JPS6365506B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing a heat-shrinkable synthetic resin film with excellent weather resistance. So-called heat-shrinkable synthetic resin films in the form of flats or tubes that shrink when heated are generally made from polyvinyl chloride resin, which is inexpensive and has excellent mechanical properties and processability. However, this polyvinyl chloride resin has poor weather resistance, and the surface will discolor especially if left outdoors for a long time, so conventional heat-shrinkable films made of polyvinyl chloride resin are not suitable for covering or packaging items used outdoors. The drawback was that it was unsuitable for this purpose. In order to overcome the above drawbacks and develop a heat-shrinkable film with excellent weather resistance, the present inventors focused on acrylic resin, which is known to have excellent weather resistance, and developed a heat-shrinkable film with a single layer of acrylic resin. Although we have considered acrylic resins, they are expensive, have poor stretching processability, and are extremely difficult to manufacture into heat-shrinkable films.Furthermore, the resulting heat-shrinkable films have low mechanical strength and high shrinkage temperatures, making them impractical. It was hot. However, as a result of further intensive studies, the present inventors found that a heat-shrinkable film made by stretching a composite sheet having an acrylic resin layer and a polyvinyl chloride resin layer not only has extremely excellent weather resistance, but also The present invention was achieved by discovering that it has a wide stretching temperature range, has excellent basic properties as a heat-shrinkable film such as shrinkage characteristics and tear strength, and is comparable to conventional heat-shrinkable films made of polyvinyl chloride resin. The gist is that at least an acrylic resin layer and a polyvinyl chloride resin layer are laminated so that at least one side is an acrylic resin layer to form a composite sheet, and the composite sheet is stretched at a temperature of 80°C to 130°C. The present invention resides in a method for manufacturing a weather-resistant heat-shrinkable film. The present invention will be explained in detail below. (In the following explanation, the term "sheet" refers to the product before stretching, and the term "film" refers to the product after stretching, and both of these include flat and tube-shaped products.) Acrylic resin in the present invention The layer is made by extrusion molding an acrylic resin such as methyl acrylate, ethyl acrylate, butyl acrylate, methyl methacrylate, or a copolymer thereof, or a polymer containing a small amount of styrene, acrylonitrile, vinyl chloride, etc. It can be obtained by Further, it is more preferable to add an ultraviolet absorber to the acrylic resin layer in order to prevent ultraviolet rays from reaching the polyvinyl chloride resin layer in order to improve weather resistance. In this case, the UV absorbers include salicylic acid esters such as methyl salicylate and phenyl salicylate, benzophenones such as 2,4 dihydroxybenzophenone and 2hydroxy-4methoxybenzophenone, and 2-(2 Examples include benzotriazole-based compounds such as 'hydroxy-5'methylphenyl)benzotriazole. In order to obtain an ultraviolet absorption effect, it is desirable to add 0.02 g/m ² or more, and since too much addition causes blistering on the film surface, it is desirable to add at a concentration of 2 weight percent or less. Next, the polyvinyl chloride resin layer is made by molding polyvinyl chloride resin, copolymer resin of vinyl chloride and vinyl acetate, etc. into a sheet shape by extrusion molding, calendar molding, etc.
Additives such as plasticizers, ultraviolet absorbers, and fillers may be added. The composite sheet in the present invention comprises laminating at least an acrylic resin layer and a polyvinyl chloride resin layer,
For example, an appropriate structure can be adopted, such as a two-layer structure consisting of an acrylic resin layer and a polyvinyl chloride resin layer, or a three-layer structure in which a polyvinyl chloride resin layer is sandwiched between an acrylic resin layer, but at least One side (the side that is exposed to light when the heat-shrinkable film of the present invention is used outdoors) must be an acrylic resin layer. Moreover, the shape may be a tube shape or a flat shape. Further, regarding the thickness structure of this composite sheet, it is desirable that the acrylic resin layer accounts for 50% or less of the total thickness of the composite sheet. If it exceeds 50%, the composite sheet as a whole becomes extremely expensive, and it becomes difficult to stretch, and even if it can be stretched, it becomes extremely brittle.
It has low tear strength. In addition, although the thickness of the acrylic resin layer on the side that should be exposed to light cannot be definitively determined, in order for the oxygen barrier properties of the acrylic resin to be effective in preventing discoloration of the polyvinyl chloride resin layer, When stretched into a heat-shrinkable film
It is desirable that the thickness is 10μ or more. for that purpose,
