JPH0657691A - Coating agent for paper - Google Patents

Abstract

PURPOSE:To provide a coating agent capable of imparting paper with emulsifiability and moisture-proofness, excellent in dispersibility in water, and capable of recovering waster paper, comprising a thermoplastic resin and a water-soluble polyvinyl alcohol-based polymer at specified proportion. CONSTITUTION:The coating agent comprising (A) a thermoplastic resin (e.g. polyethylene, polystyrene) and (B) a water-soluble polyvinyl alcohol-based polymer pref. 50-700 in mean polymerization degree and 70-90mol% in mean saponification degree at the weight ratio A/B of (45:55) to (95:5).

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a coating agent for paper, and in particular, a coating paper coated with this coating agent has a moisture-proof property, and the coating component is easily dispersed in water when immersed in water. The present invention relates to a coating agent for paper, which facilitates recovery of waste paper because it is separated from the paper.

[0002]

2. Description of the Related Art Conventionally, in order to impart moisture resistance to paper and paper products, it has been common to coat the surface of paper with a plastic film such as polyethylene. However, such processed paper requires the work of separating the film and the paper when recovering the waste paper, which is complicated in operation and increases the cost. Therefore, it is actually incinerated without being recovered. is the current situation. However, in recent years, from the viewpoint of nature conservation and resource saving, it has been earnestly desired that such processed paper can be easily recovered as waste paper.

By the way, as a paper coating agent, polyvinyl alcohol (hereinafter PVA), methyl cellulose,
Although starch and the like are used, they have almost no moisture-proof effect and cannot be used as a moisture-proof coating agent. In addition, paints obtained by dissolving a hydrophobic resin such as ethylene-vinyl acetate copolymer (EVA) in an organic solvent or acrylic emulsions are used as a moisture-proof coating agent because a moisture-proof film is formed when applied and dried. ing.
However, this coating was not preferable for recovering waste paper because it was neither dissolved nor dispersed in water. As described above, there is no coating agent which is an emulsion of various polymers and which can be recovered or recovered from waste paper by being dissolved or dispersed in water.

[0004]

SUMMARY OF THE INVENTION In view of such a situation, an object of the present invention is to coat paper with this coating agent so that it is moisture-proof and the coating component is easily dispersed in water when immersed in water. The purpose of the present invention is to provide a coating agent for paper, which is separated from the paper and makes it easy to recover the waste paper.

[0005]

Means for Solving the Problems As a result of various studies on the above problems, the present inventors have found that a thermoplastic resin and a specific PV are used.
The inventors have found that a composition produced by mixing A and A at a specific blending ratio under specific conditions can solve the above problems, and have reached the present invention.

That is, the gist of the present invention is that the weight composition ratio (A) / (B) of the thermoplastic resin (A) and the water-soluble polyvinyl alcohol polymer (B) is 45/55 to 95/5. A coating agent for paper, which is emulsifying and capable of imparting moisture resistance.

The present invention will be described in more detail below. The thermoplastic resin used in the present invention is not particularly limited, but examples thereof include low-density polyethylene, high-density polyethylene, ethylene-vinyl acetate copolymer and partially or completely saponified ethylene-vinyl acetate copolymer, ethylene-
Acrylic acid copolymer and its metal salts, ethylene-acrylic acid ester copolymer, Teflon resin, polypropylene, propylene-1-butene copolymer, ethylene-propylene-dicyclopentadiene copolymer, aliphatic such as polycaprolactone Polyester resins such as polyesters and aromatic polyesters, polystyrene and styrene resins, polyvinyl chloride, vinyl chloride-vinyl acetate copolymers, butyral resins, polyamide resins, vinyl acetate-veova copolymer resins,
Nylon resin, polyacrylic acid, ethylene-acrylic acid ester-maleic anhydride copolymer, silicone resin, waxes such as paraffin wax and modified wax, rosin and rosin derivatives, petroleum resin, terpene and modified terpene resin, isoprene One type or a mixture of two or more types of thermoplastic resins such as a system resin, polyvinyl acetate, and a partially saponified polyvinyl acetate partially insoluble in water is used. In particular, as the thermoplastic resin, polystyrene, polyethylene,
Since a coating agent that is water-emulsifiable and moisture-proof can be obtained even by using waste plastic (waste plastic) such as polypropylene or a composite of two or more kinds of these resins, the waste plastic can be obtained. It is also important for the effective use of recycled materials.

