JP3126079B2 - Resin coated paper - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a resin-coated paper in which one side of a paper substrate is coated with a resin layer made of a polyethylene resin composition. More specifically, the present invention relates to a polyethylene-based resin-coated paper in which the molding process of the resin layer is good, the adhesiveness between the resin layer and the paper substrate is excellent, and the resin layer has little gel.

[0002]

2. Description of the Related Art Paper substrates such as paper, paperboard, cellophane, etc.
It is widely used to melt, extrude and coat a resin capable of forming a film on a base paper), and use it for food containers, packaging materials, release paper, printing paper, photographic supports, etc. Are well known.

[0003] When extruding and coating a molten polyethylene resin onto a base paper, the temperature is considerably higher than the melting point of the polyethylene resin. For example, the melting point of low-density polyethylene is around 105 to 110 ° C. and the melting point of high-density polyethylene is around 120 to 130 ° C., whereas the melt extrusion temperature by the T-die method is 300 ° C. to perform thin film coating. It needs to be done nearby.

In general, a polyethylene molecule contains not only a linear carbon chain as a polymer of ethylene monomer but also a carbon
It is known to include an unsaturated bond such as a carbon double bond, or a side chain carbon chain having a methyl group or a higher carbon skeleton. For polyethylene, the temperature around 300 ° C is an appropriate temperature from the viewpoint of proper processing, but it is within the range that promotes activation at the molecular level. Due to the above factors, radicals are likely to be generated near unsaturated bonds and side-chain carbon in the molecule, and the radicals undergo a chain reaction to cause a crosslinking reaction, and when extruded into a film, a gel is formed. Often it manifests itself as a shape defect. This gel becomes a projection on the surface of the resin-coated paper and impairs the appearance,
There are various obstacles in function.

[0005] In a food container, printing paper, or the like, if a gel is present in the resin layer, peeling due to poor printing at that portion or poor adhesion to the base paper occurs. In the case of release paper, the presence of the gel often causes poor quality in the step of applying a release agent such as silicone on the resin layer. Further, in the case of a photographic support, the presence of the gel itself deteriorates the quality of the photographic image, or when the normal photographic image cannot be formed, the commercial value of the photographic printing paper is often lost. For this reason, it is necessary to take sufficient measures to prevent gel.

As a method for preventing the formation of such a gel, there is a method of operating at a lower extrusion temperature, but in this case, the adhesion between the polyethylene resin and the paper is reduced. In order to maintain it, the processing speed is limited and productivity is reduced. Further, if the disassembly and cleaning of the extruder is performed in a short cycle, although the effect is obtained, a decrease in productivity is inevitable.

On the other hand, in the production of a polyethylene resin film, an effect may be obtained by adding an antioxidant in order to prevent the formation of the gel. However, in the case of extruding and coating a polyethylene resin on a base paper, addition of an antioxidant to prevent gelation is generally not often performed because the adhesion between the base paper and the polyethylene resin is deteriorated.

In a release paper or the like in which the resin layer is required to have smoothness, heat resistance, friction resistance, etc., a high-density polyethylene having a high melting point is used for the resin layer. Insufficiency in molding processability such as instability of flow due to the degree of surge or draw resonance, and breakage of the film due to neck-in and draw-down properties. In particular, in the case of production under high-speed conditions in which the running speed of the base paper is 150 m / min or more, in addition to the above-mentioned problems, the problem that the adhesiveness between the resin layer and the base paper is deteriorated and the resin layer is easily peeled off. was there. As described above, conventionally, it is practically difficult to obtain a polyethylene-based resin-coated paper in which the molding process of the resin layer is good, the adhesiveness between the resin layer and the base paper is excellent, and the generation of gel in the resin layer is minimized. Met.

