JP7352488B2 - low molecular weight polyolefin - Google Patents

Description

The present invention relates to low molecular weight polyolefins.

Low molecular weight polyolefins are widely used as surface modifiers, pigment dispersants, compatibilizers, etc. for resins, and modified polyolefins obtained by modifying low molecular weight polyolefins with unsaturated (poly)carboxylic acids are also used as resin modifiers. It is widely used as a quality agent.
As a method for producing low molecular weight polyolefins, for example, a method of continuously thermally degrading polyolefins has been proposed (for example, Patent Document 1).

Japanese Patent Application Publication No. 10-158329

However, even with the above technology, the reactivity during production of modified polyolefins was not fully satisfactory.
An object of the present invention is to provide a low molecular weight polyolefin with excellent reactivity.

The present inventors have arrived at the present invention as a result of intensive studies to solve the above problems. That is, the present invention provides a low molecular weight polyolefin having a weight ratio of ethylene units to propylene units [ethylene units/propylene units] of 2/98 to 50/50 and satisfying all of the following requirements (1) to (3). (A).
(1) Contains 0.5 to 20 double bonds per 1000 carbon atoms (2) Number average molecular weight (Mn) 1,000 to 50,000
(3) Isotacticity of propylene part is 1-50%

The low molecular weight polyolefin (A) of the present invention has the following effects.
(1) Excellent reactivity.
(2) Excellent solvent solubility.
(3) A primer dissolved in a solvent has excellent adhesion to a base material.

<Low molecular weight polyolefin (A)>
The low molecular weight polyolefin (A) of the present invention contains ethylene and propylene as constituent monomers.
The weight ratio of the ethylene units and propylene units [ethylene units/propylene units] is 2/98 to 50/50, preferably 5/95 to 40/60, more preferably 10/90 to 30/70. be.
If the weight ratio [ethylene units/propylene units] is less than 2/98, the adhesion to the base material will be poor, and if it exceeds 50/50, the reactivity will be poor.
The above weight ratio [ethylene units/propylene units] can be calculated by, for example, ¹ H-MNR.

In addition to ethylene and propylene, other monomers may be used as constituent monomers in (A). In that case, the weight of other monomers is preferably 10% by weight or less, more preferably 5% by weight or less, particularly preferably 1% by weight or less, based on the weight of all monomers constituting (A). It is.
Examples of the other monomers mentioned above include 1- and 2-butene, isobutene, α-olefins having 5 to 30 carbon atoms (sometimes abbreviated as C) (1-hexene, 1-decene, 1-dodecene, etc.), C4-30 unsaturated monomers (eg, vinyl acetate).

The low molecular weight polyolefin (A) satisfies all of the following requirements (1) to (3).
(1) Contains 0.5 to 20 double bonds per 1000 carbon atoms (2) Number average molecular weight [sometimes abbreviated as Mn] of 1,000 to 50,000
(3) Isotacticity of propylene part is 1-50%

The above requirement (1): The number of double bonds per 1000 carbon atoms [the number of carbon-carbon double bonds at the molecular terminal and/or in the molecular chain of (A)] is 0.5 to 20, The number is preferably 1.0 to 18, more preferably 1.5 to 15.
When the number of double bonds is less than 0.5, the reactivity tends to be insufficient and the Mn content tends to be too high; when it exceeds 20, the reactivity tends to be too high and the Mn content tends to be too low.
Here, the number of double bonds can be determined from the spectrum of ¹ H-NMR (nuclear magnetic resonance) spectroscopy of (A). That is, the peak in the spectrum is assigned, and from the integral value derived from the double bond at 4.5 to 6 ppm of (A) and the integral value derived from (A), the number of double bonds in (A) and the integral value derived from (A) are determined. The relative value of the number of carbon atoms in (A) is determined, and the number of double bonds in the molecular terminal and/or in the molecular chain per 1,000 carbon atoms in (A) is calculated. The number of double bonds in the Examples described below was determined according to this method.

Requirement (2) above: Number average molecular weight (Mn) is 1,000 to 50,000, preferably 1,500 to 30,000, more preferably 2,000 to 15,000.
When the Mn is less than 1,000, the adhesion to the substrate tends to be poor and the number of double bonds tends to be excessive. On the other hand, when Mn exceeds 50,000, solvent solubility tends to be poor and the number of double bonds tends to be too small.

