JP2000094604A - Multilayer film for packaging - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a lap film having transparency, excellent heat resistance and stickiness by molding a three-layer laminate of both surface layers of polyethylene resins and an intermediate layer of a polypropylene resin, then orienting specific times a quenched raw film, and forming an intermediate layer thickness to a specific ratio or less to the entirety of the specific thickness. SOLUTION: After a laminate of at least three layers formed at least of both surface layers of polyethylene resins and an intermediate layer of a polypropylene resin is co-extruded, the laminate is quenched to make a raw material. The polyethylene resin for forming both the layers is not limited, and can contain an additive such as a heat resisting stabilizer, a lubricant, an antistatic agent, an anti-blocking agent or the like of the degree normally used. The polyethylene resin and the polypropylene resin are formed as two-type three-layer structure by co-extrusion molding. Then, this film is biaxially oriented twice to five times in lateral and longitudinal directions so that a total thickness is set to 5 to 50 μm and an intermediate layer thickness ratio is set to 10 to 90% to the entirety.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a food wrap film excellent in adhesiveness, drawability, heat resistance and anti-fogging property.

[0002]

2. Description of the Related Art Wrap films for food packaging are used for wrapping food in ordinary households, restaurants and the like, storing them in a refrigerator or freezer, or heating them in a microwave oven (microwave cooker). It is also used for wrapping the contents of tableware before serving ramen, soba, soup, etc. Here, the food is wrapped for preventing the food from drying (preventing water from scattering), preventing dust from entering, preventing the food from jumping out of the tableware, and the like. Such a food packaging wrap film is wound around a paper tube with a width of 20 to 45 cm and a length of about 20 to 100 m and is housed in a paper carton box. Used after being cut in quantity.

[0003] As the wrap film, the following
Is required. The contents can be seen through, can be easily pulled out of the carton box by hand, must be sticky, must have enough heat resistance to not dissolve the film when used in a microwave oven, and must not fog during use. It is.

At present, wrap films using vinylidene chloride resin are mainly used, but there is a drawback that, when cutting, they are not cut along the saw blade but cut diagonally. Ethylene-based resins have been actively developed in view of environmental problems such as generation of poisonous gas. However, the wrap film made of an ethylene-based resin is easy to stretch and hard to tear, so a considerable tensile force is required at the time of cutting, and the film cannot be pulled out well or the carton box is deformed. In addition, there are problems such as poor heat resistance when used in a microwave oven and low rigidity of the film, making it difficult to handle.Therefore, it cannot be replaced with vinylidene chloride resin and is used only in a part of the market. Absent.

In order to improve the disadvantages of such ethylene resins, Japanese Patent Application Laid-Open Nos. Sho 57-96858 and Sho 57
Japanese Patent Application Laid-Open No. 7-189850 discloses a propylene-ethylene copolymer, a propylene-butene-1 copolymer, a propylene-ethylene-butene-1 copolymer as a film capable of satisfying the cut property and the heat resistance. Laminated films with propylene homopolymer have been proposed, but these laminated films have no tackiness and cannot be used as household wrap films. In addition, Japanese Patent Laid-Open No.
No. 3 discloses heat shrinkage in which a linear low-density polyethylene (ethylene-α-olefin copolymer) is laminated on both surfaces of an ethylene-propylene copolymer or an ethylene-propylene-butene-1 copolymer. Films have been proposed, but these films also have low adhesive strength, and when heated in a microwave oven, etc., the films adhere to each other, workability is poor, and it is practically difficult to use them as household wrap films. . Further, JP-A-7-52345, JP-A-7-196738, JP-A-8-80600, JP-A-9-29908 and the like disclose an ethylene-α-olefin copolymer or a propylene-based resin,
A film having improved adhesiveness and heat resistance using a polyamide resin or an ethylene-vinyl acetate copolymer for an intermediate layer has been proposed.

JP-A-8-25596 discloses a crystalline propylene resin film layer comprising an ethylene-propylene-α-olefin copolymer and a linear ethylene-α-olefin copolymer on one or both surfaces. A film in which layers are laminated and which has excellent adhesiveness and heat resistance has been proposed. However, in the former case, since different materials are molded at the same time, molding is difficult, and the apparatus becomes complicated. For the latter, the tackiness is not always sufficient.

