JPS6224270B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a polypropylene laminated stretched film with good hand-tearability as a material film for adhesive tapes, and a method for producing the same. Cellophane is generally used for adhesive tapes. However, cellophane has the disadvantage of becoming brittle and yellowing due to deterioration due to ultraviolet rays and the like when used for a long period of time, and has the disadvantage of being inferior in dimensional stability, chemical resistance, water resistance, and abrasion resistance. In order to compensate for the above-mentioned drawbacks of Cellophane tape, adhesive tapes based solely on stretched polypropylene film have recently begun to be marketed. However, pressure-sensitive adhesive tapes based solely on stretched polypropylene film have the disadvantage of having a large elongation rate at tensile breakage (hereinafter abbreviated as "elongation rate") and poor manual tearability. The present invention relates to a laminated stretched film made of polypropylene that improves the above-mentioned drawbacks and has excellent hand-tearability, and a method for producing the same. A stretched film laminated with other stretchable thermoplastic resin sheets having a temperature range of ~130°C and an elongation rate of 30% or less at 20°C,
The stretching ratio is 2 times or more in the longitudinal direction,
A laminated stretched film with excellent transverse tearability, characterized in that the stretching ratio in the horizontal direction is larger than the stretching ratio in the longitudinal direction, and the product of the stretching ratio in the longitudinal direction and the stretching ratio is in the range of more than 4 and 56 or less, and the production thereof As a method, the above-mentioned laminated sheet is stretched at a temperature range of 120°C or higher and 165°C or lower, with a stretching ratio in the longitudinal direction of 2 times or more, a stretching ratio in the horizontal direction larger than that in the longitudinal direction, and a stretching ratio in both directions. The product is characterized by stretching within a range of over 4 and no more than 56. The polypropylene used in the present invention refers to polypropylene and copolymers with other resins such as ethylene-propylene copolymers, or copolymers based on these with other resins, such as ethylene-vinyl acetate copolymers, polyethylene, polybutene- It may also be a mixture of polyolefins such as No. 1 polyolefin. The sheet to be laminated to the above polypropylene sheet is selected from a resin sheet with a secondary transition point of 40°C to 130°C and a low elongation rate of 30% or less at 20°C. The secondary transition point as used in the present invention is a value measured with a dynamic viscoelasticity measuring device. Resins with a secondary transition point of less than 40°C have a large elongation rate at room temperature and cannot be used to improve hand-tearability even if laminated with polypropylene, while resins with a temperature of over 130°C have difficulty laminating and stretching with polypropylene. Become. Furthermore, if a resin with an elongation rate measured at 20°C (measured according to JISC2318) exceeding 30% is used, the elongation during film cutting will be large, and the hand tearability of polypropylene will not be improved even if laminated. Examples of resins with a low elongation rate and a secondary transition point within the above range include polymethacrylic acid alkyl ester polymers and their copolymers, and styrene polymers (polystyrene, acrylonitrile-styrene copolymers). etc.). These resins may be used alone or mixed with each other, or may be blended with other resins, antistatic agents, colorants, etc. When laminating the above-mentioned resin sheet with a low elongation rate on a resin sheet made of polypropylene, the lamination can be carried out using a known method such as using an adhesive, extrusion lamination, or using a heated pressure roll. good. Using the above combination, the laminated sheet is stretched in a temperature range of 120°C to 165°C. In this case, if the stretching temperature is less than 120°C, it will be difficult to stretch the polypropylene, and if the stretching temperature exceeds 165°C, undesirable effects such as thermal deterioration will appear on the laminated sheet. The minimum stretching ratio in the longitudinal direction is 2 times, and in order to improve the hand-tearability as an adhesive tape material, the stretching ratio in the lateral direction is larger than the stretching ratio in the longitudinal direction, and the stretching ratio in the longitudinal and lateral directions is The product should be in the range of more than 4 and less than 56. If the stretching ratio in the longitudinal direction is less than 2 times, the tensile strength in the longitudinal direction required as a material film for adhesive tapes cannot be obtained, and if the stretching ratio in the lateral direction is less than the longitudinal stretching ratio, the guideline, which is the object of the present invention, cannot be obtained. Cannot achieve improvement in cleft properties. If the product of the stretching ratios in each direction exceeds 56, the stretching film often breaks, resulting in poor productivity and failure to obtain a satisfactory product. The stretching method may be either sequential biaxial stretching or simultaneous biaxial stretching. The laminated stretched film obtained in the present invention contains natural rubber, polyisobutylene, butadiene-based synthetic rubber,
Alternatively, it can be used as an adhesive tape by applying a pressure-sensitive adhesive based on a mixture of these and a polyterpene with good compatibility. Furthermore, if the obtained laminated stretched film is used for packaging, it can be used as a packaging material that has practical strength and is easy to tear by hand. Example 1 A commercially available crystalline propylene-ethylene random copolymer (hereinafter abbreviated as "PP-E resin") was melt-extruded to form a sheet with a thickness of 500 μm. A toluene solution of 20% by weight of chlorinated polypropylene (chlorine content: 29.5% by weight) was applied as a welding agent to the above sheet so that the solid content after drying was 1 g/m ² . After that, the above sheet was given an elongation rate of 3.0% before stretching.
Acrylonitrile-styrene copolymer (hereinafter referred to as "AS resin") with a secondary transition point of 100℃ was laminated by extrusion lamination method so that the thickness after stretching was as shown in Table 1 to form a laminated sheet. The obtained laminated sheet was simultaneously biaxially stretched at a stretching temperature of 135° C. at a stretching ratio of 3 times in the longitudinal direction and a stretching ratio of 6 times in the transverse direction to obtain a laminated stretched sheet. -1 No.1
- No. 4, and as a comparative example, the above physical properties of only PP-E resin are shown in No. 5. For reference, the lateral manual tearability of only cellophane is shown in Table 2, No. 1 and No.
Shown in 2. The method for measuring each physical property is as follows. Tensile strength: Measured according to JISC2318. Horizontal hand tearability; film width 20 parallel to longitudinal direction
Cut into mm pieces, pinch the ends with the fingertips of both hands, and cut horizontally without using your fingernails. This is repeated 100 times, and the number of times the cut is made is expressed as a percentage.