The conditions for measuring Mn and weight average molecular weight (Mw) by GPC (gel permeation chromatography) in the present invention are as follows.
Equipment: High temperature gel permeation chromatograph
[“Alliance GPC V2000”, manufactured by Waters Co., Ltd.]
Detection device: Refractive index detector Solvent: Orthodichlorobenzene Reference material: Polystyrene Sample concentration: 3mg/ml
Column stationary phase: PLgel 10μm, MIXED-B 2 bottles in series
[Manufactured by Polymer Laboratories Co., Ltd.]
Column temperature: 135℃

Requirement (3) above: The isotacticity of the propylene moiety is 1 to 50%, preferably 5 to 45%, and more preferably 10 to 40%.
If the isotacticity is less than 1%, the adhesion to the base material will be poor, and if the isotacticity exceeds 50%, the solvent solubility will be poor.

The isotacticity can be calculated using, for example, ¹³ C-NMR (nuclear magnetic resonance spectroscopy). In general, the side chain methyl group is present on both sides (triad, triad), on both sides of the triad (pentad, pentad), and even on both sides of the quintad (septad, heptad). It is known that peaks are observed at different chemical shifts due to the influence of the configuration (meso or racemo) with the methyl group, and stereoregularity is generally evaluated for pentads. The isotacticity in can also be calculated based on the pentad evaluation.
That is, regarding the carbon peak derived from the side chain methyl group in propylene obtained by ¹³ C-NMR, each pentad peak (H), the peak derived from the methyl group in isotactic propylene in which the pentad is formed only in a meso structure. (H _a ), isotacticity is calculated using the following formula.
Isotacticity (%) = [(H _a )/Σ(H)]×100 (1)
However, in the formula, H _a is the peak height of an isotactic signal (pentads are formed only with a meso structure), and H is the height of each peak of the pentad.

The method for producing the low molecular weight polyolefin (A) of the present invention includes, for example, heating a high molecular weight (preferably Mn of 60,000 to 400,000, more preferably Mn of 80,000 to 250,000) polyolefin (A0). One example is a method of degrading it.

Examples of (A0) include ethylene/propylene copolymers and ethylene/propylene/other monomer copolymers, with ethylene/propylene copolymers being preferred.

The thermal degradation method includes (1) thermal degradation of the polyolefin (A0) in the absence of an organic peroxide, for example at 300 to 450°C for 0.5 to 10 hours, and (2) organic peroxide. This includes a method of thermal degradation in the presence of a compound [for example, 2,5-dimethyl-2,5-di(t-butylperoxy)hexane], usually at 180 to 300°C for 0.5 to 10 hours.
Among these methods, method (1) is easy to obtain from the viewpoint of industrial aspects and modification properties, with a larger number of double bonds at the molecular ends and/or in the molecular chain.

The weight ratio [ethylene units/propylene units] of the ethylene units and propylene units in the above (A) tends to maintain the same weight ratio [ethylene units/propylene units] of the high molecular weight polyolefin (A0).
In addition, the above requirement (1): The higher the thermal degradation temperature and the longer the thermal degradation time, the larger the number of double bonds per 1000 carbon atoms tends to be.
Furthermore, the above requirement (2): The smaller the Mn of (A0), the higher the thermal degradation temperature, and the longer the thermal degradation time, the smaller the Mn of (A) tends to be.
Moreover, the above requirement (3): The greater the isotacticity of (A0), the greater the isotacticity of (A) tends to be.

Further, after thermal degradation, it is preferable to include a step of distilling off the hydrocarbons having 6 to 12 carbon atoms (B) at 200 to 270°C. This is preferred because the amount of hydrocarbon (B) can be easily adjusted. The distillation may be carried out at the above temperature by, for example, passing an inert gas (nitrogen, etc.) for 10 minutes to 1 hour, or reducing the pressure.
The above-mentioned hydrocarbon having 6 to 12 carbon atoms (B) is preferably an aliphatic hydrocarbon having 6 to 12 carbon atoms, specifically, a dimer, a trimer of the monomer constituting (A), Examples include tetramer.

The amount of (B) in (A) is preferably 0.005% to 2.0% by weight, more preferably 0.01% to 1.6% by weight, particularly preferably from the viewpoint of reactivity and adhesion. is 0.02 to 1.2% by weight.
The weight of (B) can be determined by gas chromatography-mass spectrometry (GC-MS).