[0007]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems in wrapping films for food packaging, and its object is to provide not only transparency but also heat resistance. Another object of the present invention is to provide a wrap film which is extremely excellent in adhesiveness, adhesiveness and drawability.

[0008]

According to the present invention, as a result of intensive studies to produce a multilayer film for packaging which has solved the above-mentioned problems of the conventional wrapping film, polyethylene-based films have been formed on both sides of the polypropylene-based resin layer. The present invention was found to solve the above-mentioned problems and obtain a multilayer film for packaging excellent in heat resistance, adhesiveness, and drawability by biaxially stretching a resin laminated by a co-extrusion method. Reached. That is, the gist of the present invention is to coextrude a laminate of at least three layers in which both surface layers are made of a polyethylene-based resin and the intermediate layer is made of a polypropylene-based resin, and then quenched to obtain a raw film. A biaxially stretched film obtained by stretching the film in the direction and the transverse direction by a factor of 2 to 5 times, wherein the film has a thickness of 5 to 50 μm.
Wherein the thickness of the intermediate layer made of a polypropylene resin is in the range of 10 to 90% of the total thickness of the film.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be further described below.
The multilayer film for packaging of the present invention has a layer constitution of at least three layers, for example, three layers of a surface layer / intermediate layer / surface layer (back layer).
Consists of layers. Of course, an adhesive layer may be provided between the surface layer and the intermediate layer and / or between the back layer and the intermediate layer. As such an adhesive layer, any material can be used as long as it can adhere the surface layer (including the back layer) and the medium-simplified layer. For example, those having a composition close to that of the polyethylene resin used for the surface layer, for example, those obtained by mixing an appropriate amount of polybutene (B) and antifogging agent (C) with polyethylene resin (A), or an intermediate layer A resin having a composition close to that of the polypropylene resin used in the above, for example, a mixture of a propylene-ethylene random copolymer and an appropriate amount of a propylene-butene-1 copolymer is suitably used.

[0010] The polyethylene resin constituting both surface layers of the multilayer film for packaging is not limited, and may be a mixture of course as well as an ethylene homopolymer. Examples of the ethylene homopolymer include high-density polyethylene, medium-density polyethylene, and low-density polyethylene, and low-density polyethylene is particularly preferable. Further, a mixture of 97 to 90 parts by weight of linear low-density polyethylene and 3 to 10 parts by weight of high-pressure low-density polyethylene is preferred. The physical properties of the polyethylene resin may be selected according to the application, conditions, etc., and usually, the melt flow rate (MFR) is 0.5 to 10 g.
/ 10 min, linear low density polyethylene having a density of 0.920 g / cm ³ or less, melt flow rate 0.5 to 10 g / 1
The high-pressure low-density polyethylene having a density of 0.930 g / cm ³ or less for 0 minute is preferable. Melt flow rate is JI
It is measured at 190 ° C. under a load of 2.16 kg according to SK6758.

[0011] By adding the following additives to the above-mentioned polyethylene resin, excellent performance as a wrap film, that is, adhesiveness, heat resistance and the like can be obtained.
(A) 100 parts by weight of polyethylene resin, (B)
2 to 20 parts by weight of polybutene, antifoggant (C) 0.1 to 10
Add parts by weight.

The component (B), polybutene, acts as a thickener and imparts excellent tackiness to the film. The compounding amount of this butene is 2 to 20 parts by weight, preferably 3 to 100 parts by weight of the polyethylene resin as the component (A).
To 15 parts by weight. If the amount is less than 2 parts by weight,
On the other hand, if it does not show a sufficient thickening, and if it exceeds 20 parts by weight, stickiness due to a large amount of bleeding occurs and heat resistance is undesirably reduced. The physical properties of the polybutene used here are not particularly limited because they can be appropriately determined according to the compounding amount, the type of the other components, the intended use of the composition, and the like, but the number average molecular weight is usually 500 to 300.
0, preferably 600-2500, more preferably 7
Those having a range of 00 to 1500 are used.