[0009]

DISCLOSURE OF THE INVENTION The present invention solves the above-mentioned problems in polyethylene-based resin-coated paper, provides good molding of the resin layer, has excellent adhesion between the resin layer and the base paper, It is an object of the present invention to obtain a polyethylene-based resin-coated paper that prevents the formation of a gel as much as possible and does not impair the performance as a resin-coated paper without lowering the productivity.

[0010]

Means for Solving the Problems The inventors of the present invention have repeatedly studied to achieve this object, and as a result, as a resin-coated paper having a resin layer mainly composed of polyethylene resin on one side of a base paper, It has been found that the intended resin-coated paper can be obtained by using a melt-mixed composition of a specific high-density polyethylene resin and a low-density polyethylene resin or a medium-density polyethylene resin, and by setting the critical shear rate to a specific value. The present invention has been reached.

That is, the gist of the present invention is to provide a resin-coated paper having a resin layer composed of a resin composition mainly composed of a polyethylene resin on one side of a paper substrate, wherein the resin layer has a melt flow rate of 10.0 g. / 10 minutes to 40.0 g / 10 minutes,
90 parts by weight to 65 parts by weight of a high-density polyethylene resin having a density of 0.960 g / cm ³ or more;
0.2 g / 10 min to 2 g / 10 min, density 0.93
Low-density polyethylene resin or medium-density polyethylene resin 1 having a ratio of 5 g / cm ³ or less, a molecular weight of 500,000 or more, 10% by weight or more, and a critical shear rate of 0.5 (1 / second) or less
A resin-coated paper comprising a polyethylene resin composition obtained by melt-mixing 0 to 35 parts by weight, wherein the melt-mixed resin composition has a critical shear rate of 10 (1 / sec) or less. Exists. Here, the critical shear rate is defined as the shear rate at the point where the first normal stress difference is equal to the shear stress measured at 240 ° C. by a method described later using a cone-plate rotary viscometer. That means.

Hereinafter, the present invention will be described in detail. The high-density polyethylene resin used for the resin layer in the resin-coated paper of the present invention has a melt flow rate (hereinafter, referred to as MFR) of 10.0 g / 10 min to 40.0 g / 10 min, preferably 10.0 g. / 10 min in the range of ～30.0G / 10 min, density of 0.960 g / cm ³ or more, preferably 0.962 g / cm ³ or more. As the high-density polyethylene resin having the above physical properties (hereinafter, referred to as HDPE), in addition to HDPE alone, a copolymer containing ethylene as a main component and propylene, a lower α-olefin such as butene, or a mixture thereof, or the like Is raised.

When the MFR of HDPE is lower than 10.0 g / 10 min, the adhesiveness between the base paper and the resin layer, the moldability and the like are deteriorated. Molding processability etc. deteriorate. The density is 0.960
If it is lower than g / cm ^{3, the} secondary workability such as cutability will be deteriorated, and a favorable result cannot be obtained. If the MFR and density of the resin are in the above ranges, various MFRs, densities, molecular weights,
Those having a molecular weight distribution can be used alone or in combination.

On the other hand, a low-density polyethylene resin or a medium-density polyethylene resin (hereinafter referred to as LD) used for the resin layer.
PE) has an MFR of 0.2 g / 10 min to 2 g
/ 10 min, preferably 0.2 g / 10 min or more and 1.0 g /
Less than 10 minutes, with a density of 0.935 g / cm ³
Or less, preferably 0.930 g / cm ³ or less, and the proportion of a molecular weight of 500,000 or more is 10% by weight or more, preferably 1% by weight or more.
It is 2% by weight or more, and has a critical shear rate of 0.5 (1 / sec) or less, preferably 0.4 (1 / sec) or less.

