JP2552337B2 - Heat shrinkable polyurethane film - Google Patents

Description

TECHNICAL FIELD The present invention relates to a heat-shrinkable polyurethane film excellent in mechanical strength against puncture, impact, etc., which is extremely suitable as a shrink wrapping material for various articles.

[Prior Art] Conventionally, as shrink-wrapping films, heat-shrinkable films such as polyvinyl chloride-based, polypropylene-based, and polyethylene-based films have been known, and are widely used in fields utilizing their respective characteristics.

However, among these, polyvinyl chloride heat-shrinkable films are excellent in low-temperature shrinkability, but on the other hand, chlorine gas is generated during heat sealing, or in addition to hygiene problems due to migration of plasticizer, etc. It has many defects such as poor mechanical strength such as tearing, piercing, and impact. On the other hand, polypropylene-based and polyethylene-based heat-shrinkable films are low in cost and widely used, but in addition to having a relatively high shrinkage temperature, there is a problem that the strength of puncture, impact, etc. is weak and easy to tear. Shrink wrapping film is a puncture,
At present, there is no one that can meet the user's request in terms of resistance to shocks.

[Problems to be Solved by the Invention] The present invention has been made in view of such circumstances, and an object of the present invention is to provide flexibility, high strength such as tension and tear, and resistance to external force such as piercing and impact. On the other hand, it is to provide a heat-shrinkable polyurethane film having particularly excellent resistance.

[Means for Solving the Problems] In order to achieve the above-mentioned object, the present inventors have focused on a thermoplastic polyurethane resin having high mechanical strength and excellent properties in terms of flexibility and elasticity. As a result of diligent studies on a polyurethane resin-based heat-shrinkable film, a polyurethane film having specific crystallinity, heat-shrinkability, and permanent elongation is not found in conventional heat-shrinkable films such as polyvinyl chloride resins. It was found that a film suitable for a shrink wrapping material having excellent mechanical strength against puncture, impact, etc. was obtained, and the present invention was completed.

That is, the present invention is a film made of a thermoplastic polyurethane resin having a heat of crystal fusion of 0.1 to 3.0 cal / g, and the heat shrinkage ratio of the film in a 120 ° C. glycerin bath is at least one of length and width directions. On the other hand, the present invention relates to a heat-shrinkable polyurethane film which is 20% or more and has a permanent elongation of 30% or less.

Hereinafter, the heat-shrinkable polyurethane film of the present invention will be described in detail.

In the present invention, the thermoplastic polyurethane resin, the rubber-like elastic polymer containing a urethane group in the molecular structure of the bifunctional polyol and diisocyanate and glycol as a main raw material is a generic term for those having thermoplasticity,
Specifically, it is composed of one or more thermoplastic polyurethane resins such as adipate ester-based, polyether-based, caprolactone ester-based, and polycarbonate-based thermoplastic resins, which are distinguished by the type of raw material such as the polyol used. The heat of fusion of crystal is 0.1 to 3.0 cal / g, preferably 0.5 to 2.0 cal / g.

Here, the heat of crystal fusion of the thermoplastic polyurethane resin is 0.
When the amount is less than 1 cal / g, the adhesiveness is strong and the film and the film to be encapsulated are easily adhered to each other, resulting in insufficient contraction of the adhered part or occurrence of a twitching phenomenon, resulting in poor appearance. While a fatal problem occurs as a packaging material, when the heat of crystal fusion exceeds 3.0 cal / g,
The flexibility, elastic force, and further heat shrinkability are deteriorated, and the heat shrinkable film intended by the present invention cannot be obtained.

Incidentally, the thermoplastic polyurethane resin used in the present invention,
If the heat of crystal fusion satisfies the above conditions, a thermoplastic polyurethane resin having crystallinity and an ordinary thermoplastic polyurethane resin having no crystallinity can be blended and used, and its properties are not significantly changed. Within the range, it blends thermoplastic resins such as polyvinyl chloride, polyester, polyamide, acrylic, and polyolefin, or UV absorbers, antioxidants, and coloring for the purpose of improving weather resistance and handleability. Agents, lubricants, etc. may be added as necessary, as appropriate.