For example, in the case of a composite sheet that is planned to be biaxially stretched 2×2 times, the thickness of the acrylic resin layer is preferably 40 μm or more. When laminating an acrylic resin layer and a polyvinyl chloride resin layer in close contact with each other, the extremely high compatibility between the two can be used, for example, to form a double-layer sheet.
It is preferable to carry out thermocompression bonding at a temperature of 140°C to 190°C, or by in-die adhesion using coextrusion of both resins, as it is economical and does not require the use of adhesives or adhesive resins. . Of course, it is also possible to use a conventional dry lamination method using an adhesive, extrusion sandwich lamination using an adhesive resin, or the like. Next, in order to obtain a weather-resistant heat-shrinkable film from the composite sheet according to the present invention, the composite sheet having the acrylic resin layer and the polyvinyl chloride resin layer as described above is stretched using a roll, tenter, etc. Stretching may be performed by air pressure, tubular stretching using a diameter expanding device, or the like. The stretching temperature condition is preferably 80°C to 130°C, particularly 80°C to 120°C. Non-uniform stretching occurs at temperatures lower than 80°C, and 130°C
At temperatures higher than ℃, the tear strength of the sheet decreases, causing the sheet to break during stretching, and
If the temperature is higher than 120°C, flow stretching of the polyvinyl chloride resin occurs and the shrinkage rate of the resulting stretched film decreases, so the above range is preferable. In addition, a stretched film obtained by stretching at 100°C or lower can be shrunk to most of its ultimate shrinkage rate by heating with hot water at 100°C, which is extremely easy to obtain. It is particularly preferable for practical reasons such as showing the shrinkage rate. The stretching ratio is determined in relation to the heat shrinkage rate required for the use of the film, but it is generally recommended that the film be stretched 1.5 times or more in at least one direction. In this way, the weather-resistant heat-shrinkable film obtained according to the present invention has extremely excellent weatherability because the polyvinyl chloride resin, which has poor weatherability, is covered with an acrylic resin. In addition to being excellent in properties, tear strength, etc., the production method of the present invention allows stable stretching of acrylic resin sheets, which are extremely difficult to stretch individually, and at a lower stretching temperature of the polyvinyl chloride resin sheet alone. Since it can be stretched over a wider range of conditions, weather-resistant heat-shrinkable films can be produced extremely efficiently. Hereinafter, the present invention will be further explained in detail by giving examples. Example 1 A polyvinyl chloride sheet with a thickness of 400 μm prepared by adding 3 parts by weight of dibutyltin malate and 1.1 parts by weight of barium stearate to 100 parts by weight of a polyvinyl chloride resin with an average degree of polymerization of 800 and calender-molding the same, and methyl methacrylate. 1 part of 2-(2'hydroxy-5methylphenylbenzotriazole) was added to 100 parts of acrylic resin (Mitsubishi Rayon Co., Ltd., Acrypet IRH50), and an acrylic resin sheet with a thickness of 100μ was extruded at a pressing temperature of 150°C. A composite sheet with a thickness of 500μ was made by thermocompression bonding, and this was stretched 2×2 at each temperature shown in Table 1 using a test stretcher.
Table 1 shows the results of evaluating the stretching processability by performing biaxial stretching. Further, the results of evaluating the shrinkage characteristics of the heat-shrinkable film thus obtained are shown by solid lines in FIG. Furthermore, when this heat shrink film was subjected to a weather resistance acceleration test by irradiating light from the acrylic resin layer side using a standard sunshine weather meter manufactured by Toyo Rika Kogyo, there was almost no change in the surface color even after 1000 hours had passed. It was found to have excellent weather resistance. Furthermore, for samples stretched at 80℃, JIS
Table 2 shows the results of measuring tear strength using Z1702. Comparative Examples 1 to 2 The same acrylic resin and polyvinyl chloride resin used in Example 1 were used in Comparative Example 1 and Comparative Example 2, respectively.
The sample was molded into a single-layer sheet with a thickness of 500 μm, and its stretchability was evaluated in the same manner as in Example 1. The results are shown in Table 1. Further, the shrinkage characteristics of the heat-shrinkable film thus obtained are shown in FIG. 1, where the acrylic resin (Comparative Example 1) is shown by a dotted line and the polyvinyl chloride resin (Comparative Example 2) is shown by a broken line. Furthermore, Table 2 shows the tear strengths of single-layer films made of acrylic resin stretched at 120°C and polyvinyl chloride resin stretched at 80°C. In addition, the weather resistance of the polyvinyl chloride resin film (Comparative Example 2) was evaluated in the same manner as in Example 1.
After 1000 hours, the surface color changes and the color changes.
It wasn't something that would be practical.