The low molecular weight polyolefin (A) of the present invention may further contain various additives (G) as necessary to the extent that the effects of the present invention are not impaired, to form a low molecular weight polyolefin (composition).
(G) includes colorant (G1), flame retardant (G2), filler (G3), lubricant (G4), antistatic agent (G5), dispersant other than (A) (G6), and antioxidant. (G7), a mold release agent (G8), an antibacterial agent (G9), a compatibilizer (G10), and an ultraviolet absorber (G11).

Colorants (G1) include inorganic pigments [white pigments, cobalt compounds, iron compounds, sulfides, etc.], organic pigments [azo pigments, polycyclic pigments, etc.], dyes [azo type, indigoid type, sulfide type, alizarin, etc.]. type, acridine type, thiazole type, nitro type, aniline type, etc.] etc.;

Flame retardants (G2) include halogen-containing flame retardants, nitrogen-containing flame retardants, sulfur-containing flame retardants, silicon-containing flame retardants, phosphorus-containing flame retardants, etc.;

Examples of the filler (G3) include inorganic fillers (calcium carbide, talc, clay, etc.) and organic fillers (urea, calcium stearate, etc.);

Examples of lubricants (G4) include calcium stearate, butyl stearate, oleic acid amide), plasticizers (e.g., phthalate esters, aliphatic glycol polyesters, phosphate esters, toluenesulfonamide, etc.);

As the antistatic property improver (G5), nonionic, cationic, anionic or amphoteric surfactants described below and in U.S. Pat. Can be mentioned.
(1) Nonionic surfactants AO-adducted nonionics, such as active hydrogen atom-containing compounds having hydrophobic groups (C8-24 or higher) [saturated and unsaturated, higher alcohols (C8-18), higher (poly)oxyalkylene derivatives (AO adducts and higher fatty acid mono- or di-esters of polyalkylene glycols) of fatty amines (C8-24) and higher fatty acids (C8-24); polyhydric alcohols (C3-24); 60) (poly)oxyalkylene derivatives of higher fatty acid (C8-24) esters (Tween type nonionics, etc.); (poly)oxyalkylene derivatives of (alkanol) amides of higher fatty acids (above); polyhydric alcohols (above) (Poly)oxyalkylene derivatives of alkyl (C3-60) ethers; and polyoxypropylene polyols [polyoxypropylene derivatives (Pluronic type and Tetronic type nonionics) of polyhydric alcohols and polyamines (C2-10)]; Alcohol (above) type nonionics (e.g. fatty acid esters of polyhydric alcohols, polyhydric alcohol alkyl (C3-60) ethers and fatty acid alkanolamides); and amine oxide type nonionics [e.g. (hydroxy)alkyl (C10-18) di(hydroxy)alkyl (C1-3) amine oxide].

(2) Cationic surfactant Quaternary ammonium salt type cationics [tetraalkylammonium salt (C11-100) alkyl (C8-18) trimethylammonium salt and dialkyl (C8-18) dimethylammonium salt, etc.]; trialkyl Benzyl ammonium salts (C17-80) (lauryldimethylbenzylammonium salts, etc.); Alkyl (C8-60) pyridinium salts (cetylpyridinium salts, etc.); (poly)oxyalkylene (C2-4) trialkylammonium salts (C12-100) ) (polyoxyethylene lauryl dimethyl ammonium salt etc.); and acyl (C8-18) aminoalkyl (C2-4) or acyl (C8-18) oxyalkyl (C2-4) tri[(hydroxy)alkyl (C1-4) )] Ammonium salts (sapamine-type quaternary ammonium salts) [These salts include, for example, salts of halides (chloride and bromide, etc.), alkyl sulfates (methosulfate, etc.) and organic acids (see below)]; and amines. Salt-type cationics: primary to tertiary amines [for example, higher aliphatic amines (C12-60), polyoxyalkylene derivatives (EO adducts, etc.) of aliphatic amines (methylamine, diethylamine, etc.), and acylaminoalkyl or acyloxyalkyl Inorganic acid (hydrochloric acid, sulfuric acid, nitric acid, phosphoric acid, etc.) salts and organic acids (C2-22 )salt.

