JPH024808A - Polypropylene film for tacky tape - Google Patents

Abstract

PURPOSE:To obtain the subject product with a low amount of dimensional change during application of a tacky agent, etc., or a drying process and resistance to occurrence of earth-shaped blemish by specifying an amount of strain in the longitudinal direction of a film, the starting temperature of width direction heat-shrinkage strain and the maximum value thereof. CONSTITUTION:An objective product with an amount of strain (Y)% of a film in the longitudinal direction satisfying the formula [T is measured temperature ( deg.C); W is applied load (g/mm<2>)], >=116 deg.C starting temperature of width direction heat-shrinkage strain and 100-500g/mm<2> maximum value thereof. The above- mentioned product is obtained, e.g., by melt extruding polypropylene with 1.6-2.4 intrinsic viscosity [eta] at 220-280 deg.C, preheating the resultant cast film at 115-145 deg.C, stretching the film to 5-8 times in the longitudinal direction and 6-12 times in the width direction and carrying out heat treatment at 150-166 deg.C while loosening by 3-15% in the width direction.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a polypropylene film for adhesive tape.

[Conventional technology]

BACKGROUND ART Conventionally, adhesive tapes having an adhesive layer on one side of a tape-shaped support are widely known and widely used.

Polypropylene film is no exception, and due to its excellent properties, an adhesive layer is applied to one side of the polypropylene film support and a release agent layer is applied to the opposite side.
Damplon tape, intertape, vegetable binding tape, etc.) are used.

For example, JP-A-60-88049 describes a biaxially oriented polypropylene film in which a nucleating agent and a silicon compound are contained in crystalline polypropylene whose intrinsic viscosity [η] and degree of isotacticity are specified. It is disclosed that it can be used for tapes.

[Problem to be solved by the invention]

However, the conventional two-wheel stretched polypropylene film has the following problems. In other words, there are problems such as dimensional changes in the film during coating of the adhesive layer and release agent layer and subsequent drying process, and "worm"-like defects due to air entrainment in the adhesive layer during the winding process. be.

In addition, "'worm"-like defects are caused when a polypropylene film coated with a release agent on one side and an adhesive on the other side is rolled up as a wide tape after passing through a hot air drying oven. Due to factors such as solvent properties, thermal dimensional changes, slippage, and winding tension, a part of the film becomes rippled and wound, and this becomes a state in which air is engulfed with a width of 5 to 10 mm and a length of about 10 cm. This is a defect that looks like a worm when viewed from the surface of the tape.

The present invention improves these problems and provides polypropylene for adhesive tapes, which has small dimensional changes in the adhesive layer, release agent coating, and subsequent drying process, and has almost no possibility of producing "worm"-like defects. The purpose is to provide film.

[Means to solve the problem]

In order to achieve the above-mentioned object, the present invention has been developed so that the strain IY (%) in the longitudinal direction of the film is -3<Y≦{(W-8
0)/220)exp(0,035(T-80)) However, T: Measurement temperature (℃) W: Applied load (CJ/mm2') and the width direction heat shrinkage stress starting temperature is 116 ℃ or higher, the maximum value of heat shrinkage stress in the width direction is 100 to 500 g/mm
2, the polypropylene film for adhesive tape is characterized.

The polypropylene for adhesive tapes of the present invention includes polypropylene homopolymers and propylene copolymerized with monomers such as ethylene and butene within 2% by weight, such as ethylene propylene copolymers and propylene butene copolymers. In the case of the invention homopolypropylene is preferred. Among these, (1, I
: about 98 to 99.5%) homopolymers are particularly preferred.

The intrinsic viscosity [η] of polypropylene is not particularly limited, but is preferably 1.6 to 2.4 in terms of ζ film-forming properties and solvent resistance. For polypropylene, if necessary, an antistatic agent consisting of an amphoteric or nonionic antistatic agent or a mixture of both may be added.
．． Antioxidants, heat stabilizers, lubricants, crystal nucleating agents, ultraviolet absorbers, pigments, etc. may be added within a range of 1 to 1.0% by weight, and within ranges that do not impair the effects of the present invention.

In addition, the film applied to the adhesive tape of the present invention is:
The above-mentioned polypropylene film is preferably -axially stretched, particularly biaxially stretched from the viewpoint of rigidity, transparency, strength and elongation.

Strain in the longitudinal direction of the polypropylene film of the present invention ff
1Y (%) must satisfy the following formula (1).

−3<Y≦{(W-80)/220)exp(0,03
5 (Ding-80)) - (1) However, the king is the measured temperature (℃),
W is the applied load (Q/mrr+2>).