If the MFR of the LDPE is lower than 0.2 g / 10 minutes, the mixing properties of the resin, the adhesion between the base paper and the resin layer, the moldability, etc. are deteriorated. Worse. On the other hand, if the density is higher than 0.935 g / cm ³ , the adhesiveness between the base paper and the resin layer, the moldability and the like are deteriorated, so that favorable results cannot be obtained. The resin has a molecular weight of 50.
If the ratio is more than 10% by weight, molding processability, especially neck-in, is undesirably large. Here, the measurement of the molecular weight was carried out using Waters 150-C (column: GMH-XL HT 8 mmφ × 30 cm × 3 made by Tosoh Corporation).
Book, solvent: 1,2,4-trichlorobenzene, temperature: 135
(C, flow rate: 1 ml / min).

The critical shear rate of LDPE is 0.5
(1 / second) or less, and if it is larger than this, problems such as moldability and gelation of the resin layer occur. FIG. 1 is a chart showing the relationship between the shear stress and the first normal stress difference, and the shear rate. In FIG. 1, the vertical axis indicates the shear stress and the first normal stress difference, and the horizontal axis indicates the shear rate. Show. In addition, a line a in FIG. 1 indicates a shear stress, and a line b indicates a first normal stress difference.

In the present invention, the critical shear rate is measured by using a cone-plate type rotary viscometer (Rheometric Mechanical Spectrometer, manufactured by Rheometrics Co., Ltd.).
Plate diameter: 25 mm, angle: 0.1 rad, temperature 2
40 ° C.), and the shear rate at the point where the shear stress equals the first normal stress difference in FIG. 1 (the intersection of line a and line b). The shear stress and the first normal stress difference are represented by the following equations. Shear stress = (viscosity) x (shear rate) First normal stress difference = (first normal stress difference coefficient) x (shear rate) ²

The resin layer of the resin-coated paper according to the present invention may comprise 90 to 65 parts by weight of HDP having the above-mentioned properties.
E and 10 to 35 parts by weight of the LD having the above physical properties
A compound resin composed of a polyethylene-based resin composition prepared by previously melt-mixing PE with PE is used. It is necessary that the critical shear rate is 10 (1 / sec) or less, and particularly preferably 8 (1 / sec) or less.
If the critical shear rate is higher than 10 (1 / second), a gel is easily formed, which is not preferable.

It is considered that the suppression of gel formation according to the present invention is caused by the viscoelastic properties of the resin at a high resin temperature during melt extrusion coating. At a critical shear rate, the properties of the resin change from viscous to elastic. It is thought that the suppression of gel is exhibited by reducing the chance of gelation and crushing and kneading the gel.

As a method of melt-mixing the above ratios of HDPE and LDPE, a simple melt-mixing method, a multi-stage melt-mixing method, or the like can be used. For example, Banbury mixer,
A pressure kneader, a heating roll kneader, an extruder, a twin screw extruder and the like are used. In addition, when the HDPE and LDPE are not melt-mixed in advance and are extrusion-coated using a melt-coating extruder in a dry-mixed state, the adhesiveness between the base paper and the resin layer, the mixing property of the resin, Molding processability etc. deteriorate.

The polyethylene resin composition used in the resin layer may contain, as long as the effects of the present invention are not impaired, an ultraviolet ray inhibitor, a heat stabilizer, an antistatic agent, an antioxidant, a light stabilizer, a lubricant, a nucleating agent, Various additives such as a coloring agent can be appropriately added. These additives are used in HDPE or LLD
A so-called masterbatch may be added in advance to PE, added during melt mixing, or added to these resins at a high concentration, and the masterbatch may be added to the resin during melt extrusion coating.

The base paper used in the present invention is a natural pulp paper mainly composed of ordinary natural pulp, a mixed paper made of natural pulp and synthetic fibers, a synthetic pulp, a synthetic fiber or a synthetic resin film. Any of synthetic paper may be used. Further, the base paper may contain various additives such as a sizing agent, a paper strength enhancer, a filler, a fixing agent, a pH adjuster, a colorant, and a fluorescent whitening agent.