The average degree of polymerization of PVA used in the present invention is not particularly limited, but the average degree of polymerization is preferably 50.
-700, especially preferably, the average degree of polymerization is 50-400. If the average degree of polymerization exceeds 700, the water-emulsifying property of the obtained coating agent tends to decrease. However, P
If a plasticizer is added to VA, the average degree of polymerization is 700.
More than PVA can also be used. Further, when PVA having a relatively high degree of polymerization is used, the adhesive strength and the mechanical strength of the adherend also become high. Therefore, when such characteristics are desired, it is preferable to use PVA having a relatively high degree of polymerization. When PVA having a low degree of polymerization is used, the water emulsification property becomes particularly good. The reason for this is not clear, but since PVA having a low degree of polymerization has good water solubility, and is heat-meltable and has a large number of terminal groups, the thermoplastic resin is more finely dispersed in PVA by kneading. It is presumed that PVA is likely to be grafted on the surface. However, the average degree of polymerization is preferably 50 or more in consideration of mechanical strength and adhesive strength.

The average saponification degree of the PVA used in the present invention is not particularly limited, and those having an average saponification degree of 70 to 90 mol% are preferably used.
If the average degree of saponification is less than 50 mol%, the water-solubility is low, and thus the water-emulsifying property of the obtained resin composition is not sufficient. However, in order to increase the water solubility of PVA, for example, when olefin sulfonic acid such as allyl sulfonic acid, ethylene sulfonic acid, methallyl sulfonic acid, sodium allyl sulfonate, N-sulfoisobutylene acrylamide sodium, etc. are copolymerized, saponification is performed. Less than 50 mol% PVA
However, since it is water-soluble, a coating agent capable of forming a water-emulsifiable and moisture-proof coating can be obtained.

When the average degree of saponification exceeds 95 mol%, it is difficult to melt-knead the thermoplastic resin because it has no heat melting property. However, in order to increase the thermoplasticity of PVA,
For example, when an allyl compound such as allyl acetate or allyl chloride is copolymerized, or when a plasticizer such as glycerin or ethylene glycol having a plasticizing effect on PVA is used in combination,
Even with PVA having a saponification degree of 95 mol% or more, thermal melting properties are exhibited, so that a water-emulsifying and moisture-proof coating agent can be obtained. Further, two or more kinds of PVA having different average saponification degrees may be mixed to adjust the average saponification degree to 50 to 95 mol%. Therefore, the average degree of polymerization and average degree of saponification of PVA are not particularly limited, but those having water-soluble and heat-melting properties can be preferably used.

The plasticizer used in the present invention is PV
Any compound may be used as long as it has a plasticizing effect on A. For example, ethylene glycol, glycerin, propylene glycol, trimethylene glycol, trimethylolpropane, triethylene glycol, dipropylene glycol, diethylene glycol,
Hexamethylene glycol, polyethylene glycol,
Examples thereof include sorbitol, pentaerythritol, urea derivatives such as urea and ethyleneurea, and one or a mixture of two or more such as caprolactam and dimethyl sulfoxide.

The weight composition ratio of thermoplastic resin / PVA in the coating agent for paper of the present invention is 45 / 55-55.
95/5, preferably 50 / 50-9
Set to 0/10. At this time, although it depends on the specific gravity and particle size of the thermoplastic resin dispersed in PVA, the moisture resistance is extremely poor in a system in which the thermoplastic resin is as small as less than 45%. This cause is not always clear, but PV
It is presumed that since the fine particles of the thermoplastic resin dispersed in A are not densely packed, the moisture resistance is deteriorated. On the other hand, if the thermoplastic resin exceeds 95%, it will not be completely emulsified in water, and the wire will be clogged in the papermaking process when collecting waste paper, or it will remain as foreign matter in the recycled paper.

When a plasticizer is used, it is preferable to use a PVA / plasticizer weight composition ratio of 1/0 to 1/2.
When the plasticizer is used in an amount of more than twice the PVA, not only does the composition become sticky due to bleeding of the plasticizer, a blocking phenomenon occurs, but also the moisture resistance tends to decrease.