Here, the longitudinal strain mY (%) is calculated by applying a load W l/mm2) to a sample with a sample length of 1o and heating it from 40°C to 140°C at a heating rate of 5°C/min. T
When the expansion/contraction length Δp at (° C.) is measured, it is defined by the following formula.

Y=100 (ΔfJ/, j!o) However, the load W is 80 g/mm2 or more and 1000 g/mm2 or less. That is, Y is a value given for each load W and each temperature T, and when the load W is 80 to 1000 g/mm2 and the temperature T is 4
It is sufficient to satisfy the above formula (1) at each load and each temperature within the range of 0 to 140°C. If the load W is less than 80 g/mm2, it will be due to thermal shrinkage stress, and if it exceeds 10,000/mm2, the polypropylene will be in a region of significant plastic deformation at high temperatures, resulting in large fluctuations in measured values.
It is not necessary to satisfy the formula.

In addition, the measurement temperature T is near the melting point of polypropylene (approximately 1
50° C.) or above, viscous flow occurs, so the measurement temperature range is 40 to 140° C. Outside this temperature range, Y does not need to satisfy the above formula (1).

If the strain in the longitudinal direction IY is lower than -3, the dimensional change (elongation) of the film will be significant during the drying process after applying the adhesive or mold release agent, and furthermore, the film will develop welts due to air entrapment in the adhesive layer during the winding process. On the other hand, if the strain ff1Y is larger than the value on the right side of equation (1) above, the tension in the adhesive coating process, the drying process after coating, and the winding process will be delicate. In response to tension fluctuations, the film stretches in the tension direction (longitudinal direction) and at the same time width fluctuations (dimensional changes) occur in a direction perpendicular to the tension direction, inducing "worm-like defects."

The polypropylene film of the present invention needs to have a heat shrinkage stress initiation temperature in the width direction of 116°C or higher, preferably 120°C or higher.

Here, the width direction heat shrinkage stress starting temperature is the sample 100m
m, a film with a width of 10 mm is fixed with a load of 50 g/mm2, and the temperature is raised from 25 °C at a rate of 3 °C/min. The horizontal axis is the temperature, and the vertical axis is the heat shrinkage stress in the width direction. When drawing a heat shrinkage stress curve, it is the temperature at which the heat shrinkage stress in the width direction begins to increase rapidly. An example of a temperature-width direction heat shrinkage stress curve is shown in FIG. 1, where T1 is the width direction heat shrinkage stress starting temperature.

If the width direction heat shrinkage stress onset temperature T1 is less than 116°C, preferably less than 120°C, dimensional changes (width shrinkage) occur in the process of drying the adhesive and mold release agent, and "worms" due to air entrainment occur. defects occur. The upper limit of the heat shrinkage start temperature T1 is not particularly limited, but it will be about 150° C. in view of the melting point of polypropylene, etc.

Next, the maximum width direction heat shrinkage stress value 5IIlax of the polypropylene film of the present invention must be 100 to 500 q/mm2.

Here, the maximum width-direction heat-shrinkage stress value refers to the width-direction heat-shrinkage stress at the peak point in the above-mentioned temperature-width-direction heat-shrinkage stress curve. In FIG. 1, 5fflax is the maximum value of the heat shrinkage stress in the width direction.

If the width direction heat shrinkage stress maximum value Smax is less than 100q/mm2, the film will stretch or sag during the application of the adhesive layer and release layer and during the drying process, resulting in "worm"-like defects, and in severe cases, the waveform It becomes wrinkled. On the contrary, 5
If IIlax exceeds 5000/mm2, the film will shrink during the application of the adhesive and release agent and during the drying process, and at the same time, "worm"-like defects will also occur.

As a polypropylene film for adhesive tapes, it is preferable to use a film with a low temperature dependence of the heat shrinkage rate in the width direction. Specifically, if the heat shrinkage rate at 130°C is set to ±1.0%, dimensional changes and "worm" appearance will be avoided. This is particularly preferable since the occurrence of defects can be largely prevented.

Further, it is preferable to set the static friction coefficient of the polypropylene film at 80° C. to 1.0 or less and the dynamic friction coefficient to 0.8 or less, since this improves the slipperiness during the drying process and prevents the occurrence of "worm"-like defects.

Furthermore, the Young's modulus of the film (especially in the longitudinal direction) is 250K.
Q/mm2 or more, preferably 275 Kg/mm21X or more, is more preferable because it prevents the occurrence of "worm"-like defects and improves handleability.

