JPH01125226A - Production of laminate sheet - Google Patents

Abstract

PURPOSE:To obtain a laminate sheet having excellent bonding strength of the two sheets, by laminating a rigid sheet comprising a specified resin and a flexible sheet with each other without using an adhesive. CONSTITUTION:A rigid sheet 1 of a material selected from a polypropylene resin, a rigid polyvinyl chloride resin and a polystyrene resin and a multilayer flexible sheet 2 comprising a gas barrier resin layer as an intermediate layer and having an outermost layer comprising an ethylene-vinyl acetate copolymer having a vinyl acetate content of 10-20wt.% are opposed to each other, with the layer of the copolymer on the inside. The opposed surfaces of the sheets are subjected to a corona discharge treatment to provided the surfaces with a wettability index of at least 50, and the sheets are directly adhered to each other by heating and pressing. The bond strength at the interface between the rigid sheet 1 and the flexible sheet 2 is at least 150g/20mm-width. The thickness of the sheet 1 is preferably 20-500mum. If the thickness if less than 20mum, stiffness is poor, whereas if the thickness is more than 500mum, properties for secondary forming such as vacuum forming is poor.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a method for manufacturing a rigid or semi-rigid laminated sheet that has excellent gas barrier properties and can be suitably used particularly as a deep-drawn container for food packaging.

(Prior Art) Multilayer flexible sheets in which a gas barrier layer is made of a gas barrier resin such as polyvinylidene chloride resin or saponified ethylene vinyl acetate copolymer have been known. These soft sheets tend to wrinkle during deep drawing (vacuum forming) due to the lack of sheet rigidity, so in order to provide even more rigidity, polypropylene resin or hard polyester is added to the outermost layer of the soft sheet. 2. Description of the Related Art A laminated sheet provided with a hard sheet made of vinyl chloride resin or the like is known.

(Problems to be Solved by the Present Invention) Laminated sheets with such a configuration are laminated using ordinary solvent-based adhesives such as urethane adhesives, and in order to increase the strength after lamination, This method requires an aging period, and there is a problem in that residual solvent in the adhesive can cause odor to the packaged food.

(Means for Solving the Problems) The present invention provides a laminated sheet with excellent adhesive strength between the two sheets by laminating a hard sheet and a soft sheet made of a specific resin without using an adhesive. The company has discovered a manufacturing method that allows for the production of a rigid sheet 1 selected from polypropylene resin, hard polyvinyl chloride resin, and polystyrene resin, and a gas barrier resin layer as an intermediate layer. , a multilayer soft sheet 2 whose outermost layer is made of an ethylene vinyl acetate copolymer having a vinyl acetate content of 10 to 20% by weight, and the ethylene vinyl acetate copolymer layers of the hard sheet 1 and the soft sheet 2 facing each other, After applying corona discharge treatment to the sheet surfaces on both opposing sides to make the treated surfaces have a wettability index of 50 or more, they are immediately heat-pressed to increase the adhesive strength at the interface between the hard sheet 1 and the soft sheet 2 to 150 g/ The present invention relates to a method for producing a laminated sheet having a width of 20 mm or more.

The present invention will be explained below with reference to the drawings. FIG. 1 is a schematic cross-sectional view showing an example of an apparatus used in the manufacturing method of the present invention.

Symbol 1 in the figure is a hard sheet, and this hard sheet is made of polypropylene resin (PP), which is a relatively rigid resin.
, a hard polyvinyl chloride resin (PVC), and a polystyrene resin (PS), or a multilayer sheet having these resins as the outermost layer.

As PP, in addition to homopolymers, copolymers such as propylene-ethylene copolymers, mixtures of polypropylene and polyethylene resins, hydrogenated petroleum resins, terpene resins, etc. can be suitably used. Furthermore, as PS, polystyrene homopolymer, styrene-butadiene copolymer,
High impact styrene (HIPS) etc. can be used.

Further, as PVC, a composition mainly composed of polyvinyl chloride homopolymer and various vinyl chloride copolymers and having a low plasticizer content can be used.

The thickness of the hard sheet 1 is preferably from 20 to 500 μm, preferably from 30 to 100 μm; if it is less than 20 μm, it will have poor rigidity, and if it exceeds 500 μm, it will have poor secondary formability such as vacuum forming.

Next, the flexible sheet 2 in the present invention is a multilayer sheet having a gas barrier resin as an intermediate layer and an ethylene-vinyl acetate copolymer as the outermost layer.

Various types of flexible sheets can be used depending on the required quality, such as (a) EVA/gas barrier resin/adhesive resin/sealing resin, (b) EVA/gas barrier resin/sealing resin, etc. can be mentioned.

The EVA used for the outermost layer other than the sealing resin used in the above-mentioned flexible sheet 2 has a vinyl acetate content of 10 to 10%.
It is necessary to use 20% by weight, preferably 15 to 20% by weight; if it is less than 10% by weight, the adhesive strength after corona discharge treatment will be insufficient, and if it exceeds 20% by weight, the lamination will be difficult. There is a problem in that the odor peculiar to vinyl acetate tends to remain on the sheet.

Resins used for the gas barrier resin layer include nylon resin (Ny), saponified ethylene-vinyl acetate copolymer (EVOH), and polyvinylidene chloride resin (PVDC).
) Resin etc. can be used.

As Ny, 6 nylon resin, 66 nylon resin, 6
/66 nylon copolymer resin etc. can be used, and EVOH has an ethylene content of 25 to 75 mol% and a saponification degree of 90.
% by mole or more can be suitably used, and as PVDC, homopolymers and copolymers with vinyl chloride and other monomers can be used.

