JPS6151993B2 - - 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 drawback of becoming brittle and yellowing due to deterioration due to ultraviolet rays and the like when used for a long time, and also has the drawback 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 put on the market. However, pressure-sensitive adhesive tapes based solely on stretched polypropylene film have the disadvantage that they have a high elongation rate at tensile breakage and are poor in manual tearability. The present applicant has previously filed an application for a laminated stretched film with excellent hand-tearability that improves the above-mentioned drawbacks, and a method for manufacturing the same. Curving (hereinafter referred to as "curling") of the film due to differences in expansion coefficient, internal strain, etc. of each film layer that is laminated and stretched without damage.
That's what it means. ) and a method for producing the same. The gist of the present invention is that the secondary transition point is 40
The intermediate layer is a thermoplastic resin layer that is in the range of ℃ to 130℃ and has an elongation rate of 30% or less at tensile break at 20℃,
It is a stretched film in which polypropylene resin layers are laminated on both sides, and 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 stretching ratio in the longitudinal direction and the lateral direction is The product of magnification is in the range of more than 4 and less than 56, and the thickness of the intermediate layer is the total thickness of the laminated stretched film.
30% to 80%, and the composition ratio of the thickness of the polypropylene resin layers on both sides is 0.25 to 4. A laminated stretched film with excellent lateral hand tearability and a method for producing the same. be. Polypropylene as 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 resin used for the intermediate layer of the laminated stretched film in the present invention has a secondary transition point in the range of 40°C to 130°C, and is a low elongation resin sheet with an elongation rate of 30% or less at tensile break at 20°C. Select. The secondary transition point as used in the present invention is a value measured with a dynamic viscoelasticity meter. Resins with a secondary transition temperature of less than 40°C have a large elongation rate at room temperature, and even if laminated with polypropylene, the hand tearability will not be improved, and resins that can reach temperatures of 130°C have difficulty laminating and stretching with polypropylene. becomes. In addition, the elongation rate at tensile break measured at 20℃ (JIS
Measured with C2318. ) is 30%, the elongation rate during furme cutting will be large, and even if laminated, the hand tearability of polypropylene will not be improved. Examples of the resins having a low elongation rate include polymethacrylic acid alkyl ester polymers and copolymers thereof, and styrene polymers (polystyrene, acrylonitrile-styrene copolymers, etc.). These resins may be used alone, or may be mixed with each other, or may be blended with a colorant or the like. The polypropylene mentioned above and a resin with a low elongation rate and a secondary transition temperature of 40°C to 130°C are laminated together, but if they are laminated one layer at a time, the laminated stretched film will not work due to the difference in the expansion coefficient of both resins. Curl to one side. In order to prevent this curling and improve the hand-tearability, it is preferable to bond the laminated film with polypropylene resin layers on both sides and a thermoplastic resin layer as specified above in the middle layer. However, if the ratio of the thicknesses of the polypropylene resin layers on both sides is outside the range of 0.25 to 4, the thinner polypropylene resin layer cannot correct curling.
Therefore, the ratio of the thicknesses of the polypropylene resin layers on both sides is preferably within the above range. In addition, the thickness ratio of the resin with low elongation used as the intermediate layer is 30% to 80% of the total thickness of the laminated film.
It should be within the range of %. If it is less than 30%, the hand tearability of polypropylene will not be improved, and if it is more than 80%, breakage will occur during the lamination stretching ratio with polypropylene, resulting in poor stretchability. The above resin layers may be bonded together by a known method such as a dry lamination method, an extrusion lamination method, or a method using a hot pressure roll. The laminated unstretched sheets laminated using the above combination are 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 horizontal direction is 2 times, and in order to improve the hand-tearability of the adhesive tape material, the horizontal stretching ratio is higher than the longitudinal stretching ratio, and the horizontal and vertical stretching ratios are It is preferable that the number of stacked layers is more than 4 and less than 56. The stretching ratio in the longitudinal direction is less than 2 times, and the product of the stretching ratios in the longitudinal direction and the transverse direction is 4 times or less,
It does not have the necessary longitudinal tensile strength as a raw material film for adhesive tapes, has large thickness fluctuations, and has uneven hand tearability. Furthermore, if the stretching ratio in the transverse direction is lower than the stretching ratio in the longitudinal direction, the improvement in the hand tearability in the transverse direction, which is the object of the present invention, cannot be achieved. If the product of the stretching ratios in each direction exceeds 56, the film will often break during stretching, resulting in poor productivity and failure to obtain a satisfactory product. Note that the stretching method may be either sequential biaxial stretching or simultaneous biaxial stretching. The laminated stretched film obtained in the present invention can be used as an adhesive tape by applying a pressure-sensitive adhesive based on natural rubber, polyisobutylene, butadiene-based synthetic rubber, or a mixture of these and a polyterpene with good compatibility. can. 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] Elongation rate at tensile break at 20°C 2.4%, secondary transition point
Commercially available unstretched polystyrene (hereinafter referred to as "PS") at 90℃
It is abbreviated as ) as the middle layer and a sheet of chlorinated polypropylene (chlorine content
An 8% by weight toluene solution (29.5% by weight) was applied so that the solid content after drying was 1 g/m ² . Thereafter, a commercially available crystalline propylene-ethylene random copolymer (hereinafter referred to as "PP--
Abbreviated as "E". ) was laminated into a laminated unstretched sheet, and then the longitudinal stretching ratio was 3 at a stretching temperature of 135°C.
Stretching was performed at a transverse stretching ratio of 6.0 times. Note that the thicknesses of PS and PP-E to be laminated are configured so that the respective thicknesses after stretching become the thicknesses shown in Table 1. The degree of lateral hand tearability and curling of each obtained laminated stretched film is hereinafter referred to as "curl degree". ) are shown in Table-1. Hand-tearability in the horizontal direction; width of the film in the vertical direction is 2.0 mm
Cut it out, then pinch the lateral ends with the fingertips of both hands and cut horizontally without using your nails. This is repeated 100 times, and the number of cuts at this time is expressed as a percentage.In the case of a thick cellophane tape with a thickness of 40μ, the lateral manual tearability is 60%, and anything above this value is practical. Curling degree: The stretched film is stretched both vertically and horizontally.
Cut the film into 1m square pieces and cut out 20
℃ and relative humidity of 65℃ on a flat surface, the radius of curling at that time is γcm, and the curl degree =
It is expressed as 1/γ. When γ≧20cm, it is assumed that the curl is not substantially curled, and the curl degree is set as 0.

