200 mm and a width of 25 mm at a distance between grips of 150 mm and a test speed of 100 mm / min. The value was calculated.

[Preparation of molded article for evaluation]
Using the m-width continuous vacuum forming machine (FLC415 type manufactured by Asano Laboratories), the laminated foamed sheet was formed into a molded body mold having an opening of 167 mmφ, a bottom portion of 82 mmφ, a height of 68 mm, and a clearance of 2.2 mm (number: Matched mold double-sided vacuum forming was performed at 25 pieces / shot). The upper heater set temperature is 430 ° C., the lower heater set temperature is 400 ° C., the upper mold is a female mold, the lower mold is a male mold, and the non-foamed layer of the polypropylene resin laminated foam sheet is outside the molded body ( Molding was performed so that the non-foamed layer was the upper surface. The molded body was punched into 173 mmφ using a puncher, and one shot was used as a molded body for evaluation.

[Method for evaluating molded article]
Table 1 shows the results of evaluating the following items for the obtained molded product.
(Appearance evaluation of molded body)
The appearance of 25 compacts (one shot) was observed and evaluated according to the following criteria.
○: No tears are observed in any of the molded products.
X: There exists a molded object with which a tear is seen in a film.
(Evaluation of lip compression rigidity of molded products)
Using an autograph AG2000 manufactured by Shimadzu Corporation, the molded body opening was supported so as to be vertical and compressed at a speed of 100 mm / min in order to apply compression in the extrusion direction or width direction of the laminated foamed sheet before molding. The load value at a displacement of 20 mm at this time was defined as the lip compression stiffness value in that direction.
From the average value of 25 molded bodies (one shot), the lip compression rigidity was evaluated according to the following criteria.
：: Lip compression stiffness value in the extrusion direction and the width direction is 0.5 kgf or more ○: Lip compression stiffness value in the extrusion direction and the width direction is 0.4 kgf or more and less than 0.5 kgf ×: Lip in either the extrusion direction or the width direction Compression rigidity value is less than 0.4 kgf (Evaluation of top and bottom compression rigidity of molded products)
An autograph AG2000 manufactured by Shimadzu Corporation was used, a load cell was provided with a 200 mmφ aluminum plate, and the molded body was compressed from the opening of the molded body through the same plate at a speed of 50 mm / min. Of the load values at this time, the load value that first yielded was the top-down compression stiffness value.
From the average value of 25 molded bodies (one shot), the top and bottom compression rigidity was evaluated according to the following criteria.
A: The top and bottom compression stiffness value is 15 kgf or more. O: The top and bottom compression stiffness value is 10 kgf or more and less than 15 kgf. X: The top and bottom compression stiffness value is less than 10 kgf.

(Example 2)
In forming the laminated foam sheet of Example 1, the front and back of the laminated foam sheet are reversed so that the non-foamed layer is the inside of the molded body (the non-foamed layer is the bottom surface), the upper heater set temperature is 410 ° C., and the lower heater set temperature is Changed to 420 ° C. The evaluation results are shown in Table 1.

(Example 3)
Laminated foam in the same manner as in Example 1 except that HD film (tensile fracture elongation 600% / 350% (extrusion direction / width direction), thickness 20 μm) manufactured by Tamapoly Co., Ltd. was used as the high-density polyethylene resin film. A sheet was obtained and molded. The evaluation results are shown in Table 1.

(Comparative Example 1)
Laminated foam as in Example 1, except that Rupic (80% / 60% tensile elongation / extrusion direction / width direction, thickness 20 μm) manufactured by Tonen Chemical Co., Ltd. was used as the high-density polyethylene resin film. A sheet was obtained and molded. The evaluation results are shown in Table 1.

Example 4
By adjusting the discharge amount of the polypropylene resin extruded from the T-die and obtaining a laminated foamed sheet in the same manner as in Example 1 except that the thickness of the polypropylene resin non-foamed layer was set to 60 μm, and again through the lamination process A laminated foamed sheet was obtained in which high-density polyethylene-based resin films were laminated on both sides of the foamed sheet via a polypropylene-based resin non-foamed layer having a thickness of 60 μm. Molding was performed by changing the upper heater set temperature to 420 ° C. and the lower heater set temperature to 410 ° C. The evaluation results are shown in Table 1.

(Comparative Example 2)
Implemented except using Santox Co., Ltd. polypropylene resin film, TK film (tensile elongation at break 540% / 770% (extrusion direction / width direction), thickness 25 μm) instead of high density polyethylene resin film In the same manner as in Example 1, a laminated foam sheet was obtained and molded. The evaluation results are shown in Table 1.

(Comparative Example 3)
In the molding of the laminated foam sheet of Comparative Example 2, the front and back of the laminated foam sheet are reversed so that the non-foamed layer is the inside of the molded body (the non-foamed layer is the bottom surface), the upper heater set temperature is 410 ° C, and the lower heater set temperature is Changed to 420 ° C. The evaluation results are shown in Table 1.

(Comparative Example 4)
Instead of polypropylene resin, Mitsui Chemicals high density polyethylene (Hi-Zex 2200J, melt flow rate at 190 ° C., 5.2 g / 10 min) is extruded from a T-die, and is made of high-density polyethylene directly on a polypropylene resin foam sheet. A laminated foam sheet was obtained and molded in the same manner as in Example 1 except that the non-foamed layer was formed at 120 μm. The evaluation results are shown in Table 1.

本発明のポリプロピレン系樹脂積層発泡シートは、非発泡層が成形体のいずれの面になる様用いても、リップ圧縮剛性が押出方向と幅方向でいずれも値が高く、非発泡層が成形体外面の場合には天地圧縮剛性が、成形体内面の場合にはリップ圧縮剛性が特に高く、両面に非発泡層を形成するとさらに剛性に優れることがわかる。一方、比較例１における成形体はフィルムが裂けており剛性も低く、比較例２，３の成形体はリップ圧縮剛性の低い方向があることが判る。また、比較例４の成形体は、リップ圧縮剛性がいずれの方向でも低いことが判る。

The polypropylene resin laminated foam sheet of the present invention has a high lip compression rigidity in both the extrusion direction and the width direction, and the non-foamed layer is a molded body, even if the non-foamed layer is used on any surface of the molded body. In the case of the outer surface, the top and bottom compression rigidity is particularly high, and in the case of the inner surface of the molded body, the lip compression rigidity is particularly high. On the other hand, it can be seen that the molded body of Comparative Example 1 has a film that is torn and has low rigidity, and the molded bodies of Comparative Examples 2 and 3 have a direction of low lip compression rigidity. Moreover, it turns out that the molded object of the comparative example 4 has low lip compression rigidity in any direction.

Claims (2)

A polyolefin resin film is laminated on at least one surface of a polypropylene resin foam sheet having a density of 90 to 145 kg / m ³ and a basis weight of 0.30 to 0.45 kg / m ² via a polypropylene resin non-foamed layer. A polypropylene resin laminated foam sheet, wherein the polyolefin resin film is a high density polyethylene resin film having a tensile fracture elongation of 100% or more. The polypropylene-based resin laminated foam sheet according to claim 1, wherein the high-density polyethylene-based resin film has a thickness of 10 to 30 µm.