JPS6241110B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to polypropylene sheets suitable for deep drawing thermoforming.

The purpose of the present invention is to provide a thick heat-resistant, ultra-deep-drawn cup-shaped thin-walled hollow molded product with an excellent performance such as transparency, rigidity, and impact resistance, and a ratio of molding depth to opening diameter of 2 or more. An object of the present invention is to provide a polypropylene sheet for molding.

Cup-shaped thin-walled hollow molded products manufactured from polypropylene sheets by thermoforming have features such as water vapor barrier properties, heat resistance, rigidity, and hygiene, and have been widely used as food containers in recent years.

Thin-walled hollow containers manufactured by vacuum forming by heating a polypropylene sheet to a temperature above its crystal melting point are translucent and have insufficient surface gloss.

As a method for manufacturing thin-walled hollow containers with a deep molding depth from plastic sheets, the pressure forming method that uses plugs as an aid has been known for a long time. After preheating a thin polypropylene sheet to a temperature below its melting point, By performing molding, it is possible in principle to produce a strong, deep-drawn cup-shaped container.

However, if a cup-shaped deep-drawn container with a large ratio of molding depth to opening diameter is manufactured by plug-assisted pressure forming from a polypropylene sheet manufactured by the commonly used T-die melt extrusion method,
The disadvantage is that the unevenness of the wall thickness is noticeable, and the wall thickness of a part of the side wall becomes extremely thin, making the container weak.

In order to manufacture ultra-deep-drawn containers with a molding depth to opening diameter ratio of 2 or more from polypropylene sheets and maintain the strength of the container, a raw sheet with a thickness of 2 mm or more is required. be. However, when such a polypropylene sheet with a thickness of 2 mm or more is manufactured using the T-die extrusion method and used to manufacture ultra-deep drawn containers, the molded product has uneven wall thickness, is weak, and has poor transparency. It also gets worse.

The present inventors conducted research in an attempt to obtain a polypropylene sheet for thermoforming with a thickness of 2 mm or more with good moldability and physical properties, which was previously impossible to manufacture.
It was discovered that a polypropylene sheet with a laminated structure in which a propylene copolymer is sandwiched between propylene homopolymers has good moldability, and based on this knowledge, various studies were conducted and the present invention was completed. It is.

The polypropylene laminated sheet of the present invention is a plastic sheet having a thickness of 0.5 mm or more and having a three-layer laminated structure, the first layer and the third layer being a crystalline propylene homopolymer or 100 parts by weight of a crystalline propylene homopolymer. A resin composition comprising 0.2 to 80 parts by weight of one or more types of crystalline propylene copolymers, and the intermediate second layer is a resin composition mainly composed of crystalline propylene copolymers, The thickness of the second layer is 1 to 20 times the thickness of the first layer, the thickness of the third layer is 1 to 10 times the thickness of the first layer, and the thickness of the third layer is 1 to 20 times the thickness of the first layer. is characterized in that it does not exceed the thickness of the second layer.

In the present invention, the polypropylene laminate sheet is preferably produced by a coextrusion method. In order to obtain a three-layer laminated structure, two to three extruders are used.
When changing the resin composition of the first layer and the third layer, or when making a large difference in the thickness of the first layer and the third layer, three extruders are used.

The first and third layers are crystalline propylene homopolymer or crystalline propylene homopolymer
A resin composition consisting of 100 parts by weight and 0.2 to 80 parts by weight of one or more types of crystalline propylene copolymers, especially a resin composition with a melt index (ASTMD-1238, hereinafter abbreviated as MI) of 7 or less. is preferred. The propylene copolymer to be added to the propylene homopolymer may be a random copolymer, a block copolymer or a graft copolymer, and is not particularly limited, but from the economic point of view, a random copolymer or a block copolymer is preferred. Among the random copolymers, α-olefin/propylene random copolymers are preferred, and in particular, the addition of ethylene/propylene random copolymers with an MI of 10 or less and containing 1 to 20% by weight of ethylene improves the moldability of the sheet and the transparency of the molded product. It can be significantly improved. If the ethylene content of the ethylene-propylene random copolymer is less than 1%, the effect of improving the transparency of the molded product will not appear, and if the ethylene content exceeds 20%,
The crystallinity of the copolymer decreases, and the effect of improving the transparency of sheets and molded articles becomes weaker.