The heat-shrinkable polyurethane film of the present invention also has a heat shrinkage ratio of the film in a 120 ° C glycerin bath of at least 20% or more in at least one of the length direction and the width direction, and preferably 30% or more, and The permanent set should be less than 30%, preferably less than 20%.

This is because the present inventors have noticed that when a thermoplastic polyurethane film having peculiar properties to flexibility and elastic force is used as a shrink wrapping material, excellent binding properties can be obtained even at a relatively low shrinkage ratio. As a result of a detailed examination of the shrinkage rate of the film and the binding property after packaging and the resistance to puncture, impact, etc., the binding property is improved when the shrinkage rate of the film is increased, but on the other hand, the molecular orientation is too advanced to cause permanent elongation. It is possible to apply polyurethane film to shrink wrapping material only when both heat shrinkage rate and permanent elongation satisfy specific conditions, such as increase in mechanical strength such as puncture, impact, etc. Because.

Therefore, in the polyurethane film of the present invention,
If the thermal shrinkage in a 0 ° C glycerin bath is less than 20% in at least one of the length and width directions, the shrinkage will be insufficient and the finished appearance after packaging will be poor, while the permanent elongation of the film If it exceeds 30%, the mechanical strength such as puncture and impact is significantly reduced, and the disadvantage of the properties of the polyurethane film is lost.

Incidentally, in the present invention, the reason why the heat shrinkage rate of the polyurethane film is expressed as a value in a glycerin bath is that heat conduction to the film is higher than that of a heat medium such as hot air or steam that is usually used in shrink wrapping. Is uniform, and the heat shrinkage rate can be accurately evaluated quantitatively.

Further, the thickness of the heat-shrinkable polyurethane film of the present invention is appropriately selected according to its application and is not particularly limited, but film strength, tightness, economical efficiency, and further to an article to be included. In consideration of the fit and the like, the film thickness of 10 to 300 μ is usually preferable.

[Examples] Hereinafter, the heat-shrinkable polyurethane film of the present invention will be described in more detail with reference to Examples.

The methods for measuring and evaluating the physical properties used in the present invention are as follows.

(1) Heat of fusion of crystals Put 15 mg of sample into a differential scanning calorimeter (DSC),
The temperature was raised at a heating rate of 5 ° C./min, the calorific value was determined from the area of the exothermic peak that appears during melting, and this was converted to 1 g of the sample.

(2) Heat Shrinkage The sample film was immersed in a 120 ° C glycerin bath for 10 seconds, and the heat shrinkage during that time was determined.

(3) Permanent Elongation A sample film punched into dumbbell No. 1 type was pulled to a length corresponding to 100% elongation between marked lines, held for 10 minutes and then contracted, and the permanent elongation was measured by the following formula.

L ₀ : Distance between marked lines L ₁ : Distance between marked lines after contraction (4) Puncture strength After fixing the sample film on the cross section of a cylindrical ring with a diameter of 75φ, fix it on the center of the circular film surface. A conical head with a tip angle of 53 degrees was pierced at a speed of 200 mm / min, and the maximum load (unit: g) until a hole was formed in the film was defined as the puncture strength.

(5) Impact strength The impact strength (unit: kg-cm) was measured under the conditions of a full scale of 30 kg-cm and an impact head of 1/2 inch using a pendulum impact tester (manufactured by Toyo Seiki Seisaku-sho, Ltd. film impact tester).

(6) Appearance after shrink wrapping When the sample film is biaxially shrinkable by using a shrink tunnel device in which the temperature inside the tunnel is set to about 140 to 160 ° C. and the passage time is set to about 10 seconds (Examples 1 to 7, Comparative Examples) 1 to 4) was shrink-wrapped by three-way seal packaging, and when the sample film was uniaxially shrinkable (Examples 8 to 10 and Comparative Examples 5 to 6), the spray container was shrink-wrapped. The state after packaging was visually evaluated, and those with good binding and appearance were rated (◯), and those with poor binding or significant uneven shrinkage were rated (x).