The component (C), the antifogging agent, is a mixture of acetylated monoglyceride, polyethylene glycol ester and polyoxyethylene alkyl ether. The acetylated monoglyceride, which is one component of the component (C), increases the adhesiveness of the film when used in combination with the polybutene (B). There is also an anti-fogging effect that fogging is unlikely to occur even when steam adheres. The acetylated monoglyceride is a compound obtained by esterifying a fatty acid such as a higher fatty acid having 8 to 22 carbon atoms in at least one of hydroxyl groups of a condensation polymer of glycerin. Here, the degree of polymerization of the glycerin condensation polymer is usually 2-1.
0, preferably 2 to 6 condensation polymers. Among the hydroxyl groups of the glycerin condensation polymer, the number of esterified hydroxyl groups is one or more, preferably one or more and 70% or more of the number of hydroxyl groups.

The higher fatty acid may be saturated or unsaturated as long as it has 8 to 22 carbon atoms, and usually has 10 to 18 carbon atoms.
Is preferred. Examples of the acetylated monoglyceride include diglycerin monolaurate, diglycerin monopalmitate, diglycerin monooleate, diglycerin dilaurate, triglycerin monooleate and the like. Particularly, diglycerin monolaurate and diglycerin monooleate are preferred. The amount of the acetylated monoglyceride is 0.1% with respect to the polyethylene resin as the component (A).
To 4 parts by weight, preferably 0.2 to 2 parts by weight. When the amount is less than 0.2 parts by weight, a synergistic effect with the polybutene as the component (B) does not occur.

The polyethylene glycol fatty acid ester, which is another component of the component (C), is a compound obtained by esterifying a fatty acid such as a higher fatty acid having 8 to 22 carbon atoms at the terminal hydroxyl group of a condensation polymer of ethylene glycol. . Here, the condensation polymer of ethylene glycol is a condensation polymer having a polymerization degree of usually 2 to 10, preferably 2 to 6.
The higher fatty acid may be saturated or unsaturated as long as it is a fatty acid having 8 to 22 carbon atoms, and is usually preferably a fatty acid having 10 to 18 carbon atoms. Examples of the polyethylene glycol fatty acid ester include polyethylene glycol oleate, polyethylene glycol laurate, polyethylene glycol palmitate, polyethylene glycol stearate and the like. Particularly, polyethylene glycol oleate and polyethylene glycol laurate are preferred. The film molded from the composition containing the polyethylene glycol fatty acid ester of the present invention,
Good tackiness. The amount of the polyethylene glycol fatty acid ester is 0.1 to 4 parts by weight, preferably 0.2 to 2 parts by weight, based on the polyethylene resin as the component (A). When the amount is less than 0.1 part by weight, the tackiness is not sufficiently imparted. When the amount exceeds 4 parts by weight, for example, when the amount exceeds 10 parts by weight, the resulting film may be sticky or may have a significant slippage. Will be reduced.

The polyoxyethylene alkyl ether which is another component of (C) is a compound in which a terminal hydroxyl group of a condensation polymer of ethylene glycol is etherified with a higher alcohol having 8 to 22 carbon atoms. Here, the condensation polymer of ethylene glycol is a condensation polymer having a polymerization degree of usually 2 to 10, preferably 2 to 6. The higher alcohol may be saturated or unsaturated as long as it is an alcohol having 8 to 22 carbon atoms, and is usually preferably an alcohol having 10 to 18 carbon atoms. Particularly, lauryl alcohol is preferred. The film molded from the composition containing the polyoxyethylene alkyl ether of the present invention has good adhesiveness, and can easily adhere to an object without pressure bonding. At the same time, the releasability between the films is improved. The amount of the polyoxyethylene alkyl ether used in the present invention is 0.1 to 0.1 with respect to the polyethylene resin as the component (A).
2 parts by weight, preferably 0.2 to 1 part by weight. If the amount is less than 0.1 part by weight, sufficient tackiness cannot be obtained. If the amount exceeds 2 parts by weight, the balance between the components of the anti-fogging agent is lost, which is not preferable.