Propylene homopolymer in the first and third layers
When 10 to 50 parts by weight of ethylene/propylene random copolymer and 1 to 30 parts by weight of ethylene/propylene block copolymer are added to 100 parts by weight, the gloss and transparency of sheets and molded products are particularly improved.

There is no problem in adding a coloring agent, a nucleating agent, an ultraviolet absorber, an antistatic agent, etc. to the resin compositions of the first and third layers as necessary.

The intermediate second layer is a resin composition containing a crystalline propylene copolymer as a main component, and preferably contains 60% by weight or more of the propylene copolymer. The propylene copolymer is a random copolymer, a block copolymer or a graft copolymer, and a random copolymer is particularly preferred. The random copolymer is preferably an α-olefin/propylene copolymer, especially one with an MI of 1 to 1.
The resin composition is preferably a resin composition whose main component is an ethylene/propylene random copolymer containing 1 to 20% by weight of ethylene.

A coloring agent, a nucleating agent,
There is no problem in adding an ultraviolet absorber or the like.

The thickness of the second layer relative to the thickness of the first layer is 1 to 20
The thickness of the third layer is 1 to 10 times the thickness of the first layer, and the thickness of the third layer does not exceed the thickness of the second layer.

The thickness of the polypropylene laminate sheet is 0.5 mm or more, and the structure of the present invention is particularly effective for thermoforming sheets having a thickness of 2 mm to 5 mm.

If the thickness of the laminated sheet is 0.5 mm or less, it is possible to improve the rigidity, transparency, moldability, etc. of the polypropylene sheet by other methods, and the sheet of the present invention is not necessarily required. . When the thickness of the laminated sheet is 2 mm to 5 mm, the sheet of the present invention has particularly good deep drawing processability during thermoforming, has a wide forming temperature range, and is a thin ultra-deep drawn sheet with a good balance between transparency and rigidity. Cup-shaped containers can be manufactured.

In this case, if the thickness of the intermediate second layer is equal to or less than the thickness of the first layer, the effect of the intermediate layer will be weakened, the moldability will be reduced, and the transparency of the molded product will also be deteriorated. If the thickness of the second layer is 20 times or more the thickness of the first layer, the rigidity of the sheet decreases and the stiffness of the molded product becomes weak.

In the laminated sheet of the present invention, the first layer and the third layer on the surface mainly contain propylene homopolymer, and therefore have high crystallinity, high elastic modulus, and high melting point. The stiffness of a thin cup-shaped container manufactured from a sheet by thermoforming is closely related to the bending rigidity of the side wall of the container. This bending rigidity strongly depends on the sheet thickness, but when comparing the same thickness, it increases as the elastic modulus of the sheet surface layer increases. The heat resistance strength of the container also strongly depends on the bending rigidity of the container during heating, and the heat resistance strength increases as the elastic modulus of the sheet surface layer on the side wall and bottom of the container during heating increases. Therefore, propylene homopolymers are generally preferable to propylene copolymers in terms of container stiffness and heat resistance, but homopolymers have the drawbacks of insufficient moldability and poor transparency.

When manufacturing a sheet with a thickness of 2 mm or more using the T-die extrusion method as a material sheet for manufacturing ultra-deep-drawn thin-walled cup-shaped containers, the sheet exiting the T-die is rapidly cooled in the gap between cooling rolls to improve moldability. Even if an attempt is made to produce a sheet with good transparency, the central layer of the thick sheet cannot be rapidly cooled because the sheet itself has low thermal conductivity. Therefore, the central layer of the sheet has a high degree of crystallinity and spherulites grow large, resulting in poor moldability and poor transparency of the molded product.