【table】

[Table] As shown in Table 1, according to the method of the present invention,
Since the acrylic resin layer and the polyvinyl chloride resin layer are combined and stretched, it is possible to stretch the acrylic resin, which is extremely difficult to stretch with a single layer, and the stretching temperature range is wider than that of a single layer of polyvinyl chloride resin. , it is easier to stretch than ever before. In addition, as shown in Figure 1, the heat-shrinkable film obtained in this way has comparable shrinkage characteristics to conventional polyvinyl chloride heat-shrinkable films, and is actually superior in terms of ultimate shrinkage rate. By stretching in a wide temperature range of .degree. C., heat-shrinkable films having a wide variety of shrinkage characteristics can be obtained. In particular, those with a stretching temperature of 120°C or lower are preferable because they exhibit a high shrinkage rate, and those with a stretching temperature of 100°C or lower shrink close to their ultimate shrinkage rate at a heat shrinkage temperature of 100°C, so they are easily available as heating media. It has the advantage that hot water can be used. Next, as shown in Table 2, the tear strength of the heat-shrinkable sheet obtained by the present invention is comparable to that of the conventional heat-shrinkable film made of polyvinyl chloride resin, and is excellent in practical use. Example 2 A polyvinyl chloride resin layer with a thickness of 450μ was prepared by adding 10 parts by weight of dioctyl phthalate, 1.2 parts by weight of cadmium stearate, and 1.1 parts by weight of barium stearate to 100 parts by weight of polyvinyl chloride resin with an average degree of polymerization of 800. Inner layer, methyl methacrylate-based acrylic resin (Acrypet IR manufactured by Mitsubishi Rayon Co., Ltd.)
-D50) with 1.5 parts of 2-hydroxy-4methoxybenzophenone added to form an acrylic resin layer with a thickness of 50μ.
A tube-shaped composite sheet with an inner diameter of 10 mm was formed by coextrusion molding from an annular die while adhering inside the die so as to form the outer layer of the composite sheet, and this was stretched 2.5 times in the circumferential direction in hot water at 90°C by applying air pressure. The tubular heat-shrinkable film thus obtained has an axial tear strength of
The shrinkage rate in the circumferential direction when heated with hot water at 100°C was also 58.
% was excellent. Furthermore, when the weather resistance was evaluated in the same manner as in Example 1, there was no change in surface color tone even after 1000 hours had passed and it was excellent. Example 3 Polyvinyl chloride resin with the same formulation as Example 1,
An acrylic resin layer made by adding 0.5 parts of 4'-t-butyl phenyl salicylate to 100 parts of methyl methacrylate-based acrylic resin (Acrypet MF manufactured by Mitsubishi Rayon Co., Ltd.) was coextruded from a T-die while adhering inside the die. A composite sheet with a thickness of 100μ for each layer and a total of 200μ is created, and this is stretched to 80μ by a stretcher.
It was biaxially stretched 2×2 times at ℃. The tear strength of the resulting heat-shrinkable film was 8.5Kg/cm, which is not much different from the 9.5Kg/cm of a conventional polyvinyl chloride resin heat-shrinkable film of the same thickness (200μ).
This is an excellent heat-shrinkable film with a longitudinal shrinkage rate of 49% in warm water at 100°C, which is much better than the 2.3Kg/cm of acrylic resin heat-shrinkable film. Example 4 The inner layer was made of polyvinyl chloride resin having the same composition as in Example 2 and had a thickness of 400 μm, and the inner layer was made of methyl methacrylate-based acrylic resin (Acrypet IR manufactured by Mitsubishi Rayon Co., Ltd.).
D70) was co-extruded from an annular die while adhering inside the die to form an outer layer with a thickness of 100μ, with an inner diameter of 15 mm.
A tubular composite sheet of
A tubular heat-shrinkable film was obtained by stretching the film twice. This heat shrink film has an axial tear strength of 8.3Kg/cm
It is an excellent heat-shrinkable film, showing a circumferential shrinkage rate of 45% in hot water at 100°C. Also, Example 1
Weather resistance was evaluated in the same manner as above, and the surface color tone did not change even after 1000 hours and was excellent. Example 5 A polyvinyl chloride resin sheet with a thickness of 300μ having the same composition as in Example 1 and 2-(2' hydroxy-
A 100μ thick polyvinyl chloride resin sheet containing 1.5 parts by weight of benzotriazole (5-methylphenyl) and a 100μ thick acrylic resin (Mitsubishi Rayon Co., Ltd. AcryPets IR D50) sheet were thermocompressed in this order at a press temperature of 170°C. 3 with a thickness of 500μ
A layered composite sheet is made, and this is stretched using a stretcher.
Biaxial stretching was carried out at 90° C. to 2×2 times. The heat-shrinkable film thus obtained exhibited a tear strength of 8.4 Kg/cm.
It has a vertical shrinkage rate of 48% in hot water of 100℃, etc.
It is an excellent heat shrink film. Furthermore, when the weather resistance was evaluated in the same manner as in Example 1, the surface color tone did not change even after 1000 hours and was excellent.

[Brief explanation of drawings]

FIG. 1 shows the heat shrinkage characteristic curves of Example 1 and Comparative Examples 1 and 2, where the vertical axis is the vertical shrinkage rate (%) and the horizontal axis is the heating temperature. In the figure, the solid line shows the shrinkage characteristics of the heat shrinkable film of Example 1, the dotted line shows the shrinkage characteristics of the heat shrinkable film of Comparative Example 1, and the broken line shows the shrinkage characteristics of the heat shrinkable film of Comparative Example 2, and the temperature on the line shows the stretching temperature.

Claims (1)

[Claims] 1. A composite sheet is obtained by laminating at least an acrylic resin layer and a polyvinyl chloride resin layer so that at least one side is an acrylic resin layer, and the composite sheet is stretched at a temperature of 80°C to 130°C. A method for producing a weather-resistant heat shrinkable film.