On the other hand, examples of the polypropylene resin constituting the intermediate layer of the multilayer film for packaging of the present invention include a propylene homopolymer and a copolymer with an α-olefin having 2 to 10 carbon atoms such as ethylene and butene. However, a copolymer of propylene and an α-olefin having 2 to 10 carbon atoms is preferred. Particularly, a mixture of a propylene-ethylene copolymer and a propylene-butene copolymer is preferable. More preferably, the composition of the mixture is propylene-ethylene copolymer 7
0 to 90 parts by weight and a propylene-butene copolymer 30 to 1
0 parts by weight, more preferably 75 to 85 parts by weight of propylene-ethylene copolymer, propylene-butene copolymer 25
~ 15 parts by weight of the composition. The ethylene content in the propylene-ethylene copolymer is preferably in the range of 2 to 7% by weight, and the butene content in the propylene-butene copolymer is preferably in the range of 5 to 30% by weight. The physical properties of the polypropylene-based resin may be selected according to the application, conditions, etc., and usually, the melt flow rate is 0.5 to 10 g / 10.
Minutes are preferred. Melt flow rate is JIS
It is measured at 230 ° C. under a load of 2.16 kg in accordance with K6758.

The polyolefin composition used for both the surface layer and the intermediate layer according to the present invention contains a heat stabilizer of a level generally used,
Additives such as a weather stabilizer, a lubricant, an antistatic agent, a nucleating agent, a filler, and an antiblocking agent may be contained in an amount of about 0.0005 to 5%. The multilayer film for packaging according to the present invention is obtained by specific coextrusion molding of the above-mentioned polyethylene resin and polypropylene resin with at least two and three layers, for example, lamination of [polyethylene resin / polypropylene resin / polyethylene resin]. A raw film comprising a body is formed, and then the film is biaxially stretched in both the longitudinal and transverse directions. The order of stretching may be vertical or horizontal, whichever may be first, or may be simultaneous vertical and horizontal stretching.

As the co-extrusion molding, a T-die molding method or a water-cooled inflation molding method is applied. That is, by rapidly cooling the melt-extruded resin by the above-mentioned molding method, a film having more excellent transparency and stretchability can be obtained as compared with an air-cooled inflation molding method which is usually used frequently. At the time of raw material forming, quenching can suppress the crystallinity to a low level, which improves transparency and stretchability. An air-cooled inflation molding method can also be used in the present invention, but care must be taken because, since the cooling effect is small, breakage may occur during stretching. In particular, careful attention is required because the film is easily torn during stretching in the transverse direction. In the case of the water-cooled inflation molding method, cooling may be performed by contacting cooling water having a temperature of 50 ° C. or less, preferably 30 ° C. or less.

The unstretched multilayer film obtained by the coextrusion molding is then biaxially stretched in both longitudinal and transverse directions of the film at a stretching ratio of 2 to 5 times, preferably 2.5 to 4.5 times. If the stretching ratio is less than 2 times, the cutability of the film is insufficient, and if it is more than 5 times, the stretchability decreases, and breakage or uneven stretching of the film is undesirable. In the case of tubular simultaneous biaxial stretching, the unstretched film is heated as it is, for example, by changing the peripheral speed of the stretching roll, the film is stretched in the take-off direction, that is, in the longitudinal direction, and simultaneously with the inside of the film. The film is stretched in the lateral direction by changing the diameter of the tubular film by blowing air. The preheating temperature in the stretching treatment is generally a temperature lower than the melting point of the polyethylene resin by 20 ° C. or more, preferably 25 to 60 ° C.
It is preferred to work in a low temperature range. Moreover, you may heat-set after extending | stretching as needed. The heat setting temperature is not particularly limited, but is preferably a temperature that does not cause wrinkles,
Usually, it is preferable to carry out in the range of 40 to 110 ° C.

If the preheating and heat setting temperatures are higher than the appropriate temperature, the stability of the tube diameter becomes poor. If the preheating temperature is lower than the appropriate temperature, the drawing becomes difficult due to insufficient preheating of the polypropylene resin. This is undesirable because film breakage occurs. In addition to the tubular simultaneous biaxial stretching method described above, a tenter simultaneous biaxial stretching method and a sequential biaxial stretching method can also be applied, and the preheating temperature and the heat setting temperature may be selected according to the above.