Examples of the method for producing the water-soluble polyvinyl alcohol polymer used in the present invention include a method of saponifying a polyvinyl ester obtained by solution polymerization, bulk polymerization, emulsion polymerization or suspension polymerization of vinyl ester. To be In particular, since PVA used in the present invention is preferably one having a relatively low degree of polymerization, a solvent such as ethanol or isopropyl alcohol having a large chain transfer coefficient is used, or chain transfer such as mercaptans such as n-butyl mercaptan is used. Solution polymerization is preferably carried out by adding an agent.
Examples of the method for saponifying the vinyl ester include direct saponification such as alkali saponification and acid saponification, or a conventional saponification method by alcoholysis. Further, in the saponification, it is also possible to use one in which the intramolecular distribution state of the vinyl alcohol unit is changed by mixing water, methyl acetate, benzene or the like into the saponification system.

Examples of vinyl esters include vinyl formate, vinyl acetate, vinyl propionate, vinyl butyrate,
Examples thereof include vinyl laurate, vinyl trifluoroacetate, vinyl pivalate, and the like, and these may be used alone or as a mixture of two or more kinds. Of these, vinyl acetate is industrially preferable.

Further, it is possible to use a partially copolymerized saponified or acetalized compound of these vinyl esters, which is copolymerizable with the vinyl ester, as long as the effect of the present invention is not impaired. Examples of the copolymerizable compound include olefins such as ethylene and propylene, olefin sulfonic acids such as allyl sulfonic acid, ethylene sulfonic acid and methallyl sulfonic acid, and alkyl vinyl ethers such as methyl vinyl ether, tert-butyl vinyl ether and stearyl vinyl ether. , Vinyl chloride, vinyl halides such as vinyl fluoride, acrylic acid and its salts and acrylic acid esters such as methyl acrylate, methacrylic acid and its salts and methacrylic acid esters such as methyl methacrylate, maleic acid and its Salts and maleic acid esters such as monomethyl maleate, acrylamide, acrylamide derivatives such as N-methylol acrylamide, vinyl silyl compounds such as vinyltrimethoxysilane, isopropenyl acetate, and versatile Examples thereof include branched fatty acid vinyl such as vinyl, olefin sulfonic acid and sodium allyl sulfonate, sodium N-sulfoisobutylene acrylamide, and allyl compounds such as allyl acetate and allyl chloride. Among them, allyl sulfonic acid and ethylene sulfonic acid described above are mentioned. , Olefin sulfonic acid such as methallyl sulfonic acid, sodium allyl sulfonate, sodium N-sulfoisobutylene acrylamide, etc., and allyl compounds such as allyl acetate, allyl chloride, etc., are water-soluble PVA obtained by saponification. It is particularly preferable because it improves the thermoplasticity.

In the paper coating agent of the present invention, for example, polyoxyethylene lauryl ether,
It is also possible to use an emulsifying dispersant such as sodium lauryl sulfate, triethanolamine lauryl sulfate, an alkylnaphthalene sulfonate or dodecylbenzene sulfonate in combination.

Further, fillers (clay, silica, talc, light calcium carbonate, glass fibers, etc.), lubricants, foaming agents, cross-linking agents, release agents, defoamers, pigments, dyes, etc. can be applied to the effect of the present invention. It is also possible to mix an appropriate amount as long as it does not damage.

The coating agent for paper of the present invention is (A)
After kneading the thermoplastic resin and the water-soluble polyvinyl alcohol-based polymer (B) at a temperature equal to or higher than the softening point of the thermoplastic resin, rapidly cooling at a temperature equal to or lower than the softening point of the thermoplastic resin within 10 seconds. Obtained by solidifying. The product produced in this way has extremely good water emulsification and moisture resistance. The softening point referred to here is JIS K676.
The Bicatt softening point defined as 0 is shown. The cause of this is not always clear, but the fine particles of the thermoplastic resin are dispersed in PVA by mixing at a temperature equal to or higher than the softening point, and the fine particles of the thermoplastic resin solidify when cooled rapidly in a short time. It is presumed that this is because the dispersed thermoplastic resin fine particles do not re-fuse.

In the cooling, when it is cooled by passing it through water, it is immediately emulsified in water. Therefore, it is cooled by passing through a non-solvent for the components of the resin composition, or by air cooling or by directly contacting the water on a steel belt. It needs to be cooled in the absence. The kneading method is not particularly limited, but a single-screw extruder, a multi-screw extruder, a kneader-type melt-kneader, or the like can be preferably used, and the thermoplastic resin and PVA to be used can be melt-mixed by heat. If there is no particular restriction.