Although the thickness of the polypropylene film of the present invention is not particularly limited, 30 to 60 μm is preferably used.

It is clear that the film of the present invention may be subjected to a corona discharge treatment in the presence of air, carbon dioxide gas, nitrogen gas, etc. alone or in a mixed gas to improve the adhesion of the pressure-sensitive adhesive and mold release agent.

Next, a method for producing a polypropylene film for adhesive tape according to the present invention will be described, but the method is not necessarily limited thereto. As polypropylene, the intrinsic viscosity [η
] - Using polypropylene of 1.6 to 2.4, the polymer was fed to an extruder and melted at 220 to 280"C, and then the melt was extruded from a die and cooled to 13 to 50"C. It is cooled and assimilated on a drum by a known contact method such as an air knife method or a press roll method.

The cast film is preheated with a group of preheating rolls heated to 115 to 145°C, then stretched in the longitudinal direction by 4 to 10 times, preferably 5.0 to 8 times, and then stretched to 154 to 169°C.
The film is stretched 6 to 12 times in the width direction using a stenter in an atmosphere of 100° C., and then heat treated at 150 to 166° C. while relaxing 3 to 15% in the width direction. In the case of the present invention, the stretching temperature and magnification in the longitudinal direction and the width direction are set relatively high.
9 to 12 times at a temperature in the width direction of 158 to 169° C.).It is important to subsequently perform a relaxation heat treatment in the width direction at a sufficiently high temperature to sufficiently relieve stress and strain caused by stretching. Here, the stretching ratio in the longitudinal direction is set high, but care is taken to keep the orientation in the longitudinal direction low (for example, the value obtained by subtracting the refractive index nTO in the width direction from the refractive index 'HD in the longitudinal direction is 0.02 or less). This is suitable for the polypropylene film of the present invention.

The polypropylene film of the present invention thus obtained is
Used to make adhesive tape. To make an adhesive tape, for example, the polypropylene of the present invention is used as a tape-shaped support, an adhesive layer is provided on one side, and a release agent layer is provided on the opposite side.

In addition, the method of measuring the characteristic value and the method of evaluating the effect of the present invention are as follows.

(1) Strain amount Y (%) Using a balance type automatic recording creep tester manufactured by Toyo Sokki ■,
Sample length 1o is 130mm and width is 15mm at 40℃
Then, the expansion and contraction of the sample was automatically recorded using a DC differential transformer while the temperature was raised at a rate of 5°C/min, and the amount of expansion and contraction Δρ was calculated as a percentage (%
). Note that the load W applied at this time is the sample cross-sectional area m
It is calculated using Q per m2.

(2) Heat shrinkage stress start temperature heat shrinkage stress maximum value Trial length 100
A load of 50Q/mm2 is fixed at 25°C on a predetermined film with a width of 'lQmm, and the temperature is raised at a rate of 3°C/min. And so.

Further, the maximum value point of the heat shrinkage stress (T2 in FIG. 1) was defined as the peak temperature.

The stress at the maximum thermal shrinkage stress point (T2) was expressed as stress per unit cross-sectional area (c+/mm2>).

(3) Intrinsic viscosity [η] This value was obtained by measuring the relative viscosity in a tetralin solution at 135° C. and extrapolating it to determine the limiting value.

(4) Isotactic degree (1, I) Extract 5 g of sample with n-hebutane at 120°C for 12 hours (
After n-hebutane (number of drops 80 drops/min), 100 mm
1-10.Dry for 2 hours in an atmosphere of 80°C, and calculate from the weight before and after extraction using the following formula.

1, I (%) = (b/a) x 100 where a: Sample weight before extraction (g) b = Sample weight after oil extraction (g) (5) Friction coefficient 24 in a room at 20°C and 65% RH 100 hours humidity controlled
mm (MD)
After 15 seconds had elapsed with a load of 5 mm) placed on the sample, the - sample was moved at a speed of 162 mm/min, and its resistance was read and expressed as a calculated value of resistance (g)/200 Cl. In addition,
μ is a static friction coefficient, and μd is a dynamic friction coefficient.

(6) Heat shrinkage rate Based on JIS K 6782, the shrinkage rate was measured in a Kier oven at 130°C for 15 minutes. The values in the table indicate the values in the film width direction.

(7) Worm-like defects ◎ means no "worm"-like defects, O means almost no "worm"-like defects, and X means there are "worm"-like defects.

(8) Dimensional change ◎ means the width variation with respect to the overall width is less than 0.05%, O means 0.
Less than 1%, X represents 0.1% or more.