【table】

[Table] As is clear from the above examples, although the lateral hand tearability of the stretched film made of PP-E resin alone is low at 37%, the stretched film laminated with AS resin has a significantly higher tearability of 100%. The tensile strength in the longitudinal direction also has a practical strength (500 kg/cm ² ) required as a tape material. Example 2 Commercially available polypropylene (hereinafter abbreviated as "PP resin"; the isotactic index indicated by the residue after extraction at the boiling point of n-heptane is 97.0%) and a secondary polypropylene with an elongation rate of 5.0% before stretching were used. A polymethyl methacrylate resin (hereinafter abbreviated as "PMMA resin") having a transition point of 76° C. was melt-extruded into an unstretched sheet, and was applied as an adhesive to the surface of the PP resin sheet as shown in Example 1. After applying and drying a solution of chlorinated polypropylene in the same manner as in Example 1,
Table 3: PMMA resin is laminated and stretched at a stretching temperature of 155℃.
The film was stretched at the respective stretching ratios shown below. Their stretchability and transverse tearability are shown in Table 3. The resins were laminated so that the total thickness after stretching was 35μ (PP resin 25μ, PMMA resin 10μ).

[Table] As is clear from No. 1 in Table 3, when the minimum magnification in the longitudinal direction is less than 2.0 times, continuity during film stretching is good, but thickness fluctuations are large, resulting in variations in tearability. It turns out that there is. Also, from No. 2 to No. 5, the minimum stretching ratio in the longitudinal direction is
2.0 times, the transverse direction draw ratio is always larger than the machine direction draw ratio, and the product of the machine direction draw ratio and the transverse direction draw ratio is greater than 4 and equal to or less than 56 to ensure continuity during stretching. It is possible to obtain a film with good film thickness, good thickness fluctuation, and excellent transverse hand tearability.If the product of the stretching ratio from No. 6 exceeds 56, there will be many breaks during stretching, and production I know it's going to get worse. Furthermore, from No. 7 and No. 8, even if the product of the draw ratios is within the above range, if the draw ratio in the transverse direction is less than the draw ratio in the longitudinal direction, the hand tearability in the transverse direction will be as shown in Table 2.
Lateral hand tearability (60%) of cellophane 40μ shown in
It turns out it's going to get worse. Example 3 Laminated sheet obtained in Example 1 (PP-E resin
500μ, AS resin 200μ) vertically at a temperature of 130℃.
The film was stretched 3.0 times and then sequentially stretched 6.0 times in the transverse direction at 140° C. to obtain a laminated stretched film with a PP-E resin layer of 25 μm and an AS resin layer of 10 μm. Its transverse hand tearability was 100%, and its longitudinal tensile strength was 631 Kg/cm ² , which is the same as in Example 1. Even by sequential biaxial stretching, a film with good transverse hand tearability was obtained. Manufactured. As is clear from the above Examples and Comparative Examples, according to the present invention, a laminated stretched film suitable for a raw material film for adhesive tapes, which has the excellent durability and chemical resistance of polypropylene and has excellent manual tearability. can be obtained, and the effect is great.

Claims (1)

[Claims] 1. Stretched sheet made of polypropylene laminated with a thermoplastic resin sheet having a secondary transition point in the range of 40°C to 130°C and an elongation at 20°C tensile breakage of 30% or less It is a film, and its stretching ratio is
A transverse direction characterized in that the longitudinal stretch ratio is 2 times or more, the transverse stretch ratio is greater than the longitudinal stretch ratio, and the product of the longitudinal and transverse stretch ratios is in the range of more than 4 and 56 or less. Laminated stretched film with excellent tearability. 2 A thermoplastic resin sheet having a secondary transition point in the range of 40°C to 130°C and an elongation at 20°C tensile breakage of 30% or less is laminated on a sheet made of polypropylene, and the laminated sheet is In the temperature range from ℃ to 165℃, the stretching ratio in the longitudinal direction is 2 times or more, the stretching ratio in the lateral direction is larger than the stretching ratio in the longitudinal direction, and the product of the stretching ratio in the longitudinal direction and the lateral direction is more than 4 and 56 or less. 1. A method for producing a laminated stretched film, which comprises stretching within a range.