In addition, ordinary modified polyolefin resin grafted with carboxylic acid, carboxylic acid anhydride, etc. can be used as the adhesive resin, and as the sealing resin, low-density polyethylene resin, ethylene-vinyl acetate resin, etc., which have excellent heat sealability, can be used.
Ionomer resins and the like can be suitably used.

The total thickness of the flexible sheet having the above structure is preferably in the range of 30 to 200 μm, preferably 50 to 100 μm; if it is less than 30 μm, the sheet is likely to tear, and if it exceeds 200 μm, there is a problem of poor flexibility.

Note that the soft sheet 2 may be manufactured by a normal lamination method, and a coextrusion method using a multilayer die is preferable from the viewpoint of productivity.

In the present invention, the above-mentioned hard sheet 1 made of PP, PVC, or PS and the EVA layer, which is the outermost layer of the soft sheet 2, are made to face each other, and the surfaces of the facing sheets on both sides need to be subjected to corona discharge treatment. Corona discharge treatment has a high-frequency oscillator and electrodes, and a corona discharge treatment device (corona discharge electrode 3) that can perform continuous treatment as shown in Figure 1.
and counter electrode 4).

Corona discharge treatment is performed using the wettability index (JISK676) of the treated surface.
Processing conditions such as corona discharge output and processing speed are adjusted as appropriate so that the value (measured by 8) is 50 or more, preferably 54 or more. If the wetting index is less than 50, the adhesive strength at the interface after lamination is likely to be less than 150 (g/20 mm width), making it difficult to satisfy the requirements for a laminated sheet.

After the corona discharge treatment, it is necessary to heat and press both sheets immediately, and the adhesive strength tends to decrease over time.In the apparatus shown in FIG. This is done by contact pressure. The heating conditions of the heating roll 6 are usually 50°C or higher, preferably 140-1
A temperature of about 80°C is best; if the temperature exceeds 180°C, the sheet will tend to stick to the roll surface and shrink.
In addition, the contact pressure of the roll is 3 to 20 Kg/c in linear pressure.
It is preferable to set it to about m.

In addition, the above adhesive strength was measured at a take-up speed of 200 mm/min and 18
These are values measured in a 0° peel test.

Hereinafter, the present invention will be explained by examples.

(Example) Samples 1 to 3 Hard sheet; Hard PVC (thickness 40 μm) soft sheet;
A coextruded multilayer sheet (thickness: 90 μm) with the following configuration (EVA*/acid-modified polyolefin resin/EVOH/nylon resin/EVA) Using the above hard sheet and soft sheet, the sheet surface shown in Table 1 is shown in Figure 1. Do not laminate with equipment.

*The vinyl acetate content of sample 1.2 is 15% by weight, sample 3
The vinyl acetate content of is 5% by weight.

Corona discharge treatment machine (manufactured by VETAPHONE) High frequency oscillation part; Set output 4KW, oscillation frequency 30KHz electrode; Counter electrode roll 120mmφ Corona discharge electrode 5mm thickness x 2 main electrode spacing 2mm Processing speed; 15m/ Immediately after the corona discharge treatment, the hard sheet and the soft sheet were inserted between the heated metal roll 6 and the rubber roll 7 and bonded by thermocompression. The adhesive strength between the hard sheet and the soft sheet was measured for the obtained laminated sheet, and the results are shown in Table 1.

Bad ball 1 Heating metal roll temperature = 140 ~ 160'C, roll contact pressure = 5 ~ 10 K g / cm Sample No. 4, 5 Hard sheet is PP (30 μm) Other descriptions of No. 1 ~ 2 Same as.

Samples Nos. 6 and 7 Same as Nos. 1 and 2 except that the hard sheet is HIPS (300 Atm) and the soft sheet is EVA*/EVOH/f-ion resin/EVA (total thickness 52 μm).

*The vinyl acetate content of sample 6 is 15% by weight, and the vinyl acetate content of sample 7 is 5% by weight.

Table 1 From Table 1, N is the laminated sheet according to the present invention.

It can be seen that samples No. 1.4 and No. 6 have excellent adhesive strength. On the other hand, for NO2, 5, and 7, which were not subjected to double-sided corona treatment, the adhesive strength was poor, and even though both sheet surfaces were corona-treated and the wetting index was 50 or more, the vinyl acetate of the outermost layer EVA It can be seen that the adhesive strength is similarly inferior when the content of NO3 is low.

(Effects of the Invention) As explained above, the laminated sheet produced by the manufacturing method of the present invention is composed of a soft sheet with excellent flexibility and a hard sheet with excellent rigidity, has excellent adhesive strength, and is free of adhesives. Since it is not used, there is no problem with residual odor caused by adhesive.
Furthermore, it has excellent moldability and gas barrier properties, making it highly usable as containers for packaging various foods.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing an example of a manufacturing apparatus according to the present invention. 1...Hard sheet 2...Soft sheet Patent applicant Mitsubishi Plastics Co., Ltd.

Claims (1)

[Claims] A hard sheet (1) made of a polypropylene resin, a hard polyvinyl chloride resin, and a polystyrene resin is used as an intermediate layer, and a gas barrier resin layer is used as an intermediate layer, and the outermost layer is made of ethylene acetic acid with a vinyl acetate content of 10 to 20% by weight. A multilayer flexible sheet (2) made of a vinyl copolymer is placed so that the hard sheet (1) and the ethylene vinyl acetate copolymer layer of the soft sheet (2) face each other, and a corona discharge is generated on the sheet surfaces on both sides of the facing sheet. After applying the treatment to make the wettability index of the treated surface 50 or more, the above hard sheet (1
) and the soft sheet (2) at an interface adhesive strength of 150 g/
A method for producing a laminated sheet, characterized in that the sheet has a width of 20 mm or more.