JPH0771845B2 - Tarpaulins and their uses - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention relates to an ethylene / vinyl acetate copolymer (hereinafter, EVA).
May be abbreviated)) as a resin component. More particularly, the invention relates to tarpaulins suitable for heat resistant flexible containers.

[Conventional technology and problems]

Tarpaulins, which consist of a fiber substrate coated with flexible synthetic resin or rubber, have been used for a wide range of applications such as waterproof sheets and flexible containers. The coating layer is required to have various physical properties such as strength, flexibility, weather resistance, and workability.
In the past, cheap polyvinyl chloride was used exclusively. However, when polyvinyl chloride is used to coat tarpaulin, it is essential to use a plasticizer together, and in the use of flexible containers, the problem of migration of plasticizer to the contents arises, so EVA has begun to be used rapidly in recent years. There is.

By the way, when manufacturing a flexible container from a tarpaulin, a high-frequency welder process is adopted for joining the tarpaulins in terms of sealing property and processability. EV
When A is used, EVA having a low vinyl acetate content is unsuitable from the viewpoints of flexibility and high-frequency welder processability, and in general, the content of EVA is, for example, 15% by weight or more.

On the other hand, in flexible containers, along with the diversification of the contents to be filled, various improvements that cannot be handled by conventional EVA products have been required.
For example, in the filling of various chemical products, due to problems such as process restrictions or cooling cost reduction, it is possible to cool the products to a higher temperature without cooling them to the ambient temperature.
Filling may be done at temperatures such as 60 ° C. When a plurality of containers filled with such high temperature contents are stacked, there is a problem that the lowermost container is broken. This phenomenon is thought to be due to the lack of heat-resistant creep of EVA, and conventional EVA products were not sufficient. To improve this, a method using EVA with a low vinyl acetate content and a method using high-pressure method low-density polyethylene, linear low-density polyethylene, high-density polyethylene, etc. can be considered, but the time required for high-frequency welder processing significantly increases. However, it is difficult to say that it is a practical method because it causes the problem that the flexible container becomes difficult to fold due to its high rigidity.

[Means for solving problems]

The present inventors have examined a formulation for improving heat resistance without substantially impairing the high-frequency welder processability and flexibility in a tarpaulin suitable for a flexible container containing EVA as a resin component that does not have the drawback of plasticizer migration. . As a result, they have found that such a problem can be effectively solved by using a polymer composition in which two types of EVA having specific properties are blended in a specific ratio.

That is, the present invention has a vinyl acetate content of 10 to 20 wt% and a melt flow rate of 0.1 to 10 g / 10 min EVA 60 to 90 wt% and a vinyl acetate content of 22 to 35 wt%.
A tarpaulin obtained by coating a fiber base material with an EVA composition comprising 0.1 to 10 g / 10 min EVA of 10 to 40% by weight and having an average vinyl acetate content of 15 to 22% by weight. The invention also relates to a flexible container based on said tarpaulin.

In the present invention, two types of vinyl acetate having different vinyl acetate contents are used.
Use EVA. For EVA with a low vinyl acetate content,
Vinyl acetate contains 10 to 20% by weight, preferably 12 to 18% by weight, and has a melt flow rate (190 ° C, 21%
The amount of 60 g) is 0.1 to 10 g / 10 minutes, preferably 0.3 to 5 g / 10 minutes. This EVA has a vinyl acetate content of 10% by weight
If less than 1 is used, the vinyl acetate content described later is high.
Even if combined with any EVA, tarpaulin with excellent flexibility and high-frequency welder workability cannot be obtained. Further, if the vinyl acetate content exceeds 20% by weight, the one having excellent heat resistance cannot be obtained, and the bag breakage problem tends to occur when used in the flexible container. Furthermore, when forming the tarpaulin by calendering,
Roll kneading can be done in a short time, and in order to reduce the load, the EVA melt flow rate must be 0.1 g / 10 minutes or more, but if it is too large, the heat-resistant creep resistance will deteriorate, so 10 g / 10 minutes Must be:

On the other hand, in the present invention as an EVA having a high vinyl acetate content, the content thereof is 22 to 35% by weight, preferably 25 to 30% by weight, and the melt flow rate is 0.1 to 10 g / 10 minutes,
It is preferably 0.3 to 5 g / 10 min. Using a vinyl acetate content of less than 22% by weight does not substantially change from the above-mentioned EVA having a low vinyl acetate content,
The effect of the present invention cannot be obtained. The vinyl acetate content is 35
If it exceeds 5% by weight, the heat creep resistance is significantly impaired, which is not preferable. Further, the reason why the melt flow rate must be in the above range is the same as in the case of EVA having a low vinyl acetate content.

In the present invention, EVA with a low vinyl acetate content,
EVA with a high content thereof, the former 60 to 90% by weight, preferably 70 to 80% by weight, the latter 10 to 40% by weight, preferably 20 to 30% by weight, and the average vinyl acetate content. But
The composition is used in a proportion of 15 to 22% by weight. By using such an EVA composition, a high-frequency welder processability and flexibility are not substantially changed, and a tarpaulin excellent in heat-resistant creep property is obtained, as compared with the case where a single EVA having the same vinyl acetate content is used. be able to.
In this EVA composition, if the average vinyl acetate content is less than 15% by weight, the high-frequency welder workability and flexibility of the tarpaulin deteriorate, and if it exceeds 22% by weight, the heat creep resistance of the tarpaulin deteriorates. Become.