The coating agent for paper of the present invention has an extremely excellent emulsifying property in water, and can be used as a coating liquid by emulsifying and dispersing in water. The solid concentration of the coating liquid used for coating the paper is appropriately selected from the range of 10 to 70% by weight. The coating liquid is applied to the paper surface using a known coater such as an air knife coater, a blade coater, a roll coater, and a size press coater, dried in a drying step, and then finished through a super calendar. When performing drying and heat treatment with a super calender, it is preferable to treat at a temperature not higher than the softening point of the thermoplastic resin in the coating agent, since water emulsifiability is not impaired when recovering waste paper. The coating amount will be in a wide range depending on the desired level of moisture resistance, etc., and is not limited, but it is 0.1
It is preferably about 100 g / m ² .

[0022]

EXAMPLES The present invention will be specifically described below with reference to examples, but the present invention is not limited thereto. The performance characteristics were measured as follows.

[Characteristic of coating liquid] 1. Emulsifying property A coating agent for paper was put into water at 30 ° C. and stirred for 15 minutes to examine the emulsion dispersion state (adjusted to a solid content concentration of 40%) when used as a coating liquid. ◎: Complete emulsification ○: Almost emulsified ×: No emulsification at all

2. Dispersed particle size The average dispersed particle size of the thermoplastic resin component dispersed in the coating liquid was measured using an automatic particle size distribution measuring device (Horiba Seisakusho; centrifugal sedimentation type). ⊚: less than 0.3 μm ◯; 0.3 to 10 μm ×; 1
0 μm or more

3. Stability upon standing The state when the above coating solution was allowed to stand at 10 ° C for 30 days was examined. ◎: No separation at all ○: Slight water separation ×: Separation and aggregation

[Characteristics of coated paper] The above coating liquid was coated on kraft paper with a bar coater at a solid content of 50 g / m ² ,
After drying at 105 ° C. for 70 seconds, roll pressing was performed at 140 ° C. for 110 seconds to obtain a coated paper.

4. Moisture resistance The above coated paper at 30 ° C has a moisture permeability tester (MODERN CONTOROL, I
Permeability coefficient (g / m ² · day) using NC PERMATRAN-WID)
Was measured. ◎; less than 1.0 ○; 1.0 to 15 ×;
20 or more

5. Dispersibility The state of the coating components when the coated paper was immersed in water at 30 ° C. for 30 minutes and stirred was examined. ◎: Shape collapse and redispersion ○: Almost shape collapse ×;
Shape retention without dispersion

6. Bleed resistance (exudation resistance) The bleed state of the coated paper coating surface was examined. ◎: No exudation at all ○: Almost no exudation ×: Remarkably exudation

Examples 1 to 5 and Comparative Examples 1 to 2 Various thermoplastic resins and PVA were melt-kneaded at 170 to 270 ° C. in various weight composition ratios shown in Table 1 using a twin-screw melt extruder and melted. The product was extruded in a strand shape, cooled to 30 ° C. for 10 seconds on a steel belt, cut with a pelletizer to produce a pellet-shaped coating agent for paper, and its performance characteristics were measured. The results are shown in Table 1.

[0031]

[Table 1]

The symbols in Table 1 are as follows. Thermoplastic resin PS; Polistrene PAN; Polyacrylonitrile high density PE; High density polyethylene butyral; Polybutyl acetate PCV; Vinyl chloride-vinyl acetate copolymer PA; Average degree of polymerization DS; Average degree of saponification (mol%) * 1; Allyl sulfone Acid-modified PVA (degree of modification; 2 mol%) * 2; Allyl acetate-modified PVA (degree of modification; 3 mol%) Plasticizer G; Glycerin E; Ethylene glycol S;
Sorbitol

Example 6 Low-density polyethylene (melt flow rate; 3 g / 10
min Bicatt softening point 91 ° C) 70 parts by weight and PVA (
An average degree of polymerization of 230 and an average degree of saponification of 80.3 mol%) (30 parts by weight) were kneaded at 250 ° C. using a single-screw melt extruder to extrude the melt in a strand form, which was then placed on a steel belt for 5 seconds. The mixture was cooled to 50 ° C. with a pelletizer and cut with a pelletizer to obtain a pellet-shaped coating agent for paper. This pellet-shaped coating agent for paper was put into water at 20 ° C. and stirred for 15 minutes to obtain an emulsion-type coating liquid (solid content concentration: 40% by weight) having a milky white color and good fluidity. The particle size of the dispersed particles was 1.3 μm.