By performing this stretching step, the cutability of the film is greatly improved, and the film can be cut to a desired length with a light force using a saw blade. The total thickness of the multilayer film for packaging of the present invention is in the range of 5 to 50 μm, preferably in the range of 5 to 30 μm, and more preferably in the range of 8 to 25 μm. If the total thickness of the multilayer film for packaging is larger than 50 μm, the tear strength at the time of cutting the film becomes too large, which is not suitable for the use of the wrap film. On the other hand, if the total thickness is less than 5 μm, the film does not have sufficient stiffness and tends to wrinkle, which is not suitable for a wrap film. The thickness ratio of the polypropylene resin layer in the intermediate layer is 10 to 90%, preferably 15 to 80%, based on the thickness of the entire film.

If the thickness of the intermediate layer is less than 10% of the total thickness, the inherent heat resistance and mechanical strength of the polypropylene resin cannot be exhibited. If the thickness is more than 90%, the thickness of the polyethylene-based resin layer becomes too thin, and it becomes difficult to uniformly cover the intermediate layer by co-extrusion. The multilayer film for packaging of the present invention is used for various packaging applications such as food packaging. Further, by giving self-adhesiveness to both surface layers by the method described above, it can be suitably used as a wrap film.

[0024]

EXAMPLES Hereinafter, specific embodiments of the present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples unless it exceeds the gist thereof. The measurement in the examples was performed by the following method.

(1) Transparency (haze) Measured according to a method according to ASTM D-1003.

(2) Heat-resistant temperature A strip film having a width of 30 mm and a length of 140 mm, a paper is placed on the top and bottom 25 mm of a sample piece and a weight of 10 g is lowered. The maximum ambient temperature that could not be cut in one hour was measured at 10 ° C intervals.

(3) Adhesiveness Two 80 mm-wide films are lightly overlapped, and the film is pressed three times with a roll having a width of 25 mm and a width of 150 mm at a linear pressure of 0.3 kg / cm ² within 5 minutes. The force required for peeling in the 180-degree direction was measured with a push-pull scale (PSM2K manufactured by Imada Co., Ltd.) to determine the maximum load g.

(4) Pullability When a wrap film wound on a paper tube and having a width of 300 mm and a length of 20 m is put in a paper box, the end face of the film is sandwiched by clips, and the clips are pulled by a push-pull scale to pull out the film. Measure the maximum load.

(5) Tensile strength, elongation and modulus of elasticity Using a universal testing machine ABS100B manufactured by Shimadzu Corporation, J
It measured using the IS1 test piece. The tensile strength and elongation were measured at a tensile speed of 500 mm / min and the elastic modulus was 5 mm / min.

[Example 1] Water cooling system 3 having a diameter of 135 mm
The resin shown in Table 1 was simultaneously extruded from three extruders at a die temperature of 200 ° C. using a seed five-layer coextrusion annular die molding machine.
A film was formed under the conditions of a cooling water temperature of 20 ° C. and a take-off speed of 3 m / min, and was composed of a surface layer (polyethylene resin) / intermediate layer (polypropylene resin) / back layer (polyethylene resin).
A layer film (230 μm thick, layer ratio 1: 2: 1) was formed. Table 1 shows the composition of each raw material used.

[0031]

[Table 1]

Polyethylene resin: manufactured by Ube Industries, Ltd.
Linear low density polyethylene, UBE polyethylene SPE204
0F (trade name) MFR 4.0 g / 10 min, density 0.91
8 g / cm ³ , manufactured by Ube Industries, Ltd .; high-pressure low-density polyethylene UBE polyethylene F222N (trade name) M
FR 2.0 g / 10 min, density 0.922 g / cm ³ Polybutene: manufactured by NOF Corporation Average molecular weight: 1000 Acetylated monoglyceride: diglycerin laurate (manufactured by Marubishi Yuka Kogyo) Polyglycerin fatty acid ester: apolyethylene glycol ole Eate (manufactured by Marubishi Yuka Kogyo) Polyoxyethylene alkyl ether: polyoxyethylene lauryl ether (manufactured by Marubishi Yuka Kogyo) Ethylene-propylene copolymer: PP FL-454 (trade name) manufactured by Grand Polymer MFR
2.7 g / min, Propylene-butene copolymer: Tuffmer A4085 (trade name) MFR 4.0 g / 10 manufactured by Mitsui Chemicals, Inc.
Min, density 0.890 g / cm ³

Next, the film was stretched 4.5 times in the machine direction and 4.2 times in the transverse direction at a preheating temperature of 80 ° C. and a stretching temperature of 100 ° C. The transparency (haze), heat resistance, tackiness, drawability, tensile strength, elongation, and elastic modulus of the obtained film were evaluated by the methods described above. Table 2 shows the results.