In order to produce the resin-coated paper of the present invention, the above-mentioned polyethylene resin composition is cast on a running base paper from a slit die into a film by using a melt extruder. A coating method is employed. The melt extrusion temperature is usually preferably 280 ° C. to 340 ° C., and the base paper is subjected to an activation treatment such as corona discharge treatment or flame treatment before coating the polyethylene resin composition on the base paper. Is preferred. The thickness of the resin layer is not particularly limited, but is generally applied to a thickness of about 5 to 50 microns.

[0024]

EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples, but the present invention is not limited to these examples unless it exceeds the gist of the present invention.

Example 1 MFR 15.0 g / 10 min, density 0.967 g / cm ³
70 parts by weight of HDPE (A in Table 1 described below) and MFR
0.6 g / 10 min, density 0.924 g / cm ³ , molecular weight of 500,000, 15% by weight or more, critical shear rate of 0.0
30 parts by weight of 6 (1 / sec) LDPE (e in Table 1) were melt-mixed in advance, and the mixture was extruded at a resin temperature of 320 ° C. from an extruder to a basis weight of 1
It was prepared by extrusion coating a 70 g / m ² highly smooth paper to a thickness of 25 μm.

As a method of evaluating the moldability during melt extrusion coating of the resin, the length of the resin-coated portion in the lateral direction is measured to evaluate the degree of neck-in, and the degree of occurrence of streaks in the molten resin film. Molding processability such as the presence or absence of film breakage due to the degree of drawdown, and instability of flow due to surge or draw resonance were comprehensively evaluated. The evaluation criteria are as follows: ：: good, Δ: slightly bad but no practical problem, x: bad and practically problematic.

As a method for evaluating the adhesiveness between the base paper and the resin layer of the resin-coated paper, a sample is separated into the base paper layer and the resin layer, and the area ratio of the base paper layer adhered to the separated resin layer is measured. Then, the adhesiveness between the base paper and the resin layer was evaluated. The evaluation criteria were as follows: ：: good at 100% area ratio, Δ: 80% or more with less than 100% area ratio, a little poor adhesion but practically no problem, x: 80% area ratio , Which indicates that the adhesion is poor and there is some practical problem.

As a method for evaluating the gel at the time of melt extrusion of the resin, 0.01 m ² after extruding into a film for 8 hours at a set temperature of 320 ° C. and 2.5 kg per hour.
The gel was evaluated by measuring the number of gels having a size of 0.1 mm or more in the film and comparing with the initial value.
As evaluation criteria, ○: the number of gels after 8 hours does not change from the initial value, x: the degree to which the number of gels after 8 hours increased from the initial value.

The secondary workability of the resin-coated paper was evaluated by evaluating the cuttability of the sample cut with a commercially available guillotine cutter based on the degree of fluffing of the cut edge, and overlapping the resin layer surfaces of the resin-coated paper with each other. Comprehensive evaluation was performed on the friction resistance according to the degree of scratches on the resin layer surface when rubbing, and the secondary workability such as the stiffness of the resin-coated paper. As evaluation criteria,
：: good, △: slightly bad, but no practical problem, ×:
It is bad and has some practical problems. Table 1 shows the physical properties of HDPE and LDPE used in this example, and Table 2 shows the evaluation results obtained by the above-described evaluation method for the obtained resin-coated paper.

Examples 2 to 9 In place of the combination of HDPE and LDPE used in Example 1, various resin compositions each combining HDPE and LDPE shown in Table 1 were used. A coated paper was obtained. Table 2 shows the results of the evaluation by the above evaluation method.

Comparative Examples 1 to 9 In Comparative Examples 1 to 8, the HDPE and LD used in Example 1 were used.
Instead of the combination of PE, HDPE and LD shown in Table 1 respectively
A resin-coated paper was obtained in the same manner as in Example 1, except that various resin compositions in which PE was combined were used. Table 3 shows the results of the evaluation by the above evaluation method. Comparative Example 9
Then, the same kind and composition of HDPE and L
A resin-coated paper was obtained in the same manner as in Example 1, except that a resin composition of DPE was used, and the mixture was dried and mixed without being melt-mixed. Table 3 shows the evaluation results obtained by the above evaluation method.