This coating solution was applied to kraft paper using an air knife coater so that the solid content was 50 g / m ² , dried at 105 ° C. for 70 seconds, and then finished at 80 ° C. for 110 seconds with a super calendar, I got coated paper. The moisture permeability coefficient of this coated paper was measured to be 1.5 (g / m ² ·
day) and showed good moisture resistance. Further, when this coated paper was immersed in water at 20 ° C., the coating component was re-emulsified and separated from the paper, and there was no problem in collecting the waste paper. [Reference] Moisture Permeability Coefficient of PVA: 270 (g / m ²
・ Day) Moisture permeability of polyethylene; 0.4 (g / m ² · day)

Example 7 Polypropylene (melt flow rate; 9 g / 10 mi
n Vicat softening point 150 ° C.) 78 parts by weight and PVA (average degree of polymerization 150, average degree of saponification 88 mol%) 15 parts by weight,
PVA (average degree of polymerization 1700, average degree of saponification 80 mol%)
A mixture of 7 parts by weight and 7 parts by weight of glycerin was melt-kneaded at 190 ° C. using a uniaxial melt extruder and cooled to 10 ° C. for 10 seconds to obtain a strand-shaped molded product. This molded product was pulverized to prepare a powdery coating agent having 16 mesh passes. This powdery coating agent 15
The mixture was poured into water at 0 ° C. and stirred for 10 minutes to obtain a coating liquid having good fluidity (solid content concentration: 30% by weight). (Emulsion particle size: 2 μm, emulsion stability (10 ° C., 30 days); good). The coating solution was applied to kraft paper at a solid content of 10 g / m ² and dried at 105 ° C. for 70 seconds, and then 1
Roll pressing was performed at 40 ° C. for 110 seconds. The moisture permeability coefficient of this coated paper was measured and found to be 3.0 (g / m ² · day), indicating good moisture resistance. Also, this coated paper at 20 ℃
When the mixture was stirred in water, the coating component was re-emulsified and there was no problem in collecting the waste paper.

Comparative Example 3 Low density polyethylene (melt flow rate; 3 g / 10
min, Bicatt softening point 91 ° C) 10 parts by weight and PVA
(Average degree of polymerization 430, average degree of saponification 80.3 mol%) 90
A part by weight was melt-kneaded at 190 ° C. using a uniaxial melt extruder and cooled to 20 ° C. for 10 seconds to obtain a strand-shaped molded product. The molded product was pulverized to prepare a 30 mesh pass granule product. Put the granules in water at 20 ° C for 1
The mixture was stirred for 0 minutes to obtain a slightly white and very viscous coating liquid (solid content concentration: 20% by weight). This coating liquid has a solid content of 50
It was coated on kraft paper so as to be g / m ² , dried at 105 ° C for 70 seconds, and then roll pressed at 140 ° C for 110 seconds. When the moisture permeability coefficient of this coated paper was measured, it was 2
It was 50 (g / m ² · day) and had almost no moisture resistance. That is, this coating agent was no different from PVA alone.

Comparative Example 4 97 parts by weight of an ethylene-vinyl acetate copolymer (vinyl acetate content: 7% by weight) and 3 parts by weight of PVA (average degree of polymerization 230, average degree of saponification 80.3 mol%) were biaxial. Using a melt extruder, the mixture was kneaded at 190 ° C. and cooled to 20 ° C. for 10 seconds to obtain a strand-shaped molded product. The molded product was pulverized to prepare a 30 mesh pass granule product. 20-9 this granule
The mixture was poured into water at 5 ° C and stirred vigorously for 60 minutes, but it was not emulsified and dispersed at all and a coating liquid could not be obtained.

[0038]

As described above, the coating agent for paper of the present invention, when dispersed in water, becomes a stable emulsion and can be a good coating liquid. When this coating solution is applied to paper, a coating paper with excellent moisture resistance can be obtained, and when this coating paper is immersed in water, the coating components disperse in water, so it can be easily removed and the waste paper can be recovered. It will be possible.

Claims (1)

[Claims] 1. A weight composition ratio (A) / of a thermoplastic resin (A) and a water-soluble polyvinyl alcohol polymer (B).
(B) is 45/55 to 95/5, and is a coating agent for paper, which is emulsifying and can impart moisture resistance.