【table】

[Example 2]

Commercially available polypropylene (hereinafter referred to as "PP") was placed on both sides of an unstretched sheet of polymethyl methacrylate (hereinafter referred to as "PMMA") with an elongation rate of 5.0% at 20°C tensile breakage and a secondary transition point of 76°C. The isotactic index (residue after extraction at the boiling point of n-heptane is 97.0%) was laminated into an unstretched sheet using the same adhesive as in Example 1, and the laminated unstretched sheet was stretched at 155°C. It was stretched at various stretching ratios shown in Table 2 at various temperatures. Their stretchability and transverse tearability are shown in Table 2. The resins were laminated so that the total thickness after stretching was 30μ (PP: 7μ, PMMA: 16μ, PP: 7μ).

[Example 3]

Elongation rate at tensile break at 20℃ 3.0%, secondary transition point
A laminated unstretched sheet obtained by laminating commercially available PP on both sides of an unstretched sheet of acrylonitrile-tyrene copolymer (hereinafter abbreviated as "AS") at 100°C via an adhesive layer as in Example 1. was simultaneously biaxially stretched at a stretching temperature of 155° C. at a stretching ratio of 3 times in the longitudinal direction and 7 times in the transverse direction to obtain a laminated stretched film of PP8μ/AS14μ/PP8μ. The film had a lateral hand tearability of 100% and a curl degree of 0. As is clear from the above examples, according to the present invention, a laminated stretched film suitable for a material film for tapes, which has the excellent durability and chemical resistance of polypropylene, and has excellent hand tearability and secondary processability. The effect is great.

Claims (1)

[Claims] 1. The secondary transition point is in the range of 40°C to 130°C, and 20°C
A stretched film with a thermoplastic resin layer having an elongation rate at tensile break of 30% or less at temperature as an intermediate layer, and a polypropylene resin layer laminated on both sides of the thermoplastic resin layer, and the stretching ratio in the longitudinal direction is 2 times. In the above, the transverse stretching ratio is larger than the longitudinal stretching ratio, and the product of the longitudinal and transverse stretching ratios is in the range of more than 4 and 56 or less, and the thickness of the intermediate layer is the entire length of the laminated stretched film. The thickness is 30% to 80%, and the ratio of the thickness of the polypropylene resin layers on both sides is
A laminated stretched film with excellent transverse tearability characterized by having a composition ratio of 0.25 to 4. 2 The secondary transition point is in the range of 40℃ to 130℃, and 20
A thermoplastic resin sheet with an elongation rate at tensile break of 30% or less at °C is used as the intermediate layer, and a polypropylene resin is laminated on both sides to form a laminated unstretched sheet, and the thickness of the intermediate layer of the laminated unstretched sheet is 30% of thickness
~80%, and the ratio of the thickness of the polypropylene resin layers on both sides is 0.25 to 4, and then the laminated unstretched sheet is stretched at a longitudinal stretching ratio in the temperature range of 120°C to 165°C. is 2 times or more, the lateral stretch ratio is greater than the longitudinal stretch ratio, and the product of the longitudinal and lateral stretch ratios exceeds 4 and is 56 or less. A method for producing an excellent laminated stretched film.