As the fibrous base material forming the tarpaulin, generally used is a plain weave, a twill weave, or a satin weave of synthetic fibers such as polyester, polyamide, polyacrylonitrile, or polyolefin, or filaments or staples such as natural fibers or semi-synthetic fibers. To be For example, 100-2
A woven yarn of about 000 denier, especially about 500 to 1200 denier, which is woven in a mesh shape so as to have 60 or less, especially about 10 to 20 threads per inch, is preferably used.

The production of tarpaulin is carried out by applying the above EVA composition to the above-mentioned fiber base material. If necessary, various fillers such as clay, talc, calcium carbonate, colorants such as titanium oxide and organic pigments, antioxidants, weathering stabilizers, antistatic agents, etc. are appropriately added to this EVA composition. You can keep it. EVA composition consists of two types of EVA,
The above-described compounding agent which is optionally further added can be prepared by dry blending or melt blending simultaneously or sequentially. Dry blend is Henschel mixer, tumbler mixer, ribbon blender, and melt brand is
It can be carried out using a single-screw extruder, a twin-screw extruder, a Banbury mixer, or the like. To apply the EVA composition to the fiber substrate, a calender molding method, an extrusion lamination method, a dry lamination method, or the like may be adopted, and the calender molding method is preferable. The tarpaulin has a thickness of, for example, 0.
It is sufficient to manufacture the one having a thickness of 4 to 2 mm, especially about 0.5 to 1.2 mm.

Such a tarpaulin is used for a waterproof sheet, a flexible container, and various other applications, but in the present invention, it is particularly suitable for a flexible container having improved heat resistance. In order to manufacture a flexible container from tarpaulin, it may be pasted in a bag shape with a high frequency welder.

〔The invention's effect〕

The tarpaulins obtained using the composition of the two EVAs of the present invention have a single vinyl acetate content and melt flow rate that are approximately similar to the average vinyl acetate content and melt flow rate of the composition. Compared with the one using EVA, the high frequency welder processability and flexibility are almost equal,
Heat resistance is improved. Therefore, in the case of using the flexible container, in addition to the advantages of low productivity and easy folding, there is an advantage that there is no bag breakage trouble even if the contents are filled at a higher temperature than in the conventional case and stacked. Thus, without completely cooling the product from the chemical plant, such as terephthalic acid, isophthalic acid, maleic anhydride, phthalic anhydride, bisphenol A, for example 60
It can be filled at temperatures such as ~ 80 ° C and stored in multiple stacks.

Hereinafter, the present invention will be described in more detail with reference to Examples.

〔Example〕

In the following examples and comparative examples, the flexural modulus MFR (melt flow rate), hardness, self-weight deformation amount, and high-frequency welder workability of the polymer composition were measured by the following methods and their performances were evaluated. .

1. Bending rigidity was measured according to JIS K-7106 using a short shelf sample with a size of 20 mm × 100 mm × 3 mm.

2. Measured according to MFR JIS K-6730 under conditions of 190 ° C and load of 2160g.

3. Hardness (A) Four short shelf-shaped samples of 20 mm × 100 mm × 3 mm were stacked and the A hardness was measured according to JIS K6301.

4. Deformation amount of self-weight 20 mm × 100 mm × 3 mm Short shelf-shaped sample Hold one end of the sample and keep it horizontal to the sample. The heat resistance of the polymer composition was evaluated by measuring and displaying in mm.

5. High frequency welter processability The processability was evaluated under the following conditions.

Frequency 40.46MHz, Sheet thickness 0.8mm Weld width 6mm Welding time 3 seconds (S), 5 seconds (S) Welding is ○, peeling at interface is X, middle is △
And

Examples 1 to 4 and Comparative Examples 1 to 5 Each component shown in Table 1 was melt-blended with each constituent ratio using a 40 mm single screw extruder. Evaluate various physical properties of the composition,
The results are shown in Table-1. However, for high-frequency welder processability, roll surface temperature of 190 ℃
A polyester woven fabric (800 denier, 18 woven fabrics / inch) was applied under the conditions described above to prepare a tarpaulin having a thickness of 1.0 mm, and the test was performed.

The vinyl acetate content in the table is a calculated value.

Example 5 and Comparative Example 6 Using the tarpaulins obtained in Example 4 and Comparative Example 1, a 1000 kg filling flexible container was prepared by high-frequency welding. (Eighteen flexible containers each based on Example 4 and Comparative Example 1) Ten terephthalic acids were added to each of these flexible containers.
It was filled by 00 kg at a temperature of 60 ° C. Further, each of the 18 bags was divided into 3 groups such as the bottom 3 bags, the middle 2 bags, and the top 1 bag, which were stacked in a pyramid shape, and left outdoors for 2 months, and the breakage of the flexible container at the bottom was observed. As a result, in the group of Comparative Example, rupture was observed in 3 out of the bottom 9 bags, whereas in the group of Example-3, rupture was not observed in all the bags.

Claims (2)

[Claims] 1. An ethylene / vinyl acetate copolymer having a vinyl acetate content of 10 to 20% by weight and a melt flow rate of 0.1 to 10 g / 10 min. 60 to 90% by weight and a vinyl acetate content of 22 to 35% by weight. An ethylene / vinyl acetate copolymer composition having a flow rate of 0.1 to 10 g / 10 min and an ethylene / vinyl acetate copolymer of 10 to 40% by weight and an average vinyl acetate content of 15 to 22% by weight is provided. A tarpaulin formed by coating a fiber base material. 2. A flexible container based on the tarpaulin according to claim 1.