(3) Anionic surfactants Higher fatty acid (above) salts (sodium laurate, etc.), ether carboxylic acids [carboxymethylated products of EO (1 to 10 mol) adducts, etc.] and their salts; sulfate ester salts (alkyl and alkyl ether sulfates), sulfated oils, sulfated fatty acid esters, and sulfated olefins; sulfonates [alkylbenzene sulfonates, alkylnaphthalene sulfonates, sulfosuccinic acid dialkyl ester types, α-olefin (C12-18) sulfones] acid salts, N-acyl-N-methyltaurine (Igepon type T, etc.); and phosphate ester salts (alkyl, alkyl ether, and alkylphenyl ether phosphates, etc.).

(4) Amphoteric surfactant:
Carboxylic acid (salt) type amphoteric [amino acid type amphoteric (laurylaminopropionic acid (salt), etc.) and betaine type amphoteric (alkyl dimethyl betaine, alkyl dihydroxyethyl betaine, etc.)]; Sulfuric acid ester (salt) type Amphoterix [laurylamine sulfate ester (salt), hydroxyethylimidazoline sulfate ester (salt), etc.]; Sulfonic acid (salt) type Amphoterix [pentadecylsulfotaurine and imidazoline sulfonic acid (salt), etc.]; ), etc.]; and phosphate ester (salt) type amphoterics, etc. [phosphate ester (salt) of glycerin lauryl ester, etc.].

Salts in the above anionic and amphoteric surfactants include metal salts, such as salts of alkali metals (lithium, sodium, potassium, etc.), alkaline earth metals (calcium, magnesium, etc.), and group IIB metals (zinc, etc.); Ammonium salts; and amine salts and quaternary ammonium salts.

The dispersant (G6) is a polymer having an Mn of 1,000 to 20,000, such as a vinyl resin, and includes vinyl resins other than the above-mentioned low molecular weight polyolefins [polyvinyl halides [polyvinyl chloride, polyvinyl bromide, etc.], polyvinyl chloride, polyvinyl bromide, etc.) Vinyl acetate, polyvinyl alcohol, polymethyl vinyl ether, poly(meth)acrylic acid, poly(meth)acrylic ester [methyl poly(meth)acrylate, etc.], styrene resin [polystyrene, acrylonitrile/styrene (AS) resin, etc.], etc. ]; Polyester resins [polyethylene terephthalate, etc.], polyamide resins [6,6-nylon and 12-nylon, etc.], polyether resins [polyether sulfone, etc.], polycarbonate resins [polycondensates of bisphenol A and phosgene, etc.]; Examples include block copolymers thereof.

As the antioxidant (G7), phenolic compounds [monocyclic phenol (2,6-di-t-butyl-p-cresol, etc.), bisphenol [2,2'-methylenebis(4-methyl-6-t-butylphenol)] ), etc.], polycyclic phenols [1,3,5-trimethyl-2,4,6-tris(3,5-di-t-butyl-4-hydroxybenzyl)benzene, etc.], sulfur compounds (dilauryl 3 , 3'-thiodipropionate, etc.), phosphorus compounds (triphenylphosphite, etc.), amine compounds (octylated diphenylamine, etc.);

As the mold release agent (G8), lower (C1 to 4) alcohol esters of fatty acids (C8 to 24) (butyl stearate, etc.), polyvalent (bivalent to tetravalent or higher) fatty acids (C2 to 24); Alcohol esters (hydrogenated castor oil, etc.), glycol (C2-8) esters of fatty acids (C2-24) (ethylene glycol monostearate, etc.), liquid paraffin, etc.;

Antibacterial agents (G9) include benzoic acid, sorbic acid, halogenated phenols, organic iodine, nitrile (2,4,5,6-tetrachloroisophthalonitrile, etc.), thiocyano (methylene bisthyanocyanate), N-halo Alkylthioimides, copper agents (8-oxyquinoline copper, etc.), benzimidazole, benzothiazole, trihaloallyl, triazole, organic nitrogen sulfur compounds (Suraoff 39, etc.), quaternary ammonium compounds, pyridine compounds, etc.;

Examples of the compatibilizer (G10) include modified vinyl polymers having at least one functional group (polar group) selected from the group consisting of carboxyl groups, epoxy groups, amino groups, hydroxyl groups, and polyoxyalkylene groups: e.g. , the polymer described in JP-A-3-258850, the modified vinyl polymer having a sulfonic acid group described in JP-A-6-345927, and the block polymer having a polyolefin part and an aromatic vinyl polymer part. Combination, etc.;

As the ultraviolet absorber (G11), benzotriazole [2-(2'-hydroxy-5'-methylphenyl)benzotriazole, etc.], benzophenone [2-hydroxy-4-methoxybenzophenone, etc.], salicylate [phenyl salicylate, etc.] etc.], acrylates [2-ethylhexyl-2-cyano-3,3'1-diphenylacrylate, etc.], and the like.