(9) Tape appearance ○ indicates good, X indicates poor winding appearance or uneven thickness.

[Effect]

The polypropylene film for adhesive tape according to the present invention has a longitudinal strain ff1Y (%) of −3<Y≦{
(W-80)/220)exp(0,035(D-80)
)), it is possible to prevent dimensional changes due to tension during the drying process and winding process when applying an adhesive or release agent, and also to reduce the temperature at which heat shrinkage stress begins in the width direction to 116°C or higher.
Shrinkage stress value at peak shrinkage stress of 100 to 500Q/m
m2, it was possible to obtain a polypropylene film for adhesive tapes that had small width shrinkage during the drying process and was less likely to cause welt-like defects.

〔Example〕

Next, an actual 1M aspect of the present invention will be explained based on Examples.

Examples 1 to 3 Crystalline homopolypropylene having the composition shown in Table 1 was supplied to an extruder, extruded from a T-die at 280°C, and cast using a cast drum at 20°C to obtain an unstretched sheet. The sheet was stretched 5 times in the longitudinal direction while being heated to 135°C with a group of rolls, cooled, introduced into a tenter heated to 165°C, stretched approximately 10 times in the width direction, and roughly relaxed by 8% in the width direction. A biaxially stretched polypropylene film having a thickness of 40 μm was obtained by heating the film in an atmosphere at 157°C. After applying 30 μm of rubber adhesive (using toluene as a solvent) on one side of this film and 0.1 μm of silicone mold release agent (using toluene as a solvent) on the other side, dry it for 40 seconds at 130°C in a hot air dryer. do,
It was made of polypropylene adhesive tape. The physical properties of the film and the properties of the adhesive tape are summarized in Table 1. It can be seen that when the film strain fflYl width direction heat shrinkage stress onset temperature and heat shrinkage stress value are within the specified ranges of the present invention, the adhesive tape has an excellent appearance with no 'worm'-like defects or dimensional changes. .

Comparative Examples 1 to 4 The crystalline polypropylene of Example 2 was fed to an extruder, and 2
It was extruded from a T-die at 80°C and cast using a casting drum at 25°C to obtain an unstretched sheet.

The unstretched sheet was heated to 120 to 130°C with a preheating roll, stretched 5 times in the longitudinal direction, cooled, and stretched to 158 to 164°C.
The film was stretched about 10 times in the width direction in a tenter heated to 150°C, and the heat treatment was changed as appropriate at a rough temperature of 150 to 158°C and a relaxation rate in the width direction of 6 to 13% to obtain a film having the physical properties shown in Table 1. The polypropylene film was made into an adhesive tape in exactly the same manner as in the example. Table 1 shows the adhesive tape characteristics.
If the shrinkage stress onset temperature is less than 116° C. or if the peak value of shrinkage stress is not within a specific range, “worm”-like defects or large dimensional changes will occur.

Comparative Example 5 An adhesive tape was prepared in exactly the same manner as in Example 1, except that the stretching ratio in the longitudinal direction was 3.7 times.

When the strain ff1Y was not within a specific range, the dimensional change of the tape was large and the appearance was poor.

Comparative Example 6 An adhesive tape was prepared in the same manner as in Example 2, except that no stretching or heat treatment was performed in the width direction (film thickness: 40 μm)
m). The physical properties of the film and tape properties are shown in Table 1. If the shrinkage stress value at the peak shrinkage stress value is not within a specific range, the film may sag, resulting in "worm"-like defects and poor appearance. Recognize.

〔Effect of the invention〕

The polypropylene film of the present invention has specific values for the amount of strain, the temperature at which thermal shrinkage stress begins, and the shrinkage stress value at the peak of shrinkage stress, so it has a good appearance as an adhesive tape and is free from dimensional changes and "worm"-like defects. There is little risk of

[Brief explanation of the drawing]

FIG. 1 shows an example of a temperature-width direction heat shrinkage stress curve. T1...Temperature at which heat shrinkage stress starts in the width direction T2...Peak temperature of heat shrinkage stress

Claims (1)

[Claims] (1) The amount of strain Y (%) in the longitudinal direction of the film is -3<
Y≦{(W-80)/220}exp{0.035(T
-80)} However, T: Measurement temperature (°C) W: Applied load (g/mm^2), and the width direction heat shrinkage stress starting temperature is 116°C or higher, and the width direction heat shrinkage stress maximum value is 100~500g/mm
A polypropylene film for adhesive tape characterized by ^2.