[0032]

[Table 1]

[0033]

[Table 2]

[0034]

[Table 3]

From the results shown in Table 2, it is found that a resin composition containing 90 to 65 parts by weight of HDPE and 10 to 35 parts by weight of LDPE having the physical properties defined in the present invention and having a critical shear rate of 10 (1/1). Seconds) It is understood that the resin-coated paper having a resin layer of (less than or equal to) (Examples 1 to 9) has good moldability and adhesiveness, and has excellent quality with little gel.

On the other hand, from the results in Table 3, when the requirements of the present invention are not satisfied, for example, when the content of HDPE is more than 90 parts by weight (Comparative Examples 1 and 2), the moldability and adhesiveness are poor. Bad gel. When the content of HDPE is less than 65 parts by weight (Comparative Example 3), the secondary molding processability is poor, and when the critical shear rate of LDPE is more than 0.5 (1 / sec) (Comparative Examples 4 to 5). In 7), the gel is large, and when the ratio of the molecular weight of 500,000 or more in LDPE is less than 10% by weight (Comparative Examples 5 to 8), the moldability is poor.

Further, when the critical shear rate of the resin composition of HDPE and LDPE is larger than 10.0 (1 / sec) (Comparative Examples 1, 2 and 4 to 7), the gel content is large. Also, HDP
When the composition of E and LDPE is dry-mixed as it is without being melt-mixed (Comparative Example 9), the moldability is poor and a favorable result cannot be obtained.

[0038]

According to the present invention, there is provided a polyethylene resin-coated paper having good moldability in the resin layer, excellent adhesion between the resin layer and the base paper, and low gel.

[Brief description of the drawings]

FIG. 1 is a chart showing a relationship between a shear stress and a first normal stress difference and a shear rate, wherein the vertical axis represents the shear stress and the first normal stress difference, and the horizontal axis represents the shear rate.

[Explanation of symbols]

 a Shear stress b First normal stress difference

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Nobushige Iketani 3-10-10 Shiodori, Kurashiki-shi, Okayama Prefecture Inside Mizushima Plant, Mitsubishi Kasei Co., Ltd. (72) Inventor Takuya Seri 3-chome, Kuroshiki-shi, Okayama Address: Mizushima Plant, Mitsubishi Chemical Co., Ltd. (72) Kohei Nitta 3-10, Ushidori, Kurashiki-shi, Okayama Prefecture, Mizushima Plant, Mitsubishi Chemical Co., Ltd. (56) References JP-A-60-150049 (JP, A) JP-A-60-35728 (JP, A) JP-A-58-95732 (JP, A) JP-A-5-107688 (JP, A) JP-A-5-40327 (JP, A) 307228 (JP, A) Fully open sho 59-149944 (JP, U) (58) Fields investigated (Int. Cl. ⁷ , DB name) B32B 1/00-35/00 D21H 11/00-27/42

Claims (1)

(57) [Claims] 1. A resin-coated paper having a resin layer comprising a resin composition containing a polyethylene resin as a main component on one surface of a paper substrate, wherein the resin layer has a melt flow rate of 10.0.
g / 10 min to 40.0 g / 10 min, density 0.960 g
A high density polyethylene resin 90 parts by weight to 65 parts by weight is / cm ³ or more, melt flow - Le - DOO is 0.2 g / 10
Min to 2 g / 10 min, the density is 0.935 g / cm ³ or less,
A polyethylene-based mixture obtained by melt-mixing 10 parts by weight to 35 parts by weight of a low-density polyethylene resin or a medium-density polyethylene resin having a molecular weight of 500,000 or more at a rate of 10% by weight or more and a critical shear rate of 0.5 (1 / sec) or less. The melt-mixed resin composition has a critical shear rate of 1
Resin-coated paper characterized by being at most 0 (1 / second).