The total content of (G) in the low molecular weight polyolefin is, for example, 20% by weight or less based on the total weight of the composition, preferably 0.05 to 10% from the viewpoint of functional expression of each (G) and industrial aspects. % by weight, more preferably 0.1 to 5% by weight.
The amount of each additive used based on the total weight of the low molecular weight polyolefin is, (G1) is, for example, 5% by weight or less, preferably 0.1 to 3% by weight; (G2) is, for example, 8% by weight or less, preferably is 1 to 3% by weight; (G3) is, for example, 5% by weight or less, preferably 0.1 to 1% by weight; (G4) is, for example, 8% by weight or less, preferably 1 to 5% by weight; (G5) is, for example, 8% by weight or less, preferably 1 to 3%; (G6) is, for example, 1% by weight or less, preferably 0.1 to 0.5% by weight; (G7) is, for example, 2% by weight or less, preferably is 0.05 to 0.5% by weight; (G8) is, for example, 5% by weight or less, preferably 0.01 to 3%; (G9) is, for example, 25% by weight or less, preferably 0.5 to 20%. (G10) is, for example, 15% by weight or less, preferably 0.5 to 10%; (G11) is, for example, 2% by weight or less, preferably 0.05 to 0.5% by weight.

If the additives (G1) to (G11) above are the same and overlap, do not use the amount of each additive that produces the corresponding additive effect as is, but also the effect of the other additive at the same time. The amount used shall be adjusted depending on the purpose of use, taking into consideration the benefits obtained.

<Primer for plastic molded products>
The primer for plastic molded products of the present invention (hereinafter sometimes abbreviated as primer) contains the low molecular weight polyolefin (A). The primer for plastic molded products preferably contains the above (A) and a solvent (S). Examples of the solvent (S) include known solvents, but aromatic hydrocarbons (toluene, xylene, etc.) are preferred.
In that case, the weight ratio [(A)/(S)] between the (A) and the (S) is preferably 10/90 to 50/50, more preferably 20/80 to 40/60.

The low molecular weight polyolefin (A) of the present invention can be used for various purposes, preferably as a modifier for resins, a raw material for (acid) modified polyolefins, a raw material for chlorinated polypropylene, a raw material for polyurethane, a raw material for cured resin, a raw material for adhesives, and an emulsion. It can be suitably used as a raw material or as a primer.

The present invention will be further explained below with reference to Examples, but the present invention is not limited thereto. In the examples, parts represent parts by weight, and percentages other than mol% represent weight%.

<Example 1>
In a reaction vessel, polyolefin (A0-1) [trade name "Vistamaxx6202", manufactured by Exxonmobil, hereinafter the same applies. ] 1000 g was charged, heated and melted with a mantle heater while blowing nitrogen into the liquid phase, and thermal degradation was performed at 380° C. for 40 minutes while stirring.
Next, the liquid phase was aerated with nitrogen at 60 mL/min for 20 minutes at 250° C. to obtain polyolefin (A-1).
The Mn of polyolefin (A-1) was 5,800, the number of double bonds at the molecular end and/or in the molecular chain per 1,000 carbon atoms was 5.3, and the isotacticity was 18%.

<Examples 2 to 8, Comparative Examples 1 to 2>
In Example 1, each polyolefin (A) was obtained in the same manner as in Example 1 except that Table 1 was followed. Each obtained polyolefin (A) was evaluated by the following method. The results are shown in Table 1.
Note that in Table 1, in Examples where ventilation after thermal degradation was "-", ventilation was not performed after thermal degradation.

<1> Solvent solubility 30 g of each polyolefin (A) obtained and 70 g of xylene were placed in a container, stirred at 40°C for 3 hours, and then left to stand at room temperature (25°C) for 3 hours to dissolve the polyolefin. A solution (solid content concentration 30%) was prepared.
The prepared polyolefin solution was kept at 25° C. for one day, and the properties of the solution were observed. The solvent solubility of the polyolefin solution was evaluated using the following <Evaluation Criteria>.