The polypropylene laminate sheet of the present invention is made of a polypropylene laminate sheet of the present invention, in which the first layer and the third layer are made of a resin composition containing a propylene homopolymer as a main component, and the intermediate second layer is made of a resin composition containing a propylene copolymer as a main component. When manufactured by extrusion, even if the sheet is thick, the degree of crystallinity in the center layer of the sheet is low and the spherulites are small, so moldability is good and transparent molded products can be produced.

In this way, in the sheet of the present invention, the surface layer has properties such as stiffness and heat resistance, and the intermediate layer has properties such as moldability and transparency, so that it is a thick sheet. However, it has extremely good thermoformability.

Instead of the laminated structure of the present invention, in a three-layer sheet in which the first and third layers are made of polypropylene and the middle second layer is made of a soft resin such as an ethylene/vinyl acetate copolymer or an ionomer, interlayer separation occurs during molding. The elongation of the sheet during molding is not uniform, resulting in poor appearance of the molded product. There are drawbacks such as the stiffness of the molded product.

The polypropylene laminate sheet of the present invention has good adhesion between layers, and there is no need to use any special adhesive resin.

When the laminated sheet of the present invention is manufactured by the co-pressing method, it is possible to cut the so-called selvedge parts at both ends of the wide sheet, crush it, collect it, and feed it again to the extruder together with the virgin resin. This has the advantage that the occurrence can be minimized.

By applying the principles of the present invention, polypropylene laminate sheets and molded articles having four or more layers can be manufactured. In a polypropylene laminated sheet where n is 4 or more and has a laminated structure of n layers, the first layer and the nth layer are a crystalline propylene homopolymer, or 100 parts by weight of a crystalline propylene homopolymer and one or more types. A resin composition comprising 0.2 to 80 parts by weight of a crystalline propylene copolymer, and the intermediate second layer and the (n-1) layer are resin compositions containing 60% by weight or more of a crystalline propylene copolymer. The thickness of the second layer is 0.5 to 10 times the thickness of the first layer, the thickness of the n-th layer is 1 to 10 times the thickness of the first layer, and the thickness of the n-th layer is 0.5 to 10 times the thickness of the first layer. The thickness of the (n-1)th layer is 0.5 to 10 times the thickness of the sheet. It is preferable that it occupies 80% or more of the thickness.

For example, when n is 5, by adding a resin with excellent gas barrier properties such as saponified ethylene vinyl acetate copolymer resin or polyvinylidene chloride resin as the intermediate third layer, molded products with good gas barrier properties can be created. It is also possible to produce the effects of the present invention. If delamination between the gas barrier resin contained in the third layer and the resin compositions of the second and fourth layers is noticeable, the polypropylene resin of the second and fourth layers may have a reactive functional group at the molecular chain end. It is preferable to use an adhesive propylene-based copolymer into which .

As described above, the thin cup-shaped molded product produced from the polypropylene laminate sheet of the present invention has a uniform wall thickness distribution, is strong, and has good transparency, impact resistance, and heat resistance.

Examples will be described below.

Example 1 The first and third layers are resins in which 40 parts by weight of ethylene-propylene random copolymer with MI of 1 are blended with 100 parts by weight of propylene homopolymer with MI of 1, and ethylene-propylene with MI of 2 is used. A polypropylene laminate sheet with a thickness of 2.5 mm was produced by coextrusion using a random copolymer resin as the second intermediate layer. The thickness of each layer is 0.5mm for the first layer,
The second layer was 1.5 mm and the third layer was 0.5 mm.

Using this sheet, a round thin-walled cup-shaped container with a diameter of 60 mm and a depth of 120 mm was manufactured by plug-assisted pressure forming.