Example 2 A film was formed in the same manner as in Example 1 except that the amount of prebutene was changed to 4 parts by weight. Table 2 shows the evaluation results such as the performance of the film.

Example 3 A film was formed in the same manner as in Example 1 except that the amount of the ethylene-propylene copolymer was 90 parts by weight and the amount of the propylene-butene copolymer was 10 parts by weight. did. Table 2 shows the evaluation results such as the performance of the film.

Comparative Example 1 The physical properties of a commercially available polyethylene resin wrap film are shown in Table 2. Comparative Example 2 95 parts by weight of linear low-density polyethylene SP2040F and ethylene-octene copolymer: Affinity kc-88 manufactured by Dow Chemical Co., Ltd.
A film was formed in the same manner as in Example 1 except that 5 parts by weight of 52 (trade name) was used. Table 2 shows the evaluation results such as the performance of the film.

Comparative Example 3 The raw materials for both surface layers were 90 parts by weight of linear low-density polyethylene SP2040F and 10 parts by weight of ethylene-octene copolymer: affinity kc-8852 (trade name) manufactured by Dow Chemical Company. A film was formed in the same manner as in Example 1 except for the above. Table 2 shows the evaluation results such as the performance of the film.

[0038]

[Table 2]

[0039]

The multilayer film for packaging according to the present invention is excellent in heat resistance, adhesiveness, and drawability. Since the whole film is a polyolefin resin, it does not generate toxic gas during incineration and has high toxicity. It does not generate combustion residues and is excellent in safety from environmental issues.

 ──────────────────────────────────────────────────の Continued on the front page F term (reference) 3E086 AD13 BA04 BA15 BA33 BB02 BB22 BB41 BB57 CA01 CA17 CA18 CA22 4F100 AK04A AK04B AK05A AK05B AK07C AK08A AK08B AK66C AL05A AL05B AL05C BA03 BA06 BA10BBAE BAB BAB BAB BAE JA06A JA06B JA07A JA07B JA13A JA13B JB05 JJ03 JL12 YY00 YY00C 4F210 AA04H AA05 AA11E AA11H AA12E AB09 AG01 AG03 AH52 AH54 QA01 QA02 QC07 QD13 QD32 QD42 QG01 QG18 QK01 M02

Claims (3)

[Claims] 1. A co-extruded laminate of at least three layers having both surface layers made of a polyethylene resin and an intermediate layer made of a polypropylene resin, and then quenched to form a raw film, and the raw film is stretched in the longitudinal and transverse directions. A biaxially stretched film obtained by stretching the film in the direction of 2 to 5 times in each direction, wherein the total thickness of the film is 5 to 50 μm, and the thickness of the intermediate layer made of polypropylene resin is the thickness of the entire film. A multilayer film for packaging, characterized by being in the range of 10 to 90% of the above. 2. The polyethylene resin of both surface layers contains 2 to 20 parts by weight of polybutene (B) and 0.3 to 10 parts by weight of antifoggant (C) based on 100 parts by weight of polyethylene resin (A). The intermediate layer polypropylene resin is a mixture of 70 to 90 parts by weight of a propylene-ethylene random copolymer and 30 to 10 parts by weight of a propylene-butene-1 copolymer. The multilayer film for packaging according to the above. 3. A linear low-density polyethylene having a density of 0.920 g / cm ³ or less and a melt flow rate of 0.5 to 10 g / 10 min. 97 to 90 parts by weight of the polyethylene resin (A) on both surface layers. And a high-pressure method low-density polyethylene having a density of 0.930 g / cm ³ or less and a melt flow rate of 0.5 to 10 g / 10 minutes, and a polybutene (B) having a number average molecular weight of 500 to 10 parts by weight. 3,000, and the ethylene content in the propylene-ethylene random copolymer of the intermediate layer is 2 to 7% by weight;
The multilayer film for packaging according to claim 2, wherein the butene-1 content in the butene-1 copolymer is in the range of 5 to 30% by weight.