<Evaluation criteria>
◎: The solution is transparent and has fluidity.
○: The solution is slightly hazy and has fluidity.
△: There is haze in the solution and there is no fluidity.
×: Hardly dissolved.

<2> Substrate Adhesion Each polyolefin solution evaluated in <1> above was used as a primer solution to spray polyolefin using a spray machine [trade name "EBG-115EXB", manufactured by Anest Iwata Co., Ltd.]. The resin base material [trade name "PP1300", polypropylene, manufactured by Takin Co., Ltd.] was spray coated on the surface and dried at 80° C. for 10 minutes (film thickness after drying was 80 μm).
Next, a polyurethane paint [trade name "Ucoat UX-150" manufactured by Sanyo Chemical Industries, Ltd.] was spray applied using the same spray machine, and after drying at 80°C for 10 minutes (dry urethane paint film thickness 100 μm). An adhesion test (checkerboard test) was conducted on the painted surface using a checkerboard tape method in accordance with JIS K5400, and the adhesion was evaluated using the following evaluation criteria.
The number of areas where the coating film did not peel off out of a grid of 100 is expressed as 0 to 100, and the larger the number, the better the adhesion between the substrate and the coating film.
Note that in <1> above, those marked Δ and × were not evaluated because they could not be sprayed.

<Evaluation criteria>
◎:99-100
〇:95-98
△:90-94
×: Less than 90

<3> Reactivity Into a reaction vessel, 100 g of each polyolefin (A) and 1.5 equivalents of commercially available 2-mercaptoethanol "manufactured by Nacalai Tesque Co., Ltd." (b -1), 100 g of xylene (c-1) was charged, and the temperature was raised to 80° C. under nitrogen aeration to uniformly dissolve it. To this, xylene ( C-2) A solution dissolved in 10 g was added dropwise over 10 minutes, and stirring was continued at 80° C. for 8 hours.
Thereafter, xylene and unreacted 2-mercaptoethanol are distilled off under reduced pressure (1.5 kPa, the same applies hereinafter), and the unsaturated carbon-carbon double bond of the polyolefin (A) is reacted with 2-mercaptoethanol. The gender was evaluated.

Reaction rate (%) = 100-100 × [(Amount of unsaturated carbon-carbon double bonds after reaction)/(Amount of unsaturated carbon-carbon double bonds before reaction)]

The larger the reaction rate value, the better the reactivity.
For example, for (A-1), the amounts of (b-1) and (D-1) were determined as follows.
(A-1) per 1000 carbons: 14 x 1000 = 14000
Amount of (b-1) prepared: 78.1 x 1.5 (equivalent) x 5.3 (pieces) / 140 = 4.4 g
Amount of (D-1) prepared: 164 x 0.5 (equivalent) x 5.3 (pieces) / 140 = 3.1 g

From the results in Table 1, it can be seen that the low molecular weight polyolefin (A) of the present invention has excellent reactivity and solvent solubility compared to the comparative ones, and that the primer dissolved in the solvent has excellent adhesion to the base material. I understand.

The low molecular weight polyolefin (A) of the present invention can be used for various purposes, preferably as a modifier for resins, a raw material for (acid) modified polyolefins, a raw material for chlorinated polypropylene, a raw material for polyurethane, a raw material for cured resin, a raw material for adhesives, and an adhesive. It is extremely useful because it can be suitably used as a raw material for agents, raw materials for emulsions, primer applications, and adhesive applications.

Claims (3)

A low molecular weight polyolefin (A) having a weight ratio of ethylene units to propylene units [ethylene units/propylene units] of 2/98 to 50/50 and satisfying all of the following requirements (1) to (3).
(1) Contains 0.5 to 20 double bonds per 1000 carbon atoms (2) Number average molecular weight (Mn) 1,000 to 50,000
(3) Isotacticity of propylene part is 1-50% The low molecular weight polyolefin according to claim 1, wherein the weight of the hydrocarbon (B) having 6 to 12 carbon atoms contained in the low molecular weight polyolefin (A) is 0.005 to 2.0% by weight. A primer for a plastic molded article, comprising the low molecular weight polyolefin (A) according to claim 1 or 2.