The container is strong, has excellent transparency, and has a rating of 95
There was no deformation at all after boiling at ℃ for 10 minutes. The sheet had good moldability and it was possible to manufacture containers with uniform wall thickness distribution.

Comparative Example 1 A polypropylene sheet with a thickness of 2.5 mm was produced using the same sheet extrusion equipment as in Example 1 using only a propylene homopolymer resin with an MI of 1.

Using this sheet, a round thin-walled cup-shaped container with a diameter of 60 mm and a depth of 120 mm was manufactured by the same molding method as in Example 1.

The container was strong and did not deform at all after being boiled at 95℃ for 10 minutes. However, the container had insufficient gloss and was opaque, and the unevenness of the wall thickness was noticeable.

Comparative Example 2 A polypropylene sheet with a thickness of 2.5 mm was produced using the same extrusion equipment as in Example 1 using only an ethylene-propylene random copolymer resin having an MI of 1.

Using this sheet, a round thin-walled cup-shaped container with a diameter of 60 mm and a depth of 120 mm was manufactured by the same molding method as in Example 1.

The container had excellent gloss and transparency, and had a uniform wall thickness, but it was weak and was slightly deformed by boiling at 95°C for 10 minutes.

Example 2 The first and fifth layers are resins in which 40 parts by weight of ethylene-propylene random copolymer with MI of 1 are blended with 100 parts by weight of propylene homopolymer with MI of 1, and ethylene-propylene with MI of 2 is used. A 5-layer polypropylene sheet with a thickness of 2.5 mm was made by coextrusion, with random copolymer adhesive resin as the second and fourth layers, and saponified ethylene/vinyl acetate copolymer resin in the middle third layer. was manufactured. The thickness of each layer is 0.5 for the first and fifth layers.
mm, the second and fourth layers were 0.7 mm, and the third layer was 0.1 mm.

Using this sheet, a round thin-walled cup-shaped container with a diameter of 60 mm and a depth of 120 mm was manufactured by the same molding method as in Example 1.

Like the container of Example 1, this container was strong, had excellent transparency, and did not deform at all after boiling at 95° C. for 10 minutes. The sheet had good moldability, the thickness distribution of the container was uniform, and the oxygen barrier property of the container was significantly better than that of the container of Example 1.

Claims (1)

[Scope of Claims] 1. A plastic sheet having a thickness of 0.5 mm or more and having a laminate structure of three layers, wherein the first and third layers are made of a crystalline propylene homopolymer or 100 parts by weight of a crystalline propylene homopolymer. A resin composition comprising 0.2 to 80 parts by weight of one or more types of crystalline propylene copolymers, and the intermediate second layer is a resin composition mainly composed of crystalline propylene copolymers, The thickness of the second layer is 1 to 20 times the thickness of the first layer, the thickness of the third layer is 1 to 10 times the thickness of the first layer, and the thickness of the third layer is 1 to 20 times the thickness of the first layer.
A polypropylene laminated sheet characterized in that the thickness of the layer does not exceed the thickness of the second layer. 2 A plastic sheet with a thickness of 0.5 mm or more having a laminated structure of n layers, where the first layer and the n-th layer are a crystalline propylene homopolymer, or 100 parts by weight of a crystalline propylene homopolymer and one or more types. A resin composition comprising 0.2 to 80 parts by weight of a crystalline propylene copolymer, and the intermediate second layer and the (n-1) layer are resin compositions containing 60% by weight or more of a crystalline propylene copolymer. The thickness of the second layer is relative to the thickness of the first layer.
The thickness of the nth layer is 1 to 10 times the thickness of the first layer, and the thickness of the (n-1)th layer is 0.5 to 10 times the thickness of the nth layer. 10 times and n is 4
A polypropylene laminate sheet as described above, characterized in that the sum of the thicknesses of the first layer, the second layer, the (n-1) layer, and the n-th layer accounts for 80% or more of the thickness of the sheet.