(7) Comprehensive evaluation A comprehensive evaluation was made based on the results such as puncture strength, impact strength and appearance after shrink wrapping. A film suitable for shrink wrapping (○), an unsuitable film (x) And

Examples 1 to 4 and Comparative Examples 1 to 2 Using an inflation extrusion molding machine having a diameter of 50 mm, thermoplastic polyurethane resins having different heats of crystal fusion as shown in Table 1 were melt-kneaded at a temperature of 160 to 200 ° C. After extruding from an inflation die, the film was blow-molded at a blow-up ratio of 2.8 to 3.0 and a take-up speed of 10 to 12 m / min to form a heat-shrinkable polyurethane film having a film thickness of 30 μm.

Table 1 shows the results of evaluating the heat shrinkage rate, the permanent elongation, the puncture strength, the impact strength, the appearance after shrink-wrapping, and the like of these polyurethane films. From the same table, those whose heat of crystal fusion, heat shrinkage, and permanent elongation are all within the scope of the present invention have high mechanical strength such as puncture and impact, and have a good appearance after shrink wrapping. Suitable as a film,
Furthermore, it was confirmed that these properties were far superior to those of the commercially available polyvinyl chloride heat-shrink film (Reference Example 1) and polypropylene heat-shrink film (Reference Example 2) shown as reference examples. Was done.

Examples 5 to 7 and Comparative Examples 3 to 4 A thermoplastic polyurethane resin having a heat of crystal fusion of 0.8 cal / g was used.
Resin temperature by inflation extrusion molding machine with 40 mm diameter
After extruding at 180 ℃, blow-up ratio of 1.8 to 4.0 and take-up speed of 6 to 20m / min, respectively. I made a film.

For these polyurethane films, permanent elongation,
Table 2 shows the results of evaluation of puncture strength, impact strength, appearance after shrink-wrapping, and the like. From the table, those having both thermal shrinkage and permanent elongation within the scope of the present invention are machines for puncture, impact, etc. It was confirmed that the mechanical strength was strong and the appearance after shrink-wrapping was also good.

Examples 8-10, Comparative Examples 5-6 A thermoplastic polyurethane resin having a crystal fusion heat of 1.5 cal / g was used.
Using a T-die extruder with a diameter of 50 mm, the resin temperature is 190 ° C.
Extrusion molding was performed under the conditions of. At that time, the molten sheet extruded from the die was collected by a cooling roll rotating at a peripheral speed of 3 to 12 m / min to prepare polyurethane films having various heat shrinkage rates in the length direction.

These polyurethane films were evaluated for permanent elongation, puncture strength, impact strength, appearance after shrink wrapping, etc., and as shown in Table 3, those having thermal shrinkage and permanent elongation within the scope of the present invention were pierced, It was confirmed that the strength against impact was strong and the appearance after shrink-wrapping was also good.

[Effects of the Invention] As described above, the heat-shrinkable polyurethane film of the present invention is
It has excellent mechanical strength against piercing, impact, etc. that could not be used with this type of film until now, and also has high tensile properties and abrasion resistance, moisture permeability, flexibility and thermal adhesion unique to polyurethane resin. Since it has both properties, it can be applied not only to shrink wrapping materials, but also to industrial materials such as shrink tapes and gloves for precision work, and has a wide range of applications.

Claims (1)

(57) [Claims] 1. A film made of a thermoplastic polyurethane resin having a heat of crystal fusion of 0.1 to 3.0 cal / g, wherein the film has a thermal shrinkage in a glycerin bath at 120 ° C. of at least one of length and width directions. On the other hand, a heat-shrinkable polyurethane film which is 20% or more and has a permanent elongation of 30% or less.